Abstract
The International Commission on Radiological Protection (ICRP) recently issued ICRP Publication 142 on radiological protection from naturally occurring radioactive material (NORM) in industrial processes. Industries involving NORM may give rise to multiple hazards, and the radiological hazard is not necessarily dominant. They are diverse and may involve exposure of people and the environment where protective actions need to be considered. In some cases, there is a potential for significant routine exposure of workers and members of the public. Releases of large volumes of NORM may also result in detrimental effects on the environment from radiological and non-radiological constituents. However, industries involving NORM present no real prospect of a radiological emergency leading to tissue reactions or immediate danger for life. Radiological protection in these industries can be appropriately addressed on the basis of the principles of justification of the actions taken and optimisation of protection using reference levels. An integrated and graded approach is recommended for the protection of workers, the public, and the environment, where consideration of non-radiological hazards is integrated with the radiological hazards, and the approach to protection is optimised (graded) so that the use of various radiological protection programme elements is consistent with the hazards while not imposing unnecessary burdens.
1. INTRODUCTION
The International Commission on Radiological Protection (ICRP) has recently engaged in a set of publications dedicated to applying the system of radiological protection to existing exposure situations. Publication 126 (ICRP, 2014b) updated the recommendations for protection against exposure to radon. Publication 132 (ICRP, 2016) is devoted to radiological protection from cosmic radiation in aviation. Publications 109 and 111 (ICRP, 2009a,b) – on emergency exposure situations and living in long-term contaminated areas following a radiological emergency, respectively – are currently being updated. A publication is also in preparation dedicated to exposures resulting from contaminated sites from past industrial, military, and nuclear activities.
In the same line, in 2007, ICRP launched Task Group 76 (TG76) with the mandate to develop a report on the application of the Commission’s recommendations on radiological protection of workers, the public, and the environment against exposures resulting from industrial processes using naturally occurring radioactive material (NORM). The aim of TG76 was to develop recommendations to cover the broad range of activities associated with the processing, production, use, and disposal of materials with enhanced levels of naturally occurring radionuclides. The report should also clarify the issues concerning the type of exposure situation, the categories of exposure, and the basic principles to be applied for the management of NORM. TG76 was relaunched in 2013 with a new membership.
The draft report by TG76 was available for public consultation on the ICRP website from 20 November 2018 to 22 February 2019. Twenty-five individuals and organisations provided comments, which were analysed and addressed by TG76. The report, modified accordingly, was approved by the Commission in July 2019, and issued in December 2019 as Publication 142 (ICRP, 2019).
2. GENERALITIES ABOUT NORM
Radionuclides of natural origin are ubiquitous and are present in almost all materials on Earth. In general, they are not of radiological concern. Some human activities, however, have the potential to enhance radiation exposures from handling these materials.
Many organisations have produced comprehensive reviews of industries that may cause NORM-related radiation exposure of workers, the public, and the environment (UNSCEAR, 1982, 2008; EC, 1999; IAEA, 2006; EURATOM, 2013). Examples are given below. Further, previous industrial sites could have involved NORM, and these legacy sites may require attention.
Extraction of rare earth elements. Production and use of metallic thorium and its compounds for their metallic properties and not for their fissile, fertile and radioactive properties. Mining and processing of ores (other than uranium or thorium for the nuclear fuel cycle). Oil and gas recovery process. Manufacture of titanium dioxide pigments. The phosphate mining and processing industry. The zircon and zirconia industries. Production of metal (tin, copper, iron, steel, aluminium, niobium/tantalum, bismuth, etc.). Combustion of fossil fuel (mainly coal). Water treatment. Geothermal energy production. Cement production and maintenance of clinker ovens. Building materials (including building materials manufactured from residues or by-products).
Typical industries involving NORM process a wide range of raw materials with different levels of activity concentrations, producing a variety of products, by-products, discharges, residues, and wastes. Although the radionuclides are not concentrated for their radioactive properties, these industries may or may not be of radiological concern depending on the activity concentrations in the raw materials handled, the processes adopted, the uses of final products, the reuse and recycling of residues, and the disposal of wastes.
