Effect of Crack Detection Performance and Sizing Accuracy on Reliability of Piping With Stress Corrosion Cracks

Integrity assessment of primary recirculation system (PLR) piping with stress corrosion cracks is one of the recent interests in Japanese BWR plants. Crack detection performance and a sizing error in non-destructive test (NDT) have a great influence on the integrity assessment of piping. This paper presents effects of crack detection performance and sizing accuracy on the reliability of PLR piping with stress corrosion cracks. Failure probability (leak and break) of PLR piping maintained according to the rules in Fitness-For-Service (FFS) Codes of JSME was analyzed using a probabilistic fracture mechanics (PFM) code which could analyze initiation and growth behavior of stress corrosion cracks. For the reliability of PLR piping, reducing oversight of cracks and crack sizing error are effective, and detectable crack size has not much influence on reliability of piping. For the higher reliability, reducing oversight of cracks is more important than the improvement of the detectable crack size in NDT, and the qualified inspectors should be employed for sizing of detected cracks in order to be suitable measurement in NDT.