Risk assessment provides a key input for determining the need for and extent of remedial actions necessary for sites contaminated with naturally occurring radioactive material or nuclear legacy sites. The choice of a modelling approach for risk assessment, and the corresponding toolsets should fit the assessment context, taking account of the complexity, and be clearly related to the questions to be addressed in the decision-making process. One of the objectives of Working Group 1 of IAEA Modelling and Data for Radiological Impact Assessments II (MODARIA II) Programme is to perform intermodel comparisons for case studies of selected sites, in particular, to help illustrate the applicability of different models and approaches as inputs to decision-making processes. This intercomparison exercise, which included the analysis of potential consequences on the management strategy for contaminated sites, has been performed for two sites: The former uranium mill tailings facility at Zapadnoe, Ukraine, and the phosphate processing facility at Tessenderlo, Belgium. Several models and computer codes have been used for one or both of these cases: AMBER, GoldSim, NORM And LegacY Site Assessment, Preliminary Remediation Goals (PRG)-dose compliance concentration calculator, and RESRAD-OFFSITE. The assessments explore the implications of using differing assessment frameworks and assumptions, as well as alternative modelling tools, on model outputs and as input for corresponding decisions on remediation strategy. This paper reviews both similarities and differences in the results of assessments performed using these different models. It discusses how different approaches can complement one another to help build confidence in the evidence base underpinning decisions. It also discusses the appropriateness of the different modelling approaches in a given assessment context. In one of the case studies in particular (Tessenderlo case study), the remediation strategy is essentially driven by the contamination of the site with heavy metals, such as cadmium. This has significant consequences on the choice of the most adequate approaches and scenarios for assessing the radiological risk and balancing their relative importance with other impacts. The development of a holistic approach to risk assessment is, therefore, highlighted.

The international community has come a long way in developing a consensus that the remediation and management of naturally occurring radioactive materials and nuclear legacy sites will benefit from the use of the framework for risk-informed decision-making. Such a framework should ideally integrate risk assessment and decision-making. The framework presented in this paper specifically addresses the needs and expectations in the wider socio-economic and environmental context, as well as a narrower human health context. The framework was demonstrated as part of the International Atomic Energy Agency’s second Modelling and Data for Radiological Impact Assessments Programme. Three case studies, which have used or could use this integrative approach, are used for illustration. The first concerns remediation from uranium mining activities at Beaverlodge Lake in northern Saskatchewan, Canada, engaging stakeholders (also called ‘interested parties’) in the decision-making process on further options. The second case study suggests how decision analysis could support the selection of the best option for waste disposal for uranium ore processing at Žirovski vrh, Slovenia, taking into account a potential landslide and migration of waste throughout the adjacent valley in the event of flooding. The third case study presents the process and results of radiological safety assessment of the Kepkensberg sludge basin in Tessenderlo area, Belgium both before and after the disposal of material from remediation of the nearby Winterbeek River. It illustrates how such assessments could interface with decision analysis for the purpose of supporting the regulatory decisions related to future approval of a waste disposal option. Results show that formal stakeholder engagement in decision analysis provides a strong contribution to objective, robust, and transparent decision-making not only for radiation protection area but also in others where health and environmental impacts are of concern. A number of recommendations for future work have also been made.

In large parts of Europe, the Chernobyl accident of 1986 caused fallout of Cs-137. This led to the uptake of Cs-137 in trees or other materials used for bioenergy production or as firewood for domestic purposes. This Cs-137 may concentrate in the ashes of the combustion process in such a way that the clearance level of 100 Bq per kg, defined in Directive 2013/59/Euratom (EU BSS), may consequently be exceeded. There is currently no clear consensus in Europe regarding the regulatory approach to this issue: should the import and use of Cs-137 contaminated biomass and its ashes be considered as a planned exposure situation or rather as an existing exposure situation? If considered as an existing exposure situation, which reference level should be applied? We compare the approaches in various European countries, such as Finland, Norway, Sweden, Belgium and the Netherlands. Results of a recent measurement campaign performed in Belgium on firewood imported from Belarus, Ukraine and other countries show a quite large range of Cs-137 activity concentration in firewood. Analysis of samples from biomass combustion confirms that the clearance level of 100 Bq per kg Cs-137 may be exceeded even when the activity concentration in the initial pellet is trivial. A review of dose-assessment studies performed by STUK and from the literature is presented. The general context of biomass energy production is sketched: for instance, in the Netherlands, 40 large biomass firing plants (capacity > 10 MW) are operational and some 20 more are already planned. The fly ashes from the biomass combustion may be a valuable resource for the construction industry, and the issue of Cs-137 contamination is connected with the requirements of the EU BSS regarding the natural radioactivity of building materials. Assessing the impact of Cs-137 contamination and clarifying regulations in the frame of a graded approach are important elements in this context.

The IAEA fundamental safety objective is ‘to protect people and the environment from harmful effects of ionizing radiation’ and this must be done ‘without unduly limiting the operation of facilities or the conduct of activities that give rise to radiation risks’, while ensuring that people and the environment, present and future are protected against radiation risks (IAEA 2006 Fundamental Safety Principles, Safety Fundamentals No. SF-1). In addition, ‘protective actions to reduce existing or unregulated radiation risks must be justified and optimized’ (IAEA 2006 Fundamental Safety Principles, Safety Fundamentals No. SF-1). An international system of radiological protection can be applied such that processes, such as remediation, can be systematically undertaken to address the wide range of ‘existing exposure situations’ present globally. In doing so, decisions made regarding actions undertaken can be demonstrated to be ‘justified’ and ‘optimized’ (i.e. balanced), such that the amount of effort should be commensurate with the risk (applying a ’graded approach’). In addition, protection of people and the environment can be demonstrated by comparing the actual exposure to appropriate criteria over the lifetime of remediation. This paper provides an overview of the current IAEA safety standards on remediation of sites or areas contaminated with residual radioactive material within the international system of radiological protection and provides practical examples of their application through case studies considered in IAEA international model validation programs.

Exposure of aircrew to cosmic radiation had already been identified as an issue of concern in the European BSS of 1996 which requested airlines to assess the exposure of the crew and to inform their workers of the health risks their work involves. These requirements have been implemented in Belgian regulations in 2001 and updated with the transposition of the 2013/59/Euratom directive. Dosimetry data show that aircrew is the group of workers, which contributes the most to the collective dose of occupationally exposed workers in Belgium. In order to verify the extent of the information received by Belgian aircrew regarding their exposure to cosmic radiation, FANC, the Belgian radiation protection authority, launched in 2019 a large survey in collaboration with the Belgian Cockpit Association (BeCA), the professional association representing airline pilots in Belgium. The survey included 8 questions regarding the information of aircrew on cosmic radiation in general, on the individual dose level and on the risk related to exposure during pregnancy. A total of about 400 responses to the survey were received. Overall, the survey reveals that aircrew members in Belgium receive too little information about the potential risks, that they are not sufficiently informed about their own exposure and that female staff members are insufficiently informed about the hazards for the unborn child in case of pregnancy, and 66% of the respondents answered that their employer has never informed them about their exposure to cosmic radiation. However, most are aware of this phenomenon, either because they have looked up information or because they have discussed the topic with colleagues and professional associations. The results also showed that 17% of female crew continued to fly while being pregnant. Finally, the survey also allowed to identify differences and similarities between different groups of workers: cockpit and cabin crew, men and women. For instance, cabin crew was even less informed about their individual exposure than cockpit crew.