Industries involving NORM are diverse, they do not correspond to a sector in itself, and they are often large industries of economic importance. These industries may give rise to multiple hazards, and the radiological hazard is not necessarily dominant. They may involve exposure of people and the environment where protective actions need to be considered. In some cases, there is a potential for significant routine exposure of workers and members of the public if suitable control measures are not considered. Releases of large volumes of NORM may also result in detrimental effects on the environment from radiological and non-radiological constituents. However, due to the activity concentration in NORM before and after processing, industries involving such materials present no real prospect of a radiological emergency leading to tissue reactions or immediate danger for life.
Industries involving NORM are generally subject to authorisation, although, in many cases, this is because of conventional hazards and not for radiological protection purposes, and these industries are familiar with risk management frameworks for the protection of workers, the public, and the environment. They should generally be able to apply the criteria and requisites set for radiological protection purposes. Most industries involving NORM have been ongoing for a long time, with concern about radiological protection being a relatively recent addition. While they have experience in risk management, these industries often have limited awareness of radiological protection; this can and should be developed.
Several stages of production involving NORM can be identified: mineral extraction and processing, fabrication and use of products, reuse and recycling of residues, management of waste, and dismantling or rehabilitation of sites. Some industries may involve almost all of these stages, and others may involve only some of them. When by-products and residues are used as feedstock by other industries involving NORM and/or in common practice (e.g. building materials), NORM enters a cycle which is possibly endless (i.e. NORM can be moved and/or reprocessed from place to place).
Industries involving NORM may need to be controlled, and the system of protection, including the principles of justification of the actions taken and optimisation of protection, as well as the corresponding dose criteria and requisites, can be applied.
3. THE NEED FOR A GRADED APPROACH
3.1. Taking account of the diversity of radiation exposures
The primary purpose of the ICRP recommendations is to contribute to an appropriate level of protection for people and the environment against the detrimental effects of radiation exposure without unduly limiting the desirable human actions that may be associated with such exposure. The ICRP system of radiological protection aims primarily to protect human health, with the objective of managing and controlling exposures to ionising radiation so that deterministic effects (tissue reactions) are prevented and the risks of stochastic effects (mainly cancer) are reduced to the extent reasonably achievable. The system applies to all radiation exposure to any natural or man-made controllable sources (ICRP, 2007).
The radiological protection system was developed gradually during the 20th century, integrating advances in knowledge about the effects of radiation, the evolution of ethical and societal values, and the feedback experience from its practical implementation. On these bases, ICRP issued several sets of fundamental recommendations describing its radiological protection system, particularly: Publication 26 (ICRP, 1977), Publication 60 (ICRP, 1991), and Publication 103 (ICRP, 2007).
From a historical perspective, it should be noted that the scope and priorities of protection have changed. Until the Second World War, the Commission was almost dealing solely with the protection of medical staff. After the War, the focus was mainly on nuclear energy and radiological protection developed to protect workers inside nuclear installations and members of the public outside. This resulted in a coherent and effective regime of radiological protection based on solid concepts, principles, and norms issued in Publication 60 (ICRP, 1991).
However,the reality of nuclear accidents, together with the threat of malevolent events and rising concerns on natural exposures and exposure situations inherited from the past, in the 1990s profoundly challenged the Publication 60 (ICRP, 1991) system and resulted in the general principles presented in Publication 103 (ICRP, 2007).
3.2. Through the structure of the ICRP system of protection
The main innovation of Publication 103 (ICRP, 2007) was the end of the two-speed protection system (practices vs interventions) set in Publication 60 (ICRP, 1991). In one case, that of practices, the protection system included the setting of maximum dose criteria which should not be exceeded (individual-related dose limits and source-related dose constraints) framing the implementation of the optimisation principle. In the other case, that of interventions, the protection system used minimum dose criteria, such as action levels or intervention levels. Their numerical values were generally higher than the maximum dose criteria for practices, and action was only required when they were exceeded.
