Activities to attain integrity of embrittled reactor pressure vessel for plant lifetime management program

The reactor pressure vessel (RPV) is the most critical component of pressurized water reactor. It has to comply with various rules and regulatory guides to ensure sufficient safety and operating margins during its lifetime including extended operation. Thus, it is crucial to assure the integrity of RPV for effective Plant Lifetime Management Program (PLIM). In this paper, various aspects of RPV integrity and their implication for life extension of the nuclear power plant were examined followed by a brief introduction of the status of the RPV of Kori Unit 1. A circumferential weld in the beltline region was projected to be unable to satisfy the minimum upper shelf energy requirement and maximum reference temperature-pressurized thermal shock requirement before 40-year lifetime. The results of detailed integrity analyses on both issues are briefly summarized. As integral parts of PLIM Phase II Program of KEPCO, several actions were taken to attain the integrity of embrittled reactor pressure vessel, such as, redefining initial RTNDT, ex-vessel dosimetry, and early withdrawal and testing of surveillance capsule. The applicability of these and other options including thermal annealing were examined.