Stochastic dynamic and reliability analysis of AP1000 nuclear power plants via DPIM subjected to mainshock-aftershock sequences

Earthquakes usually consist of a mainshock and a series of aftershocks, both of which are random. The mainshock can damage structures, and the subsequent aftershocks may cause further damage. However, no studies have considered the effects of stochastic seismic sequences on nuclear power plants (NPPs). We propose a new framework to analyze the stochastic dynamic response and dynamic reliability of AP1000 NPPs. First, stochastic mainshock-aftershock sequences are generated by combining a physical random function model, the narrowband harmonic group superposition method and the copula function. Then, the effects of aftershocks on NPPs are highlighted using acceleration and displacement as response indices and the tensile damage ratio (TDR) and plastic strain as damage indicators. Finally, probabilistic information and reliability of NPPs are obtained based on the direct probability integration method (DPIM) and the absorbing condition method (ACM). The results show that the dynamic response is larger for seismic sequences than a single mainshock, and seismic sequences cause more damage to the NPPs. When the peak ground acceleration (PGA) increases, the effect of the aftershock becomes more pronounced, and the response of the NPP becomes more random. Moreover, aftershocks reduce the reliability of NPPs, and the degree of reduction is related to the thresholds.