Classification of radioactive material release timing for emergency preparedness

Abstract

Following the Fukushima accident in 2011, concerns about nuclear accident risk and consequence management and emergency response intensified. For such severe conditions, promptly implementing a proper emergency response and effectively minimizing the impact on the public and environment is essential. To model it efficiently, a number of elements must be taken into account. In particular, the release starting time after the initiating event and the release behavior characteristics of radioactive materials (e.g., Cs-137) are essential for accurate modeling. In the radiological emergency plan, a conservative estimate for the release starting time of 4 h is assigned in the emergency actions for the public. However, for specific NPPs, the characteristics of the release starting times and Cs-137 release points in each accident are different. Therefore, to construct proper radiological emergency plans for specific NPPs, this study aimed to cluster the proper ranges of release starting times and estimate the confidential Cs-137 release points under the uncertainty analysis scheme of the Optimized Power Reactor-1000 (OPR-1000) during a station blackout (SBO) and Total Loss Of Component Cooling Water (TLOCCW) accident using the Dirichlet process mixture clustering approach. As a result, the SBO scenario having the long range of release starting time showed the highest Cs-137 release in the range of 11–19 h which could help provide more flexible emergency actions and timelines. The TLOCCW scenario showed the overall short range of release starting time already agreed with the conservative estimation at 4 h to consider as the priority of the radiological emergency plan and the decision making.