Assessment of radiation dose to people and wildife inhabiting the Grote Nete catchment in Belgium.

We evaluate the impact of the radiological contamination of the Grote Nete catchment in Belgium to people and non-human biota. This region has received effluents from the phosphate and nuclear industries via tributaries of the Grote Nete river in past decades, resulting in the presence of radionuclides such as 241Am, 60Co, 137Cs, 40K, 210Pb, 238Pu, 239,240Pu, 226Ra, 228Ra, 228Th, 232Th, 234U, 235U and 238U. During the period 2016-2021, we measured these radionuclides in the water column, the bed sediment and riverbanks. Additionally, we carried out radon measurements on the riverbanks in 2022. Based on these measurements, the dose rates to people were calculated for different potential exposure scenarios, using the SCK CEN biosphere tool. We also performed an assessment of exposure of ionising radiation to non-human biota (including 222Rn and its daughters) using the ERICA Tool. We observed three types of areas at the Grote Nete riverbank: (a) a lower category exposure with 226Ra concentrations reflecting purely Belgian background values; (b) a middle category with enhanced 226Ra, mainly adsorbed on clay minerals and (c) an upper category extending to maximum values in the order of 103 Bq kg-1. The main component of the dose rate for terrestrial and aquatic organisms is 226Ra followed by 210Pb (terrestrial) or 228Ra, (aquatic). The anthropogenic vector of the contamination (40K, 60Co, 90Sr, 137Cs, 228Th, 232Th, 234,235,238U, 238,239Pu, 241Am) makes a negligible contribution to dose. Overall, the Grote Nete wildlife is not under significant risk from exposure to soil or water-borne radionuclides and radon emanating from the soil, even if the ERICA benchmark of 10 µGy h-1 is occasionally exceeded for 226Ra, 210Pb or 228Ra, because exposures are below the levels at which effects are known to occur. For people, radon inhalation is the main exposure pathway and exposures can reach 1 mSv y-1 for hypothetical residents living at the riverbanks and remaining most of their time in the area, but it can be expected that exposures are much lower at increasing distances from the river. It is concluded that neither people nor the environment are at any significant radiological risk from this situation.

Impact of medical radionuclide discharges on people and the environment.

We present a novel methodology to dynamically calculate dose rates to people and wildlife from hospital-released radionuclides reaching the environment through water treatment plants (WTPs), using the biokinetic model D-DAT for aquatic wildlife, applied to 18F, 123I, 131I, 153Sm, 99mTc and 201Tl. We have also developed a method to calculate doses to WTP workers and to farmers from agricultural practices. This proof-of-concept study simulates a generic source term of radionuclide levels in the Belgian Molse Nete River during the year 2018, chosen because the river flow was very low during that year, which constitutes a very conservative, bounding case. The dose rates to wildlife calculated for this hypothetical scenario under conservative assumptions, are well below the ERICA predicted no effects dose rate to wildlife of 10 µGy h-1. Human exposures are also very low, in most cases not exceeding 10 µSv y-1. This work identifies important data gaps and areas of uncertainty in the assessment of radiopharmaceutical effluents. The study, which is part of the EC project SINFONIA, paves the way for a dynamic screening assessment methodology able to perform consistently assessments of the impact of radiopharmaceuticals on people and wildlife. This is particularly relevant since discharges of radiopharmaceuticals in rivers are on the increase and it is necessary to explicitly demonstrate that people and the environment are adequately protected.

Role of modelling in monitoring soil and food during different stages of a nuclear emergency.

In case of a nuclear accident, adequate protection of the public and the environment requires timely assessment of the short- and long-term radiological exposure. Measurements of the radiation dose and the radioactive contamination in the environment are essential for the optimization of radiation protection and the decision making process. In the early phase, however, such measurements are rarely available or sufficient.To compensate for the lack of monitoring data during nuclear emergencies, especially in the early phase of the emergency, mathematical models are frequently used to assess the temporal and spatial distribution of radioactive contamination. During the transition and recovery phase, models are typically used to optimise remediation strategies by assessing the cost-effectiveness of different countermeasures. A prerequisite of course is that these models are fit for purpose. Different models may be needed during different phases of the accident. In this paper, we discuss the role of radioecological models during a nuclear emergency, and give an outlook on the scientific challenges which need to be addressed to further improve our predictions of human and wildlife exposure.

