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Radiation versus : Nuclear in perspective

A comparative analysis of radiation in the living environment by Abel J. Gonzalez and Jeanne Anderer

Many people are anxious about releases of radio- Effects of Atomic Radiation (UNSCEAR).* The report active materials into the environment and their possible and its scientific annexes provide an authoritative and consequences for humanity. And yet throughout history dispassionate factual basis for examining radiation from people have lived in a changing radiation environment. all sources. One part is natural, the other man-made. Gradually, The comparison of radiation exposures in the living even this artificial radiation has been integrated in the environment is made in terms of radiation doses, and the steady radiation environment. Human interaction with results are expressed on an individual basis, with aver- this environment and the resulting modifications under- age (per coput) values and with extremes; and on a col- score the dynamic of change: today's radiation environ- lective basis, with values representative of the total ment differs from that of yesterday, and will be collective radiation impact from a source or practice. continuously transformed in the future. The paradox extends further: nuclear energy, a The natural radiation environment negligible contributor to the average dose of radiation Natural sources deliver the highest radiation dose that people receive, is the target of most public concern, people normally receive. (See accompanying graph.) whereas radiological , the largest sources of exposure from man-made sources, is prudently wel- comed for its benefits. There is even less apprehension about the most prodigious and least controlled sources of * Sources, Effects and Risks of , United Nations exposures: natural radiation sources. Scientific Committee on the Effects of Atomic Radiation, report to the UN General Assembly, with Annexes, New York (1988). In fact, it is virtually impossible for people to avoid exposures to radiation from their living environment, although some are more exposed than others because of their type of dwelling, where they live, their lifestyle, and the level of medical care they receive. Estimated annual doses per head from natural sources There is good reason to believe that a proper perspec- tive on the impact of nuclear energy in the living Other (from U-238 -40 environment emerges from looking with fact and fore- and Th-232 series) 0.33 mSv (14%) sight at radiation exposures from all radiation sources. -_»^^ / -87 \ ^^v. /"0.006mSv Insights gained from this comparative approach can help } \// to illuminate how humanity in and modifies the ^^\ cosmic) radiation environment and, more importantly, how E j^^\ 0.015 mSv reasonable judgements can be made about all human -•— Cosmic rays practices involving radiation. This article aims to con- 0.37 mSv tribute to this understanding. Its main source is the 1988 ( ^ report of the United Nations Scientific Committee on the x^ 1.3mSv(53%) ^~-

Mr Gonzalez is Deputy Director of the Division of Nuclear Safety and jx&ij Terrestrial total: 2.0 mSu (84%) Ms Anderer is a staff member in the Division. The article is adapted from a paper delivered in September 1988 at the 13th International | | Cosmic total: 0.4mSv(16%) Symposium of the Institute in London.

