Improvement of PFM analysis code PASCAL-SP2 for evaluating the failure probability of stainless steel pipe with a stress corrosion crack in PWRs

PWR一次系環境下での応力腐食割れを有するステンレス鋼管を対象とした破損確率評価のためのPFM解析コードPASCAL-SP2の改良

山口 義仁 ; Li, S.  ; 勝山 仁哉  

Yamaguchi, Yoshihito; Li, S.; Katsuyama, Jinya

Recently, in Japan and France, the intergranular stress corrosion cracking (SCC) has been detected in welded joints of stainless steel pipes in primary piping systems in Pressurized Water Reactors (PWRs). It was observed that hardness in the welded joints with SCC was higher than that of the base metal. It is shown that hardness is an important parameter in the SCC propagation in the PWR primary system water environment. In our previous studies, a numerical method was proposed for the prediction of hardness and weld residual stress in Type 316 stainless steel welded joints. The proposed numerical method was validated through the comparisons between predicted results and measurements for welded stainless steel specimens. And then, the effect of welding condition on hardness and residual stresses in stainless steel pipe welds was investigated by using above method. In this study, probabilistic fracture mechanics analysis code PASCAL-SP Ver.2 developed by Japan Atomic Energy Agency is improved to be able to evaluate the failure probability of stainless steel pipe with SCC in PWRs by considering the effect of hardness, and the verification is carried out for an improved function. Additionally, failure probabilities are calculated considering crack growth due to SCC and fatigue in PWR primary water environment. The effect of welding condition such as heat input at welding is quantitatively evaluated based on the failure probabilities.