An Overview of PSA Importance Measures_201612

by M. Van der Borst, H. Schoonakker

Summarize

To optimize the systems reliability level, risk importance is used for quantifying and optimizing reliability. FV (Fussell-Vesely) importance, RAW (Risk Achievement Worth) and BI importance are well known parameters to quantifying reliability level.

Risk Importance Measures

 From the definition of FV importance, following equation can be driven.

When the case of 

FV is highly depends on Xi. It means that FV describes the direct effect of the components unavailability.

 However, the case of RAW (Risk Achievement Worth) with same approximation, RAW is not a function of Xi. Therefore, RAW shows that the defence of the rest of the installation against a failure of component i.

 BI is closely related with RAW. Therefore, we can deal BI as similarly as RAW.

Which importance parameter is suitable?

Test and maintenance activities

 If the failure rate is too low, then truncation error can occur. Truncation has an impact on the importance evaluation, in that events with high RAW may be deleted. Therefore, only BI importance is not suitable for this condition. Usually we prefer to use both FV-ranking and BI for safety improvement application.

 

 Design of nuclear power plant

 FV uses for optimizing risk and BI stands for optimizing safety.

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