a -Cut method based importance measure for criticality analysis in fuzzy probability – Based fault tree analysis

ABSTRACK
Fuzzy probability – based fault tree analysis (FPFTA) has been recently developed and proposed to deal
with the limitations of conventional fault tree analysis. In FPFTA, reliabilities of basic events, intermediate
events and top event are characterized by fuzzy probabilities. Furthermore, the quantification of the
FPFTA is based on fuzzy multiplication rule and fuzzy complementation rule to propagate uncertainties
from basic event to the top event. Since the objective of the fault tree analysis is to improve the reliability
of the system being evaluated, it is necessary to find the weakest path in the system. For this purpose,
criticality analysis can be implemented. Various importance measures, which are based on conventional
probabilities, have been developed and proposed for criticality analysis in fault tree analysis. However,
not one of those importance measures can be applied for criticality analysis in FPFTA, which is based
on fuzzy probability. To be fully applied in nuclear power plant probabilistic safety assessment, FPFTA
needs to have its corresponding importance measure. The objective of this study is to develop an
a
-
cut method based importance measure to evaluate and rank the importance of basic events for criticality
analysis in FPFTA. To demonstrate the applicability of the proposed measure, a case study is performed
and its results are then benchmarked to the results generated by the four well known importance mea-
sures in conventional fault tree analysis. The results confirm that the proposed
a
-cut method based
importance measure is feasible to evaluate critical basic events in FPFTA.