Probabilistic Fracture Mechanics Analysis of Boiling Water Reactor Vessel on Relatively Low Failure Probability Problem Using PROFAS-RV PFM Analysis Code

The PFM approach has been widely used to evaluate the integrity of reactor pressure vessel (RPV) in nuclear power plant. Since the 1980s, a number of probabilistic fracture mechanics (PFM) analysis codes have been developed to perform the probabilistic analysis for RPV, and these codes are continuously updated by reflecting recent irradiation shift model, database of fracture toughness and compendia of stress intensity factors. The author developed a PFM analysis program for RPV, PROFAS-RV (PRObabilistic Failure Analysis System for Reactor Vessel), recently, which can evaluate failure probability of RPV using recent RTNDT shift model of 10CFR50.61a and stress intensity factor calculation method of RCC-MRx A16 code as well as required basic functions of PFM program. In this paper, the failure probabilities of boiling water reactor (BWR) for cool-down and low temperature over pressurization (LTOP) transient are calculated by using the own PFM analysis code, PROFAS-RV. This work was conducted as part of an international collaborative study. The effects of key parameters such as transient, fluence level, Cu and Ni content, initial RTNDT and RTNDT shift model on the failure probability are systematically compared and reviewed. As expected, the failure probability increases with increasing fluence, Cu and Ni contents, and initial RTNDT. However, the effect of Cu and Ni content is negligible for the very low fluence of 0.02×1019 n/cm2 because there is no additional irradiation embrittlement. The effect of initial RTNDT on the failure probability is more significant for the lower fluence region in both transients. The failure probability of LTOP transient is lower than that of cool-down transient, and the probability of failure with irradiation shift model of 10CFR50.61a is larger than that of R.G.-1.99 rev. 2 at the fluence ranges 0.2×1019 n/cm2 to 0.5×1019 n/cm2.