Study on the Structural Integrity of RPV Using PFM Analysis Concerning Inhomogeneity of the Heat-Affected Zone
Koichi MASAKI 1,*, Jinya KATSUYAMA1 and Kunio ONIZAWA1
1Nuclear Safety Research Center, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
Abstract
To acquire a technical basis from which to judge the need for surveillance test specimens of heat-affected zone (HAZ) materials, the features of HAZ inhomogeneity in reactor pressure vessel (RPV) steels were investigated. HAZ materials in close proximity to weld metal (WM) were found to exhibit higher fracture toughness than that of base metal (BM) owing to their mixed structure of martensite and lower-bainite, while HAZ materials close to BM had equivalent or slightly lower fracture toughness than that of BM because the HAZ shared the same phase as the BM, upper-bainite. A structural integrity assessment method concerning such inhomogeneous distribution of fracture toughness for HAZ materials was developed and incorporated into the probabilistic fracture mechanics (PFM) analysis code PASCAL3. Case studies on postulated flaw distributions and chemical compositions were performed with PASCAL3. It was shown that in highly irradiated conditions, the conditional probabilities of crack initiation (CPI) and fracture (CPF) in HAZ close to WM were lower than those of BM, whereas CPI and CPF in HAZ close to BM were almost equivalent to those of BM for most steels.