Use of uncertainty importance measures to complement risk importance measures in PSA

Liu, Q.; Homma, Toshimitsu

Proceedings of 9th International Probabilistic Safety Assessment and Management Conference (PSAM-9) (CD-ROM), 7 Pages, 2008/00

Fussel-Vesely (FV) and Risk Achievement Worth (RAW) are two commonly used measures in importance ranking of basic events in PSA. Both measures are based on point-estimates of the risk. However, realistic failure characteristics of components are associated with some kinds of uncertainty. The uncertainties of component failures are propagated through the model and bring about the uncertainty of the model risk. Therefore, it is necessary to take uncertainty into consideration when the contribution of a basic event to risk is estimated. By using two fault tree models as examples, the authors calculated the FV and the RAW as well as the uncertainty importance of each basic event. The results show that the uncertainty importance ranking of each basic event does not always agree with the ranking with regard to FV (or RAW). It is argued that uncertainty importance measures provides complementary perspectives of the roles of a basic event in determining the risk.