IAEA BULLETIN, 2/1989 21 Features

The average annual dose from natural sources is some documented areas where people are exposed to excep- 2.4 millisievert (mSv). This value is used here as the tionally high levels of terrestrial . In the reference level of natural . Hidden coastal areas of Kerala and Tamil Nadu in , within this statistical average are individual doses that -rich sands result in dose rates that can range from 1 to 5 mSv a year and, in extreme cases, to be up to 1000 higher than the normal radiation 1 Sv or;more. background. Elsewhere, in the Brazilian areas of The two major natural radiation sources are the Guarapari, Meaipe, and Pocos de Caldas, dose rates can cosmos, which irradiates people continuously with cos- be as much as 100 times the normal level. mic rays; and the 's , comprising radio- Since people spend most of their indoors, radia- nuclides that have existed mainly in the earth's crust for tion levels in dwellings are crucial to their exposures. billions of years. Irradiation occurs externally, through Practically speaking, most internal terrestrial irradiation exposures to extraterrestrial radiation and to radiation can be traced to one all-pervasive source: the odourless from radioactive natural materials remaining outside the gas radon. (Radon refers here to the nuclides ; and internally, through exposures to -222 and radium-220 and the chain of their decay natural radionuclides biologically present in the human products — so-called radon daughters.) body or incorporated in inhaled air and ingested On average, radon constitutes slightly more than half and drink. These distinctions are important, as terres- of the per caput dose from natural background radiation trial radiation is by far the largest source of natural (or 1.3 mSv per annum). For buildings there are several irradiation, contributing as much as 85% to the average channels for radon entry, the most important being the annual dose. Moreover, more than two-thirds of natural underlying or surrounding , and to a lesser extent, irradiation occurs internally, and a substantial fraction building materials, outdoor air, tap , and natural of such exposures can be technically controlled. gas. (See accompanying figure.) Indoor survey results The cosmic source. Effectively all the cosmic irradia- are only recently available and it is likely that exception- tion comes from one source: cosmic rays. Cosmic-ray ally high radon levels will be recorded for dwellings in levels are relatively stable at the earth's surface, but they many areas of the world which are either built on or with are affected by the earth's magnetic , the polar area highly radioactive materials. receiving more than the equatorial zones. More impor- Internal irradiation by terrestrial sources other than tantly, the level increases greatly with altitude, nearly radon is caused mainly by the intake of potassium-40, doubling every 1500 metres. Most people live at or close -210, and -210. Compared with radon to level, so there is little variation around the average exposures, their contribution to the average annual dose dose from cosmic radiation of 0.37 mSv. However, in level is small. As the intake of potassium-40 is high altitude cities (such as Denver, USA; Bogota, homeostatically controlled in the body, the variability Colombia; and La Paz, Bolivia) the annual cosmic doses range is low. Conversely, dietary patterns can influence to residents may be as much as four times the normal internal exposures to lead-210 and polonium-210. For level, reaching 1 mSv or more. example, these nuclides concentrate in seafood, and in Similarly, air travel subjects passengers and crews to Japan, where this is a preferred food, concentrations abnormally high cosmic irradiation, although for limited periods. Terrestrial sources. Terrestrial radiation can be found throughout the environment at various levels, depending on the activity concentration in such natural materials' as rocks, soils, water, air, food and even the Radon entry rates in a reference house human body. The most important terrestrial sources are potassium-40, rubidium-87 and the two series of radio- - 1.7 active elements arising from the decay of uranium-238 soil-diffusion 6.4 and thorium-232. Other radionuclides, such as those in building materials the uranium-235 decay series, have little effect on total t* ! radiation exposures. outdoor air 5 — — — Total range (1 -200! The radioactivity in certain rocks and soils is the main water 0.1 0.3 source of terrestrial irradiation to people while outdoors. M Generally, igneous rocks such as granite are more radio- _ _, active than sedimentary ones, but with highly radio- O 50 100 150 200 25( active shales and rocks as notable exceptions. Bequerel per cubic metre per hour

Recent surveys of outdoor external radiation levels in 23 Radon entry rates in a reference house. Parameters: countries, representing more than half of the world's 250 m3; 100 m2 surface floor area; 300 m2 wall-ceiling sur- population, revealed only minor variations. These face area; 450 m2 total surface area; 1 h-1 air exchange rate; 0.2 m thickness of floor-ceiling; 0.2 m thickness of studies suggest that about 95 % of the world's population external brick walls. lives in areas where the average annual dose of 0.4 mSv is distributed normally. Even so, there are well-

