Probabilistic safety assessment of the loss of offsite power accident for AP1000 under earthquake

As one of the important external events, the earthquake has a huge threat to the safety of nuclear power plant. The SPSA (Seismic probabilistic safety assessment) method can be used to qualitatively and quantitatively evaluate the characteristics of the system under earthquake and the impact on core damage. The accident of LOOP (loss of offsite power) is one of the important initiating events of nuclear power plants. In this paper, the LOSP accident event tree and related system fault tree model under internal initiating events are established, and calculating the frequency of core damage and the maximum core damage accident sequence when the LOCP accident occurs in the nuclear power plant. Then, based on the seismic hazard curve, random sampling is performed by Monte Carlo method to obtain the failure probability of the relevant equipment under different peak ground accelerations. It is added to the fault tree model as the basic event of the earthquake, and the relevant basic events of the earthquake are set as common cause failure group, the event tree model of LOSP was obtained under the earthquake condition, the frequency of core damage under earthquake was calculated, and the minimum cut set analysis of core damage was performed. According to the series of analysis results, the most important basic events which lead to core damage under earthquake conditions are obtained, and the weak links in the system can be found. (authors)