PROBABILISTIC FRACTURE-MECHANICS ANALYSIS OF A NUCLEAR PRESSURE-VESSEL FOR ALLOCATION OF IN-SERVICE INSPECTION

To find whether there are significant differences in fracture probabil ity between various regions in a reactor pressure vessel a limited pro babilistic fracture mechanics (PFM) study was carried out. The loading was assumed to be deterministic, whereas some of the other quantities involved were assumed to be of random character. A simple, mainly ana lytical probabilistic model was developed. The critical event was take n as unstable crack growth without any ensuing crack arrest. All rando m information on the J(R) vs DELTAa behaviour was assumed to be contai ned in a single scalar parameter. Various distributions such as the We ibull and the log-normal distributions were assumed for this parameter to judge the sensitivity of results to various assumptions. The initi al size of pre-service defects was assumed to follow the OCTAVIA distr ibution. Possible time-dependent crack growth such as fatigue or stres s corrosion cracking was treated in a simplified manner assuming deter ministic material properties. Various regions (and crack geometries) w ere considered and the fracture and leakage probabilities were calcula ted for a number of load cases. The fracture probabilities were strong ly dependent on the assumption made for the fracture toughness distrib ution, but the order of the fracture probabilities of the regions seem ed to be relatively unaffected by this. The leakage probabilities are in most cases much lower than the fracture probabilities, indicating t hat consequence considerations are not very important for non-destruct ive test (NDT) allocation purposes. It is also concluded that probabil istic methods of the present kind may be a useful tool for judging whi ch locations should be the primary targets for NDT.