Evaluation of Seismic-Response-Correlation Effect on Seismic Risk by the Initiating Event Matrix Method

The hierarchization of initiating events (IEs) has been widely applied in seismic probabilistic risk assessments of nuclear facilities. In our previous study, we proposed the Initiating Event Matrix Method (IEMM) with a focus on IEs involving multiple failures of structures, systems, and components; such IEs are normally ignored in hierarchization for simplicity. In this study, we applied the IEMM to a case study to evaluate the seismic response correlation effect in a hypothetical fuel cycle facility to validate the applicability of the IEMM to such a case. This case study is suitable for this purpose since it is well known that the occurrence frequencies of IEs with multiple failures may increase significantly when the seismic response correlation is considered. As a result of the case study, the increase in severe-accident frequency due to the correlation effect was reasonably evaluated by the IEMM, and therefore, we confirmed the applicability of the IEMM to cases involving such an effect. Additionally, it was found that the event tree of IEs could be greatly simplified by contraction in the IEMM depending on the event trees of mitigation systems following the IEs. © 2023 Atomic Energy Society of Japan, All Rights Reserved.