Thermal Discharges at Nuclear Power Stations Their Management and Environmental Impacts

TECHNICAL REPORTS SERIES No. 155

INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1974 THERMAL DISCHARGES AT NUCLEAR POWER STATIONS

Their management and environmental impacts The following States are Members of the International Atomic Energy Agency :

AFGHANISTAN HAITI PAKISTAN ALBANIA HOLY SEE PANAMA ALGERIA HUNGARY PARAGUAY ARGENTINA ICELAND PERU AUSTRALIA INDIA PHILIPPINES AUSTRIA INDONESIA POLAND BANGLADESH IRAN PORTUGAL BELGIUM IRAQ ROMANIA BOLIVIA IRELAND SAUDI ARABIA BRAZIL ISRAEL SENEGAL BULGARIA ITALY SIERRA LEONE BURMA IVORY COAST SINGAPORE BYELORUSSIAN SOVIET JAMAICA SOUTH AFRICA SOCIALIST REPUBLIC JAPAN SPAIN CAMEROON JORDAN SRI LANKA CANADA KENYA SUDAN CHILE KHMER REPUBLIC SWEDEN COLOMBIA KOREA, REPUBLIC OF SWITZERLAND COSTA RICA KUWAIT SYRIAN ARAB REPUBLIC CUBA LEBANON THAILAND CYPRUS LIBERIA TUNISIA CZECHOSLOVAK SOCIALIST LIBYAN ARAB REPUBLIC TURKEY REPUBLIC LIECHTENSTEIN UGANDA DENMARK LUXEMBOURG UKRAINIAN SOVIET SOCIALIST DOMINICAN REPUBLIC MADAGASCAR REPUBLIC ECUADOR MALAYSIA UNION OF SOVIET SOCIALIST EGYPT, ARAB REPUBLIC OF MALI REPUBLICS EL SALVADOR MEXICO UNITED KINGDOM OF GREAT ETHIOPIA MONACO BRITAIN AND NORTHERN FINLAND MONGOLIA IRELAND FRANCE MOROCCO UNITED STATES OF AMERICA GABON NETHERLANDS URUGUAY GERMAN DEMOCRATIC REPUBLIC NEW ZEALAND VENEZUELA GERMANY, FEDERAL REPUBLIC OF NIGER VIET-NAM GHANA NIGERIA YUGOSLAVIA GREECE NORWAY ZAIRE, REPUBLIC OF GUATEMALA ZAMBIA

The Agency's Statute was approved on 23 October 1956 by the Conference on die Statute of the IAEA held at United Nations Headquarters, New York; it entered into force on 29 July 1957. The Headquarters of the Agency are situated in Vienna. Its principal objective is "to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world".

Permission to reproduce or translate the information contained in this publication may be obtained by writing to the International Atomic Energy Agency, Kammer Ring 11, P.O. Box 590, A-1011 Vienna, Austria.

Printed by the IAEA in Austria May 1974 TECHNICAL REPORTS SERIES No. 155

THERMAL DISCHARGES AT NUCLEAR POWER STATIONS Their management and environmental impacts

A REPORT PREPARED BY A GROUP OF EXPERTS AS THE RESULT OF A PANEL MEETING HELD IN VIENNA, 23-27 OCTOBER 1972

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1974 THERMAL DISCHARGES AT NUCLEAR POWER STATIONS Their management and environmental impacts IAEA, VIENNA, 1974 STI/DOC/ 10/155 FOREWORD

The thermal efficiency of nuclear power reactors in electricity generation is such that there is a need to dissipate a considerable amount of energy as waste heat. The discharge of this waste heat without disturbing the environment is a factor that must be taken into account in the siting of nuclear power plants, and this factor, will grow in importance with the predicted rapid increase in nuclear power production throughout the world. To examine in depth the problems of management of waste heat at nuclear power plants, the environmental impacts of thermal discharges, and the possibilities for beneficial use of waste heat, the Agency convened a panel of experts in Vienna in October 1972. The writing of this report, which was started during the meeting, was continued by the panel members in the twelve months that followed. Much of the information contained in it is common to all steam-powered electricity generation and is not unique to the nuclear industry, although with the present generation of nuclear power reactors the waste heat ratio is higher than in a modern fossil-fuelled plant. The Secretariat gratefully acknowledges the keen co-operation and extensive work of all the panel members, in particular Dr. B. Pellaud, Dr. J. Swinebroad and Mr. W. G. Belter for their additional work, as leaders of the three drafting groups, in preparing the texts of the chapters to which they were assigned.

CONTENTS

INTRODUCTION 1

CHAPTER 1. THE MAGNITUDE OF THERMAL DISCHARGES FROM A DEVELOPING NUCLEAR ECONOMY 3 1. 1. The growth of nuclear power 3 1.2. Thermal efficiency of nuclear reactors 5 1. 3. The magnitude of thermal discharges 7 References to Chapter 1 8

CHAPTER 2. ENGINEERING TECHNIQUES FOR NUCLEAR PLANT COOLING ... .. 9 2.1. Heat rejection to surface water 10 2.1.1. Rivers, streams and canals 2.1.2. Ponds, reservoirs, and lakes 2. 1. 3. Estuaries and coastal sites 2.2. Heat rejection to air 20 2.2.1. Cooling towers 2.2.2. Spray ponds [22, 23] 2. 2. 3. Mixed systems References to Chapter 2 30

CHAPTER 3. MATHEMATICAL AND PHYSICAL MODELS OF HEAT DISSIPATION 33 3. 1. Aquatic system models 33 3. 1. 1. Introduction 3.1.2. Mathematical models 3. 1. 3. Hydraulic or physical models 3.1.4. Field studies 3.2. Atmospheric system models 50 3.2. 1. Models for predicting atmospheric plume behaviour 3.2.2. Physical models References to Chapter 3 52 CHAPTER 4. PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS AND THERMAL DISCHARGES ON THE ENVIRONMENT 55 4. 1. Effects on water 55 4. 1. 1. Physical effects 4. 1. 2. Chemical effects 4.1.3. Water consumption 4.2. Potential atmospheric effects 58 4. 2.1. Ground level fog and icing 4.2.2. Clouds and precipitation 4.2. 3. Severe weather effects 4.2.4. Plume length and shadowing 4.2.5. Drift 4. 3. Other effects 66 4.3.1. Noise 4.3.2. Aesthetics References to Chapter 4 67

CHAPTER 5. BIOLOGICAL EFFECTS OF THERMAL DISCHARGES FROM NUCLEAR POWER PLANTS... 69 5.1. Introduction 69 5.2. General considerations 69 5. 2.1. Responses of biota to heat 5.2.2. Dose effect 5. 2. 3. Thermal discharges and dissolved oxygen 5.2.4. Thermal effects and chemical reactions 5. 3. Effects on aquatic organisms 74 5.3.1. Decomposers, detrital feeders and benthic macroinvertebrates 5.3.2. Producers 5. 3. 3. Consumers 5.3.4. Harvest 5.4. Effects on aquatic ecosystems 91 5.4.1. Ecosystem studies 5.4.2. Species diversity 5. 4. 3. Ecosystem stability 5. 4. 4. Eutrophicatión 5.4. 5. Disease and host-parasite relationships 5.4.6. Additive effects — toxicity 5. 5. Research recommendations 94 5. 5. 1. Chemical and physical (hydrological) research as related to the biota 5. 5. 2. General ecological studies 5. 5. 3. Studies on fish and other commercial and recreational resources 5.5.4. Other studies References to Chapter 5 96 Annexes to Chapter 5 Annex 1: Equilibrium constant 100 Annex 2: Rate constant 100 Annex 3: Preferred and lethal temperatures of fish 101 Annex 4: Fish oxygen demands and temperature 102 Annex 5: Fish development and growth related to temperature 103 Annex 6: Upper temperature tolerances of fish 104 Annex 7: Maximum temperatures reported at which eggs of marine fishes will hatch in laboratory experiments 108

CHAPTER 6. BENEFICIAL USES OF WASTE HEAT 109 6.1. General 109 6.2. Physical applications of low-grade and process heat 110 6. 2. 1. Low-grade heat from condenser cooling 6.2.2. High-grade (process) heat 6. 3. Biological applications of waste heat (low-grade) 120 6.3.1. Aquatic cultivation (aquaculture) 6.4. A global approach 124 References to Chapter 6 126

CHAPTER 7. THERMAL DISCHARGES AND THE SITING OF NUCLEAR POWER PLANTS 129 7.1. General considerations 129 7.2. Criteria for site selection 130 7. 2. 1. Thermal receptivity of the environment 7. 2. 2. Relevant factors for the assessment of the thermal receptivity of a given environment

7.3. Conclusions 134

Bibliography 137

APPENDIX A. HEAT DISSIPATION BY A WATER SURFACE 141

APPENDIX B. STANDARDS OF WATER PROTECTION 147

List of Participants 151

INTRODUCTION

The growing demand for energy to support and improve the quality of life throughout the world, coupled with the limitation of the world's resources of conventional fuels such as coal and oil, has required the development of alternative sources for electricity supply. There is little doubt that at least for the remainder of this century nuclear power will provide the principal alternative to conventional fuel for electricity generation. It has been estimated that by the year 1990 the nuclear share of the world electricity generating capacity will be equal to the total world generating capacity at the present time. The nuclear power plants of today have a thermal efficiency of about 33%. The balance of this energy must be discharged to the environment, and therefore the management of this waste heat to provide the minimum impair- ment to environmental quality is of great importance, together with the advance of reactor technologyto improve the thermal efficiency and so reduce the quantity of heat for disposal. Considerable work has been done in the industrialized countries in regard both to waste heat management and environmental effects of thermal discharges. In compiling this report the panel has drawn on existing knowledge from many sources and the report is supported by a considerable number of bibliographical references. It is hoped that the report will provide for those who will be concerned with these problems in electricity generation both useful reference material and a stimulus for further research and development to ensure the maintenance of environmental quality.

Chapter 1

THE MAGNITUDE OF THERMAL DISCHARGES FROM A DEVELOPING NUCLEAR ECONOMY

Over the next decades, nuclear power plants of the fission type will in most countries produce an increasing share of the electricity demand. The growth of nuclear generating capacity will therefore be particularly strong because of the continued effect of the increasing nuclear share and the expanding electrical demand, the latter being due in no small way to the environmental benefits of electricity when compared to other forms of energy. But electricity production by means of a heat source creates waste heat which must be disposed of in the site environment. This is true for a nuclear boiler, as well as for fossil-fired boilers. The matter of thermal discharges is therefore not unique to nuclear plants. The wide experience accumulated in many countries has shown that waste heat from the fossil- fired power plants built up to now has not caused a noticeable impact on the environment. But these plants were relatively small in comparison with the nuclear and central-station fossil-fuelled plants now under construction (up to 1300 MW(e)) and the cumulative impact of waste heat disposal from all plants, due to a representative 10-year doubling time of electricity consumption, had not reached in the late sixties the magnitude that will prevail in 1980 and later, when the nuclear and large fossil-fuelled plants being planned today will go into operation. The growing energy demand and the number of new plants of any type which must be built to meet this demand means that waste heat disposal becomes now a major consideration in the siting of nuclear plants. By taking advantage of the experience gained with fossil-fired plants and by planning carefully discharge methods, nuclear power should be able to play its role in the generation of electricity without detrimental consequences for the environment.

1.1. THE GROWTH OF NUCLEAR POWER

After having reached the threshold of economical competitivity, nuclear power has now matured to such a point that its dominance over the fossil- based production is generally unquestioned, at least above a minimum of a few hundred megawatts. The reasons are well known. The cost and the required maintenance of fossil plants increase roughly with total boiler tube length, which is itself proportional to plant capacity. This is not the case for nuclear plants. Furthermore, nuclear fuel costs are lower and more stable than fossil fuel costs. It follows that nuclear power tends to be economically preferred when large sizes are possible.

3 TABLE I. EXPECTED ELECTRICAL CAPACITY AND SHARE OF TOTAL CAPACITY OF NUCLEAR POWER STATIONS IN PERIODS SHOWN

DEVELOPING REGIONS a ADVANCED REGIONS Total,'' • woriWnplíol b A. Period 1970 - 1985 developing Eastern c Latin North Western Otherd total Africa Asia k'c countries USSR Europe America America Europe advanced

1970 Population (millions of people) 330 1075 155 285 1845 230 345 240 150 2810

1970: Capacity (GW) 0 0.5 0 0 0.5 10 10.5 1.7 1.3 24 ff») 0 1.3 0 ' 0 0.4 2.6 3.6 1.0 1.5 2.2 1975: Capacity (GW) 0 2.7 0.5 1.2 4.4 65 38 9 7 123 m 0 4. 1 0.9 2.0 2.2 12 9.5 3.5 5.1 8.0 1980: Capacity (GW) 0 11 5.5 6.0 22.5 155 100 43 24 345 (*> 0 10 7.2 6.8 7.3 21 18 11 12 13 1985: Capacity (GW) 1 24 11 16.5 52.5 320 210 160 65 810 ff») 2.2 14 10 13 11.6 32 29 30 23 27

DEVELOPING REGIONS a ADVANCED REGIONS a Total, b B. Period 1985-2010 developing Eastern Latin North Western Other total Africa Asia b countries USSR Europe America America Europe advanced

1985 Population (millions of people) 470 1560 180 440 2650 275 390 285 180 3780

1985: Capacity (GW) 1 24 11 16.5 52.5 320 210 160 65 810 ff») 2.2 14 10 13 11.6 32 29 30 23 27

1990: Capacity (GW) 5 68 42 52 167 570 400 320 160 1610 ff»> 7.9 24 28 27 25 44 42 44 40 40

1995: Capacity (GW) 16 175 100 115 405 880 640 540 310 2780 ff») 17 42 46 47 42 55 54 56 55 52 2000: Capacity (GW) 45 355 185 210 790 1220 910 805 530 4260 ff») 33 58 60 61 57 64 63 65 67 63

2005: Capacity (GW) 100 610 305 340 1350 1590 1200 1100 840 6070 ff») 51 69 70 70 68 70 70 71 75 70

2010: Capacity (GW) 185 950 470 530 2130 1970 1500 1420 1270 8290 ff») 64 77 77 77 76 75 75 75 80 76

a The nomenclature does not necessarily conform to standard political divisions. c Note that Turkey has been included with Eastern Europe. Excluding Mainland China. ^ Australia, Japan, New Zealand, South Africa. THE MAGNITUDE OF THERMAL DISCHARGES 5

TABLE II. PERCENTAGE OF NEW ELECTRICAL GENERATING CAPACITY WHICH IS NUCLEAR

Advanced Latin Eastern Period Asia Africa countries America Europe

1985-1990 78 41 18 68 68

1990-1995 88 74 38 87 87

1995-2000 90 90 65 90 90

2000-2005 90 90 86 90 90

2005-2010 90 90 90 90 90

The growth of the nuclear electrical capacity and its share of the total capacity in various parts of the world is shown in Table I [ 1 ]. The percentage of the new electrical generating capacity that is nuclear is shown in Table II [ 1 ] .

1.2. THERMAL EFFICIENCY OF NUCLEAR REACTORS

The thermal efficiency (r¡) of a power plant indicates how much of the produced thermal energy gets converted into useful electric power, with the remainder being discharged to the surroundings through condensers, and also the stack in the case of fossil plants. A plant with an electrical capacity of megawatts rejects then megawatts of thermal waste:

1 - T)

The thermal efficiency r) depends on many design factors which are selected on the basis of an overall plant optimization. However, in the first approximation, r¡ may be expressed as the product of two terms, namely

r? = g1c

The Carnot ideal efficiency r;c depends on the hot end temperature T2 and the cold end temperature Tj^ of the heat cycle (both temperatures being in degrees Kelvin):

= 1 * £ 2

The correction factor g, which represents the departure from the ideal Carnot cycle, in particular the irreversibilities at both ends, depends formally on type and layout of the heat cycle. The following values are representative and adequate for first-order approximations of thermal 6 CHAPTER 2

efficiency changes, caused for example by temperature changes at the cold end [2]:

Steam cycle without superheat g = 0.68 Steam cycle with superheat g = 0.65 Closed gas turbines (helium) g = 0.63

A modern fossil-fired plant, based on the steam cycle with superheat, has a thermal efficiency of around 40%. The thermal efficiency of fossil plants has steadily increased over the last decades, but technological improve- ments to reach higher efficiencies become more and more difficult to achieve. On the other hand, it should be emphasized that in countries with a large number of fossil plants, the average thermal efficiency of all plants is generally less than 35%. Thermal efficiencies of nuclear plants vary with reactor type, depending on the reactor' s ability to deliver high temperature to the turbine inlet nozzle. The following values summarize reactor performance in terms of waste heat production. (The cold end temperature is set equal to 17° C.)

Range of Hot Correction Waste thermal temp. factor, heat ratio, g efficiency (°C) P„/Pe (%) Heavy water reactor 240 0. 68 29 2.4 (HWR) Light water reactor 2 77 0. 68 32 - 34 2.1 - 1.9 (LWR) Breeder (sodium or 510 0.65 38 - 41 1.6-1.5 helium) High temperature 530 0. 65 39 - 41 1.6-1.4 reactor (HTR) High temperature 850 0.63 37 - 47 1.7-1.1 helium turbine reactor (HHT)

Only high temperature reactors and breeders exhibit the same level of thermal efficiency as modern fossil-fired plants. But in general, regardless of reactor type, existing and future nuclear plants based on the steam cycle reject to the environment large quantities of low-grade heat which are difficult to use beneficially and which often require large discharge structures, such as cooling towers. It is therefore noteworthy to mention the increasing attention which is devoted in many countries to gas turbines coupled with high temperature gas cooled reactors (HHT). Unlike steam turbines, gas turbines have the potential to produce high-quality waste heat, at temperatures well in excess of 100°C, and this without an appreciable economical or operational penalty to electrical generation. Industrial process heat or district heating utilization of the gas turbine waste heat could then lead to much higher overall thermal efficiencies, as, high as 80%. When not otherwise usable, waste heat could THE MAGNITUDE OF THERMAL DISCHARGES 7 be discharged to the atmosphere by means of natural draught dry cooling towers not much larger than the reactor building. There is indeed reason to hope that in the future high temperature reactors with associated helium turbines could alleviate the cooling problem of nuclear plants.

1. 3. THE MAGNITUDE OF THERMAL DISCHARGES

Most industrial countries which are favoured with large rivers have been able up to now to use these rivers directly for cooling purposes. However, with the prospect of electricity demand doubling every ten years or so, river temperatures would rise to unacceptable levels if this practice were to be continued unrestrictively. The same conclusion applies to lakes and estuaries. A shift to atmospheric cooling and sea cooling can therefore be observed in many countries. A comparison between total heat releases from thermal plants and total water run-off in a given region illustrates well the fact that once-through condenser cooling is indeed a limited solution for power plant cooling. Such a comparison is of course very rough, since it does not take into account such factors as run-off distribution in large or small streams, seasonal flow variations and other heat releases (industrial cooling water, industrial and community waste water). For that purpose one can assume that 1 GW(e) of electrical capacity requires about 50 m3/s of cooling water (temperature step 10°C, thermal efficiency 33%). At least twice that amount of water must be available if the temperature of the receiving waters may not exceed some reasonable temperature increment. Then, on the basis of 100 m3/s for each electric gigawatt of capacity, one can estimate in a very general way the capacity of the available run-off to receive thermal discharges. In the United Kingdom (England and Wales), the average run-off amounts to 2100 m3/s. The reference ceiling of 21 GW(e) was reached there in the 1950s and at that time a shift to cooling towers and sea cooling was indeed initiated. Because of the lack of surface water, the United Kingdom has now more than 300 wet towers, which provide cooling for approximately 50% of the total installed generating capacity. With an average run-off of 4000 m3/s, the Federal Republic of Germany reached its reference ceiling of 40 GW(e) in the 1960s. Thus, cooling towers are already commonplace and most nuclear power plants will be equipped with wet towers. In the United States of America, the run-off of 53 000 m3/s would correspondingly permit the installation of some 530 GW(e ). This level should be reached around 1980. Water is already regionally lacking and 13% of the existing thermal power plants are equipped with cooling towers. This percentage amounts to 35% for the new power plants under construction or ordered. Once-through cooling becomes also the exception in the Soviet Union, where in 1965 about 60% of the plants were cooled in this fashion, and only 40% in 1970. Artificial lakes and cooling towers are adopted more and more often, since the possibilities for using once-through cooling in large power plants have virtually been exhausted in most areas of the country. The increasing concern in many countries over the effects of increased temperature in surface waters and also the long-term availability of adequate 8 CHAPTER 2 cooling water supplies have resulted in a trend towards various alternative methods of thermal discharges from the large power plants being planned and built. Where it is possible to install generating plants on the shore or offshore, sea cooling represents an attractive solution for the dissipation of waste heat, provided that local effects are duly taken into account. On the other hand, atmospheric cooling with cooling towers or ponds can replace once-through cooling for inland sites. The capacity of the atmosphere to absorb heat is extremely large. In attempting to compare the artificial production of heat by human activities, it is however necessary to consider all forms of energy production and consumption _ transportation, space heating, industrial and domestic uses of oil, coal, gas, electricity — since all energies (with the exception of some chemical processes) end up as waste heat in the environment. Weinberg and Hammond [3] estimate that the ultimate energy generation by man will approach a maximum level of 20 kW per person (that is twice the current value in the United States of America). For a maximum world population of 25 x 109 people (that is about six times more than now), the artificial production from below the atmosphere would then be 0. 8 W/m2 [ 4] . As a comparison, the solar flux through the top of the atmosphere amounts to 350 W/m2 . However, human agglomerations in industrialized areas constitute heat islands with substantially larger heat output, as much as 1000 W/m2 in the centre of a city. Such large energy inputs are known to have local climatic effects. But in a wider geographical area, even in the industrialized and densely populated countries of Western Europe, the average heat output will not exceed over the next several decades a level of a few watts per square metre. As far as thermal discharges from nuclear plants are concerned, they will in all countries during that same period remain under 1 W/m2. Under such circumstances and with careful planning to avoid local effects, waste heat disposal to the atmosphere from nuclear plants should not result in a detrimental impact on the environment.

REFERENCES TO CHAPTER 1

[1] SPINRAD, B.I., "The role of nuclear power in meeting world energy needs", Environmental Aspects of Nuclear Power Stations (Proc. Symp. New York, 1970), IAEA, Vienna (1971) 57. [2] ACKERET, ]., "Abwármeprobleme der thermischen Kraftwerke", Neue Zürcher Zeitung, 13 Apr. 1970. [3] WEINBERG, A.M., HAMMOND, R. P., Limits to the use of energy, Am. Sei. 58 4 (1970). [4] HANNA, S.R., SWISHER, S.D., Meteorological effects of the heat and moisture produced by man, Nucl. Saf. 12 2 (1971). Chapter 2

ENGINEERING TECHNIQUES FOR NUCLEAR PLANT COOLING

Most modern power plants operate on the steam cycle by which pressurized hot steam drives a turbine that converts part of the input heat into mechanical and then electrical energy. Rejection of the unused heat occurs through steam condensers located after the steam turbine exhaust. Steam is condensed by contact with cold cooling water, either directly as in the spray condensers of dry cooling towers (system Heller) or indirectly across tubes as in the more common surface condensers. Cooling water comes from a body of water or from a cooling tower, and it may pass only once through the condensers or be recycled. The quantity and the temperature of cooling water are governed by basic heat flow relationships. For an electrical power plant capacity of

P£ megawatts (MW(e)), the waste heat amounts to

P =0.24 —5 p v(1) w -q e '

where n is the net plant efficiency and Pw is expressed in megacalories per second. The cooling water flow-rate R' through the condenser (in cubic metres per second) and the corresponding temperature rise AT1 (in °C) are such that

Pw= AT' • R' (2)

Engineering design determines the optimum values of AT1 and R' for a particular plant. In general, AT' lies within a few degrees above or below the typical value of 10°C. On that basis, a 1000 MW(e) nuclear plant equipped with a light water reactor (r¡ = 0.33) requires 48 m3/s of cooling water. The warmed up cooling water carries away the waste heat for disposal into a body of water or to the atmosphere by means of a suitable device. The available engineering techniques for nuclear plant cooling can therefore be divided into two broad categories. The first category concerns arrangements where cooling water is taken from and returned directly to a body of water, whence practically all the added heat reaches ultimately the atmosphere. The second category covers the various techniques such as cooling towers, whereby heat is rejected directly to the atmosphere. The final choice on the heat rejection technique to be adopted for a particular nuclear plant at a given site depends on a wide array of economical, environmental and technical factors strongly affected by local conditions.

9 10 CHAPTER 2

The method of discarding waste heat from a power station will be determined essentially by the availability of water and this in turn depends on local conditions at the site and on the economics of one method as compared with others. Economic operation of steam turbines in nuclear power stations depends on the temperature of steam condensation and this in turn is a function of the condenser cooling water temperature. This condition is best satisfied by a once-through cooling system in which the cooling water temperature is equal to the natural water temperature in the feed source. The use of once-through cooling seemed to present no particular difficulties until recently, and its widespread adoption was based purely on economic considerations. This was and still is a perfectly feasible approach when power stations are of small size and sparsely distributed near waterways and large bodies of water. But, this is no longer the case in many geographical areas. For that reason atmospheric cooling is being adopted more and more often, both on the ground of environmental consideration and for sheer lack of water in many cases. The resulting evaluation of the various engineering techniques of plant cooling is effectively a cost-benefit analysis of all economical and environmental factors, based on suitable criteria. Chapter 2 reviews some technical aspects entering into such an analysis, whereas Chapters 4 and 5 cover the environmental criteria that may in the last resort affect the choice of a cooling method.

2.1. HEAT REJECTION TO SURFACE WATER

When waste heat carried by condenser cooling water is discharged into a water body, the transfer to the atmosphere occurs over relatively large areas by evaporation, radiation, convection and conduction [1, 2], Systems are termed 'once-through' when the cooling water flow is circulated only once through the system and waste heat is discharged into natural water bodies such as rivers, lakes, or coastal waters. Heat dissipation from the receiving water surface will ultimately return the water to its natural temperature state within a certain distance from the point of heat discharge. This distance depends on a number of processes, e.g. the amount of mixing or dilution between the heated condenser water discharge and the receiving water and the transfer of heat from a water surface to the atmosphere through the combined mechanisms of evaporation, radiation convection, and conduction. The percentage of the total heat dissipation by evaporation increases as the temperature of the water surface increases above the air-water interface equilibrium temperature. The smaller the heat loss by evaporation, the lower the consumptive use of the water. The physical aspects of heat transfer from a water body to the atmosphere are discussed in greater detail in Appendix A. The proper design of discharge structures for once-through systems is a particularly important factor in determining the magnitude, extent, and distribution of thermal effects in the receiving water bodies. There is a high degree of flexibility in tailoring the temperature distribution in the receiving water to minimize the biological impact. At opposite ends of the design capability are complete stratification or complete mixing of the heated effluent. ENGINEERING TECHNIQUES 11

In the former case, mixing is avoided and the heated water is 'floated' onto the receiving water in a relatively thin surface layer. Heat transfer to the atmosphere is at a maximum rate, and there are no temperature changes at or near the bottom of the receiving water, as long as there is no significant turbulence. Because of the ability of the heat layer to spread, precautions must be taken which can be accomplished by means of an intake with a bottom opening known as a skimmer wall. This extreme type of non- mixing discharge allows fishes and other organisms to avoid the thermal plume, but among the disadvantages one should mention the strong temperature gradients at the plume boundary which can be detrimental to some aquatic organisms. The alternative is complete and rapid mixing of the warm water into the whole water body. In this design, the condenser cooling water is conducted through a diffuser pipe or tunnel and discharged through nozzles or ports near the bottom of the waterway. Entrainment of surrounding water into the high velocity jets produces rapid dilution, with minimum temperature gradients. Being the simplest and least expensive cooling technique, once-through cooling remains the first choice, whenever applicable. The environmental advantages of this method are the low consumption use of water, the ability to tailor the temperature distribution field in the receiving water to meet biological and temperature objectives and heat dissipation to the atmosphere

• DISCHARGE

FIG.l. General outline of an electric plant with direct intake and discharge in a water stream. 12 CHAPTER 2 over a large area. Other factors which must be carefully assessed in a proper design of discharge structures include entrainment of aquatic organisms, discharge jet effects on benthic organisms, bed erosion, and effects on navigation. Figure 1 shows schematically a cooling system where water is simply taken from a surface water body, passed through the condenser tubes and returned.

2.1.1. Rivers, streams and canals

When a river or stream is used as a source of cooling water, the water is discharged downstream of the intake. Provided the flow-rate is sufficient to satisfy environmental requirements, this method consists in using the water surface downstream as a natural heat-exchange surface to the atmosphere. A schematic representation of once-through river cooling is shown in Fig.2. At the discharge location A, the water temperature amounts to T1 = T+AT1. Assuming full mixing, the river temperature will have increased by AT at the end of the mixing zone, with respect to T. From Eqs (1) and (2) it follows that with respect to the upstream temperature T, the average temperature at point B is higher by

P T _ w _ 0.24 1 - r; p R R 17 e { '

Furthermore, the following relationship holds between flow-rates and temperature rises:

AT=^- AT' (4) It

FIG. 2. Once-through river cooling. R = Total river flow-rate (m3/s) T = Upstream river temperature (°C) R' = Cooling water requirement (m3/s) T' = Condenser exit temperature (°C) A = Discharge point B - Ehd of mixing zone ENGINEERING TECHNIQUES 13

The so computed AT corresponds to full mixing of the heated effluents with the river main flow. For partial mixing, the temperature in the thermal plume is characterized by a larger temperature increment, which varies between AT and AT1 . Under the influence of various meteorological factors (evaporation, convection, radiation), the downstream river temperature will tend to decrease. In other words, the initial temperature step AT decreases as a function of elapsed distance or time. An exponential decay is usually assumed (see Appendix A).

A0 = AT- e_d/D (5)

In this representation, AO = T(d)-T is the remaining temperature increment due to waste heat discharge at a distance d downstream from the power plant. The parameter D is the relaxation distance, corresponding approximately to a reduction of AT to one-third its initial value. The relaxation distance D depends on many physical and meteorological parameters which are difficult to assess for practical applications. By assuming constant meteorological conditions along the river and by using some simplifying assumptions, as described in Appendix A, it is possible to derive an empirical formula which accounts for the most important phenomena:

5TTF- <6> 0.01 T" + 0.95 + (0.62+ 0.37 u) (1+0.87 e ) where D is in kilometres. Here R is the average river flow-rate (m3/s), b the average river width (m), T" the surface water temperature (°C), and u the average wind velocity (m/s) at 2 metres above the water surface. Furthermore, h' (m) is the thickness of the surface water layer affected by the thermal discharges. With full mixing, as previously implied, h1 is equal to the average river depth h and T" is approximately equal to T + AT. For a non-mixing case, h1

A = (T" + 95) + (54 + 32 u)e0'05T" + (62 + 37 u) (7) derived in Appendix A, where the first term corresponds to radiation losses, the second to evaporation losses and the third to convection losses. A is expressed in kcal-m"2- d"1-^"1. As an illustration, consider the following example, with full mixing (h1 = h), for a very large nuclear station of 2000 MW(e).

Average river width (b) 200 m 1 Condenser flow-rate (R ) 100 m3/s Condenser temperature step (AT1 ) 10°C 14 CHAPTER 2

Winter Summer Upstream river temperature (T) 10°C 20°C Flow-rate (R) 300 m3/s 600 m3/s Wind velocity (u) 4 m/s 2 m/s

These results are then obtained:

Temperature after mixing (T") 13.3°C 21.7°C Relaxation distance (D) 193 km 430 km Relaxation time* (t) 4.5 d 5 d

Temperature after 100 km 12°C 21.3°C 200 km 11.2°C 21 °C 300 km 10. 7°C 20.8°C

* For a flow velocity (v) of 0. 5 m/s in winter, and 1 m/s in summer, on the basis of t = D/v, and also R = hbv

Downstream temperature computed with the help of Eqs (5) and (6) should be interpreted with great caution and placed in the proper perspective. Such a theoretical approach is simple and convenient, but is also known to underestimate dissipation of heat by the river and thereby overestimate downstream temperature. As discussed in Chapter 3, detailed mathematical models are indeed required to accurately predict the thermal behaviour of a river. Firstly, these formulae are based on average yearly conditions, and thus no seasonal and diurnal variations nor changing weather conditions are taken into account. Quite different results are obtained when these effects are duly considered in the analysis. Recent studies on the Ohio River in the United States of America, using the Orsanco model which is based on observed and measured values and then fitted, indicate a more rapid dying out of temperature effects from heated effluent discharges. Actual measurements carried out in France on the Marne River [ 3 ] have led to a relaxation distance half as long as that given by Eq. (6). Furthermore, in assessing the importance of downstream river temperature, it should be kept in mind that natural temperature fluctuations of 1 to 2°C within 24 hours are not uncommon. Because of natural phenomena it is unlikely that- detectable evidence of heat discharges below a one degree difference can be accounted for far away from the plant. In the example shown, the impact of waste heat would cease to be measurable at most after 200 km, more likely after 100 km. In regard to the amount of water evaporated from a river due to waste heat discharge, it is in first approximation derived from the ratio of the evaporation term to the whole heat transfer coefficient in Eq.(7).

0.05 T" M = 58?A<54 + 32 u>el (8) where M is expressed in cubic metres per second. Thus M is about 1 m3/s for the 2000 MW(e) station of the example shown. Possible effects of waste heat disposal in a river, which may have to be taken into account are considered in detail in Chapters 4 and 5. It will suffice for the moment simply to list these effects: ENGINEERING TECHNIQUES 15

Increase in river mean water temperature could lead to: (1) A decrease of oxygen solubility at saturation. (2) A decrease in the river re-aeration rate due to the reduced oxygen saturation deficit. (3) An increase in Biological Oxygen Demand (BOD). Under certain conditions further effects may be felt also, namely: (4) A possible deterioration in quality of drinking water if the river is used as a source for this. (5) A change in aquatic population, both qualitatively and quantitatively. (6) An augmentation of undesirable aquatic flora (micro- and macroflora). Aeration of the cooling water in the discharge process will lead to: (7) An increase in the specific oxygen content of the river water leading to a slight increase in water quality. An increase in particular of the river surface temperature can lead to: (8) A reduction in ice formation in winter. (9) An increase in evaporation from the surface of the order of 0.5 m3/s per 1000 MW(e) leading to possible mist formation and in extreme cases of accumulation to a reduction of depth usable for navigation. Transverse velocity of the discharge water relative to the river flow can lead to: (10) Complications to river nagivation. Inlet or outlet velocity of the condenser cooling water can lead to: (11) Scouring of the river bed and erosion over a limited area.

2.1.2. Ponds, reservoirs and lakes

Cooling ponds are water bodies which in general are used exclusively for power plant cooling. Two types of cooling pond operation are possible: recirculation or "once-through. In the recirculation type the condenser cooling water is discharged at one end of the pond and pumped at the other end, thereby forming a closed system with the power plant. The water surface area determines the pond effectiveness to deliver cold cooling water to the condensers. The area of a closed cooling pond required to reach a given cold water temperature maybe computed on the basis of Eqs (5) and (6). To do so, it is sufficient to redefine the variables appearing in those equations, with respect to the air temperature Ta, and introduce the surface area instead of the distance:

A0 = TC0ld - Ta (> °)

AT = Thot - Ta = Tcoid + AT' - Ta = A6 + AT*

AT = T - Ta with Tcold = inlet condenser temperature Thot = outlet condenser temperature T = average water temperature in pond Then cS R A0 = AT e ' (9) 16 CHAPTER 2

AT S = in ( 1 + (10) a T - T C cold a' where S,the pond area,is given in km2,- R1, the cooling water flow-rate,in 3 1 m /ss and AT , the temperature increment through the condensers,in °C. The average temperature increment in the pond follows from the overall heat balance:

AT (11)

In all these equations a, expressed in Meal-km"2-s"1-"C"1, represents the average heat transfer coefficient per unit area:

a - 1.16 [0.01 T + 0.95 + (0.62 + 0.3 7 u) (1 + 0.87 e°- 05 T)] (12)

with T = Ta + AT . As an example, consider the case of a 1000 MW(e) nuclear plant requiring 50 m3/s of cooling water (R1 ) with a condenser temperature step (AT1 ) of 10°C. In order to maintain an acceptable condenser vacuum in

summer also, a cold temperature (Tcold) of 25°C is stipulated. Then, for an air temperature (Ta) of 20°C and a wind velocity (u) of 1 m/s, the pond area (S) should amount to 8 km2. In that case, cooling water enters the ponds at 35°C and then leaves it at 25°C. It should be mentioned that Eq. (9) ignores, among other factors, the temperature influence of the make-up water, natural or artificial, which is required to compensate for evaporation losses given by the expression derived in Appendix A:

05T 05T M = 0.01 S (2.12 + 1.25 u) (e°- -

where q> is the relative air humidity, and M is expressed in m3/s. This amounts to 0.64 m3/s for the example shown (with cp = 0. 7). Cooling ponds can also be used in a once-through mode. In that case, condenser intake water is withdrawn from a body of water other than the cooling pond, passed through the condensers, discharged to the pond and then returned to the water body. In this type of operation the pond is used as a buffer to reduce the potential thermal effects upon the receiving water body (see Pig. 3).

