Abstract
The radiological consequences of a nuclear power plant (NPP) accident, resulting in the release of radionuclides to the environment, will depend largely on the mitigating actions instigated shortly after the accident. It is therefore important to make predictions of the radiation dose to the affected population, from external as well as internal exposure, soon after an accident, despite the fact that data are scarce. The aim of this study was to develop a model for the prediction of the cumulative effective dose up to 84 years of age based on the ground deposition of 137Cs that is determined soon after fallout. The model accounts for different assumptions regarding external and internal dose contributions, and the model parameters in this study were chosen to reflect various mitigating actions. Furthermore, the relative importance of these parameters was determined by sensitivity analysis. To the best of our knowledge, this model is unique as it allows quantification of both the external and the internal effective dose using only a fallout map of 137Cs after a nuclear power plant accident. The cumulative effective dose over a period of 50 years following the accident per unit 137Cs deposited was found to range from 0.14 mSv/kBq m-2 to 1.5 mSv/kBq m-2, depending on the mitigating actions undertaken. According to the sensitivity analysis, the most important parameters governing the cumulative effective dose to various adult populations during 50 years after the fallout appear to be: the correlation factor between the local areal deposition of 137Cs and the maximum initial ambient dose rate; the maximum transfer from regional average fallout on the ground to body burden; the local areal deposition of 137Cs; and the regional average 137Cs deposition. Therefore, it is important that mapping of local 137Cs deposition is carried out immediately after fallout from a nuclear power plant accident, followed by calculations of radiation doses for different scenarios using well-known parameters, in order to identify the most efficient mitigation strategies. Given this 137Cs mapping, we believe our model is a valuable tool for long-term radiological assessment in the early phase after NPP accidents.
Highlights
The consequences of the release of radionuclides to the environment following a nuclear power plant (NPP) accident will depend to a high degree on the steps taken to mitigate the effects shortly after the accident
To the best of our knowledge, this study is the first attempt to develop a model in which both the external and internal exposure pathways are implicitly linked to a fallout map of 137Cs after a NPP accident
Our model shows that the long-term total effective dose, expressed as cumulative internal and external effective dose (CED)(50), including both internal and external dose contributions, per unit 137Cs deposition, ranges from 0.14 mSv/kBq m-2 to 1.5 mSv/kBq m-2
Summary
The consequences of the release of radionuclides to the environment following a nuclear power plant (NPP) accident will depend to a high degree on the steps taken to mitigate the effects shortly after the accident. In our recently published study, by Jonsson et al, a model was presented describing the cumulative external effective dose from short-lived nuclides and the gamma-emitting Cs isotopes 134Cs and 137Cs in the most affected counties [4]. Integrated over a 70-year period, the model predicted that 137Cs would account for 60%, and 134Cs for 30%, of the projected external effective dose, and that the timeintegrated external effective dose over 70 years, to an unshielded person resulting from all nuclides, per unit total activity of 137Cs deposition, would be 0.29 ± 0.08 mSv/(kBq per m2). The model was based on an initial activity ratio between 134Cs and 137Cs in the Chernobyl fallout in 1986 of 0.56, replacing this value with the corresponding ratio from the Fukushima Daiichi NPP accident (1.1) showed that the 70-year integrated external dose would be only moderately affected (an increase of only 20%) [7]. We believe that the previously developed model is applicable for future releases, where the initial 134Cs/137Cs activity ratios will probably be more similar to that from the Fukushima accident
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