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

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.

Preliminary safety assessment for planning near surface disposal of low-level radioactive waste in Greece

This paper presents the approach, assumptions, and computational analysis of the preliminary safety assessment, regarding the post-closure period for the disposal of radioactive waste in Greece. The assessment was implemented in the context of the National Program for the disposal of radioactive waste in the country, which is currently in the early stage for the investigation of facility siting. The basis scenario selected for this investigation was the leaching of radionuclides and the exposure in a residence offsite. Moreover, a scenario involving the intrusion in the facility and construction of a dwelling that disturbs the disposal zone is also considered. Due to the significant uncertainties in the current phase, the simulations related to leaching of the waste both in the offsite and intrusion scenarios are based on an uncertainty analysis with 25 site and scenario related parameters. The most important contribution is attributed to Ra-226 with an annual dose equal to about 2 and 3 μSv per MBq disposed, for the offsite and intrusion scenario, respectively. Th-232, Cl-36, C-14, Ag-108m and Pu-239 follow with a dose one order of magnitude less, compared to Ra-226. In the leaching scenarios examined, and for the most dose relevant radionuclides, the exposure related to drinking water from the well and the use of this water to irrigate fruits and vegetables are by far the dominant pathways due to the environmental transfer of the radionuclides and their associated dose coefficients. Th-232 dominates the direct exposure pathways (direct external radiation and plant contamination from the contaminated surface soil) in the intrusion scenario with an annual dose of about 1.4 mSv per Bq/g disposed. Ra-226, Cl-36 and Ag-108m cause exposure levels higher than 0.2 mSv/y per Bq/g disposed in the facility. A wide range was considered for the uncertainty parameters that led to a significant variation in the predicted doses that is expected to envelope the potential exposure for each radionuclide.

How dynamic transfer models can complement an equilibrium-based approach: Case studies of radiocesium transfer to forest trees following accidental atmospheric release

Accidental release of radionuclides caused by nuclear accidents like those in Fukushima and Chernobyl can result in pulses of radioactivity entering the forest environment. Due to intense recycling in the forest, equilibrium between radioactivity concentrations in trees and in soil may not be reached during the period of severe short-term radionuclide transport following the accident. Another question arises as to whether the equilibrium hypothesis using empirical concentration ratios (CRs) can be applied to the long-term period. Using two atmospheric ¹³⁷Cs fallout scenarios in the Fukushima and Chernobyl sites, this study investigated whether the CR approach could provide conservative predictions of ¹³⁷Cs levels in trees following ¹³⁷Cs fallout events by comparing predictions from the CR approach using data gathered for trees by the IAEA to those from dynamic transfer models and actual measured data. The inter-comparisons also aimed to investigate whether the CR approach could account for the variability of ¹³⁷Cs levels across different tree organs. The results showed that caution may be necessary when using the CR approach, which relies on the IAEA dataset, to estimate ¹³⁷Cs accumulation in forest trees in the short - and long term following atmospheric ¹³⁷Cs fallout events. A calculation by TRIPS 2.0 demonstrated the importance of considering the distribution within tree organs for in-depth analysis of radiological impact of forest trees. Our findings suggest that it may be preferable to use CR values based on site-specific data rather than generic data collected from various sites. This is particularly relevant when studying the sites where the bioavailability of ¹³⁷Cs for trees and thus possible exposures are higher. This study also showed that dynamic modeling approaches could offer an alternative means of estimating CR values of the entire tree or specific tree organs in situations where empirically derived values are not available.

Radiation exposure and risk assessment to earthworms in areas contaminated with naturally occurring radionuclides

The assessment of radiation exposure on biota is one of the main parts of environment protection system. Earthworms have been recognized as an important organism group in the terrestrial ecosystems. According to many researchers the potential risks of naturally occurring radionuclides for soil invertebrates were not significant because the exposure doses to the invertebrate populations were low. Our study aimed to assess the radiation exposure and the radiological risks from naturally occurring radionuclides for earthworm populations at four sites. This research was based on three dosimetric approaches simultaneously: ERICA and RESRAD-BIOTA-the commonly used ones, and also on the original method proposed by Thomas and Liber (Environment International, 27, 341-353, 2001) for aquatic organisms. To calculate radiation dose rates to soil invertebrates inhabiting background and contaminated areas, the specific activities of radionuclides in soil, and, depending on the model, the default, or determined in this study, input mass-geometric parameters had been applied. The weighted absorbed dose rates calculated by different models and site-specific data were 0.3-1.4 μGy/h for the background and from 3.4 to 170 μGy/h for the contaminated sites. Analysis of radiation risks for earthworms indicated that ²²⁶Ra was the key contributor to the external dose rate; ²²⁶Ra and ²¹⁰Po played a dominant role in formation of internal dose rate for radioecological situations in our study. More conservative radiation risk assessments were derived from RESRAD-BIOTA tool. Dose assessments obtained using various models had shown that there are real environmental situations in which the radiological risks to reference organisms are significantly higher than the lowest benchmark protection level proposed for ecosystems.