Publication 103 (ICRP, 2007) now recommends a unified approach modelled on that for practices, regardless of the exposure situation. This unified approach provides the use of maximum dose criteria (dose constraints or reference levels) selected in accordance with the characteristics of the exposure situation, and implementation of the optimisation process with the aim of reducing exposures to as low as reasonably achievable. The dose limit can still be used when the source is fully controllable (i.e. in planned exposure situations, excluding medical exposure).
The unified approach of Publication 103 (ICRP, 2007) does not prevent the use of a graded approach according to the type of exposure situation. This publication introduced three types of exposure situation: existing exposure situations, where the source already exists when a decision on control has to be taken; planned exposure situations, involving the deliberate introduction and operation of sources; and emergency exposure situations, which may occur from any unexpected situation and require urgent action in order to avoid or reduce undesirable consequences.
Beyond the inevitable overlaps between the three types of exposure situation, the new situation-based system has not always been fully understood, especially the distinction between existing and planned exposure situations. Many people consider that a source is no longer ‘existing’ when it is included in a controlled process. While the keyword in the definition of a planned exposure situation is ‘deliberate’ (but ICRP could not call it a ‘deliberate exposure situation’), many people consider that an exposure situation is planned as soon as its management can be planned (forgetting that plans also exist to manage emergency situations). Sometimes, it sounds like a return to the old system of practices vs interventions, with planned exposure situations grouping situations under regulatory control while the others can be called ‘existing exposure situations’. From the point of view of ICRP, all exposure situations should be controlled appropriately, and the type of an exposure situation is determined by the status of the source.
Since the system of protection should be commensurate with the level of risk, the situation-based system recommended in Publication 103 (ICRP, 2007) should be seen as a way to allow for a graded approach in protection. In this regard, several elements founding the gradation of radiological risk warrant the distinction between existing and planned exposure situations.
Controllability of the source: when a source is introduced deliberately (essentially for its radioactive properties), it can be fully controlled from design to disposal. A decision on control of a source that already exists has to take the state of it into account, even when the source is deliberately modified from its original state. This can affect the controllability of existing exposure situations. Level of risk: the level of risk is not only dependent on the level of exposures, but more globally on the distribution of the individual doses of all exposed people, including its evolution. It means that individual and collective exposures, as well as acute and chronic exposures, should be taken into account. Experience shows that exposures in existing exposure situations are generally chronic, and they can be higher than those in many planned exposure situations (well controlled). However, apart from some radon exposures, doses are rarely of a high level, regardless of the degree of control. Anticipation of exposures: when the source is introduced deliberately, the quantities of radioactive materials, their physicochemical forms, their concentrations, and flows are known precisely in advance. The facility is designed accordingly, including workstations. The level of corresponding exposures can be anticipated fairly precisely, facilitating control. When the source already exists, the above-mentioned parameters may be variable. Exposures can be anticipated but their levels cannot be fully assessed without characterisation of the exposure situation. This may be an impediment to control. Prospect to deterministic effects: in a planned exposure situation, without permanent vigilance in control, doses can reach a high or very high level, potentially inducing deterministic effects. On the contrary, whatever the degree of control, exposures arising from existing exposure situations are ‘capped’. For example, no process involving NORM leads to a concentration of radionuclides such that the associated exposure can exceed a dose ceiling of the order of a few mSv per year – at worst, a few tens of mSv per year in a few cases – even without protective action. Exceptions would be very rare. For diverse reasons, other existing exposure situations present the same feature. Such levels of exposure cannot induce deterministic effects, even radon exposure. It is a key characteristic of existing exposure situations from a radiological protection point of view. Prospect of emergency: in the same line, while the loss of control of the source in a planned exposure situation may lead to an emergency exposure situation, it is quite never the case from an existing exposure situation. Multi-hazards situation: although it is grossly in line with the protection approach for conventional hazards, the system of radiological protection is generally more complex, more detailed, and more demanding, and it includes many specific features (e.g. specific expertise, specific procedures, specific controls). Practically, the focus is on the radiological hazard as soon as it is identified, even when it is not dominant. Controlling this hazard requires considerable attention and resources, potentially to the detriment of the control of other hazards. In the end, control of the different hazards may be unbalanced. Furthermore, in the case of limited resources, protection against hazards other than radiological hazards may be neglected. The problem can arise in both existing and planned exposure situations. When Publication 103 (ICRP, 2007) explains how to select dose constraints and reference levels according to the characteristics of the exposure situation, some key characteristics are mentioned: controllability of the source, benefit from the exposure situation (individual or societal, direct or indirect), and additional protection requirements for individuals who are more exposed (e.g. workers vs public). These characteristics can be used not only for the selection of dose criteria but also for a broader graded approach. Finally, economic and societal considerations may intervene in the establishment of a graded protection approach, whatever the type of exposure situation.
