ICONE19-43924 Thermally Induced Over-Pressurization Assessment on Isolated Piping through Containment of Nuclear Power Plants

One of the technical issues addressed in Generic Letter 96-06 and its supplement by the U.S. NRC is related to the possibility of thermally induced over-pressurization (TIP) at isolated water-filled piping sections that penetrate the containment during design basis accident conditions such as a loss-of-coolant accident (LOCA) or a main-steam line break (MSLB)[1,2]. This is a safety-significant issue because TIP at an isolated water-solid piping section can threaten the containment integrity by causing a breach at the piping segment that penetrates through the containment and by in turn permitting bypass leakage at the containment. This constitutes a failure of the intended isolation function of the containment, which should be ensured during the conditions of a LOCA or MSLB for the health of the public in the vicinity of nuclear power plants. This issue is dealt with from a regulatory aspect in Periodic Safety Reviews (PSR) on operational NPPs in Korea. A methodology to evaluate the possibility and the effects of TIP has been established for application to Korean NPPs. In this paper, the assessment methodology is presented in a step by step manner and representative assessment results for a Korean NPP are also described.