Principles of reliability analysis methods applied to an emergency core cooling system

A reliability analysis is given for a model system of an emergency core cooling system of a pressurized water reactor. In order to demonstrate some basic relationships and influences on the system's failure probability the analysis deals only with some of the main-components and subsystems of the emergency core cooling system. With reference to the design basis accident, i.e. the total rupture of a main coolant line, only the low pressure system is considered. The overall system's failure probability is determined by the failure probability per demand, i.e. the unavailability of the system when called on for operation in the emergency case, and the cumulative probability of failure during the subsequent phase of residual heat removal. Detailed calculations have shown that the failure probability per demand is the leading term. Special attention is given to some parameter calculations dealing with the influence of inspection time intervals and repair procedures for different components and subsystems with respect to system failure behaviour.