Impact of component outages on ECCS/ECI unavailability

A general methodology has been developed which provides a quantitative basis for setting Limiting Conditions of Operation (LCO) governing Emergency Core Cooling System (ECCS) component outages. The analysis represents an extension of the techniques of the Reactor Safety Study and specifically addresses scheduled test and non-routine maintenance outages which impact the unavailability of the Emergency Coolant Injection (ECI) mode of the ECCS. The methodology can provide a basis for limiting both the short-term effects of outages, in terms of conditional unavailability constraints, and the long-term effects, measured by the average state of the system over a time interval. The methodology is not meant to replace engineering judgement in establishing LCOs, but to provide a framework for its application. No attempt has been made to optimize LCOs, nor are any specific recommendations made for establishing them, either directly or in terms of criteria. The objective is to present a possible approach and to demonstrate the viability of the probabilistic risk analysis methodology in addressing a specific problem in the licensing and regulatory decision-making process