Interception of radionuclides by planophile crops: A simple semi-empirical modelling approach in case of nuclear accident fallout.

Shortly after an atmospheric release, the interception of radionuclides by crop canopies represents the main uptake pathway leading to food chain contamination. The food chain models currently used in European emergency decision support systems require a large number of input parameters, which inevitably leads to high model complexity. In this study, we have established a new relationship for wet deposited radionuclides to simplify the current modelling approaches. This relationship is based on the hypothesis that the stage of plant development is the key factor governing the interception of radionuclides by crops having horizontally oriented leaves (planophile crops). The interception fraction (f) and the leaf area index normalized (fLAI) and mass normalized (fB) interception fractions were assessed for spinach (Spinacia oleracea) and radish (Raphanus sativus) at different stages of plant development and for different contamination treatments and plant densities. A database of 191 f values for Cs-137 and Th-229 was built and complemented with existing literature covering various radionuclides and crops with similar canopy structure. The overall f increased with the plant growth, while the reverse was observed for fB. The fLAI significantly decreased by doubling the contaminated rainfall deposited. Fitting a multiple linear regression to predict the f value as a function of the standing biomass (B), and the radionuclide form (anion and cation) led to a better estimation of the interception (R2 = 81%) than the ECOSYS-87 model (R2 = 35%). Hence, the simplified modelling approach here proposed seems to be a suitable risk assessment tool as fewer parameters will minimize the model complexity and facilitate the decision-making procedures in case of emergencies, when countermeasures need to be identified and implemented promptly.

Climate change and landscape development in post-closure safety assessment of solid radioactive waste disposal: Results of an initiative of the IAEA.

The International Atomic Energy Agency has coordinated an international project addressing climate change and landscape development in post-closure safety assessments of solid radioactive waste disposal. The work has been supported by results of parallel on-going research that has been published in a variety of reports and peer reviewed journal articles. The project is due to be described in detail in a forthcoming IAEA report. Noting the multi-disciplinary nature of post-closure safety assessments, here, an overview of the work is given to provide researchers in the broader fields of radioecology and radiological safety assessment with a review of the work that has been undertaken. It is hoped that such dissemination will support and promote integrated understanding and coherent treatment of climate change and landscape development within an overall assessment process. The key activities undertaken in the project were: identification of the key processes that drive environmental change (mainly those associated with climate and climate change), and description of how a relevant future may develop on a global scale; development of a methodology for characterising environmental change that is valid on a global scale, showing how modelled global changes in climate can be downscaled to provide information that may be needed for characterising environmental change in site-specific assessments, and illustrating different aspects of the methodology in a number of case studies that show the evolution of site characteristics and the implications for the dose assessment models. Overall, the study has shown that quantitative climate and landscape modelling has now developed to the stage that it can be used to define an envelope of climate and landscape change scenarios at specific sites and under specific greenhouse-gas emissions assumptions that is suitable for use in quantitative post-closure performance assessments. These scenarios are not predictions of the future, but are projections based on a well-established understanding of the important processes involved and their impacts on different types of landscape. Such projections support the understanding of, and selection of, plausible ranges of scenarios for use in post-closure safety assessments.

Environmental risks of radioactive discharges from a low-level radioactive waste disposal site at Dessel, Belgium.

The potential radiological impact of releases from a low-level radioactive waste (Category A waste) repository in Dessel, Belgium on the local fauna and flora was assessed under a reference scenario for gradual leaching. The potential impact situations for terrestrial and aquatic fauna and flora considered in this study were soil contamination due to irrigation with contaminated groundwater from a well at 70 m from the repository, contamination of the local wetlands receiving the highest radionuclide flux after migration through the aquifer and contamination of the local river receiving the highest radionuclide flux after migration through the aquifer. In addition, an exploratory study was carried out for biota residing in the groundwater. All impact assessments were performed using the Environmental Risk from Ionising Contaminants: Assessment and Management (ERICA) tool. For all scenarios considered, absorbed dose rates to biota were found to be well below the ERICA 10 µGy h-1 screening value. The highest dose rates were observed for the scenario where soil was irrigated with groundwater from the vicinity of the repository. For biota residing in the groundwater well, a few dose rates were slightly above the screening level but significantly below the dose rates at which the smallest effects are observed for those relevant species or groups of species. Given the conservative nature of the assessment, it can be concluded that manmade radionuclides deposited into the environment by the near surface disposal of category A waste at Dessel do not have a significant radiological impact to wildlife.

