A fast method of finding minimal cutsets in a risk monitor

Abstract

This paper introduces a new fast method to find minimal cutsets to calculate CDF (core damage frequency) in a risk monitor. The new method, called McFarm (a Missing Cutsets Finding Algorithm for Risk Monitor), is a fast and accurate algorithm to find minimal cutsets to calculate CDF by changing the fault tree to a simpler one. McFarm shows good results especially for non-safety systems out-of-service (OOS) cases and for OOS cases of supporting systems, such as the diesel generator and component cooling water, which are located at many places and lower levels in the fault tree structure. The fast calculation achieved in the OOS cases of supporting systems is due to adopting the `Super OOS AND gate' concept. McFarm can be used for multiple-equipment OOS as well as single-equipment OOS. McFarm was tested by using two risk-monitor models for Korean nuclear power plants (i.e. for YGN 3,4 and for UCN 3,4) with KIRAP. However, McFarm can be used for the risk monitors which use any quantification methods such as CAFTA, IRRAS, etc. Because McFarm just changes the fault tree to a simpler one, thereafter any quantification methods can be applied to the simplified fault tree.