Effects of clad yielding and warm prestress on fracture-margin assessment of pressurized water reactor pressure vessels

Abstract

Potential benefits from the inclusion of clad-yielding and warm-prestress (WPS) effects toward decreasing the conditional probability of vessel failure (P(F/E)) of a pressurized water reactor vessel are summarized. Potential reduction in P(F/E) is quantified based on comparison with (P(F|E) calculated within a linear-elastic fracture mechanics (LEFM) framework that does not take into account either clad-yielding or WPS effects. Three postulated pressurized-thermal shock (PTS) transients that simulate conditions of no repressurization, early and late repressurization to full operating pressure are considered. Preliminary analysis results for the transient without repressurization indicate that inclusion of clad-yielding effects can significantly reduce P(F|E) relative to LEFM-based values. Numerical results also indicate that clad-yielding can similarly reduce P(F|E) for the transients with repressurization, and that the reduced P(F|E) can be conservatively estimated based on results for the case of LEFM analysis of the transient without repressurization. The decrease in P(F|E) is predicted to be greater for the transient involving early vs. late repressurization.