Probabilistic Fracture Mechanics Analyses Comparison to LBB Assessments

Analysis of a generic dissimilar metal weld (DMW) susceptible to primary water stress corrosion cracking (PWSCC) in a pressurized water reactor (PWR) is used to compare the newly developed probabilistic models (xLPR code) to the previously performed deterministic leak before break (LBB) analyses. The objective of this scoping analysis is to develop a generic reactor loop composed of representative welds and to investigate the safety margins in the presence of PWSCC at the Alloy 82/182 locations. These locations have been previously studied and approved for LBB, however not in the presence of active degradation such as PWSCC. The purpose of this study is to investigate potential increase in risk due to this mechanism. Comparisons of the individual weld probabilistic results to the deterministic LBB analysis are made as the first results of this study. Additionally the individual welds are combined into a configuration representative of the primary loop. This configuration is then tested against the criterion recommended by the xLPR acceptance group. This xLPR criterion is then compared to the existing LBB criterion to assess the change, if any, in risk due to PWSCC.