INTERPRETATION OF PROBABILISTIC STRUCTURAL-ANALYSIS OF AN AGING PASSIVE COMPONENT

This article describes a technique to calculate the risk from failure of passive components over time, and demonstrates the technique by app lying it to a weld in the auxiliary feedwater (AFW) system. It uses a modified version of the PRAISE computer code to perform a probabilisti c structural analysis to calculate the probability that crack growth d ue to aging would cause the weld to rupture. It then uses the weld rup ture probability as input to a modified existing PRA to calculate the change in plant risk with time. The results show an insignificant effe ct on plant risk because of the low calculated rupture rate of the wel d in this particular calculation over 48 yr of service. A decreasing y early rupture rate for this weld is calculated. This results from infa nt mortality; that is, most of those initial flaws that will eventuall y lead to rupture will do so early in life.