22 IAEA BULLETIN, 2/1989 Features

were found to be 5 times higher than those in the Federal conceal widespread variations in both the radiodiagnosis Republic of and India and 10 times higher than intensity and the impact of this practice. For example, those in the United States. An exceptionally large intake on average one X-ray is shared by 4000 people of these radionuclides is also known to occur in the in countries with the highest level of (as extreme northern hemisphere where tens of thousands of grouped by UNSCEAR) and by 170 000 people in coun- people subsist on mainly reindeer or caribou meat. tries with the lowest level. In the first group of coun- These , grazing on lichens that concentrate lead tries, on average there are 800 examinations annually and especially polonium, result in doses to this exposed per 1000 people; in the other group, there are less than group that are about 10 times higher than the normal 30 examinations per 1000 people. level. Lead-210 and polonium-210 have also been Independently of the practice intensity, individual detected in and in cigarette smoke. doses also differ, depending on such factors as the type of examination, the procedure adopted, and the perfor- mance efficiency of the equipment. For one thing, the Altering the radiation environment standard practice of mass chest X-rays is no longer con- Three major human practices unrelated to the genera- sidered relevant in most developed countries, whereas in tion of nuclear alter the radiation environ- many developing countries the situation appears to be ment: the expanding use of medical radiation, the opposite. In some Asian countries, for example, atmospheric testing of nuclear weapons, and industrial more than three-quarters of all diagnostic medical processes involving natural radionuclides. Related examinations are of the chest. More importantly, while occupational exposures seemingly play a lesser modify- radiographic techniques are used exclusively or exten- ing role. sively for chest examinations in most developed coun- Medical uses of radiation. Medical irradiation is a tries, data for the developing countries suggest major modifier of the radiation environment. The annual large-scale use of fluoroscopic techniques which can average dose is between 0.4 and 1 mSv, depending on result in 15 times higher doses to patients than the methodology used to estimate doses. . Medical radiation is used largely for diagnostic X-ray The lack of data on the use of in coun- examinations, including medical and dental radio- tries with less developed health care systems is a major graphy, diagnosis in involving inter- uncertainty constraining robust conclusions about doses nally administered radionuclides, and radiation from diagnostic X-rays. Another open question affecting in treating and other . dose levels is the performance efficiency of the diagnos- in the context of this article is unique. Unlike dental and tic equipment, particularly in many developing coun- other radiological examinations that people experience tries. Significantly, 30-70% of the equipment is frequently and indifferently, they regard radiation ther- estimated to be malfunctioning. apy as highly improbable, remote from their lives, and . Dental radiography represents unrelated to their radiation environment. As such, peo- only \% of medical exposures, with the dose for ple are not directly concerned with radiation from ther- individuals averaging 0.04 mSv per examination. This is apeutic practices. In effect, the risks of this high-level the most frequently used type of diagnostic X-ray exami- radiation practice have remained outside the agenda of nation; some 340 million procedures are performed the public debate about radiation hazards. Statistically, yearly, mainly in countries with well-developed health the reality is likely to be otherwise: some one-quarter of care systems. the population will probably require radiation therapy Diagnostic nuclear medicine. Worldwide the fre- during their lifetime. However, radiation exposures quency of nuclear medical practices has progressed from therapeutic medical practices are excluded from since these practices were introduced some 30 years the comparative analysis. ago. In a few countries, the has declined Unfortunately, reliable and well-defined information periodically, because of the alternative use of computer on radiation in medical practices are available mainly for for brain scans and other, non- the populations of the well-developed countries, which ionizing radiation techniques such as . represent less than one-quarter of the 5 billion global Exposures represent only 4% of all medical irradiation. inhabitants. Sparser data exist for yet another quarter of All medical irradiation practices differ among and the population. For more than two and a half billion within countries; diagnostic nuclear medicine is no people, virtually nothing is known about what medical exception. The type of radionuclide used, (e.g., irradiation they receive, if any. The information gap -131 versus -99m) accounts for the suggests a truly disproportionate situation, leading some wide range in the average annual doses. experts to conclude that nearly three-quarters of the . Since 1945 more than 400 people in the world have not benefited from substantial nuclear explosions have been carried out in the diagnostic radiological assistance. to test nuclear weapons, most recently in Diagnostic radiography. Diagnostic X-ray examina- 1980. (See graphs, page 24.) Atmospheric testing tions account for nearly 95 % of the total doses people reached two peak periods: 1957-1958 and 1961-1962, received yearly from medical irradiation. These totals each with 128 tests but with the yield for the latter period

IAEA BULLETIN, 2/1989 23 Features

about four times higher than the earlier peak. Irrespec- tive of judgements about the ethics of this practice, the Number and yield fact is these tests occurred, injecting substantial amounts of atmospheric nuclear weapons tests of radioactive materials into the environment. The fallout from atmospheric testing contains several Year hundred radionuclides, but only four are of concern to 1945-51 )26 present and future populations: -14 (with a half- of 5730 years), -137 (half-life 30 years), 1952-54 |31 -90 (half-life 30 years) and (half-life 12 years). Currently, carbon-14 accounts for some two- 1955-56 thirds of these exposures; given the half-life of the other radionuclides, by the end of this century only carbon-14 1957-58 1128 will be important. A very small contribution from -239, plutonium-240, and -241 1959-60 (0.1%) to the dose rate will occur over thousands of years. Individually, the average annual dose is only 1961-62 128 0.01 mSv but the commitment for future 1963 generations is the highest from man-made sources. Industrial processes and natural radionuclides. 1964-69 Industrial processes, such as produc- tion and phosphate , bring to the earth's surface 1970—74 materials with above average concentrations of natural radionuclides. Other processes, such as combustion 1975 and phosphate fertilizer production, treat materials with average or above average amounts of natural radio- 1976-80 nuclides, concentrating them in one or more products or

I I I I I I I by-products. The impact of these exposures on the radia- 20 40 60 80 100 120 140 tion environment has not been noticeable. However, Number of tests these exposures are not systematically monitored, and the accelerated growth patterns associated with many processes, particularly energy production, strongly sug- gest a sizeable impact in the decades ahead. In fact, elec- Year tricity generation from energy sources other than 1945-51 i0.8 nuclear results in radiation exposures to the public, and the radiological impact from some conventional power is comparable to that from plants. (See accompanying diagram.)