FIG. 3. Cooling pond. ENGINEERING TECHNIQUES 17

In that case, one has

A0 = T" - Ta 1 1 AT = T - Ta = T - Ta + AT

In order to cool the condenser outlet water, the condition T'> Ta must 1 be satisfied. This means that Ta - T < AT , a condition which would normally be satisfied since the air temperature and the upstream river temperature would tend to be in equilibrium with each other. Then, A0 = AT e R' (14) with a given by Eq. (12) in which T is in first approximation set equal to T + AT1 . The following example shows that it takes a rather large pond to lower the temperature by just a few degrees. For T = 20°C, Ta = 20°C, AT' = 10°C, R' = 50 m3/s, u = 1 m/s, and a pond surface area of 2 km2, the water returned to the water body has a temperature of T" = 27.6°C, instead of what it would be without a pond (that is T' = 30°C). Lakes and reservoirs are also suitable for power plant cooling when they are sufficiently large. This latter condition is necessary in order to avoid detrimental consequences of the heated effluents on the lake1 s aquatic life. Whereas cooling ponds may be evaluated strictly from an engineering viewpoint because they are not supposed to sustain any life, environmental factors need be considered when dealing with natural lakes and reservoirs (for hydropower or drinking water supply). The heat transfer analysis of deep lakes and reservoirs requires sophisticated theoretical and computational tools because of the complexity of the underlying physical phenomena. For continuous plant operation also, it is basically a time-dependent, three-dimensional problem. Stratification and the corresponding seasonal variations play a significant role in this respect. So do the intake and discharge methods which are adopted. The average annual increase in water-surface temperature may, however, be calculated from the overall heat balance (first part of Eq. (11)):

P (15) b a

with Pw given by Eq. (1) and a by Eq. (12). Three different patterns of cooling water intake and discharge may, in principle, be adopted: (a) Surface intake and discharge (b) Deep-water intake, surface discharge (c) Deep-water intake and discharge Examples of the physical effects of these three methods on a particular lake are shown in Figs 4-6. The natural temperatures in Lake Lucerne (Vierwaldstättersee) in Switzerland have been thoroughly measured [4] and used as a base in these figures. Each figure shows the types of temperature profile to be expected in a lake of this type (114 km2) over the course of a year, with and without waste heat discharges. 228 CHAPTER 2

SPRING SUMMER 0 10 20 0 10 20 °C

FIG. 4. Surface intake and discharge.

SPRING SUMMER 0 10 20 0 10 20 °C

FIG. 5. Deep-water intake, surface discharge.

SPRING SUMMER

FIG. 6. Deep-water intake and discharge. ENGINEERING TECHNIQUES 19

The characteristics of the lake's natural temperature turn-over are briefly as follows: In late winter (February/March) the lake shows a very flat temperature profile. Accumulated heat from the previous summer has been given off, and mixing due to wind-induced turbulence removes temperature peaks. In large lakes the usual minimum winter temperature is not less than 4°C (max. density). (The turbulence during this early part of the year offers the lake its greater chance of regeneration.) During spring and summer (until September) the lake surface is warmed by radiation. The mean water surface temperature is such that heat is given off at night and taken in by day. Stratification progresses downward. Wind turbulence affects only the uppermost water layers. In shallow lakes this can occupy the full water depth. During autumn and winter the air is cooler, so a cooling of the warmed surface layer takes place. This leads to an unstable stratification which favours mixing. Strong currents in the lake can limit the vertical spread of a thermal plume by causing it to flow over the water surface as shown for instance by the measurements of temperature profiles of the plume from Douglas Point power station beside Lake Huron in Canada. Here, in spite of a local lake depth of only 5 m, heating was not detectable below a depth of 1.5 m. How- ever, in that case the heat flux to the atmosphere from the identifiable plume is only approximately 1/3 of the total reject heat flux. Thus, outside this identifiable region the temperature difference above the natural level and hence heat transfer to the atmosphere is very low. As to the effects of the plant's heated effluents the figures show that they depend strongly on the intake and discharge method which is adopted. Surface intake and discharge affects only the upper layers and atmospheric cooling is then better. But, for a relatively large plant, surface temperatures become excessive. Deepwater intake and surface discharge results in lower surface temperature, but the overall mixing is from an ecological viewpoint undesirable since nutrients are thereby being circulated. This solution is therefore not suitable for lakes with high eutrophication levels. Deepwater intake and discharge minimizes both surface temperatures and vertical water circulation. However, since atmospheric cooling is then small, most of the plant waste heat ends up as stored heat in the deeper layers of the lake. Lakes or reservoirs must therefore be large in order to serve as heat sink for power plants. The magnitude of the impact can roughly be assessed by comparing the plant waste heat output with some natural heat quantity. As noted previously, lakes absorb and reject heat from and to the atmosphere in a cyclical pattern. For example, under the conditions prevailing in Central Europe, at the end of summer, a lake has stored an excess energy of about 250 teracalories per square kilometre, an energy which is then released during the subsequent six-month winter period. During that same period, a 1000 MW(e) nuclear plant (light water reactor) produces 7500 Teal. This would thus represent more than 5% of the heat energy stored in the largest European lakes (Balaton, Geneva, Constance) having an area of close to 600 km2. Nothwithstanding local effects of heat discharges a few such plants would already correspond to a sizable fraction of the natural heat balance of such lakes. In general, if one wishes to 20 CHAPTER 2 limit at, say, one degree Celsius the average vertical temperature increase at the most unfavourable time of the year, the lake should have a volume of about 10 km3 per 1000 MW(e) (that is a 200 km2 area for a 50 m depth). This corresponds to the method of deepwater intake and discharge. With the other methods, the more important atmospheric cooling reduces the volume requirements.

2.1.3. Estuaries and coastal sites

Sea water offers good potential as coolant for electrical generating plants. When due care is taken to avoid local effects in the discharge area, the ocean offers the possibility of large-scale heat rejection with a small environmental impact. Once-through cooling with sea water is already extensively used, especially in countries with a small river run-off and short access to coastal sites, such as Japan and the United Kingdom. Estuaries have some common characteristics with rivers. However, tidal flow and the stratification of fresh and salt waters represent unique features of estuaries. There are few problems associated with cooling water discharges to the sea along an open coastline. The mixing of effluents depends upon tidal movements, shore currents and wind driven circulation. The local hydro- graphic conditions need to be studied and precautions taken to avoid recirculation of the discharged water. As described in Chapter 3, extensive analytical studies may be required to gain a full understanding of the heat dissipation capability of a site.

2.2. HEAT REJECTION TO AIR

There are occasions when it is not possible or practicable to reject heat to a natural water body, especially when no land is available for any type of cooling pond or reservoir. In these cases it might simply be that water in sufficient quantity and quality cannot be found in the neighbourhood of the site. On the other hand, it might be that local natural water bodies could not accept the thermal load without causing offence to water quality regulations, or that severe ecological consequences would result. In such cases, one of the following cooling devices must be adopted for a nuclear plant: (a) Evaporative cooling towers (b) Spray ponds or canals (c) Dry cooling towers

(d) Hybrid evaporative/dry cooling towers

2.2.1. Cooling towers In most cases cooling towers of one type or another are used. There are many types available and the terminology applied stems from basic differences in design or operation which serve to categorize them. A tower may be either 'wet' (evaporative) or 'dry' depending on whether or not the cooling water is exposed to the air; 'mechanical draught' or 'natural draught' depending on whether or not fans are employed for inducing air movement; 'cross flow' or 'counter flow1 depending upon ENGINEERING TECHNIQUES 21

COOLING TOWER

FIG.7. Simplified flow diagram.

whether the air flow through the heat transfer section ('packing1 ) is horizontal or vertical. In mechanical draught towers air flow may be either 'forced draught' or 'induced draught" depending on whether the fans push the air through from the bottom or side or pull it through from the top of the packing.

2.2.1.1. Evaporative cooling towers

Figure 7 shows a simplified plant cycle with an evaporative cooling tower as heat rejection device. Figures 8-11 are schematic drawings of four evaporative tower types [ 5-10]. Figure 8 shows a natural draught tower with counter flow 'film' packing. This is to say, where the packing consists of vertical sheets of asbestos, either flat or corrugated filling the whole cross-section of the tower just above the air inlet opening. Figure 9 shows the alternative cross-flow packing, of the 'splash' type. Here the water falls through a mass of laths of wood, asbestos or plastic. Figure 10 shows a mechanical draught tower of the cell type, seen from the end. These cells are arranged in blocks, in practice up to several hundred metres long. This tower is shown with an induced draught fan, but could equally well be equipped with forced draught fans at both air inlets. Figure 11 shows another type of mechanical draught tower — the round, induced draught type, using a small concrete shell. 22 CHAPTER 2

FIG. 8. Natural draught tower Wet (evaporative) counter-flow.

COLD WATER BASIN

FIG. 9. Natural draught tower. Wet (evaporative) cross-flow. ENGINEERING TECHNIQUES 23

AIR OUTLET t t

FIG. 10. Mechanical (induced) draught cooling tower with cross-flow splash packing.

FIG. 11. Round (induced) draught tower with film type counter-flow packing.

The natural draught tower has two distinct practical advantages over the mechanical draught tower in that the lack of mechanical and electrical components reduces both operating and maintenance costs, and that it offers the most compact solution in terms of ground use. Against this a modern mechanical draught unit with variable speed fans or variable pitch fan blades can offer closer control of cooling water temperature over a wide range of atmospheric conditions in addition to sustaining less wind resistance than natural draught towers. In hot, dry climates natural draught towers would have to be higher than in temperate climates in order to provide the same draught and cooling effect. 24 CHAPTER 2

TABLE III. WET BULB TEMPERATURE

Dry bulb Wet bulb temperature (°C) with relative air humidity of: temperature CC) 30% 50% 70% 90% 100%

5 0 1.4 2.9 4.3 5

7.5 1.8 3.5 5.2 6.7 7.5

10 3.7 5.6 7.5 9.2 10

12.5 5.5 7.6 9.7 11.6 12.5

15 7.3 9.8 12 14 15

17.5 9.2 11.8 14.2 16.4 17.5

20 11 14 16.5 18.9 20

22.5 12.7 15.9 18.6 21.3 22.5

25 14. 5 18 21 23.5 25

27.5 16.4 20.1 23.2 26 27.5

30 18.1 22.1 25. 5 28.4 30

All evaporative towers have a common principle — that is that the warm condenser cooling water is sprayed evenly down through the packing, whose role is to increase the air/water heat exchange surface. Heat exchange with the air occurs partly by conduction/convection and partly by evaporative heat transfer. The ultimate limit to which condenser water can theoretically be cooled is the wet bulb temperature of the air. In practice this is never reached, but more or less approached. The 'approach1 is defined as the difference between the achieved cold water temperature and the wet bulb temperature. The wet bulb temperature depends on both the air temperature (dry bulb temperature) and the relative humidity of the air. It is defined in the following way: When air and water are in close contact, the wet bulb temperature corresponds to the temperature reached by the water under the influence of water evaporation into the air. This process should occur adiabatically and at constant pressure. Palling rain drops approach the wet bulb temperature of the surrounding air (and not the air temperature itself). As seen in Table III, the wet bulb temperature is lower than the normal air temperature. Of particular importance is the fact that the wet bulb temperature decreases with the relative humidity. In many regions, to the warm summer days correspond generally low humidities, and therefore low wet bulb temperature, which maintains a good efficiency of the wet cooling towers. For the same wet bulb temperature — that is approximately the same tower efficiency — cooling occurs by different heat transfer mechanisms, depending on the relative air humidity. At, say, 11°C and 100% humidity (i. e. 11°C wet bulb), the saturated inlet air is schematically warmed up by ENGINEERING TECHNIQUES 25

TABLE IV. DISTRIBUTION OF WET AND DRY BULB TEMPERATURE

Number of days in a year Temperature with wet bulb temp, with dry bulb temp, co higher than that given higher than that given in left-hand column in left-hand column

-5 350 356

0 310 330

5 250 270

10 170 , 200

15 70 160

20 6 100

25 0 30

TABLE V. NATURAL DRAUGHT WET COOLING TOWER (RANCHO SECO)

Height 130 m

Bottom diameter 95 m

Throat diameter 52 m

Top diameter 61 m

Volume of concrete 8 500 m3

Collecting basin 10 000 m3

Thickness of hyperbolic shell (bottom) 60 cm

Thickness of hyperbolic shell (throat) 18 cm

Droplet carry-over 3 litres/s

Evaporation losses (winter) 250 litres/s

Evaporation losses (summer) 350 litres/s

Cooling water flow-rate 14.2 m3/s

Reference operating conditions:

Air at 11° C and 6 (fjo humidity Hot temperature 39.4°C Cold temperature 23. 9°C Condenser temperature step 15. 5°C Heat removed 221 Mcal/s

convection/conduction and then saturated at the higher temperature before leaving the tower. At 20°C and 30% humidity (i.e. 11°C wet bulb), heat transfer would result mostly from evaporation. Under such circumstances, a wet cooling tower retains its efficiency during the summer months much more than a dry cooling tower, which depends exclusively on the dry bulb temperature. On the other hand, the 26 CHAPTER 2

TABLE VI. WET TOWER PERFORMANCES

Plant thermal Dry bulb Humidity Wet bulb Power loss efficiency (°C) (°Q (<7°) (<7°)

- - - 33.3 0.0

4 50 0.5 32.8 -1.6

10 70 7.5 32.2 -3.4

20 50 14 31.6 -5.1

30 30 18 31.0 -7.0

wet bulb temperature varies much less than the dry bulb temperature over the diurnal cycle. Tables IV and V illustrate the cumulative occurrence of various temperatures (at 2 p.m. ) for a typical Central European location. Natural draught wet cooling towers are generally adopted for large base-load nuclear plants in preference to other types of towers, but in some instances mechanical draught wet cooling towers are preferentially used. As an example, the nuclear plant to be operated in Rancho Seco (California) will be equipped with two natural draught towers to reject the waste heat produced by the generation of 850 MW(e). The characteristics of the tower are shown in Table V. Performances of wet natural draught towers depend on the following parameters: Height and diameter Hot and cold water temperature Water flow-rate Wet bulb temperature (to a smaller extent dry bulb temperature also). Appendix B discusses in greater detail some technical aspects of cooling towers. As far as tower dimensions are concerned, the equivalent electrical capacity cooled by a tower increases as D2N/H, where D is the bottom diameter and H the height. This is for fixed air cooling water conditions. For a fixed flow-rate, the wet bulb temperature influences the cold water temperature, which determines condenser vacuum and ultimately the electrical output. This influence is shown in Table VI. The above comments regarding performances of natural draught wet towers are also broadly applicable to forced draught wet towers. In the latter case, fan speed constitutes a degree of freedom to compensate performance losses due to temperature drops. In wet towers the cold water is collected in a basin under the packing structure and then returned to the condenser. Water losses by evaporation and droplet carry-over are compensated by make-up water drawn from an external water body. On the other hand, the concentration of salts in the circulating water tends to build up due to the evaporative loss of pure water. The system must therefore be purged and the rate of make-up water increased. The resulting total make-up water flow-rate is then typically of the order of 3 to 5% of the circulating water quantity. ENGINEERING TECHNIQUES 27

Modern cooling towers (see Figs 8-11 ) are all equipped with efficient drift (droplet carry-over) eliminators which reduce the quantity of water emitted in droplet form to less than 0.1% of the circulating water rate. Guarantee figures are at present 0. 03% and seem likely to reach 0. 002% in the near future. It is this feature which has reduced precipitation and icing problems to negligible levels during the last few years.

2.2.1.2. Dry cooling towers

The constraints imposed by the unavailability of make-up water, and potential adverse increases in concentrations of solids from plant purge lead sometimes to the employment of dry cooling towers as the only alternative. In dry cooling towers, exhaust heat is rejected to the atmosphere through an extended surface heat exchanger. The application of dry cooling towers was analysed in a number of previously published papers (see Refs [ 11-21]).

FIG. 12. Dry cooling tower - GEA system.

AIR EXIT

FIG. 13. Dry cooling tower — Heller system. 28 CHAPTER 2

Although direct air condensers (Fig. 12) have been used for conventional power plants, they cannot practically be used for nuclear plants because of size limitations (only suitable for up to several hundred MW(e)). Therefore, the indirect system, known mostly as the Heller system, represents the most probable application of dry towers to nuclear plant cooling. The Heller system (see Fig. 13) utilizes a direct contact, or jet condenser instead of the conventional tubed condenser. Circulating water, which must be high quality condensate, is sprayed into the jet condenser where it mixes with and absorbs the heat from the exhaust steam as condensation occurs. Large circulating water pumps recycle most of the heated condensate to the dry-type cooling tower and return the remaining condensate to the feed- water cycle. Although an induced mechanical draught type tower is shown, a natural draught type tower could be utilized. The type of tower selection would, of course, be a major factor in the overall economics of system design. Many of the dry towers now in service operate on natural draught. The largest towers are located in Rasdan in the Soviet Union and at Gyöngyös in Hungary. Their characteristics are shown in Table VII. Large dry towers are also in operation in the Federal Republic of Germany (Ibbenbueren), and the United Kingdom (Rugeley). All these towers

TABLE VII. DRY COOLING TOWER (HELLER SYSTEM)

Rasdan Gyöngyös

Corresponding electrical output 220 MW(e) 220 MW(e) (conventional)

Bottom diameter 108 m 109 m

Height 120 m 116 m

Heat removed 67 Mcal/s 63.4 Mcal/s

Temperature approach 30° C 26°C

Water flow-rate 6.1 m3/s 5. 8 m3/s

TABLE Vni. DRY TOWER PERFORMANCES

Air temperature Water condenser Plant thermal Power loss (dry bulb) inlet temperatute efficiency CO fC) m m

-11 17 33.3 0.0

- 5 23 32.5 -2.5

4 32 31.4 - 5.7

10 38 30.7 - 8.0

20 48 29.5 -11.5

30 58 28.3 -15.1 ENGINEERING TECHNIQUES 29 are natural draught and are used in conventional generating stations. The largest forced draught version of the Heller system cools a small nuclear plant of 48 MW(e) in Bilibino in Siberia. Dry towers for large nuclear plants would reach impressive dimensions. For example, for a 600 MW(e) nuclear plant, the tower diameter would be 205 m at the bottom and 125 m at the top and its height 172 m. The efficiency of a dry tower is determined by the temperature approach, which is defined as the difference between the cold cooling water temperature and the air temperature (dry bulb). The smaller the approach, the better the plant thermal efficiency, but to a smaller approach correspond also greater heat transfer surfaces and higher costs. For a conventional plant, the typical approach amounts to 25-30°C. A somewhat higher approach may be desirable for nuclear plants. Table VIII shows the influence of air temperature on electrical output. The percentage power loss during the summer months is seen to be considerable. The accumulated energy loss during the summer months leads to a large economic penalty, especially for electrical systems with a summer peak demand. Operating experience with existing dry cooling towers has been generally good. However, this experience is limited to relatively small conventional plants and it cannot be directly extrapolated to the large nuclear plants being now under consideration. The natural draught dry tower requires a diameter even greater than that of a wet natural draught tower of comparable capacity (the necessary air throughput is up to six times greater). The aesthetical impact of such towers may preclude their installation in many areas. This problem is compounded by the currently adopted construction technique of truncated cylinders, which is not particularly elegant. The use of dry cooling towers with spray condensers may be impossible in combination with a direct-cycle boiling water reactor, due to the presence of radioactivity in the reactor water and to the risk of tube leak in the dry tower. A surface condenser could eliminate the problem. It appears, however, that an intermediate heat exchanger between the high-pressure and low-pressure parts of the turbine could be a more efficient solution. Dry cooling for large light water reactor plants should be feasible once solutions have been found to some technical problems such as pH incom- patibility between the tower's aluminium and the turbine's steel or water flow control in large towers, but all these problems may be eliminated by the use of a surface condenser. It is, however, clear that the ideal application of dry towers will be in combination with high temperature gas turbine reactors. The higher temperature level of the discharged heat causes in that case a smaller efficiency decrease than in a steam-turbine process, thereby alleviating the economic penalty of dry cooling. The same higher temperature permits higher air exit temperature, smaller air throughput and, therefore, much smaller towers. As far as the environmental impact is concerned, dry cooling towers may represent the best method of discarding waste heat. Except for the possible formation of cumulus clouds, direct effects on the environment are at a minimum. But the aesthetical impact associated with tower shape and dimensions constitutes a major hurdle for an application to nuclear plants to be sited in inhabited regions. Smaller forced draught towers could help, but with an even higher economic penalty. 30 CHAPTER 2

2.2.2. Spray ponds [22, 23]

A spray pond is a pond with a spray system located about 2 to 3 m above a large natural or artificial reservoir. A louvre fence on the ponds' leeward side keeps the water from being blown away. Although more compact than a cooling pond it has some disadvantages:

(1) Limited performance available because the contact time of the sprayed water-with-the-air before reaching the surface of the pond is comparatively limited; (2) A nuisance is created by the high water loss at certain times of the year during high winds, activating corrosion through carry-over of droplets; (3) Since they are open to the atmosphere, ponds collect considerable quantities of foreign matter which pollutes the water.

But spraying reduces considerably the pond area required: by a factor between 30 and 100.

2.2.3. Mixed systems

Mixed systems are required:

(a) As series devices to achieve the thermal quality standards before direct discharges can be made to the water body. Examples of these are the use of spray ponds, cooling ponds or cooling towers prior to such discharge. (b) As parallel stand-by devices where large seasonal changes occur in air temperature and humidity and in water temperature and availability. Extreme annual range of air temperature may require dry cooling in winter and wet cooling in summer: Hybrid cooling towers which can be operated either as evaporative or as dry are now being conceived to satisfy this requirement.

Where river flow or lake storage is poor in certain seasons and undergoes large seasonal variations cooling towers may be used instead of direct cooling in such seasons.

REFERENCES TO CHAPTER 2

[1] U.S. National Academy of Engineering, Engineering for the Resolution of the Energy-Environment Dilemma, Committee on Power Plant Siting - Working Group on Environmental Protection: Water, Washington, D.C. (1972). [2] Federal Water Pollution Control Administration (N.W. region, U.S. Dept of Interior), Industrial Waste Guide on Thermal Pollution. Sep. 1968 (revised) 112. [3] GOUBET, A. , Influence des centrales thermiques sur les cours d'eau, Terres et Eaux 52 (1966). [4] Gewässerschutztechnische Gesichtspunkte im Zusammenhang mit der Kühlwasserentnahme und -ruckgabe bei konventionell- und nuklearthermischen Kraftwerken, Eidgenössisches Department des Innern, Bern, 19 Mar. 1968, 2ndedn. Sep. 1970. [5] JONES. W. J. , Natural draft cooling towers, Ind. Water Eng. (March 1968) 21. [6] STOCKHAM, J., Cooling Tower Study, Final Rep. for Contract No. CPA 22-69-122, IITRI Rep. No. C6187-3, EPA Air Poll. Cont. Office, Durham, N.C. (1971). ENGINEERING TECHNIQUES 31

[7] McKELVEY, K.K. , BROOKE, M. , The Industrial Cooling Tower, Elsevier Publishing Co. , New York (1959) 429 p. [S] DeHARPPORTE, D.R. , Cooling tower site considerations, Power Eng. (Aug. 1970) 49. [9] DAVIDSON, W. C., Tower's Cooling Doubled by Fan-Assisted Draft, Electr. World 69 13 (1968) 19. [10] BIERMAN, G.F., et al., "Characteristics, classification, and incidence of plumes from large natural draft cooling towers", Proc. Am. Power Conf. , Vol. 33, 1971. [11] CHAVE, C.T. , "Applicability of air cooling to siting problems in the Pacific coast area", Pacific Coast Electrical Association Conf. , Mar. 1970. [12] Dry Versus Wet Cooling Towers — Which is Best?, Electric Light and Power Special Rep. , Nov. 1965. [13] HEEREN, H., HOLLY, L. , "Air cooling for condensation and exhaust heat rejection in large generating stations", Proc. Am. Power Conf. Vol. 32, 1970. [14] RETI, G.R., "Dry cooling towers", Proc. Am. Power Conf. Vol. 25, 1963. [15] RITCHINGS, F.A., LÖTZ, A. VI., "Economics of closed versus open cooling water cycles", Proc. Am. Power Conf. Vol. 25, 1963. [16] RITCHINGS, F.A., "Closed cooling water cycle for electric power generation", Rocky Mountain Electrical League Spring Conf., Apr. 1964. [17] RITCHINGS. F.A. , "Closed cooling water cycle saves water", eectrical West, Nov. 1964. [18] SMITH, E. C. , LARINOFF. M.W.. "Power plant siting, performance and economics with dry cooling tower systems", Proc. Am. Power Conf. . Vol. 32, Apr. 1970. [19] FORTESCUE, P., Tomorrow's plants: gas turbines, nuclear power, dry cooling, Power Eng. 75 8 (1971) 45. [20] ROSSIE, J.P., CECIL, E.A. CUNNINGHAM, P.R., STEIERT, C.J., "Electric power generation with dry-type cooling systems", Proc. Am. Power Conf. Vol. 33 (1971) 524. [21] LEUNG, P. , MORE, R. E. , Power plant cycles for dry cooling towers, J. Power Div. Am. Soc. Civ. Eng. 97 (P04) (1971) 729. [22] MALKIN, S. , Converting to spray pond cooling, Power Eng. 76 1 (1972) 48. [23] FROHWERK, P.A. , Spray modules cool plant discharge water. Power 115 9 (1971) 52.

Chapter 3

MATHEMATICAL AND PHYSICAL MODELS OF HEAT DISSIPATION

3.1. AQUATIC SYSTEM MODELS

3.1.1. Introduction

Before one can assess the biological or ecological impact of thermal releases on a particular receiving body of water, it is necessary to determine the areal extent and temporal behaviour of the temperature changes within the body of water induced by the heated discharges. The proper design of discharge structures for once-through systems is the most important factor in determining the magnitude, extent, and distribution of thermal effects in the receiving water bodies. The increased size of both nuclear and fossil-fuelled units and a growing concern with the environmental effects of water temperature changes have combined to limit the number of sites where once-through condenser cooling can be used. However, by combining good engineering design with proper assessment of biological effects, it is believed that once-through cooling can remain a viable mechanism for heat dissipation in major rivers, reservoirs, large lakes, and coastal waters. Heat dissipation from the receiving water surface will ultimately return the water to its natural temperature state within a certain distance from the point of heat discharge. In the USSR, the flow-rate in a river or reservoir must be at least three times the discharge flow from the power plant and complete mixing of the heated water with the river (or reservoir) flow is required within a zone of not greater than 500 metres from the point of release [1]. This distance depends on the amount of mixing or dilution between the heated condenser water discharge and the receiving water. The transfer of heat from a water surface to the atmosphere occurs through the combined mechanisms of evaporation, radiation, advection and conduction. Kolflat [ 2] has provided typical values for each of these heat dissipation mechanisms for open water surfaces such as lakes, ponds, rivers, reservoirs, and estuaries. These values are given as: evaporation 40%, radiation 30%, conduction 25%, and advection 5%. If cooling towers are used, over 75% of the heat is transferred by evaporation in the 'wet' type in the summer, and in dry cooling towers 100% of the heat is dissipated by conduction and convection. This extreme type of non-mixing discharge is usually prohibited by present thermal discharge regulations which prescribe natural temperature differentials in the receiving water. This restriction can be overcome by a design which provides for partial or complete mixing of the heated discharge

33 34 CHAPTER 2 with the available flow past the plant site. In this design, the condenser cooling water is conducted through a diffuser pipe or tunnel and discharged through nozzles or ports near the bottom of the water-way. Entrainment of surrounding water into the high-velocity jets produces a rapid dilution. This type of discharge device provides the most rapid temperature reduction within the smallest area. On the other hand, a maximum amount of heat is stored in the water since surface heat dissipation is relatively slow at the very low temperature rises permitted. In the consideration of once-through cooling systems, the primary advantages of this method are the lower consumptive use of water and the ability to tailor the temperature distribution field in the receiving water to meet biological and temperature objectives.

3.1.2. Mathematical models

A most valuable tool in the overall design of intake and discharge facilities for once-through cooling water systems is the use of appropriate analytical models for describing the physical interaction of the heated effluent with the receiving water body. A basic description of the mechanics involved in understanding heat transfer from a water surface to the atmosphere is provided in Appendix A. In Table IX, the major parameters which influence the shape and areal extent of thermal plumes, i. e. the discharge, receiving water, and atmospheric characteristics, are summarized. 'Mathematical modelling' of thermal discharges aids in the prediction of possible biological effects which may result from changes in physical and chemical properties of water due to the extent of the influence of thermal discharges. Modelling also provides a technical basis for developing a discharge structure design which disperses the heat effluent in a manner which will satisfy temperature standards and also estimates the possible recirculation of heated water back into the intake structure. In general, heated water releases are commonly divided into two broad categories, namely: surface and submerged discharges. In these categories, there are five basic processes which contribute to the dispersion of heat in a large receiving body of water [4]. The first three of these processes — jet entrainment, turbulent diffusion, and buoyant spreading — contribute primarily to the mixing of the heated and ambient fluids. In contrast to these hydrodynamic processes which merely redistribute the heat in the receiving water, the fourth process, heat transfer to the overlying air, transfers the thermal energy to the atmosphere. The fifth process, interaction of the initial jet momentum and ambient cross current, generally determines the location of the plume temperature field in relation to the outfall structure and receiving water body. None of the mathematical models developed to date has successfully simulated all five processes. When heated water is discharged into a water body, the resulting temperature field can be divided into two distinct zones or regions, and the majority of the mathematicál models developed to date consider only one of these specific flow regions [ 5] : (1) An initial or near-field region in which temperature changes are governed primarily by the geometry and hydrodynamics of the discharge. Mechanisms which affect the temperature reduction in the near-field region are the dilution and entrainment due to the momentum of the discharge jet MODELS OF HEAT DISSIPATION 35

TABLJE IX. PARAMETERS INFLUENCING THERMAL PLUMES [ 3]

I. Effluent characteristics

a. Flow-rate b. Density difference (relative to reference density in receiving water) c. Velocity at outlet

II. Outlet characteristics

a. Location b. Orientation c. Submergence d. Shape

e. Size (depth, width)

Receiving water

I. Flow dynamics a. Pre-existing velocity field (magnitudes and directions of local velocities) b. Tidal currents c. Wind-induced and other currents d. Surface waves e. Free turbulence

II. Stratification

a. Pre-existing stratification due to temperature, solids, and solvents b. Wind and tidal effects on stratification

III. Geometrical characteristics

a. Shape b. Size

c. Bottom configuration and roughness near outlet

Atmosphere

I. Wind a. Velocities (magnitude and direction) b. Shear stresses at water surface

II. Air

a. Temperature b. Relative humidity

III. Solar radiation

and the buoyancy effects due to the temperature difference between the discharge and the receiving water. Any 'near-field model' or 'jet model' must simulate the full characteristics between the heated effluent and the ambient receiving fluid. Compliance with water temperature standards is also generally determined in the near-field region. 36 CHAPTER 2

(2) A far-field region in which the temperature distribution is governed by conditions in the receiving water. The important properties of the receiving water body are natural temperature stratifications, advection, diffusion and dispersion due to tidal currents, wind-driven currents and wave action, and heat dissipation from the water surface. A 'far-field model' generally needs to describe only the motion of the ambient currents while, at the same time, satisfying the basic conservation laws for mass and heat. These models generally use the diffusion concept to describe the rate of effluent mixing, with the assumption that transport due to turbulent velocity fluctuation can be lumped into horizontal and vertical diffusion coefficients. Some attempts have been made to couple the intermediate region between near- and far-field regions into a 'complete-field model'. With this region there is a transition from inertially-dominated flow to ambient turbulence and gravity-dominated flows. Ideally, the coupling between the hydrodynamic equations should be considered in this intermediate flow regime and much work remains to be done to adequately understand this area. It should also be noted at this point that there is no universal accepted criterion for defining the exact limits of the transition zone between the near and far-fields; in general the use of only a 'near-field model' has been adequate to determine whether required temperature standards are being met. However, in the implementation of the U.S. National Environmental Policy Act it is necessary to assess the total environmental impact and therefore the 'far-field' effects also require evaluation. During the past several years various research programs in a number of countries have focused on the development of suitable mathematical models that can be used to predict the physical extent of heated effluents in all types of water bodies. For example, models for describing the physical characteristics of surface and submerged thermal discharges have been developed at the U.S. Atomic Energy Commission and Environmental Protection Agency laboratories and a number of universities. Extensive efforts have been carried out during the past two years to prepare state- of-the-art reports on mathematical models, hydraulic models, and prototype field data which have been collected to verify both analytical and physical models. The Argonne National Laboratory Centre for Environ- mental Studies and Vanderbilt University have prepared detailed model assessments (seeRefs [3,4,6,7,24]). These reports describe the mechanics of model development and application and also provide a technical basis for assessing the ecological impact of thermal releases on the receiving water systems. In the latter work, Policastro [ 4] reviews 31 different models which have been considered appropriate for predicting surface thermal plumes in large lakes. Eleven jet or near-field models, 13 far-field models, and seven complete-field models are discussed and compared according to the following characteristics: method of analytical approach, dimensionality, buoyancy, ambient stratification, surface heat loss, shoreline and bottom effects, discharge position and configuration, flow-establishment considerations, and availability of computer routines. It is noted that significant differences in modelling approaches exist. Previous model comparisons with prototype field data and laboratory hydraulic data are summarized in the report and the inadequacy of most of those comparisons is reported. Tables X - XII summarize the characteristics of the jet models, far-field MODELS OF HEAT DISSIPATION 37 models, and complete-field models which were analysed by Policastro in his recent work. It is also noted at this point that the companion work of Policastro and Tokar has provided a more detailed critique of sixteen of the models [6], Predictions of these 16 models are also described schematically in Figs 14-16. A further detailed analysis of mathematical models has been provided by Benedict and colleagues [7]. Their engineering handbook approach to model selection is especially noteworthy in that the models analysed are representative of groups of models and include methods applicable to river, lake and estuary conditions. A special effort was made to eliminate duplicating work which had been already done by Policastro and Tokar. The most popular means for disposing of heated water in the United States of America has been through discharge by a surface channel into a receiving water body. This method is the simplest and least expensive means of discharge. However, in recent years, more stringent thermal standards have stimulated an increased interest in submerged discharges. While this alternative way may be more costly, submerged discharges may provide higher initial dilutions, thereby providing a means for meeting more restrictive thermal standards. Benedict and his colleagues have also performed a detailed assessment of single port submerged jets (round and slot) [7], They have done similar analyses of submerged multiport diffusers. In the case of single port submerged jets, ambient environments have been considered as stagnant or flowing, and uniform or stratified. Three general classes are recognized according to ambient velocity considerations, density structure of receiving body (due to thermal or selective differences), and type of discharge structure. A number of models have been analysed, including a range of variables in the discharge structure design and receiving water, all factors which might limit the use of the various models being considered. A similar evaluation has been made of multiport submerged diffuser discharges by Benedict and his colleagues [7], Several sets of experimental data are presented along with a computer model to aid in evaluating such discharge systems. As with surface discharges, short of going to physical models, transient conditions are handled only by application of steady-state models to selected critical conditions. Most of the mathematical model studies analysed include experimental investigations with some analysis. The authors caution against the use of various models outside the range for which they have been verified. A comprehensive set of references are included with Benedict's report [ 7] in order to assist in providing details on the ranges of pertinent parameters which have been verified [ 8]. Another important piece of work on submerged diffusers (and single port submerged discharges) is the issuance of an engineering handbook by Davis and Shirazi of the U.S. Environmental Protection Agency. A compilation of 180 graphs showing the solutions to a wide variety of submerged jet problems is included in the handbook. The report is based primarily on the mathematical modelling work of Fan [9], Hirst [ 10] and Koh and Fan [11]. In the area of estuarine modelling, the U.S. Environmental Protection Agency as part of its National Coastal Pollution Research Program during the period of 1969 - 1971 conducted a detailed technical review and critical appraisal of the capabilities and limitations of both mathematical and physical models, and of various solution techniques for mathematical 38 CHAPTER 2