Whether industries involving NORM are existing or planned exposure situations is a controversial issue. It was the main point raised in comments during the public consultation. While both international (IAEA, 2014) and European (EURATOM, 2013) basic safety standards consider that these industries should be managed as planned exposure situations as far as exemption levels are exceeded, Publication 103 (ICRP, 2007) indicates that NORM is a ‘well-known example’ of existing exposure situations. This opinion is repeated in Publication 142 (ICRP, 2019). However, when NORM is processed for its radioactive, fissile, or fertile properties, ICRP considers it a planned exposure situation.
Indeed, although industries involving NORM are diverse, their main characteristics put them on the side of existing exposure situations rather than planned exposure situations: the source already exists and, even if it can be introduced deliberately in the industrial process, it is mainly incidentally; the source may be modified from its original state, but not for its radioactive properties (otherwise the exposure situation is considered as planned); exposures can be anticipated but, because the quantities, physicochemical form, concentrations, and flows of NORM are intrinsically variable, the level of exposures cannot be fully assessed without characterisation of the exposure situation; and exposures can be higher than those in nuclear industry, for example, but the exposure situation presents no real prospect of emergency leading to tissue reaction or immediate danger to life.
A graded approach is also appropriate for industries involving NORM due to the economic importance of these industries, large volumes of residues and wastes, limited options for management, and potentially high regulation costs in relation to reduced exposure. Industries involving NORM are generally situations where multiple hazards and pollutants can be present and where the radiological hazard is not dominant.
In such a context, the radiological protection system is not necessarily the only driving force in safety, and an integrated approach to all hazards should be employed. The graded approach to protection should first take account of the existing knowledge and experience of these industries in the management of industrial hazards, and then pragmatically integrate any additional measures necessary for the purposes of radiological protection (ICRP, 2019).
The ICRP system of radiological protection is also structured with categories of exposure. Processes involving NORM may lead to occupational exposure, public exposure, and environmental exposure. It should be noted that not all workers are intended to be considered as occupationally exposed. As explained in Publication 103 (ICRP, 2007), the Commission limits its use of ‘occupational exposures’ to radiation exposures incurred at work as a result of situations that can reasonably be regarded as being the responsibility of the operating management. A specific graded approach is recommended in Publication 142 (ICRP, 2019) for the protection of workers (see below).
3.3. Through implementation of the radiological protection principles
Implementation of the three basic principles of radiological protection can also be the subject of a graded approach.
According to Publication 103 (ICRP, 2007), the principle of justification requires that any decision that alters the radiation exposure situation should do more good than harm. It is also emphasised that for existing exposure situations, the justification principle is applied in making the decision regarding whether to take action to reduce exposure and avert further additional exposures. In industries involving NORM, as recommended in Publication 142 (ICRP, 2019), it is primarily applied for both ongoing and new processes when making the decision regarding whether or not to implement a protection strategy for radiation exposures, after radiological characterisation of the exposure situation and taking into account health, economic, societal, environmental, and ethical considerations. As many industries involving NORM already exist, it has been suggested that a national list of industries involving NORM for which a radiological risk assessment should be undertaken in order to determine if a protection strategy is justified should be established. The level of control may then be determined through implementation of the optimisation principle.
