Seismic Performance And Fragility Analyses Of Reactor Building Structures In Nuclear Power Station

Owing to the increasing global demands for energies and the exhaustion of non-renewable resources such as fossil fuels, nuclear power as an economic, efficient and clean energy, have been used extensively in the world. However, nuclear accidents will cause catastrophic damages to the safety of human lives and properties. The Fukushima nuclear accident drew the reexamination and attention of the whole world on the seismic hazard risk of nuclear power station. One major focus of aseismic design of nuclear power station is the seismic performance and fragility analyses of reactor building structures. In this paper, seismic response performances of the reactor building structures under strong earthquakes are investigated by use of the seismic simulation software OpenSees. The fragility curves of the reactor exterior building (REB) and the prestressed concrete containment vessel (PCCV) are built based on the structural reliability theory, which aim to promote the seismic fragility research of the nuclear power station and the aseismic design of the reactor building structures for our country. The main contents and achievements of the thesis are as follows:(1) Based on a lumped mass model to account for nonlinear shear-flexure interaction behaviors, elasto-plastic dynamic time history analyses are carried out by use of the seismic simulation software OpenSees for the reactor building structures of the nuclear power plant located in the strong earthquake area abroad. According to the design spectrum with annual exceedence probability of10-4～10-6given by seismic risk analysis of the site, seismic response performances of the reactor building structures are investigated under the design and beyond-design basis earthquakes. The results show that the deformations of the reactor building structures are small and they are basically in elastic state under the design basis earthquake. However, some structures of the reactor buildings characterize the nonlinear behavior in shear and their deformations are relatively large under two times the design basis earthquake. Particularly, the bottom of the containment reaches to the yielding state. Although a certain degree of residual deformations of the upper structures may occur after two times the design basis earthquake, but the majority of the structures remain integrity, and the reactor building structures could wholly meet the seismic safety requirements.(2) On the basis of the finite element reliability theory, structural performance functions are fitted by means of the response surface methodology and reliabilities of reactor building structures are calculated with the central point method, design point method and Monte-Carlo simulation method. The calculating results of three methods are compared with design variables assumed to be distributed normally and lognormally respectively. Based on these results, the seismic fragility curves of REB and PCCV are built. The results show that the calculating fragility curves of three methods are similar when variables are distributed normally, but different when variables are distributed lognormally. The difference betweent the calculating fragility curves varies with the seismic intensity, which indicate that the distribution types of design variables will have a certain influence on the reliability analyses of structures.(3) Based on the results of structural reliability analyses, several groups of seismic fragility curves with different confidences are fitted with the seismic fragility model recommended by NRC and EPRI. The results indicate that the median acceleration capacities of REB and PCCV structures are about four and six times the design basis earthquake respectively, that the whole level of seismic failure probabilities of the reactor building structures is relatively low, and that the reactor building structures have good operational reliabilities and aseismic performances.