TABLE X. SUMMARY OF THE CHARACTERISTICS OF THE JET MODELS3

Direction of Ambient Mathen latical approach Initial Time temperature variation turbulence mixing dependent (far-field (Jet regime) solution Longitudinal Lateral Vertical region) Numerical Integral Closed form Semi-empirical

Hoopes et al. YES YES NO YES NO NO YES YESb YES NO

Hayashi and Shuto YES YES YES YES NO NO YES YES YES NO

Wadá YES YES YESC YES NO YES NO NO YES YES (model No.4)

Caites YES YES NO YES NO NO YES NO YES NO

Motz and Benedict YES YES NO YES NO NO YES NO YES NO

Koh and Fan YES NO YES YES NO NO YES YES (2D model) NO NO

Koh and Fan YES YES YES YES (axisymmetric model) NO NO YES NO YES NO

Barry and Hoffman YES YES YES YES NO YES NO NO YES NO

Stolzenbach and YES YES YES YES NO NO YES NO YES NO Harleman

McLay et al. YES YES YES NO YES YESd YES"1 NO NO NO

Stefan YES YES YES YES NO NO YES NO YES NO

a Wada model No. 3 can alto be used for near-field or complete-field applications, b A closed form solution lias been derived for the case of zero wind stress. c The model is actually quasi three-dimensional within a semi-infinite system having two-layer flow. Fluid properties ate "averaged" vertically within each layer. ** The zone of flow establishment is handled numerically; the established flow region is treated by integral methods.

formulations [12], The use of one-, two-, and three-dimensional mathematical models for estuarine hydrodynamics, and the principles and applicability of physical models in estuarine analysis are considered in this assessment report, where there is also a discussion of models of estuarine temperature structure with special attention given to the modelling of thermal discharges. Although one-dimensional and vertically averaged two-dimensional models have been employed in numerous estuaries, field verification is again lacking. For many types of estuaries, observational data are needed to identify the relative importance of hydrodynamic influences [ 13]. Benedict and colleagues have also assessed' several mathematical models used in estimating or predicting cooling pond performances [ 7]. Two types of cooling pond operation, i. e. recirculation and once-through cooling, are evaluated in their assessment. Recirculation pond effluents are returned to the condenser intake with the pond thereby forming a closed system with the power plant. However, in once-through cooling, condenser intake water is withdrawn from a body of water other than the cooling pond; in this type of operation the pond is used as a buffer system to reduce the potential thermal impact of the effluent upon the receiving waters. Both types of cooling pond operation are analysed in Benedict's assessment. Caution must be exercized in the choice of the evaporation formula used for both modes of cooling pond operation. Depending upon the type of pond MODELS OF HEAT DISSIPATION 39

Direct Compared or Surface Provides .Ambient Recirculation Cross Bottom Discharge wind fined with Computer Buoyancy heat ta flow stratification of flow slope geometry stress program loss establishment interaction ' plume water effects Field data Tank data

NO YES NO® YES YES NOe NO YES NO YES NO YESf

YES NO NO YES YES NO NO NO NO NO YES NO 8

YES NO YES YES YES NO NO NO YES UNKNOWN UNKNOWN YESb

NO YES NO NO YES YES NO NO NO NO YES YES'

NO YES NO NO YES YES NO NO NO YES YES YES*

YES NO NO YES YES NO NO NO NO NO NO YES'

YES NO NO YES YES NO NO NO NO NO NO NO

YES YES YES YES YES NO NO NO NO YES NO YESh

YES YES YES YES YES YES NO NO NO NO YES YESf

NO YES NO YES YES YES NO YES NO YES NO YESf

YES YES NO YES YES NO NO YES NO NO YES YES'

e Flow development and bottom effects were considered indirectly via wind speed correlations. ' Computei p*ogram included with model or available from authors. 8 Computer code does not exist yet may be easily written from model equations. 11 Computer code exists but is presently unavailable from authors. 1 Computer program written and available at Argonne National Laboratory.

used, the choice of an improper evaporation formula can introduce an effective error of between 5 and 10°C. Evaporation characteristics can be very localized, depending upon such factors as the degree of exposure of water to wind, width of cooling pond, and any energy input or output that affects the water surface temperature. Available climatological data from national meteorological and water resources organizations can be useful in order to improve the reliability of the mathematical model being used, provided that stations giving these data are not too far removed from the site, but it is preferable to obtain the data from the site itself. If the cooling pond is more than about ten metres in depth, it may develop a cycle of stratification through the year characteristic of many deep lakes and reservoirs. In this case, inflows and outflows from sources other than the power plant may be significant. Also, the power plant may draw water from one level and return it to another. For these deeper ponds, analysis may require the use of a model to predict vertical temperature structure in the lake. Benedict and his colleagues have also reviewed several deep reservoir mathematical models in their assessment study [7], Generally, the solutions are obtained by finite-difference techniques on a digital computer. Inputs usually require various meteorological data (often daily averages), reservoir geometry, inflows and inflow temperatures, outflows, diffusion coefficients, and possibly other empirical parameters. The output obtained from these programs is the temperature structure with 40 CHAPTER 5

TABLE XI. SUMMARY OF THE CHARACTERISTICS OF THE FAR-FIELD MODELS

Direction of Ambient Mathen latical approac h Time temperature variation Initial turbulence dependent mixing (far-field solution Longitudinal Lateral Vertical (Jet regime) region) Numerical Integral Closed form Semi-empirical

Wada YES YES YES NO YES YES (model No. 1) NO NO NO NO

Wada YES YES NO NO YES YES (model No. 2) NO NO NO NO

Wada» YES NO YES NO YES YES NO NO YES (model No. 3) NO

Lawler et al. YES YES NO NO YES NO NO YES NO NO

Palmer and b YES YES NO NO YES NO Izatt NO YES YES YES

Edinger and Polk YES YES NO NO YES NO (2D model) NO YES NO NO

Edinger and Polk YES YES YES NO YES NO NO YES (3D model) NO NO

Csanady YES YES NO NO YES NO (offshore model) NO YES NO NO

Csanady YES YES NO NO YES NO NO YES YES (shoreline model) NO

Koh and Fand YES YES YES NO YES YES NO NO YES NO (FTD)

Koh and Fan6 YES YES YES NO YES YES NO NO YES YES (UTD)

Koleiar and YES YES NO NO YES YES NO YES NO YES Sonnichsen

Wnek YES YES YES NO YES NO NO NO NO YES

a Model can alio be uBd for near-field or complete-field applications. h The model is a simple stochastic one based upon site current meter data which yields dilution ratios with time. c A constant vertical eddy thermal diffusivity was used in the model. Buoyancy is defined as being considered if the coupling of flow and energy has been treated. d This model is developed for the case of passive turbulent diffusion from a steady continuous source in a undirectional steady shear current with constant surface heat exchange (PTD). ® This model treats the jxoblem of unsteady continuous source in an unsteady uniform current with unsteady surface exchange (UTD).

depth at some designated time step (often one day) as well as outflow temperatures. Again model users are encouraged to make a complete analysis of the meteorological data for the region with emphasis on evaluation of the local evaporation term. The mathematical analysis may be simplified if the pond is strongly stratified and the intake and discharge are on the surface of the pond. It may then be possible in the analysis to treat the upper portion of the pond as a shallow pond. On the other hand, if the intake or discharge structures are located in the deeper part of the pond, it may be necessary to use a deep reservoir computer model for the cooling pond analysis. In France, researchers of Electricité de France have also developed mathematical models for predicting river temperatures [14]; these models MODELS OF HEAT DISSIPATION 41

Direct Compared or Surface Provides Ambient Recirculation Cross Bottom Discharge wind fitted with Computer Buoyancy heat for flow stratification of flow slope geometry stress program loss establishment interaction plume water effects Field data Tank data

1 NO YES YES YES YES -- YES NO YES YES UNKNOWN YES

f NO NO NO YES YES -- NO NO YES UNKNOWN UNKNOWN YES'

YES NO YES YES YES -- NO NO YES UNKNOWN UNKNOWN YES'

NO NO NO YES YES NO NO NO NO NO NO'

NO YES NO YES 8 NO - NO NO NO NO NO NO'

k NO YES NO YES NO - NO NO NO YES NO YES

c k NO YES NO NO NO - NO NO NO YES NO YES

NO YES NO YES NO NO NO NO NO NO NO1

k NO YES NO YES YES -- NO NO NO NO NO YES

h NO YES NO YES NO -- NO NO NO NO NO YES

NO YES NO YES NO NO NO NO NO NO YESh

h NO YES YES YES NO -- NO NO NO YES NO YES

c NO YES NO YES YES YES NO YES NO NO NO

' There is a possibility that this model may be able to handle the effects of ambient cross cisrents. This is not clear from Wada's papers, g The model has been extended to incorporate surface heat exchange by l.G. Asbury. ^ Computer code included with model or available from authors. 1 Computer program exists but is presently unavailable from authors. Í Computer code does not exist yet is easily written from model equations. k Computer program written and available at Argonne National Laboratory.

have been applied in some instances to rivers in other countries (Italy, Switzerland, Great Britain, and Germany). The comparison between model predictions and nature is found satisfactory when the parameters which fit into the model have sufficient experimental data. There are two main types of models: one is a deterministic model for the prediction of temperature in rivers, which is being used for the study of the effects of a power plant on a stretch of a river, or the thermal behaviour of the river itself, and the other is a stochastical model that is being studied with particular regard to the possibility of evaluating natural temperatures of water bodies. In Japan, most of the conventional power stations as well as all nuclear power stations are located at coastal sites and their cooling water is withdrawn from and released into the coastal zone. Mathematical models have 42 CHAPTER 5

TABLE XII. SUMMARY OF THE CHARACTERISTICS OF THE COMPLETE-FIELD MODELSa

Direction of Ambient Mathematical approach Initial Time temperature variation turbulence mixing dependent (far-field (Jet regime) solution Longitudinal Lateral Vertical region) Numerical Integral Closed form Semi-empirical

Pritchard YES YES YES YES YES NO YES YES YES NO

Stindaram et al. YES YES NO YES YES NO NO YES YES NO

Tsalb YES YES NO c YES YES NO NO YES YES NO

Asbury and Frigod YES® YES® NO YES YES NO NO YES YES NO

Elliott and d Harkness YES YES NO YES YES NO YES NO YES NO

Giles et al. YES YES YES YES YES YES YES NO YES NO

Loziuk et al. YES YES NO YES YES YES NO NO NO NO

* Wada model No. 3 may alio be used for complete-field applications. b The Tsai model has been developed fer a unique submerged diffuser situation. Because of this the general applicability of the model is limited. The table description under Tsal applies only to the analytical portion of his model synthesis describing surface spreading. Hydraulic modelling was used in the Initial regime of flow. c The cross current model is strictly two-dimensional. The no current case uses three-dimensional tank studies fas heated surface Jeu. However, only the surface temperature predictions were utilized in the Tsai model. d Factors such as buoyancy, bottom slope, surface heat loss, flow establishment region, ambient stratification, wind effects and plume recirculation are implicit in the empirical data utilized for model development yet are not specifically modelled. This also holds true for cross flow and discharge geometry considerations with reference to the Asbury-Frlgo model.

been developed by the research organization of the electric power industries since 1964 to predict the physical extent of the thermal discharge from power stations, and these models have been applied by each electric power company to solve the siting selection and hydraulic design of coastal structures [15-19], The problem of heat dissipation into coastal waters is complicated by thermal diffusion mechanisms in the sea [ 20]. In the open-sea situation, an essentially large scale of eddies is predominant in the diffusion process, whereas in the case of a bay or estuary tidal currents affect heat dissipation. In developing an understanding of heated water discharges into coastal areas three approaches have been studied in parallel: theoretical analysis of fundamental phenomena; simulation analysis including mathematical and hydraulic modelling; and field surveys at each site of power stations. The following material describes the mathematical models applicable to heat dissipation in coastal areas [16, 17],

3,1. 2. 1. Basic description of mathematical modelling

On the basis of a general consideration of diffusion phenomena of thermal discharge it is noted that, in order to predict the thermal diffusion of cooling water discharged into the sea, account should be taken of the hydraulic and thermodynamic behaviour of the released water. Therefore, three fundamental sets of equations are used for the analysis, namely equations of motion considering eddy viscosity; equations of continuity; and thermodynamic equations including heat budgets and heat exchange MODELS OF HEAT DISSIPATION 43

Direct Compared ot Surface Provides Ambient Recirculation Cross Bottom Discharge wind fitted with Computer Buoyancy heat for flow stratification of flow slope geometry stress program Ion establishment interaction plume water effects Field data Tank data

NO NO NO YES YES YES NO NO YES YES YES YESh

NO YES NO YESS YES NO NO NO NO YES NO YESh

NO YES NO NO YES YES NO NO NO NO NO NO

NO NO NO NO NO NO NO NO NO YES NO YESh

NOf YES NO NO YES NO NO NO NO YES NO YES1

NO YES YES YES YES NO NO YES YES YES NO YES'

NO YES NO YES YES NO NO NO NO YES YES YES1

e Only plume surface areas are predicted in this model. No temperature distributions are given. ^ Froude number dependency is included in the model although buoyancy is not specifically modelled, g Surface heat loss was considered only in the far-field regime. b Computer program written and available at Argonne National Laboratory. 1 Computer code exists but is presently unavailable from authors, i Computer pcogram included with model or available from authors.

between the sea surface and the atmosphere. Solving numerically these simultaneous equations under the boundary conditions concerning factors such as quantity, velocity and temperature of released cooling water, topography of the coast, location of the outlet, natural structure of temperature in the sea region, meteorological parameters (wind, insolation, air temperature, humidity, cloud cover, etc. ), characteristics of turbulence in the sea, and maritime conditions (tidal, coastal and wind driven currents and waves), one can obtain a detailed distribution both of velocity and temperature in the sea region in front of the outlet for each power station.

3.1.2.2. Mathematical model of two-layer sea [19]

Although the basis of numerical simulation is as mentioned above, it is difficult to deal with the thermal diffusion phenomena by means of a three- dimensional analysis. From the results of theoretical studies and field surveys concerning the mechanisms of thermal diffusion it is noted that discharged warm cooling water spreads horizontally forming a surface layer in the sea region. Accordingly, a two-layer sea mathematical model may be proposed as one of the analytical methods to approach the problem. Based on our present theoretical understanding of thermal diffusion phenomena, computer solutions with this model will provide perhaps the most probable estimate of thermal dispersion in a coastal area. However, a large amount of computer capacity and time is required, thereby reducing the practical application of this approach. In view of this, other simplified methods have been developed to analyse heat dissipation into coastal waters. CHAPTER 3

UNIFORM CROSS CURRENT Ulli

UNIFORM CROSS CURRENT i 1 il 1

JJ_

•W/V \ 7////W7//'//////?/

(e) HOOPES, ZELLER AND (b) CARTER MODEL ROHLICH MODEL

UNIFORM CROSS CURRENT H i U

(cl MOTZ AND BENEDICT (d) STOLZENBACH AND MODEL HARLEMAN MODEL

FIG. 14. Near-field (jet) models. Typical isotherm sketches as predicted by models reviewed. MODELS OF HEAT DISSIPATION 45

UNIFORM CROSS CURRENT

UNIFORM CROSS CURRENT HEAT— Ulli SOURCE- ^fiîftS:' SHOWN FOR JET SITUATION

2-D 3-D NQ1 NO. 2 NO. 3

(a) WADA MODELS (b) EDINGER AND POLK MODELS

UNIFORM CROSS CURRENT UNIFORM CROSS CURRENT i I 1 I UNIFORM UNIFORM I I II I I J CROSS CURRENT CROSS CURRENT I I I i II i

J_L

[OFF SHORE) (SHORE LINE)'

FIG. 15. Far-field models. 46 CHAPTER 5

(a) PRITCHARD MODEL

UNIFORM CROSS CURRENT UNIFORM CROSS CURRENT HUH iimn

lb) SUNDARAM ET AL.MODEL (c)TSAI MODEL

FIG. 16. Complete-field models.

3.1. 2. 3. Practical methods of simulation analysis

In developing practical methods of simulation analysis it is necessary to understand the effect of current in sea regions on the diffusion process. Therefore, long-term observation of coastal currents is a necessary prerequisite. From statistical analysis of the observed data on turbulent velocity it can be deduced that there are two distinct patterns for the heat dispersion process in the sea. One is affected by an irregular coastal current (Type I) and the other is due to the effect of tidal oscillation (Type II) 118]. MODELS OF HEAT DISSIPATION 47

Assuming from a practical point of view dynamic movement and heat dispersion of warmed cooling water released from the outlet is limited in the surface layer with a certain thickness according to the nature of density current, it is possible to deal with the thermal dispersion phenomena with a two-dimensional analysis in the horizontal plane by averaging the variables in the vertical direction within the surface layer. Based on this assumption, the following methods of mathematical analysis have been proposed.

The case of the open sea

(a) Steady-state two-dimensional analysis This analytical method corresponds to the dispersion pattern of Type I described above. In this method it is assumed that the oscillatory flow does not act as the advective effect but rather contributes to dispersion as large-scale eddies. Accordingly, this method can give the average temperature distribution which may take place frequently for a long term.

(b) Unsteady-state two-dimensional analysis This analytical method corresponds to the dispersion pattern of Type II described above. When there exists a tidal current with a regular period parallel to the coastline, such oscillatory flow is considered as a function of time in this method, in order to obtain the time-dependent change of water temperature distribution resulting from thermal discharge. By this method the unsteady phenomena of thermal dispersion can be simulated by numerical analysis.

The case of a bay

In the case when warmed cooling water is discharged into a narrow bay with small width and great depth, the thermal dispersion may be treated approximately as a one-dimensional phenomenon. In the case when the bay is relatively wide, it is necessary to deal with the dispersion phenomenon as two-dimensional and the analytical method described in the above paragraph (b) should be applied. Another analytical method has been developed for computing the heat budget for divided segments. In this method the sea region is divided into as many segments as possible. The distribution of average water temperature for each segment can be obtained by calculating the heat budget with respect to each segment, i. e. by consideration of the heat exchange between the sea surface and the atmosphere, and the thermal dispersion and advection caused by tidal flow and the cooling water discharge.

3.1. 3. Hydraulic or physical models

Hydraulic models have been an important engineering tool for many years and have been used as a means for developing quantitative estimates of some of the flow quantities such as velocities, depths, and pressures, to aid in the design of prototype water works. A thorough review of the use of hydraulic models for thermal plume modelling has been prepared 48 CHAPTER 5

TABLE XIII. HYDRAULIC MODELLING OF THERMAL PLUMES [3]

Most important

Model physical " a Remarks * parameters " phenomena r

Near-field Entrainment Geometry : densimetric Can be modelled with (outlet region) Froude number; local any two miscible Richardson numbers; fluids of different boundary conditions at density. Undistorted end of model scale required.

Joining region Entrainment Boundary conditions at May be combined Buoyancy upstream and downstream with near-field model Surface cooling ends of model; rate of to eliminate problem Convection surface cooling; local of upstream boundary Richardson numbers; condition. This pre-existing stratification; complicates the near- pre-existing currents; wind field model.

Far-field Surface cooling Boundary conditions at Distorted model Convection upstream and downstream usually required. Dispersion ends of model; rate of Latter part of joining surface cooling; densi- region may be placed metric Froude number; in far-field model, but pre-existing currents; wind combination with near- field is impracticable.

a It is assumed that suitably large Reynolds numbers are obtained in each case.

by Silberman and Stefan as part of the overall Argonne National Laboratory thermal effects research program [3]. The significant parameters involved in the conduct of hydraulic modelling for thermal plumes are summarized in Table XIII [ 3]. Parker and Krenkel [ 21] also review some of the physical modelling work which has been carried out in the United States of America, and Ackers [22] summarizes requirements for hydraulic models and also shares some of the broad experience which has been gained in this area in Great Britain. The modelling of thermal plumes has posed several problems in hydraulic models. Problems of distortion of horizontal relative to vertical scales, the effect of stratification on model-prototype relations and modelling of the air-water interface have been recognized and these problems have been solved to a certain extent. Table XIII describes some of the important parameters and physical phenomena involved in hydraulic modelling of thermal plumes. In a related area Harleman [23] discusses the use of physical models for estuaries and the present inadequacies in the use of models for general water quality problems. In this analysis, caution is expressed concerning building of physical models too hastily, as they are not only expensive but verification is difficult. One of the major needs in physical modelling of thermal discharges is the collection of adequate prototype data to check the results obtained from physical models. While Silberman discusses some data of this sort which are available, much more is needed. MODELS OF HEAT DISSIPATION 49

3.1.4. Field studies

Perhaps the greatest gap in our thermal plume technology is the fact that most hydraulic and analytical models have not been thoroughly compared or verified with prototype field data. Field data are needed not only for field model verification but to check and improve the model assumptions. Data should be collected from numerous river, lake and estuarine sites which provide a wide range of initial Froude numbers, meteorological conditions, and receiving water body geometry. Only in this way can a model be tested properly under a wide range of input conditions. Data collection should be carried out with the model testing in mind; entrainment coefficients, eddy diffusivities, and heat transfer parameters are only a few of the factors where good field measurements are required for determining model validity. Tokar [24] in his analysis of a compilation of field experience in the USA characterizes most of the field data which have been obtained as no more than 'reconnaissance surveys'. Such surveys usually consist of measuring temperatures at selected times and positions in a thermal plume; other easily determinable parameters such as wind velocity, power-plant loading, condenser flow, and temperature rise are usually but not always included in such surveys. The objective of reconnaissance surveys may vary; however, for the most part, these surveys are used to gauge the physical and thermal extent of the plume under certain power-plant loading and environmental conditions. For example, it is desirable to know whether a power plant operating at full capacity during a particularly hot windless summer day in July or August might violate state-water quality criteria, or whether for certain conditions of current flow, there is an appreciable recirculation problem, or whether the addition of more capacity at a power plant location may potentially create water-quality problems. Problems such as these can be answered relatively easily by performing reconnaissance type surveys. Unfortunately, however, such surveys are not for the most part suitable for supplying the basic field information for validating thermal plume predictive models since generally they are too coarse in the number of measurements taken, the type of measurements, or how measurements were made. In Japan, the coastal area studies at the Anegasaki Thermal Power Station, Tsuruga (Nuclear) Power Station and Mihama (Nuclear) Power Station are reported [15]. In addition, a number of field surveys on actual behaviour of thermal dispersion have been carried out at the existing thermal power stations by each electric power company for the past several years, and a field survey is also being performed periodically and continuously at nuclear power stations which have started operation recently. The results of field surveys have been compared with the analytical results using various mathematical models mentioned previously and, contrary to experience in the USA, comparatively good agreement has been obtained. As a means of measuring sea water temperature, an automatic water temperature recording system with a thermistor mounted on a boat operating along with the measurement lines and an aerial survey technique with infra-red scanning are used. The latter technique should be used simultaneously with the direct measurement technique of water temperature. Policastro [4], in his previously noted detailed evaluation of many mathematical models (31 in his latest analysis), has concluded that none of 50 CHAPTER 5 the near-field, far-field, and complete-field models have been objectively and sufficiently validated with prototype field data to enable them to be used with confidence in a predictive sense. With this in mind, the Argonne National Laboratory has undertaken the collection of perhaps the most comprehensive prototype field data available for the near-field region of a power plant discharge [25, 26], Eight of the available mathematical models were selected and predictions of these eight models were developed for three separate types of ambient conditions at the Point Beach Power Station on Lake Michigan. Field data involving simultaneous temperature and velocity profiles were taken in three dimensions near the outfall of the plant. Policastro has evaluated the data on plume centreline trajectories, centreline temperature decays, plume widths, and plume areas for the various models. Significant differences in model predictions and data comparisons are described in his most recent work. Additional field measurements are planned in order to clarify some of the uncertainties found in some of the data collected.

3.2. ATMOSPHERIC SYSTEM MODELS

3.2. 1. Models for predicting atmospheric plume behaviour

In considering the modelling of atmospheric plumes from the discharge of heated effluents from power plant auxiliary cooling systems, it is noted that a great deal of study has been devoted to the behaviour of smoke or dry plumes originating from large stacks [27], Briggs [28] has summarized some of the physical considerations and the equations which have been used to predict the height to which plumes rise. By use of these equations one can predict the rate at which such plumes are diluted and dispersed in atmospheres of varying stability and wind structure. Vapour plumes from cooling towers are similar in many respects to smoke plumes; however, there are certain significant differences that must be considered when predicting the behaviour of vapour plumes. For example, size differences are very great. Smoke stack diameters are typically in the order of 3 metres or less, whereas many modern hyperbolic cooling towers have diameters of about 100 metres. Also, the dynamics of cooling towers are considerably different due to the energies involved in evaporation and condensation in the wet plume and the buoyancy accelerations produced. Since the buoyancy of a plume depends on the mixing between the plume and its environment, large plumes from cooling towers with their smaller surface to-volume ratios maintain more of their temperature excess than smaller plumes. Therefore, for a given set of initial velocity and temperature conditions, a large plume will rise faster and reach a greater altitude. Another important difference between dry and moist plumes is the fact that a vapour plume will, upon leaving the tower, start to cool immediately and result in a visible cloud of liquid droplets. This condensation contributes to the buoyancy of the rising plume by releasing the latent heat of condensation. At the edge of the buoyant plume, where liquid water droplets are in contact with dry air, there will be evaporation and resultant cooling. The water which has been condensed represents a mass of material that is carried along in the plume and contributes to negative buoyancy. Fortunately, a great deal of study has been given to the complex dynamic and thermodynamic MODELS OF HEAT DISSIPATION 51 processes that occur in a buoyant mass of cloudy air, which has led to the development of growth equations for cumulus clouds. It should be noted, however, that most of the previous studies on the behaviour of stack effluents have been based on the concept that the horizontal diffusion is equivalent to that from a source at an 'effective' stack height in place of the actual source, where the effective stack height is defined as the height at which the plume comes nearly horizontal [29]. Methods for determining effective stack height have been analysed by Briggs in 'Meteorology and Atomic Energy' (1968). Over the past several years considerable progress has been achieved in the application of numerical models to cumulus clouds (similar to moist buoyant plumes). The work of Austin [ 30 ], Austin and Fleisher [31], Malkus [32], Orville [33], and Weinstein and Davis [ 34] has led to the development of models which predict the height to which a buoyant plume will rise, given the atmospheric structure at the time. EG & G [29] have modified the cumulus model as developed by Weinstein and Davis in a manner such as to make it more applicable to wet effluent plumes. In their modelling approach, they applied the vertical equation of motion and the First Law of Thermodynamics containing relations that have as parameters plume mixing, water particle growth, fall-out, and evaporation. Numerical calculations are carried out by lifting incremental portions of the plume adiabatically through successive vertical steps and at each interval allowing mixing or entrainment to occur with the environment. One approach to the problem of predicting the behaviour of cooling tower plumes involves first the determination of the height to which the plume will rise using the same considerations employed in predicting the rise of cumulus clouds [27], Secondly, what is known from measurements and diffusion equations about the rate of dilution of this plume with distance downwind is then used to determine the horizontal and vertical contours of vapour concentration. Finally, the saturation deficit (i. e. the difference between the mass of water per unit volume at saturation at the ambient temperature and the mass of water per unit volume that is actually present) in the layer in which the plume will be travelling is used to determine where a visible plume of fog will persist. This occurs where the vapour addition exceeds the saturation deficit. Obviously there are difficulties and uncertainties in this approach because of our limitations in defining atmospheric conditions and in approxi- mating the physical interaction between the plume and the atmosphere. One of the more difficult assessments to make is the determination of the rate of dilution of the plume as it moves downwind due to the wide variability of the atmosphere from place to place and from time to time. To begin with, then, in regard to the plume rise problem, the cumulus model as developed by Weinstein and Davis was used in field studies at the Keystone power plant in western Pennsylvania to determine the plume rise for natural draught cooling towers. Over a period of two years (1969 - 70), observations and photographs were made of the behaviour of these plumes in order to compare predictions of plume rise and horizontal plume extent with the physical models. Hosier [27] reports the results of this work and shows that equations for the rise of buoyant saturated plume indicate rather clearly that the buoyant rise is almost linearly related to the radius of the initial plume. For example, doubling the radius of the cooling tower would result in a doubling of the height of buoyant rise. A tower with a 120 metre diameter would result in buoyant rise of the plume to an altitude of from 600 to 52 CHAPTER 5

1200 metres, even under the strongest inversion conditions. In relatively- flat terrain this would indicate that the plume could never reach the ground in the vicinity of the tower and would likely be rapidly dispersed at high altitude. Only in deep valleys would there be much likelihood that inversions would become sufficiently strong and deep to confine the plume below the inversion within the stable air. Once the height has been established to which the plumes from a given type of wet cooling tower will extend, determining the extent of the visible plume reduces to a problem of determining the rate of downwind diffusion of the plume. A variety of diffusion equations and experimental data exist which relate dispersion of stack effluents to effective stack height and stability, wind and terrain characteristics. In general, predictive equations are slight modifications of those first proposed by Sutton [35] with appropriate modifications by Pasquill [36], and Gifford [37]. These equations have been conveniently reduced to a simple set of graphs which express diffusion coefficients as functions of distance and stability class [ 38, 39], Having obtained a reasonable idea of the mass of water vapour added per cubic metre of air at any given distance downwind, it is necessary to know the saturation deficit in the ambient air at that distance and level in order to determine whether or not the amount added will be sufficient to result in saturation and a visible plume [27]. For mechanical draught cooling towers, where most of the plume will be mixed into the lower-level surface layers, a first approximation can be obtained by using standard meteorological data to determine the atmospheric moisture content. For natural draught cooling towers it is necessary to obtain the saturation deficit at the altitude of equilibrium for the plume. This requires low level soundings from a representative point nearby or at the site itself.

3.2.2. Physical models

Physical models are useful for determining the aerological influence of nearby buildings, mountains or the towers themselves on plume behaviour. These models which can be constructed in wind tunnels or hydraulic test facilities are generally not conclusive by themselves but are useful in combination with mathematical models or field observations. Physical models have a major limitation in that the plume thermodynamics (condensation, adiabatic cooling etc.) cannot be effectively simulated. The use of plume rise and diffusion models for analyses of cooling tower effluents upon the environment has been studied by a number of investigators including De Harpporte [40], Aynsley [41], Overcamp and Hoult [42], Davis and McVehil [43], and Visbisky, Bierman and Bitting [44]. The assessment of fog and persistent plume frequency is possible utilizing existing techniques and meteorological data.

REFERENCES TO CHAPTER 3

[1] MINASYAN. R.G., private communication. [2] KOLFLAT, T.D., "Thermal discharges: An overview", Proc. Am. Power Conf. 3 (20 - 22 Apr.1971) 412. [31 S1LBERMAN, E., STEFAN, H., Physical (Hydraulic) Modelling of Heat Dispersion in Large Lakes: A Review of the State-of-the-Art, Aigonne National Laboratory, ANL/ES-2 (1970). MODELS OF HEAT DISSIPATION 53

[4] POLICASTRO, A.]., "State-of-the-art of surface thermal plume modelling for large lakes", Argonne National Laboratory, Paper presented at the 1972 Annual Meeting of the American Institute of Chemical Engineers, New York City (26 - 30 Nov. 1972). [5] Ü. S. NATIONAL ACADEMY OF ENGINEERING, Engineering for the Resolution of the Energy-Environment Dilemma, Committee on Power Plant Siting — Working Group on Environmental Protection: Water, Washington, D. C. (1972). [6] POLICASTRO, A.]., TOKAR, J.V., Heated-Effluent Dispersion in Large Lakes: State-of-the-Art of Analytical Modelling, Part I. Critique of Model Formulations, Argonne National Laboratory, ANL/ES-11 (1972). [7] BENEDICT, B.A., ANDERSON, J.L., YANDELL, E.L., Jr., Analytical Modelling of Thermal Discharges: A Review of the State-of-the-Art, Vanderbilt University (1972). [8] DAVIS, L.R., SHIRAZI, M. A., Workbook on Thermal Plume Prediction 1, Submerged Discharges, EPA-R2-72-005a. [9] FAN, L.N., Turbulent Buoyant Jets into Stratified or Flowing Ambient Fluids, W.M. Keck Laboratory Rep.No. KH-R-15, California Institute of Technology, Pasadena, Calif. (1967). [10] HIRST, E.A., Analysis of Round, Turbulent, Buoyant Jets Discharged to Flowing Stratified Ambients, ORNL Rep.No. 4685 (1971). [11] KOH, C.Y., FAN, L.N., Mathematical Models for the Prediction of Temperature Distributions Resulting from the Discharge of Heated Water into Large Bodies of Water, Rep.No.l6130DWO 10/70, Washington, D.C. (Oct. 1970). [12] TRACOR, Inc., Estuarine Modelling: An Assessment, A Report for the Water Quality Office, U.S. Environmental Protection Agency, Project 16070 DZV (Feb. 1971). [ 13] A Users Manual for Three-Dimensional Heated Surface Discharge Computation, MIT, Environmental Technology Series EPA-R2-72-133, Nov. 1972. [ 14] GRAS, R., Simulation du comportement thermique d'une rivière à partir des données fournies par un réseau classique d'observations météorologiques, Note HF. 041-69 no.10, Mar. 1969. [15] TAKEDA, K., SENSHU, S., private communication. [ 16] WADA, A., A Study on Phenomena of Flow and Thermal Diffusion Caused by Outfall of Cooling Water, Technical Rep. C66006, Central Research Institute of Electric Power Industry, Jan. 1967. [17] WADA, A., Numerical Analysis of Distribution of Flow and Thermal Diffusion Caused by Outfall of Cooling Water, Technical Rep. C67004, Central Research Institute of Electric Power Industry, Jan. 1969. [ 18] WADA, A., Effect of Coastal Current on Process of Thermal Diffusion Caused by Outfall of Cooling Water in the Sea, Technical Rep. C71603, Central Research Institute of Electric Power Industry, Feb. 1972. [ 19] WADA, A., Study of Thermal Diffusion in a Two Layer Sea Caused by Outfall of Cooling Water, Technical Rep. C71606, Central Research Institute of Electric Power Industry, Aug. 1972. WADA, A., "Study of thermal diffusion in a two layer sea caused by outfall of cooling water", Paper presented at the International Symposium on Stratified Flows, Int. Assoc. Hydraulic Research (Sep. 1972, Novosibirsk. [20] A Numerical Model for Predicting Energy Dispersion in Thermal Plumes Issuing from Large Vertical Outfalls in Shallow Coastal Waters, Oregon State University, Environmental Technology Series, EPA-R2-72-162, Nov. 1972. [21] PARKER, F.L., KRENKEL, P.A., Thermal Pollution, Status of the Art, Vanderbilt University Press, (1969) 417 pp. [22] ACKERS, P., "Modelling of heated water discharges", Engineering Aspects of Thermal Pollution, Vanderbilt University Press, Nashville, Tenn. (1969). [23] HARLEMAN, D.R.F., "Physical Hydraulic Models", Estuarine Modelling: An Assessment (WARD, G.H. ,Jr„ ESPEY, W.H., Jr., Eds). EPA Water Pollution Control Research Series, No. 16070 DZV 02/71 (Feb. 1971) 215. [24] TOKAR, J.V., Thermal Plumes in Lakes: Compilations of Field Experience, Argonne National Laboratory, ANL/ES-3 (1971). [25] FRIGO, A., FRYE, D., Physical Measurements of Thermal Discharges into Lake Michigan: 1971, Center for Environmental Studies, Argonne National Laboratory (in press). [26] FRIGO, A., FRYE, D., Physical Measurements of Thermal Discharges into Lake Michigan: 1972, Center for Environmental Studies, Argonne National Laboratory (to be published). [27] HOSLER, C.L., "Wet cooling tower plume behaviour", Paper presented at the AICHE Cooling Tower Symposium, Houston, Tex. (2 Mar. 1971). [28] BRIGGS, G. A., Plume Rise, AEC Critical Review Series, USAEC TID 25075 (1969). [29] EG&G, Inc., Potential Environmental Modifications Produced by Large Evaporative Cooling Towers, EPA WQO, Water Pollution Control Research Series Rep.No.16130 DNH 01/71 (1971). 54 CHAPTER 5

[30] AUSTIN, J. M., A note on cumulus growth in a nonsaturated environment, J. Meteorol. 5(1948) 240. [31] AUSTIN, J.M., FLEISHER, A., A thermodynamic analysis of cumulus convection, J. Meteorol. 5 (1948) 240. [32] MALKUS, J., "Cumulus dynamics", Pergamon Press, New York (1960) 65. [33] OR VILLE, H.D., A numerical study of the initiation of cumulus clouds over mountainous terrain, J. Atmos. Sei. 22 (1964) 684. [34] WEINSTEIN, A.I., DAVIS, L.G., A Parameterized Numerical Model of Cumulus Convection, NSF GA 777 Rep. 11, Dept. of Meteorology, The Pennsylvania State University (1968). [35] SUTTON, O.G., Micrometeorology, McGraw-Hill, New York (1953). [36] PASQUILL, F., The estimation of the dispersion of windborne material, Meteor. Mag. 90 (1963) 33. [37] GIFFORD, F. A., The rise of strongly radioactive plumes, J. Appl. Meteorol. 6 4 (1967) 644. [ 38] TURNER, D. B., Workbook of Atmospheric Dispersion Estimates, U. S. Department of Health, Education, and Welfare, Public Health Service, National Air Pollution Control Administration (1967, 1969 Revised) 84 pp. [39] SLADE, D.H., Meteorology and Atomic Energy, USAEC (July 1968). [40] DE HARPPORTE, D.R., Cooling tower site considerations, Power Eng. (Aug. 1970) 49. [41] AYNSLEY, E., Environmental Aspects of Cooling Tower Plumes, Cooling Tower Institute Meeting, New Orleans (Jan. 1970). [42] OVERCAMP, J.J., HOULT, D.P., Precipitation from Cooling Towers in Cold Climates, Fluid Mech. Lab. MIT, Pub. No. 70-7 (May 1970). [43] DAVIS, L.G., McVEHIL, G., Potential Environmental Modifications Produced by Large Evaporative Cooling Towers, FWPCA Rep. EG&G, Inc. (Apr. 1970). [44] VISBISKY, R.F., BIERMAN, G.F., BITTING, C. H., Plume Effects of.Natural Draft Hyperbolic Cooling Towers, An Interim Report, Gilbert Assoc., Reading, Pa. (1970). Chapter 4

PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS AND THERMAL DISCHARGES ON THE ENVIRONMENT

With the power industry continuing to expand its use of alternative cooling methods such as cooling towers and ponds it is becoming increasingly more important to consider the total environmental impact of such systems. In the United States of America, under the National Environmental Policy Act of 1969, operators of nuclear power plants are required to assess the various environmental effects of alternate cooling methods in conjunction with a benefit-cost analysis of each system. In this chapter the possible physical-chemical effects of various types of cooling systems and thermal discharges on our air-water environments are described. Table XIV summarizes these effects on water, meteorology, and on other features of our total environment.