Predicting the environmental risks of radioactive discharges from Belgian nuclear power plants.

An environmental risk assessment (ERA) was performed to evaluate the impact on non-human biota from liquid and atmospheric radioactive discharges by the Belgian Nuclear Power Plants (NPP) of Doel and Tihange. For both sites, characterisation of the source term and wildlife population around the NPPs was provided, whereupon the selection of reference organisms and the general approach taken for the environmental risk assessment was established. A deterministic risk assessment for aquatic and terrestrial ecosystems was performed using the ERICA assessment tool and applying the ERICA screening value of 10 µGy h(-1). The study was performed for the radioactive discharge limits and for the actual releases (maxima and averages over the period 1999-2008 or 2000-2009). It is concluded that the current discharge limits for the Belgian NPPs considered do not result in significant risks to the aquatic and terrestrial environment and that the actual discharges, which are a fraction of the release limits, are unlikely to harm the environment.

An invitation to contribute to a strategic research agenda in radioecology.

With intentions of integrating a portion of their respective research efforts into a trans-national programme that will enhance radioecology, eight European organisations recently formed the European Radioecology ALLIANCE (www.er-alliance.org). The ALLIANCE is an Association open to other organisations throughout the world with similar interests in promoting radioecology. The ALLIANCE members recognised that their shared radioecological research could be enhanced by efficiently pooling resources among its partner organizations and prioritising group efforts along common themes of mutual interest. A major step in this prioritisation process was to develop a Strategic Research Agenda (SRA). An EC-funded Network of Excellence in Radioecology, called STAR (Strategy for Allied Radioecology), was formed, in part, to develop the SRA. This document is the first published draft of the SRA. The SRA outlines a suggested prioritisation of research topics in radioecology, with the goal of improving research efficiency and more rapidly advancing the science. It responds to the question: "What topics, if critically addressed over the next 20 years, would significantly advance radioecology?" The three Scientific Challenges presented within the SRA, with their 15 associated research lines, are a strategic vision of what radioecology can achieve in the future. Meeting these challenges will require a directed effort and collaboration with many organisations the world over. Addressing these challenges is important to the advancement of radioecology and in providing scientific knowledge to decision makers. Although the development of the draft SRA has largely been a European effort, the hope is that it will initiate an open dialogue within the international radioecology community and its stakeholders. This is an abbreviated document with the intention of introducing the SRA and inviting contributions from interested stakeholders. Critique and input for improving the SRA are welcomed via a link on the STAR website (www.star-radioecology.org).

Assessment of radiation exposure in the uranium mining and milling area of Mailuu Suu, Kyrgyzstan.

The area of the town of Mailuu Suu, Kyrgyzstan, is polluted by radionuclides and heavy metals from tailing dumps and heaps resulting from the historic exploitation of uranium mines. In the frame of a European Commission-TACIS funded project, radiological assessment was performed for critical group members living in the city of Mailuu Suu, located downstream the tailings, or in the village of Kara Agach, partially located on a uranium mine waste dump. The actual external exposure is around 1.2 mSv a(-1) at both locations and exposure from radon is around 3 mSv a(-1) at Mailuu Suu and around 10 mSv a(-1) at Kara Agach. Ingestion dose was negligible for a critical group member living at Mailuu Suu. At Kara Agach, however, under the hypothesis that all food and fodder is cultivated locally, exposure from ingestion is much higher ( approximately 10-30 mSv a(-1)). In case of an accidental scenario [(part of) Tailing 3 content thrust to river], estimated additional maximum doses result in 45 and 77 mSv for an adult and a child, respectively.

Radionuclides in fruit systems: model prediction-experimental data intercomparison study.

