Evaluation of operating experience based on variation of risk

Any nuclear power plant experience evaluation program requires some form of screening process to identify events of greatest significance. If the goal of the program is to improve reactor safety, the significance of an event is a function of the increased risk to which the event exposes the public and the plant. One important class of such events is that which can be identified as having the greatest increase in the probability of core damage. This paper describes the development and use of a computerized system to calculate the change in core damage probability introduced by a specified event. The system is based on the use of a data base of cutsets, which are obtained by reducing fault trees modelling the loss of certain critical safety functions