Probabilistic fracture mechanics analyses of reactor pressure vessel under PTS transients

The probabilistic fracture mechanics (PFM) analysis code PASCAL has been developed in JAERI. This code can evaluate the conditional probabilities of crack initiation and fracture of a reactor pressure vessel (RPV) under transient conditions such as pressurized thermal shock (PTS). Based on the temperature and stress distributions in the vessel wall for four cases of PTS transients in a typical 3-loop PWR, parametric PFM analyses were performed using PASCAL on the variables such as pre-service inspection method, crack geometry, fracture toughness curve and irradiation embrittlement prediction equation. The results showed that the Arakawa's model for a pre-service inspection had a significant effect on the fracture probability and reduced it by more than 3 orders of magnitude compared with no inspection case. The fracture probability calculated by the fracture toughness estimation method in Japan was about 2 orders of magnitude lower than that by the USA method. It was found that the treatment of a semi-elliptical crack after its initiation in PASCAL reduced the conservatism in a conventional method where it is transformed into an infinite length crack.