Catastrophe Mechanism And Seismic Fragility Analysis Of The AP1000 Nuclear Power Plant Under Earthquakes

The AP1000 nuclear power plant(NPP),including the steel vessel containment(SVC),the reinforced concrete shield building(RCSB)and reinforced concrete auxiliary building(RCAB),is the core building of nuclear engineering.NPP is an important facility for shielding nuclear reactors,resisting external events,and eliminating “nuclear panic”.It is of practical significance to conduct research on the seismic safety of NPPs.This dissertation studies the catastrophic behavior and performance evaluation of NPPs under the action of beyond design basis earthquakes and mainshock-aftershocks.It aims to explore the performance states of NPPs under sequential strong mainshock-aftershock,analyzes the catastrophe mechanism and failure modes,propose linear and nonlinear mechanical behaviors of simplified systems for NPPs,and reveals the performance evaluation and analysis method of NPPs system under beyond design basis earthquake and mainshock-aftershocks.The research results have certain theoretical and practical reference value for improving the seismic safety of the NPP.The main contents are concluded as follows:1.In this dissertation,low-cycle repeated quasi-static tests are conducted on 6 steel reinforced concrete(SRC)shear walls to study the mechanical properties of the SRC shear wall,by changing the connection between the section steel and the horizontal steel bars of the boundary column as well as the angle between the boundary column and the shear walls.Under the condition of considering the complex factors such as stiffness and geometric change between the shear wall and the boundary column,internal reinforcement arrangement and other complex factors in the shear wall and the boundary column composite structure with special arrangement,this dissertation analyzes the difference between the mechanical properties of the shear wall with thin-walled steel added to the boundary column and the mechanical properties of regular reinforced concrete shear walls,and it also analyses the reliability of the connection form between the boundary column thin-walled steel and the horizontal reinforcement of the shear wall.The parameters of the concrete CDP model suitable for the NPP are selected based on the shear wall experimental data.2.The finite element(FEM)model of the whole NPP is constructed based on the parameters of the concrete CDP model suitable.The two models with and without the RCAB is compared for the top peak acceleration,the top peak displacement and plastic damage.Research work is done on the damage development of the RCSB,the RCAB and the SVC.The RCAB shows a significant damage and the damage zones are concentrated at the intersection of the RCAB and the RCSB.The SVC has good seismic performance.This dissertation compares the dynamic response and damage analysis of the whole NPP under the mainshockaftershocks and the single earthquakes.The damage residual displacement and damage energy dissipation of the whole NPP,and the plastic damage at the intersection of the RCAB and the RCSB are mainly analyzed.3.Combined with the damage characteristics of the NPP under the beyond design basis earthquake,the SVC and equivalent equipment are treated as a substructure,which is connected with the remaining structure to form a substructure(SUB)model,and dynamic response is carried out with the FEM model Comparing and verifying the damage of each zone.Based on the verified SUB model,incremental dynamic analysis is carried out to analyze the seismic fragility analysis of each zone of the SUB model,and compared with the multi-strip method analysis.The following conclusions can be drawn: there is a certain difference in the failure probability of MSA and IDA analysis methods in the SB10 zone and the L6 layer,but the difference is small.The maximum difference in the SB10 zone is 5%,and the L6 layers 7.13%.It is proved that the two calculation methods are reasonable.4.This dissertation proposes an improved lump mass model of NPP based on the Kriging surrogate model.The sensitivity analysis was performed on each node mass of the LMS model to determine the node mass for optimization.The Kriging surrogate model is established and its validity is checked,and the mass point is optimized.Comparing the dynamic response of the I-LMS model and the FEM model under the dynamic characteristics and design basis earthquake,the nonlinear mechanical equivalence of the beam elements of the I-LMS model and the FEM model is carried out.The results shown that the relative error of the 9th-order frequency is reduced,and the maximum error of the frequency is reduced from 23.04% to7.21%.The maximum difference between the I-LMS model and the FEM model in the X,Y,and Z directions of the response peaks was 6.745%,6.678%,and 6.098%,respectively.Compared with the reciprocating displacement loading,the maximum load difference between the I-LMS model and the FEM model at the peak point is 5.27%.The I-LMS model can better equivalent the nonlinear mechanical properties of each zone of the FEM model in each beam element.5.The seismic fragility analysis of the whole NPP is conducted based on Copula function.The structural parameters of the I-LMS model are sampled using Latin hypercube sampling.The IDA analysis under a single main shock is performed on the I-LMS model samples to determine the maximum damage beam elements representing the components RCSB and RCAB.IDA analysis is carried out on the I-LMS model samples under the action of mainshockaftershocks,and the edge distribution function of the beam element is constructed.The appropriate Copula function was selected by AIC and square Euler distance,and the seismic fragility analysis of the overall NPP is analyzed based on the Copula function.The results shown that under the action of a single mainshock and the action of the mainshock aftershock and the failure probability of a single RCSB(beam element(10))the maximum difference between the overall failure probability calculated based on the Copula function is 18.77%,and the maximum difference in the failure probability of a single RCAB(beam element(6))is241.11%,and the seismic fragility analysis considering the RCSB or the RCAB alone significantly reduces the failure probability of the NPP.