|NEWS AND INFORMATION
|Year : 2020 | Volume
| Issue : 1 | Page : 55-58
Salient features of ICRP publication 142: Radiological Protection from naturally occurring radioactive material in industrial processes
Ex. BARC, Mumbai, Maharashtra, India
|Date of Submission||23-Apr-2020|
|Date of Acceptance||23-Apr-2020|
|Date of Web Publication||12-May-2020|
D D Rao
Ex. BARC, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Rao D D. Salient features of ICRP publication 142: Radiological Protection from naturally occurring radioactive material in industrial processes. Radiat Prot Environ 2020;43:55-8
|How to cite this URL:|
Rao D D. Salient features of ICRP publication 142: Radiological Protection from naturally occurring radioactive material in industrial processes. Radiat Prot Environ [serial online] 2020 [cited 2020 Aug 12];43:55-8. Available from: http://www.rpe.org.in/text.asp?2020/43/1/55/284226
The International Commission on Radiological Protection (ICRP) brought out this publication to provide guidance on radiological protection in industries involving naturally occurring radioactive material (NORM). The guest editorial of this publication begins with: “Exposure to Natural Sources of Radiation is Normal, but Exposure in the Workplace shouldn't be! ” The publication comprises four sections, namely Introduction, Characteristics of Exposure to NORM, Application of the Commission's System of Radiological Protection to NORM, and Implementation of the System of Radiological Protection to Industrial Processes Involving NORM. The section-wise salient features are summarized below.
| Introduction|| |
All minerals and raw materials of a geological nature contain radionuclides of natural origin. The main radionuclides of interest are40 K and radionuclides from the232 Th and238 U decay series.232 Th and238 U decay through a series of radionuclides to stable isotopes208 Pb and206 Pb, respectively, known as “daughter radionuclides ” or “progeny. ” For most human activities involving minerals and raw materials, the level of exposure due to primordial radionuclide decay series is not a concern for radiological protection. However, there are a number of circumstances in which materials containing naturally occurring radionuclides are recovered, processed, used, or moved such that enhanced radiation exposures may result. For example, certain minerals, including some that are commercially exploited, may contain potassium and/or thorium and/or uranium progeny at significant concentrations. Furthermore, during the extraction of minerals and their processing, the radionuclides may be dispersed and/or their physicochemical properties changed so that they become unevenly distributed between the products, by-products, discharges, residues, or wastes arising from the process (es). The radionuclide activity concentrations may exceed those in the original mineral, sometimes by several orders of magnitude, which can significantly increase the exposure of workers and/or members of the public, and lead to contamination of the environment.
This publication outlines how exposures resulting from NORM industries can be managed through justification of the actions taken, optimization of protection, and use of appropriate individual dose criteria. One contributor to NORM exposures is radon (222 Rn) gas and, to a lesser extent, thoron (220 Rn) gas. ICRP recently provided information on the risk of lung cancer from radon and thoron by reviewing epidemiological studies in Publication 115. The commission recommends an integrated approach for controlling radon exposure, relying as far as possible on the management of buildings or locations in which radon exposure occurs. Thus, radon and thoron exposures in industries involving NORM should be managed in accordance with the approach of Publication 126.
Ionizing radiation may be a consideration in terms of the protection of people and the environment from NORM, but it is generally not the only hazard and perhaps not even the most dominant hazard. Indeed, NORM residues and wastes may contain toxic nonradiological constituents that may be harmful to human health and/or the environment (e.g. heavy metals). The present publication will not provide guidance on the management of these constituents, which may have to be controlled by industrial hygiene and environmental regulation. However, the commission recommends the use of an integrated approach for the management of radiation and all other hazards that may be present, so that protection is optimized for all concerns in an inclusive manner. The recommendations in the present publication for radiological protection in industries involving NORM supersede all previous related recommendations in Publications 103, 104, 124, and 126.
| Characteristics of Exposure to Norm|| |
Radionuclides of natural origin are ubiquitous and are present in almost all materials on earth. They are generally not of radiological concern. Some human activities, however, have the potential to enhance radiation exposures from these materials. Examples of industries/processes that may cause NORM-related radiation exposure of workers, the public, and the environment are given below.
- Extraction of rare earth elements
- Production and use of metallic thorium and its compounds (i.e., for their metallic, not fissile or fertile, 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, aluminum, 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).
Work activities involving NORM can give rise to external and internal radiation exposures. External exposures can arise from extended exposures to low (gamma)-dose rates; shorter exposures to high (gamma and sometimes beta)-dose rates from performing maintenance on internals of equipment, slag, scale, and sludge; or a combination of these. The potential for internal exposure is governed mostly by the way NORM appears in the workplace, and the personal protective equipment worn by workers. Radon may be an important source of exposure in indoor or underground atmospheres. Indoor radon exposure may arise from the soil, the processed NORM, or the building materials of the facility. In large-scale mining and milling operations, airborne dust is a common industrial hazard, and internal exposures from inhalation of NORM can be significant, especially where higher activity concentrations are present (e.g., above tens of Bq g−1). In contrast, internal exposures from ingestion of NORM, including in water, are usually low. Ranges of exposures to workers in some industries involving NORM are presented in tabular form. In the majority of workplaces, both the average and the maximum assessed doses received by workers are below a few mSv per year, but higher doses – in some cases, as high as a few tens of mSv – may occur in specific workplaces (approximately 100 mSv year−1 in very few underground mines). In terms of public exposure, direct external exposures (i.e., from NORM on the site) are usually negligible, although there are exceptions to this. For some specific industries involving NORM sites, it has been reported that some representative individuals in close proximity to the plant can receive annual doses in the mSv range. In general, public doses from NORM mainly arise from radionuclides released into air and water as routine discharges and the use of NORM-containing by-products in commodities such as building materials. In rare cases, NORM in drinking water may be an issue. Some data related to public exposures from NORM (annual effective dose to the public is estimated to be well below 1mSv year−1, except in rare cases such as the wide use of phosphogypsum in building material) are presented in tabular form.
| Application of the Commission's System of Radiological Protection to Norm|| |
The commission defines an exposure situation as a “network of events and situations ” that begins with a natural or artificial radiation source, the transfer of the radiation or radioactive materials through various pathways, and the resulting exposure of individuals or the environment. Protection can be achieved by taking action at the source or at any point in the exposure pathways of the exposed individuals. The commission intends its recommendations to be applied to all sources and to individuals exposed to radiation in the following three types of exposure situations, which address all conceivable circumstances: existing exposure situations, planned exposure situations, and emergency exposure situations.
