Predictive modeling of baffle-former bolt failures in pressurized water reactors

Abstract

Baffle-former bolt failures have been observed in recent inspections of pressurized water reactors (PWRs). These failures are understood to be primarily caused by irradiation-assisted stress corrosion cracking (IASCC). A prognostic method has been developed for simulating the degradation of baffle-former bolts due to IASCC. The method characterizes the evolution of stress in a reactor environment, as well as the redistribution of stress amidst neighboring bolt failures. Empirically-validated Weibull parameters are utilized in a stochastic framework, and the model is exercised as a Monte Carlo simulation to evaluate a range of plausible scenarios from which trends of bolt failure rates and patterns can be determined. This semi-empirical methodology is informed by both operating experience and a more detailed, predictive finite element analysis model that encompasses the full range of phenomenological effects common to the operating environment within a PWR.