In‐Service Inspection Optimization for Pressurized Water Reactor Primary Piping Weld Based on Probabilistic Fracture Mechanics

ABSTRACT Nuclear‐grade pipelines are essential for nuclear safety, and their failure can lead to severe accidents. Traditional deterministic methods tend to be overly conservative, overlook uncertainties in key factors, and struggle to accurately assess reliability under complex conditions. This paper aims to present a probabilistic fracture mechanics methodology to evaluate the reliability of circumferential cracks in primary piping welds under transient loads. A dedicated software tool, developed based on this method, calculates rupture and leakage probabilities by incorporating parameter uncertainties alongside deterministic fracture models. Furthermore, the influence of various in‐service inspection schedules on weld reliability is examined through case studies. The results indicate that excessively long inspection intervals result in actual failure probabilities at 60 years that exceed the safety goal of 10 −6 failures per year. In accordance with current ASME Code, Section XI, the first inspection should occur by the 10th year, while subsequent intervals may be optimized to every 20 years. Sensitivity analyses reveal that the initial crack depth and crack half‐angle have the greatest impact on probabilities, followed by the tensile strength, the safety factor, the yield strength, and the probability of detection model.