Evaluation of through-wall cracking frequency of reactor pressure vessel under pressurized thermal shock events using probabilistic fracture mechanics analysis method

Nishikawa, Hiroyuki*; Masaki, Koichi*; Osakabe, Kazuya*; Katsuyama, Jinya  ; Onizawa, Kunio 

To assure the structural integrity of a reactor pressure vessel (RPV) is one of the most critical issues to maintain the safe long-term operation of a nuclear power plant. In Japan, the assessment methods for RPV integrity using deterministic fracture mechanics, provided in the codes and standards, have been endorsed by the regulatory body. Meanwhile, a regulation on the fracture toughness requirements against PTS events with a probabilistic approach has been established in the U.S. In this paper, referring to the approach in the U.S., the through-wall cracking frequency (TWCF) for aging RPV in Japan against PTS events was calculated using a probabilistic fracture mechanics analysis code PASCAL3. As the results, we clarified that existing methodology on structural integrity assessment of RPV considering postulated axial flaw has a certain amount of conservativeness, and the value of TWCF is useful to assess impacts on structural integrity of RPV quantitatively.