1959-60 l° Estimated collective dose commitments due to systems of electricity production 1961-62 1340 (normalized)

1963

1964-69 — 4.0 coal 1970-74 12.2

1975 2.5 nuclear

1976-80 14.8 2.0 geothermal

I I I I 2.0 peat man- per 100 20 40 60 80 gigawatt year Total yield in megatons 0.5 oil of electricity 0.03 natural gas generated

24 IAEA BULLETIN, 2/1989 Features

In many countries coal is a viable energy option for Occupational exposures. Natural radiation is also meeting the increasing demand for electricity. In fact, responsible for related occupational exposures. Obvi- nearly 70% of the 2.7 x 109 tonnes of coal equivalent ously, airline flight crews encounter exceptionally high produced worldwide in 1981 was used for generating levels of cosmic irradiation. From information available electricity, 20% for carbonization, and 10% for for 1979-83, the annual individual dose approached a domestic heating and cooking. Coal, like most natural possible maxima of 15 mSv. Workers in office build- materials, contains natural radionuclides that are ings, stores, and workshops with high radon levels and released during combustion. How much is released even domestic workers in homes with high radon con- depends on the activity concentration in the coal, the ash centrations also incur natural dose levels which could be content, combustion temperature, the partitioning surprisingly high — much higher than the occupational between the heavy slag-ash at the bottom of a furnace dose limits used for the nuclear industry. and the lighter fly-ash, and the efficiency of the emission Data on occupational exposures from industrial control devices. Basically, two types of coal-fired power activities involving natural radioriuclides are available plants exist worldwide: "old" plants that release about only for a few countries and even in these cases they are 10% of the fly-ash, and "modern" plants equipped with not well-defined. Estimates can therefore only be sophisticated control devices that release only roughly made. For workers at coal-fired plants, 0.5% of the fly-ash. Assuming that two-thirds of the exposures are caused mainly by the of air- plants worldwide are characteristically old, the genera- borne fly-ash. Roughly, the collective dose worldwide is tion of a gigawatt year of would result 60 man Sv. Doses from processing and of rock in a normalized collective dose commitment of 4 man Sv are estimated collectively at 20 man Sv. For per gigawatt year of electricity generated. those engaged in handling phosphate fertilizers, world- Coal usage also gives rise to other radiation hazards. wide the collective dose may be as high as 50 man Sv. Much of the fly-ash collected by emission control Data on occupational exposures for the cycles devices ends up being used to manufacture cement and associated with weapons testing are not readily avail- concrete, so that the use of this radioactive material in able. However, given the radiotoxicity of some of the construction can enhance radiation exposures. What is radionuclides involved and the fact that these practices not commercially applied is frequently dumped in the are not always covered by the same stringent radiation vicinity of the power , posing potential measures associated with the peaceful uses of hazards from resuspension and contamination of surface nuclear energy, the radiological impacts seemingly are and underground . Unfortunately, radiation dose not insignificant. assessments for these practices are lacking. For those occupationally engaged in all uses of medi- Geothermal energy is another source of radiation cal irradiation, the annual collective dose equivalent is exposure. Although its share in electrical energy con- 1 man Sv per million population. Although medical sumption is small, its relative importance is expected to radiation practices are increasing worldwide, the limited grow. Most of the activity concentrated in the geother- trend data suggest decreases in the annual doses, by mal fluids comes from the uranium , specifi- 10-20% each decade. cally from radon. Based on measurements of radon in geothermal fluids for several countries, the normalized Radiation and nuclear energy collective dose commitment is estimated at 2 man Sv per gigawatt year of electricity generated. The following explores radiation levels for the nor- mal generation of nuclear electricity. Since the first Peat is burned for energy production in several areas commercial began operation in of the world, notably in Nordic countries. Flowing sur- 1956, the nuclear power industry worldwide has face and ground waters carry the natural radionuclides accumulated more than 5000 reactor-years of relatively into the peat bogs, where they are eventually absorbed safe operation. However, nuclear generation of electric- in the peat . Little information is available on the ity, like all human endeavours, has the potential for acci- environmental discharges of natural radionuclides from dents, although a highly improbable one. The accident peat power plants. Assuming that the combustion of 5 billion of peat is needed to generate at -4 nuclear power unit in the 1 gigawatt of electrical energy a year, the normalized underscored this possibility, essentially taking the collective dose commitment is estimated at 2 man Sv per analyses of severe accidental exposures out of the gigawatt year of electricity generated. Over the long hypothetical realm. Given the uneven distribution of term, the storage and disposal of uranium-rich peat ash exposures it is questionable whether exposures from the may have the greatest radiological impact. Chernobyl accident can be compared with those from other steady sources, including natural radiation. Even Both oil and natural gas play a lesser role in radiation so, such comparisons are useful for understanding the exposures from worldwide. The impact of this extreme case. normalized collective dose commitments are compara- Since the issue of disposal of radioactive nuclear tively low: 0.5 and 0.03 man Sv per gigawatt year of wastes commands attention in the public debate about electricity generation, respectively. the development of nuclear energy, it is useful to con-

