RC-5a

Radiation Protection in NORM industries

J. van der Steen and A.W. van Weers NRG, Radiation & Environment, Arnhem, The Netherlands Radiation Protection in NORM industries

J. van der Steen and A.W. van Weers

NRG, Radiation & Environment, P.O Box 9035, 6800 ET Arnhem, The Netherlands E-mail: [email protected]

1. Introduction

The International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (the BSS) [1] specify the basic requirements for protection of health against exposure to ionising radiation. They are based on the latest recommendations of the International Commission on Radiological Protection (ICRP) [2] and regulate both 'practices'1 and 'interventions'2.

Humans incur radiation doses from cosmic rays and radiation generated by x-ray machines and particle accelerators, or from exposure to radionuclides, either by external irradiation or by incorporation in the body. Some radionuclides are primordial, and they are usually referred to as 'natural'. Others have been created as a result of practices and are usually referred to as 'artificial'. The BSS apply to both natural and artificial sources of radiation. This refresher course deals only with radiation protection against natural sources of radiation.

Natural radionuclides are ubiquitous in the environment. As a result of the widespread presence, a certain amount of radioactivity is always present in substances. A comprehensive review of the concentrations of naturally occurring radionuclides in soil has been published by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in its 2000 Report [3]. In most naturally occurring radioactive materials (NORM), several or all of the radioactive isotopes of the three natural decay series (235U, 238U and 232Th) and 40K are present in small concentrations in the natural matrix. In the original ores, or formations in the case of the oil and gas industry, the radionuclides within a decay series are more or less in radiological equilibrium. By industrial physical, chemical and thermal processes the natural equilibrium of the radionuclides can be disturbed resulting in either an enrichment3 or decrement of some radionuclides compared to the original matrix. Breaks in the natural equilibrium occur at the isotopes with long half-lives. In table 1 these radionuclides are given together with their half-lives.

Table 1. Long-lived natural radionuclides (T½ > 1 y), with their half-life (y) 238U series 235U series 232Th series 238U 4.5 109 235U 7.0 108 232Th 1.4 1010 234U 2.4 105 131Pa 3.3 104 228Ra 5.8 230Th 8 104 227Ac 21.8 228Th 1.9 226Ra 1600 210Pb 22.3

1 A practice is defined as any human activity that introduces additional sources of exposure or exposure pathways or extends exposure to additional people or modifies the network of exposure pathways from existing sources so as to increase the exposure or the likelihood of exposure of people or the number of people exposed. 2 An intervention is defined as any action intended to reduce or avert exposure or the likelihood of exposure to sources which are not part of a controlled practice or which are out of control as a consequence of an accident. 3 This is usually referred to as technologically enhanced naturally occurring radioactive materials (TENORM).

1 The presence of NORM can lead to radiation doses that are not insignificant from a radiation protection point of view. Occupational exposure from natural radiation is, in the UNSCEAR 2000 Report [3], estimated to contribute more than 80 percent of the world-wide annual collective dose from occupational exposure, uranium mining excluded. Also individual doses of workers exposed to NORM in industry can be significant. When the operator of a practice, or the regulatory authority, is not aware of the problems associated with enhanced levels of NORM in raw materials, products or residues and when no protective actions are taken, the doses to workers may even exceed the occupational dose limit. The relevant routes of exposure of workers to NORM are external radiation and internal exposure, either by inhalation of radon in workplaces or by inhalation of aerosols in dusty working conditions.

Until the 1970s radon and its progeny were regarded as radiation health hazards encountered only in the mining and processing of uranium ore. This notion has changed markedly as a result of increasing efforts made in many studies to measure radon in dwellings, mines other than uranium mines, and workplaces suspected of having high atmospheric radon levels. In temperate and cold regions, energy conservation measures have been taken in buildings that have resulted in reduced ventilation rates. This increased radon concentrations, particularly in winter months. This rise in the indoor air concentration of radon was recognized as a radiation health hazard, potentially causing an increase in the incidence of lung cancer. Radon thus became a concern not only in underground mines but also in buildings in areas with elevated levels of radon in soil gas or in buildings constructed with materials containing significant levels of radium. According to the UNSCEAR 2000 Report [3], environmental radon accounts for half the human exposure to radiation from natural sources.

It is not only radon that gives rise to environmental problems with natural radionuclides. Mining results in large volumes of mine tailings that may contain enhanced levels of natural radionuclides. This is not only restricted to uranium or thorium mining, but can also occur with other mines, such as copper mines, gold mines, et cetera. Leaching of the radionuclides can result in contaminated groundwater, and thereby expose members of the public. In many cases, these mines have been operating for many decades without any knowledge of the radiological aspects of the mining activity. Mine tailings even exist for centuries, from mining activities in the past, giving rise to radiological legacies that have been detected only in recent times. Other examples are coal mining, when a high concentration of 226Ra in the produced water can give rise to considerable radioactive contamination of the environment. In such cases, ponds can be heavily contaminated with radioactive deposits. Also the production of fertilizers by processing phosphate ore has resulted in large landfills with phosphogypsum, which contains elevated concentrations of 226Ra. An overview of the worldwide scale of potential environmental problems with NORM has been given in IAEA Technical Report Series No. 419 [4].

Within the European Union, Council Directive 96/29/Euratom [5] paid specific attention to natural sources of radiation. EU Member States are obliged to identify the work activities that cannot be ignored from a radiological protection point of view and declare parts of the Directive applicable in their national regulations with respect to natural sources. This has increased the awareness of the potential problems enormously, and most of the EU Member States have now implemented regulations dedicated to natural sources of radiation in their national legislation. Also the BSS [1] addresses the control of exposure to natural sources. In the last decade a number of international meetings were dedicated to the radiological consequences of NORM, leading to a world-wide cognition of the issues involved. The IAEA has provided comprehensive recommendations on occupational radiation protection in general in three Safety Guides [6-8]. Occupational and public exposure to NORM is addressed in several IAEA reports, which have been published recently or are in preparation [9-17].

Nevertheless, there still is a backlog in the knowledge of the radiation protection problems with NORM, compared to artificial radionuclides. In many countries, NORM industries traditionally have not been subject to radiological protection measures. Many data on radionuclide concentrations in raw materials, residues and waste streams, and data on exposure of workers and the public are still lacking.

2 Consequently, there is a general lack of awareness and knowledge of radiological hazards and exposure levels by legislators, regulators and operators (particularly operators of small businesses). This persists in many cases, despite the number of studies and international meetings dedicated to the radiological consequences of NORM in the last 10 to 15 years. The IAEA Technical Report 419 [4] is based mainly on a comprehensive study for Europe [18] and data from North America, but it concludes that data from less developed countries are still scarce. According to this Report, the circumstances in these countries are of particular concern, namely: - A large proportion of the world mining operations and to a lesser degree also milling operations are located in less developed countries; - Environmental and radiation protection standards may be less stringent, or their enforcement may be less strict; - Artisanal mining and milling and other artisanal industries with less stringent occupational health and safety precautions are widespread. As opposed to developed countries, such activities are still more integrated with private and family life, potentially leading to exposure of the public (e.g. residential/garden plots on or adjacent to 'industrial' sites and re-use of contaminated materials to optimise resource use); - Limited or no resources are available to deal with legacy wastes and for upgrading plants and waste management infrastructure; - Responsibilities for legacy wastes and contamination are unclear [4].

Three main points are relevant to the overall management of exposure to NORM, namely awareness, regulations and guidance. As far as the general objectives of control of occupational and public exposure to ionising radiation concern, one can conclude that due to the above-mentioned developments control of exposure to NORM leads to reduction of collective and individual doses and, generally, to compliance with dose limits. Yet, there are some specific issues that make it difficult to reach compatibility with control of exposure to artificial radiation. These issues are partly related to the intrinsic differences in regulating artificial and natural radionuclides, and partly to the arrearage in a structured approach to introduce radiological protection optimisation measures for exposures due to NORM industries.

2. Examples of NORM affected industries

A large variety of industries is affected by the presence of NORM. Examples of industries and the associated problem areas are given in table 2. In fact, almost every industry with a large turnover of materials has some problems with NORM. The original concentration of radionuclides in the raw material may be small, but when hundreds of thousands of tons per year of raw materials are processed, like for instance in the phosphate industry, the steel industry or the oil and gas production, the concentration of radionuclides by the process can lead to problems. Examples are, for instance, phosphogypsum piles from the phosphate industry, containing the radium from the original ore, the waste from the steel industry, which is enriched in 210Po, and sludge from the oil and gas industry, enriched in 226Ra as well as in 210Pb and 210Po. The inner parts of the installations in the latter industry can be contaminated with the same isotopes, because the decrease in temperature and pressure of produced water causes precipitation of salts of these isotopes on the inner walls of tubing and other installation parts. This is normally not a problem, but it causes a hazard for internal contamination when the installation is opened for maintenance. An overview of industrial problems with NORM is given in Annex 1.

An example of this kind in the Netherlands is the production of elemental phosphorus by the electro- thermal process as presented in figure 1. The activity concentration of the ore is about 1 Bq/g 238U. Due to the high temperatures, 210Po evaporates and condensates on the precipitator dust. This dust is brought back into the process and thus creates a loop, causing a final activity concentration of about 1000 Bq/g 210Po (photos 1 and 2). Of this material, about 1000 ton per year is purged and processed as radioactive waste, and it is obvious that the main radiation protection measures deal with avoiding exposure to this dust. From the 600,000 tons phosphate ore, about 80,000 tons of elemental phosphorus is produced. About the

3 same amount as the original ore is slag (photos 3 to 6). This residue contains the original 238U in a concentration of approximately 1 Bq/g and is used for road construction (photos 7 and 8).

Table 2. Examples of industries affected by NORM Sector Type of industries Problem areas Mining and processing (physical, Uranium, thorium, gold, silver, Radon, dust inhalation, mine chemical, thermal) copper, nickel, iron, aluminium, tailings, residues, waste molybdenum, tin, titanium, tungsten, vanadium, potassium, rare earths, phosphate, coal, etc Mineral sands Zircon, monazite, etc Dust inhalation, external radiation Thorium industry Welding rods, gas mantles, lamps, Dust inhalation, residues etc Exploration and production Oil and gas production Dust inhalation during maintenance, waste Geothermal energy Radon, waste Electricity production Burning of coal, oil, peat Fly-ash, maintenance work Workplaces Show caves, thermal baths, etc Radon Recycling and decommissioning Scrap, slag wool, etc Dust inhalation, residues, waste Other processing or Water treatment, sewage Radon, dust inhalation, residues, manufacturing treatment, spas, paper and pulp, waste, sludge ceramics, paint and pigment, metal foundries, optics, refractory and abrasive sands, electronics, building materials

Another typical example of unexpected problems with NORM has been encountered in scrap yards. Many scrap yards in the Netherlands have installed portal radiation monitors at the entrance for control on radiation sources in the scrap. Over the last few years an increasing number of cases were detected by the portal monitors where insulation slag wool adhering to the scrap was identified as the radiation source. It appears that this wool most likely has been produced from a by-product (slag) of tin smelting between the years 1948 and 1960. It has been applied in widely ranging constructions and installations. Examples are insulation doors, bakery ovens, small steam generators and a large coal-fired power plant (photos 9-13). Average activity concentrations in the slag wool are 4 and 11 Bq/g for nuclides from the 238U and 232Th decay chains respectively. Radiation exposures at dismantling of slag wool insulated installations are estimated to remain below 2 mSv/a and are dominated by internal exposure by inhalation of dust. Respiratory protection reduces the exposures to small doses from external exposure (photo 14). On the basis of the radionuclide concentrations and a survey on mineral wool production in the Netherlands it appeared that the slag wool originates from slag of a tin smelter. It is estimated that 1400 tonnes were produced in the late forties of the last century. Tin refinement has taken place at a large scale in Western Europe in the past, in particular in Spain and the UK. In the latter country former sites of tin smelters with large inventories of tin slag have been identified and remediated. It is estimated that 30 million ton of tin slag with enhanced levels of natural radioactivity has been applied in civil engineering [19].

4

Figure 14. Phosphorus production by the thermal process (By courtesy of W.H.H. Erkens, Thermphos International B.V., The Netherlands).

Photos 1 and 2: On the left is the granulator disk with the milled ore and binder input. On the right is a view of the sintering grid roaster with glowing pellets. The burner is situated above the grid roaster. The tip of the flame is visible. (By courtesy of W.H.H. Erkens, Thermphos International B.V., The Netherlands).

4 Figure 1 and the photos 1-8 have been made available by W.H.H. Erkens, MSc, from Thermphos International B.V., The Netherlands, for the purpose of this refresher course only. The authors wish to express their gratitude to him. The copy right of figure 1 and these photographs stays with Thermphos International B.V. and they may not be used for reproduction without permission of the owner.

5 Photos 3 and 4: On the left, the slag is flowing out of the furnace into a pan. On the right, the pan is being emptied. (By courtesy of W.H.H. Erkens, Thermphos International B.V., The Netherlands).

Photos 5 and 6: On the left, the slag pan is being emptied. On the right, the material is being removed from the slag beds after cooling. (By courtesy of W.H.H. Erkens, Thermphos International B.V., The Netherlands).

Photos 7 and 8: On the left, the hydraulic slag mixture is being spread. On the right, the top layer is being applied. (By courtesy of W.H.H. Erkens, Thermphos International B.V., The Netherlands).

6 Photos 9 and 10: On the left two disused ovens from a foundry. On the right the remains of a boiler

Slag wool

Photos 11 and 12: On the left a steam generator with slag wool under the corroded area. On the right a door insulated with slag wool

Photos 13 and 14: On the left the front of a large coal fired boiler from a power plant, partly dismantled without appropriate control. On the right, outfit for personal protection during dismantling.

7 3. The scope of regulatory control of NORM

The selection of appropriate criteria for defining the scope of regulatory control is a critical issue for NORM. Although in some cases the radiological hazards can be very significant, the number of industries potentially subject to regulatory control is very large and inappropriate selection of criteria could result in many industries being regulated without any net benefit in terms of risk reduction. For this reason, the concepts of exclusion, exemption and clearance are of utmost importance in defining the scope of regulatory control of NORM. The exemption levels specified in terms of activity concentration and total activity in the BSS [1] and in the Euratom Directive [5] are based on an individual dose criterion of the order of 10 µSv/y and a collective dose criterion of about 1 manSv/y. Doses below these criteria are considered internationally as being of no regulatory concern, or trivial. These exemption criteria are applicable for practices with artificial radionuclides with moderate amounts of material, but they are not applicable to bulk quantities of natural radionuclides. Although one can argue that persons exposed to NORM should be subject to the same radiological protection standards that apply to persons exposed to artificial radionuclides, the dose criteria of 10 µSv/y and 1 manSv/y are widely regarded as being impractical for NORM industries. The range of doses resulting from terrestrial radiation (excluding radon) lies between a few hundred µSv/y to a few mSv/y. The corresponding variation in activity concentration is from a few hundredths of a Bq/g to a few Bq/g. Applying dose criteria of 10 µSv/y and 1 manSv/y to NORM activities would bring large areas of the world under regulatory control. Therefore, applying the same radiation protection standards for artificial and natural radionuclides relates to the optimization principle, rather than to trivial dose.

