A PROPOSAL OF THE METHOD TO EVALUATE THE FAILURE PROBABILITY FOR AN UNDERGROUND STRUCTURE IN NUCLEAR POWER PLANTS

Abstract

A new practical method is proposed for evaluating the failure probability of the intake tunnel for seismic PSA of the nuclear facility. The strength of the structure is specified by the limit deformation angle between the adjacent slabs and the realistic response of structure is expressed by its maximum deformation angle. The median for the stochastic characteristics of the actual response is evaluated by the non-linear seismic response analysis using FEM. The variation is evaluated conveniently based on the semi-empirical relationship between the deformation angle of the ground and that of the structure. By using this simplified method the computation time to obtain the variation was reduced extremely. The method is applied to evaluate the failure probability of the two stories intake tunnel with seven walls as the partition. As a result, the failure probability was obtained to be about 0.13 for input motion of maximum acceleration of 900 Gal. It was also found by comparing the FEM and semi-empirical methods that the estimated deformation angle by the simplified method has a sufficient accuracy for a practical use because the estimated error is less than10%.