Seismic fragility of CAP1400 nuclear power plant consisting of steel-concrete shield building under mainshock-aftershock sequences

The seismic safety of the CAP1400 nuclear power plant (NPP) is critically important as its failure would result in significant loss of life and economic damage. Currently, seismic fragility analysis for the CAP1400 NPP has been conducted solely under single ground motions. Since strong ground motions often trigger multiple aftershocks, a comprehensive seismic fragility analysis of the CAP1400 NPP under mainshock-aftershock (MS-AS) sequences is conducted in this paper. Incremental dynamic analysis results and seismic fragility curves are derived using 20 MS-AS records, scaled with different intensity ratios of 1:0.6, 1:0.8, and 1:1. The results indicate that MS-AS sequences cause more severe damage to the CAP1400 NPP compared to mainshock records, and the damage intensifies as the aftershock ratio increases. Furthermore, as the CAP1400 NPP generally adopts steel-concrete (SC) shield building instead of conventional reinforcement concrete (RC) shield building, a comparative seismic fragility analysis of the CAP1400 NPP with SC and RC shield building is conducted under MS-AS sequences. It is found that the CAP1400 NPP consisting of SC shield building exhibits significantly lower fragility than RC shield building under MS-AS sequences, and as the aftershock ratio increases, the seismic superiority of SC shield building becomes more pronounced.