For the determination of the required regulatory control of NORM, it is necessary to compare the activity concentrations and the doses due to exposure of workers and the public with certain criteria. According to the BSS, exposure to natural sources shall normally be considered as a chronic exposure situation and, if necessary, shall be subject to the requirements for intervention, except for public exposure delivered by effluent discharges and by disposal of radioactive waste arising from NORM activities, and for occupational exposure, if the natural sources lead to exposure to radon in cases as specified by the BSS and in cases specified by a regulatory body. In those cases, the exposure shall be subject to the requirements for practices, unless the exposure is excluded or the practice is exempted. The criteria for practices are based on the concepts of exclusion, exemption and clearance, as established in the BSS. Action levels are criteria that can be used in intervention situations, and are meant to decide on remedial or protective actions to reduce the exposure in existing de facto situations, because of uncontrolled human activities in the past. Situations where natural radionuclides are involved and that may require intervention include radon in workplaces, and chronic exposure to residues, such as mine tailings or land fills, from past activities and events.

3.1. Exclusion

The BSS glossary defines 'excluded' as 'outside the scope of standards' and expands on this by stating 'any exposure whose magnitude or likelihood is essentially unamenable to control through the requirements of the Standards is deemed to be excluded from the Standard' [1]. Therefore, exclusion is an important concept for limiting the scope of regulatory control, specifically for natural radionuclides.

This has also been recognized by the ICRP, by stating that 'everyone in the world is exposed to radiation from natural and artificial sources' and 'any realistic system of radiological protection must therefore have a clearly defined scope if it is not to apply to the whole of mankind activities' [2].

Also, the European Commission uses the concept of exclusion to limit the scope of regulatory control for natural radionuclides. In Council Directive 96/29/Euratom [5], natural sources of radiation are called 'work activities' and they encompass both practices and intervention situations. Those natural radiation

8 sources that are not amenable to control are excluded from the scope of the Directive and need not to be accounted for in the total exposure.

Examples of excluded exposures are given in the BSS, i.e. exposure from 40K in the body, from cosmic radiation at the surface of the earth and from unmodified concentrations of radionuclides in most raw materials5. Examples of excluded exposures in the Euratom Directive are exposure tot radon in dwellings or to the natural level of radiation, i.e. to radionuclides contained in the human body, to cosmic radiation prevailing at ground level or to aboveground exposure to radionuclides present in the undisturbed earth's crust.

In the BSS, but also in ICRP 60 and the Euratom Directive, exclusion relates to the amenability of exposures to control rather than to the actual magnitude of these exposures. However, amenability to control is a relative concept; it is a matter of reasonableness and implies recognition of the resources associated with exercising regulatory control and the benefit to be gained in terms of improved radiation protection. The 'unmodified concentrations of radionuclides in most raw materials' in the BSS refer to the fact that some raw materials may contain radioactive contaminants in such concentrations that they cannot be ignored from a radiological point of view and therefore not be subject to exclusion. The Euratom Directive specifies that work activities that lead to a significant increase in the exposure of workers or members of the public which cannot be disregarded from the radiation protection point of view. The Directive shall also apply to any intervention in cases of lasting exposure resulting from a past or old practice or work activity.

One could therefore consider the worldwide distribution of the activity concentrations of natural radionuclides in soil and in ore to derive exclusion levels for natural radionuclides. A summary of the data in the UNSCEAR 2000 Report [3] is given in table 3 for concentrations in soil. For 238U, 226Ra and 232Th, the highest mean value for an individual country is below 0.2 Bq/g and the highest measured values are below 1 Bq/g. In the case of 40K, the mean value for any individual country is below 1 Bq/g and the highest value is under 2 Bq/g. Doses to individuals as a consequence of the use of these activity concentrations are unlikely to exceed about 1 mSv in a year.

Table 3. Summary of UNSCEAR data for natural radionuclides in soil (from [3]) Nuclide Bq/kg Population weighted Highest country mean Highest value observed in a country average 238U 33 114 (Thailand) 690 (China) 226Ra 32 67 (Malaysia) 900 (Switzerland) 232Th 45 95 (Hong Kong) 360 (China) 40K 420 850 (Norway) 1800 (China & Luxembourg)

From the UNSCEAR data it can be concluded that the concentration of 238U, 226Ra and 232Th in 'most raw materials' is below a value of the order of 0.5 - 1 Bq/g and below a value of about 3 - 4 Bq/g for 40K. Values of this order could therefore be chosen as exclusion values. Since the levels in Table 3 are derived from the worldwide distribution of radioactivity concentrations, they are valid for the natural decay chains in secular equilibrium, i.e. 238U, 235U and 232Th, with the value given being applied to the parent of the decay chain. The values can also be used individually for each decay product in the chains or the head of subsets of the chains, such as 226Ra.

5 All of these examples involve natural sources of radiation although there is no explicit requirement to limit the concept of exclusion to such sources of exposure. In particular, regulatory bodies may wish to apply it to exposures from artificial radionuclides that are now widespread in the environment due to past practices and accidents.

9 3.2. Exemption

One should keep in mind, however, that the processing of raw materials, even with radioactive concentrations at a level below the exclusion level, may lead to products or waste with higher concentrations, and thus give rise to exposures that should not be excluded from regulatory control. The regulatory body should recognize that there are NORM activities, or intervention situations, with an enhanced exposure to natural sources where the associated attributable doses warrant consideration and control. It is therefore also necessary to define the scope of regulatory control on the basis of dose, by making use of the concept of exemption.

The BSS use the concept of exemption only in the context of practices. Exemption determines a priori which practices, sources and radioactive materials may be freed from the requirements for practices, and hence regulatory control, based on certain criteria. Exemption should be granted if the regulatory body is satisfied that the practices or sources meet the exemption criteria or the exemption levels specified in Schedule I of the BSS, or other exemption levels specified by the regulatory body on the basis of the exemption criteria. As explained above, the basis for exemption is the concept of trivial individual effective dose (of the order of 10 µSv or less in a year).

It should be noticed in this place that the exemption values as specified in Schedule I of the BSS are calculated assuming moderate amounts of the radioactive source, as is the case with exposure to artificial sources. For this reason, the exemption levels in Schedule I of the BSS do not apply to NORM activities, which are in most cases associated with large volumes of materials. In contrast to the concept of exclusion, the concept of exemption therefore refers in principle to practices, or work activities, where a priori decisions should be taken about regulatory control of the source.

Whereas the exemption levels for artificial sources are based on the concept of triviality of risk, associated with a dose of 10 µSv in a year, this is an impractical basis for the derivation of exemption levels for natural radionuclides. If one would impose a restriction of 10 µSv for NORM activities, it would in general not be practicable to implement a control scheme for such a small increment to the natural radiation background, which is in fact below the natural variability. Many human activities previously unregulated from a radiological standpoint, such as the construction of houses from natural building materials or even the use of land in many areas, could then be subject to regulation. Establishing levels for natural radionuclides that invoke such widespread regulatory consideration, in circumstances where in many cases it is unlikely to achieve any improvement in protection, is not an optimum use of regulatory resources. Therefore, derivation of exemption levels for naturally occurring radionuclides should be based on a methodology that places greater emphasis on optimization of protection, including regulatory resources.

ICRP Publication 60 [2] refers to a second basis for exemption, other than exemption on the basis of trivial dose, namely that 'no reasonable control procedures can achieve significant reduction in individual and collective doses'. This basis for exemption is more appropriate for NORM activities than the 'trivial dose' basis, but is not reflected explicitly in the international BSS.

For reasons as mentioned above, the European Commission has published a guidance document RP122 Part II [20] on the issue of exemption (and clearance) of natural radioactive sources. The Commission considered the impracticability of using the trivial dose concept for the establishment of reference levels for regulatory control of natural radioactive sources and made a distinction between the derivation of levels for exemption of artificial and natural sources. As in the BSS, the exemption levels for artificial sources are based on the concept of triviality of risk, associated with a dose of 10 µSv in a year. Instead of considering the worldwide range of activity concentrations, the European Commission uses in RP122 Part II the variation in the range of natural radiation background doses as a basis for setting the reference levels for NORM activities. Excluding radon, the average background radiation dose is in the order of 1 ± 0.3

10 mSv in a year. The European Commission considers the variation of 300 µSv as a suitable dose criterion to calculate activity concentrations for exemption (and clearance) of regulatory control of natural radionuclides. In RP122 Part II a set of values is proposed as guidance for the Member States of the European Union. Although this approach is different than proposed under section 3.1, the values are of the same order for the most important radionuclides (0.5 Bq/g for 238U, 226Ra and 232Th; 5 Bq/g for 210Po, 210Pb and 40K).

The European Commission used a dose level of 0.3 mSv per year as a basis to derive exemption (and clearance) levels. In some other countries a level of the order of 1 mSv is used. For occupational radiation protection, Safety Guide RS-G-1.1 (para 2.27) [6] refers to ICRP 75 [21] where is stated that in dusty conditions the annual effective dose to workers is about 1-2 mSv. When considering gamma radiation doses, RS-G-1.1 proposes to apply an approach similar to that for radon not directly related to work and concludes that an annual effective dose of about 1 mSv, or some multiple, should be adopted as an action level. If the dose rate could not be reasonably reduced to below the action level, the numerical value of the action level could be used to define when the requirements for practices should apply.

All this information points to a level of the order of some tenths to about 1 mSv per year as a basis for exemption, that could be used by the responsible authority for setting exemption levels. To be in line with the general principles of radiation protection, as given in the BSS [1] and as recommended by the ICRP [2], the upper dose level to consider as a base for exemption should be 1 mSv per year, being the maximum level of exposure for members of the public and the discrimination level for exposed workers. A lower value could be the value of 300 µSv per year, as chosen by the European Commission, being the variation of the global average individual dose of the public. The responsible authority should consider if they wish to derive a set of exemption levels on a dose level somewhere in the range of 0.3 - 1 mSv per year, taking into account economic factors, but also taking into account social and political factors. This means that a general agreement should exist in the society to use or not to use exemption levels. Regulatory bodies that wish to establish exemption levels for these purposes should balance the consequences of regulatory control, both in terms of the necessary resources available for setting up the infrastructure and in terms of the consequences for the regulated NORM activity against the benefit in terms of improved radiation protection. When the concept of exemption and clearance has been implemented, the regulatory authority should compare the NORM activities with the exemption levels. Those who comply with these levels are exempted from regulatory control, as long as the national situation doesn't change. This is the principle difference with exclusion: NORM activities are excluded on the basis of their activity concentration irrespective of the radiological consequences; NORM activities are exempted on the basis of a national evaluation of costs and benefits of regulatory control.

3.3. Clearance

When setting exemption levels, the responsible authority should also consider setting clearance levels. One should take into account that recycling and reuse of residues of NORM activities is a common procedure, which is being promoted for sustainability reasons. Cleared materials from NORM activities may thus be used as input materials in other NORM activities. It is therefore reasonable to choose the value of the clearance levels at the same level as the value of the exemption levels, although in principle the derivation of these levels may be different, due to different exposure scenarios. The European Commission followed this approach when deriving the exemption and clearance levels in RP122 Part II [20].

The BSS also use the concept of clearance only within the context of practices. While exemption is used to determine the nature and extent of application of the system of radiation protection and regulatory control, clearance is intended to establish which sources under regulatory control can be removed from this control. As such, it can be considered as a generic authorization, granted by the regulatory body, for that component of a practice that applies to the release of radioactive material. The BSS state that

11 clearance is subject to clearance levels that are defined as 'values, established by the regulatory authority and expressed in terms of activity concentrations and/or total activity, at or below which sources of radiation may be released from regulatory control'.

Many raw materials, residues and waste streams have activity concentrations in the range of a few tenths of a Bq/g to a few Bq/g. Although at first sight a difference between 0.5 and 1 Bq/g seems not to be significant, the consequences of choosing a certain level for clearance and exemption can be very large. For example, a dumpsite of millions of tons of phosphogypsum with an activity concentration of 0.7 Bq/g 226Ra should be regulated when the RP122 Part II level is chosen as a clearance level, but not when the level is set at 1 Bq/g. For the establishment of exemption and clearance levels, it is therefore very important to use country specific exposure scenarios and to evaluate the implications of regulatory control, including the net benefit of regulatory control in terms of improved radiation protection. Since different countries may have different problems with NORM, due to the character of industrial activities and associated problems of finding pragmatic solutions, a country specific approach is unavoidable. Such an approach can also take into account the resources that are available in a certain country.

Nevertheless, there is a need for international consensus on the approach. There still are large differences in the regulations and disposal options. What is allowed in one country, is forbidden in another country. There should be agreement on clearance, exemption, disposal options et cetera, in order to avoid competitive advantages and disadvantages. Disharmony in regulations can lead to sub-optimal solutions form a radiological protection point of view. Migration of industries to countries with less stringent regulations does not improve radiation protection.

With regard to clearance, and therefore also for exemption, another aspect becomes important, namely transport and im- and export of materials. International agreement about harmonization of clearance levels in this respect is very desirable, but not yet achieved. Materials that are cleared in one country don't necessarily need to be cleared in another country. But even when clearance and exemption levels have been set, the problem is not solved. The market itself plays its own role, because some materials are rejected when any detectable radioactivity, even below the exemption and clearance levels, is present, irrespective whether the nature of the radioactivity is artificial or natural.

3.4. Action levels

Action levels refer to the concept of intervention. If the dose rate could not be reasonably reduced to below the action level, the numerical value of the action level could be used to define when the requirements for practices should apply. In Schedule VI of the BSS, guidelines are given only for chronic exposure to radon, which are repeated here. The action level for radon in workplaces is a yearly average concentration of 1000 Bq/m3 of 222Rn in air. With an assumed occupancy of 2000 hours per year, this equates to an effective dose of about 6 mSv per year. This value is at the midpoint of the range of 500 - 3 1500 Bq/m recommended by the ICRP in Publication 65 [22]. ICRP has provided guidance in Publication 82 [23] on the application of the radiological protection system to chronic exposure situations affecting members of the public. It provides recommendations on generic reference levels for intervention. ICRP 82 pays specific attention to chronic exposure situations resulting from NORM activities, both from the past and from ongoing operations. In many parts of the world, these operations last for many decades, usually without specific restrictions. Such exposure situations should be treated as intervention, within the framework as recommended by ICRP. Additional individual doses resulting from current and future operations, should preferably be controlled by using the concepts of exclusion, exemption and clearance. ICRP 82 provides quantitative recommendations for chronic exposures. At the same time, ICRP warns that these recommendations should be interpreted with extreme caution. Regulatory bodies wishing to establish action levels for these purposes should carefully balance the consequences of the intervention against the benefit in terms of improved radiation protection.

