Probabilistic fracture mechanics analyses of nuclear pressure vessels under PTS events Original Research Article

This paper describes some recent research activities on probabilistic fracture mechanics (PFM) for nuclear reactor pressure vessels (RPVs) performed by the RC111 research committee of the Japan Society of Mechanical Engineers (JSME) under a subcontract of the Japan Atomic Energy Research Institute (JAERI). To establish standard procedures for evaluating failure probabilities of nuclear RPVs, we have performed PFM analyses for aged RPV under pressurized thermal shock (PTS) events. The basic problems are chosen from some of US benchmark problems such as EPRI (Electric Power Research Institute) and US NRC (Nuclear Regulatory Commission) joint PTS benchmark problems and H.B. Robinson problems. Employed in this study are four PFM computer codes developed in Japan and in USA. Various sensitivity analyses are performed to quantitatively evaluate the influences of the input data, i.e. (a) initial crack shape, (b) the probabilistic distribution of initial crack depth, (c) cladding, (d) RTNDT shift, (e) impurity content, (f) the through-wall distributions of material properties, (g) pre-service inspection (PSI) and (h) warm prestressing. It is clearly shown that in most cases, these data affect failure probabilities significantly. Therefore, we should use in the PFM analyses as reliable input data as possible. If any reliable data are not available, the data resulting in most conservative results could be chosen, referring the analysis results presented in this paper.