Code Developing of Fragility Analysis Program for Seismic Safety Evaluation of Nuclear Power Plant

For seismic safety evaluation method of nuclear power plant, nuclear power plant seismic margin analysis (SMA) and nuclear power plant seismic probability safety assessment (SPSA) are the most widely used methods. SMA is a method base on deterministic theory. Seismic capacity is valued by high confidence and low failure probability (HCLPF). Through the seismic failure logic of structure, system and components (SSCs), the method can calculated the HCLPF of the whole nuclear power plant, and verify whether the plant can withstand a SSE earthquake test. The SPSA method is the most widely used seismic safety assessment method based on probability theory. Through the analysis and quantification of earthquake accident sequence, a SPSA project can fully identify the seismic risk of nuclear power plant and seismic weak points. Also SPSA can guide the nuclear power plant seismic safety improvement. No matter which method is used to analyze the seismic safety of nuclear power plant, it is necessary to analyze and calculate the seismic fragility of the SSCs. SMA method needs to use a large number of HCLPF data, and seismic fragility analysis and calculation results is one of the main sources of HCLPF data. The SPSA method needs to use seismic fragility data of SSCs which are list in the seismic equipment list (SEL) as input data, so that it can support the quantitative analysis of the risk assessment model. Because of the existence of uncertainty, the seismic fragilities cannot be put to directly logic operation. This brings great difficulty to the using of fragility data. In the paper, the logic operation method and the uncertainty analysis method of seismic fragility is studied, and the calculation program is compiled based on the Monte Carlo method. In this paper, a program is used to calculate the case. The performance of the program is verified and the uncertainty of the system fragility is analyzed. Due to the existence of uncertainty, the fragility cannot put into the numerical calculation directly. In this paper, the calculation method of the failure frequency of components is studied, and the corresponding program is developed by using Monte Carlo method. In this paper, a program is used to calculate the failure frequency of the components under different ground motion levels, and the uncertainty of the failure frequency is also studied.