This paper presents results from an international exercise undertaken to test model predictions against an independent data set for the transfer of radioactivity to fruit. Six models with various structures and complexity participated in this exercise. Predictions from these models were compared against independent experimental measurements on the transfer of 134Cs and 85Sr via leaf-to-fruit and soil-to-fruit in strawberry plants after an acute release. Foliar contamination was carried out through wet deposition on the plant at two different growing stages, anthesis and ripening, while soil contamination was effected at anthesis only. In the case of foliar contamination, predicted values are within the same order of magnitude as the measured values for both radionuclides, while in the case of soil contamination models tend to under-predict by up to three orders of magnitude for 134Cs, while differences for 85Sr are lower. Performance of models against experimental data is discussed together with the lessons learned from this exercise.

The radiological impact from airborne routine discharges of a modern coal-fired power plant.

In this paper the radiological impact from the airborne routine discharges of a modern coal-fired power plant at Langerlo (Belgium) is evaluated. Therefore, the natural radioactivity contents of the coal and the fly-ash discharged were measured. With a bi-Gaussian plume model the maximum annual values of the 226Ra concentration in the air (4.5 nBq/m3) and of the total deposition (1.5 mBq/m2) were calculated. The transfer of the radionuclides from air and soil to the biospheric media, exposing man, were modelled and the annual, individual, effective dose to the critical group, after an assumed life span of the power plant of 70 years, was evaluated at 0.05 microSv/y. This is several orders of magnitude lower than the annual doses for most power plants reported in the literature. The flue gas purification system, extended with a denitrification unit and a desulphurisation unit, was found to be the basis for this low impact.

Radionuclides in fruit systems: model-model intercomparison study.

Modeling is widely used to predict radionuclide distribution following accidental radionuclide releases. Modeling is crucial in emergency response planning and risk communication, and understanding model uncertainty is important not only in conducting analysis consistent with current regulatory guidance, but also in gaining stakeholder and decision-maker trust in the process and confidence in the results. However, while methods for dealing with parameter uncertainty are fairly well developed, an adequate representation of uncertainties associated with models remains rare. This paper addresses uncertainty about a model's structure (i.e., the relevance of simplifying assumptions and mathematical equations) that is seldom addressed in practical applications of environmental modeling. The use of several alternative models to derive a range of model outputs or risks is probably the only available technique to assess consistency in model prediction. Since each independent model requires significant resources for development and calibration, multiple models are not generally applied to the same problem. This study uses results from one such model intercomparison conducted by the Fruits Working Group, which was created under the International Atomic Energy Agency (IAEA) BIOMASS (BIOsphere Modelling and ASSessment) Program. Model-model intercomparisons presented in this study were conducted by the working group for two different scenarios (acute or continuous deposition), one radionuclide ((137)Cs), and three fruit-bearing crops (strawberries, apples, and blackcurrants). The differences between models were as great as five orders of magnitude for short-term predictions following acute radionuclide deposition. For long-term predictions and for the continuous deposition scenario, the differences between models were about two orders of magnitude. The difference between strawberry, apple, and blackcurrant contamination predicted by one model is far less than the difference in prediction of contamination for a single plant species given by different models. This study illustrates the importance of problem formulation and implementation of an analytic-deliberative process in risk characterization.

Modelling and experimental studies on the transfer of radionuclides to fruit.

Although fruit is an important component of the diet, the extent to which it contributes to radiological exposure remains unclear, partially as a consequence of uncertainties in models and data used to assess transfer of radionuclides in the food chain. A Fruits Working Group operated as part of the IAEA BIOMASS (BIOsphere Modelling and ASSessment) programme from 1997 to 2000, with the aim of improving the robustness of the models that are used for radiological assessment. The Group completed a number of modelling and experimental activities including: (i) a review of experimental, field and modelling information on the transfer of radionuclides to fruit; (ii) discussion of recently completed or ongoing experimental studies; (iii) development of a database on the transfer of radionuclides to fruit; (iv) development of a conceptual model for fruit and (v) two model intercomparison studies and a model validation study. The Group achieved significant advances in understanding the processes involved in transfer of radionuclides to fruit. The work demonstrated that further experimental and modelling studies are required to ensure that the current generation of models can be applied to a wide range of scenarios.