Development of a probabilistic risk assessment method for combined hazards; An Application example of multihazard events

Choi, B. ; Nishida, Akemi  ; Tsutsumi, Hideaki*; Takada, Tsuyoshi  

One of the key lessons learned from the Fukushima Daiichi Nuclear Power Plant accident is the necessity of developing a probabilistic risk assessment (PRA) method that considers multiple external hazards (multi-hazards), such as earthquakes and tsunamis. In this study, we organized classification concepts for multi-hazards that could lead to significant disasters. A classification method for multi-hazard scenarios was developed based on causal relationships (dependent or independent) and temporal relationships (simultaneous or time-lagged occurrence). Furthermore, we examined modeling approaches for multi-hazard scenarios using the developed classification method. The modeling considered elements such as hazard curves, hazard intensity, hazard frequency, time, and event duration, and these were defined in terms of conditional probability density functions. This paper reports application examples of multi-hazard evaluation under hypothetical site and analysis conditions, focusing on representative scenarios such as earthquake-tornado and earthquake-tsunami combinations, based on the multi-hazard classification method developed in previous studies.