THE SEISMIC RELIABILITY OF VVER-1000 NPP PRESTRESSED CONTAINMENT BUILDING

The failure probability assessment of the containment building is an e ssential feature of the Level 2 PSA studies of nuclear power plants. T he primary purpose of this paper is to demonstrate the methodology of evaluating containment seismic induced probability of failure without containment pressurization. The Loviisa, Finland site is one of the mo st seismically stable in the world and the numerically evaluated seism ic induced failure probabilities are not representative for other site s. In addition, the containment concept described in this paper is not the typical Russian design which uses helical tendons in the cylindri cal part of the structure and has a ring girder at the spring line of the structure. So the conclusions reached are applicable only to the c ontainment configuration described in the paper. The geometry of the c ontainment was determined by its preliminary design. The seismic hazar d of the plant site was assessed during Level 1 PSA of the Loviisa pla nt. The initial information for seismic fragility analysis of the cont ainment is the seismic response of the structure. The structural model for response analysis was the stick model. The stress analysis of the containment was carried out using the shell element model. The fragil ity evaluation of the containment was performed with the PROBAN-progra m The structure was modeled as a parallel system consisting of the mos t heavily stressed elements. The resulting fragility curve gives the c onditional probability of failure as a function of peak ground acceler ation. The seismic hazard and the fragility were convolved to obtain t he annual nonexceedance probability distribution for the collapse freq uency of the structure.