IAEA BULLETIN, 2/1989 25 Features sider briefly the potential radiological impact from these and Marcoule, both in . Together these facilities wastes. Frequently, public concern stems from the mis- reprocess only a small percentage of the world's irradi- conception that radioactive wastes cannot be controlled ated fuel. The rest has been stored, pending policy deci- or managed safely over long periods. These concerns sions in countries on reprocessing. Long-lived nuclides contrast sharply with the views of specialists, who are (e.g. carbon-14, tritium, -85, iodine-129) are of confident of technical solutions. In short, the radiologi- major concern in reprocessing effluents. dis- cal impact from the proper disposal of the wastes result- charges from reprocessing plants are responsible for ing from an adequate treatment of the spent most of the collective dose commitment of 1.27 man Sv is so negligible that even under the most pessimistic per gigawatt year of electricity generated. assumptions the resulting doses to the (hypothetical) Transport. Exposures to the local and regional popu- population living thousands of years from now would be lation from transport along the fuel cycle chain are com- effectively nil. For this reason, the subject of waste dis- paratively low, with a collective dose commitment of posal is not considered in the comparative analysis of about 0.1 man Sv per gigawatt year of electricity radiation levels. generated. Routine generation of nuclear electricity. Normally, Occupational exposures. Exposures to those engaged nuclear electricity generation releases only negligible at the various facilities of the nuclear power industry amounts of radioactive materials into the environment. differ markedly. Maintenance workers and especially On average, the annual dose from all practices in the repair personnel at nuclear power plants receive the is only a tiny fraction (less than 0.1%) highest doses. Uranium miners, particularly those - of that from natural radiation. ing underground, face radiation hazards posed by radon Exposures from nuclear energy production occur at and its daughters. all stages of the fuel cycle, and radiation doses to the Long-term prospects. The fuel-cycle operations also public and workers are assessed over and time. give off much longer lived radionuclides which remain (See accompanying graphs.) in the biosphere for thousands of years. Assuming that and milling. Operations at mines these radionuclides deliver doses over a hypothetical give rise to radioactive effluents mainly in the vented air infinite time, the collective dose commitment is 69 man from underground mines or from the releases for sur- Sv per gigawatt year of electricity generated. However, face mines. The stockpiles of ore and other materials only 10% of this total will be delivered over the next 100 from uranium extraction are responsible for atmospheric years. Over the next 10 000 years, radon exposures from releases over the short term and to a greater extent for mill tailings would commit as much as 150 man Sv per the longer period. The current practice is to store tail- gigawatt year of electricity generated. ings in open uncontained stockpiles or behind The Chernobyl accident: Beyond the hypothetical engineered dams or dikes with a solid or liquid cover. realm. Although the radiological impact from the rou- Radon released over 5 years from mining and milling tine generation of nuclear electricity is very small, con- results in dose commitments of 0.1 man Sv per gigawatt cerns remain about the consequences of potential year of electricity generated. Collective dose commit- accidents. But now, radiation exposures from the Cher- ments to local and regional populations from mining and nobyl accident can be viewed through a realistic lens: the milling are 0.3 and 0.04 man Sv per gigawatt year of extensive information available from international and electricity generated, respectively. national groups collecting and analysing data on radio- Fueljabrication. Comparatively speaking, fuel fabri- logical fallout since the Chernobyl accident. In particu- cation gives rise to very few atmospheric and aquatic lar, UNSCEAR, together with the World Health discharges. Most uranium compounds are solid, and can Organization and the IAEA, assessed the global radio- be easily removed from airborne effluent streams. The logical impact of the accident, based on data from nearly collective dose commitment to the public is 0.003 man 40 countries. Sv per gigawatt year of electricity generated. The accident. The accident on 26 April 1986 at Reactor operation. Doses to the public from reactor Unit 4 of the Chernobyl nuclear occurred operations have steadily declined over the past few during a low test, when safety sys- years, even as electricity generating capacity increases. tems were switched off. The ensuing uncontrolled insta- This is attributed partly to the extensive radiation protec- bilities caused explosions and fires that severely tion systems at nuclear power plants and partly to damaged the reactor core and containment structures. increased plant operational efficiency. For example, Radioactive gases and were environmen- atmospheric releases of carbon-14 from reactor opera- tally released: 25% the first day, and the rest over the tions are now nearly half of those UNSCEAR reported next nine days. The fire was extinguished and the reactor in 1982. This is significant, as carbon-14 accounts for core was sealed off by the tenth day after the accident. much of the public's collective dose commitment of 2.5 The reactor is now permanently entombed in a sarcopha- man Sv per gigawatt year of electricity generated. gus which confines the residual radioactivity. Reprocessing. A small number of reprocessing plants The initial releases of radioactive materials spread are operating commercially, including (form- with in a northerly direction; subsequent releases erly Windscale) in the and La Hague dispersed towards the west and the southwest, and in

