起因事象マトリックス法による地震リスク評価

抄録

A method called the Initiating Event (IE) Matrix Method (IEMM) is proposed to resolve several issues regarding the hierarchization of IEs applied in the seismic Probabilistic Risk Assessments (PRAs) of nuclear facilities. In the hierarchization of IEs, the influence of low-order IEs is assumed to be smaller than that of high-order IEs. Consequently, the accident progressions of low-order IEs are basically omitted, which makes the risk assessment models simple and makes it feasible to assess the seismic risks associated with complex systems such as nuclear facilities. However, in the hierarchization, since the accident progressions of the simultaneous occurrence of multiple IEs are omitted, there is a possibility that the combinations of multiple IEs having small occurrence frequencies but large impacts on the environment might also be omitted from the risk assessment models. In addition, since there are cases where the combinations of multiple IEs may be considered only for some specific accident progressions depending on the assessor, the assessment results may depend on the assessor. Therefore, the authors propose the IEMM that assesses all the IEs with significant occurrence frequencies and all the combinations of such IEs. By comparing the IEMM and the hierarchization method in a case analysis of a simple system with a few IEs, the assessment results show less dependence on the assessor and fewer overlooks of accident progressions of significant IEs and combinations of such IEs.