The optimisation of protection is the central principle of the ICRP system. As far as human protection is concerned, it is defined as the process to keep the magnitude of individual doses, the number of people exposed, and the likelihood of incurring exposures as low as reasonably achievable, guided by appropriate individual dose criteria, and taking into account economic and societal factors. The impact to the environment should also be kept as low as reasonably achievable (ICRP, 2007). In the case of industries involving NORM, the optimisation process is implemented in generally the same way as for other industries. However, because of the prevailing circumstances, and notably as the radiological protection should be integrated in a broader protection strategy in which the radiological hazard is not necessarily dominant, the options to reduce doses may be more limited and/or may require different resources. Such challenges suggest the need for flexibility in implementation of the optimisation process and application of regulatory structures. The involvement of relevant stakeholders early in the optimisation process will contribute to selecting the best option for protection, taking into account the characteristics of the actual exposure situation, and thus potentially to making protection more effective and efficient (ICRP, 2019).
The principle of application of dose limits is normally reserved for planned exposure situations (ICRP, 2007). However, it is recognised in Publication 142 (ICRP, 2019) that some authorities have specified dose limits for some industries involving NORM, in addition to industries where NORM is processed for its radioactive, fissile, or fertile properties. This may be particularly suitable in circumstances when the source is well characterised, there is an ongoing potential for significant levels of exposure, and it is necessary to properly demonstrate ongoing control of the radiological hazards.
The Commission recommends the use of reference levels as dose criteria in existing exposure situations. The reference level represents the value of dose used to guide and drive the optimisation process. Selection of the reference level should consider the actual individual dose distribution, with the objective of identifying those exposures that warrant specific attention. Reference levels are guides for selecting amongst protective options in the optimisation process in order to maintain individual doses as low as reasonably achievable, taking into account economic and societal factors, and thus to prevent and reduce inequities in dose distribution. Reference levels are also benchmarks against which the results of protective actions can be judged to determine if protection is reasonably optimised and effective.
As far as the protection of non-human species is concerned, the Commission recommends the use of derived consideration reference levels (DCRLs). DCRLs can be considered as a band of dose rates within which there is likely to be some chance of deleterious effects of ionising radiation occurring to individuals of that type of Reference Animal or Plant (derived from a knowledge of defined expected biological effects for that type of organism).
4. PROTECTION OF WORKERS, THE PUBLIC, AND THE ENVIRONMENT
4.1. Protection of workers
Workers in industries involving NORM are frequently exposed to radiation and other hazards. The radiological risk is often not the dominant hazard, and may historically not even have been a consideration. In such a context, there is often a lack of radiological protection awareness or a culture supporting such protection. However, such industries do have experience and expertise in the management of occupational health and safety, and there is an opportunity to build a radiological protection culture in an integrated fashion. In many cases, actions to reduce workplace hazards, such as airborne dust, will also restrict radiation exposures.
Experience shows that it is easier to develop an integrated multi-hazards approach to worker protection starting from conventional health and safety standards than from the system of radiological protection. In that context, the Commission recommends a realistic and pragmatic attitude, starting with characterisation of the exposure situation, and the integration, as necessary, of specific radiological protective actions to complement the protection strategy already in place or planned to manage other workplace hazards.
In practice, a graded approach can be realised through the selection of suitable dose reference levels, the selection of appropriate collective or individual protective actions, and the integrated implementation of these actions. Exposure to radon is also treated using a graded approach, based first on application of typical radon prevention and mitigation techniques (see below), as described in Publication 126 (ICRP, 2014a). The practical implementation of this approach will also help to determine whether or not the workers should be considered as occupationally exposed to radiation.