4.1. EFFECTS ON WATER

In the operation of once-through cooling systems and alternative cooling systems such as cooling towers it is important to consider the overall effects of these operations on water quality in the receiving water system. The potential impact of higher temperatures and the associated facets, the effects of chemical blow-down from plant cooling systems, the use of biocides such as chlorine, and the quantities of water lost through evaporation by the various types of cooling systems — all are areas of increasing environmental concern.

4.1.1. Physical effects

In assessing the potential public health implications of thermal pollution, Parker [2] indicates that temperature affects nearly every physical property of concern in water quality management including density, viscosity, vapour pressure, surface tension, gas solubility and diffusion. Table XV provides a summary of the changes in physical water properties as a function of temperature change. Dissolved oxygen is considered as perhaps the most important single parameter since it is an essential element for sustaining the forms of aquatic life. High temperatures in receiving water bodies, especially if combined with organic pollution loads, may reduce the saturation capacity for oxygen to the extent that fish may not survive.

55 TABLE XIV. PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS AND THERMAL DISCHARGES ON THE ENVIRONMENT [ 1]

Effects on water (once-through Effects on meteorology (cooling towers) Other effects (cooling towers) and/ox cooling towers)

Temperature change affects: Extent of visible plume Drift — effects of salt density, viscosity, vapour pressure, water drift on vegetation surface tension, gas solubility Influence on local short-wave radiation and diffusion, rate of BOD (light in the form of shadowing) and Synergistic effects

exertion, and waste assimilation long-wave radiation (heat) (combination of tower plumes with S02 ) capacity Humidity change at ground level Bacteria release from towers Evaporation Temperature changes at ground level Dispersion of gaseous radioactivity Consumption loss — reduced water from nuclear power plants supply Creation of artificial fog Air cleaning effects of wet towers Chemical blowdown ~ effects of Artificial precipitation by droplet biocides such as chlorine emission or rain-out from the plume Noise

Icing of ground and vegetation Aesthetics

Local wind conditions

Cloud formation

Cumulative weather influences of several cooling tower plants

a Biological Oxygen Demand. PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS 57

TABLE XV. WATER PROPERTIES AS A FUNCTION OF TEMPERATURE

Vapour Surface Oxygen Oxygen Temperature pressure Viscosity Density tension solubility diffusivity fC) (mb) (CP) (g/ml) (dyn/cm) (mg/1) (cm2 /s)

0 6.12 1.787 0.99984 75.6 14.6

5 8.75 1.519 0.99997 74.9 12.8

10 12.32 1.307 0.99970 74.2 11.3 15.7

15 17.10 1.139 0.99910 73. 5 10.2 18.3

20 23.45 1.002 0.99820 72.8 9.2 20.9

25 31.77 0.890 0.99704 72.0 8.4 23.7

30 92.56 0.798 0.99565 71.2 7.6 27.4

35 56.41 0.719 0. 99406 7.1

40 74. 00 0. 653 0.99224 69.6 6.6

Vapour pressure is an important factor in the rate of water evaporation, and increases in water temperature, with other factors remaining constant, will cause an increase in evaporation. Increased temperature and decreased viscosity may also result in increased sedimentation in the receiving water body, thereby leading to potential sludge deposit problems. In this connection, water containing organic material entering a stratified reservoir may deplete the dissolved oxygen of the reservoir due to biological respiration. Mixing by wind currents, photosynthesis, and sedimentation may purify this upper-layer (epilimnetic) water. However, in the hypolimnion, oxygen removed by biological action is not replaced, algae therefore cannot grow, and with essentially no vertical mixing taking place the sedimentation products from the epilimnion may increase the organic load to be assimilated. The depletion of dissolved oxygen in the hypolimnion may be critical when this low oxygen content water is discharged through the dam. A lower waste assimilation capacity may exist below the dam and, in some cases, fish life may not be supported for several kilometres downstream. In general, higher water temperatures result in a decrease in the ability of water to hold dissolved oxygen, an increase in the metabolic activity of microorganisms, an increased rate of Biochemical Oxygen Demand (BOD) exertion, and a possible reduction in waste assimilative capacity.

4.1.2. Chemical effects

An increase in water temperature may also have a significant effect on chemical reactions, with the rate of reaction being approximately doubled for each 10-degree rise in temperature [ 3] . This may result in certain changes in ionic strength, conductivity, dissociation, solubility, and corrosion, thereby alteringthe chemical requirements for water treatment facilities which may use this water as a source of supply. 58 CHAPTER 5

In the operation of power plant cooling systems certain chemicals are added to the system for protection against corrosion and scale build-up on heat transfer surfaces. The discharge of chemical blow-down from the system in order to avoid excessive concentrations of dissolved solids within the cooling system is an essential part of plant operation. The use of oxidizing biocides such as chlorine is also periodically required to maintain the growth of algae at an acceptable low level in the cooling system. The capability of the receiving water body to accept chemical wastes in accord with established water quality standards must be determined in a site-by- site basis. Treatment of chemical blow-down wastes by ion exchange or some other treatment method may be required where local environmental conditions prevent the direct discharge to receiving streams.

4.1.3. Water consumption

In many parts of the world the quantity of water which is being transferred through evaporation by various types of cooling systems is becoming a major factor in the siting and design of large steam-electric power generating facilities. The actual amounts of water transferred depends on the specific environmental and plant condition involved. For example, for open water surfaces such as lakes, ponds, rivers, reservoirs, and estuaries, about half of the heat is dissipated by evaporation, whereas with wet cooling towers over 75% of the heat is transferred by evaporation during the summer. The magnitude of the potential water consumption problem for large power plant facilities is indicated by the fact that approximately 2000 m3/h of water are transferred to the atmosphere through evaporation in a wet cooling tower for a 1000 MW(e) nuclear power plant.

4.2. POTENTIAL ATMOSPHERIC EFFECTS

Very large cooling towers in arrays, either mechanical or natural draught design, or large arrays of cooling ponds represent much more rapid meäns of releasing heat and moisture to the atmosphere than the discharge through large natural water bodies. But the efficiency of heat removal by the atmosphere and the degree and geographic direction of heat dispersal may vary widely from day to day, unlike the more consistent behaviour of river or lake heat sinks. In an assessment of the effects of important thermal releases to the atmosphere one must therefore evaluate the possible consequences of heat rejection to the atmosphere over a variety of natural conditions. The potential atmospheric effects associated with thermal discharges may be conveniently divided into several classes: (a) ground level fog and icing; (b) clouds and precipitation; (c) severe weather effects, (d) plume length and shadowing, and (e) drift.

4.2. 1. Ground level fog and icing

More attention has been given to fog and ice associated with plumes from evaporative cooling towers than to any other effects. The cooling tower reports or environmental impact statements prepared for nuclear power plants under the United States Environmental Policy Act contain PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS 59 statements that mechanical and natural draught cooling towers have the 'potential' to cause or increase the frequency of ground level fog or icing. Theoretical analyses [4-7] all predict tower-induced ground level fog for various periods of time with a greater fog persistence existing in cold weather. In these theoretical studies maximum fog frequencies would result from mechanical draught cooling towers. The fog potential from these towers is enhanced due to the water vapour being discharged at much lower elevations (20 - 30 m) and because lower wind speeds and surface nocturnal inversions prevail. Furthermore, a mechanical draught plume with a higher entrainment rate due to smaller exit diameters, higher exit speeds, and additional turbulence created by the tower fans may also be frequently trapped in building eddies [8]. Natural draught or combination cooling towers produce lower fog frequencies with the percentages decreasing with increasing height of the towers. In a report prepared for the U. S. Federal Water Quality Administration, EG&G (1970) outlined areas within the United States having high, moderate, and low potential for adverse cooling tower effects based upon results obtained from atmospheric model computations utilizing climatic data [6]. In this study it was pointed out that local microclimates of a given region can vary considerably from the larger scale features so that each site requires evaluation on the basis of local parameters. Local topographic features can be significant. For example, valleys with local moisture sources such as ponds, rivers, and lakes will increase the fogging potential, whereas hilltops with their greater dryness will tend to disperse the tower plume more efficiently. From model computations it was concluded that typical summer conditions (warm, unstable air) will not lead to a long visible plume and that late fall and winter are the primary periods of interest because of the prevalence of stable air and relatively cold temperatures. Despite the theoretical predictions of tower-induced ground level fog, available physical observations near towers and extensive European observations indicate that the plumes do not cause surface fog [9-12] . In these field observations the warm, moist plume enters the atmosphere at heights of 100 metres or more and evaporates before it reaches ground level. These observations indicate that the above models may be too pessimistic in their assumptions. A recently developed Swiss model [1] also shows that no artificial fog should be expected in the vicinity of natural draught cooling towers. Broehl, in his 1968 field investigation (interview trip) into four Appalachian cooling tower installations at large steam electrical plants in the eastern United States, concluded that: "... the plume from large, natural draught towers does not produce, even under the most adverse weather conditions, ground level fog, since the plume does not drop below the top of the tower for an extended distance." Zeller and colleagues [11] reported on a trip to seven nuclear power plants in the United States. From interviews with plant operational personnel they reached the same general conclusion as Broehl, that is, ground fog and icing from evaporative cooling towers have not increased although some towers are in the vicinity of frequent natural occurrences of ground fog. Decker [10], in evaluating meteorological aspects of cooling tower effluents, found that modern cooling towers have apparently caused few complaints of fog except in down-wash conditions (tower plume forced 60 CHAPTER 5 downward). He points out that this condition apparently has a low probability of occurrence and that suitable sites greatly exceed the number of unfavourable sites which would trap or concentrate the fog. In general, in the vicinity of mechanical draught cooling towers of the cell type, several cases of fog formation by plume wash-down have been observed in Europe and in the United States, which has led to inconvenience for nearby roads. Icing due to cooling towers has been observed several times at natural draught cooling towers without drift eliminators in France and the Federal Republic of Germany. After drift eliminators were installed, the icing completely disappeared. Also, Swiss model calculations have shown that artificial icing may only be expected at very exceptional cases in mountainous regions, if the plume touches the vegetation on the mountains [1 ] . Even in such cases the effect is small. At mechanical draught cooling towers the icing effect is more pronounced and cannot be completely eliminated even when drift eliminators are installed. It can be seen from the lack of agreement between the physical observations made at several sites noted above and the theoretical models that this discrepancy warrants further study. It would thus appear that either the plume disperses, entrains, and re-evaporates more rapidly than the mathematical equations predict, or some of the liquid water is removed as mist or drizzle [8] . It should also be noted that most of the evidence to date on the lack of tower-induced fog was obtained from plant operating personnel who do not make systematic or regular observations, and the opinions expressed in this matter could be influenced by the lack of complaints from people living nearby. At the present time, accurate predictions of cooling tower effects on fog or other weather events are still not possible because of (1) insufficient field data from tower operations and (2) an inadequate understanding of the atmosphere behaviour of moist plume discharges and their meteorological ramifications [13] . For these reasons comprehensive field measurement programs are essential if we are to clarify some of the speculative conclusions and predictions noted above. One such field study has been performed under the National Air Pollution Control Administration sponsorship at the 1800 MW Keystone plant in the eastern USA. In this study, Aynsley [9] points out that local fog and icing are apparently not a problem with natural draught towers since their plumes tend to puncture and ventilate natural temperature inversions and reach greater heights than the plumes of mechanical draught towers. Cooling tower vapour releases could reach the ground in hilly terrain areas. An inversion aloft plus radiative and evaporative cooling from the top of the plume could create a negative buoyancy and thereby cause the plume to descend to ground level. This has not been observed in England but may occur in hilly terrain. Aynsley has observed negative buoyancy in cooling tower plumes in the previously mentioned Keystone plant study; however, no example of this phenomenon has been observed in the TVA Paradise, Kentucky, plant study [8], Photographs taken at cooling tower sites frequently show ground level fog completely separate from the rising plume from the towers. The surface fog is caused by natural processes such as nocturnal radiation; the rivers and reservoirs used to supply make-up water to the towers aid in the fog formation. PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS 61

However, from the research and plant studies conducted to date, a general statement might be made: that the areas where fogging problems are likely to be greatest are the same areas where natural fog is most frequent. The role of the cooling tower would be simply to cause the fog to form sooner, perhaps last longer and, depending upon precise meteorological conditions, there would be a greater or lesser number of occasions when the atmosphere would be close enoughto saturation to enable the evaporation from cooling towers to produce fog where none would have occurred naturally. In areas where land is available and relatively inexpensive, small cooling lakes or ponds may be used for condenser cooling (about 4 - 8 m2 of surface are required per kilowatt of electricity produced) [ 14]. In the operation of these lakes or ponds local climatological changes to be expected will be in the intensity, frequency, and inland penetration of induced fog, including the creation of freezing fog near the water's edge. Observations at cooling ponds indicate that the fog over the pond, except for cases of large- scale formation, is thin, wispy, and does not penetrate inland more than 100 to 300 metres. It would appear that because the water vapour is released slowly over large areas, ponds are not a major source of fog despite the release, at ground level. However, in weather situations producing fog over large areas, ponds would act to intensify and prolong fog conditions. Cooling pond site selection is important in order to assure that induced fogs (and freezing fogs) do not affect roads and bridges. The effective evaporation area can be greatly increased by spraying the heated water over the pond or through a canal. (It has been stated that a spray pond needs only 5% of the area of a conventional cooling pond for an equivalent heat loss. ) These spray units will also increase the frequency and intensity of dew, fog, frost, and icing conditions along the banks or downwind of the pond or canal.

4.2.2. Clouds and precipitation

Quantitative data on the effects of moist plumes from coolingtowers on clouds and precipitation are very limited. Occasional observations of light drizzle or snow have been reported in the vicinity of towers such as mentioned by Culkowski [15], Federal Water Pollution Control Administration [ 16 ], Zeller and colleagues [11], and Decker [ 10]. Calculations with mathematical models [1] have confirmed the observations that artificial precipitation should not be expected if natural draught cooling towers are equipped with drift eliminators. The droplets leaving the plume were found to re-evaporate, before reaching the ground in all cases except when the natural humidity was very high. This condition may occur when it is foggy or when there is natural precipitation. In a very few cases artificial precipitation lasted for a short time after or started a short time before natural rainfall. The contribution to natural precipitation was found to be of the order of 1 % in the immediate vicinity of the plant. In a related phenomenon at the TVA Paradise, Kentucky, plant, Colbaugh [17] reports that mist (tiny water droplets) is a frequent occurrence. This mist is not fog and is observed at a distance downwind (about 150 m) from the end of the visible plume. Interestingly enough, mist has not been reported at other sites such as Keystone, Pennsylvania, or at plants in Great Britain. However, this again may have been because no systematic measurements were made. 62 CHAPTER 5

Studies of the Zion Nuclear Power Plant, located on Lake Michigan, USA, indicate that in conduction with macroscale storm systems, annual snowfall could be increased 2 to 5 cm over a semicircle 3 km in radius [ 14] . Moist tower plumes can initiate cloud formation, according to analyses by EG&.G [6]. In field studies at the Keystone fossil-fuelled plant in the eastern United States Visbisky and colleagues [18] found that tower plumes will contribute to local cloud formations at times in varying degrees, depending upon atmospheric conditions. However, their conclusion was that any cloud effect at Keystone did not appear to have significant effect upon airport operations approximately three km northwest of the plant. Aynsley [19] in further discussions of the Keystone plant studies states: "There are frequent occasions when tower plumes can be seen to evaporate and then recondense to some extent at higher altitudes further downwind. Under stable conditions with higher humidities the plumes will persist after levelling off and appear downwind in a stratus cloud coverage or merge and reinforce existing cloud coverage. Initiation of cumulus clouds is a rare occurrence and on such occasions clouds triggered by the towers only precede natural cloud formation. " In further comments on the Keystone study it is noted that drizzle beneath the tower from water droplet carry-over was not detected and no increase in ground level humidity underneath the plume path was observed [20] . Only in July 1969 was there a possibility of precipitation enhancement according to existing local Weather Bureau climatological records. At all other times during the Keystone study (1969-70) the monthly precipitation totals were within the envelope of natural variation for the area. In Swiss studies of natural draught wet cooling towers humidity changes at ground level are normally less than 1% when averaged over the year. Short-term changes of up to 5% can nevertheless be expected. The averaged temperature changes are less than 0.1% and therefore also negligible. These data which have been determined by a model calculation [ 1 ] are not yet confirmed by measurements, since the technique of measurement available has not been able to detect these very small changes. With adverse wind conditions appreciable changes on the ground humidity can be expected at cell type mechanical draught wet towers. The corresponding data for dry towers are not yet determined. Simulations of the plume behaviour of dry towers are being carried out in Switzerland. Dry towers may slightly raise ground temperature and reduce the relative humidity. Carson [8] states that the extra heat and water vapour from cooling towers may create cumulus clouds, and a possibility of tower plumes acting as a trigger to produce extra cumulus congestus clouds and precipitation downwind of the release should be considered. In viewing the findings of the Central Electricity Generating Board of Great Britain, Carson pointed out that they had found no reports of drizzle downwind or even any measurable change in relative humidity downwind from the cooling towers. Cumulus clouds were sometimes formed, but shower precipitation being generated by the tower plumes has not been observed. However, it was observed that sunshine could be altered in the area since the visible plume persists for a certain distance downwind. In summary it is concluded that the knowledge of the effects of cooling tower plumes on clouds and precipitation with regard to both initiation and stimulation of these weather events is still incomplete. From climatological observations and cloud physics research it is known that cumulus clouds PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS 63

and rain showers or thunderstorms can be triggered by relatively small inputs of energy. For example, Changnon [21] has shown that areas downwind of Chicago, Illinois, have experienced 20 to 40% increases in precipitation due to urban-industrial effects. Therefore, one must consider the possibility that cooling tower effluents could modify the rainfall distribution on a localized scale. Research using highly instrumented aircraft and radar is planned in the U.S. Atomic Energy Commission's atmospheric science 1973-74 research program for a better understanding of the potential enhancement of clouds and precipitation in regard to their relationship with cooling tower plumes.

4.2. 3. Severe weather effects

Another question posed is whether severe weather events such as thunderstorms, hail, tornadoes, and severe rainstorms might be caused by cooling tower plumes. As might be expected, very limited research has been conducted in this area and very few observed and/or calculated effects of tower plumes in this respect have been made. Czapski [22] made certain observations and calculations of large thermal emissions and concluded that "... severe thunderstorms and even tornadoes can be caused in very unstable weather situations by dry and clean heat emission." Changnon [23] has shown that 20 to 40% increases in the number of thunderstorm and hail days over and downwind of Chicago and St. Louis have resulted from the combined effects of urban-industrial heat and aerosol releases. Based on these studies and also from consideration of atmospheric physics and dynamics one would expect a severe weather event resulting from cooling tower effluents would be attained only through a triggering or stimulation effect [ 13] . That is, the additional heat and/or moisture fed into a developing storm cloud might conceivably produce an imbalance that would result in intensification into a severe weather state. In view of the paucity of data available in this area, any effects are only conjecture at this time.

4.2.4. Plume length and shadowing

Figure 17 provides an example of the frequency curve of observable plume lengths as observed in England at a plant of the Central Electricity Generating Board, at the Keystone plant in the USA, and as calculated by a mathematical model for the Kaiseraugst plant in Switzerland I 1 ]. The plume length largely varies with the season (Fig. 18) and with the general climatic conditions of the region considered. The psychological aspects of the shadowing effect of atmospheric plumes from cooling towers have been considered in nuclear power plant studies in Western Europe. A model calculation has been performed for the 850 MW(e) Kaiseraugst power plant in Switzerland with two natural draught cooling towers [12] . Even if visible cooling tower plumes are assumed to be fully opaque, the reduction of sunlight in nearby areas would be insignificant. For the sites considered the average reduction was one minute per day corresponding to 0. 35% of sunshine. The shadowing effect of mechanical draught towers is smaller than from natural draught towers because the vapour plume through the several ejection points obtains a more rapid dilution faster with environmental air. 64 CHAPTER 5

FIG. 17. Frequency of observed plume lengths.

TIME (°M WITH LENGTH EXCEEDING VALUE IN THE ORDINATE

FIG. 18. Variation of plume length with the season (Leibstadt Nuclear Power Plant, 850 MW). PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS 65

Studies from February through July at the Keystone Plant near Indiana, Pennsylvania, with four 100-m hyperbolic towers and two 240-m chimney stacks show that over 80% of the time the plumes evaporated into invisibility with most (87. 5%) evaporating within five tower heights. In about 15% of the time the plume was absorbed in the overcast usually (— 90%) within 15 tower heights. In only 2% of the cases did the plumes lead to cloud building [24]. In addition, the mixture of the plumes from the cooling towers and the chimney stacks did lead to the formation of dilute sulphuric acid. However, the Central Electricity Generating Board in the United Kingdom has concluded that the growth rate of water droplets due to S02 is so slow that acid drops seldom reach the ground [25].

4.2.5. Drift

Another problem in the operation of wet cooling towers involves a small portion of the total water circulated in the tower which enters the atmosphere without being evaporated; this physical water loss is due to droplets entrained in the leaving air stream and is often referred to as 'drift' [8]. Drift fall-out which occurs usually not too far from the tower may cause a host of problems, such as highway icing in the winter and transmission line flash-over. Since drift is not water vapour it still contains all the salts and impurities in the intake cooling water. When these drift droplets are subsequently deposited in the area surrounding the plant site, they evaporate and leave a solid or salt residue behind. While there have been many assumptions made relative to quantities that drift from water cooling towers of all sizes and types — some in the order of 0.2% of the quantity of water circulated — actual physical water loss for large power plant towers equipped with drift eliminators is much less. Recent published test data indicate drift loss rates of 0.005 to 0.0076% for mechanical draught towers and 0. 0012 to 0. 0025% for natural draught towers [26] . Additional operating test data are needed to validate the drift loss rates in this study. Tower equipment companies are now guaranteeing drift rates of between 0. 002 and 0. 005% of the circulating water flow. For a 1000 MW power plant the loss of water due to drift can thus be reduced to less than one litre per second which should greatly minimize the drift problem in so far as potential harmful effects on agricultural crops are concerned. At the present time in the United States, wet cooling towers at power stations have been limited to non-saline make-up water. With increasing environmental concerns, evaporative towers are now being required for many estuarine or coastal locations of power plants. The first hyperbolic natural draught cooling tower in the United States using brackish water is now being installed in conjunction with a 630 Mff(e) oil-fired power plant at Chalk Point, Maryland. Plant operation is scheduled for 1974. A comprehensive soil and vegetation research program is planned for this site in order to determine the potential effects that brackish water cooling towers may have on the surrounding vegetation, particularly tobacco, a commercially important crop in the vicinity of the plant which is known to be chloride sensitive. Additional field studies of this type will be required as salt or brackish water cooling towers are introduced into common power plant use in other regions of the country. 66 CHAPTER 5

4.3. OTHER EFFECTS

In addition to the meteorological effects described above, cooling towers may impact on the environment in other ways. For example, the synergistic effects of cooling tower plumes mixing with industrial stack effluents containing oxides of sulphur and nitrogen require further study and evaluation because there are some instances of acid rains due to the mixing of the cooling tower plumes with fossil-fuelled power plant stack effluents. The environmental impact of noise and the aesthetic effects of large cooling tower arrays, deserve consideration.

4.3.1. Noise

Wet natural draught cooling towers generate noise by the intense rain of water falling free and splashing down into the collecting basin at the bottom of the tower. In the use of mechanical draught cooling towers the fan noise is added to the water noise. The noise level from a natural draught tower is in the range of 80 to 85 dB (A) decaying to acceptable levels within a distance of approximately 1500 m. The spectrum of the noise source, which corresponds to the noise emission of a waterfall, is normally not considered to be of an unacceptable nature. Noise abatement systems such as earth banks, absorption cou- lisses etc. have proven their effectiveness for a noise abatement of 15 to 20 dB (A) but only the source at the tower inlet can be damped while the weaker source at the outlet cannot be controlled by other means than distance. The noise level at the mechanical draught towers is of the order of magnitude of 80 to 100 dB (A). The noise added by the fans lies on the low frequency range which is more difficult to dampen. Even though these towers are much lower in height, the damping of the outlet source is very difficult and no plant scale installation is known of at this time. No noise emission has been observed at natural draught dry towers. Assessment of the noise isopleths around cooling towers can best be made through measurement of sound levels at existing tower installations, as a starting point for the calculation of the potential noise propagation as described in the literature [26, 27] . In regard to potential sound problems such as may occur for towers located close to residential zones there is a need to make calculations based on both surface sources of noise and also an analysis of the total audible spectrum generated in the tower. Considera- tion of sound reflection from buildings as well as noise abatement by means of earth banks, woods, and buildings is required in the analysis.

4. 3. 2. Aesthetics

Experience has shown that the public is often concerned about the impact of the towers on the landscape, especially the very large natural draught towers. The towers shall, when possible, be built in industrial regions. An evaluation of the impact onthe landscape has been made in Switzerland at several sites. The most appropriate aid for the people in charge of evaluating the landscape aspects is the visiting of similar operating plants, combined with photomontages of the towers in the landscape under consideration. PHYSICAL-CHEMICAL EFFECTS OF COOLING SYSTEMS 67

The landscape impact of the cooling tower plumes is more difficult to evaluate. On a natural draught tower for an 800 MW(e) nuclear plant, the atmospheric plume may be 400 to 800 m long. In England some experiments have been made for improving the general aesthetics of groups of cooling towers by painting them with different colours (white, dark gray, and pink). The aesthetic worth of this approach is difficult to evaluate. The Central Electricity Generating Board of the United Kingdom has also completed development work on a fan-assisted natural draught tower for a 1000 MW(e) plant at Ipswich; since the fan-assisted tower can do the work of three natural draught towers of the same height, some aesthetic enhancement is anticipated.

REFERENCES TO CHAPTER 4

[1] BOGH, P., HOPKIRK, R., JUNOD, A., ZUEND, H., A New Method of Assessing the Environmental Influence of Cooling Towers as First Applied to the Kaiseraugst and Leibstadt Nuclear Power Plants, Report on the Technical Meeting 9/25 of the International Nuclear Industries Fair (Nuclex) in Basel, Switzerland. [2] PARKER, F.L., private communication. [3] GLASSTONE, S., A Textbook of Physical Chemistry, Van Nostrand, New York, N.Y.,(1946). [4] HIGGINS, J.T., "The thermal pollution problem: A preliminary study of atmospheric effects of cooling towers", Paper No. 69-51, Proc. 62nd Annual Meeting, Air Pollution Control Association, New York, N.Y. (Jun. 1969) 22. [5] McVEHIL, G.E., Evaluation of Cooling Tower Effects at Zion Nuclear Generating Station, Final Rep., Sierra Research Corp. for Commonwealth Edison Co., Chicago (1970). [6] EG&G, Inc., Potential Environmental Modifications Produced by Large Evaporative Cooling Towers, EPA WQO, Water Pollution Control Research Series Rep. No. 16130 DNH 01/71 (1971). [7] TRAVELLERS RESEARCH CORP., Climatic Effects of a Natural Draft Cooling Tower, Davis-Besse Nuclear Plant (1969). [8] CARSON, J.E., "Some comments on the atmospheric consequences of thermal enrichment from power generating stations on a large lake". Paper presented at the 64th Annual Meeting of Air Pollution Control Association, Atlantic City, N.J. (29 Jun. 1971); The atmospheric effects of thermal discharges into a large lake, Air Pollution Control Assoc. J. 22 (July 1972) 523. [9] AYNSLEY, E., Cooling-tower effects: Studies abound, Electr. World (1970) 42. [10] DECKER, F.W., Report on Cooling Towers and Weather, FWPCA', Corvallis, Oregon (1969) 26 pp. [11] ZELLER, R.W., SIMISON, H.E., WEATHERSBEE, E.J., PATTERSON, H., HANSEN, G., HILDEBRANDT, P., Report on Trip to Seven Thermal Power Plants, prepared for Pollution Control Council, Pacific Northwest Area (1969). [12] BROEHL, D.J., Field Investigation of Environmental Effects of Cooling Towers for Large Steam Electric Plants, Portland General Electric Company (1968). [ 13] HUFF, F. A., et al., Effect of cooling tower effluents on atmospheric conditions in northeastern Illinois, 111. State Water Survey, Urbana, Cire. 100 (1971) 37 pp. [14] ACKERMANN, W.C., Research Needs on Waste Heat Transfer from Large Sources into the Environment, Illinois State Water Survey Rep. (Dec. 1971). [15] CULKOWSKI, W.M., An anomalous snow at Oak Ridge, Tenn., Mon. Weather Rev. 90 5 (1962) 194. [ 16] FEDERAL WATER POLLUTION CONTROL ADMINISTRATION, Industrial Waste Guide on Thermal Pollution, U.S. Department of the Interior, FWPCA, Northwest Region, Pacific Northwest Water Laboratory, Corvallis, Oregon (1968) 112 pp. [17] COLBAUGH, W.C., BLACKWELL, J. P., LEAVITT, J.M., Interim Report on Investigation of Cooling Tower Plume Behavior, TVA Muscle Shoals. [18] VISBISKY, R.F., BIERMAN, G.F., BITTING, C. H., Plume Effects of Natural Draft Hyperbolic Cooling Towers, An Interim Report, Gilbert Assoc., Reading, Pa. (1970). [19] AYNSLEY, E., "Environmental aspects of cooling tower plumes", Cooling Tower Institute Meeting, New Orleans (Jan. 1970). 68 CHAPTER 5

[20] STOCKHAM, J., Cooling Tower Study, Final Rep. for Contract No. CPA 22-69-122, IITRI Report No. C6187-3, EPA Air Poll. Cont. Office, Durham, N. C. (1971). [21] CHANGNON, S.A., Jr., The LaPorte Weather Anomaly - Fact or Fiction) Bull. Am. Meteorol. Soc. 49_1 (1968) 4. [22] CZAPSKI, U.H., "Possible effects of thermal emissions on the atmosphere", Paper presented at the 5th Annual Environmental Health Research Symp., Albany, N.Y. (May 1968) 12. [23] CHANGNON, S. A., Jr., "Urban-produced thunderstorms at St. Louis and Chicago", preprints, 6th Conf. Severe Local Storms, Am. Meteorol. Soc. (1969) 95. [ 24] DIRECTION DE L' EQUIPEMENT DEPARTEMENT E. G. P. S. E., private communication.

[25] HANNA, S. R.. SWISHER, S.D., Meteorological considerations of the heat and moisture produced by man, Nucl. Safety (Mar.-Apr. 1971). [26] BÖHM, A.. BUBLITZ, D., HUBERT, H., Geräuschprobleme bei grossen Reichskühlanlagen, Mitteilungen der VGBM (Jun. 1971) 235. [27] Das Problem der Schallmilderung bei Kernkraftwerkanlagen, Mitteilungen der VG349 (Apr. 1969) 73. Chapter 5

BIOLOGICAL EFFECTS OF THERMAL DISCHARGES FROM NUCLEAR POWER PLANTS

5.1. INTRODUCTION

The concern about the effects of thermal discharges on the biota is the central issue of this technical report. Without the prospects of adverse biological effects on water quality and the direct impingement of waste heat on living organisms, the physical and chemical problem of heat dispersal would be minimal. This chapter attempts to review briefly that concern and those prospects regarding thermal effects on the biota to provide some understanding of the current research on thermal effects, and either directly or by evidence of omission to indicate that which is needed to be done. However, it should demonstrate that as our knowledge has increased it has directed our attention toward sublethal and long-term thermal effects, regional as opposed to single site effects, and toward natural populations as contrasted with effects on individual organisms of the biota, or laboratory populations. This chapter after general comments deals with various trophic levels, and finally with ecosystem responses to thermal discharges in water bodies.

5.2. GENERAL CONSIDERATIONS

5.2.1. Responses of biota to heat

Temperature is an important environmental factor governing the physiology and behaviour of organisms, and consequently the structure and metabolism of ecosystems. Living organisms respond to degrees of temperature and changes and rate of changes of temperature caused by transfer of heat. The importance of temperature as a limiting phenomenon, and as a cueing or driving force is well known, and there is an extensive literature on the effects of temperature on organisms. Many of the references cited in this chapter refer to this literature [1, 2], Organisms have been recorded for given situations as having upper and lower ultimate lethal temperatures, optimum temperature ranges for processes such as growth and reproduction, and temperature cues and limits for phenological events, migration and other behaviour. The distribution of various communities is, in part, a consequence of environmental temperatures. The composition of aquatic' communities depends largely on the temperature characteristics of their

69 70 CHAPTER 5 environment. Temperature may also have an indirect effect through the physical environment, particularly in aquatic situations, where, for instance, it may induce changes in water viscosity, degree of ice cover, or oxygen capacity. Synergistic effects such as stimulation of disease organisms by thermal effluents may have an effect on organisms and populations [3]. Despite the amount of information available it is difficult to predict at present the exact effect of thermal effluents from any particular nuclear power plant or the regional effect from one or more such plants. This difficulty is because most of the literature directly applicable to plant sites deals with possible thermal effects and much of the literature deals with effects observed under laboratory conditions but little of the literature reports experiments on either individuals or communities under field conditions. Little of the literature to date (October 1972) reports any other than local effects observed as a consequence of thermal effluent discharge at operating nuclear power plants1. The possibility exists that the lack of reports of the latter is either from the want of looking or looking at the wrong thing. The literature does indicate that, according to Cairns [4] ". . . organisms can usually tolerate small changes in the temperature of their environment, that further increases will probably produce problems, and that substantial increases will produce serious problems".

