Importance of fracture criterion and crack tip material characterization in probabilistic fracture mechanics analysis of an RPV under a pressurized thermal shock

Using a probabilistic fracture mechanics code, the importance of the choice of fracture criterion and the material fracture resistance characterization at the crack tip is elucidated in the failure probability analysis of an reactor pressure vessel. The paper describes the procedure to evaluate the crack extension based on R6, where an increase in fracture resistance by ductile crack extension is considered. Two standard J-resistance curves are prepared for applying the elasto-plastic fracture criterion by R6 tearing. Case studies concerning the effect of the tearing fracture criterion were carried out using a severe pressurized thermal Shock transient. Results are discussed with respect to the fracture criterion, the material J-resistance curve, the algorithm for evaluating the crack tip fracture toughness and the initial crack geometry. The introduction of the elasto-plastic fracture criterion significantly contributes to removal of over-conservatism in applying a linear elastic fracture criterion. It was also confirmed that the algorithm of the re-evaluation method for crack tip fracture toughness has to be correctly applied