The appropriate reference level for the protection of workers can be selected based on the 1–20-mSv band recommended by ICRP for existing exposure situations (ICRP, 2007), taking into account the characteristics of the exposure situation, notably the actual and potential exposure pathways, the individual dose distributions, and the prospect for optimisation. The following values are recommended in Publication 142 (ICRP, 2019):
of the order of a few mSv year−1, or below, for most cases; and above a few mSv, but very rarely exceeding 10 mSv year−1, when necessary because of the circumstances involved.
As indicated above, these doses exclude exposures from radon or thoron.
For the selection of protective actions, the starting point should always be the existing industrial safety and hygiene controls, before the integration of additional radiological protection controls, as necessary. According to the graded approach, control of the workplace and the conditions of work to eliminate or minimise the risk should be considered first. Examples are characterisation of the situation, provision of radiological protection expertise, initial actions to prevent or reduce the hazard, delineation of areas, and engineering controls.
These protective actions, complemented by at least a general information programme for workers, may be sufficient for their protection in most industries involving NORM. However, they can be complemented, as necessary, by protective actions related to the individuals, such as: working procedures; instruction and training; personal protective equipment; dose assessment; dose recording; and health surveillance, as necessary. Moving from controls of the workplace to individual controls needs to be considered carefully as the individual controls may be costly.
Most of these collective and individual protective actions need to be implemented only to the extent necessary to achieve acceptable protection. According to the graded approach, the modalities for implementing these actions should also be adapted to the circumstances.
Workers are likely to be considered as occupationally exposed when, despite all reasonable efforts to reduce exposure, elevated individual doses persist, and when the application of special working procedures is necessary to perform the job.
This integrated and graded approach for the protection of workers can also serve as the basis for creating a common understanding between regulatory authorities and other stakeholders (e.g. operators; workers and their representatives; and health, safety, and environmental professionals) of the radiological aspects of the various processes involved, and the ways in which these aspects can be addressed reasonably and effectively.
4.2. Protection of the public
A similar integrated and graded approach should be implemented for protection of the public. The general approach should start with characterisation of the exposure situation in order to determine who is exposed, when, where, and how. This characterisation includes the analysis of exposure pathways and dose assessments, and forms the basis for the justification of a protection strategy. Next, the optimisation process should be implemented, including the selection of a reference level, the selection and implementation of protective actions, the involvement of stakeholders in the decision-making process, and the provision of long-term monitoring of the situation, if necessary. Both radiological and non-radiological exposures should be considered and integrated in the optimisation process. This process should be implemented in a reasonable way, keeping in mind the ethical values of beneficence/non-maleficence, prudence, justice, and dignity (ICRP, 2018).
A reference level for protection of the public should be selected of the order of a few mSv per year, or below, to meaningfully guide the process of optimisation of protection. Protection of the public should be addressed as a whole (i.e. taking into account the different exposure pathways). In a given situation, the pathways need to be considered with respect to NORM discharge, waste, residue, and possible legacy sites. In practice, the most exposed individuals to each pathway belong to different groups, so the reference level can generally be applied to any given pathway. The reuse and recycling of NORM residues may be the starting point of a new NORM process.
Public exposure to radon or thoron arising from industries involving NORM is mainly due to the reuse of residues (e.g. in building materials), and should be dealt with according to the national action plan (see below) as recommended in Publication 126 (ICRP, 2014b). The use of building materials should be considered as one of the exposure pathways, and addressed with the aim of promoting those that do not exceed the reference level (e.g. through information, labelling, and reasonable and feasible incentive or even mandatory provisions).
4.3. Protection of the environment
Large quantities of NORM may be present in the environment in the form of mixed material together with other contaminants. The application of an integrated and graded approach for protection of the environment, as for the protection of workers and the public, was mentioned in several comments during the public consultation.
Industries involving NORM have generally been following common standards to protect the environment from pollutants other than radioactivity. In Publication 142 (ICRP, 2019), the Commission recommends an integrated approach, which should encompass:
all stressors or factors of concern (i.e. radiological and non-radiological); and human health effects due to environmental exposure of humans, and ecological effects due to environmental exposure of non-human species and their assemblage (i.e. from populations of species to communities and ecosystems).
