STUDY ON PWSCC BEHAVIORS AT NICKEL-BASED ALLOY WELDS BASED ON WELD RESIDUAL STRESS ANALYSIS AND PROBABILISTIC FRACTURE MECHANICS

摘要

A number of cracks due to primary water stress corrosion cracking (PWSCC) in PWR and Ni-based alloys stress corrosion cracking (NiSCC) in BWR have been observed near Ni-based alloy welds. One of the causes of initiation and growth due to SCC is high tensile residual stress as well as operating stress. In this study, an analysis code, PASCAL-NP, for the PWSCC/NiSCC growth at the dissimilar metal welds based on probabilistic fracture mechanics (PFM) was developed. This PFM analysis code has a function of SCC growth calculation for some patterns of crack locations and orientations in a probabilistic manner. This code can also evaluate the failure probability of Ni-based alloy welds due to PWSCC/NiSCC. Using this code and results from welding simulations, case studies on PWSCC growth have been performed focusing on the location and orientation of PWSCC. Effects of the weld residual stress and scatter of PWSCC growth rate on the crack penetration such as leakage are shown in comparison with deterministic analyses.