26 IAEA BULLETIN, 2/1989 Features

Estimated collective dose commitments over short term to local and regional population and occupational exposures due to nuclear fuel cycle (normalized)

10.0 public (local/regional) • total ~4 3.0 occupational total ~12 8 2.5

2.0

5 en 1.5

1.0

£ 0.5

mining mine/mill fuel reactor reprocessing trans- tailing piles fabrication operation portation (radon - over 5 years

Estimated collective dose commitments over long term due to nuclear fuel cycle (normalized)

mine/mill tailing man-sievert per gigawatt year of electricity generated (radon) next 100 years 1.5 next 10 000 years 150

globally dispersed nucl ides/waste next 100 years all time 69

local/regional public exposures next 100 years all time

occupational . exposures next 100 years all time

I ^1 40 60 80 100 120 40 60 Note: All values are rounded.

IAEA BULLETIN, 2/1989 27 Features

Radiation doses: How much, where, and why. The Regional average effective dose commitment findings on the major radionuclides released indicate from Chernobyl widespread variations in the estimated doses to the pub- lic. The doses committed from the accident will be deli- 70 -i 30-year effective dose equivalent vered mainly over the next 30 years or so and mostly due -

0.1 • nomic Co-operation and Development published the findings of its evaluation of the radioactive fallout 0 recorded in the OECD countries from the accident. It concludes that "... individuals in the OECD countries are not likely to have been subjected to a radiation dose significantly greater than that received from one year of other directions as well. Long-range atmospheric trans- exposure in the natural radiation background. As a con- port spread the released radioactivity throughout the sequence, the lifetime average risk of radiation-related northern hemisphere. But no airborne activity was harm for the individual members of the public has not deposited in the Southern Hemisphere. Fallhout of air- been changed to any noticeable extent by the accident; borne radioactivity was governed mainly by sporadic the number of potential health effects ( and rainfall. Iodine-131, caesium-134, and caesium 137 genetic effects) that can be derived by calculating collec- were the more relevant radionuclides deposited, giving tive doses will not constitute a detectable addition to rise to radiation exposures externally from ground con- natural incidence of similar effects within the tamination and internally from the ingestion of contami- population". nated food. The response. The forceful measures Adding it all up initiated by Soviet authorities immediately after the acci- dent and the ongoing public health programmes have A comparative analysis of radiation in the living substantially reduced the risk of public exposures to environment can now be made on an individual basis and radiation. Decontamination measures, topsoil removal, collectively for the dose commitments to the world's food and livestock monitoring and destruction, and population. A clear factual basis emerges. agricultural restrictions have reduced radiation dose • The contribution of nuclear energy to the radiation levels in the area to well below worst-case assessments environment can be considered negligible: it is orders of made shortly after the accident and before radiation magnitude lower than the exposure an individual emergency handling had any impact on the contaminated receives from all other sources. From the perspective of areas and their populations. By summer 1987, 60 000 the collective dose commitment, under normal condi- houses and other structures in some 600 population tions and excluding the commitment from the very long- centres had been decontaminated. lived radionuclides, public global exposure from a year Outside the Soviet Union, countermeasures taken in of production of nuclear electricity is equivalent to many countries immediately after the accident effec- slightly less than one additional hour of exposure to tively lowered both individual and collective doses. natural background in that year. When these radionu-