Generally, this approach can be implemented in a graded way, as recommended in any environmental impact assessment (EIA), by starting with a very simple conservative assessment (screening stage making use of generic input data under the assumption of cautious exposure scenario) and then, if needed, by increasing the complexity and realism of the assessment as necessary (e.g. by using site-specific data and more detailed and realistic exposure scenarios) until a clear and defensible conclusion is reached (IAEA, 2018).
In the case of complex situations, the radiological characterisation of NORM released in the environment may be performed for the source and the environmental media of concern (e.g. air, water, sediment, soil). To be able to assess exposure of non-human species, it may be relevant to identify the mobility of radionuclides, their spatial and temporal variation, environmental pathways to plants and animals, and their bioavailability. An approach with Reference Animals and Plants and DCRLs has been developed in specific ICRP publications (ICRP, 2008, 2014a).
EIAs can be used as a basis for the justification of actions aimed at the protection of both human and non-human species, because decisions on restricting discharges will impact all types of exposure. The involvement of stakeholders is recommended. The long-term preservation of the environment is a global concern of the society, to which application of the ethical values of radiological protection can usefully contribute.
4.4. Protection against radon exposure
Radon may be a major source of exposure in facilities with NORM. The source of radon may be soil, processed NORM, or building materials. Some building materials may be made with NORM residues. Publication 126 (ICRP, 2014b) addresses radon exposure in general and so is relevant for radon exposures in industries involving NORM. However, in accordance with comments received during the public consultation, explanation on how radon exposure associated with NORM processes should be dealt with is provided in Publication 142 in sections related to the protection of workers and the public. This explanation is coherent with Publication 126.
An integrated approach for protection against radon exposure in all buildings is recommended, whatever their purpose and the status of their occupants. The strategy of protection in buildings, implemented through a national action plan, should include both prevention and mitigation of exposure on the basis of the optimisation principle, and use a reference level, expressed for practical reasons in concentrations in air, to facilitate implementation. The Commission recommends that national authorities should set a reference level for radon in air that is as low as reasonably achievable in the range of 100–300 Bq m−3, taking the prevailing economic and societal circumstances into account.
In workplaces, the Commission considers that radon, irrespective of the source, should be managed as a single source using the reference level set in the national action plan. When concentrations still exceed the reference level following application of radon prevention and mitigation measures, it may be necessary, within a graded approach, to undertake additional assessments of exposure in terms of dose. In such a case, a reference level of the order of 10 mSv year−1 should be used.
Workers may be considered as occupationally exposed in some workplaces identified in a national list of activities or facilities in which workers are inevitably and substantially exposed to radon, and this exposure is more intimately and obviously related to their work activities. It may also be the case if the dose associated with radon exposure cannot be reduced to the reference level of the order of 10 mSv year−1. In cases where radon exposure is concomitant with exposure from other radionuclides, the Commission recommends a pragmatic approach addressing radon exposure separately.
5. CONCLUSION
Any controllable source should be controlled as appropriate through implementation of the radiological protection system as recommended by ICRP. This system is now unified whatever the type of exposure situation. However, the basic principles of radiological protection should be applied using a graded approach, commensurate to the level of risk and other characteristics of the exposure situation. Regulatory control should be adapted accordingly.
Industries involving NORM may need to be controlled. The system of radiological protection, including the principles of justification and optimisation of protection, as well as the corresponding dose criteria and requisites, can be applied. In order to be adapted to the features of industries involving NORM, the Commission recommends, in Publication 142 (ICRP, 2019), an approach considering the protection strategies already implemented by these industries to manage the hazards they are facing as a starting point, and then estimating, after characterisation, the need for further action for protection against radiation. Such an integrated approach can then be graded with proper balance between the different hazards, adopting a reasonable and prudent attitude, and taking economic and societal factors into account. Involvement of relevant stakeholders in the decision process is crucial.