5.2.2. Dose effect

There is no single lethal temperature for an organism. Thermal death is a function of duration of exposure (time) as well as temperature and is therefore a dose response analogous to dose responses that are used in pharmacology and radiobiology. This phenomenon is often neglected and it is considered that all organisms will be dead when some lethal level of temperature has been reached. Coûtant [5] has summarized the importance of dose considerations in the following way:

"(a) In the zone of resistance (at a temperature above the lowest upper incipient lethal temperature) the lethal effect of a high temperature is manifested at a discrete time interval after beginning of exposure. (b) The higher the new temperature the shorter the time interval between beginning of exposure and death. (c) Acclimation to higher temperatures both increases the length of time an organism can survive an elevated temperature and elevates the maximum temperature that the organism can survive for a given time period. (d) There is an ultimate incipient lethal temperature below which an organism should survive indefinitely, if unaffected by other factors, but above which it cannot be acclimated successfully and it has only a discrete survival time. "

Figure 19 graphically illustrates the dose concept.

1 Except for cooling ponds developed for that purpose and used regardless of impact on the biota [6], BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 71

ACCLIMATION TEMPERATURE

i . 11 11 10 100 1000 10 000 TIME TO 50% MORTALITY (min)

FIG. 19. Median resistance times to high temperatures among young chinock (Oncorhynchus tshawyts ha) acclimated to temperatures indicated.

5.2.3. Thermal discharges and dissolved oxygen

Theoretically, thermal discharges will reduce dissolved oxygen while, at the same time, increasing the biological oxygen demand (BOD) of organisms. This process could become critical in receiving waters where saturation conditions may seldom occur [7], In such conditions, where oxygen availability is less than the theoretical capacity of the water, a thermal rise could further limit the available oxygen. Further aspects of this problem have been summarized by Parker [8]: "The increasingly rapid rates of protein denaturation, which takes place at temperatures above 30°C, must be considered. The protein portion of the enzyme is inactivated and the reactions apparently begin to slow down at temperatures above 30°C. It is, therefore, obvious that at present a semi-empirical relationship must be used to describe the variation of the BOD reaction rate with temperature. Such a relationship proposed by Streeter and Phelps2 and still favoured by most workers is:

kl(T) = kl(20) 0(T-2O)

= in which kj^Tj = the BOD rate constant at temperature T (in °C) : kj^oi the rate constant at 20°C; and 6 = a constant, usually taken to be 1. 047. If the discharge from a power plant inhibits mixing between the upper and lower layers, oxygen replacement and self-purification in the lower

2 STREETER, H.W., PHELPS, E.B., "A study of the pollution and natural purification of the Ohio River", Public Health Service, US Government Printing Office, Washington, D.C., Bulletin 146 (1925). 72 CHAPTER 5

layer will be minimized. Due to lack of mixing organic wastes discharged into the lower layer do not have access to the oxygen in that portion of the stream flowing in the upper layer. Thus, there is less dissolved oxygen, less dilution water and a more concentrated organic load in the lower layer leading to an acceleration of the dissolved oxygen depletion. The net result may be a considerable reduction in the waste assimilative capacity of the receiving water. If the heated discharge is completely mixed with the receiving water some of the above mentioned effects are eliminated; however, the rise in temperature still causes a decrease in the ability of water to hold dissolved oxygen, an increase in the metabolic activity of organisms, an increased rate of BOD exertion and a possible reduction in waste assimilative capacity. " On the positive side it should be pointed out that the greater oxygen deficit accelerates oxygen diffusion rate from the atmosphere, and that waste assimilation occurs at a shorter distance because of intensified biochemical activity. Therefore, after a certain distance, say 50 km, both dissolved oxygen and organic loads may stand at a level not much different from what they would be in the case of no temperature change, even if the sag point of the oxygen content located in-between is now lower than without heat addition. The problem of reduced oxygen depends on whether or not a high BOD exists, and how much of the source body is subjected to thermal loading. Thus, the situation may be much more critical on the Rhine, where BOD is high and a large plant may use a significant part of the flow in once- through cooling than in larger rivers elsewhere. Intolerably low oxygen content as a result of accelerated biochemical activity represents indeed the main effect of large heated discharges in strongly polluted streams. This factor more than any other led to the interdiction of direct river cooling of nuclear plants in the Swiss river-basin of the Rhine, in spite of the near-saturation dissolved oxygen levels in upstream waters. Although the direct physical loss just discussed is not of major concern, increased water temperatures can cause severe depletion in dissolved oxygen quite indirectly through acceleration of chemical and biological activity. Depending on the level of water pollution, especially with regard to suspended organic matters, the biochemical oxygen demand increases by several percentage points for every degree Celsius. An immediate consequence is that the minimum dissolved oxygen content in polluted rivers will reach a lower value and, in extreme cases, even disappear causing fishkills by suffocation and other damage to living organisms. On the other hand, field studies have been conducted under the auspices of Electricité de France on rivers with very low oxygen content. At the Gennevilliers Power Station the presence of the plant tended to increase the oxygen content of the water despite the rise in temperature. Likewise initial results of a study at Porcheville on the Seine show an increase of oxygen content. In both cases the oxygenation was attributed to turbulence in the pumps and in the downstream spillway. In the Porche- ville plant the study showed that the extra oxygen disappeared very rapidly downstream, indicating that the BOD and COD (Chemical Oxygen Demand) of the river are far from being satisfied [9]. Effer [10] reported that measurements made at operating power stations show only slight changes BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 73 and these are often toward increased concentrations. In 4000 analyses of water quality at the intakes and outfalls of power stations no deoxygenation was detected, regardless of the state of pollution of the water [11 ]. Laboratory experiments with water of the polluted River Rhine at Coblenz, Germany, however, showed that the BOD (24 h) increased by 16% for every degree Celsius rise in temperature [12], This rate can vary widely depending on the situation of self-purification and on the presence of toxic substances in the river water. Temperature rises may cause stratification to occur in a reservoir. If the inflow water is at a different density (i.e. temperature) than the ambient water it may flow as an overflow, interflow or underflow. As has been mentioned, water containing organic material entering a stratified reservoir will deplete the oxygen resources of the reservoir due to biological respiration. In the epilimnion, mixing by wind currents, photosynthesis and sedimentation may render the epilimnetic water satisfactory. However, in the hypolimnion, oxygen removed by biological action is not replaced, algae cannot grow, essentially no vertical mixing takes place and the products of sedimentation from the epilimnion may add additional organic load. The net result is a depletion of the dissolved oxygen resources, thus making septic conditions possible. If this hypolimnetic water with its low oxygen content is discharged from the dam, fish life may not be supported for several miles downstream, a lower waste assimilation capacity may exist and, in effect, the dam may be considered as being equivalent to a larger BOD concentration.

5.2.4. Thermal effects and chemical reactions

According to Parker [ 8 ] : "An increase in temperature will usually have a profound effect on chemical reactions, the rate of reaction being approximately doubled for each 10°C rise in temperature [13], Temperature affects not only the rate at which a reaction occurs, but the extent to which the reaction takes place. When considering temperature changes in a receiving water, one must contemplate changes in ionic strength, conductivity, dissociation, solubility and corrosion. With an increase in temperature these changes might very well result in differing chemical requirements in the water treatment plant. If there is a low oxidation-reduction potential at the mud water interface, conditions amenable to the dissolution of iron and manganese into the hypolimnetic waters will occur. The mechanism is not clear; however, if the oxides of these metals are present in the bottom muds, troublesome concentrations may appear in the water under reduced environmental conditions. " A report pertinent to nuclear power plant was made by Harvey [14]. He showed that sublethal variations in water temperatures (up to 40°C) had no major influence on sorption of several radionuclides (137Cs, 85Sr, 65Zn, 69Fe, 57Co) by a blue -green alga. There was some decrease in uptake of 57Co and increase of 54Mn (except at 40°C). No changes in growth rates of colonies were attributable to radioactivity. Several other interactions have been reported in the literature, largely from laboratory experiments. Field data are as yet equivocable on this matter. 74 CHAPTER 5

5.3. EFFECTS ON AQUATIC ORGANISMS

5.3.1. Decomposers, detrital feeders and benthic macroinvertebrates

5.3.1.1. Decomposers — microorganisms

The distribution, abundance, and dynamics of aquatic microorganisms unfortunately has received less attention than other areas of aquatic biology. Therefore this report can only show a few comments on the effect of thermal effluents on microorganismic decomposers: Temperature effects on microorganisms are significant to the biological processes of waste stabilization because of induced changes in growth rates and changes in death rates. In general, the higher the temperature the more active a microorganism becomes, unless the temperature or a secondary effect becomes a limiting factor. Thus, metabolic activity of thermophilic organisms is much greater at their optimum thanpsychrophilic organisms at their optimum. Examination of the known effects of temperature on waste treatment processes demonstrates the validity of this statement. It should be noted that a distinct difference exists between the ability of microorganisms to endure a given temperature and their ability to grow well under identical conditions. Temperature has a profound effect on the rate of oxidation. In the usual receiving water a multitude of different organisms are active in waste assimilation, all with their own characteristics and temperature tolerances. The distribution of organisms may change drastically with shifts in temperature or types of waste, each species having a different rate of metabolism. Because the composite metabolism includes many coupled reactions, each with its own characteristics, the composite rate-limiting steps may shift with temperature changes, thus precluding the interpretation of the process as a single reaction. The consequence is that differences between bacterial populations upstream and downstream of a nuclear power plant are difficult to determine. Even though the results of analysis are substantially the same between the measurement points upstream and down, the variations between and within each point are very large [9 ]. . Some data are available from operating nuclear stations. At the Indian Point Units, Hudson River, USA, "... bacteria are generally tolerant of exposure to temperatures that far exceed the predicted temperature rise of Indian Point Units Nos 1 and 2 cooling water and are also unlikely to be physically damaged as a result of entrainment. The only extensive bacterial mortality which might be encountered would be at times when the sodium hypochlorite is being added to the circulating water to control fouling in the condensers" [15], Similarly, a four-year study of microbiology of the Connecticut River, USA, at the Connecticut Yankee power plant (27 months pre- and 21 months post-operational start-up) found no quantitative differences in bacterial numbers above and below the plant. These findings should not be surprising as thermophylic bacteria are widely distributed. Brock [16] found survival of bacteria in hot springs up to the boiling point. Studies at Narragansett Bay, Rhode Island, USA, by Sieburth [17] show that water temperature shifts produced changes in relative abundance of thermophylic types, but no suppression or enhancement BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 75

of any taxonomic group. Cairns [18] found no degradation of protozoan communities in the Savannah River (Georgia, USA) or in the Potomac River (Virginia, USA), each of which received heated discharges.

5. 3. 1. 2. Macroinvertebrate decomposers and detrital feeders3

The macroinvertebrates of the benthos apparently are considered by some as the best indicators of the impact of thermal effluents [19 ]. Hedgepeth and Gonor [20] believe that there has been a disproportionate interest in potential lethal effects to benthos, and a lack of concern for subtile, long-term temperature changes important to population dynamics. They also emphasize that temperature fluctuations, including relatively cool water periods, are often necessary for reproductive cycles. This is an important subject worthy of considerable attention, especially in view of the enormous commercial value of shrimp, crabs, and the like, and clams and related forms. Actual experience at power plant sites both fossil-fuelled and nuclear fuelled has varied but, in general, the benthic macroinvertebrate decomposers and detritus feeders show a decrease in numbers in limited areas contiguous to the plant outfall. This decrease may be especially notable in summer and, in a few cases, there may be an increase in numbers and/or biomass in the winter. The following are a few examples: Warinner and Brehmer [21] found (York River, Virginia) the abundance of marine benthic invertebrates decreased up to 300 to 400 metres from the discharge outfall. At Turkey Point, Miami, Florida, a marked reduction in benthic animals occurred in an area of about 50 hectares adjacent to a discharge canal from a fossil fuel plant [22], Others reporting at least summer decreases in benthic macroinvertebrates are: Nauman and Cory [ 23 ] (Chalk Pt., Maryland), Merriman[24] (Connecticut Yankee, Connecticut), and Gammon [25] (Wabash River, Indiana). In all cases these are local decreases. For example Hechtel [26] (Northport Power plant, Long Island, New York) reported that the affected area extended at most 1. 5 km from the outfall, with most changes within a few hundred metres. Similar experience has been reported for the USSR, where moderate heating (AT of 5 - 6°C) has resulted in the suppression of benthic fauna during the summer period [27], At Indian Point, on the Hudson River, USA, analysis of the available information resulted in a prediction that the changes in the benthos attributable to the heated effluent plume would be inconsequential in terms of the total population at risk [15]. In another case, the benthic invertebrates were unaffected in the pathway of the heated plume, presumably because of stratification of the latter over deeper cool water [28], As an example of the reverse case in winter, Massengill [29] reported colonization and a 10 to 40% increase in standing crop of benthos at the Connecticut Yankee plant as compared to other locales on the Connecticut River. Finally, in some isolated situations exotic species have been recorded forming populations far away from natural

3 Invertebrate detrital feeders are included here for convenience. Macroinvertebrates considered as decomposers are organisms which shred larger bits of organic materials, e.g. leaves, into smaller fragments. 76 CHAPTER 5

distribution areas, e. g. the oligochaete Branchura sowerbyi in a heated bay of Lake Mälaren, Sweden, and otherwise reported from very few habitats in central Europe [30]. The organism of particular interest to water quality management is E_. coli, as it is the prime indicator of faecal pollution. Increased temperatures, 35to45°C, may lead to optimum growth conditions for this organism in receiving waters.

5.3.2. Producers

5.3.2.1. Macrophytes Macrophytes (rooted vascular plants and macroalgae) may in some limited areas be the main source of primary production for an aquatic community. This is apparently the case in South Biscayne Bay and Card Sound near Miami, Florida [22], There, at the effluent of a canal from a complex of two fossil fuel plants (operating) and two nuclear plants (not scheduled to start up until 1973 and 19 74), an area of 40 to 200 hectares of Turtle Grass (Thalassia testudinum) has been destroyed or altered in some way. This has been attributed solely to heat [ 31 ]. Yet Nakatani [ 1 ] takes exception and questions positive statements about kills attributed to heat alone. Another report for the Chalk Point Maryland Plant indicates a disappearance of rooted aquatic plants near the effluent [32],

5.3.2.2. Phytoplankton Primary production is the first step in the maintenance of complex ecosystems and, of course, phytoplankton forms together with Zooplankton are the essential food for many commercially and recreationally valuable shell and fin fish. The following is excerpted from a review by Nakatani [ 1 ] : "Inherent in the question of availability of different algal groups as food for invertebrates is the succession of these algae with increasing temperature. As Patrick [33] noted in her review of the effects of temperature on freshwater algae, each species in nature has its own range of temperature tolerance and its range of optimum growth, photosynthesis, and reproduction. Diatoms are represented by the largest number of species with relatively low temperature tolerances; namely, to temperatures below 30°C. The tolerances of the green algae cover a wide temperature span. The blue-green algae have more species that are tolerant of very high temperatures. There are some species in all groups, however, that tolerate the unusual extreme for their group. Under normal seasonal conditions there is a succession of species on the same substrate. This succession is largely the result of changes in water temperature and light intensity through the optima for the various species. As the temperature increases or decreases, one species replaces another as the dominant organisms. In nature there are also many other pressures upon a species including interspecies competition and prédation, so that the temperature of maximum development in a stream may not be exactly the same as the optimum range for growth in the laboratory. Figure 19 indicates the most commonly observed type of population shift. This figure is generally accepted, although, as Coûtant [5] points out, it is a generalized pattern which is not always followed by algal populations in the field. BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 77

The effects of temperature on phytoplankton may be separated into effects of passage through condenser (mechanical thermal shock), and effects due to thermal releases to receiving body of water.

5. 3. 2. 2. 1. Mechanical thermal shock in passage through condenser

The dangers to the food chain by plankton kills in passage through the condenser system and in the receiving water with the thermal plume have often been suggested. In many situations the task of determining in the field precisely the quantity of phytoplankton which might be killed by temperature changes may not be possible unless adequate financial support is available. Anyone who has engaged in plankton sampling soon recognizes the large effort in manpower and time which must be expended to obtain some reasonably accurate quantitative data. At present the usual methods involve time consuming and tedious microscopic identification and counting by qualified people, although other methods such as measurements of chlorophyll and deoxyribose nucleic acid have provided other means of estimating abundance. The patchy distribution of plankton, well known by limnologists and oceanographers, presents a difficult sampling problem. Replicate hauls at a single station often have greater variance than between stations. Although biologists are aware of possible damage to plankton passed through condenser cooling water, this survey showed little work being done in this problem area. Some work has been done at operating nuclear plants recently. For example, at Indian Point, Howells [34] sampled the intake water and the discharge water to determine possible damage to phytoplankton. She concluded that there was no significant effect. Patrick [33] stated that studies made concerning the effect on algae of passing them through condenser indicate that, if the temperature does not exceed 34 to 34. 5 °C, little, if any, harm is done. Morgan and Stross [35] have examined the effects of the passage through condensers upon primary productivity in some detail. They found that an increase of approximately 8°C stimulated photosynthesis when water temperatures were 16°C or cooler. A similar increase of 8°C, when water temperatures were 20°C or warmer, however, inhibited photosynthesis. They found that inherent synchrony in the algae made it mandatory to consider the time of day when performing experiments. Additional effects such as chlorination resulted in further inhibition of photosynthesis when the water was warm and nullified thermal stimulation when the water was cool. In the extreme case, photosynthetic capacity could be decreased by up to 9 5%. Phytoplankton subjected to heating during passage through the condensers showed no ability to recover their photosynthetic capacity after cooling to intake temperatures. Stockner [36] stated that there is a similarity between grossly polluted environments and thermal streams supporting blue-green populations which had high rates of primary production. " (End of excerpt from Nakatani [ 1 ]. ) Some studies were also made to determine the effect on phytoplankton of passing Potomac River water through the condenser of the Dickerson Plant (Potomac Electric Power Co., Maryland, USA) when there was an 8°C rise [37], A few algal cells showed morphological changes following condenser passage but the numbers were not significant. There was no attempt to culture the cells to determine their resultant viability. 78 CHAPTER 5

The following is excerpted from the Final Environmental Impact Statement on Indian Point No. 2, Hudson River, USA [ 15].

5.3.2.2.2. Effects due to thermal releases in a receiving water body

"Reports of field studies of the biota associated with discharge canals of power plants, where the water temperature is still essentially as high as it was when it left the condensers, have noted dominance of the periphyton community by heat-tolerant blue-green algae when water temperatures exceed about 30°C. Reports by Trembley [38] indicate that the periphyton growth on glass slides was dominated more completely by blue-green algal species in the discharge canal of the Martin's Creek Power Plant on the Delaware River when the temperature exceeded 35°C. There were fewer species on the slides than when the water was cooler, but those remaining were represented by a larger number of individuals. This condition is generally recognized as an indication of an abnormal community structure. It is difficult to determine, however, how much of the alteration of community structure was due to chlorination of the cooling water [ 5 ]. Forester [39] discussed the apparent early arrival due to heated effluent discharges of spring seasonal successions in periphyton of the discharge canal of the Yankee Atomic Power Plant on the Connecticut River. Buck [40] reported a noticeable shift from diatoms to blue-green algae in plankton in the area of thermal effluent. These planktonic forms were presumably derived from the periphyton populations of the mile-long canal, although a detailed report of this study has not yet been published. Similar changes in the species composition of plankton in cooling water were reported by Beer and Pipes [41 ], who described a shift from diatom dominance in the inlet to dominance by unicellular green algae in the effluent canal of the Dresden Station on the Illinois River. In a September survey. Os dilatoria (a blue-green filamentous alga) covered all bottom materials in shallow water of the discharge canal and the river bed close to the confluence of the discharge from the John Sevier Steam Plant (Tennessee Valley Authority) with the Holston River, Tennessee. No large-scale replacement of cold-water marine algae by warm-water-tolerant forms, however, was found by North [42] at the Morro Bay discharge canal. The entire algal flora was simply depleted at the warmer temperature. The lethal temperature of the algae varies with the species [33], For most of the algal species studied to date, the lethal temperature is in the range from 33 to 45°C, with the majority being near 44°C. Diatoms that require cooler temperature (stenotherms) are generally most sensitive to temperature change and can withstand a 10°C temperature change. Diatoms suited to warmer temperatures can tolerate temperature changes of from 15 to 20°C. At Indian Point, the diatom Melosira is dominant throughout most of the year, although their dominance declines during the summer period of high temperatures and salinity. Many other species are also consistently present [43], However, there is a seasonal change in composition characterized by diatom dominance much of the year, with green and blue- green algae becoming more abundant in late summer and early fall [44], The pattern of dominant algal forms (Fig. 20) conforms to the typical BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 79

FIG.20. Relative proportions of diatoms, green, and blue-green algae in the standing crop at Indian Point, 1970 (East Channel Station).

pattern previously described (Fig. 21), although the shifts in abundance of the green and blue-green algae seem to be occurring at lower temperatures than would be predicted. Effect on phytoplankton as determined by the ability to produce organic matter depended upon the ambient temperature of the stream as well as on the change in temperature imposed by the condensers in studies on the York River, Virginia, by Warinner and Brehmer [ 21 ]. At low winter temperatures, 0 to 10°C temperature rise increased production; with high summer temperatures, 15 to 20°C, slight increases increased production while large increases (greater than 5.6°C) depressed it. The greater the temperature rise in summer, the greater was the depression of the affected plankton's ability to photosynthesize. This paper aptly demonstrated the seasonality of temperature effects, a point often lost by investigators conducting 'one shot1 surveys." (End of excerpt from Final Environmental Impact Statement on Indian Point No. 2 [15].) 80 CHAPTER 5

FIG. 21. Population changes among algal groups with change in temperature.

In general, it appears that no investigator has yet reported on food web break-downs as a consequence of phytoplankton mortality either from entrainment or thermal shock. As was pointed out earlier, to determine this by following each pathway of a particular food web is expensive, if not impossible. Most investigators are either forced to look at only one or a few trophic taxa, or to consider higher trophic levels, such as fish, as representing integrating samples of particular food webs.

5. 3. 3. Consumers

5.3.3.1. Zooplankton

Zooplankton by virtue of their large areal biomass are a key link in all aquatic food chains. Organisms from many phyla comprise the Zooplankton and, being Poikilothermie, are sensitive to temperature changes. The possibility of detrimental effects on Zooplankton seems greater through the impact of entrainment through the cooling system than only through contact with or entrainment in the thermal plume. Because of their small size the entrainment of Zooplankton into the coolant system of power plants could pose a serious problem if a sufficiently large proportion of the population were killed. While passing through the cooling water system, Zooplankton are exposed to physical and chemical influences such as temperature rise, turbulence, pressure changes and chemicals which are added to control the slime formation on condenser tubes and fouling organisms in the cooling water channel. All these factors cause shocks that can result in reduced fertility, increased vulnerability to prédation, and/or death directly. BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 81

FIG.22. Zooplankton and water temperatures in the Green River, Kentucky, near the Paradise Stream Plant, 26-27 May 1964.

These three effects have the net effect of reducing the population. Therefore entrainment analysis of the coolant system should include an estimate of Zooplankton mortality and the potential for a rapid recovery downstream of the power plant. Such an analysis has been carried out at the Paradise Generating Station at Green River, Kentucky, USA [45] (Fig. 22). Researchers found that the volume of Zooplankton in the cooling water was drastically reduced during passage through the single-pass coolant system of the plant. However, organisms that bypassed the plant were found to reproduce at an accelerated pace in water that was warmed by mixing with a thermal discharge, 9°C above an ambient of 28°C. Coûtant [5] mentioned that decreases in Zooplankton biomass in this area could not be attributable to thermal shock effects alone. Other factors proposed were mechanical destruction in the condenser or piping system and prédation upon carcasses and weakened individuals at or near the point of discharge. The Green River report does not touch on other possible factors involved, however, Heinle [46] conducted a series of laboratory and field experiments to determine the effect of condenser passage on Zooplankton in the brackish Patuxent estuary in the vicinity of the Chalk Point power station. Not only examining survival, he also observed the productive success in subsequent laboratory culture of populations that had experienced the thermal, mechanical, and chemical shocks of condenser passage. Populations of some entrained copepods were generally not as fit for reproduction as control groups, even when the temperatures of exposure were below the laboratory-determined lethal temperatures. Part of the effect was thought to be due to chlorination of cooling water as a normal 82 CHAPTER 5 operating routine at the plant. Although effects of condenser passage were identified in this study, the methodology and the lack of control over such variables as chlorination yielded results of uncertain predictive value. Nevertheless, within the estuary, population densities of Zooplankton remained high despite high rates of natural prédation and the additional losses attributable to the power plant. Certainly, the reproductive potential of the entire population remained intact after passage through the condenser system. Normandeau [47] also identified clear effects of condenser passage on summer Zooplankton at the Merrimack Generating Station, New Hampshire, USA. Samples taken above the inlet and in the discharge canal indicated a reduction in population density of nearly all Zooplankton after passing through the cooling condensers. These effects were definitely related to absolute temperature, being discernible chiefly when the condenser cooling water was elevated in July to temperatures above 38°C. The increase in temperature by itself did not appear to be the causative factor; rather, mortality was evidenced when the maximum temperature attained exceeded the tolerance limits of the species. The depressions in Zooplankton population were also evident downstream from the plant in the mixing zone in the Merrimack River, although cooling water was a small percentage of the total river flow at this point. The ability of certain Zooplankton to maintain their level in the water column can lead to special problems concerning entrainment. Results of a study at the Indian Point plant site [15] show that between 6 and 31% of a truly passive plankton population could be withdrawn depending upon the freshwater flow. This is noteworthy since Heinle [46] found that population of the copepod Acartia tonsa, a dominant form at Indian Point, could not survive losses greater than 20 to 25% per day. Nevertheless, in the presence of convective flow, vertical migration is often used for migratory purposes and allows Zooplankton to maintain position within the estuary without expending a great deal of energy to do so. Under some circumstances this behaviour pattern can alter entrainment susceptibility a great deal from that of a truly passive organism. Therefore, the migration of organisms through the zone of exposure can occur at rates faster or slower than those of strictly passive organisms. Likewise, their concentration in the intake water could be greater or smaller than their average concentration in the river, calculated on the basis of random distribution. In nature no such random distribution of Zooplankton is normally found. As a consequence, the behaviour of each individual species must be considered separately to obtain a quantitative estimate of its population's susceptibility to withdrawal. The manner in which distribution influences susceptibility of entrainment is associated with the organisms' vertical migration patterns and the relative water velocities within the different areas. Therefore the importance of this factor must also be evaluated in relation to the entrainment susceptibility of each species considered. Preliminary investigations at the Turkey Point Plant of Biscayne Bay, Florida, showed that 80% of the Zooplankton collected were dead at discharge temperatures of 40°C in July 1969 [22], When the discharge temperature was 33°C mortality percentages of 1 2 and 7 were found. Subsequent sampling indicated that a maximum accuracy of only about 10% was possible due to deaths during collection, transportation, and counting. BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 83

Many laboratory studies also show that Zooplankton metabolism can be detrimentally affected by elevated temperatures. As an example, observations with two crustacean species (Acartia tonsa and Eurytemora affinis) show that the lethal temperature is very near the highest natural temperature of those species. Both species died after passing through a cooling system, although the temperature was lower than the lethal temperature [ 21 ]. On the other hand, some studies report little or no damage following entrainment. Adams [48] found that the discharge canal of the Humboldt Bay Nuclear Plant on the California coast was a favourable site for natural setting of native oysters (Ostrea lurida), cockles (Cardium corbis), littleneck clams (Protothaca staminae), butter clams (Saxidomus giganteus), gaper clams (Tresus nuttalli), and several other bivalves. The net flow in the canal was always outward because of domination by the cooling water flow, and dye studies showed a complete evacuation of the canal, in less than three hours. Thus, some of the free-swimming larval stages of these bivalves had to pass alive through the condenser system in order to colonize the canal. Similar successful passages must have occurred at the Chalk Point Power Station on the Patuxent estuary to account for high densities of invertebrates found in the discharge canal [49, 50], Another study reports the possible beneficial effect of heated effluents on Zooplankton production. Over a seven year period, a marked increase in size of Daphnia cu culata was noted in Lake Lichen, Poland, which had been heated to 30°C. Although the biomass of the lake was similar to that in nearby unheated lakes, productivity was greater due to the more rapid growth at elevated temperatures [51]. Confirmation of the potential importance of prédation on shocked organisms in the area of thermal discharges can be found in the many references to predators being attracted to points of thermal discharges. In one such case Neill [ 52] reported intensive feeding by fish on entrained Zooplankton in the outfall area of a power plant on Lake Monona, Wisconsin. Abundant Zooplankton was entrained in cooling water taken from 100 metres offshore and 5. 2. metres below the water surface. The temperature rise of 10°C may have killed or debilitated the Zooplankton sufficiently allowing enhanced prédation. The important factor will be whether or not the ability for population recovery has been altered. It should also be kept in mind that evidence is accruing which indicates that small perturbations of the environmental temperature regime do influence the presence or absence of many marine species. Therefore one must take into consideration these little understood, long-term natural fluctuations when trying to evaluate the possible thermal effect on any biological system by industrial effluent [20]. For example, breeding seasons for many species were several weeks early at the Hunterston power plant in Scotland. This apparently resulted in abnormally high mortalities to young copepods unable to find appropriate food [53]. Once again, however, no investigator has yet related these various sources of mortality, be they entrainment, prédation, thermal impact, temporal, to the total effect on the population of the river, lake, or pond etc. used as a source of cooling water, nor have these mortalities been discussed fully in terms of resilience of Zooplankton populations, e. g. compensatory generation times. Clearly, both vigilance and research are needed. 84 CHAPTER 5

5.3.3.2. Fish

5.3.3.2.1. Fish mortality No other aquatic resource is as commercially valuable as fisheries. In addition, the recreational value of fishing ranks high. For these reasons, as well as concern for man's total environment, the possible impact of thermal effluents on fish populations is an area of prime interest. The study of fish populations, as has been mentioned, may yield an integrated picture of entire food webs. Carnivorous fish represent the top trophic levels and, as a result, reflect all that has gone before them in their particular food chain. Natural variation, which might alarm one looking at a particular plankton population, may not show up at all in fish populations. The latter may have taken advantage of multiple sources of supply, favouring now one then the other depending on abundance and availability. As Nakatani [1 ] states: "It would seem that any large effort expended to answer questions concerning the impact of plankton kills by towing plankton nets may be more effectively spent in other research areas, especially if the project has limited funding. If important food organisms for desired fish are being killed, a study of the growth, gut-contents and health of the desired fish population might be undertaken. " In other words, if one is concerned about fish populations, that is the place to begin the investigation. Perhaps the most widely used diagram to describe the effect of heat on fish is Brett's temperature tolerance trapezium [54] which describes the effect of acclimation on the tolerable temperatures for spawning, activity and death. These data from the laboratory do not necessarily reflect field conditions and specifically ignore activity, body size, age, season, general health, day length, sex, water chemistry, osmotic stress, diet, hormonal variations etc. Even more importantly, they ignore the time during which the temperature is exerted. That would, in essence, be like looking at the radioactive dose rate and ignoring the time during which the dose was exerted. A preferred diagram might be one showing median resistance times for fish acclimated at various temperatures (Fig. 23). Then one might calculate the degree of stress undergone by an organism by summing up the amount of time it spent at various temperatures (see also Fig. 19). It should be noted that aquaria tests do not reflect field conditions and H.B.N. Hynes [55] has stated: "The final question as to how much of any particular poison can be tolerated by a population of fishes living a natural life in a river still remains unanswered except where it is based on field observations" [56]. The main questions related to the study of intake/outlet of cooling water are (a) adult and juvenile fish killed at the screens, (b) fish eggs and larvae killed in condenser systems and (c) various effects at the outlet region. Temperature effects in the outlet region can be caused by direct lethal or sublethal temperatures. Lethal temperatures for adults are not as a rule of importance in evaluating effects in the recipient water body. They might however be of importance in the grouping of fish families/groups from sensitive to tolerant in this respect. As a rule Salmonoid fishes are most sensitive, pike and perch fishes are moderately tolerant and carp fishes tolerant to excess heat. BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 85

FIG.23. Yield for rod fishing in warm waters as a function of temperature and season. Catches in warm waters are expressed in per cent of the total.

Such grouping gives some idea of what might happen to the balance between species in the vicinity of the outlets 50 km2 coastal). Most of these data come from laboratory studies which, as a rule, indicate higher temperature tolerance than investigations in the field. In reality temperatures far below so-called lethal temperatures may be of importance for the species due to varying sensitivity in different phases of development from egg to adult; and the varying tolerance during the year. There is a general rule that the range of temperature tolerances for spawning and embryonic development and the tolerance for growth and feeding are less than the lethal temperature limits of adults. Principles given for Oncorhynchus nerca [56] seem to be valid for other species of fish as well as invertebrates. This means that interaction between species, e.g. interspecific competition, is affected far below noticed lethal effects of adults resulting in elimination of species, or at least increasing the stresses on some populations. In a series of experiments Coûtant [57] demonstrated that thermally treated (at ~ 28°C) young salmon (Oncorhynchus sp.) were differentially selected by predator fish from a mixed school of treated and non-treated fish. He had similar results with treated rainbow trout (Salmo gairdneri). The effect was noted at about 10 to 11% of the mean equilibrium case dose. Research reported by Barber [58] has shown that thermal treatment increases the vulnerability of whitefish fry to prédation. These laboratory studies are interesting, but what is needed is some measure of the serious- ness of this problem in the field. As to actual kills of fish, during the years 1962 to 1969 the Federal Government of the USA listed only eighteen voluntarily reported fish kills associated with temperature rises and involving some 700 000 fish. There 86 CHAPTER 5 is even some question whether or not some of these kills were in many cases in fact due to thermal changes. Barber [58] believes that the only public record of fish kills is in newspaper reports and that most fish kills at power plants in the past have gone unrecorded in the public record. Whether or not this is true, where scientific studies have been made, thermal kills are rare. Consider the following examples: Studies have been made for twenty-five years of the effect of heated effluents from as many as nine production reactors on the Columbia River at Hanford, Washington, USA. These production reactors release more heat to the water than do nuclear plants. No thermal kill of any significance has been observed, despite detailed investigations [59]. In Japan, Takeda [60] reports that so far very little has been reported of cases where thermal discharge of power stations has actually done damage to fisheries. (However, local fishermen are compensated for giving up their fishery rights in a specific area near the discharge outlet where the AT is expected to be relatively large.) In France, in in situ studies at the Montereau power station, several thousand fish were tagged. No deaths were found to occur as a result of temperature, which reached 31°C in the experimental canal [61]. Fish kills, apparently due to thermal changes, have been reported recently at two nuclear power stations in the USA. As documented kills seem scarce these will be reported here in some detail. One was at Oyster Creek, New Jersey. The following is from the USAEC. Draft Environmental Statement for the Forked River Nuclear Station Unit 1, issued October 1972. "Sharp declines in temperature that potentially would occur in the event of plant shut-down may result in fish mortality. Following shut-down of the Oyster Creek Station in January 19 72, a substantial loss of Atlantic menhaden occurred in the discharge canal. The shut-down consisted of a rapid partial (approximately one-half) load reduction followed by a normal shut-down from one-half load over a period of 6| hours. The discharge canal water temperature underwent a sharp decline of about 4°C in a short period of time followed by a gradual cooling to ambient over the next 6^ hours. There also occurred a rapid natural change in ambient temperature during the 48 hours preceding this shut-down in which ambient water temperature (inlet to plant) dropped 7°C (8 to 1°C). The discharge water from the condensers, reflecting this lowering in ambient temperature, dropped from 22 to 15°C. Dead fish were first reported the morning of 29 January. The fish kill was limited almost exclusively to the Atlantic menhaden (Brevoortia tyrannus). The extent of the fish kill cannot be verified, however, estimates range between 100 000 to 200 000 fish lost. Menhaden normally migrate from the bay in late fall. During the period of 17 September, 1971 to 11 November, 1971 the Station was shut down for routine maintenance and no heated effluent was discharged. It is likely the fish entered the canal during the period of shut-down and remained there after plant start-up. Furthermore, it is likely that the warmer water discharged after start-up represented a preferred temperature for menhaden, hence they did not migrate to more southern latitudes. The estimated loss of fish at Oyster Creek in January 19 72 was insignificant in terms of the total annual catch of menhaden in New Jersey waters" [62]. BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 87

The second kill, in the spring of 19 72, also involving menhaden, occurred at the Millstone Plant, Waterford, Connecticut. The estimated toll was put at about 30 000. It was suspected that the fish died from thermal shock, but the evidence is not conclusive [63]. The plant was in essentially normal operation before and during the kill. One pump was not working, and the AT rose from about 13 to about 17°C, the circulating water outlet rose from about 19 to about 23°C. Again the numbers of menhaden involved are insignificant compared to the total annual catch of the species. There is a growing concern for the problems connected to the intake of cooling water. Fish kills have been observed at the screens. Of relevance is the water flow speed and the technical solutions of the intake. The effects are of interest ecologically as well as economically for the function of the station. Fish eggs and larvae are to a certain degree killed in the condenser system by heat and/or mechanical damage. Various percentage losses have been reported. In this respect a power plant, by entrainment, is similar to a large non-discriminating predator. The importance of such prédation is related to the rate and amount of organisms consumed compared to the total population, and its ability for compensatory reproduction. The latter in turn depends on whether or not the induced mortality is density dependent or independent. Without getting into a long discussion on this point, it will suffice to say that such may be significant. It was in part because of this concern that the Final Environmental Impact Statement for Indian Point No. 2, Hudson River, USA [15] recommended the installation of a closed- cycle cooling system by 19 78, unless evidence of no significant environmental damage was forthcoming before then. In a preliminary study, observations obtained at the Connecticut Yankee Atomic Power Plant on the Connecticut River showed that larval river herring (Alosa spp.) was able to successfully pass through condensers in July when the temperature was raised to 34°C. All larvae were found to be in good condition following the rapid thermal shock and subsequent collection by a plankton net in the plant's discharge canal [64], However, more detailed studies (March 19 71) at this site found that no larval fish of the nine species which were entrained in the cooling water system survived when the temperature of the canal water exceeded 30°C (March 19 71). As an example of the problem, the following is taken from the Final Environmental Impact Statement on Indian Point No. 2 [ 15] : "Substantial fish kills at Unit No. 1 were observed during January 19 70 and were thought to be the result of openings under the fixed screens. This conclusion is supported by the fact that a significant reduction of the number of fish counted on the travelling screens occurred after the openings were eliminated. These data indicate that the magnitude of the fish kill was reduced from highs in excess of 16 000 to 18 000 fish per screen washing on February 1-3, to sustained counts of less than 50 fish per washing after February 6, 1970. However, collections of fish on the travelling screens when the fixed screens are in place do not adequately represent the extent of the fish kill, especially during periods when dead fish were netted from in front of the fixed screens and consequently could not have had a chance to be included in the counts of fish on the travelling screens. For instance, when the travelling screen count was reported to total 388 for March 6 and 7, 19 70, there were approximately 120 000 fish netted in front of the fixed screens. 88 CHAPTER 5

In essence, the impingement problem was simply shifted from the travelling screens to the fixed fine mesh screens. However, this process did reduce the average size of the fish which were captured. These kills have included some twenty-three species, white perch being by far the predominant species, and account for over 90% of winter fish kills. However, because of the large number of fish involved, substantial numbers of other species are also killed. For instance, from data obtained by Raytheon Corporation, the total of fish killed from 6 November, 1969 to 11 January, 1970 at Unit No. 1 was 1 310 345 fish, 137 649 of which were striped bass.