12 4. Regulatory requirements

4.1. Regulatory infrastructure

The BSS presume the existence of a national infrastructure for radiation safety and the basic requirements for the legal and governmental infrastructure that is necessary in order to implement the Standards effectively. An essential component of this infrastructure is the existence of a competent national regulatory body that has the authority to establish regulations, as well as the power to enforce compliance with the regulations. The regulations shall, inter alia, define the scope of situations to be regulated for purposes of radiation protection.

As explained in the previous section, not everything that contains NORM should fall under regulatory control. The regulatory system should define the scope of the relevant regulations, the implication being that material containing an amount of radioactivity higher than a prescribed level will require regulation. If this is the case, there are several regulatory vehicles that can be used for controlling these materials, depending on the level of exposure of workers and members of the public.

The regulatory system should make a distinction between practices and interventions and specify for both situations the provisions for regulatory control. In the case of a practice, the vehicles for control of NORM activities, when they are not excluded or exempted, are notification and authorization. Notification is an obligation on the legal person who intends to carry out a NORM activity. Authorization is an obligation of the regulatory authority, and can take the form of a registration or a license. For interventions, the regulatory authority has the obligation to establish action levels and action plans, whenever the regulatory authority has justified an intervention.

4.2. Practices

The BSS has described basic obligations and administrative requirements that should be fulfilled if a certain NORM activity is deemed to be under regulatory control. The application of the requirements, as specified by the regulatory authority in accordance with the BSS, to any practice shall be commensurate with the characteristics of the practice. Not all the requirements are relevant for every practice. This is certainly the case for NORM activities and a graded approach is recommended, depending on the magnitude and likelihood of the exposures.

For many NORM industries, simple control measures, similar to those already in place for normal occupational hygiene reasons, may often provide sufficient radiological protection. In many cases, occupational hygiene requirements are imposed as a matter of course by a regulatory authority that may not have particular knowledge of radiation hazards. Guidance is needed for both the operator and the regulator on appropriate control measures, and the extent to which these can be achieved by normal occupational hygiene requirements.

4.2.1. Notification

Notification is an administrative requirement, necessary to inform the regulatory authority about intentions to carry out a certain practice. In the Glossary of the BSS [1], notification is defined as 'a document submitted to the Regulatory Authority by a legal person to notify an intention to carry out a practice or any other action described in the General Obligations for practices of the Standards'. Notification alone is sufficient provided that the normal exposures associated with the practice or action are unlikely to exceed a small fraction, specified by the regulatory authority, of the relevant limits, and that the likelihood and expected amount of potential exposure and any other detrimental consequence, if applicable to NORM activities, are negligible.

13 4.2.2. Authorisation

Authorisation has been defined in the BSS [1] as 'a permission granted in a document by the Regulatory Authority to a legal person who has submitted an application to carry out a practice or any other action described in the General Obligations for practices of the Standards. The authorization can take the form of a registration or a license'. The legal person therefore shall, unless the NORM activity is excluded or exempted, apply to the regulatory authority for an authorization.

Registration is defined as 'a form of authorization for practices of low or moderate risks whereby the legal person responsible for the practice has, as appropriate, prepared and submitted a safety assessment of the facilities and equipment to the Regulatory Authority. The practice or use is authorized with conditions or limitations as appropriate. The requirements for safety assessment and the conditions or limitations applied to the practice should be less severe than those for a license'.

A license is defined as 'an authorisation granted by the Regulatory Authority on the basis of a safety assessment and accompanied by specific requirements and conditions to be complied with by the licensee'.

4.3. Interventions

In order to reduce or avert exposures in intervention situations, protective and/or remedial actions shall be undertaken whenever they are justified by the regulatory body. The form, scale and duration shall be optimized so as to produce the maximum benefit, taking into account the prevailing social and economic circumstances. The regulatory infrastructure should make it possible to determine the allocation of responsibilities for the management of intervention in chronic exposure situations between the regulatory authority, national or local intervening organizations and registrants or licensees.

Generic or site-specific remedial action plans for chronic exposure situations shall be prepared, as appropriate. The plans shall specify action levels and the type of actions to be taken, as long as they are justified and optimized, taking into account the individual and collective exposures, the radiological and non-radiological risks, and the financial and social costs, the benefits and the financial liability for the intervention.

The “grey area” between practice and intervention is a particular problem for NORM, because many industries – including their bulk wastes that are exposed to the environment – existed already long before (radiological) regulatory control was established. Regulatory control of these industries therefore has to be applied retrospectively. If they are treated as pure “practices”, this may impose impractical requirements on many industries where radiological protection was not taken into account in the design of facilities. Non-uranium/non-thorium mines have in many cases been operating for several decades and are only now being brought under regulatory control. Many mines have managed to accommodate the retrospective introduction of radiological protection requirements. However, in some instances achievable reductions in radon concentrations are not sufficient to ensure compliance with dose limits, due to the physical difficulty and high capital cost of making major changes to the ventilation system. Rigid enforcement of dose limitation requirements would most likely result in the affected shafts having to close prematurely, with potentially severe implications for the workforce given the high unemployment situation in some of the regions where these mines are situated.

5. General process to determine the extent and nature of required regulatory control

The starting point of the process to determine the required regulatory control of NORM activities is knowledge about the situation with regard to past, present and intended NORM activities in a country. It is the responsibility of the national authority to get a clear overview of the type of industries, the industrial processes, the activity concentrations in products, residues and waste streams and the exposure of workers

14 and members of the public, in order to be able to decide on the necessary steps to ensure an optimized level of protection. This also implies that the necessary resources are available for implementing the control system. Economical, social and political factors should be taken into account to determine what the optimized level is.

5.1. Inventory of NORM activities

The first step should be to make a national inventory of NORM activities. The responsible authority should gather all the available information about the industries in the country that may be affected by the presence of natural radionuclides in its materials. The type of information, necessary for such an inventory, contains both process related information and radiological data.

There are several other sources to guide the responsible authority in his search for information. Several sector-specific Safety Reports on NORM activities have been published by the IAEA, or are in the process of publishing, where general information can be found about the radiological aspects of industries in the various sectors [13-17]. The European Commission has also published guidance reports with generic information about different industries [24-29]. As a result of the implementation of the Euratom Directive, Member States of the European Union had to identify NORM activities that cannot be ignored from a radiation protection point of view. Such studies may be used as an example to guide an authority in performing this first step for its own country [30-39]. At a Technical Committee Meeting on the Assessment of Occupational Protection Conditions in Workplaces with High Levels of Exposure to Natural Radiation, held by the IAEA [40], a number of presentations have been given on assessments of NORM activities in different countries. A summary of these presentations is given in Annex 1.

The result of this step is a comprehensive overview of the national NORM activities and the associated radiological data. Due to the fact that NORM activities are only recently being regulated, only a fraction of the necessary data may be available, certainly on a country-specific level where the identification of NORM activities takes place for the first time. The above-mentioned guidance documents should point to the direction where additional data should be sought. If, for instance, an industry uses hundreds of thousands of tons per year of ores with known but low radioactive concentrations of uranium and thorium in secular equilibrium, and the industry uses a high temperature process giving rise to tens of thousands of tons of waste with unknown radioactive concentrations, the waste may be enriched in uranium and/or thorium but depleted in volatile daughter nuclides such as polonium and lead, or the other way around depending on the process that gave rise to the considered waste stream. Also, parts of the industrial installation may be heavily contaminated by scales or dust with a high radioactive concentration, giving rise to increased external exposures or increased risk of internal contamination when maintenance work is carried out during outages.

5.2. Categorization of the data with regard to radiological concern

The compiled data need to be categorized in order to make a distinction in the degree of radiological concern. A first categorization should be based on the activity concentration of the materials. This categorization can be used to screen the industries on their compliance with exclusion or exemption levels.

A second categorization should be based on exposure levels for workers and members of the public. For such a categorization dose assessments are necessary. The database might already have information for some of the industries, but this may also be not complete. Prioritization of actions should be carried out here to complete the data. The prioritization could be based on information from Safety reports and other studies.

A third categorization should be based on the waste generated by the industries. The volumes, activity concentrations, chemical and physical characteristics and the characteristics of the used waste storage sites

15 are important issues in order to judge the level of radiological concern. This area will also contain legacies from past NORM activities. The issues mentioned will give relevant information for the assessment of the doses received by the population.

5.3. Screening against exclusion or exemption criteria

The list of industries resulting from the categorization based on activity concentrations should be compared with the generic exclusion criteria. When the raw materials, products, by-products and wastes, including dust and scales on installations, fall under the exclusion criteria, the NORM activity should be excluded from further consideration by the responsible authority.

This will lead to a smaller list of NORM activities that are not excluded. These NORM activities are in principle subject to regulatory control, but the next steps should define the degree of control that is necessary, including the possibility of exemption. The categorization of the remaining NORM activities should now be related to the radiological consequences of the NORM activities, including the radiological consequences of waste management. The exemption criteria, although based on radiation dose, may be transformed for operational purposes to exemption levels expressed in radioactivity concentrations. When comparing the NORM activities with the exemption levels, it is necessary to specify whether or not attention has already been paid to radiological protection of the workers and the most exposed members of the public. If this is the case, the NORM activity may be considered as optimized, i.e. ALARA. In case of legacies of past NORM activities the measurements and assessments should be carried out either by the owner of the legacy or by the government, depending on the national situation and the financial power of the owner.

The result will be an overview of NORM activities that are: - excluded from regulatory control; - exempted from regulatory control; - subject to regulatory control.

For the latter category, the different vehicles for regulatory control come into play. Given the nature of many of the industrial processes, it is important that a graded approach for imposing regulatory control is being applied; keeping in mind what control measures are necessary and sufficient to reach an optimal level of radiation protection. The responsible authority should consider the use of notification, registration and licensing as legal instruments for regulatory control.

When possible and useful, again with due account of costs, benefits and social and economic factors, the responsible authority should establish registration and licensing levels, expressed in activity concentrations. The range between exemption and registration levels could then be used for notification, the range between registration and licensing levels for registration and above licensing levels for a full license of the operation.

An example of applying the above-mentioned methodology to the inventory of NORM industries in the Netherlands is elaborated in Annex 2.

5.4. Considerations for interventions

Intervention situations are a special case in the considerations to apply regulatory control. When it applies to radon in dwellings or in workplaces, there are a number of recommendations and guidance reports published, by ICRP with respect to the concept of intervention to be applied for radon in dwellings and workplaces [22], by the IAEA [13] and the European Commission [27, 41] with respect to the procedures to establish a national policy. The NORM activities may have an impact on radon in dwellings when the

16 products or residues are used in the building material industry. The use of such materials can be restricted by regulations, according to recommendations developed by the IAEA [13] and the EC [27].

When the intervention situation applies to old NORM activities or waste storage sites, such as phosphogypsum landfills or mine tailings, the decision to take any action should be clearly underpinned. ICRP 82 provides guidance for the protection of the public in situations of prolonged radiation exposure and addresses the application of ICRP's radiation protection system to such situations. It also provides recommendations on generic reference levels for interventions. However, these reference levels are to be used with great care. In most cases, the best solution is to leave the waste where it is and, if deemed necessary, only to take action to prevent resuspension or to avoid external exposure or contamination of ground water. The benefits from such actions should be carefully judged against the costs, which are in most cases considerable, if not prohibitive.

6. Radiological protection issues

Up to now, and in contrast with external exposures, relatively few efforts have been devoted directly to implementing the ALARA approach for internal exposures. For practices with artificial radionuclides, internal exposures are in most cases not the dominant exposure pathway. However, due to the large volumes of NORM containing materials in industry, in connection with dusty work conditions, internal exposure is in many cases the dominant potential exposure pathway for NORM. Exposure situations of workers in these industries differ considerably with respect to type of industry, work place conditions and radionuclides involved. There is a need for guidance on appropriate radiological protection measures for workplaces in NORM industries, specifically for recommended monitoring strategies and methods for optimisation of internal exposures. This guidance needs to be specific for the type of industry and be directed at assisting regulatory bodies and operators in identifying effective ways of meeting the radiological requirements. For this purpose, the IAEA is producing sector-specific Safety Reports [14-17].

6.1. Radon in workplaces

Radon can present a hazard in a wide range of workplaces. This is well known in the mining industry, but it also accounts for workplaces other than mines. While this includes below ground workplaces such as subways, tunnels, stores, show caves, closed-out mines open to visitors, and radon spas, the majority of such workplaces will be above ground. Specific guidance is needed on effective means for reducing radon concentrations in air and water, given that without appropriate controls radon concentrations can reach very high levels even where uranium and radium concentrations in the raw material may be very low [13].

In buildings with high radon levels, the main mechanism for the entry of radon is the pressure driven flow of gas from soil through cracks in the floor. This flow arises because buildings are normally at a slight underpressure with respect to their surroundings. This underpressure is a consequence of the air inside buildings being warmer than that outside, especially in temperate and cold regions, and also of the drawing effect of the wind blowing over chimneys and other openings. However, various other mechanisms can affect the concentrations of radon in dwellings. Most building materials produce some radon but building materials of certain types can act as significant sources of indoor radon. Such building materials have a combination of elevated levels of 226Ra and a high porosity that allows the radon gas to escape. Examples are lightweight concrete made with alum shale, phosphogypsum and Italian tuff.

Levels of radon can be high in groundwater, particularly in areas of granite rock. Radon levels may be high in workplaces such as laundries and restaurant kitchens as a result of the use of such water. Since many municipal water supplies are provided from surface reservoirs filled by rain catchments, radon levels in public water supplies are not normally high. In Germany some treatment and distribution stations for water supplies drawn from groundwater have been found to have radon concentrations in air of up to several hundred thousand Bq/m3 [31]. Generally, the annual exposure time of workers in these workplaces

17 is low, but several such water treatment plants are subject to monitoring. Some countries have issued recommendations on radon concentrations in drinking water [42].

Underground workplaces can accumulate high levels of radon in the same way as occurs in caves or abandoned mines. It cannot be assumed that high radon levels in underground workplaces will be limited to those parts of the country where elevated radon levels have been found in above ground workplaces. The possibility of high radon levels exists in any underground workplace. Elevated levels of radon have been found in workplaces in various countries. More information can be found in [13]. A summary is given in Tables 4 and 5 (from [13]. It can be seen that radon levels are rather variable. Some countries, but not all, have identified certain workplaces with radon concentrations exceeding 1000 Bq/m3. However, some of the surveys were small and — even if the mean concentration is low — most distributions are skewed, so there could be a minority of workplaces in which radon concentrations are significantly above the average.

Table 4. Radon concentrations in underground workplaces (non-mining) (from [13]) Workplace type Country Radon concentration range (Bq/m3)

Tourist caves Germany 400–11,180 Hungary 130–21,100 Ireland] 260–19,060 Slovenia 20–10,000 USA 48–1,850 Mines open to visitors Germany 400–20,280 Tunnels Czech Republic 229–3,312 Finland 500–7,000 Norway 250 (mean) Power stations Norway 20–4,000 Underground railways Finland 45–200 (stations) 20–790 (workplaces) Greece 9–22 (stations)

More details, including a scheme for the control of radon, techniques for measuring radon and remedial actions can be found in [13].

