Failure probability analyses for PWSCC and NiSCC in Ni-based alloy welds

Udagawa, Makoto; Katsuyama, Jinya  ; Onizawa, Kunio 

A probabilistic fracture mechanics (PFM) analysis code PASCAL-NP has been improved continuously with reference to the latest knowledge. This code treats not only primary water stress corrosion cracking (PWSCC) in PWR but also Ni-based alloy stress corrosion cracking (NiSCC) in BWR. This code can also evaluate both leakage and break probabilities due to these types of SCC, considering the scatters of parameters which affect the structural integrity of Ni-based alloy welds. In this paper, failure probability analyses have been performed focusing on vessel head penetrations affected by PWSCC detected at Ohi unit 3 nuclear power plant as well as control rod drive housings affected by NiSCC at Hamaoka unit 1. In order to perform case studies for these actual plants, analytical models of predicting the incubation time to PWSCC and NiSCC initiation were introduced to PASCAL-NP. Failure probabilities calculated by PASCAL-NP reasonably agreed with inspection results in these plants.