28 IAEA BULLETIN, 2/1989 Features

elides (mainly carbon-14) are included, the is equivalent to roughly 37 additional hours of Collective dose commitments natural irradiation. (See graphs.) (millions of man ) Even in the extreme case of Chernobyl, the collective and equivalent time of natural background exposure dose commitment (mainly from caesium-137, delivered Excluding commitment from very long-lived radionuclides over the next 30 years) is equivalent to only 21 days of additional exposure to the natural background. Natural background 11 1 year • Medical irradiation is a major modifier of the radia- tion environment. The average annual dose from the uses of medical radiation, particularly diagnostic X-ray examinations, is 20-45% of that an average person receives yearly from the natural radiation background. Nuclear power The frequency and intensity of these practices vary dra- Chernobyl production 0.001 accident 0.6l matically among the population, with typical individuals | 1 hour receiving twice as much irradiation from medical uses 21 days than from natural exposures. Collectively, the exposures from medical irradiation are equivalent to 1.4-6 months Medical of additional exposures from the natural background. exposures All nuclear test 1.4-6 months explosions 5 Moreover, medical irradiation is likely to increase over 6 months the next several decades, as people live longer and medi- Occupational cal services reach more of the population in the develop- exposure 0.01 9 hours ment world. By 2000, the collective dose will probably have increased by 50% and by 2025 by 100%. Including commitment from very long-lived radionuclides • Obviously, irradiation from carbon-14 affects the dose commitment from the atmospheric nuclear tests Natural background 11 that have occurred over the past few decades. When the 1 year human exposure from this very long-lived radionuclide Chernobyl Nuclear power is included in the estimate, the collective dose commit- accident 0.6 production 0.03 ment is equivalent to 28 months of additional natural 21 days 37 hours irradiation. Medical To complete the picture, human exposures that are exposures 5 1.4—6 months incurred occupationally are equivalent to slightly less than 9 hours of additional natural irradiation yearly. Occupational exposure 0.01 9 hours

All nuclear test explosions 26 Present annual doses for 28 months typically exposed individuals (mSv)

Low estimates Natural background

Present annual (per caput) individual radiation doses All nuclear test explosions 0.01 from natural and man-made sources