6.2. Number of exposed workers in industry

Following a recommendation of the third European ALARA Network Workshop [43] to pay more attention to a systematic ALARA approach for internal contamination, specifically in NORM industries, the European Commission ordered a project6 under the 5th Framework Programme. The project has been carried out in close co-operation between scientific institutes and industry. The SMOPIE project dealt with occupational internal exposures from practices and work activities in NORM industries. It covered a broad variety of practical situations, including the generation of (and exposure to) dust, whether the exposure is continuous or discontinuous, whether dust levels are worker induced or process induced and the variability of doses between workers. The characterisation of these practical situations has been carried out in case studies describing real exposure situations encountered in different industries involving natural

6 Strategies and Methods for OPtimisation of Internal Exposure of workers from industrial natural sources (SMOPIE). The study has been performed by NRG (The Netherlands), CEPN (France), IRSN (France) and NRPB (United Kingdom), in co-operation with Thermphos International B.V. (The Netherlands), Kerr-McGee (The Netherlands, COMURHEX (France) and the United Kingdom Heavy Mineral Sands Association (UK), under contract no FIGM-CT2001-00176.

18 radionuclides. The project also gave an overview of monitoring methodologies and available monitoring devices than can be used in different exposure situations. The case studies and the overview have provided the basis for recommended monitoring strategies and methods for optimising internal exposure control in a wide range of industrial situations. More information about this project can be found in poster 0257 of this IRPA 11 congress [44].

Table 5. Radon concentrations in above ground workplaces (from [13]) Workplace type Location Number surveyed Radon concentration (Bq/m3) Public buildings Belgium (Luxembourg 36 10% > 200 province) 3% > 400 Finland 155 Mean 505, 37% > 300 400 Mean 284, 17% > 300 USA 3901 22% > 150, 0.2% > 1000 Schools Belgium (Luxembourg 421 12% > 200, 2% > 400 province) Islamic Republic of Iran 16 Mean 256 55% < 100 100 < 30% < 400 400 < 15% < 1400 Ireland 1762 23% > 200, max. 2688 Italy (3 of 21 regions) 486 Range 13–1450 geometric mean 78–129 4–17% > 400 USA 927 2.7% > 150, 0.1% > 1000 max. 2500 Kindergartens Italy (5 of 21 regions) 1687 Range 6–1400 geometric mean 38–118 0.1–15% > 400 Norway 3600 Range 5–2800, mean 88 geometric mean 44 Slovenia 730 Range 7–5750 Geometric mean 58

Various workplacesa Finland 3050 Mean 255, 37% > 300 993 Mean 171, 12% > 300 Germany ~60 000 workers exposed to >1000 Bq/m3 Germany (Saxony) 36 Range 25–7000 10% > 1000, 20% > 800 Sweden 150 10% > 400 United Kingdom 8000 Mean ~100, max. 7500 a This includes industries using large volumes of groundwater and workplaces in which large quantities of materials with elevated concentrations of radium are stored or processed.

The SMOPIE study summarized the available information in Europe on the number of workers exposed to internal contamination and the dose levels involved. The results have revealed that there still is a severe lack of information on these issues. Several studies have been reviewed, but they do not provide the information for a scientifically sound evaluation of the problem. However, the scarce information

19 indicates that there may be about 85,000 exposed workers (see table 6). This number certainly warrants more research in this area.

Table 6. Estimates of the number of potentially exposed workers in EU NORM industries (from [44]) NORM industry and work Number of exposed Basis for estimate activity workers (rounded) Thoriated electrodes, Extrapolation of Dutch and German 70 000 production, grinding and use data Phosphate fertiliser trade 10 000 German data multiplied by 4 and use Based on 1000 production Oil and gas production, installations and two workers exposure to scale dust at 2 000 potentially exposed annually per maintenance installation Zircon sands, milling and UK and German estimate multiplied 500 processing by 5 for European Union Rare earth extraction Based on French data, multiplied by 3 industry, 400 for other producers (Y, Ce, Eu, La, etc.) Cement production, Based on 60 cement production plants maintenance of clinker 300 and 5 exposed workers per plant ovens Coal-fired power plants, Based on 70 plants and 2 exposed 100 Maintenance of boilers workers per plant annually Ten plants producing phosphoric acid Phosphoric acid production, 100 from phosphate rock. Ten exposed scale removal workers per plant. Based on 7.4 million tons total annual Primary iron production, EU blast furnace primary iron 100 exposure to sinter dust production in 20 plants. Five exposed workers per plant Based on 16 production plants, TiO pigment, solid waste 2 80 sulphuric acid and chloride process. and Ra-scale Five exposed workers per plant. Largely replaced by much cleaner Rare earth catalyst “concentrates” as raw material. production, maintenance, 20 Assumed number of plants 10, and scales two exposed workers per plant Thermal phosphorus Based on Thermphos input into 20 production SMOPIE, one plant Number of plants 20 and 1 exposed Lead/zinc smelters 20 worker per plant Tantalum, niobium Not known Number of plants at least 1. extraction from ores or slags Ground water treatment, Not known scales and sludges Residues from past Not known industrial activities Total (rounded) 85 000

20 6.3. General considerations for dose assessments

In many studies the assessment of the occupational dose due to exposure to NORM has been carried out by calculations, making use of exposure scenarios and more or less conservative parameter values. For accurate dose assessments, it is necessary to set up monitoring programs taking into account the representativity of the worker's external exposure and, more important, the inhaled activity. While static air sampling (also called general air sampling, workplace air sampling or area sampling) has sometimes been used to estimate workers exposure by dust inhalation, it is now considered that, if the dose estimate will be based on air sampling, the air samples should be representative of the air breathed by the worker and that general air sampling is generally not a good tool to estimate internal doses. In industrial hygiene, where limits of exposure by inhalation are directly expressed in terms of the average air concentration of the considered airborne contaminant, it is recognised that for the assessment of inhalation exposure, it is necessary to characterise the air that workers are actually inhaling and that, as long as there are spatial and temporal variations of the concentrations in any work environment, a sampling strategy must be designed so that the data obtained are representative of the worker’s exposure, accounting for all factors that may lead to a variation in the results and that, in particular, it is not appropriate to compare general air samples with the exposure limit because the distribution of dust in the workplace is not uniform. Important issues for establishing monitoring programs are the spatial variation of dust concentrations, the time variation of the exposure, the mobility of workers, multiple dust sources of exposure and the non-uniformity of the composition of the dust. In those cases personal air sampling (PAS) should be preferred above static air sampling (SAS).

The results of the SMOPIE project [44] provide a scientific and practical basis for monitoring programs, both for individual workers and for the workplace. The importance for radiation protection is illustrated by the fact that it describes the way to use sampling equipment which has intrinsically be designed for industrial hygiene instead of radiation protection purposes. This is by no means self-evident, since samplers cannot sample the true ambient aerosol required for radiation protection purposes. This has two notable effects, firstly in terms of assessing the activity concentration in air, and therefore the intake in Becquerels, and secondly in terms of assessing the effective dose. The results show that for specific situations a preferred sampling protocol should be used.

6.4. Aerosol characteristics, lung clearance classes and dose coefficients

For an accurate assessment of the dose from occupational exposure to NORM it is necessary to have information about use the characteristics of the aerosols, in terms of Activity Median Aerodynamic Diameter (AMAD) and Geometric Standard Deviation (GSD), the lung solubility class of the radioactive compounds in the aerosol (Fast, Moderate and Slow), and the right dose coefficients for these compounds. Dose coefficients for occupational exposure are provided in ICRP publication 68 [45] and the ICRP databases [46] for one up to all three default rates of absorption (Fast, Moderate and Slow) and a limited set of Activity Median Aerodynamic Diameter (AMAD, 1 and 5 µm) and Geometric Standard Deviation (GSD, 2.5).

Dose coefficients for other lung solubility classes and particle size characteristics have been calculated for the SMOPIE project [44] for the main radionuclides belonging to the two 238U and 232Th natural chains for a wider range of particle size dispersion characteristics than available in the ICRP databases and for default rates of absorption that were not considered by the ICRP calculation for occupational exposure. An example is provided in table 7 for inhalation of particles with AMAD 5 µm and GSD 2.5. From this table several important observations follow with respect to the ratios between the dose coefficients for particles with lung solubility class Slow and Fast respectively: - The S/F ratio is particularly high for 226Ra (16) and even higher (87) for 226Ra with low emanation rate; - The SF ratio is about 10 for 238U, 234U and 228Ra and about 4 for 210Pb and 210Po;

21 - The S/F ratio is particularly low for 232Th and 230Th; - For the 238U decay chain in secular equilibrium the S/F ratio is less than 1 (0.28 or 0.53 depending on the radon emanation rate of the material considered); - For the chain segment 226Ra+ the S/F ratio is about 6 or 20, depending on the radon emanation rate of the material considered; - For the 232Th decay chain in secular equilibrium the S/F ratio is 0.3; - A choice of default solubility class S for dose calculations is not conservative for materials containing the 238U and/or 232Th decay chain radionuclides in secular equilibrium; - A choice of default solubility class F when the true solubility class would be S results in underestimates of exposures ranging from a factor of 4 for 210Pb and 210Po to a factor of about 90 for 226Ra containing particles with low radon emanation rate. - Dose coefficients for natural radionuclides in matrices of lung solubility classes S and M are rather strongly AMAD dependent and those for class F are only slightly dependent on AMAD (see figure 2 for 210Pb).

Table 7. Workers dose inhalation coefficients (Sv/Bq) and their ratios for individual radionuclides and chain segments. AMAD 5 µm, GSD 2.5 (from [44]) Nuclide, chain or chain Fast Moderate Slow Ratio S/F Ratio S/M segment 238U 5.9E-07 1.7E-06 5.7E-06 9.8 3.5 234U 6.5E-07 2.1E-06 6.8E-06 10 3.2 230Th 1.2E-04 2.8E-05 7.2E-06 0.06 0.26 226Ra 4.4E-07 2.2E-06 6.9E-06 16 3.2 226Ra *) 4.4E-07 1.4E-05 3.8E-05 87 2.8 210Pb 1.1E-06 7.4E-07 4.3E-06 3.8 5.7 210Po 7.3E-07 2.2E-06 2.7E-06 3.7 1.25 238Usec 1.2E-04 3.7E-05 3.4E-05 0.28 0.92 238Usec *) 1.2E-04 4.8E-05 6.5E-05 0.53 1.36 226Ra+ 2.3E-06 5.1E-06 1.4E-05 6.1 2.7 226Ra+ *) 2.3E-06 1.6E-05 4.5E-05 20 2.8 *) Low Rn emanation rate Fast Moderate Slow Ratio S/F Ratio S/M 232Th 1.3E-04 2.9E-05 1.2E-05 0.09 0.41 228Ra 1.1E-06 1.7E-06 1.1E-05 10 6.7 228Th 3.4E-05 2.2E-05 2.5E-05 0.74 1.14 232Thsec 1.6E-04 5.3E-05 4.9E-05 0.30 0.92

Special attention should be paid to NORM materials which have a very low radon emanation, since these may have a much higher dose coefficient than the standard radium compounds, for which ICRP assumes by default a high radon emanation rate. The current ICRP biokinetic model for radium assumes that radon, which is formed by radioactive decay of radium, emanates very efficiently from the inhaled particle. An escape rate of 100 d-1 from the respiratory tract is assumed. This means that radon, and consequently the short-lived daughters of radon, do not contribute to the dose to the lungs, even when the particle is poorly soluble. Many NORM materials, however, show a very low radon emanation fraction of only a few percent. It is not expected that when such a particle is inhaled the emanation will change significantly. Since a large part of the potential alpha energy of radon and the short-lived radon daughters is not taken into account, the dose to the lungs is underestimated by a factor of 5 to 6 for these materials.

22 210Pb

1.00E-05

F; GSD = 2.5 1.00E-06 M; GSD = 2.5 S; GSD = 2.5 Sv/Bq 1.00E-07 5 10 15 20 AMAD (um)

Figure 2: Dependence of the dose coefficient for 210Pb aerosol on lung solubility class and AMAD. Note that for solubility classes S and M the dose coefficient is much stronger AMAD dependent than for class F (from [44]).

The biokinetic model for radium further assumes that radon entering the blood is removed from the body at a rate of 1 min-1. This means that radon and the short-lived radon daughters cannot be transported to the tissues at risk. Therefore the doses to organs other than the respiratory tract are not or only slightly underestimated. As a consequence only the effective doses of class S and M 226Ra need to be reconsidered, since these are determined for over 95% by the doses to the respiratory tract. In order to determine the upper bound of the dose coefficients it is assumed that the inhaled particles have zero radon emanation as long as they are retained in the respiratory tract. The results of the calculations are presented in table 8.

Table 8.: 226Ra (low radon emanation); variation with absorption rate, AMAD and GSD of the workers dose coefficients (from [44]) 226Ra Inhalation dose coefficients, e(50), worker, Sv/Bq GSD = 1.5 GSD = 2.5 AMAD Fast Moderate Slow Fast Moderate Slow * (µm) f1 =0.2 f1=0.2 f1=0.01 f1=0.2 f1=0.2 f1=0.01 1 3.4E-07 1.5E-05 4.3E-05 3.6E-07 1.6E-05 4.4E-05 2 5.2E-07 2.4E-05 5.7E-05 4.4E-07 1.8E-05 4.4E-05 3 5.4E-07 2.4E-05 5.2E-05 4.5E-07 1.7E-05 4.7E-05 4 5.2E-07 2.0E-05 5.0E-05 4.5E-07 1.5E-05 4.3E-05 5 4.9E-07 1.5E-05 4.0E-05 4.4E-07 1.4E-05 3.8E-05 6 4.6E-07 1.1E-05 3.1E-05 4.3E-07 1.2E-05 3.4E-05 8 4.1E-07 5.6E-06 2.0E-05 4.0E-07 9.4E-06 2.8E-05 10 3.7E-07 3.0E-06 1.4E-05 3.7E-07 7.4E-06 2.3E-05 12 3.4E-07 3.1E-06 1.1E-05 3.5E-07 6.9E-06 1.9E-05 14 3.2E-07 2.4E-06 9.4E-06 3.4E-07 5.8E-06 1.7E-05 16 3.0E-07 1.9E-06 8.3E-06 3.2E-07 4.9E-06 1.5E-05 18 2.8E-07 1.7E-06 7.6E-06 3.1E-07 4.2E-06 1.3E-05 20 2.7E-07 1.5E-06 7.2E-06 3.0E-07 3.7E-06 1.2E-05 *) f1: gut transfer factor

23 The SMOPIE project provides correction factors, to be used to minimise the bias in the dose assessment, either because of unknown parameters or because of a non-ideal sampling procedure. Without such correction factors, significant errors bias can arise in the assessment of internal exposures.

