Level 2 (L2) PSA is focused on the severe accident phenomenon, progression and source terms release to generally evaluate the containment response after core damage takes place. Fukushima accident was caused by seismic and tsunami which are beyond design basis. It indicates that evaluating the risk for extremely external hazards is vitally important. Therefore, how to perform the study on L2 PSA for external events (especially seismic and flood) has become a crucial problem needed to be considered deeply for both regulators and operators. In this paper, the methodology of flood and seismic-induced flood L2 PSA was developed and applied for a Gen III NPP in China. The key factors include:

(1) Focusing on crucial elements of L2 PSA in view of seismic and flood characteristics, including PSA interfaces, design features, severe accident phenomenon and progression, containment performance analysis, etc.

(2) Building integrated internal flood and seismic L2 PSA models.

(3) Developing an analytical method to evaluate seismic-induced flood L2 PSA.

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