The fish that have been collected on the intake screens, identified and measured are generally larger than 45 to 50 mm in length. Since smaller fish are known to exist in the area, it is assumed that the minimum sereenable size (at least for striped bass) is in the neighbourhood of 40 to 45 mm. Smaller fish would be expected to go through the condenser. The precise cause of the impingement problem is not completely understood. All the fish kills at Indian Point Unit No. 1 appear to have been associated with the plant's condenser cooling water system. Fish appear to be caught against the screens by the force of the river water drawn into the plant. Once caught against the screens, they are unable to escape and eventually succumb to exhaustion, although the precise cause of death is unknown. A number of possible factors contributing to the problem have been examined. The wharf and related structures located over the intakes may contribute by appearing to provide refuge for fish. Another factor may be related to the existence in winter-time of warmer river water in the vicinity of the plant caused by discharge of heated river water from the plant. There is a definite seasonal variation in the magnitude of the kill, the highest mortalities occurring in the winter months and the lowest mortalities in the summer. Apparently, this is due to reduced swimming ability of many fishes at the very low winter temperatures. The most important contributing factor is the capturing capacity of the large volume of water withdrawn from the river. The only action that really seems to reduce the level of mortality is a reduction in the intake velocity. Present evidence indicates that a reduction in the water velocity may greatly reduce the fish kill problem. " Positive rheotaxis may be a behavioural act of significance leading to impingement of fish so responding in the intake structures of plants. This, however, is not a thermally caused behaviour. Considering the most recent Impact Statements issued by the USAEC, impingement and entrainment seem to be problems of more concern than effects of the thermal plume. What is most lacking in all of the foregoing discussions of fish mortality is the relation of this mortality to the species population. Do these kills, singly or in toto, significantly affect the population? Will these kills show up in reduced harvests, or in reduced fish per hour for the sportsman? These questions remain unanswered, yet one should remember that fish are not immortal until they are killed by a power plant. The effect of power plant operation, if any, must be considered in terms of total natality and mortality factors of a population. BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 89

5.3.3.2.2. Fish behaviour

Possible behavioural effects of thermal shock have been reported in the literature. As has been mentioned Coûtant [57] has shown that thermal shock may increase the susceptibility of young salmon to prédation. Research at the Great Lakes Fishery Laboratory [58] has shown that similar results occur when whitefish prey are thermally shocked and subsequently subject to prédation. The consequences and/or likelihood of such events being significant in nature are not known, as previously stated. Todd [65] has reported on the break-up of social behaviour in yellow bullheads (Ictalurus sp.) at elevated temperatures. Again, whether or not this type of effect is of consequence has not been explored in the field. Losses of equilibrium due to thermal stress in the field have been reported by several authors [ 5]. Reduction of activity and immobilization have also been noted [5], Many observers report that fish tend to gather in thermal plumes, especially during the colder season, a behaviour well known to fishermen in temperate areas. Fish migration may be inhibited by this response to the plume; the fish may be subsequently subjected to cold shock under certain circumstances. Also predators may be attracted to points of thermal discharge. Fish attracted to warm water plumes, or to discharge canals may be induced by the higher temperatures to spawn earlier than usual. For example, white suckers (Catostomus connersonni) spawned prematurely in the discharge canal of the Martin's Creek Power Plant on the Delaware River [66], This premature spawning probably requires residence in the thermal effluent area for several months. Speculations may be made as to the effect of this action "... ranging from loss of progeny due to lack of proper food to species changes brought about by the dominant large warm- water fry" [15]. Of course, spawning times in unaltered bodies of water vary from year to year depending on seasonal temperature input. In this case, an entire water body may be affected thus resulting in some kind of more-or-less synchrony between predator and prey population, and plant production. Local warming, as brought about by a power plant, may result in patches of dissynchrony. How critical this may be in the long run has not been determined. Another problem is that fish remaining in thermal plumes may subject themselves to accelerated metabolic rates compared to their seasonal norm in other parts of their environment [15]. 'Skinny fish' have been identified at the Connecticut Yankee plant, on the Connecticut River [67] in winter accumulations of brown bullheads (Ictalurus nebulosus) and white catfish (I. catus) in the discharge canal. Individuals tagged early in the winter and recovered four months later had lost up to 60% of their weight. Fish outside the canal also lost weight, but at a much slower rate. Channel catfish (I. punctatus), however, showed no such decline. The significance of this weight loss to the Connecticut River populations of bullheads and white catfish is unknown. The attracting and repelling nature of thermal plumes for fish has also been noted in France [68]. On the Seine at the site of the Montreaux power station, the largest population of fish occurs in the fall. A number of species leave the site in the warm season. Barb (Barbus barbus) are 90 CHAPTER 5 present during the cold season possibly because of rheotactic responses in part. Black bass (Micropterus salmoides) remain in the heated zone. In Sweden because of their economical importance special interest is given to migratory fish species, like plankton feeder (herring, sprat) or migrating fishes like eel, salmon and sea trout. Heated coastal water might attract herring and sprat during the cold season, increasing availability for fishing. Positive effects can be noticed for eel regarding availability, since they are attracted as a rule by higher temperatures. Signals from coastal areas influenced by heat might influence the navigation along gradients and disturb or block the migration route for salmon or sea trout. Studies of river sited power plants indicate however limited effects on salmonoid spawning migration. Tulkki [69] reports for Finland: "The unpredicted 'sweeping plume1 may cause rapid small changes of temperature with consequences in behaviour and ecology of fish in large sea areas. There is also the problem of migrating salmonoid fish, whitefish and the Baltic herring, which may vary their migrations due to coastal warm water currents. A change of migrations and behaviour causes changes in fishing practice and brings thus also local economic consequences." In summary, both mortality and physiological and behavioural changes of fish have been observed in conjunction with operation of nuclear power stations. Many of the possible effects as can be demonstrated in the laboratory have not been observed. However, the significance of what has occurred has not yet been interpreted in terms of the effect on total species populations or even for regional sub-populations of fish species. Thus far the evidence seems negative that any immediate effect of significance has occurred. Long-term changes, and the impact of multiple siting and increased numbers of nuclear stations on fish populations need further investigation.

5.3.4. Harvest

Besides direct effects on fish population, thermal discharges may modify the behaviour of fishes with respect to catchability. Elser [ 70] has conducted field studies on that problem which has apparently not been much investigated by other biologists. This author has attempted to determine the influence on rod fishing of the thermal effluents from a power plant located on the Potomac River. With this objective, a rigorously controlled fishing program has been undertaken. Fishing zones were circumscribed both in normal and heated waters. Three paid fishermen had the task every week-end to fish under identical conditions (same equipment, same bait etc.). A prepared schedule made sure that every zone was checked the same number of hours and at the same period of the day. Catches were controlled and the temperatures measured for each period and each zone. The results of this experiment, shown in Fig. 24, demonstrate quite clearly that the yield of rod fishing is significantly affected by increased temperature, according to a net seasonal pattern. Catches in warmed-up zones, which in March are larger than in normal water, decrease rapidly and regularly to zero in August. Subsequently, they increase again rather rapidly up to November. These variations are inversely proportional to BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 91

100 1000 10 000 TIME TO 50% MORTALITY (MINUTES)

FIG.24. Effect of acclimatization temperature on upper lethal limit of speckled trout.

temperature changes. The yield loss in summer can, to a large extent, be explained by the behaviour of fishes which avoid the warm waters. It seems, however, that in warm waters fishes are also for some reason more difficult to catch. It should be noted that these results are valid only for worms, the only fishing bait that was used. It is not without interest to notice that the loss in catches during the summer months occurs precisely during the most popular sport fishing period for this locale. On the other hand, during most of the year, the yield in rod fishing seems to be equal or even clearly better in warm waters.

5.4. EFFECTS ON AQUATIC ECOSYSTEMS

5.4.1. Ecosystem studies

There are very few studies on the impact of thermal discharges on aquatic ecosystems. Most attention, because of case of study, and the training of many scientists, is paid to one or two species of a given taxon, or a few elements of a given trophic level. Nothing is more complex than an ecosystem. This report can only briefly speak about a few ecosystem problems and principles of management. 92 CHAPTER 5

5.4.2. Species diversity

In attempts to characterize an ecosystem by a limited number of parameters, many ecologists have been using various measures of 'species diversity'. The concept is that an ecosystem or community with a fair distribution (evenness) of individuals among several species is a more stable, less stressed system than one with fewer species, and in which most individuals belong to one or two species. The concept is still in the developmental stage, but, nevertheless, species diversities using one method or another have been calculated for some thermal effluent areas. In general, where changes in diversity have been reported for temperate areas there is a decline near the outfall, or in the effluent canal, especially during summer months. This change seems to be inconsequential when considering the population of the lake or stream used for cooling water [71], Changes in colder climates may be toward increased diversity [72].

5.4.3. Ecosystem stability

As suggested in the foregoing comments on species diversity, diverse systems are thought to be more stable than monocultures. One effect of pollution, of any form, seems to be to reduce diversity and, in extreme conditions, force a monoculture, at least of prominent or dominant taxa. The latter situation, to take the converse approach, represents an unstable condition. Monoculture agriculture may be in some areas a desirable instability, maintained through man's energy impact. However, in natural and man-linked ecosystems, monocultures are less desirable. For example, harvesting predictions and management schemes of fisheries resources are very difficult in widely oscillating marine ecosystems. There is some evidence that diverse systems are so because they are stable — less diverse systems may also be stable (and perhaps on their way to develop diversity?). So the question is, regardless of diversity: is there evidence of thermal effluents reducing stability in the environment? Extensive losses of Zooplankton were reported for the Paradise Power Plant, Kentucky, USA, in May 1964. The volume of Zooplankton in the river decreased immediately below the plant, then recovered several miles downstream, accompanied by high accelerated productivity in the mixed flow below the plant [58], One would suspect that a consequent oscillation in the numbers of organisms or of concentrations of materials, was set up in the ecosystem, though data at that level are lacking. Nor was the question of significance to the river system answered. Assuming similar high mortalities of entrained organisms in other plants, local oscillations must be induced in at least the portion of the aquatic ecosystem adjacent to the outfall. How rapid these oscillations are dampened, if at all, depends on a number of factors such as generation times, turnover rates, seasonal inputs and the like, many of which can be estimated by present methods. Presumably the dampening may be more rapid in a diverse system, or less noticeable at the level of the top consumers. Studies by Morgan and Stross [73] suggest that phytoplankton photosynthetic productivity is reduced by entrainment passage, and may remain reduced when returned BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 93 to cool (ambient) temperatures. If the rate of photosynthesis is herbivore limited, then the effect of the plant must cause some oscillation through the whole food chain. How important such a near plant oscillation may be is not yet answered fully. The evidence thus far suggests that, as in the case of the Paradise Plant, the source body of water as a whole may remain unaffected [2], but the data are yet sparce.

5.4.4. Eutrophication

This type of process occurs when a body of water receives a continuous in-flow of nutrients, coming generally from agricultural fertilizers, from detergents, from domestic sewage (nitrates, phosphates, organic matter). In these conditions there is an excess primary production (algae) and, later, an excess secondary production (heterotrophic organisms, decomposer bacteria). These processes are remarkably influenced by temperature;oxygen demand increases while its production by photosynthesis remains more or less constant; this leads to the development of anaerobic bacteria which increase the water load of sulphides, of ammonia compounds, of nitrates and of methane. These eutrophication conditions are particularly severe for closed basins and may reduce the receptive capability of lakes for wastes of any kind — including thermal effluents — to minimum values. But even in a lotie environment it is quite possible that local conditions related to morphology and to hydrodynamic regime may favour eutrophication. As a result of these interactions, chemical and organoleptic properties of water may not be able to sustain fish life. The most tolerant species may still survive, but the most demanding ones, which are generally the most valuable, may be eliminated. Extreme cases of eutrophication have been reported for cooling ponds (size and thermal load not specified) in the USSR [27], However, these apparently are managed as cooling ponds and not as wildlife resources.

5. 4. 5. Disease and host-parasite relationships

Temperature affects the development of parasites and pathogenic bacteria, and may also affect the resistance of aquatic organisms to disease (e.g. by affecting antibody production). Some parasites, as the flat-worm Bothriocephalus gowkongenis, reach sexual maturity in the gut of grass carp (Ctenophoryngodon idella) twice as fast at 22 to 25°C than at 16 to 19°C (Musselius, 19 63). The development of Dactylogyrus vastator eggs has been accelerated and also the most violent invasion of common carp by this parasite has been observed at 22 to 24°C. Mass mortality of common carp, caused by abdominal dropsy, is usually observed in the warmer season of the year. Thus, some parasites and diseases might be a greater danger to fish at high temperature. In Poland, in the ponds receiving the thermal discharges of a power station excessive rates of infestation of bream by the Ligula have been observed. In France, in the Hérault River, on one occasion of a rise in temperature to 32 - 33°C there appeared in the fish an illness caused by Clostridium chauvei, the agent responsible for symptomatic anthrax in 94 CHAPTER 5 cattle. Nevertheless, some recent research seems to show that for certain diseases an elevation of temperature can accelerate and improve the immunity of the fish [68], The problem is less certain for the risk to human beings due to the presence of dangerous and pathogenic microorganisms in the water. Pathogenic bacteria in water bodies are considered to be 'resting cells', because they are obligate parasites. Although few thorough studies have been carried out there is reason to believe that an elevation of water temperature promotes the survival, if not development, of pathogenic organisms to which warm blooded animals act as hosts.

5.4.6. Additive effects — toxicity

Until now it was considered that the aggravation of the toxicity of different pollutants for the fish under the influence of elevated temperature was a completely general effect due certainly to a more rapid penetration and intensity of the toxins resulting from acceleration of metabolism. According to Laberge [74] the toxicity of cyanide of potassium should be multiplied by two for each elevation of temperature of 10°C. The toxicity of orthoxylene should be multiplied by three for an elevation of 7°C. In the studies of toxicity of zinc sulphate in connection with young salmon, Sprague [75] states that the time of life for a given concentration is four times greater at 5°C than at 15°C, and that the dose for the acclimatized fish is 1. 5 times lower at 15°C than at 5°C. Nevertheless a recent study shows some less specific results. In the laboratory mortality of juvenile sockeye salmon infected with low-virulence strains of Chondrococcus columnaris increased as water temperature increased [76]. Another disease-producing organism, Ceratomyxa, seems to be most virulent when water temperatures exceed 16°C. More recent work by Fujihara and associates [77] indicates that, for C. columnaris at any rate, there is a temperature-disease relationship but the situation is more complex than previously thought.

5. 5. RESEARCH RECOMMENDATIONS

Research is needed for a better understanding of the ecological effects of thermal discharges on the biota, to predict the future condition and use of that receiving body of water and to register changes after a power plant has been brought into operation. But, first of all, research is needed to determine the most suitable site for a power plant. On the basis of a full-scale biological and ecological study, one should also be able to determine the maximum absolute temperatures and changes of temperatures permissible for the receiving water. An ideal full-scale biological and ecological research program consists therefore of physical, chemical and biological field and laboratory studies. As environmental conditions vary greatly according to the geographical position of the power plant, no absolute research standards can be stated. In tropical areas attention must be paid to lethal temperatures, whilst in cold and temperate areas effects of waste heat on populations and behaviour of organisms are more critical. The pollution from various BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 95 sources must usually be taken into consideration. Because the synergistic effects of several environmental stresses ön biota until now are less known, considerable attention to synergistic effects is needed. Methodologically the biological and ecological researchers of thermal effects have used conventional techniques and these methods are well documented in the international literature. However, new methods are under development, particularly for determining long-term sublethal effects, total ecosystem effects and regional effects. Worth mentioning is, e. g., the Swedish research program in the Baltic Sea archipelago, where a basin of 1 km2 will be built in connection with a nuclear power station for large-scale biological and ecological studies. In this research basin the temperature can be regulated and the effects of thermal load can be tested in many ways under natural conditions. In order to obtain good data about thermal effects on the biota, at least two years' research at a site is needed. Longer periods, however, are absolutely necessary if reliable predictions are to be formulated. In ecological studies the knowledge of physical and chemical properties is an important basis for biological studies. Because fish, shellfish and also some other organisms are economically and recreationally an essential component of the biota, special studies on those resources are usually necessary. The following are examples of biological and ecological studies of the effects of waste heat on the aquatic biota:

5. 5. 1. Chemical and physical (hydrological) research as related to the biota

(i) The amount of heat to be added to the water mass and the , distribution of that heat (ii) Current patterns before the heat discharge and the expected changes thereafter (iii) Stratification (thermal and chemical) of the water mass and the alterations expected (iv) The oxygen content of the receiving body of water and the changes expected due to waste heat (v) Nutrient salts, especially N and P, in the water and in the bottom layers (vi) Large-scale descriptions of the chemical consistency of the water

5.5.2. General ecological studies

(i) Inventory of plant and animal species and their distribution and biomasses, or other pertinent population parameters (ii) Effects of heat load on the populations of microorganisms, plankton, benthos, and vegetation (iii) Effects of temperature alterations on the most important organisms and populations (iv) Synergistic effects of thermal load and other factors stressing organisms and populations simultaneously, e.g. heavy metals, nutrients, saline or fresh water. (v) Temperature effects causing alterations in reproduction and mortality of different life cycles 96 CHAPTER 5

(vi) Temperature effects causing alterations in relations between different species (e. g. in predator-prey and host-parasite relations) (vii) Temperature effects on migration, and other behavioural phenomena of the most important species (viii) Low temperature requirements in the life cycles of the most important species (ix) Adaptation capability of the most important species to varied temperature conditions.

5.5.3. Studies on fish and other commercial and recreational resources

(i) Determining the most important food organisms of fish (see 5. 5. 2. above) (ii) Existing populations and production (iii) Effects of heat discharge on the growth and production of fish (iv) Determination of the highest temperatures at which normal or optimum growth and reproduction can take place (v) Determining the maximum changes and rate of changes of termpera- ture at which the normal or optimum growth and reproduction can take place (vi) Determining the lower temperatures necessary for reproduction (vii) Possibility for diseases in heated environment (viii) Capability of fish species to alternative feeding in heated environment, where the food web has been changed (ix) Prediction of migrations in varied temperature conditions

5. 5. 4. Other studies

Studies of the significance of any and all of the above which put in perspective the area of plumes and mixing zones, the effects of thermal plumes, and entrainment and impingement, on the populations and ecosystems of the source body at risk.

REFERENCES TO CHAPTER 5 tl] USAEC, Division of reactor development and technology, Thermal Effects and U.S. Nuclear Power Stations, Wash-1169 (Aug. 1971) 15. [2] COUTANT, C.C., Thermal pollution - Biological effects, J. Water Pollut. Control Fed. (1971) 1292. [3] MIHURSKY, J.A., et al., Thermal pollution, aquaculture and pathobiology in aquatic systems, I. Wildl. Diseases 6 (1970) 347. [4] CAIRNS, J., Jr., Ecological management problems caused by heated waste water discharge into the aquatic environment, Water Resour. Bull. 6 6 (1970) 868. [5] COUTANT, C.C., "Biological aspects of thermal pollution. I. Entrainment and discharge canal effects", CRC Critical Reviews in Environmental Control 1 3 (1970) 341. [6] ABREMSKAYA, S.I., Comparative hydrochemical characteristics of cooling ponds of large thermal power stations in the Ukraine, Hydrobiol. J. 5 (1969) 31. [7] ANTONELLI, A., "Thermal pollution with respect to environmental contamination", 12th In-service Training Course for Field Advisers from Countries in the Mediterranean Area, Lombard Centre for the Development of Flow, Vegetable and Fruit Culture of the Savings Bank of the Provinces of Lombardy, Minoprio (Como). BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 97

PARKER, F.L., private communication. DIRECTION DE L'EQUIPEMENT DEPARTEMENT E.G.P.S.E., private communication. EFFER, W.R., "Some biological effects of thermal discharges into the Great Lakes", Paper No. 70-CNA-642, 10th Annual Conf. of the Canadian Nuclear Association, Toronto, May 1970. SPURR, G., private communication. KNOPP, New investigations into the effects of cooling water self-purification, Deutsche Gewässer- kundliche Mitteilungen 1969, Sonderheft (1972) 63. GLASSTONE, S., A Textbook of Physical Chemistry, Van Nostrand, New York (1946). HARVEY, R.S., "Effect of temperature on the sorption of radionuclides by blue-green algae", Proc. 2nd Natl Symp. Radioecology, Ann Arbor, Michigan, 1969. USAEC, Final Environmental Impact Statement, Indian Point No. 2. BROCK, T.P., DARLAND, G.K., Limits of microbial existence: temperature and pH, Science 1969 (1970) 1136. SIEBURTH, J., McN., Seasonal selection of estuarine bacteria by water temperature, J. Exp. Mar. Biol. Ecol. 1 (1967) 98. CAIRNS, J.H., Jr., The response of freshwater protozoa communities to heated waters, Chesapeake Sei. H> 3,4 (1969) 177. WURTZ, C.B., Progress Reports. A biological survey of the Susquahanna River in the vicinity of York Haven, Pa., Prepared for Pennsylvania Power and Light Co. and Metropolitan Edison Co. (1969-1971). HEDGEPETH, J.W., GONOR, J.J., "Aspects of the potential effect of thermal alteration on marine and estuarine benthos", Biological Aspects of Thermal Pollution (KRENKEL, P.A., PARKER, F.L., Eds), Vanderbilt University Press, Nashville, Tenn. (1969) 80. WARINNER, J.E., BREHMER, M.L., The effect of thermal effluents on marine organisms, Int. J. Air Water Pollution K> 4 (1966) 277. BADER, R.G., TABB, D.C., An Ecological Study of South Biscayne Bay in the Vicinity of Turkey Point, Progress Rep. to USAEC, University of Miami, Fla. (1970). NAUMAN, J.W., CORY, R.L., Thermal additions and epifaunal organisms at Chalk Point, Md, Chesapeake Sei. _10 (1969) 218. MERRIMAN, D., The califaction of a river, Sei. Am. 222 (1970) 42. GAMMON, J.R., Aquatic life survey of the Wiebash River with special reference to the effects of thermal effluents on populations of macroinvertebrates and fish, Process Rep. (1970). HECHTEL, G.J., et al., Biological Effects of Thermal Pollution, Northport, Stony Brook Tech. Rep., New York, Marine Sciences Res. Center, State University of New York (1970). MINASYAN, R.G., private communication. CRAVEN, R.E., BROWN, B.E., Power plant heated discharge water and benthos in Boomer Lake, Payne County, Oklahoma, J. Kans. Entomol. Soc. 43 (1970) 24. MASSENGILL, R.R., "Changes in species of bottom organisms composition relative to Connecticut Yankee Plant Operation"; The Connecticut River Investigation (MERRIMAN, D.E., Ed.) 9th Semi- annual Progress Report to Connecticut Water Resources Commission (21 Oct. 1969). GRIMÂS, U., Warm water effluents in Sweden, Mar. Pollut. Bull. 1 10 (1970) 151. FEDERAL WATER POLLUTION CONTROL ADMINISTRATION, USDI, Report on Thermal Pollution of Intrastate Waters, Biscayne Bay, Florida Mimeo Rep. Southeast Water Laboratory (1969). ANDERSON, R.R., Temperature and rooted aquatic plants, Chesapeake Sei. _1£ (1969) 241. PATRICK, R., "Some effects of temperature on freshwater algae", Biological Aspects of Thermal Pollution (KRENKEL, P.A., PARKER, F.L., Eds), Vanderbilt University Press, Nashville, Tenn. (1969). HOWELLS, G.P., Hudson River at Indian Point, Ann. Rep. 4/16/68 to 5/15/69, Institute of Environmental Medicine, New York Univ. Medical Center, New York, N.Y. (1969). MORGAN, R.P. O, STROSS, R.G., Destruction of phytoplankton in condensers of an electric power generating station, Chesapeake Sei. 10 3,4 (1970) 165. STOCKNER, J.G., Algal growth and primary productivity in a thermal stream, J. Fish. Res. Board Can. 25 (1968) 2037. PATRICK, R., "Some effects of temperature on freshwater algae", Biological Aspects of Thermal Pollution (KRENKEL, P.A., PARKER, F. L., Eds), Vanderbilt University Press, Nashville, Tenn. (1969). TREMBLEY, F.J., "Effects of cooling water from steam-electric power plants on stream biota", Biological Problems in Water Pollution (TARZEWELL, C.A., Ed.), U.S. Public Health Service, Cincinnati, Ohio, Pub. No. 999-WP-25 (1965). FORESTER, J.W., "A discussion of heat and freshwater algae", Biological Aspects of Thermal Pollution (KRENKEL, P.A., PARKER, F.L., Eds), Vanderbilt University Press, Nashville, Tenn. (1969). 98 CHAPTER 5

[40] BUCK, J.D., "Summary of Connecticut River microbiology study". The Connecticut River Investigation (MERRIMAN, D.E., Ed.), 10th Semiannual Progress Report to Connecticut Water Resources Commission (1970). [41] BEER, L.O., PIPES, W.O., The effects of discharge of condenser water into the Illinois River, Industrial Bio-Test Laboratories, Inc., Northbrook, 111. (1969). [42] NORTH, W.J., "Biological effects of a heated water discharge at Morro Bay, California", Proc. Int. Seaweed Symposium 6 (1969). [43] HOWELLS, G.P., WEAVER, S., "Studies on phytoplankton at Indian Point", Hudson River Ecology (HOWELLS, G.P., LAUER, G.J., Eds), New York State Department of Environmental Conservation (1969) 231. [44] HEFFNER, P..L., HOWELLS, G.P., LAUER, G.J., HIRSHFIELD, H.J., "Effects of power plant operation on Hudson River Estuary microbiota", Radioecology (Proc. 3rd Natl. Symp., Oak Ridge, Tenn., May 1971). [45] CHURCHILL, M. A., WO JTALIK, Effects of heated discharges: The TVA experience, Nucl. News 80 (1969). [46] HEINLE, D.R., Temperature and Zooplankton, Chesapeake Sei. _10 3,4 (1969) 186. [47] NORMANDEAU, D.A., The Effects of Thermal Releases on the Ecology of the Merrimack River, Rep. to the Public Service Co. of New Hampshire. [48] ADAMS, J.R. , Thermal power, aquatic life and kilowatts on the Pacific coast, Nucl. News_12 9 (1969) 75. [49] CORY, R.L., NAUMAN, J.W., Epifauna and thermal additions, Chesapeake Sei. _1£ (1969) 210. [50] NAUMAN, S.W., CORY, R.L., Thermal additions and epifaunal organisms at Chalk Point, Maryland, Chesapeake Sei. 22 (1969) 218. [51] Water Quality Criteria for European Freshwater Fish (1969). [52] NEILL, W.H., Ecological Responses of Lake Monona (Dode County, Wisconsin) Fishes to Heated Influent Water, Ann. Progr. Rep. to Wisconsin Utilities Association (Sep. 1969). [53] BURNETT, P.R.O., HARDY, B.L.S., The effect of temperature on the benthos near the Hunterston Generating Station, Scotland, Chesapeake Sei. 10 (1969) 255. [54] BRETT, J.R., Thermal Requirements of Fish - Biological Problems in Water Pollution, 1959 Ser., R.A. Taft Engineering Center, Cincinnati, Ohio, Rep. No. W60-3 (1959). [55] HYNES, H.B.N., Biology of Polluted Waters, Liverpool Press (1960) 71. [56] BRETT, J.R., "Thermal requirements of fish, three decades of study. 1940-1970", Biological Problems in Water Pollution, Trans. 1959 Seminar, R.A. Taft Sanit. Eng. Center, Cincinnati, Ohio, Rep. No. W60-3 (1960). [57] COUTANT, C.C., "Columbia river thermal effects studies", Second Thermal Pollution Seminar, Inst. Environmental Sei., Chicago, 111., 20-22 Oct. 1970. [58] BARBER, Y. M., Jr., Statement as presented before the Fourth Session of the Lake Michigan Enforcement Conference, Sherman House, Chicago, 111., 19-21 Sep. 1972. [59] TEMPLETON, W.L., COUTANT, C.C., "Studies on the biological effects of thermal discharges from nuclear reactors to the Columbia River at Hanford", Environmental Aspects of Nuclear Power Stations (Proc. Symp. New York, 1970), IAEA, Vienna (1971) 591. [60] TAKEDA, K., private communication. [61] DIRECTION DE L' EQUIPEMENT, DEPARTEMENT E.G.P.S.E., private communication. [62] USAEC, Draft Environmental Impact Statement for Forked River Nuclear Power Plant, Docket No.50363 (1972). [63] USAEC, Investigation Rep. No.50-545/72-01 (1972). [64] MARCY, B.C., Jr., "Resident fish population dynamics and early life history of the American shad in the lower Connecticut River", The Connecticut River Investigation (MERRIMAN, D.E., Ed.), 9th Semiannual Progr. Rep. to Connecticut Water Resources Commission (1971). [65] TODD, J.H., The chemical languages of fishes, Sei. Am. 224 5 (1971) 98. [66] TREMBLEY, F.J., Research Project on Effects of Condenser Discharge Water on Aquatic Life, Institute of Research, Leihgh University, Bethlehem, Pa., Progr. Rep. 1956-59 (1960). [67] MERRIMAN, D., etal., The Connecticut River Investigation, 1965-1972, Semiannual Progr. Rep. to Connecticut Yankee Atomic Power Co., Haddom, Connecticut, 1965 and continuing (1972). [68] LEVINA, R.I., Survival of Streptococcus faecalis, Salmonella typhi and E. coli in river water, Hyg. Sanit. (USSR) 33 10-12 (1968) 125. [69] TULKKI, P., private communication. [70] ELSER, H.J., Effect of a warmed water discharge on angling in1 the Potomac River, Maryland, 1961-62, The Progressive Fish Culturist 27 2 (1965) 79. BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 99

[71] LEVIN, A.A., BIRCH, T.J., HILLMAN, R.E., RAINES, G., Thermal discharges: Ecological effects. Environ. Sei. Technol. (1972) 224. [72] POLTORACKA, J., Specific composition of phytoplankton in a lake warmed by water from a thermoelectric plant and lakes with a normal temperature, Acta. Soc. Bot. Pol. 37 (1968) 397. [73] MORGAN, H.P., STROSS, R.G., Destruction of phytoplankton in the cooling water supply of a steam-electric plant, Chesapeake Sei. _10 (1969) 1965. [74] LABERGE, R.M., Thermal discharges, Water Sewage Works (1959). [75] SPRAGUE, J.B., Lethal concentrations of copper and zinc for young Atlantic salmon, J. Fish. Res- Board Can. 21 1 (1964) 17. [76] COLGROVE, D.J., WOOD, J.W., Occurrence and Control of Chondrococcus columnaris as related to Fraser River Sockeye Salmon, Int. Pac. Salmon Fish. Comm. Progr. Rep. 15 (1966). [77] FUJIHARA, M.P., et al.. Temperature and Fish Disease, Pacific Northwest Annual Report for 1969 to USAEC, BNWL-1306, Battelle Northwest, Richland, Wash. (1970). 100 CHAPTER 5

ANNEX 1 TO CHAPTER 5

EQUILIBRIUM CONSTANT

The variation of an equilibrium constant, k, may be expressed as:

d(ln k) . Ea dT RT2 where

T = absolute temperature,

Ea = activation energy, R = gas constant.

Integration of the equation between temperatures Ti and T2 yields:

E ln h. - a(T2-T!) ki RTjT2

ANNEX 2 TO CHAPTER 5

RATE CONSTANT

The rate constant, ki, which is conventionally used to describe the rate at which biological oxidation takes place in laboratory investigations, is defined as :

dL , r dF - -kl L

where L = Biochemical Oxygen Demand (BOD), t = time (in days), k} = rate constant (in days"1) BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 101

ANNEX 3 TO CHAPTER 51

PREFERRED AND LETHAL TEMPERATURES OF FISH

Preferred temperatures

This is the temperature that a fish selects when it has a choice.

Fresh water fishes Preferred temperatures (°C) Trout 10-15 Bass, rock 15-21 Bass, largemouth 28 - 30 Perch 20 - 21 Carp 21 - 32

Estuarine or coastal fishes Atlantic salmon 14-16 Winter flounder 12-15 Striped bass 13-16 Silverside 22 - 23

In general, cold water fishes exhibit a narrower preferred temperature range than warm water species. In most cases a limited temperature step, e.g. less than 3°C, would not induce migrations of fish populations.

Lethal temperatures

Lethal temperatures (50% killing ratio) are also strongly dependent on natural conditions and acclimation characteristics.