6.5. Requirements for monitoring techniques

The technical capabilities and general suitability of different internal monitoring techniques, in relation to implementing ALARA, have been considered in the SMOPIE project. The types of monitoring strategy currently applied in practice have been described and the technical capabilities and limitations of different forms of internal radiation monitoring have been reviewed. The aim of the review was to determine which types of monitoring are the most effective in terms of contributing to the optimisation of internal exposures from inhalation. The review also considered whether further developments are needed, especially in relation to existing monitoring equipment. The judgement has been based on the following four criteria:

Sensitivity It is clear that the monitoring technique should have sufficient sensitivity to assess doses well below dose limits. For NORM industries, an annual occupational dose of 1 mSv/y is often the trigger level for the application of regulatory controls. Consequently, the monitoring undertaken should be sensitive enough to assess doses of this magnitude. In most cases, this application level relates to the dose from all exposure pathways: internal doses much lower than 1 mSv/y may, therefore need to be assessed.

Accuracy Reliable estimates of doses are fundamental to the ALARA process. The monitoring method should, therefore, be capable of provide a reasonably accurate estimate of internal dose, avoiding (or correcting for) any bias, and minimising any uncertainties. ALARA information Sensitivity and accuracy provide a sound base for optimisation. However, to implement ALARA in practice, the monitoring results must also provide more detailed information on the pattern of exposures. This might include doses from specific tasks, or information on how airborne contamination levels vary in the workplace. Such information can then be analysed, for example to identify the main sources of exposure, and to help in the selection of protection options.

Equipment suitability For certain types of monitoring, there is little or no choice in the type of equipment that can be used. For air sampling, however, a variety of devices are available with different sampling characteristics. In such cases, the aim has been to identify which types of equipment are most suitable, in terms of the above three criteria, and also in terms of their practical use in the workplace. The review also aimed to identify whether any further developments or improvements to monitoring equipment are needed. There are two basic forms of monitoring internal radiation exposures, i.e. bioassay monitoring techniques, either in-vivo (e.g. activity retained in the lung and the whole-body), or in-vitro (e.g. urine or faeces sampling), or air sampling (personal or static).

The main conclusions drawn from the SMOPIE project are presented below, together with some further explanations: - Bioassay techniques (in-vitro or in-vivo) are not suitable for ALARA purposes due mainly to insufficient sensitivity. Even if this were not the case, such techniques are not considered capable of providing the type of dose information required to implement ALARA. - Personal air sampling (PAS) is the best method of assessing occupational doses from internal radiation. The first step in any monitoring strategy should be an assessment of worker doses using this technique.

24 - Personal air samplers follow the inhalable, thoracic or respirable dust sampling conventions. None of these is a perfect match for radiation protection purposes, and all produce a bias in the results when the particle size dispersion characteristics (AMAD and GSD) of the airborne aerosol are not perfectly known. Respirable sampling efficiency is highly AMAD-dependent and is not generally recommended. - For the assessment of effective dose, either inhalable or thoracic sampling conventions may be used, provided that the AMAD is reasonably well known. In such cases, an appropriate correction factor for sampling efficiency should be applied. The use of the relevant dose coefficients will then ensure that any bias in the dose calculation is eliminated. - Where the AMAD is not perfectly known, the possibility of an associated bias in the calculated effective dose cannot be eliminated. However, the possible range of this bias can be minimised by: - using the AMAD value (or assuming a default AMAD of 5 µm if the dose coefficient is AMAD dependent but the true AMAD is not known), to select both the sampler efficiency correction factor and the dose coefficients; and - using an inhalable sampler in the case of soluble materials (lung class F), or using a thoracic sampler for all other materials (lung class S and M). NB: most mineral sands are expected to fall into this second category. - From the above, thoracic sampling would seem to be the preferred option for many NORM industries. In practice, however, this would appear to be the least used sampling convention. Further development and use of this type of sampler should be encouraged. The potential for introducing bias in the dose estimate when using a default AMAD of 5 µm for lung class S aerosol sampled with inhalable sampling convention is illustrated in figure 3.

238Usec, class S, GSD 2.5 150% Inhalable 100% Thoracic Respirable 50% Bias 0%

-50%

-100%

AMAD D = 5 µ m -150% 0 5 10 15 20 AMAD ( µm)

Figure 3: Bias in the estimate of the dose from intake of 238Usec in class S aerosol depending on the sampling convention. Note that with a default AMAD of 5 µm (AMADD) the bias in the dose estimate is small when sampling was thoracic, even at a true AMAD of 20 µm. With inhalable sampling the bias increases to 125 % positive with increasing true AMAD of the ambient aerosol (from [44]).

- More generally, the development of PAS sampling heads following either the inhalable or the thoracic sampling convention, with good, robust and established sampling performances, and adapted to radiometric counting, should be encouraged.

25 - The sampling rate of currently available personal air samplers is not an essential obstacle for ALARA purposes. However, in some cases a higher flow rate (for periods of up to a few hours) would be an advantage, and the possibility of this should be explored. - Analysis of air samples by gravimetric techniques may be preferred in practice to radiometric analysis, provided radionuclide activity concentrations (Bq.g-1) in the airborne aerosol are reasonably constant with time and particle size (for accuracy) and of the order of 10 Bq/g or less (for sensitivity). - Real-time dust monitoring (RTDM) is not suitable for assessing doses directly, but has the greatest potential in terms of providing rapid and easy to collect information on the spatial and temporal variation of airborne dust concentrations for ALARA purposes. Specifically, it is capable of providing comprehensive and detailed results, especially for the identification of dust sources during walk-through surveys, and for identifying short-term variations in the airborne dust concentration. - The further development of low cost and easy to use individual devices integrating direct-reading instruments and video imaging should be encouraged. - Static air sampling should not be used to assess workers individual exposure but can be used to complement PAS, to provide additional information for ALARA purposes, mainly by the analysis of trends with time of the daily variations in airborne activity. - In addition to spatial and temporal variability of airborne activity concentrations, inter and within (day to day) workers variability of exposures is potentially one of the greatest source of uncertainty in the estimate of annual exposures, and should be a major consideration when establishing a monitoring strategy. These have only been briefly explored in SMOPIE, and further work to develop guidance for users is recommended.

6.6. Graded approach for establishing a monitoring programme

In the case of external exposure, it is possible to (conservatively) estimate likely annual worker doses from workplace measurements (e.g. dose rates) and assumptions about working patterns. This type of approach is not normally appropriate for estimating internal exposures, due to the large variations in airborne activity and dust that can be present in workplaces. Instead, there is no reliable alternative to a measurement campaign based on personal air sampling. It is, however, very important not to embark on a full scale monitoring programme without having knowledge of the seriousness of the radiological problems, i.e. the range of exposures of workers performing different tasks at different workstations under the normal variation of working conditions. It is acknowledged that the costs associated with such measurements can be very significant. Moreover, in practice most workplaces have a limited number of PAS at their disposal. The strategy for establishing a monitoring programme recommended in the SMOPIE project [44] is, therefore, a stepwise or graded approach. In a simplified form this approach is presented schematically in figure 4.

When it is recognised that the nature of the process in an industry as well as the characteristics of the raw materials, products and residues can potentially give rise to significant exposure of workers by inhalation, the first step is to visually identify sources of dust. Measurement campaigns to assess the exposure of workers should in the first place be directed to these visible sources. However, visible proof of sources of dust such as apparent deposition on surfaces does not on its own indicate potentially significant exposure. The dust may have accumulated over long time periods, and may also have characteristics quite different from the inhalable dust that remained airborne. Extensive dust abatement measures cannot be justified on the basis of visible traces of dust sources alone, without any indication of the significance of these sources with respect to the exposure of the workers. Therefore the evaluation of the exposure situation of workers should start with a first screening of their exposures.

26 Step 1: Judgement on potential significance of workers internal exposure - Choose dose level of no further radiological concern - Collect data from non-radiological Industrial hygiene (IH) - Obtain radiological characteristics (RC) of raw materials, products and residues - Use EC Guidance RP-95 on the basis of actual data from process, IH and IC - Assess likeliness of exposure of workers to air borne dust

If exposure potentially significant

Step 2: Prepare for and conduct first screening of exposures - Obtain info on actual radionuclide composition of dust - Derive most likely solubility class of dust (F,M or S) - Select and prepare for analytical method; gravimetric or radiometric - Select inhalable or thoracic PAS with > 2 l/min flow rate - Select and group workers to be monitored - Decide on number of workers to be monitored within each group - Decide on number of shifts to be monitored for each selected worker

Step 3: Assess exposures and compare with level of no concern - Correct for sampler bias to true ambient aerosol concentration - Correct for bias in dose estimate if bias is negative - Use appropriate dose coefficient based on solubility class, default AMAD and GSD - Convert conservatively intakes from monitored shifts to annual intakes

Exposures exceed level of no concern

Step 4: Validate exposure assessment of step 3 - Validate experimentally the most likely solubility class of the aerosol - Validate the radionuclide composition of the ambient aerosol - Recalculate exposures on the basis of step 3

Exposures still exceed level of no concern

Step 5: Detailed assessment of ranges of individual exposures and their causes - Use RTDM to monitor dust levels at workstations and during task performance - Use switch on/of PAS to assess relative contributions of workstations and tasks to exposures - Assess annual occupancies in performance of tasks at workstations - Reassess exposures on the basis of annual occupancies in performing tasks at workstations - Most exposing workstations and tasks identified

Step 6

27

Step 6: Identify sources and spatial variation of airborne dust - Use visual inspection with light source to identify locally high levels of air borne dust and their source - Use RTDM for identification of dust generating machinery and process steps - Use visual inspection and wipe test to identify potential sources for resuspension - Use multiple FAS for spatial variation of dust concentration

Step 7: Define and implement countermeasures

Step 8: Assess effectiveness of countermeasures and improve them if needed and possible - Repeat monitoring with RTDM and FAS and compare with results from step 6 - Repeat detailed exposure assessment as in step 5

Step 9: Define annual routine sampling programme for dose assessment on the basis

of levels of exposure of worker groups

Figure 4: Graded approach for actions to identify and monitor exposure situations (from [44]).

Even for the first screening of worker exposures, some information is needed about the dust to which the workers are exposed. The likely radionuclide composition of the dust may be derived directly from the nature of the process. For instance industries processing heavy mineral sands can be expected to know what radionuclides occur in what concentrations in the raw materials. These characteristics are likely to be retained if the processing only involves mechanical methods like milling and sieving. The likely lung solubility class is S, irrespective of particle size.

At other workplaces the radionuclide composition of airborne aerosols may not be so easily derived, and this information, therefore, must be part of the output of the first screening by sampling and sample analysis. In this phase of the process an inherent lack of knowledge is assumed with respect to particle size distribution of ambient aerosols and to their solubility class.

With a small workforce (e.g.10 workers or less), it should be practicable to sample all the exposed workers within the period of the measurement campaign. Where larger workforces are involved, this may well be impractical. However, even then a large number of samples may still be required to determine the mean exposure with any degree of precision, due to the significant variation in individual PAS results that is typically seen. Moreover, the usefulness of the mean exposure of the whole exposed population, comprising workers achieving different tasks and/or working at different workstations, may be questionable. Consequently, to adequately estimate average exposures, and to concentrate sampling resources on groups at the higher risk, it is recommended that the exposed population is divided into worker groups based on the similarity of functions, e.g. similar tasks performed in the same areas.

28

The analysis of the PAS filters must provide the identification of radionuclides and their activities on the filters if such information cannot be obtained otherwise. Radionuclide identification is not necessary if there can be only one well-known source of air borne material, independent of the workplaces involved. This is likely to be the case for instance in the processing of heavy mineral sands by milling and sieving, but is not necessarily so in the process industry.

It is noted here that: - Low-background alpha and beta counting have low limits of detection but do not provide radionuclide identification. - Gamma spectrometry is useful to identify and quantify radionuclides on the filters but will not detect pure alpha emitters such as 232Th and 210Po). Minimum detectable activities (MDA) for 238U (234Th), 226Ra, 210Pb, 228Ra and 228Th are of the order of 0.2 Bq, which may exceed that collected on a PAS filter. If so, it may be necessary to obtain a higher volume sample (e.g. by high volume SAS, or long duration PAS) purely for the purpose of radionuclide characterisation. This technique will normally only be available at specialised laboratories. - Radiochemical analysis of 210Pb and 210Po is very sensitive (MDA is a few mBq) but requires specific laboratory skills and alpha spectrometers. Radiochemical analyses of 210Pb takes a few months of waiting for ingrowth of 210Po. - Radiochemical analysis of pure alpha emitters (232Th, 230Th) is very costly and time consuming and requires very special skills and equipment. It is unlikely to be a practical option for NORM workplaces, except as a special monitoring tool. - All radiometric analyses methods require considerable operational skills. For gross alpha and beta counting the correct calibration of the counting system for the specific radionuclide composition of the material to be analysed is not a straightforward and simple action.

Gravimetric analysis may replace radiometric analysis in cases in which the mass of material of low specific activity on the filter can be directly related to the radionuclides and their activities. This may be the case in sampling of heavy mineral sand dust (i.e. where this is the predominant source of dust) or other comparable cases.

The activities obtained from the analysis of the filters must be corrected for the estimate of the true ambient aerosol concentration. Default correction factors for an assumed AMAD of 5µm (GSD 2.5) are 1.2 for inhalable samplers, and 1.5 for thoracic samplers.

After annual intakes having been assessed for each of the radionuclides from the ambient aerosol the main factor affecting the outcome of the dose estimate is the choice of the dose coefficients. These depend strongly on the lung solubility class of the aerosol particles. With thorium isotopes as clear exceptions, the dose coefficients for the nuclides of interest are the highest for lung solubility class S. In the absence of information on the solubility of the particles in lung fluid the default solubility class therefore should be assumed to be S for all radionuclides on the filter. There is little doubt that this is a realistic choice for mineral sands or ores. It is also likely the correct choice for Ra bearing scales from the oil and gas industry, TiO2 pigment production and phosphoric acid production.

