The Dynamic Response And Fragility Analysis Of Nuclear Island Plant Based On Mainshock-aftershock Seismic Sequences

The nuclear power plants,which as a complex system engineering would cause the incalculable economic losses or casualties,once destroyed by earthquakes.Although the selection of the location of nuclear power plants is very strict and the occurrence of the possibility of high-intensity earthquakes is low,the situation of nuclear power plants experiencing super-design requirements for ground motion also occurs frequently.Therefore,for the safety design of nuclear power plants,it is necessary to consider the seismic performance of nuclear power plants as an important factor.There are often many aftershocks occurs after a strong earthquake happening.However,the current seismic code only considers the influence of a single earthquake and ignores the effect of the aftershocks.A large number of seismic damage examples show that the cumulative damage of buildings with multiple earthquakes is more obvious than the damage which under only one main shock.Therefore,it is of great significance for the seismic design of nuclear power plants to study whether nuclear power plants have the ability to resist aftershocks again.This paper takes AP1000 nuclear island as the research object,to study the seismic performance of the nuclear island structure under the main shock-aftershock,which aims to provide some feasible suggestions for the seismic safety assessment of nuclear plants.The main contents and conclusions are as follow:(1)The finite element model of non-isolated and isolated AP1000 nuclear island are established based on ANSYS software.The modal analysis of the two models is carried out to obtain the periods,frequencies and mode shapes,which are used to analyze the rationality of the isolated system and verify the reliability of the models.(2)The dynamic responses of non-isolated and isolated nuclear island structures under main shock-aftershock seismic sequences are analyzed,and the acceleration response spectra of nuclear island structures under different seismic sequences are obtained through dynamic time history analysis.It is concluded that the effects of aftershock on the dynamic behaviors are related to the magnitude of main shock and the spectral of aftershock,and the seismic response of the nuclear island under the main shock-aftershock can be reduced by base-isolation systems.(3)As for the non-isolated nuclear island structure,the strain of concrete is selected as damage index to study the fragility curves of nuclear island under the main shock-aftershock seismic sequences and the effects of different aftershock amplitude are analyzed.It is concluded that the effect of aftershock will affect the damage of nuclear island,and with the increase of the magnitude of aftershock,the probability of the damage for nuclear island increases by 10% to 40%.(4)As for the base-isolated nuclear island structure,the fragility curves of the base-isolated nuclear island are analyzed,through the incremental dynamic analysis(IDA)and the multiple strip analysis(MSA)methods.The deformation coefficient of isolation layer is selected as a damage index.The fragility curves obtained by the two methods are compared to verify the rationality of the results,the results show that fragility curves obtained through IDA is similar with the results of MSA method.