The commission has considered exposures resulting from many industries involving NORM as examples of existing exposure situations. However, when NORM is processed for its radioactive, fissile, or fertile properties, the commission considers it a planned exposure situation. There is generally no prospect of a radiological emergency or deterministic effects involving NORM. A graded approach is recommended for the protection of workers in industries involving NORM based on the selection of the reference level as well as selection and implementation of reasonable protective actions. This approach should also consider, as explained above, the integration of radiological protection in procedures for the control of other hazards in a more global and synergistic approach to hazard management. In rare cases, the level of dose remains high or the application of special working procedures is needed for radiological protection purposes. In these cases, the measures recommended for occupationally exposed workers would apply. Public exposure is addressed through the control of NORM discharges, wastes, residues (including recycling and reuse), and possible legacy sites.
The responsibility for judging justification usually falls on governments or other national authorities to ensure that an overall benefit results, in the broadest sense, to society and thus not necessarily to each individual. However, input to the justification decision may include many aspects that could be informed by the industry involving NORM, workers, the public, and organizations other than the government or national authority. In this context, radiological protection considerations will serve as one input to the broader decision-making process.
When a decision has been taken to implement a protection strategy, the principle of optimization of protection becomes the driving principle to select the most effective actions for protecting the exposed public, workers, and the environment. As far as human protection is concerned, it is defined by the commission 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, taking into account economic and societal factors. The impact to the environment should also be kept as low as reasonably achievable. This means that the level of protection should be the best possible under the prevailing circumstances, adopting a prudent and reasonable attitude.
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 optimization process. Selection of the reference level should consider the actual individual dose distribution, with the objective of identifying those exposures that warrant specific attention. For the protection of humans in existing exposure situations, the commission recommends setting reference levels typically within the 1–20 mSv year−1 band, with the possibility that the most appropriate reference level to guide optimization of protection could be <1 mSv year−1. The 1–20 mSv year−1 band presupposes that the sources or pathways can generally be controlled, and individuals receive direct benefits from activities associated with the exposure situation, but not necessarily from the exposure itself. NORM generally gives rise to low or moderate levels of individual exposure, and the appropriate reference level can, in most cases, be less than a few mSv per year. According to the characteristics of the exposure situation, notably the actual and potential exposure pathways, an appropriate reference level can, in most cases, be less, perhaps well less, than a few mSv annual effective dose. If, in rare instances with larger individual doses in the dose distribution, a reference level could be selected above a few mSv, the commission would expect that the level would rarely need to exceed 10 mSv annual effective dose. The reference level applies to the dose added to the natural background.
| Implementation of the System of Radiological Protection to Industrial Processes Involving Norm|| |
The main exposure pathways for work with NORM are as follows: external exposure (mostly due to gamma-radiation, but occasionally, beta-radiation exposure to the lens of the eye and the skin may need to be considered) and internal exposure from inhalation dust and, to a much lesser extent, ingestion of radioactive dust, as well as exposures due to radon gas and its progeny, which can occur above ground or underground (e.g., the buildup of radon gas in underground workplaces), and sometimes thoron emanating from NORM. Commission considers that radon and thoron in the workplace, irrespective of the source, should be managed as a single source. The commission recommends that national authorities should set a derived reference level that is as low as reasonably achievable in the range of 100–300 Bqm−3, taking the prevailing economic and societal circumstances into account.
According to the characteristics of the exposure situation, notably the actual and potential exposure pathways, the individual dose distribution, the appropriate reference level can be selected based on the 1–20 mSv band recommended by the commission, noting that the selection could be:
- Of the order of a few mSv per year, or below, for most cases
- Above a few mSv, but very rarely exceeding 10 mSv year−1, when necessary because of the circumstances involved.
An assessment of the exposure of workers is required as part of the initial characterization described above. It is envisaged that this will be based on workplace measurements and other information (e.g., about the process and working practices) rather than individual dosimetry. Where doses are above a few mSv per year, it is expected that they may be estimated on the basis of workplace measurements. Individual dose assessment (e.g., through the use of personal dosimeters) may be useful as a means of providing information to help optimize exposures but is not expected to be undertaken on a routine basis. Where doses are well above a few mSv per year, individual dose assessments should be undertaken. For external radiation, this should be done with personal dosimeters (passive or electronic). Assessment of internal exposures from dust inhalation is much more challenging; however, in very dusty NORM workplaces, there may already be a dust monitoring program which can be adapted to provide estimates of radiation dose. If not, and if internal doses are high, arrangements with a suitable internal dosimetry service will need to be considered. It should be noted, however, that such exposures are unlikely to be considered optimized and that suitable protective actions should be more than capable of reducing internal exposures.
As far as radon and thoron are concerned, exposure should be assessed, but not necessarily in terms of dose, as long as the concentration can be controlled. When radon or thoron dose assessment is relevant, it may be performed through collective or individual monitoring or inferred from monitoring of the workplace.
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Conflicts of interest
There are no conflicts of interest.