29 References 1. International Atomic Energy Agency, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115, IAEA, Vienna (1996). 2. International Commission on Radiological Protection, 1990 recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Pergamon Press, Oxford (1991). 3. United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionizing Radiation; Report to the General Assembly with Scientific Annexes, Vol. 1 & 2,UN, New York, 2000. 4. International Atomic Energy Agency, Extent of Environmental Contamination by Naturally Occurring Radioactive Material (NORM) and Technological Options for Mitigation, Technical Report Series No. 419, IAEA, Vienna (2003). 5. Commission of the European Communities, Council Directive 96/29/EURATOM/ of 13 May 1996 Laying Down the Basic Safety Standards for the Protection of the Health of Workers and the General Public Against the Dangers Arising from Ionising Radiation, Official Journal of EC, Series L, No. 159, (1996). 6. International Atomic Energy Agency, Occupational Radiation Protection, Safety Standards Series No. RS-G-1.1, IAEA, Vienna (1999). 7. International Atomic Energy Agency, Assessment of Occupational Exposure due to Intakes of Radionuclides, Safety Standards Series No. RS-G-1.2, IAEA, Vienna (1999). 8. International Atomic Energy Agency, Assessment of Occupational Exposure due to External Sources of Radiation, Safety Standards Series No. RS-G-1.3, IAEA, Vienna (1999). 9. International Atomic Energy Agency, Radiation Monitoring in the Mining and Milling of Radioactive Ores, Safety Series No. 95, IAEA, Vienna (1989). 10. International Atomic Energy Agency, Radiation Protection of Workers in the Mining and Milling of Radioactive Ores, Safety Series No. 26, IAEA, Vienna (1983). 11. International Atomic Energy Agency, Monitoring and Surveillance of Residues from the Mining and Milling of Uranium and Thorium, Safety Reports Series No. 27, IAEA, Vienna (2002). 12. International Atomic Energy Agency, Management of Radioactive Waste from the Mining and Milling of Ores, Safety Standards Series No. WS-G-1.2, IAEA, Vienna (2002). 13. International Atomic Energy Agency, Radiation Protection against Radon in Workplaces other than Mines, Safety Reports Series No. 33, IAEA, Vienna (2003) 14. International Atomic Energy Agency, Radiation Protection and the Management of Radioactive Waste in the Oil and Gas Industry, Safety Reports Series No. 34, IAEA, Vienna (2003). 15. International Atomic Energy Agency, Occupational Radiation Protection in the Mining and Processing of Raw Materials, Safety Standards Series No. RS-G-1.6, IAEA, Vienna (in preparation). 16. International Atomic Energy Agency, Radiation Protection and Radioactive Waste Management in the Phosphate Industry, Safety Report XXX, IAEA, Vienna (in preparation). 17. International Atomic Energy Agency, Radiation Protection and the Management of Radioactive Waste in the Zircon/Zirconia Industry, Safety Report XXX, IAEA, Vienna (in preparation). 18. European Commission, Investigations of a Possible Basis for a Common Approach with Regard to the Restoration of Areas Affected by Lasting Radiation Exposure as a Result of Past or Old Practice or Work Activity - CARE, Radiation Protection 115, 2000. 19. A.W. van Weers, A. Stokman-Godschalk, Radiation protection, regulatory and waste disposal aspects of the application of mineral insulation wool with enhanced natural radioactivity, Proceedings of the Third International Symposium on the Treatment of Naturally Occurring Radioactive Materials (NORM III), Brussels, September 17-21, 2001. 20. European Commission, Practical use of the Concepts of Clearance and Exemption, Part II, Application of the Concepts of Exemption and Clearance of Natural Radiation Sources, Radiation Protection 122, Part II, (2002).

30 21. International Commission on Radiological Protection, General Principles for the Radiation Protection of Workers, ICRP Publication 75, Pergamon Press, Oxford, (1997). 22. International Commission on Radiological Protection, Protection against Radon-222 at Home and at Work, ICRP Publication 65, Pergamon Press, Oxford, (1993). 23. International Commission on Radiological Protection, Protection of the Public in Situations of Prolonged Radiation Exposure, ICRP Publication 82, Pergamon - Elsevier, Stockholm, (2000). 24. European Commission, Recommendations for the implementation of Title VII of the European Basic Safety Standards Directive concerning significant increase in exposure due to natural radiation sources, Radiation Protection 88, (1997). 25. European Commission, Reference Levels for Workplaces Processing Materials with Enhanced Levels of Naturally Occurring Radionuclides, Radiation Protection 95, (1999). 26. European Commission, Establishment of reference levels for regulatory control of workplaces where materials are processed which contain enhanced levels of naturally occurring radionuclides, Radiation Protection 107 (1999). 27. European Commission, Radiological protection principles concerning the natural radioactivity of building materials, Radiation Protection 112 (1999). 28. A. Martin, S. Mead, B.O. Wade, Materials containing natural radionuclides in enhanced concentrations. European Commission, Report EUR 17625, 1997. 29. J. Hofmann, R. Leicht, H.J. Wingender, J. Wörner, Natural radionuclide concentrations in materials processed in the chemical industry and the related radiological impact, European Commission, EUR Report 19264 (2000). 30. German Commission on Radiological Protection, Radiological protection principles concerning the safeguard, use of release of contaminated materials, buildings, areas or dumps from uranium mining. Recommendations of the Commission on Radiological Protection with explanations, Band 23, Gustaf Fisher Verlag, (1993). 31. German Commission on Radiological Protection, Strahlenexposition an Arbeitsplätze durch natürliche Radionuklide, Heft 10, Gustaf Fisher Verlag, (1997). 32. T. John, W. Hake, S. Thierfeldt, Bewertung von Reststoffen mit natürlichen vorkommender Radioaktivität im Hinblick auf Arbeitsplätze, Brenck Systemplanung, Aachen, (1999). 33. D.E. Becker, A. Reichelt, Anthropogene Stoffe und Produkte mit natürlichen Radionukliden - Teil I: Überblick über die wichtigsten Expositionspfade, TÜV Bayern e.V., (1991). 34. A. Reichelt, K.H. Lehmann, Anthropogene Stoffe und Produkte mit natürlichen Radionukliden - Teil II: Untersuchungen zur Strahlenexposition beim beruflichen Umgang, TÜV Bayern e.V., (1993). 35. A. Reichelt, J. Röhrer, K.H. Lehmann, Anthropogene Stoffe und Produkte mit natürlichen Radionukliden - Teil Ia: Strahlungseigenschaften von Roh- und Reststoffen - Literaturrecherche, TÜV Bayern e.V., (1994). 36. A. Reichelt et al, Anthropogene Stoffe und Produkte mit natürlichen Radionukliden - Teil III: Untersuchungen zur Strahlenexposition der Bevölkerung, TÜV Bayern e.V., (1994). 37. C.W.M. Timmermans, A.W. van Weers, Identification of occupational exposures to natural radiation sources in the Netherlands, Proceedings of the Second International Symposium on the Treatment of Naturally Occurring Radioactive Materials (NORM II), Krefeld, November 10-13, 1998. 38. C.W.M. Timmermans, A.W. van Weers, Inventory of work activities with exposure to natural radiation sources,; Working document 121 of the Ministry of Social Affairs and Employability; 1999, The Netherlands (in Dutch). 39. C.W.M. Timmermans, A.W. van Weers, Inventory of work activities with exposure to natural radiation sources: Actualisation of the inventory of 1999, Working document 200 of the Ministry of Social Affairs and Employability; 2001, The Netherlands (in Dutch). 40. International Atomic Energy Agency, Assessment of Occupational Protection Conditions in Workplaces with High Levels of Exposure to Natural Radiation, Working Material of a Technical Committee Meeting, 7-11 May 2001, IAEA, Vienna (2002).

31 41. European Commission, Enhanced radioactivity of building materials, Radiation Protection 96, 1999. 42. G. Åkerblom, Radon legislation and national guidelines, SSI report 99:18, Swedish Radiation Protection Institute, Stockholm, (1999). 43. European ALARA Network, 3rd European ALARA Network Workshop on "Managing Internal Exposure", Neuherberg, November 1999. 44. J. van der Steen, A.W. van Weers, C.W.M. Timmermans, C. Lefaure, J.-P. Degrange, P.V. Shaw, O. Witschger, Strategies and Methods for Optimisation of Internal Exposures of Workers from Industrial Natural Sources (SMOPIE), Paper 0257, this proceedings. 45. International Commission on Radiological Protection, Dose coefficients for intakes of radionuclides by workers. ICRP Publication 68 Annals of the ICRP 24 No 4 Pergamon Press, Oxford, 1994. 46. International Commission on Radiological Protection, ICRP Database of Dose Coefficients: Workers and Members of the Public, Version 1.0 (2001). 47. Koninklijk Besluit van 16 juli 2001, houdende vaststelling van het Besluit stralingsbescherming Staatsblad 2001, 397 (Translated document title: Royal Decision of 16 July 2001 holding the establishment of the Radiation Protection Decree, State Journal 2001, 397, The Netherlands) (in Dutch). 48. C.W.M. Timmermans, Scenarios and reference levels for the disposal and reuse of large quantities of residues from the non-nuclear industry, KEMA report 22727-NUC 97-9002, 1997. 49. C.W.M. Timmermans, Conditional clearance levels for the use of residues from the non-nuclear industry as building materials, KEMA report 22892-NUC 98-9002, 1998 (in Dutch). 50. M.J.M. Pruppers, R.O. Blaauboer, C.J.W. Twenhöfel, Research for discharge criteria for licensing according to the Nuclear Energy Act in the process industry, RIVM report nr. 610310002, 1999 (in Dutch). 51. A.W. van Weers, C.W.M. Timmermans, E.I.M. Meijne, Evaluation of the substantiation of proposed clearance levels in the draft Radiation Protection Decree, NRG report 20293/00.31670, 2000 (in Dutch). 52. A. Reichelt, K-H. Lehmann, Anthropogene Stoffe und Produkte mit natürlichen Radionukliden – Teil 2: Untersuchungen zur Strahlenexposition beim beruflichen Umgang. Bayerisches Staatsministerium für Landesentwicklung und Umweltfragen, 1993. 53. H.P. Leenhouts, P. Stoop, S.T. van Tuinen, Non-nuclear industries in the Netherlands and radiological risks. RIVM report 610053003, March 1996. 54. Proceedings of the International symposium on radiological problems with natural radioactivity in the Non-Nuclear Industry (NORM I), Amsterdam, September 8 – 10, 1997. 55. L.C. Scholten, Approaches for regulating management of large volumes of waste containing natural radionuclides in enhanced concentrations. European Commission, Report EUR 16956, 1996. 56. V.J.M. Steenhof, Opslagmogelijkheden van zeer laag radioactief afval in Nederland (translated document title: Possibilities for disposal of very low level radioactive waste in the Netherlands), DHV Milieu en Infrastructuur BV, DHV Report ML-TE19980130, 1999 (in Dutch).

32 Annex 1

Summary of presentations, given at a Technical Committee Meeting on the Assessment of Occupational Protection Conditions in Workplaces with High Levels of Exposure to Natural Radiation, 7-11 May 2001, IAEA, Vienna (from [40]).

DESCRIPTION OF NORM ACTIVITIES IN VARIOUS COUNTRIES

Three major phosphate-processing industries have been investigated in Belgium. In one of them the activity concentration of 226Ra in the ore was quite high, almost 1,100 Bq/kg, and the concentration in the silt waste was exceeding 7,000 Bq/kg. The radon concentration at ground level in the silt basin was more than 500 Bq/m3 and in some of the buildings radon levels of up to 800 Bq/m3 were measured. Gamma radiation levels from 0.1 to 4.4 µSv/h were found. The area downstream from one of the plants is being investigated. The riverbanks have been found to be highly contaminated up to 5 to 10 m from the river. The radium concentration at 30 cm depth ranged between 400 to 4,000 Bq/kg and in river sediments between 400 to 2,000 Bq/kg. The gamma radiation levels reached 2 µSv/h.

In Brazil, a preliminary survey has been performed of exposure of workers to natural radiation in industries that mine, mill or process minerals rich in uranium and thorium. The survey included six mines, two coal mines, one niobium mine, one nickel mine, one gold mine and one phosphate mine. The study included collection and analysis of urine samples complemented by faeces and air samples. The concentrations of uranium, thorium and polonium were measured in the samples and compared to background data from the general population of Rio de Janeiro and the workers’ families. The results of the study showed that radon progeny could be a problem in the coal mines and that in some areas of the niobium mine internal contamination to uranium and thorium and their decay products could occur. For the nickel, gold and phosphate mines the conclusion was that no programmes to control internal doses were necessary.

Canada has experienced NORM problems in mineral extraction and processing industries, oil and gas production, metal recycling, thermal-electric production, in water treatment facilities and in underground workings etc. High concentrations of 226Ra are found in scales and sludge from the oil industry. NORM issues fall under the jurisdiction of the provinces and territories. Guidelines for the management of NORM have been issued, where a NORM classification system has been established. If a workplace is suspected of giving rise to incremental doses exceeding 0.3 mSv/y a dose assessment should be carried out. An incremental dose of 0.3 mSv/y is adopted as the NORM Investigation Threshold. Where the estimated incremental annual effective dose to the public or incidental workers is greater than 0.3 mSv/y the classification is NORM Management which might mean that public access to the workplace would need to be restricted. Where the estimated incremental dose to occupationally exposed workers is greater than 1 mSv/y, the Dose Management Threshold, the classification will be Dose Management. The programme under Dose Management should include dose estimation and information and training of the workers to control and reduce doses. At an assessed or measured incremental dose greater than 5 mSv/y Radiation Protection Management is required. Whenever a NORM Management, Dose Management or Radiation Protection Management has been implemented, a periodic review is needed. The frequency will depend on ability of conditions to change and the NORM programme. Derived Working Limits (DWL) have been determined from the annual radiation dose limits to assist in dose assessment. The DWLs provide an estimate of the dose from the quantities that are directly measured at the workplace.

A fourteen-year follow-up study of the thorium lung burden of workers has been carried out at an iron and rare earth metals mine in China. The results showed that the highest thorium lung burden of the more than 600 miners was about 11 Bq. The conclusion is that no adverse health effects could be detected due to

33 inhaled thorium and that the possible practical threshold for thorium lung burden to induce lung cancer might be higher than 11 Bq.

Natural radiation in Finland is regulated in the Finnish Radiation Act from 1992. Occupational exposure to natural radiation is regulated by an amendment of the Radiation Decree in 1998. The most important issues in Finland are radon in workplaces, radioactivity in drinking water and in building materials, and mining and industrial processes. Radon levels in mines have been measured regularly since 1972. Finland has an action level for radon in workplaces of 400 Bq/m3. Radon prone areas have been identified primarily from measurements of radon in dwellings. Radon measurements are compulsory in workplaces in radon prone areas unless it can be shown by other means that radon levels are low. A programme focusing on radon in workplaces was initiated in 1992. To date, radon measurements have been carried out in 10,000 workplaces and remedial actions have been taken in 200 of these. The average reduction in radon concentration in remediated buildings is about 1,500 Bq/m3. Identification of NORM industries is based on the radionuclide content of the materials used (>1.4 Bq/g U and >0.4 Bq/g Th). The occupational exposure should not exceed 1 mSv/y (excluding radon).

Germany has a reference level of 2 106 Bqh/m3 for radon in workplaces, corresponding to an annual dose of 6 mSv and a limit of 6 106 Bqh/m3, corresponding to 10 mSv/y. If the reference level is exceeded remedial action has to be taken and a new radon measurement should be carried out. If it is not possible to reduce the radon concentration below the reference level the competent authority has to be notified and monitoring of the radon concentrations performed. Germany has performed a study to investigate the exposure by natural radionuclides in workplaces in a large number of industrial activities, with a dose assessment of the workers under normal circumstances. They made a categorization of NORM activities in dose ranges of <1, 1-6, 6-20 and >20 mSv/y. Most of the NORM activities fall in the category <1 mSv/y when normal occupational hygiene measures are taken.