Bounding uncertainties around the conceptual representation of species in radiological assessment in the context of routine atmospheric release

Wildlife protection has become of regulatory interest since the International Commission on Radiological Protection (ICRP) developed an approach to assess the level of radiological protection specifically for animals and plants. For the purpose of demonstrating compliance with regulation to protect the environment against routine authorised discharges from nuclear facilities, the wide variety of biota inhabiting an ecosystem needs to be condensed to a limited set of representative organisms, as proposed by the ICRP with a set of 'reference animals and plants' which can be considered representative of many other species. It is now recommended in the International Atomic Energy Agency Safety Standards, and internationally accepted, that the use of such a limited number of organisms to represent a pool of species is adequate for radiation protection purposes, particularly in planned exposure situations. Adding site-specific species to that set of surrogate species can respond to various interests, such as ensuring a site-specific context to the assessment that addresses stakeholder interests and can aid in stakeholder consultation and risk communication. Moreover, there is a need to question whether the use of the set of surrogate organisms is conservative enough to cover a wider range of biodiversity. Previous studies partially answered this question and this paper adds a range of test cases. A selection of hypothetical representations of possible site-specific species are assessed on the basis of possible variations in size (mass) and occupancy habits. Dose rates are evaluated to determine the greatest difference between hypothetical organisms and those for reference organisms (ROs), considering radionuclides (RNs) potentially discharged in atmospheric routine release from different nuclear facilities. Differences observed in the results between hypothetical organisms and ROs were less than one order of magnitude in all cases, the difference being dependent on the RNs considered. These findings do not preclude the inclusion of site-specific species in environmental radiological assessments if it is considered necessary, but they provide reassurance that using ROs for radiological impact assessments in the case of routine atmospheric discharges is sufficient.

Does the use of reference organisms in radiological impact assessments provide adequate protection of all the species within an environment?

Non-human biota in radiological risk assessment is typically evaluated using Reference Organisms (ROs) or Reference Animals and Plants (RAPs), for all exposure situations. However, it still remains open whether the use of an increased number of species would improve the ability to demonstrate protectiveness of the environment. In this paper, the representativeness of a broader list of fauna is tested in terms of the geometrical characteristics and habits for radiological risk assessments in the case of routine discharges from a nuclear installation: the Cadarache centre. A list of terrestrial animal species, compiled from ecological inventories carried out around it was evaluated. A first survey around the centre inventoried >400 terrestrial fauna species, which were then filtered to reduce the number to 28 species for which dose assessments were carried out. Despite the differences between geometries for those site-specific species and the ROs (including RAPs), the absorbed dose rates calculated for both were very close (within a factor of two). Regardless of the studied organism, the absorbed dose rates calculated for the discharge scenario were mainly related to internal exposure, particularly for tritium (³H) and carbon 14 (¹⁴C), showing that there would be an acceptable dose rates difference between species from the same organism group. Additionally, sensitivity analyses were conducted to determine if the use of generic, predefined ROs was enough to assure an adequate protection of endangered species. It was observed that for every radionuclide the difference between assessments for site-specific species and ROs are unlikely to exceed a factor of 3. Hence, the result of this evaluation indicates that the use of generic ROs for non-human biota radiological risk assessment covers sufficiently other species, including endangered ones.

The tubercular badger and the uncertain curve:- The need for a multiple stressor approach in environmental radiation protection

This article presents the results of a workshop held in Stirling, Scotland in June 2018, called to examine critically the effects of low-dose ionising radiation on the ecosphere. The meeting brought together participants from the fields of low- and high-dose radiobiology and those working in radioecology to discuss the effects that low doses of radiation have on non-human biota. In particular, the shape of the low-dose response relationship and the extent to which the effects of low-dose and chronic exposure may be predicted from high dose rate exposures were discussed. It was concluded that high dose effects were not predictive of low dose effects. It followed that the tools presently available were deemed insufficient to reliably predict risk of low dose exposures in ecosystems. The workshop participants agreed on three major recommendations for a path forward. First, as treating radiation as a single or unique stressor was considered insufficient, the development of a multidisciplinary approach is suggested to address key concerns about multiple stressors in the ecosphere. Second, agreed definitions are needed to deal with the multiplicity of factors determining outcome to low dose exposures as a term can have different meanings in different disciplines. Third, appropriate tools need to be developed to deal with the different time, space and organisation level scales. These recommendations permit a more accurate picture of prospective risks.