Lethal temperatures (°C) Trout 29 Bass, striped 26 Silverside 28 Winter flounder 25 Perch, white 28 Salmon 27 Carp 36

t PELLAUD, B., private communication. 102 CHAPTER 5

ANNEX 4 TO CHAPTER 5

FISH OXYGEN DEMANDS AND TEMPERATURE

Temperature and oxygen content of water are of great importance for fish. Metabolism of fish accelerates with increasing temperature and simultaneously increases the oxygen demand. The table below shows the demand of minimum content of oxygen in the water in given temperatures.

t CC) 02 (mg/1)

Sea trout 21 2. 53 Rainbow trout 21 1.82 Salmon 15-25 1. 51-2. 85 Pike 15-29 0. 72-1.40 Roach 15-23 0.60-1.60 Perch 15-25 0.40-1.40 BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 313

ANNEX 5 TO CHAPTER 5

FISH DEVELOPMENT AND GROWTH RELATED TO TEMPERATURE

FISH SPECIES AND WASTE HEAT

There are plenty of studies on the warm water tolerance of fishes. In the table below some figures are collected of the temperatures connected with some common northern fish species.

Development Maximal Species Spawning of fry growth Optimum Lethal (°C) (°C) (°C) (°C) (°C)

Burbot 1.5-1.0 1.5 max. Whitefish - for species 0.0-4.0 6.1 fry Cod max. 14 10.0 19.8-24.4 Plaice 14 28-31 Flounder 31-34 Char 4-6 Salmon max. 10 4-8 15-18 14-15 23 Sea trout, young natu- 23 ral Sea trout, tem- adult pera- 16-19 13-17 25-26 Rainbow ture trout 14-18 13 23-24 Pike 6-15 29

Perch 12-15 30-33

Bream 10-18 31-38 Roach 10-14 12-19 23-24 33 Carp 13-24 20-25 27-32 35-37 Herring max. 5. 5 18-24 19.5-24.7

A more comprehensive list is given in Annex 6. 104 CHAPTER 5

ANNEX 6 TO CHAPTER

UPPER TEMPERATURE TOLERANCES OF FISH

Tolerance Acclimation limit Species . , , _ temperature temperature Duration (°C) (°C) (h)

Abudefduf saxlatilis 35 - 40 Alosa pseudoharengus 15 23 90 Alosa pseudoharengus3 26. 7 - 32. 2 Alosa pseudoharengus3 31. 4 Alosa pseudoharengus3 26. 7 - 32. 2 Aspidophoroides monopterygius 24. 4 - 25 Atherinops affinis 20 31 24 Atherinops affinis 12. 8 - 26. 8

Biennis pholis, larva 30 Box salpa 31

Calotomus japonicus 28 Caranx mate, prelarva and postlarva 30 Centronotus gunnellus larva 15 - 20

Clinocottus globiceps 26 Clupea harengus, larva 15.5 23. 0 24 Clupea harengus, larva3 18 Clupea harengus, larva3 22 - 24 Clupea harengus, adult 19. 5-21.2 Clupea harengus juvenile-adult 20. 8 - 24. 7 Crenilabrus ocellatus 33 Cyclop te rus lumpus 25. 5 - 26. 9 Cynoglossus lingua prolarva and postlarva 30 juvenile 23

Dussumieria acuta 31

Enchelyopus cimbrius 27. 2

Fundulus heteroclitus 40 2 BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 105

Tolerance Acclimation limit Species temperature temperature Duration (°C) (°C) (h)

Fundulus heteroclitus 28 37 Fundulus heteroclitus juvenile -adult 40. 5 - 42b Fundulus parvipinnis 30 37 24 Fundulus parvipinnis larva 16. 6 - 28. 5 Fundulus sp. 3 5°

Gadus morhua 19. 8 - 24. 4 embryo 10 Gambusia nicaraguensis 35 - 40 Gasterosteus aculeatus, adult 31. 7 - 33 larva 37. 1 Girella nigricans 20 - 28 31 72 Girella nigricans2 31. 4 Gobius paganellus 32 Haemulon bonariense 35 - 40 Hemitripterus americanus 28 Hippocampus sp. 30 Hippoglossoides platessoides 22. 1 - 24. 5 Hypomesus olidus 10 Hypsoblennius sp. 12. 0 - 26. 8

Leuresthes tenuis 14. 8 - 26. 8 Limanda ferruginea 24 Liopsetta putnami 31.6 - 32. 8 Lutjanus apodus 35 - 40

Macrozoarces americanus 26. 6 - 29 Megalaspis cordyla prolarva and postlarva 31 Melanogrammus aeglefinus 18.5 - 22. 9 Menidia menidia, adult 22. 5 - 32. 5 Microgadus tomcod 29 2 cm 19 - 20. 9 14-15 cm 23. 5 - 26. 1 22-29 cm 25. 8 - 26. 1 106 CHAPTER 5

Tolerance Acclimation limit Species temperature temperature Duration (°C) (°C) (h)

Mu gil cephalus prolarva and postlarva 32 Mullus barbatus 32 Mullus surmuletus 31 Myoxocephalus aeneus 26.3-27 M. groenlandicus 25 M. octodecemspinosus 28

Oncorhynchus gorbuscha juvenile 20 23. 9 168 O. keta, juvenile 20 23. 7 168 O. kisutch, juvenile 20 25 168 O. masou, embryo 13 O. nerka, juvenile 20 24. 8 168 O, tshawytscha 20 25. 1 168 Osmerus mordax 21. 5 - 28. 5

Pagrosomus major 21 Petromyzon marinus prolarva and postlarva 20 34. 0 1. 5 Plecoglossus altivelis 22 Pleuronectes flesus 31 - 34 Pleuronectes platessa, embryo 14 Pleuronectes platessa 28 - 31 Pollachius virens 28 Polynemus indicus prolarva and postlarva 31 yearling 9 23 40 Pseudopleuronectes americanus 27. 9 - 30. 6 Pseudopleuronectes americanus juvenile 22 - 29 Pseudopleuronectes americanus adult 27

Raja erinacea 29. 1 - 29. 5 juvenile 30. 2 BIOLOGICAL. EFFECTS OF THERMAL DISCHARGES 107

Tolerance Acclimation limit Species temperature temperature Duration (°C) (°C) (h)

Raja ocellata 28 24 R. radiata 26. 5 - 26. 9 Roccus saxatilis, adult 32

Salmo salar prolarva and postlarva 28 1 S. trutta trutta prolarva and postlarva 28 1 alevin 20 26 7 Sardinella longiceps prolarva and postlarva 31 Sargus vulgaris 33 Saurida tumbil prolarva and postlarva 31 Scarus croicensis 35 - 40 Scomber scombrus, embryo 21 Scorpaena porcus 32 Solea elongata prolarva and postlarva 32 juvenile 23 Sphaeroides maculatus juvenile 28. 2 - 33. 0 Squalus acanthias 28. 5 - 29. 1

Tautogolabrus adspersus 29 Triacanthus brevirostris prolarva and postlarva 30

Ulvaria subbifurcata 27 - 29 Urophycis chuss 27. 3-28 U. tenuis 24. 5 - 25. 2

î DE SYLVA, D.P., "Theoretical considerations of the effects of heated effluents on marine fishes", Biological Aspects of Thermal Pollution (KRENKEL, P.A. PARKER, F. L., Eds), Vanderbilt University Press, Nashville, Tenn., USA (1969). a Other investigators, b Recovered with temperature decrease. c Acclimated. 108 CHAPTER 5

ANNEX 7 TO CHAPTER 5 MAXIMUM TEMPERATURES REPORTED AT WHICH EGGS OF MARINE FISHES WILL HATCH IN LABORATORY EXPERIMENTS

Temperature Hatching time Species (°C) (d)

Achirus fasciatus 23.3-24.4 1.5 Alosa aestivalis 22 2 Anchoa hepsetus 19-21 2 A. mitchilli 27. 2-27.8 1 Anguilla rostrata 24-28 7 Apeltes quadracus 22 6 Archosargus probatocephalus 24. 7 1. 7 Atherinops affinis 26.8 8 Bairdiella chrysura 27. 2-27. 8 0. 75 Calotomus japonicus 27. 6 1.0 Chaetodipterus faber 26. 7 1 Chasmodes bosquianus 24. 5-27. 0 11 Clupea harengus harengus 5. 5 20-34 Cynoscion regalis 20.0-21.1 1.5-1.7 Fundulus heteroclitus 25 12 Fundulus parvipinnis 28. 5 14 Gadus sp. 12 8. 5 G. merlangus 14 5. 8 G. morhua 14 8. 5 Gasterosteus aculeatus 27 4. 3 Gobionellus boleosoma 20 0. 75 Gobiosoma bosci 26-28 4 Hypleurochilus geminatus 26-28 6-8 Hypomesus olidus 18. 5 8. 7 Hypsoblennius sp. 26. 8 6 Hypsoblennius hentzi 24.5-27.0 10-12 Leuresthes tenuis 26. 8 9 Melanogrammus aeglefinus 14 8. 8 Menidiâ beryllina 26-28 8-10 M. menidia notata 22 8-9 Menticirrhus saxatilis 20.0-21.1 2 Merluccius bilinearis 22 2 Oncorhynchus masou 16. 1 29 Pagrosomus major 21. 8 1.4 Petromyzon marinus 25 6 Piecoglossus altivelis 24. 0 8. 5 Prionotus carolinus 22 2. 5 Pseudopleuronectes americanus 20. 6 15 Roccus saxatilis 17.9 2 Salmo salar 10 50 Scomber scombrus 21 2 Stenotomus chrysops 22 1. 7 Tautoga onitis 22 1.7 Tautogolabrus adspersus 22 1. 7 Urophycis chuss 15. 6 4 Chapter 6

BENEFICIAL USES OF WASTE HEAT

6.1. GENERAL

The waste heat discharged by steam power plants represents considerable amounts of energy which can be beneficially used under favourable circumstances. One can distinguish between physical applications such as process heating and district heating, and biological applications such as fish harvesting. The most important single parameter of a heat source, which determines the kind of applications that enter into consideration, is its temperature. Low-grade heat is characterized by a low temperature, whereas high-grade or process heat occurs at high temperature, with the threshold lying around 100°C. This distinction is quite essential for any assessment of potential beneficial uses of waste heat from nuclear plants. Generally speaking, a nuclear power plant may be seen as a potential producer of electricity, high-grade heat and low-greade heat. In most cases electricity is the main product and the plant is accordingly optimized. With the present generation of nuclear plants, based on the steam cycle, this optimization entails the discharge as a by-product of low-grade heat at about 30°C. High-grade heat, if desired, can be produced only at the expense of electricity generation. The production of high-grade heat in the form of steam or hot water requires that the steam cycle nuclear plant be equipped with extraction/condensing or back pressure turbines. In that case the plant can produce more or less electricity, with or without low- grade heat discharges, depending on the operating conditions selected. It is therefore important to keep in mind that, with steam cycle electrical generating plants, waste heat means low-grade heat having a limited number of applications. Any attempts to raise the temperature of the waste heat to make it more useful lead to a reduction in electrical output or imply a decision to partially use the plant as a heat source for non-electrical applications, by production of high-grade heat, a choice that can be economically and environmentally advantageous. In the future, the widespread utilization of waste heat should be possible with the direct cycle nuclear plant equipped with gas turbines, now under development. Gas turbine nuclear plants can produce electricity and high- grade waste heat without mutual economic penalties. Some factors to be borne in mind when considering beneficial uses of waste heat from nuclear power plants are: (a) In general,waste heat can be utilized to a greater extent in regions with a cold climate. (b) The higher the discharge temperature the wider and more beneficial its utilization.

109 110 CHAPTER 5

(c) In regions with wide seasonal temperature changes the demand for heat utilization may be seasonal. (d) The total waste heat from the projected nuclear power program in the next decades will be vastly in excess of that which can be used beneficially under currently envisaged techniques.

6. 2. PHYSICAL APPLICATIONS OF LOW-GRADE AND PROCESS HEAT

6. 2. 1. Low-grade heat from condenser cooling

6.2.1.1. Space heating

There are a number of possible physical applications of the use of low- grade waste heat from condenser cooling. Its economic application to space heating, by making use of the heat pump principle in which the heat in the condenser cooling water could be used to evaporate the refrigerant as in a standard compression air conditioning cycle, is of doubtful value [1]. Some practical applications of this principle have been made, but they were made on such a small scale as to use only insignificant portions of the total waste heat which has to be disposed of from a large power plant.

6.2.1.2. Agricultural use

There are also possible physical applications in the agricultural field. The most straightforward utilization of the heated waters from a thermal power station in agriculture is mixing them with water too cold for irrigation, to avoid damage to downstream cultivations. An example is reported by Parker and Krenkel[2]. Two projects devised to test the beneficial uses of heated water on cropland are quoted by Carter: the Eugene (Oregon) Water and Electric Board has invested US $ 475 000 in an irrigation project on a 68 ha tract lying within a bend of the McKenzie River. The goal is to demonstrate that warm water can be used to stimulate and enhance plant growth and to protect fruit from frost damage [3]. The other project is supported by Pacific Power and Light Company and studied by Oregon State University [3], The aim is to see if growing seasons are lengthened and crop yields increased by warming the soil. At a first approach, the network of pipes carrying heated water from power plants are simulated with buried electric cables. This small project might have some development, from the situation of a single farmer which could call for warm water when needed (and the power plant still would have an independent cooling system) to a planned situation of several large food factory type operations, including greenhouses, using all available heat, thus eliminating the need for an alternate cooling system [ 3 ]. The solution is promising for some arid regions, where there are millions of hectares of potentially irrigable land and a rising demand for electric power which will have to be met by construction of steam plants. Also in Japan the effective utilization of heated discharges from thermal power plants has been carried out in the electric power industry for more BENEFICIAL USES OF WASTE HEAT 111 than ten years in Hokkaido, by flowing the warm water over the roof and along the wall of greenhouses which has made possible the cultivation of vegetables, keeping the inside temperature at 15 to 25°C. The warm water is also used in irrigation for the growth of rice plants. For rice fields, indeed, an abundant quantity of heat is required so that the water temperature suitable for each stage of rice growth can be controlled [4], Another application of waste heat related to agriculture, reported in Ref. [1 ], is poultry house heating and cooling. In conclusion,according to Carter: "if it should prove possible to develop a closed system in which heated plant effluents are cooled through useful farm applications and then recycled, the power industry's problem of heat disposal would have been turned to good account. Development of a once-through system, in which effluents were cooled through farm use and then discharged back into a stream, would be less of a breakthrough but would still represent a major gain. Even if heated water were no better for crops than unheated water, the cost and drawbacks of cooling lakes and towers make preferable farming utilities to dissipate effluent heat" [3]. On this matter Parker and Krenkel point out that: "with a world-wide shortage of food it may be worthwhile to determine the extent to which the growing season could be extended by the use of heated waters and the creation of a warmer microclimate for agricultural regions" [2],

6. 2.1. 3. Sewage and water treatment

Beneficial use of low-grade waste heat might also be made in sewage and waste water treatment and in water works treatment. Parker and Krenkel [2] report of many studies that have been made on the effect of temperature on water treatment processes. For instance, Fair and Geyer in 1954 found that the efficiency and effectiveness of flocculation and of filtration of floc-bearing water rises with raising temperature [5], Other authors agreed with the above-mentioned findings, showing also that the isoelectric point of a flocculating system shifts drastically with temperature [2,6], These results suggest the utilization of waste heat from power stations in water works treatment, also because of the economical savings obtained by raising the treatment temperature. On this matter, in fact, the State of Pennsylvania's Committee on the Effects of Heated Discharges stated in 1962 that savings in chemicals for water treatment would be 30 to 50 cents per 450 m3 water for each 5°C rise in temperature, compared with an average cost of chemicals of US $ 14. - per 450 m3 of treated water [ 2, 7 ].

6.2.1. 4. Other uses

Other possible beneficial uses of low-grade waste heat have been reported or proposed, though much less information on them is available. For example, the warm water discharged by power plants could be utilized to maintain ice-free ports, harbours, or water-ways on a seasonal basis. Parker and Krenkel [ 2] report of a recent study by Dingman et al. who showed that significant portions of the Saint Lawrence Seaway could be maintained free from ice and open to navigation around all the year by 112 CHAPTER 5 a suitable location of thermal power stations. It was in fact estimated that a 600 MW(e) nuclear power station could keep a stretch of the river between 18 and 25 km ice free [8]. The transportation costs savings would be of the order of several million dollars per year [2], It has however to be observed that adequate studies would be necessary to understand the possible ecological effect of such an undertaking. Although there may be a real practical problem in effecting distribution, another useful winter application of low-grade heat could be the use of it to keep streets and sidewalks ice and snow free. Also recreation lakes could be maintained at a comfortable temperature in cold climates: this positive result could be the by-product of the use of cooling ponds for dissipation by evaporation of the heat rejected in the warm effluent water.

6.2.2. High-grade (process) heat

High-grade heat may be utilized in the form of steam or hot water for the supply of process heat to nearby factories, for urban and district heating and air conditioning, for waste treatment, for water desalination etc. With the present generation of nuclear power stations this approach may have strong limitations and would require careful consideration, especially for boiling water reactors for which the turbine is directly inserted into the primary cooling circuit because of the radioactive contamination of the primary fluid. In general, the utilization of waste heat at a higher temperature level appears to be much more efficient from a global standpoint, but presupposes the realization of quite complex integrated systems between the power station and the nearby utilizers. This type of integrated approach is certainly attractive, but requires careful planning and management. This system provides for the power generating station to be equipped with extraction/condensing or back-pressure turbines. Steam for process heating is extracted from a suitable tapping on the turbine (extraction/ condensing case) or supplied as back-pressure steam (back-pressure case) [1]. The rejection of waste heat into the environment, by comparison with a straight condensing turbine producing the same electrical output is negligible in the back-pressure case, whilst in the extraction/condensing case the quantity rejected is reduced, though the amount of reduction depends on turbine cycle arrangement and the pressure at which the process steam is extracted [1],

6. 2. 2. 1. Supply of steam for process heating

A typical example of process steam supply, which is at the same time a good example of integrated total energy utilization complex is that of the industrial and power complex of Point Tupper (Nova Scotia), in Canada. This complex comprises the Nova Scotia Power Commission Thermal Generating Station, supplying electricity and process steam, the Canadian General Electric Heavy Water Plant, producing 400 tons of heavy water per year, the Gulf Oil Refinery, designed for 60 000 barrels per day, and the mill of Nova Scotia Pulp Ltd., with an output of 350 tons per day. A schematic diagram of this integration is shown in Fig. 25. a Q PRODUCT > TO EXPORT TO EXPORT

PRODUCT TO EXPORT

FIG.25. Schematic diagram of Point Tupper Complex utilizing total energy concept radius - 3 km. ; 1925 lbf/in (g)/1025° 1200000 lb/h

80.55 kW=275«106 Btu/h LOSSES I5WU«106 Btu/h BOILERS -TOTAL STEAM 6 GENERATION-1200000 Ib/h 289*10 Btu/h AT 2020 lbf/in2 lg)/1030°F HEAT ADDED IN BOILER = (1790-8-433)*106 Btu/h = 1365 * 10s Btu/h ¿,¿.000 Ib/h DESUPERHEATERS 298 °F 1244000 tb/h 267.5 Btu/lb 1216.6 Btu/lb 6 12«10 Btu/h 1513« 106 Btu/h TO PLANT SERVICES: 26000 Ib/h 1030000 Ib/h 185lbf/in2(gl/410°F TO CGE HEAVY 1216.6 Btu/lb WATER PLANT 6 1216.6 Btu/lb 32 *10 Btu/h 60000 Ib/h 6 1252*10 Btu/h BLOW DOWN 1 212000 Ib/h FROM PLANT SERVICES: 1216.6 Btu/lb >S 6 TO WASTE 380 °F 26 000 Ib/h 73*10 Btu/h 42000tb/h I 12 000 Ib/h 357.1 Btu/lb 267 5 Btu/lb 60 °F I 6 6 MAKE-UP 671.7 Btu/lb 433 *10 Btu/h 7 *10 Btu/h 28.1 Btu/lb f 6 8«106Btu/h 1« 10 Btu/h J

HEAT USED BY HEAVY WATER PLANT =(1252- 206.3 i *106Btu/h »1043.7 x 106 Btu/h DEAERATOR 1256000 Ib/h 290 °F 267.5 Btu/lb 335«106 Btu/h 1000000 Ib/h 240°F FROM CGE HEAVY 1365 208.3 Btu/lb BOILER FEED PUMP 6 WATER PLANT TURBINE HEAT RATE = "^'go441'10 = Btu/kWh 208.3«10 Btu/h

FIG.26. Simplified heat balance diagram of Unit No. 1 Point Tupper Generating Station. BENEFICIAL USES OF WASTE HEAT 115

The fast that the entire complex is within a 3 km radius provides • substantial economy in overall transportation costs for all the integrated supplies and services [1,9]. The net electric power output of the generating station is 80 MW, of which 26 MW are supplied as electricity to the Heavy Water Plant. In the same time the back-pressure turbine supplies the Heavy Water Plant with 464 000 kg/h of steam at 12 kg/cm2 and 210°C. The turbine heat cycle is based on the return of condensate from the Heavy Water Plant at a rate of 454 000 kg/h and 115°C [1, 10], A simplified heat balance of this solution is shown in Fig. 26 where it can be seen that "of the 451 X 106 kg-cal/h available in the steam supplied to the turbine, only 73 X 10 kg-cal/h is used to generate power. The amount of heat supplied to the heavy water plant in the form of 12 kg/cm2 210°C steam, is 384 X 106 kg-cal/h, of which about 52 X 106 kg-cal/h is returned to the power plant cycle in the form of condensate. The remainder of the heat available in the exhaust steam from the turbine, that is 67 X 106 kg-cal/h, is used for plant and feed water heating purposes" [ 1 ]. Heat rejection from the unit to cooling water is almost completely eliminated since there is no turbine condenser, with the exception of 2 X 106 kg-cal/h rejected in the form of continuous boiler blow-down. On the other hand, the waste heat rejection to cooling water from a conventional steam cycle, employing a condensing steam turbine for power generation only, would be approximately 160 X 106 kg/h. The disadvantage of the system lies, however, in the fact that, because the turbine is of the back-pressure type, only about 20% of the heat added in the boiler is converted into electrical output, whilst, in the case of a conventional condensing turbine generator, the corresponding percentage would be of the order of 40 to 45% [ 1 ]. The economics of such systems cannot be defined in a generalized way, but "must be considered separately, and on its own merits, in order to determine the most suitable system for each particular situation" [1 ].

6.2.2.2. Urban and district heating

For urban and district heating the heat has to be extracted in the form of 150 to 19 5°C steam or hot water in order to be economical [1], a method which involves the use of either extraction/condensing or back-pressure turbines. This steam or hot water is carried to the premises' and buildings' heating systems by means of an appropriate network of underground or above the surface thermally insulated pipes. This system would not be in operation during the summer months and therefore the waste heat load would have to be dumped into the streams just during this most critical portion of the year. The system would become more attractive, both ecologically and economically, if one could economically design large scale air conditioning systems using the small differences in temperature between the waste heat and the atmosphere [1,2], A study by the Commission of the European Communities [11 ] is skeptical about this particular way of recovery of waste heat, at least for European countries'. This document states, in fact, that "for example, during six winter months an average domestic consumer might be assumed to use 50 000 calories per hour (this is an overestimate). A 1000 MW(e) 116 CHAPTER 5 nuclear power plant would produce 1. 7 X 109 kcal/h, therefore a population of 150 000 inhabitants would be needed to consume these calories. In practice, a town using this type of domestic heating would have to be planned at the same time of the power plant, and no estimate has ever been made of the capital investment this would entail" [11]. In addition, the installation of air conditioning as a standard practice which would be necessary to justify continued recovery of the energy during the summer, is considered hardly worthwhile in most European climates [11]. On the other hand, recent studies carried out in the United States of America indicate that "the cost for providing heat for space heating purposes from a nuclear fuelled power plant, to customers up to 10 miles from the plant, would amount to about US $4. 00 per 106 kcal (compared to US $4. 00 to US $6. 00 per 10s kcal for oil fired heaters)" [1,12]. These values are to be also compared with the cost of US $8. 00 to US $10. 50 per 106 kcal for small individual heating systems, suggested in the previously quoted Canadian study [ 1 ]. A typical example of full application of an integrated system of power generation and urban heating supply may be drawn from the same study [1 ], where the case of Inuvik, a small administrative centre in northern Canada, is described. The area is in a region of permafrost, i. e. the ground is perennially frozen. The ground temperature at 8 m to 30 m below the surface is a relatively constant -5°C, while the mean annual air temperature is about -10°C. Reference [1] states that: "at Inuvik studies indicated that substantial savings could be made with regard to heating of the major premises and buildings by using a central heating system. By combining the heat loads of many buildings into a central power plant it would be possible to burn residual oil instead of the more expensive high grade fuel oil necessary in small heating plants in each building. The combined power and central heating plant would also eliminate the hazard of fire present with numerous individual heating units each with its own fuel storage tank". A system of heat distribution using high pressure, high temperature hot water was considered to be the most suitable. This water, when circulated at 10. 5 kg/cm2 and 170°C, has a carrying capacity through 8 inch supply and return lines of 18 X 106 kcal/h [13], The heating load required consists of a 'base' load requirement for domestic hot water, laundries etc., and a seasonally varying space heating load. It must be mentioned that Inuvik, due to its position, represents an above average heat load demand (the maximum heating load is of the order of 15 X 106 kcal/h) but, though an extreme case, it provides a good example of an integrated urban heating-power generating system. The present peak electrical power requirement at Inuvik is of the order of 4 MW. However, because of its remote, isolated location and the extreme climatic conditions the actual installed capacity is of the order of 9 MW, to ensure a reliable power supply at all times. The power plant capacity at Inuvik consists of one 5180 kW, two 1000 kW, one 960 kW and two 375 kW diesel generators and one 600 kW back-pressure steam turbine generator [1]. Under design conditions about 90% of the peak heat demand is provided by the steam exhausting from the 600 kW back-pressure turbine generator 500 Ibf/in Ig) 550°F ¿2 000 Ib/h THREE OIL FIRED BOILERS EACH RATED AT: 1260.5 Btu/lb 53*106 Btu/h STEAM FLOW 30 000 Ib/h ENTHALPY 1260.5 Btu/lb 600 kW = 2.05x10 Btu/h HEAT FLOW 37.8 * 10® Btu/h TOTAL T/G LOSSES = 0.25*10 Btu/h DESIGN OPERATING CONDITION 150 ibf/in 2 (g) 2 BOILERS OPERATING ¿2 000 Ib/h 1 ON STAND-BY 1206 Btu/lb TOTAL STEAM GENERATION 60000Ib/h 50.7*106Btu/h ENTHALPY 1260.5 Btu/lb 2 6 150 Ibf/in Ig) O HEAT FLOW 75.6 * 10 Btu/h > 18000 Ib/h _FROM UTIL1DOR 1260.5 Btu/lb ¿22000 Ib/h 22.7»106 Btu/h 225 °F 193.2 Btu/lb 81.5»106Btu/h

DEAERATORS

TO UTILIDOR

60000 Ib/h ¿22000 Ib/h 350 °F —G 350 °F BOILER HTPW 321.6 Btu/lb 321.6 Btu/lb FEED CIRCULATING 19.3 * 106 Btu/h 135.7* 10® Btu/h PUMPS PUMPS

FIG.27. Simplified heat balance diagram of combined power and central heating plant at Inuvik. =1 SCALE

FIG.28. Townsite plan - Inuvik N. W.T. BENEFICIAL USES OF WASTE HEAT 119 unit, the remainder being obtained by recovering heat, in a waste heat boiler, from the exhaust of the 5180 kW diesel. However, since the latter system forms a relatively small part of the central heating system, and because it is concerned with recovery of heat that would otherwise be wasted to the atmosphere, only the steam turbine system will be considered in detail. A simplified heat balance diagram of the system is shown in Fig. 27. The heat balance shown is for the case when the back-pressure turbine is generating its maximum output, i. e. 600 kW, and 13 X 106 kcal/h of heat is being used in the central heating system. Under this condition the total steam generation would be 27 000 kg/h of which 13 000 kg/h would be used by the steam turbine. The remaining 8 000 kg/h would by-pass the turbine and feed directly into the high pressure water heaters. The high pressure water would be fed into the pipes system (see Fig. 28) at a temperature of 175°C and would return to the power plant at about 105°C [ 1 ]. If a conventional condensing steam turbine were used to generate the same power when supplied with steam at the same conditions, its steam consumption would be about 4000 kg/h and the heat rejected to condenser cooling water would be about 2. 25 X 106 kcal/h [1]. On the other hand, the combined system described in Ref. [1] generates 600 kW while supplying 13 X- 106kcal/h for central heating purposes and reducing heat rejection to the environment to negligible levels. In more temperate localities the system more likely to be utilized would be one where extraction/condensing steam turbine generators are employed. Because-of the interrelationship between heat extracted and power produced in this type of plant, selection of unit sizes would be governed to a large extent by the power and heat demand curves. Examples of this kind of application can be found in a number of European and American towns. In addition to the economic benefits, combined power/heating plants would help to improve the air quality in the large towns and cities. Other advantages of these plants include a reduction in the quantity of heat rejected to the aquatic environment, less risk of fires and making fuller use of the energy which is being produced.

6.2.2.3. Sewage and waste water treatment

Another possible useful application of waste heat is for heating sludges in sewage treatment plants [2], In this case steam or hot water at about 100°C would be necessary. Some recent studies, in fact, showed that heat treated waste sludges are more homogeneous and settle faster [14], improving in this way their physical and biological treatments. Also in this field an integrated cyclic system based on the presence of a thermal power station may be conceived. In fact, as it was recently proposed, part of the sewage or waste water from a city could be purified by evaporation using steam from a thermal station and the water could be used to augment the city water supply [ 1]. A study made in the USA on this subject showed that a power station of about 500 MW(th) (with back-pressure turbine) could significantly contribute to satisfy the water needs of a city of 1 000 000 inhabitants. 120 CHAPTER 5

In fact, these needs could be supplied by evaporating 157 000 m3/d of waste water, requiring 400 MW of heat, and blending the distillate with 298 000 m3/d of filtered, carbon treated secondary effluent and 227 000 m3/d of treated natural water supply [1,12]. The cost of producing water in this way would be not competitive, amounting to about 20 cents per 4. 5 m3, but this application could be a possible way of alleviating the thermal pollution problem in cases where it would be necessary to treat the effluents from urban sewage treatment in order to reduce their total dissolved solids content before discharging them to natural waters [1,12].

6.2.2.4. Desalination

One significant application of waste heat, either in the form of warm water or of steam or hot water, is the desalination by distillation of brackish water or sea water. A thermal power station of the order of 2000 to 4000 MW(th) should give rise to a production of the order of 2. 7 X 106 m3/d [12],

6.3. BIOLOGICAL APPLICATIONS OF WASTE HEAT (LOW GRADE)

6.3.1. Aquatic cultivation (aquaculture)

It is well known that temperatures higher than those normally existing in a water body can result in a change in the species composition of the fauna. This effect can be either adverse or beneficial, depending on the species which are to be protected and harvested. According to Mount [15]: "the first task is to determine the thermal requirements of the species that are to be harvested and then make additional studies on the food-chain organisms. There is a substantial amount of evidence that fishes frequently are more sensitive to elevated temperatures than are most of the food-chain organisms: this is not to say that some varieties of invertebrates are not more sensitive than fishes, but it does imply that, under increased temperature, sufficient food organisms will be present, though they may be of different kinds, to support the harvested crop". It is interesting to note that the maintenance-food requirements of fish in nature may be considerably greater than those of fish held in laboratory aquaria, as pointed out by Doudoroff: "a successful population of fish inhabiting a cold, oligotrophic water that is very deficient in fish foods may become unable to maintain itself when the temperature is raised to a level that is optimal for growth of the species when food is very abundant" [16]. Therefore, when the goal is to utilize waste heat with the purpose of growing a monoculture, one has not only to fulfil the thermal requirements for the spawning and growth of the desired species, but to assure well the availability of their feeding organisms. This is particularly feasible with integrated waste heat utilization projects, where aquaculture is performed by side of urban wastes treatment [17], In the same Reference [17] it is stated that "aquatic cultivation has been practised for centuries and has the same objective as agriculture and stock breeding, namely, to scientifically increase the production of food and sport species beyond the level which would be produced naturally. BENEFICIAL USES OF WASTE HEAT 121

As with agriculture, aquaculture seeks to eliminate unwanted plants and animals, to replace them by desirable species, to improve the environment by whatever means necessary, such as using fertilizers, controlling water exchange, installing underwater habitats, and other scientific controls".

6.3.1.1. Freshwater aquaculture

6.3.1.1.1. Carp

Use of heated natural waters from power stations for commercial production of carp (Cyprinus carpió) in the USSR is described by Gribanov et al. [18]. Special floats have been developed for spawning,fry nursing, rearing and wintering. Results show that the optimum temperature range for carp growth in floats is from 23 to 30°C. At 22°C the growth rate is decreased and virtually no growth is observed at 20°C. Temperatures up to 34°C are not lethal although growth is suppressed to some extent. Today carp-cultivation is practised successfully in Central Russia in artificially heated water. Normally the power plant discharge is 10 to 15°C above ambient water temperature. At some stations the winter temperature exceeds 20°C, permitting efficient growth even during the colder months. Artificially prepared foods enriched with vitamins and antibiotics are used in the Russian carp culture projects, and experimentation with various food mixtures, feeding rates, stocking densities and water exchange rates continues. Through experience and refinements, production yields have rised from 15 kg/m2 in 1960 to 100 kg/m2 in 1965. Biochemical and haematological analyses indicate a normal, wholesome product [17],

6.3.1.1.2. Catfish4

Research has been performed also on catfish. Carp and catfish are reported as examples of fish with a high heat-tolerance, and at the same time highly valued for sport or commercial purposes [15], Channel catfish (Ichtalurus nebulosus) were raised in replicate experiments at a series of constant temperatures. At the end, the largest growths were obtained at 29 and 31°C, with reasonable growth rates ranging from 27 to 34°C. Food conversion rates have proved best at 29°C and were very good at the 27 to 31°C range. Also in a temperature choice tank, 7 m long, it was interesting to note the similarity of preferred temperatures (between 28 and 29°C) to optimal temperatures for growth and food conversion. Tilton and Kelley (quoted in Ref. [19]) have been raising channel catfish in cages in the discharge canal of the Texas Electric Service Company at Lake Colorado City, Texas. They found that temperatures in the canal from January 10 through January 26, 19 70, were high enough for channel catfish to have a 45% increase in weight and that fish kept in an unheated hatchery pond failed to gain in weight. Based on these observations, farming of channel catfish in a power plant discharge canal and reservoir

4 This section is chiefly extracted from Strawn [19], 122 CHAPTER 5 would be extremely profitable at current market prices and would still be very attractive at 30 cents a pound, a price that would either lose money for or give little profit to the farmer raising catfish in ponds (Brown, La Plante and Covey, 1969 and Greenfield, 1970, quoted in Ref. [ 19 ]). A 4 km2 reservoir in Texas supplying cooling water for a power plant could produce two crops of 1000 tonnes each worth a total of US $1 600 000 at a reasonable current market price of 80 cents per kilogram. Capital and production costs are estimated to be US $894 850, leaving a power plant with a first year net profit of US $705 150 less interest and taxes. The cool season crop would be raised in the discharge canal and the warm season crop in front of the power plant intake. The pumps that provide cooling water for the plant furnish a flow of water that supplies oxygen to the catfish and removes waste products. More than two crops can be produced per year by reducing the rate of water flow through the condensers to produce optimum temperatures for growth and food conversion during the cool months. The problem is to find out the cost of a 29°C (84. 2°F) water in terms of decreased generating efficiencies. The increased production of catfish might more than pay for the added cost in generation of electricity. The standard figure for catfish production is 250 g/m2. Water circulation by the plant would permit more weight of fish to be raised per unit area. Jeffrey (quoted in Ref. [19]) found that 500 g/m2 could be raised in ponds by circulating water with air. Catfish farming in raceways incorporated into the design of the plant before it was built could prove more profitable than basket (or cages) culture. An original suggestion, reported by Parker and Krenkel [2] is that heated waters from nuclear plants be used to raise ornamental fish, some of which sell for over US $300 per kilogram [20],

6.3.1. 2. Saltwater production (mariculture)

The possibility of aquaculture utilizing warm water effluents from power stations are limited to carp, catfish, and some other thermotolerant species. Very promising is the application of thermal discharges to mari culture. Some species, like oysters, are able to live successfully at temperatures above and below those required for spawning. If the temperature requirements are not satisfied the eggs and sperm are reabsorbed, eliminating thus the spawn for that year. The presence of a continuous heated discharge in a natural area having the required conditions for successful larval production and settling (spat fall) could be made beneficial by increasing the spawning period and by increasing the growth rate. On the other hand, fluctuations in the discharge water temperature could trigger a spawn in the wrong season of the year when the proper food is not available for the larval oyster. Thus, the problem . is to provide in synchrony oyster larvae with the necessary food species [ 21 ]. As Parker and Krenkel [2] report. Long Island Lighting Company at Northport, N. Y., is experimenting aquaculture of oysters in the heated discharge from the nuclear power plant. Oysters also are considered as filter-feeding organism of commercial value in a circuit proposed by Mihursky [22] quoted elsewhere in this report; in a complete recycling of organic matter, utilization of residual heat for BENEFICIAL USES OF WASTE HEAT 123

waste treatment (and for district heating) results in the enhanced growth of algae, Zooplankton and shellfish (oysters and clams). Lobsters, as high value seafood, have been studied with the purpose of utilizing their thermal requirements: the larvae of lobster apparently do not tolerate temperatures below 15°C [21]. Furthermore this species has received consideration in order to determine if an increase in the growth rates does occur in warmed waters. The Maine Department of Sea and Shore Fisheries is now experimenting with lobsters near a power plant discharge on the Coast of Maine [21]. At the Tokai Atomic Power Plant in Japan an experimental project is in operation to utilize the heated water in the coolant discharge for the culturing of sea bream, abalones, and prawns. The equipment is as shown in Fig. 29 but at present has only 24 culturing ponds totalling 720 m2 in area. The number of ponds is planned to be increased by 10 each of larger area so as to have a total of 2000 m2 under evaluation. The water supplied to these ponds is drawn from the cooling water and coolant discharge, at the rate of 13 tons per minute each from the intake and discharge pipe, respectively. It is estimated that as many as 50 000 bream, 50 000 abalones, and 100 000 prawns will be produced annually from this project. 124 CHAPTER 5

FIG. 30. Closed cycle system.