From India, a report on monitoring for occupational exposure to natural radiation was provided. Three uranium mines are operational at present in India. For the protection of the workers, ambient radon measurements, personal radon and gamma monitoring, and internal contamination measurements are performed. Track etch films and TLD (thermoluminescence dosimeters) are used for the personal monitoring. Assessments of radium body burdens are being done by measurements of radon in exhaled breath using a low level radiation detection system based on electrostatic collection of charged 218Po atoms. The technique, which has been developed in India, is simple, fast and sensitive enough for routine measurements, the sampling time being ten minutes. The equipment is designed for field use and can easily be transported between different facilities.

In Ireland, extensive measurements of radon in show caves and recreational caves have been carried out. In some show caves it will be necessary to either limit the number of working hours underground and/or introduce a control/monitoring system. In 1998 a three-year programme was launched to identify schools with radon levels exceeding the guidance level of 200 Bq/m3. Measurements and remediation is funded by the government. 37,000 measurements were carried out in 4,000 schools. 23 per cent of the schools had radon levels exceeding the guidance level. The maximum radon concentration found was 3,000 Bq/m3. A pilot campaign for measuring radon in aboveground workplaces will be launched during the summer of 2001. Ireland has based the identification of NORM industries mainly on information from international literature, and individual industries are identified on the basis of licences that have already been issued. Codes of practice and guidance notes are the main instruments to comply with the regulations.

In the Netherlands a first survey of NORM activities with regard to occupational exposure was carried out in 1998/1999 and has been updated in 2001. The basic criteria for the identification of a NORM activity being of concern is that the effective dose for normal working conditions exceeds 0.1 mSv/y or that 1 mSv/y could be exceeded during unlikely conditions. Three categories of NORM activities are identified, A, B and C. For category A the likely effective dose for normal working conditions does not exceed 0.1

34 mSv/y or 1 mSv/y for unlikely conditions. For category B the dose would be between 0.1 and 1 mSv/y for likely conditions or 1 - 6 mSv/y for unlikely conditions, and for category C 1 - 6 mSv/y for likely conditions or 6 - 20 mSv/y for unlikely conditions. Work activities falling into category C are thermal phosphorus production (decontamination), oil and gas production (overhauling components), TIG (Tungsten Inert Gas) welding and aircraft operation (scheduled flight above 8 km altitude). Specific attention was paid in the presentation to a special type of mineral slag wool containing elevated concentrations of U and Th, in the order of 5 - 10 and 10 - 15 Bq/g respectively. This material has been used in a large variety of installations as an insulating material. It was shown that it potentially gives rise to enhanced exposures during decommissioning.

In Poland the miners are divided into class A workers, if the annual effective dose lies between 5 and 20 mSv, and class B workers, if the dose exceeds 20 mSv in a single year. For class A workers prevention measures must be applied such as improving the ventilation, filtration of air, isolation of parts of the mine that are no longer used and removal of radium in waters in non-active areas. For class B workers individual doses must be measured. For coal and copper mines the major exposures originate from inhalation of radon progeny and internal contamination and external gamma radiation from radium-rich water and sediments. The concentration of 226Ra can be very high in deposits in coal mines, up to 400 kBq/kg and the concentration in water can reach 400 Bq/L. The doses in the coal mines have decreased steadily between 1993 and 1999. A Polish study of cancer risks for miners exposed to radon decay products was presented. A computerized database covering the exposures to radon progeny for more than 9,000 workers has been in use since 1977. The average annual dose to the Polish miners during the period 1972 to 1998 was about 2.7 mSv (0.54 WLM). The exposure-age duration model of the BEIR VI study was used to evaluate the risk for lung cancer. The conclusion of the study was that the occupational lifetime risk of lung cancer for the miners was 1.8 per cent assuming an average lifetime of 75 years and an occupancy period from 20 to 55 years of age.

South Africa has a very large mining and minerals processing industry exploiting a variety of ores and minerals containing elevated levels of NORM. The industry employs more than 300,000 persons. Doses have been assessed to workers in the mining industry in South Africa. In the gold mining industry radon measurements have been performed since the early 1970s. Regulations have been in force since 1990. The mean annual dose to underground gold mine workers, mostly from radon progeny, is about 5 mSv with maximum doses exceeding 20 mSv. The maximum annual dose to surface workers in gold mines is 5 mSv. In South African coal mines the mean annual dose from inhalation of radon decay products has been estimated from limited radon concentration measurements to be about 0.6 mSv. In the phosphoric acid and fertilizer production industry the doses to the workers do not exceed 6 mSv/y. There are 3 mineral sands operations in South Africa, for which the maximum annual dose to workers is 3 mSv. One open pit copper mine contains elevated levels of U, which is extracted as a by-product. The maximum annual doses to workers are 5 mSv for workers in the mine and 20 mSv for workers in the metallurgical plant. Worker doses in the metallurgical plant have since been reduced with the introduction of radiation protection measures.

Fifty four health spas have been investigated in Spain. The most exposed people were the bath attendants. Doses of up to 44 mSv/y were registered. Radon levels have been measured in a number of show caves. The Altamira cave had maximum radon levels of about 5,000 Bq/m3. In Spain, the phosphate and fertilizer industry have been identified as NORM activities of concern, as well as the building materials industry. A study for a more comprehensive identification has been launched in 2001.

In Sweden regular monitoring of radon in mines has been performed since 1972. Today the radon situation in Swedish mines is satisfactory. The radon levels are normally well below the action level which corresponds to 1,500 Bq/m3. Radon in workplaces has been regulated in Sweden since 1990. Although no representative survey of radon at regular workplaces has been carried out in Sweden, smaller surveys and the high radon concentrations in dwellings indicate that workplaces with elevated radon levels are

35 common in Sweden. The situation in schools and day-care centres was thoroughly investigated in 2000. The estimated number of school and child-care buildings with radon concentrations exceeding the action level, 400 Bq/m3, is 800; about 200 of these have been identified and in about 100 buildings remedial measures have been taken. Very high levels of indoor radon have been found in waterworks in Sweden. Groundwater from aquifers in bedrock and soil and surface water that has been infiltrated through deposits of sand or gravel have the potential to cause high radon levels in indoor air. Three waterworks in central Sweden have been studied. The radon concentrations in the raw water of these waterworks ranged from 85 Bq/L to 300 Bq/L. In one waterworks average indoor radon concentrations exceeding 17,000 Bq/m3 have been measured. Peaks exceeding 56,000 Bq/m3 have been measured in another. It is quite possible that employees of waterworks can receive doses exceeding 20 mSv/y. New knowledge, at least for Sweden, is that radon can be forced into the premises by changes in the water level in a reservoir. This can also give rise to substantial diurnal variations in the indoor radon concentration. Normally, applying a ventilation system with suction points above the open water surfaces can successfully reduce the high indoor radon levels. In Sweden, because of the geological conditions, with an abundance of granites and pegmatites rich in uranium and thorium together with large areas of uranium-rich alum shale, exposure to natural radiation is not unusual in certain types of industries and other work activities. Regulations on natural radioactivity in building materials (for new buildings) have been in force since 1980. Lightweight concrete produced from uranium-rich alum shale was in use between 1929 and 1975. Almost 400,000 dwellings, 10 per cent of the Swedish building stock, contain this material. The situation at NORM industries is currently being investigated. Since the beginning of the 1950s, it has been known that residues from several industrial activities contain enhanced levels of natural radioactivity. Some examples are burnt alum shale from lime burning, radium-rich slag from metal production and waste gypsum from phosphoric acid production. The impact of the exposure from these residues is now being reinvestigated.

In a presentation from the Zircon Industry, it was shown that zircon sand contains significant concentrations of uranium, 3,500 to 4,500 Bq/kg, and thorium, 400 to 600 Bq/kg. Deposits mainly occur in South Africa, Australia, India and the USA. The mining is done by dredging or by just shoveling the sand onto trucks. The separation could be done by dry or wet concentration. Also the milling could be by dry or wet processes. The dry process has the highest risk of dust generation. The maximum potential annual dose for the milling process has been assessed to be about 5 mSv. Measurements from South Africa and Australia indicate lower doses, 0.2 to 1 mSv/y.

The Natural Materials Radiation Control Initiative (NMRCI), a forum of regulators, advisory bodies and operators in NORM industries from Australia, Brazil, Malaysia, Netherlands, Poland, South Africa and USA, reported on its activities that were aimed at addressing NORM regulatory issues through industry/regulatory co-operation. The objective was to generate comprehensive information on quantifying exposures to both workers and the general public, through the consolidation of existing data and the collection of data from new studies. In its interactions with the IAEA to date, the NMRCI had proposed that it assist in drafting a Safety Report identifying exposure sources and providing information on suggested methods for national regulatory bodies, advisory bodies and NORM industries to make quantitative assessments and to identify how best to meet the requirements of the BSS. It was envisaged that the Safety Report should reflect the principles contained in ICRP recommendations and IAEA Safety Standards, should make maximum use of measured data, and should deal separately with different industries such as phosphates, coal and niobium, taking account of the differences in chemical, physical and radiological properties of the materials as well as differences in work practices. It had been decided that occupational exposure issues should be addressed as a first priority, before moving on to the public exposure arena where waste management issues such as waste disposal and remediation of contaminated sites would be addressed. The NMRCI also aimed to promote co-operation between NORM industries and regulatory authorities on the matter of regulations and their impact on international trade in commodities containing NORM.

36 In 1991 ICRP first included exposure of aircraft crew to cosmic radiation as occupational exposure. The European Dosimetry Group (EURADOS) established a working group in 1992 to address this issue. The report “Exposure of Air Crew to Cosmic Radiation” was published in the European Commission’s Radiation Protection series as report 85. The first section of the report assesses the existing data on radiation exposure, describes the radiation environment at civil aviation altitudes and summarizes the computational models that have been developed to describe the cosmic ray radiation field in the atmosphere. The second section describes the quantities used to assess the radiation doses. It is clear that conventional radiation protection dosimetry as applied on the ground is not quite applicable to the situation for air crews. A multinational European research project was launched to investigate the problem of cosmic rays and dosimetry at aviation altitudes. The major objective was to measure the flux and energy spectra of neutrons and charged particles over a wide energy interval at aviation altitudes and compare the results with those calculated with various computer codes. Within the project much progress was made in different areas, for instance the determination of the fundamental physical characteristics of the cosmic radiation field at aircraft altitudes, development of instrumentation, measurements of dose rates and route doses and application of routine radiation protection. Surveys of air crew exposure have been carried out with different advanced dosimetric systems and comparisons were made between passive and real-time detector systems.

37 Annex 2

THE MAIN ISSUES CONCERNING NORM IN THE NETHERLANDS

A2.1. Introduction In May 1996 the Council of the European Union adopted the new Euratom Council Directive 96/29 laying down basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionising radiation [5]. The Member States have implemented this directive in their national legislation. The Directive applies to all practices, which involve a risk from ionising radiation emanating from an artificial source or from a natural source in cases where natural radionuclides are processed in view of their radioactive properties. It also applies to work activities, which involve the presence of natural radiation sources, which cannot be disregarded from a radiation protection point of view.

Title III of the Directive deals with the system of reporting, authorisation and clearance for practices. Exemption levels for reporting of practices are specified in Annex 1 of the Directive, but it is left to the Member States to establish clearance levels for disposal, recycling or reuse of radioactive materials. Apart from some specific practices that always require prior authorisation, Member States may define a dividing line between reporting and authorisation for other practices.

Title VII of the Directive specifically addresses enhanced exposures due to natural radiation sources. In article 40 it is stated that each Member State shall ensure the identification by means of surveys or by any other appropriate means, of work activities which may be of concern, in particular: a. work activities where workers and, where appropriate, members of the public are exposed to thoron or radon daughters or gamma radiation or any other exposure in workplaces such as spas, caves, mines underground workplaces and aboveground workplaces in identified areas; b. work activities involving operations with, and storage of, materials, not usually regarded as radioactive but which contain naturally occurring radionuclides, causing a significant increase in the exposure of workers and, where appropriate, members of the public; c. work activities which lead to the production of residues not usually regarded as radioactive but which contain naturally occurring radionuclides, causing a significant increase in the exposure of members of the public and, where appropriate, workers; and d. aircraft operation. Moreover, article 41 specifies that Member States may also decide on the applicability of all or parts of the relevant Titles, including Title III, for work activities of concern.

These issues are very important for industries dealing with NORM, because they may threaten a harmonised implementation of the BSS in the legislation of the different Member States. Specifically, the levels for clearance of natural radionuclides have a direct effect on the volumes of waste and residues for which the regulations are applicable. To avoid problems with competition and transboundary transport of materials within the European Union it should be highly desirable to decide on an internationally agreed set of clearance levels. In order to stimulate harmonisation, the European Commission has published a guideline to assist Member States in regulating natural radioactive sources [24]. Reference levels for workplaces processing NORM contaminated materials have also been published [25].

A2.2. The Dutch Radiation Protection Decree

A2.2.1. Methodology for derivation of exemption and clearance levels

The Dutch Radiation Protection Decree [47] has been published in 2001 and came into force on 1 March 2002. The scope of the Decree has excluded:

38 - Exposure to radon and daughters from undisturbed earth crust, from burning of natural gas and from building materials in buildings; - Above ground exposure to radionuclides from undisturbed earth crust and from building materials in buildings; - Naturally occurring radionuclides in the body; - Cosmic radiation (except aircrew).

Chapter 8 of the Decree deals with natural sources and work activities that are covered by the regulations. The approach is that all work activities should be reported or licensed when both the total activity and the activity concentration exceed nuclide specific exemption levels. The Decree contains a single table of activity and activity concentration levels for a large number of radionuclides, both of artificial and of natural origin. The values in the table are both for exemption and clearance, so there is no numerical difference between these two concepts. The values for artificial radionuclides are based on Annex 1 of the Euratom Directive (with the exception of 60Co, for which a 10 times lower activity concentration level is specified). For those radionuclides that are not mentioned in Annex 1, the same methodology for derivation of the values has been used, based on an effective dose criterion of 10 µSv per year. However, the values for natural radionuclides have been calculated using a 300 µSv/y effective dose criterion and exposure scenarios that are considered to be realistic, but conservative, for the Dutch situation. This dose value, which is approximately the same as the variation of the natural background, is considered as a pragmatic choice in order to avoid regulating a large number of industries. This wouldn’t have a beneficial effect on radiation protection. The exemption and clearance levels that are specified in the Radiation Protection Decree are based on several studies carried out for the Dutch Ministry of Housing, Spatial Planning and the Environment [48-51].

