Study on Methodology and Application of Seismic Level 2 Probabilistic Safety Assessment for Nuclear Power Plants

Many countries have paid more attention to seismic risk in nuclear power plants after the Fukushima nuclear accident. It indicates that evaluating the risk for seismic event is vitally important. Seismic Level 1 probabilistic safety assessment (PSA) has a mature methodology, but how to perform the study on seismic Level 2 PSA has become a crucial problem needed to be considered deeply by both regulators and operators. In this paper, the methodology of seismic Level 2 probabilistic safety assessment (PSA) is developed for nuclear power plants. Seismic Level 2 PSA is focused on the severe accident phenomenon, progression and source terms release to evaluate the containment response after core damage caused by seismic event. To demonstrate the effectiveness of the proposed approach, this study took a nuclear power plant under construction in China as an example. Seismic Level 2 PSA focuses on crucial elements including Level 1/ Level 2 PSA interface analysis, severe accident design features, severe accident phenomenon, containment event tree analysis, seismic fragility analysis, etc. A risk-informed seismic Level 2 PSA model is developed to evaluate large release frequency (LRF) caused by seismic event. The proposed methodology can be expected to provide an effective framework for performing the seismic Level 2 PSA and decision support to improve the nuclear power plant safety.