Risk Importance Measures for Maintenance in Non-Coherent Systems

Probabilistic Safety Assessment (PSA) has been an important tool to assist Nuclear Power Plants (NPPs) management over the years. Through PSA, the weak links of the whole system can be identified by component importance measures. The importance measures can be classified according to risk significance and safety significance. They signify the role that each component plays in either causing or contributing to the occurrence of an undesired event. A wide range of importance measures have been developed over the years and most of them are geared towards coherent systems. Importance analysis of non-coherent system is rather limited. In this paper, a set of component importance measures for non-coherent systems is analyzed and investigated. The comparison and the selection of the most informative and appropriate measures for guiding the maintenance of a system are presented. A steam generator level control system of NPP is used to demonstrate the application of the results.