Interfacing system LOCA risk assessment: Methodology and application

The United States Nuclear Regulatory Commission (NRC) is sponsoring a research program to develop an improved understanding of the human factors hardware, and accident consequence issues that dominate the risk from an Interfacing Systems Loss-of-Coolant Accident (ISLOCA) at a nuclear power plant. To accomplish this program, a methodology has been developed for estimating the core damage frequency and risk associated with an ISLOCA. The steps of the methodology are described with emphasis on one step which is unique, estimation of the probability of rupture of the low pressure systems. A trial application of the methodology was made for a Pressurized Water Reactor (PWR). The results are believed to be plant specific and indicate that human errors during startup and shutdown could be significant contributors to ISLOCA risk at the plant evaluated.