Natural background

Medical (diagnostic) Occupational Nuclear power production 0.01

High estimates

Natural background All nuclear test explosions 0.01 mSv Occupational 0.002 mSv

Medical {diagnostic} All nuclear test explosions 0.01

Medical (diagnosticl

Nuclear power cupational production 0.0002 mSv Nuclear power production 0.1

IAEA BULLETIN, 2/1989 29 Features

The implications nium tailings could be significantly reduced; reduction factors of more than 6 million are considered feasible. The problem. Logically, it can be Similar trends can be found throughout the fuel cycle. concluded that the normal generation of - Doses from operations are declining ity does not significantly change the radiation environ- despite increasing capacity, mainly because of advanced ment. Properly viewed, the consequences of the protection systems and the expanded use of robots. The Chernobyl accident are not as catastrophic as often mis- backend of the fuel cycle is no exception: an important takenly depicted. Why, then, has the impact of nuclear role for fuel reprocessing is to diminish the radiological energy been so deeply misunderstood? One possible impact from the direct disposal of spent fuel elements. explanation is that people view radiation somewhat The dominant trend in reprocessing is towards greater myopically: it is considered to be primarily a nuclear- efficiency, particularly at Sellafield. related agent, offering no tangible benefits. Indeed, Radiation exposures and radiation safety. Surpris- exposures from other human practices are welcomed or ingly, the marked variations in contributions from radia- tolerated. For a patient, the benefits of medical irradia- tion sources and the potential for controlling these tion are apparent. For an unquestioning person exposures have had a relatively minor influence on set- accustomed to the convenience of electricity, the advan- ting priorities in radiation safety. Ironically, radiation tages of nuclear energy and the disadvantages of a safety efforts have concentrated mainly on nuclear nuclear phase-out are less obvious. energy, effectively ignoring or underplaying the much The communication problem is serious, caused by the larger hazards posed by other radiation sources. lack of common levels of understanding between the Given the enormous variation in radiation levels and specialists knowledgeable about the low-level exposures the potential for reducing exposures to all radiation from nuclear energy and a concerned public whose sources, it is regrettable that these considerations have uneasiness is not easily soothed by bland expert reassur- had such a minor influence on the prioritization of radia- ances. There is a need to frankly address public concerns tion safety. about radiation, communicating factually in a language In principle, radiation protection standards exist for that fosters understanding, trust, and credibility. The occupational exposures from all practices involving UNSCEAR evaluation provides an opportunity for radioactive materials. These are strictly enforced in the bridging this gap. nuclear industry, whose staff includes many highly- Dose reductions: vast possibilities. Additionally, trained radiation protection professionals. Generally, many possibilities exist for reducing radiation doses such high levels of protection do not prevail elsewhere, without jeopardizing the benefits of radiological prac- with notable exceptions such as technically advanced tices. Efforts to control natural irradiation show promis- hospitals. Even so, the occupational exposures to wor- ing results. For example, the application of aluminium kers at nuclear installations are on the order of one mag- foil to walls built with radioactive alum shale-based con- nitude higher than those recorded for other radiation crete has reduced the radon entry rate nearly 50%, and practices, such as medical irradiation. These numbers wall surface coatings have lowered radon rates by should be interpreted cautiously. For one thing, 20-80%. There are also possibilities for eliminating record-keeping at nuclear installations is comprehensive unnecessary medical irradiation. New diagnostic tech- and stringent. Moreover, sophisticated occupational niques, such as ultrasound and magnetic resonance monitoring systems are enforced throughout the nuclear iniaging, are replacing X-rays, particularly for the fuel cycle; this sophistication is unmatched elsewhere. spine, kidney, and gall bladder. Technological progress Dose reductions versus increases: the tradeoff. over the past two decades has paved the way for much People are often confronted with a tradeoff involving lower doses to patients. By far, the largest reduction is radiation exposures: to opt, say, for a relatively high feasible through the replacement of chest fluoroscopy dose from a computer tomography scan, or to incur the and photofluorscopy with radiography, by factors of 20 risk of an undetected and untreated illness. Medical and 5, respectively. Some simple and low cost methods specialists face a similar conflict: an underexposed known to offer modest dose reductions involve collima- radiograph that cannot be interpreted is of no benefit to tion, added beam filtration, and gonadal and a patient, even though the is low. shielding during radiographic examinations. Training in Collectively, the goal of avoiding radiation exposures the use, calibration, and quality assurance of medical or reducing them per se is not always the ideal in a equipment could reduce doses, possibly by as much as dynamic world in which populations are growing, econ- 50%. In many countries more than half of those per- omies are expanding, people are living longer, and the forming radiological examinations have little or no for- aspirations for a quality life spread throughout the globe. mal training. Over the next 30 years, the world faces the steepest In spite of its small contribution to the radiological growth in population, from 5 billion to slightly more impact, this progress can be and is being matched by the than 8 billion in 2015. The trend towards urbanization nuclear power industry. According to the Nuclear continues worldwide, with the urban population Energy Agency of the Organisation for Economic Co- expected to be some 57% by 2015, in contrast with the operation and Development, radon exposures from ura- present share of 30%. Traditionally, city dwellers have

30 IAEA BULLETIN, 2/1989 Features received a higher share of medical services than the rural population. The recent phenomenon of population aging, particularly in the developed countries, necessar- Radiation doses ily increases demands for medical services. Whereas in 1980 some 380 million people worldwide were 60 years Absorbed dose: The amoJnt of radiation energy that is old or more, by the year 2000 the number could be absorbed per gram of tissue. It is expressed in a unit called the (Gy). 607 million, reaching nearly 1200 million by the year Dose equivalent: The absorbed dose weighted to take 2025. into account different types of ionizing radiation and their Social and economic development requires energy, . It is expressed in a unit called the sieved (Sv), especially electricity. Nuclear and coal are viable and the submultiples millisievert (mSv, microsievert options for meeting large-scale electricity demands, but 0*Sv), etc. For most practical applications, the weighting is unity; that is, one sievert is equal to one gray. both result in radiation exposures. Consumers in the Effective dose equivalent: The dose equivalent industrial and domestic sectors are shifting from oil to weighted to express the sensitivity of different human electricity, not only for the greater organs to . Since it is a (modified) but also for the economic advantages associated with the dose equivalent, it is also expressed in sievert. high end-use efficiency of electricity. While the other Collective effective dose equivalent: The effective dose equivalent to a group of people from a source of fossil and the renewables can contribute to supply, radiation. It is expressed in a unit called man sievert for most countries nuclear and coal are the most viable (man Sv). options for meeting these large-scale demands. The projected increases in nuclear generating capac- ity will increase the levels of radiation exposures. Note: In practice, these quantities are expressed as rates (for Viewed from a proper perspective, these exposures can example, mSv per hour, or man sievert per year). If the rates are be seen as representing then, as now, only a small per- summed up over time, the resulting quantity is generally called centage of the living radiation environment. However, commitment. Unless specified, the integration time for a dose commitment is theoretically infinite; for example, the collective an expanded role for coal generated electricity is dose commitment is the sum of all doses received by all attended by not only larger radiation exposures but also individuals (present and future individuals over all time) as a the myriad environmental hazards .of result of a practice or action involving . combustion.

IAEA BULLETIN, 2/1989 31