Simulation methods have become an important tool to reveal radionuclide migration during accidental radionuclide releases and predict influences of accidents on the marine environment. The instantaneous point source model is a useful method to simulate the large-scale radionuclide diffusion in marine areas. However, the simulation accuracy of this method requires improvement as it didn’t take radionuclide decay into account. In this study, an improved instantaneous point source model considering radionuclide decay was proposed on the basis of the original model. Furthermore, the instantaneous point source model and the improved version were used to simulate the concentrations of 131I and 137Cs following the Fukushima Dai-ichi nuclear power plant accident. The results showed that the relative error of 131I concentrations decreased from 136.03% to 37.59% when using the improved model; and improvements in relative errors for 137Cs concentrations were not apparent as the simualtion period was much shorter than its half-life period. Therefore, the improved model can accurately simulate the diffusion process for radionuclides following an accident and provides an efficient decision support tool for risk assessment managers and for use in safety guarantees of nuclear power plants during siting and operational phases.

中文翻译：

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核电厂事故下模拟海洋放射性核素扩散瞬时点源模型的改进

模拟方法已成为揭示放射性核素意外释放过程中放射性核素迁移和预测事故对海洋环境影响的重要工具。瞬时点源模型是模拟海洋区域大规模放射性核素扩散的有效方法。然而，该方法的模拟精度有待提高，因为它没有考虑放射性核素衰变。本研究在原有模型的基础上提出了一种改进的考虑放射性核素衰变的瞬时点源模型。此外，瞬时点源模型和改进版本用于模拟福岛第一核电站事故后 131I 和 137Cs 的浓度。结果表明，131I浓度的相对误差从136下降。使用改进模型时为 03% 至 37.59%；137Cs 浓度的相对误差改善并不明显，因为模拟期远短于其半衰期。因此，改进后的模型可以准确模拟事故发生后放射性核素的扩散过程，为风险评估管理人员和核电厂选址和运行阶段的安全保障提供有效的决策支持工具。