6.4. A GLOBAL APPROACH

The various solutions outlined in the previous paragraphs are generally of a sectorial character, except the described examples of integrated system among power stations and nearby factories or district heating networks. A much more global approach is proposed by Mihursky [22], This author, in fact, starting from the ascertainment of the detrimental effects of thermal pollution, states, on the other hand, that "few are willing to do without electricity in order to return to primitive temperature regimes. Consquently, future technology must either (I) produce electricity in a radically different manner with a resultant reduced thermal load into the aquatic habitat, which will not be the case in the foreseeable future, or (II) find ways to redirect temperature loads into new controlled ecosystems to produce desirable products. Rather than to allow huge thermal energy loads to go undirected into natural and at times delicately balanced and complex environments, the task is to design ecosystems that will take advantage of waste calories and make them biologically useful. As Odum [23] suggested, we must select components from the world's stock shelves and use them to redesign new circuits in the environment: new circuits being new ecosystems composed of component species that will fit efficiently into a new food web and biologically convert available waste energy obtained from technological progress into desirable recreational materials or food stuffs" [22], On the basis of these considerations, Mihursky suggests the closed cycle system of Fig. 30. This system according to Mihursky: "takes advantage of two waste products (organic wastes, waste heat), both containing potentially useful energy supplies. Organic wastes provide necessary nutrients while waste heat from steam electric installations provides optimal temperature ranges for maximum biological activity and production" [22], BENEFICIAL USES OF WASTE HEAT 125

TABLE XVI. ENERGY CENTRE HEAT APPLICATIONS 2000 to 4000 MW(th) [12]

Approximate quantity of product Application Particular use rr with heat

Central heating Steam and hot water for For a city of 500 000 to 1000 000 residential, commercial and people industrial heating

Central cooling Evaporative cooling for residential For a city of 500 000 to and commercial needs 1 000 000 people

Manufacturing Electricity and heat for (typical mix)

Evap. salt 2775 t/d Petrochemical 60 000 barrels/day Arc process acetylene 220 t/d Polyvinyl chloride 500 t/d Sodium hydroxide 1695 t/d Kraft paper 500 t/d

Desalination for Waste water recycling To 3 x 106 m3/d municipal water Brackish water distillation To 3 x 10® m3/d

Seawater distillation To 3 x 106 m3/d

Agriculture Arid land irrigation with To 3 x 106 m3/d distilled water (128 000 hectares)

Arid land irrigation with condenser To 5 x 106 m3/d discharge water (80 000 ha)

Greenhouse heating and cooling To 400 ha

Poultry house heating and cooling To 400 ha

Transportation Stored steam for buses and trucks 54 kg water (condensate of exhaust vapour) per bus mile

Ice-free shipping lanes 16- 32 km ice-free water

Aquaculture Warm water and sewage for culture:

Shell fish Unknown

Crustaceans 900 000 kg/a (400 ha)

Fish 4 270 000 kg/a (860 ha)

Algae 20 x 106 kg/a

Miscellaneous Outdoor heating To 3.6 x 106 m2 (410 ha)

Snow melting To 3.6 x 106 m2 (410 ha)

a The applications shown would each absorb the waste heat from plants in the range mentioned. Actual mix of applications would depend on the circumstances of each specific location. 126 CHAPTER 5

In this paper Mihursky feels quite optimistic about the practical feasibility of his scheme, though admitting the need for further research, but concludes that "it is quite apparent that this recommended approach to controlling and redirecting a major environmental change is not a task for a single individual, discipline, or institution; it requires a multi- disciplined effort with international co-operation and a 'megadollar1 investment" [22]. As summarized in Table XVI, there are indeed many potential applications of waste heat in the form of low grade heat, and even more for high-grade heat. For most nuclear plant sites many of these applications are not possible or not economical and it would be difficult to satisfy simultaneously the operating requirements of several users. Yet, a better management of natural resources and of the environment will require an optimum utilization of the heat produced by nuclear reactors. This goal would entail multipurpose nuclear plants with a minimum discharge of waste heat.

REFERENCES TO CHAPTER 6

[1] MONTREAL ENGINEERING COMPANY LTD., Thermal Inputs into Canadian Waters, 1970-2000 A.D. (excluding the Great Lakes Basin), Report prepared for the Department of Energy, Mines and Resources and the Department of the Environment of Canada, Oct. 1971. [2] PARKER, F.L., KRENKEL, P.A., Thermal Pollution: Status of the Art, National Center for Research and Training in the Hydrologie and Hydraulic Aspects of Water Pollution Control, Rep. No. 3, Vanderbilt University, Nashville, Tenn. 1969. [3] CARTER, L.J., Warm-water irrigation: An answer to thermal pollution} Science 165 (1969) 478. [4] JAPAN I.E.R.E. COUNCIL, "Research on environmental problems by the electric power industry of Japan", Third General Meeting International Electric Research Exchange, Tokyo, Japan, 12-14 May, 1971. [5] FAIR, G.M., GEYER, J.C., Water Supply and Wastewater Disposal, John Wiley and Sons, New York, N.Y. (1954). [6] VELZ, C.J., Influence of temperatures on coagulation, Civ. Eng. 4 (1934) 345. [7] ARNOLD, G.E., Thermal pollution of surface supplies, J. Am. Water Works Assoc. 54 (1962) 1336. [8] DINGMAN, S.L., WEEKS, W.F., YEN, Y.C., The effects of thermal pollution on river ice conditions, Water Resour. Res. 4 (1968). [9] JEFFRIES, A.T., BUCKLEY, F.W., "Total energy utilization with particular reference to the Point Tupper Industrial Complex", World Energy Conf., Bucharest, Jun. 1971. [10] KALISNYK, Z., McGIBBON, C.M., The Point Tupper Generating Station, The Engineering Institute of Canada, Halifax, N.S., May 1968. [11] COMMISSION OF THE EUROPEAN COMMUNITIES, DIRECTORATE-GENERAL FOR INDUSTRIAL, TECHNOLOGICAL AND SCIENTIFIC AFFAIRS, Thermal Pollution of Rivers due to Thermal Power Plants in the EEC Countries, doc. XV/115/1/71, Jun. 1971. [12] BEALL, S.E., Jr., "Uses of waste heat", ASME Paper 70-WA/Ener-6, ASME Winter Annual Meeting, New York, N.Y., 1970. [ 13] DOBSON, A., A high pressure hot water district heating scheme at Inuvik in Canada arctic region, Inst. Heating and Ventilating Eng. 1. 30 11 (Nov. 1962). [14] CROTTY, P., FENG, T., SKRINDE, R., KUZMINSKI, L., "The use of heat to improve water treatment", presented at the First Annual Northeastern Regional Anti-Pollution Conf., University of Rhode Island, 1968. [15] MOUNT, D.I., "Developing thermal requirements for freshwater fishes", Biological Aspects of Thermal Pollution (Proc. National Symp., Portland, Oregon, June 3-5, 1968), (KRENKEL, P.A., PARKER, F.L., Eds), Vanderbilt University Press (1969) 140. [16] DOUDOROFF, P., contribution to Discussion, see Ref.[15], [17] GAUCHER, T. A., "Mariculture", in Hearings before the Subcommittee on Air and Water Pollution of the Committee on Public Works, United States Senate, Nineteenth Congress, Second Session, Therm. Pollution (Part 1) (1968). BENEFICIAL USES OF WASTE HEAT 127

[18] GRIBANOV, L.V., KORNEEV, A.N., KORNEEVA, L.A., Use of Thermal Waters for Commercial Production of Carps in Plants in U.S.S.R., F AO Fish Rep. 44 (1966) 218. [19] STRAWN, K., "Beneficial uses of warm water discharges in surface waters", Electric Power and Thermal Discharges (EISENBUD, M., GLEASON, G., Eds), Gordon and Breach Science Publishers (1970) 143. [20] ILES, R.B., Cultivating fish for food and sport in power station water, New Sei. _U7 (1963) 227. [21] JENSEN, L.D., DAVIES, R.M., BROOKS, A.S., MEYERS, C.D., The Effects of Elevated Temperature upon Aquatic Invertebrates, Department of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore, Md., Sep. 1969. [22] MIHURSKY, J. A., On possible constructive uses of thermal additions to estuaries, Bioscience 17 (1967) 698. ~~ [23] ODUM, H.T., "Energy transfer and the marine systems of Texas", presented at the Conf. Pollution and Marine Ecology, Galveston, Texas, 1966.

Chapter 7

THERMAL DISCHARGES AND THE SITING OF NUCLEAR POWER PLANTS

7.1. GENERAL CONSIDERATIONS

The environmental impact of waste heat disposal has been recognized for many years and has had already a marked influence on power plant siting and the choice of cooling methods. The early adoption in the United Kingdom of coastal sites and cooling towers constitutes perhaps the most outstanding example. The severity of this environmental impact is intensified by the introduction of large nuclear power plants with poor thermal efficiencies. Faced with fast rising costs, utility companies search for optimal economic solutions by pooling their networks and by ordering large nuclear plants with lower unit costs. The siting at the same location of several units with an electrical capacity of more than 1000 MW(e) each leads to large waste heat emissions which must still be disposed of in a manner compatible with environmental protection requirements. Of all the cooling methods which are available, once-through water cooling remains by far the most desirable, not only from an economical viewpoint, but also in terms of the environment. Even if once-through cooling has to be abandoned in many industrial countries for various reasons, there are still many areas of the world where this technique of wáste heat disposal can be used without any problem. The knowledge available today for the prediction by mathematical and physical models of heat dissipation in the environment, as well as the better understanding of the chemical, physical and biological effects of heated effluents means that once-through cooling can be selected with due consideration given to the impact of waste heat upon the surroundings . As shown in Chapters 3, 4 and 5, there is a considerable body of analytical and experimental experience which has been accumulated over the years. Adequate supplies of cooling water are, however, becoming increasingly difficult to find in most densely populated and heavily industrialized countries. There are two alternatives to once-through cooling from rivers or lakes:

(1) Inland sites with atmospheric cooling (towers or ponds) (2) Shore sites along the sea or off-shore

When an inland site must be adopted, waste heat disposal to the atmosphere remains the only alternative. This solution covers wet and dry cooling in all its forms : natural and forced draught towers, cooling ponds with or without spraying. As noted in Chapter 4, atmospheric cooling creates in

129 130 CHAPTER 5 general few environmental problems, since for most sites the dispersion capacity of the atmosphere is so great that sizable adverse effects do not occur. The shift to atmospheric cooling which is under way in Europe and the United States of America results to a great extent from environmental considerations. For the same reasons, sea cooling either on- or off-shore is also gaining in importance. Off-shore nuclear plants constitute a very attractive technique of waste heat disposal into water with practically no environmental consequences. On-shore siting has already been widely adopted by countries such as the United Kingdom and Japan with a long shoreline close to population centres. With better interconnected electrical networks, sea cooling is likely to become a preferred solution in other regions as well.

7.2. CRITERIA FOR SITE SELECTION

The adequacy of a particular site or cooling method, in terms of impact on the environment, should be determined on the basis of relevant scientific criteria. What kind of scientific criteria are then required to allow an overall evaluation of the suitability of a site? In the case of heat disposal to a water body three categories are suggested:

(a) The general physical, chemical and biological effects of temperature increases (b) The condition of the receiving waters in terms of natural temperatures, flow rates, degree of organic and inorganic pollution, fish population, type of biota etc. (c) External factors of the receiving waters: other uses of the resource such as water supply, irrigation, recreational etc.

Waste heat disposal directly to the atmosphere, largely by means of evaporation evokes a new set of criteria. But, in general, environmental problems associated with atmospheric cooling appear to be minimal, except for the aesthetic impact of natural draught cooling towers.

7.2.1. Thermal receptivity of the environment

Limits for the disposal of waste heat to the environment should be fitted to each particular site by means of an appropriate method of assessment. An approach which is proposed is that of the 1 environmental receptivity' The concept is used more and more for the assessment of radiation hazards due to discharges of radioactive effluents into the environment. In this field the environmental receptivity is defined as the quantity of radioactivity which can be released to the environment in a given period of time without giving rise to unacceptable risks to the most exposed population group (' critical group'). An analogy with this approach, which is very successful in the nuclear field, should be attempted by defining a 'thermal receptivity' of a given environment as the ' environmental receptivity for thermal energy' . This can be defined as the amount and rate of thermal energy disposal into the THERMAL DISCHARGES 131

FIG. 31. Method of analysis for the assessment of thermal receptivity.

hydrosphere and atmosphere which will not exceed a determined limit. This limit should be set for each case by an evaluation of benefit versus detrimental effects to the environment, taking into account integrated optimum resource management and expected beneficial effects. The method of analysis to be used for the assessment of such thermal receptivity is shown in Fig. 31. General scientific factors (such as effect of temperature on oxygen content and on biological oxygen demand, flow and temperature regimes etc.) are considered in the upper boxes, along with technical data on the source of waste heat (amount, temperature). These factors would then be fed into a mathematical model which would evaluate the physical perturbation brought upon the existing ecosystem. The evaluated environmental effects are then weighed in a cost-benefit analysis for the determination of the thermal receptivity of this environment. The social, political, economic and administrative factors would also influence any decision regarding the thermal receptivity of a site. For example, if the decision is taken that no fish should be killed by thermal discharges then by utilizing the mathematical model one can determine the allowable heat input. For each permissible thermal receptivity the costs and benefits of such an action can be determined. If the cost-benefit ratio is unacceptable this will feed-back to the social, political, and economic factors and change them until a satisfactory cost-benefit ratio is achieved. These cost-benefit ratios will be listed for each site investigated and for the various levels of development at each site. The final output of this scheme will be a table of alternative possible actions at various sites and their associated benefit and costs. 132 CHAPTER 5

7. 2. 2. Relevant factors for the assessment of the thermal receptivity of a given environment

An indicative list of some relevant factors which are necessary for the practical application of the procedure indicated in the preceding section is given below:

I. Data on source of waste heat

A. Discharge into a water body

1. Effluent characteristics

1(a) Flow-rate 1(b) Temperature distribution 1(c) Density differences (relative to reference density in receiving water) 1(d) Velocity at outlet

2. Outlet characteristics

2(a) Location 2(b) Orientation 2(c) Submergence 2(d) Shape 2(e) Size (depth and width)

B. Discharge into the atmosphere

1. Effluent characteristics

1(a) Flow-rate 1(b) Temperature 1(c) Density differences 1(d) Droplet size distribution 1(e) Velocity at outlet 1(f) Water-vapour load 1(g) Relative humidity at outlet

2. Outlet characteristics

2(a) Location 2(b) Orientation 2(c) Height 2(d) Shape 2(e) Size THERMAL DISCHARGES 133

II. Environmental factors

A. Physical and chemical factors

1. Receiving water

l(a Volume — flow characteristics l(a (i) Seasonal variations l(a (Ü) Extreme rates l(a (iii) Plow duration curve l(b Flow dynamics l(b (i) Pre-existing velocity field (magnitude and directions of local velocities) l(b (ii) Free turbulence l(b (iii) Tidal currents l(b (iv) Wind-induced and other currents l(b (V) Surface waves l(c Stratification l(c (i) Pre- existing stratification due to temperature, soiids and solvents l(c (ii) Wind and tidal effects on stratification l(d Geometrical characteristics l(d (i) Shape l(d (ii) Size (width and depth) l(d (iii) Bottom configuration and roughness near outlet

2. Receiving atmosphere

2(a Wind 2(a (i) Directions and velocities (magnitude and direction, average and instantaneous at different elevations) 2(a (Ü) Shear stresses at water surface 2(b Air 2(b (i) Temperature 2(b (ii) Relative humidity, vertical profile 2(b (iii) Stability and stratification factors 2(b (iv) Pollution levels and date 2(b (V) Solar radiation and heat radiation balance 2(b (vi) Fog records 2(b (vii) Rain records

B. Biological factors

1. Aquatic flora 2. Aquatic fauna (biota, fish, benthos) 3. Relevant ecosystems 4. Dissolved oxygen regime — dissolved oxygen — oxygen saturation — biological oxygen demand — chemical oxygen demand 5. Organic and inorganic pollution — types and levels of existing pollution 134 CHAPTER 5

III. Site factors

(a) Zone planning and alternative possibilities (b) Nearness to sensitive areas (e. g. residential areas) (c) Suitability of geological factors for plant construction

IV. Utilization of the environment

(a) Municipal water supply (b) Industrial use (c) Navigation (d) Irrigation (e) Fishery (f ) Sewage disposal (g) Recreational uses (swimming, fishing, boating, etc.)

7.3. CONCLUSIONS

The overall cost-benefit analysis of the environmental impact of waste heat versus the social benefits of the electricity generated by nuclear plants includes by necessity a wide array of economical and social factors which cannot always be quantified. Weighting of the individual factors will be different for each country, each region and most likely for each site. Many countries have translated the results of some kind of cost-benefit analysis into standards applicable to waste heat disposal. Such standards cover techniques, rules and limits that should prevent or circumscribe deleterious effects of waste heat. As shown in Appendix B, a maximum temperature increase of 3°C for rivers has, for example, been adopted by several States in the United States of America, by the Soviet Union, the Federal Republic of Germany and Switzerland. Standards with respect to maximum temperature and mixing zones also exist in those countries. Though rigid standards will most likely be set in most countries for administrative ease, the option of a comprehensive study to show that the objectives can be achieved with different standards should be left open. In general, the policy adopted should be least restrictive in precluding other options. Environmental protection requirements in regard to waste heat will increasingly affect the siting of nuclear power plants, to a much greater extent than nuclear safety and radiation constraints which are comparatively easier to comply with. In spite of longer transmission distances for the electricity produced, the location of nuclear plants on sea shores may become more and more commonplace throughout the world. However, the need for inland sites will remain. In that case, wet cooling towers offer for the near term a technically acceptable solution compatible with both environmental and economic objectives. But, aesthetic considerations associated with increasing tower sizes may severely limit the applicability of natural draught wet cooling. For the same reason, it appears unlikely that dry cooling towers could be widely used with the current generation of nuclear plants based on the steam cycle. Yet, in the long term, dry THERMAL DISCHARGES 135 cooling appears as the most promising method of waste heat disposal when combined with gas-turbine nuclear plants, a solution that would offer greater flexibility in the siting of nuclear power plants. Although the environmental impact of waste heat will continue to influence the siting of nuclear power plants and limit the applicability of some particular cooling methods, nuclear power will still be able to satisfy the increasing needs for electricity without undue risks for the environment.

BIBLIOGRAPHY

CHAPTER 2

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CHAPTERS 3 and 4

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CHAPTER 5

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CHAPTER 6

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Various Authors, Proc. Conf. Beneficial Uses of Thermal Discharges (13 papers), New York State Department of Environmental Conservation (Sep. 1970) 223 pp. Appendix A

HEAT DISSIPATION BY A WATER SURFACE

The behaviour of a large body of water supplied with an artificial heat load such as the warm water from the condensers of a power station is simply an extension of its natural behaviour under the influence of natural heat exchanges with the atmosphere. In the natural state, a heat balance is established in the water body between incoming energy fluxes and outgoing heat losses. The heat is dissipated from the water by three main processes, namely, evaporation, long-wave radiation and convection. The equilibrium water temperature at which the heat balance is established in the lake is also dependent on the amount of heat stored in the water and on any heat which may be advected into or out of the lake. The net heat flux H from a water surface can be expressed by the equation:

H=B+E+C+F-S- L (A-1)

The natural heat input from the sun and space (S) is just the diffuse short-wave radiation reaching the water surface. This short-wave radiation is a function of the altitude of the sun, the presence of clouds and the reflectivity of the water surface. The long-wave radiation from the atmosphere (L) is a function of the air temperature, the atmospheric water vapour content and the presence of clouds. The heat loss by long-wave back radiation (B) depends on the temperature of the water surface. The heat loss by evaporation (E) is the latent heat of evaporation dissipated by the mass of evaporated water. It depends on the air movement over the water surface, the temperature of the water surface and the humidity and temperature of the atmosphere. The heat loss by convection (C) is the sensible heat conducted from the body of water to the atmosphere and can be expressed as a function of evaporation by means of the Bowen Ratio (see below). The heat advected into or out of the water (F) is the net energy gained or lost through any flows into or out of the lake such as rainfall, snow, surface run-off, in-flowing streams and seepage. The following table (Ref. [1]) shows the order of magnitude of the various terms in Eq. (A-l ) for Central Europe, as expressed in kcal • m"2, d"1.

141 142 APPENDIX A

Yearly Extremes average

Back radiation (B) 7 300 10000 7 000 Evaporation (E) 900 4 000 - 500 Convection (C) 100 1 500 - 1 000 Precipitations (part of F) 20 1 000 0 Short-wave radiation (S) 2 900 100 7 000 Long-wave radiation (L) 5 600 3 000 8 000

The net heat flux H between a water body and the atmosphere depends therefore on a large number of physical parameters which are both space and time dependent. The temperature of the water body will tend to adjust itself continuously to the changing conditions reflected by H, but the greater the heat storage potential of the water body, the larger the damping effect on the rate of change in the water temperature with time. 'By assuming average conditions it is, however, possible to define an equilibrium surface water temperature (T) for which water body and atmosphere are in thermal equilibrium (H = 0) under the influence of natural phenomena. ' The discharge of heat into a water body increases its temperature (T) above the natural equilibrium temperature. As a result, the heat loss to the atmosphere increases also. For small temperature differences the heat loss due to this temperature increment becomes

H = ||-(T-T*)=A(T-T*) (A-2)

where A is the total heat exchange coefficient. For a good mixing over a depth h (metres), the change in water temperature over time due to a heat loss H is given by

H=-h.g.c.^L (A_3)

where g is the water density (about 1000 kg'm"3), c the specific heat (about 1 kcal • kg"1 • °C _1). Together with Eq. (A-2), this last expression yields

dT A 7¡r = -T—^ (T-T*v ) (A-4) dt h • g•c ' ^ '

and the exponential solution

tA T-T* = (To0 -T*)e" r (A-5)

with the relaxation time tr (days) given by

t^í^P (A-6)

Equation (A-5) shows that the water temperature approaches asymptotically the equilibrium temperature. APPENDIX A 143

The heat exchange coefficient A can then be derived from the individual terms of H that depend on the water temperature, i. e. B, E and C:

= (A-Ï) A 3T 9T 3T 9T ''

Back radiation. To a very close degree, water radiates as a black body at ambient temperature and Stefan's law of radiation can be applied:

B = 0.97ctT4 with ct= 1. 171xl(T6 kcal • m'2-d"1 • °K"4 (A-8) where Tk is the Kelvin temperature of the water. Then,

||=92.6(^|) s (95+T) kcal-m^-d"1-^-1 (A-9)

Evaporation E. The evaporation rate from a water surface depends on the water surface temperature, the vapour pressure in the air and the wind velocity. A large number of empirical equations have been developed from actual investigations carried out in evaporation pans, lakes and reservoirs. The basis of these equations (see for example Ref. [1]) is Dalton's expression:

E=(e„-ea)-f{u) (A-10) where ew is the saturation vapour pressure for the surface water temperature, ea the actual vapour pressure in air and f(u) a function of the wind velocity u (at 2 metres above the surface). The dependence on wind velocity can be represented by the following expression f(u) = 0. 17+0.10 u (mmHjO) d"1 • mbar ~1 (A-ll) with u in m/s, an expression which is in good agreement with the formula proposed in Ref. [2], with a formula for cold rivers (Ref. [3]) and also with field studies made at Lake Trawsfynydd in the United Kingdom during the period 1962-1970 (Ref. [4]). If the wind speed data are recorded at a height different from 2 metres, say z metres, then the wind speed at 2 metres can be calculated by means of the relation:

, \ 0.142 u2 = «z(|) (A-12)

After multiplying with the latent vaporization heat (585 kcal/kg at 20°C), Eq. (A-10) becomes

2 1 E=(100 + 59u)(ew-ez) kcal • m" • d" (A-13)

Differentiating with respect to T gives

(A-14) ff = (100+59u)^ 144 APPENDIX A

The first derivative of the saturation vapour pressure of water is the practical temperature range quite accurately represented by the following empirical formula:

^ = 0.54 e°-05T m bar • °C ~1 (A-15) o 1 which leads to

|j| = (54 +32 u)e°-05T kcal • m "2-d"1-°C (A-16)

Convection. Sensible heat loss by convection takes place by much the same diffusion process as evaporation, so that the two are most often related by a fixed constant called Bowen's Ratio ß. Thus,

C = j3E (A-17) or

2 1 C = 0. 62 (100+59u)(T- Ta ) kcal • m" • d" (A-18)

The derivative with respect to water temperature is then

|^ = (62 +37u) kcal • m"2 • d"1 • "C"1 (A-19) d 1

Heat exchange coefficient. Summing up Eqs (A-9), (A-16) and (A-19), the total heat exchange coefficient becomes:

A = 95+T+(62 +37 u)(l+0. 87 e°-05T) kcal • m"2 • d"1 • "C"1 (A-20)

Mass of water evaporated. From the expression giving the heat exchange coefficient

A. ~ A.^ + Ag with

incremental radiation loss A2 = (54 +32 u)e°-05T incremental evaporation loss

A3 = 62 +37 u incremental convection loss one can calculate in first approximation the incremental amount of water evaporated from a water body in which waste heat is discharged from a power plant:

where M is given in m3/s and W is the amount of waste heat in Mcal/s. APPENDIX A 145

Equation (A-21) is meant to apply to water bodies whose temperature is not much different from equilibrium, that is, when Eq. (A-2) is valid. For cooling ponds with higher water temperature it is more appropriate to integrate over the temperature range, i.e. to use Eq. (A-13). Based on the empirical formula of Eq. (A-15), this yields for the total amount of water evaporated from a unit area at a surface temperature T:

M = 0.01S (2.12+1.25 u)(e°-05T-

REFERENCES TO APPENDIX A.

[1] KUHN, W., Physikalisch-meteorologische Überlegungen zur Nutzung von Gewässern für Kühlzwecke, Arch. Meteorol. Geophys. Bioklimatol., Ser. A 21 (1972) 95. [2] WORLD METEOROLOGICAL ORGANIZATION, Measurement and Estimation of Evaporation and Evapo- transpiration, Techn. Note No. 83, WMO - No. 201. TP. 105, Geneva, 1966. [3] DINGMAN, WEEKS, YEN, The Effects of Thermal Pollution on River Ice Conditions, I. A General Method of Calculation, Cold Regions Res. Eng. Lab., Res. Rep. No. 206, Hanover, N.H., USA, 1967. [4] SPURR, G., private communication.

Appendix B

STANDARDS OF WATER PROTECTION

Waste heat from power plants can be safely discharged in surface waters — with a limited impact on the environment — provided that due consideration is given to the wide spectrum of ecological, economical and social criteria. Together, ecologists, engineers and public authorities can get up the appropriate standards of water protection. Many countries have already adapted tentative guidelines applicable to waste heat disposal from nuclear power plants.

UNITED STATES OF AMERICA

The responsibility for environmental protection is in the USA split between the Federal Government and the State authorities. General guidelines set at the federal level can therefore be locally implemented by taking into account regional characteristics which are particularly important in the case of heat releases into water bodies. In April 1968 the Federal Water Pollution Control Administration published the 'Water Quality Criteria' which set some guidelines with regard to waste heat disposal:

Maximum temperatures: depending on the organisms living in a particular ecosystem Maximum temperature increment: — in streams 2. 8°C — in lakes (epilimnion) 1. 7°C _ in estuaries and coastal waters (summer) 0. 8°C — in estuaries and coastal waters (winter) 2. 2°C Mixing zone: — defined as the area in which the temperature is higher than the temperature permitted under the receiving water standards — for estuaries and streams it is recommended that adequate passage- ways will be provided to permit movement or drift around the potentially harmful mixing zone. Passage-ways should preferably be 75% of the cross-sectional area and/or volume flow. Mixing should be accomplished as quickly as possible through the use of devices which ensure that the waste is mixed with the allocated dilution water in the smallest possible area.

147 148 APPENDIX A

A revised edition of the 1 Water Quality Criteria1 by the Environmental Protection Agency takes into account more recent research findings in the field of temperature effects and recognizes more explicitly that temperature criteria are a matter of local evaluation to be defined on a case-by-case basis.

UNION OF SOVIET SOCIALIST REPUBLICS

Regulations in the matter of waste heat discharges exist in the Soviet Union since 1961. The Code of Water Protection rigorously limits to 3°C in summer and 5°C in winter the permissible temperature increment of rivers and lakes open to public use. Once-through river cooling is therefore practically limited to large streams whose flow-rate is at least three times larger than the required condenser flow-rate. Furthermore, the Code of Water Protection specifies that complete mixing of the heated effluents with the river water must take place within 500 metres from the release point.

FEDERAL REPUBLIC OF GERMANY

The following standards are being applied to once-through river cooling: Maximum temperature at the end of the condenser discharge canal: 30°C Maximum temperature in surface water after mixing: 28°C Maximum temperature increment in surface water after mixing: 3°C

The above temperature limits are valid only for waters of good quality. In any case, dissolved oxygen should not fall below 5 mg/l.

FRANCE

No national legislation exists in France in the matter of waste heat discharges into water bodies. However, all projects of thermal and nuclear plants must be approved by the Prefectoral Authority of the relevant Department. The investigations are carried out by the Public Works or Waterway services. There is no preset pattern for determining allowable temperature limits.

SWITZERLAND

Since 1968, thermal releases from power plants into rivers are subject to the following temperature limits: APPENDIX A 149

Maximum, temperature at the end of the condenser discharge canal: 30°C Maximum temperature after mixing: 25°C Maximum temperature increment after mixing: 3°C Maximum ground water temperature, as a result of heated infiltrations: 15°C

These temperature limits are applicable only to rivers exhibiting a low pollution level. This latter condition being not fulfilled for most large rivers (the Rhone excepted), once-through river cooling is not possible for the new nuclear plants being planned.

LIST OF PARTICIPANTS

CANADA

Ophel, I. L. Atomic Energy of Canada Ltd. , Chalk River Nuclear Laboratories, P. O. Box KOJ/IJO, Chalk River, Ont.

CZECHOSLOVAK SOCIALIST REPUBLIC

Klik, F. Czechoslovak Atomic Energy Commission, Slezská 7, Prague 2

FINLAND

Tulkki, P. National Water Board, Fabianinkatu 32, SF-00100 Helsinki 10

FRANCE

Gaudfroy, -. Electricité de France, Direction de l'équipement. Division environnement, Département études générales et programmes — Sites environnement, 3, rue de Messine, F-75 Paris 8e

GERMANY, FEDERAL REPUBLIC OF

Günneberg, F. Bundesanstalt für Gewässerkunde, Postfach 309, D- 54 Koblenz

INDIA

Shirvaikar, V. V. Health Physics Division, Bhabha Atomic Research Centre, Trombay, Bombay 85

151 152 LIST OF PARTICIPANTS

ITALY

Ilari, O. Comitato Nazionale per 1'Energia Nucleare, Divisione di Protezione Sanitaria e Controlli, Viale Regina Margherita 125, 00198 Rome

JAPAN

Takeda, K. Nuclear Power Generation Division, Public Utilities Bureau, Ministry of International Trade and Industry, Tokyo

SWEDEN

Grimâs, U. Zoological Institute, Uppsala University, P.O. Box 561, 75122 Uppsala 1

SWITZERLAND

Pellaud, B. Gulf General Atomic Europe, Weinbergstrasse 109, CH-8006 Zurich

UNION OF SOVIET SOCIALIST REPUBLICS

Minasyan, R. G. Hydro-Technical Institute 'Toploelektroproekt' Spartakovskaya ulitsa 2a, Moscow

UNITED KINGDOM

Spurr, G. Planning Department, Central Electricity Generating Board, Sudbury House, 15 Newgate Street, London E. C.1

UNITED STATES OF AMERICA

Belter, W. G. Division of Environmental Affairs, United States Atomic Energy Commission, Washington D. C. 20545 153 LIST OF PARTICIPANTS

Swinebroad, J. Ecological Sciences Branch, Division of Biomedical and Environmental Research, United States Atomic Energy Commission, Washington D. C. 20545

Observers

FRANCE

Balligand, P. CEA, 29-33 rue de la Fédération, F-75 Paris 15e

Département de recherche fondamentale, Fourcy, A. Laboratoire de biologie végétale du CEN, Cedex 85, 38 041-Grenoble

Division qualité des eaux, pêche et Leynaud, G. pisciculture (C. T. G. R. E. F. ), 14 avenue de Saint-Mandé, F-75 Paris 12e

GERMANY, FEDERAL REPUBLIC OF

Hübschmann, W. Gesellschaft für Kernforschung mbH, Postfach 3640, D- 75 Karlsruhe

ITALY

Antonelli, A. Comitato Nazionale per 1'Energia Nucleare, Divisione di Protezione Sanitaria e Controlli, Viale Regina Margherita 12 5, 00198 Rome

Boeri, G. Comitato Nazionale per l'Energia Nucleare, Divisione di Protezione Sanitaria e Controlli, Viale Regina Margherita 125, 00198 Rome

JAPAN

Senshu, S. Central Research Institute of Electric Power Industry, Tokyo 154 LIST OF PARTICIPANTS

SWITZERLAND

B^gh, P. Motor Columbus Consulting Engineers, Parkstrasse 2 7, CH- 5401 Baden

Hopkirk, R. J. Elektro-Watt Engineering Services Ltd. , P.O. Box, CH-8022 Zurich

Mayor, J. C. Swiss Federal Institute of Reactor Research (EIR), CH-5303 Würenlingen

Representatives of International Organizations

ECONOMIC COMMISSION FOR EUROPE

Lopez-Polo, C. Energy Division, ECE, Palais des Nations, CH-1211 Geneva 10, Switzerland

INTERNATIONAL ATOMIC ENERGY AGENCY

Fowler, S. International Laboratory of Marine Radioactivity, Monaco

West, P. J. Division of Nuclear Safety and Environmental (Scientific Secretary) Protection, IAEA, Karntner Ring 11, A-1011 Vienna, Austria

NUCLEAR ENERGY AGENCY/OECD

Stadie, K. Nuclear Development Division, NEA/OECD, 38 boulevard Suchet, 75015 Paris 16e, France 155 LIST OF PARTICIPANTS

WORLD HEALTH ORGANIZATION

Parker, F. L, Vanderbilt University, (Consultant to WHO) Nashville, Tenn. 37235, USA

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