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

International audienceWildlife 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 authorized 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 (IAEA) 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, considering radionuclides potentially discharged in atmospheric routine release from different nuclear facilities. Differences observed in the results between hypothetical and reference organisms were less than one order of magnitude in all cases, the difference being dependent on the radionuclides 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 reference organisms for radiological impact assessments in the case of routine atmospheric discharges is sufficient

Quantifying exposure of plants and animals to radiation: a new methodology

The IAEA is updating its simple methodology for calculation of doses to people from radioactive discharges. The update will provide a harmonised dose assessment methodology for both humans and flora and fauna. The approach is intended for the assessment of planned releases from facilities and estimates radiation exposure during the 100th year of discharge (expected life-time of a nuclear facility). The environmental protection elements of the methodology will, as far as practicable, utilise relevant aspects of the ICRP’s framework for environmental protection. Here we describe the new IAEA methodology for calculating the radiation exposure of terrestrial wildlife focussing on differences with existing methodologies and demonstrating the potential impact of these differences. The application of whole body concentration ratios, CRwo-soils, is often aimed to be conservative. However, it has been suggested that the application of CRwo-soils in situations of prolonged atmospheric discharges will result in an underestimation of the exposure of plants and some animals. This is because radionuclides deposited onto plant surfaces are predicted to contribute a significant component of the total plant activity. Ignoring externally deposited radionuclides from the assessment is also inconsistent with models used to assess human exposure. Consequently, the new methodology adopted by the IAEA incorporates an explicit consideration of this exposure pathway, including consideration of herbivorous animals feeding on plants with external deposition. Other differences in the new approach compared to existing environmental assessment tools are the correction of CRwo-soils for radionuclide physical half-life and the approach used to consider the scenario-specific contribution of radioactive progeny to parent radionuclide dose. The paper will compare results using the existing and new methodologies

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

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