Probabilistic fracture mechanics analyses of RPV under some PTS transients

Probabilistic Fracture Mechanics (PFM) has been used in the fields of reliability analysis, life cycle assessment and risk management for important structural components as a promising and rational evaluation methodology. At JAERI, the PFM analysis code PASCAL has been developed. This code evaluates the conditional probabilities of crack initiation and fracture of a reactor pressure vessel (RPV) under transient conditions such as pressurized thermal shock (PTS). Four cases of PTS transients were selected in this study for a typical 3-loop PWR. Based on the temperature and stress distributions in the vessel wall for each transient, PFM analyses are performed using PASCAL to obtain the fracture probability of RPV. Parametric analyses using some evaluation methods incorporated in PASCAL are performed on some variables including pre-service inspection method, crack geometry, fracture toughness curve and irradiation embrittlement prediction equation. The results showed that a pre-service inspection had a significant effect and reduced the fracture probability by more than three orders of magnitude. The comparisons of the analysis results using fracture toughness estimation methods between in Japan and USA, and crack geometries between a semi-elliptical surface crack and an infinite surface crack are also made. (author)