FUNCTIONAL RELIABILITY ANALYSIS OF SAFETY GRADE DECAY HEAT REMOVAL SYSTEM OF PFBR BY AUGMENTATION OF APPROXIMATE LINEAR RESPONSE SURFACES

摘要

Functional reliability analysis of passive safety systems is necessary to quantify the ability of the system to accomplish the intended function unaffected by the uncertainties pertained to the underlying physical processes. Functional reliability analysis includes Monte Carlo sampling of the uncertainties followed by computation of system response by a deterministic system code. For complex passive safety systems of small failure probability, Monte Carlo simulations using deterministic system codes are computationally expensive and often prohibitive. Functional failure analysis using computationally efficient approximate solutions like response surfaces has been quite popular. But in high dimensional problems, due to their approximate nature, response surfaces are not accurate enough. Nevertheless, approximate solutions provide a great source of insight for understanding system behavior. In this respect, the recently proposed Response Conditioning Method (RCM) based on Subset Simulation (SS) is considered in this paper to incorporate the knowledge obtained by approximate solutions in functional reliability analysis for obtaining consistent and computationally efficient reliability estimates. The method is applied to evaluate functional reliability of Passive Safety Grade Decay Heat removal system of Indian 500 MWe Prototype Fast Breeder Reactor (PFBR). The results are compared with direct Monte Carlo simulation and observed that the method considered is computationally very efficient and provides consistent reliability estimates.