DEVELOPMENT OF SYSTEMS RELIABILITY-ANALYSIS CODE SECOM-2 FOR SEISMIC PSA

An integrated code system SECOM-2, developed at the Japan Atomic Energ y Research Institute (JAERI), has the following functions for systems reliability analysis in seismic probabilistic safety assessments (PSAs ): (1) calculation of component failure probability, (2) extraction of minimal cut sets (MCSs) from a given fault tree (FT), (3) calculation of frequencies of accident sequences and core damage, (4) importance analysis with several measures with consideration of unique parameters of seismic PSAs, (5) sensitivity analysis, and (6) uncertainty analys is. This paper summarizes the special features of SECOM-2 to perform t he analyses mentioned above. At JAERI, using an integrated FT which re presents seismically induced core damage due to all initiating events as a system model to calculate core damage frequency of a nuclear powe r plant, SECOM-2 can calculate conditional point estimate probabilitie s of system failures, losses of safety functions, and core damage as a function of earthquake motions. The point estimate is computed by a m ethod which gives an exact numerical solution using the Boolean arithm etic model method. As for consideration of correlation of component fa ilure, which has been an important issue in seismic PSAs, a new techni que based on direct FT quantification by a Monte Carlo simulation is b eing added to SECOM-2. Adding this technique, the core damage frequenc y can be calculated not only with the upper bound approximation based on MCSs but also with a near exact solution taking into account the co rrelation among all components. This paper also presents the prelimina ry results of a seismic PSA of a generic BWR plant in Japan performed at JAERI to demonstrate the functions of the SECOM-2 code. (C) 1998 El sevier Science Ltd. All rights reserved.