A2.2. Identification of work activities

Identification of work activities with emphasis on occupational exposure has been carried out for the Ministry of Social Affairs and Employment [38, 39]. In general, the methodology of Penfold et. al., described in Radiation Protection 107 [26], was followed for these studies. Industries in the Netherlands with potentially significant NORM aspects were identified, based on data from literature, and work activities were classified within these industries with the aid of exposure scenarios for both normal and unlikely conditions. The effective annual doses for workers are calculated using exposure scenarios, which are specific for the type of industry considered. The exposure scenarios are limited to external irradiation and internal contamination by inhalation of dust. Details of the work activities, the scenarios and the parameters used are given in [37-39].

The studies gave a clear picture of the industries in the Netherlands where exposure to NORM may not be ignored from a radiological point of view. They showed that, except for exposure of aircraft personnel to cosmic radiation, most exposure situations in the Netherlands are related to the processing of ores, products and residues with enhanced concentrations of natural radioactivity. This is in accordance with data from other studies [26, 28, 52-55], that show that such exposures occur at various types of industry. The most important of these are the phosphate and fertiliser industry, the metal and rare earths production industry, the ceramic industry, the production and use of thoriated materials, the pigment industry and the oil and gas production.

In the Dutch studies, doses were calculated for selected work activities leading to enhanced exposure to natural radiation, based upon scenarios for normal and unlikely conditions. The work activities were then classified according to the methodology of Penfold [26] in the following dose categories:

Category A: doses under normal conditions less than 0,1 mSv per year and for unlikely conditions less than 1 mSv per year;

39 Category B: doses under normal conditions between 0,1 and 1 mSv per year and for unlikely conditions between 1 and 6 mSv per year; Category C: doses under normal conditions between 1 and 6 mSv per year and for unlikely conditions between 6 and 20 mSv per year; Category D: doses under normal conditions between 6 and 20 mSv per year and for unlikely conditions between 20 and 50 mSv per year; and Categroy E: doses under normal conditions above 20 mSv per year and for unlikely conditions above 50 mSv per year.

Figure A2.1 gives a graphical representation of the classification scheme.

Normal Unlikely circumstances circumstances E 20 mSv 50 mSv

D

6 mSv 20 mSv

CC

1 mSv 6 mSv

B

0,1 mSv 1 mSv A

Figure A2.1: Classification of working activities in the Netherlands based on doses received under normal and unlikely conditions. The most restrictive condition determines the classification.

The studies have shown that work activities generally lead to exposures below 1 mSv per year under normal conditions (category B). Most of the work activities even fall in dose category A, which means an exposure under normal conditions of less than 0.1 mSv per year. A number of work activities may lead under unlikely conditions to doses above 1 mSv per year. These are classified in categories B and C and are mostly associated with fairly high dust concentrations and maintenance and cleaning of radioactively contaminated equipment. Exposure of aircraft personnel during intercontinental flights falls in category C: normal exposures are in the range of 2-4 mSv per year, but exposures up to 10 mSv per year are possible. The use of thoriated welding rods may lead under unlikely conditions to doses above 10 mSv per year. The results of the study are shown in table A2.1.

40 Table A2.1. Identification of work activities leading to enhanced occupational exposure to natural radionuclides in industries in the Netherlands (from [39]).

Category C: significant exposure Dose under normal conditions between 1 and 6 mSv and under unlikely conditions between 6 en 20 mSv per year: Aircraft operation - scheduled flights above 8 km altitude Mechanical welding - TIG welding Thermal phosphorus production - decontamination Oil & Gas production - revision at a specialized company

Category B: small exposure Dose under normal conditions between 0,1 and 1 mSv and under unlikely conditions between 1 en 6 mSv per year: Mineral sands industry - milling, bag filling Mineral sands industry - storage of raw material and milled products (zircon sands) Thermal phosphor production - sintering plant Thermal phosphor production - phosphor production plant Electricity production - maintenance of furnace walls Slag wool - decommissioning of installations Slag wool - external exposure Steel production - sintering plant Metal recycling - 226Ra scale containing components Metal recycling - shreddering components of E&P industry Catalyst production - maintenance of installations Phosphoric acid production - maintenance of installations Fertiliser production - maintenance of installations Fertiliser production - storage of phosphate ore and fertiliser TIG welding - grinding of welding rods TiO2 pigment production - release of MeOH dust Cement production - maintenance brick ovens Use of phosphor slag - road construction Glass ovens (ZAC bricks) - external exposure Zinc production - storage cobalt cake

A2.2.2. Public exposure Apart from occupational exposures, industries are identified, using a generic dose assessment methodology, for which external radiation and the airborne or water releases could give rise to concern [50, 53]. The results of both investigations for public and occupational exposures have been used to indicate work activities that might be subject to regulatory control.

A2.2.3. Clearance and exemption levels for natural radionuclides The results of the calculations in the different studies for the Ministries of Housing, Spatial Planning and the Environment [48-51, 53] and of Social Affairs and Employment [38,39] were comparable. This led to the single set of exemption and clearance levels as defined in the Dutch Radiation Protection decree. The values for the natural radionuclides differ considerably from the values that have been established in the guidance document of the European Commission (RP122/II, [20]), which are based on generic exposure scenarios. The values for the most relevant natural radionuclides, both in the Dutch Radiation Protection Decree and in RP122/II, are given in table A2.2.

41 Table A2.2. Exemption/clearance levels for some natural radionuclides in the Dutch Radiation Protection Decree [47] and in RP122/II [20]. For “s” and “+” see Annex I, table B of the Euratom Directive [5]. Summation rule to be applied when more than one radionuclide is present: Σ(Ci/ELi) < 1. Radionuclide Dutch Decree, Dutch Decree, RP122/II (Bq/g) Total Activity (Bq) Activity Concentration (Bq/g) 238Us 1,000 1 0.5 232Ths 1,000 1 0.5 228Ra+ 100,000 1 1 226Ra+ 10,000 1 0.5 210Pb+ 10,000 100 5 210Po 10,000 100 5

It is important to notice that work activities are exempted from reporting when either the total activity or the activity concentration is lower than the values in table A2.2. Since industries use large amounts of materials, the total activity will always exceed the levels specified in the Dutch Radiation Protection Decree. Therefore, for the process industry the activity concentration is the discriminating factor for exemption and clearance.

The difference between the activity concentrations in the Dutch decree and RP122/II for Po/Pb-210 is a factor of 20, but it is believed that the exposure scenarios in RP122/II for the main Po/Pb-210 containing waste streams, which are in the Netherlands mainly related to exposure to sludge and scales of the oil and gas production industry, are over conservative.

A2.2.4. Clearance levels for discharges The Dutch Radiation Protection Decree contains also a table with clearance levels for aerial and liquid discharges, in terms of GBq per year, as a consequence of work activities. The values for the most relevant radionuclides are given in table A2.3.

Table A2.3. Clearance levels for aerial and liquid discharges of natural radionuclides as a consequence of work activities (GBq/y per installation). Radionuclide Aerial discharge Liquid discharge 238U 10 1,000 232Th 1 100 228Ra 1 100 226Ra 10 10 210Pb 10 10 210Po 10 10

A2.2.5. System of exemption/clearance, reporting and authorisation

The system of exemption and clearance, reporting and authorisation of work activities, as described in the Dutch Radiation Protection Decree, can be summarised as shown in table A2.4.

42 Table A2.4. System of exemption/clearance, reporting and authorisation of work activities in the Dutch Radiation Protection Decree. Total activity < EL/CL value - Exempt/Clear

Total activity ≥ EL/CL value - Concentration < EL/CL value - Exempt/Clear - Concentration ≥ EL/CL value - Report - Concentration ≥ 10 times EL/CL value - Authorise

Total discharged activity - < EL/CL value - Clear - ≥ EL/CL value - Authorise

A2.3 NORM Residues and Wastes in the Netherlands

The most important residues and waste streams from NORM industries in the Netherlands and the approach for management of the residues is summarised in table A2.5.

With respect to the sludge from the oil and gas production industry, one can conclude that there is no final solution for the management of this waste stream. The activity concentration is varying, but most of the sludge can be considered as reported or some cases even authorised material. The composition of the waste, with organic and heavy metal components, makes it unsuitable for long term storage at the radioactive waste repository site and at the moment there is no work up process available. Re-injection in abandoned wells is not allowed, as the Dutch government policy forbids waste disposal in the deep underground.

The activity concentration in the slag from the phosphorus production industry is around the reporting level. The slag is used as a road construction material. Doses for road construction workers are estimated to be 0.3 mSv/y under working normal conditions [38, 39]. The calcinate, with an activity concentration of 1000 Bq/g 210Pb, is clearly authorised material. No reuse is foreseen. The material is being stored at the radioactive waste repository site. This is long term storage for decay of 210Pb. Because of the high temperatures used in the phosphorus production process, much of the 210Po is discharged. The total discharge exceeds the clearance level for discharges; therefore, the discharges are authorised.

The phosphoric acid production has been discontinued in the Netherlands since 2000. The phosphogypsum itself, with a 226R content of 0.5 Bq/g, could be considered as cleared material. It has always been discharged as slurry in the Nieuwe Maas, the mouth of the river Rhine. The discharges have been authorised.

The calculated aerial discharges of the cement production industry are above the clearance level for 210Po. If these discharges are confirmed, the industry should apply for an authorisation.

The zinc-rich filter cake (blast furnace dust) from the steel industry can be categorised as cleared or in some cases reported material. At the moment, this material is not reused, but stored at the site of the industrial plant (approximately 200 kton). Up to now, there is no disposal route for this waste stream. Precautions are taken to prevent resuspension. The slag is cleared material. It is reused as an additive in cement. The discharges are authorised.

Fly-ash from coal-fired stations is cleared material. The mass of fly-ash is roughly 10 % of the mass of coal, and since almost all radioactivity of the coal goes into the fly-ash, the concentration factor is about

43 10. The activity range of coal is rather broad, but in all cases a mix of coal is used for burning. This keeps the activity concentration at a few tenths of a Bq/g. Specific problems may be encountered at maintenance work in the kettle. Scales can have 210Pb concentrations of more than 100 Bq/g. This makes it necessary to take precautionary measures to avoid inhalation during maintenance work. The volume of scale, however, is very small and doesn’t create a waste management problem.

Brick production doesn’t create a waste or discharge problem. The (calculated) discharges are about a factor of 10 below the authorisation level.

The solid residues of titanium dioxide production are mostly categorised as reported material. They have been used as backfill material in landfills.

A specific problem has been encountered during the last years, after installing portal monitors at scrap yards in the Netherlands. Since that time, loads with scrap are regularly identified to contain scrap with slag wool that has been used as thermal insulating material or as substrate in green houses. It has been discovered in a wide variety of installations. The most likely origin of this material is from slag from tin production in the period of about 1946 to 1960. This slag wool contains elevated concentrations of 238U and 232Th, thus causing the triggering of the portal monitors. The activity concentrations are such that the use and disposal of the material should be reported, or in some cases even authorised, but large volumes may already have been disposed as non-radioactive waste. Looking at production data of tin in the European Union, one can conclude that the Netherlands only produced some percent of the total, while the largest production took place in Spain and the United Kingdom. However, at the moment there is no written evidence of application of tin slag in mineral wool in other European countries. At the moment, a feasibility study is going on to incorporate the slag wool in the slag of the phosphorus production plant. If this is possible, it will be reused as road construction material.

A2.4. Conclusions

The implementation of Title VII of the Euratom Directive in the Dutch regulations has been based on a pragmatic approach. The exemption and clearance levels for natural radionuclides are based on a dose criterion of 300 µSv/y to avoid unnecessary regulation of a large number of industries without any radiological protection benefit. There is no distinction in the numerical values of exemption and clearance levels.

The identification of work activities gave a clear view of the industrial processes that encounter problems with natural radionuclides in the Netherlands. In many cases, the problems are related with the processing of ores, products and residues with enhanced concentrations of natural radioactivity. This is in accordance with data from other studies [26, 28, 52-55] that show that such exposures occur at various types of industry. The most important of these are the phosphate and fertiliser industry, the metal and rare earths production industry, the ceramic industry, the production and use of thoriated materials, the pigment industry and the oil and gas production.

For most of the waste streams, pragmatic solutions are possible, without excessive cost for the industry. Large volumes of residues are reused, either as road construction material or as additive in cement. In the case of slag wool, a feasibility study is carried out to see whether a pragmatic solution for reuse is possible. For some other waste streams, however, there still isn’t a solution available at the moment. A recent study [56], carried out on behalf of the Ministry of Housing, Physical Planning and Environment, has explored the possibility of using disposal sites for chemical waste for the disposal of very low level radioactive waste, i.e. waste with an activity concentration lower than 10 times the clearance levels (the level for authorisation). It is expected that such a disposal route will be created for certain types of industrial residues and waste.

44

Table A2.5. Characteristics of and management options for the most important NORM residues and wastes produced in the Netherlands. The table also includes data on discharges.

Industry Waste / Residue Production Activity Discharges (GBq/y) Management options rate concentration range Aerial Liquid (kton/a) (Bq/g) Oil and gas Sludge 0.1 Up to 25 226,228Ra; Reported or authorised production Up to 250 Pb/Po material. No reuse foreseen: radioactive waste. No conditioning method for storage at radioactive waste repository. Disposal in abandoned wells forbidden. No final solution.

Phosphorus Slag 600 1 238U (Pb/Po Reported material. Reused production depleted) for road construction. Calcinate 10 1,000 210Pb Authorised material. No reuse foreseen. Radioactive waste, stored long-term for decay. 300-800 210Po; 30-160 210Po; Authorised. 30-100 210Pb 20-70 210Pb

Phosphoric acid Phosphogypsum 650 0.5 226Ra 250-380 226Ra; Cleared material. Discharges production (discharged as 230-300 210Po; authorised. (discontinued in slurry) 240-340 210Pb 2000)

Cement 3,200 in Calculated for 2000 Calculations not yet production 1998 ktonne/y confirmed. Authorisation? production: 78 210Po

45 Steel production Zinc rich filter 10 15-25 210Pb Cleared or reported material. cake Reusable? At the moment stored on-site. Slag 1,000 0.15 238U; Cleared material. Reused in 0.15 232Th cement production. (Pb/Po depleted) Calculated 1990 Calculated 1990 Discharges authorised. 91 210Po; 8 210Po; 55 210Pb 0.5 210Pb

Electricity Fly-ash 1,000 0.05 - 0.2 238U; Cleared material. Reused in production by 0.06 - 0.3 232Th cement production. coal burning

Brick 3,200 0.035 238U; Calculated Discharges cleared from production 0.035 232Th 1.2 210Po; authorisation. 0.2 210Pb

Titanium oxide Solid residues 10 per 90 Up to 7 238U; Mostly reported material. pigment ore Up to 11 232Th Used as backfill. production (chloride process) Calculated Figures depend on pH of 22 226Ra; process. Discharges 38 228Ra; authorised. 3 210Po; 9 210Pb

Tin production Slag wool (used as 0.5 at 4 238U; Feasibility study for reuse in (historic residues) thermal insulating present 10 232Th slag for road construction. material or as detected substrate in greenhouses)

46