Risk Importance Measures in the Design and Operation of Nuclear Power Plants
8. Risk Importance of Component Represented by a Single Basic Event (Failure Mode) Involved in a CCF Group
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Up to now we have considered importance measures for a component represented by a FT module (sub-tree) involving a group of basic events (Section 6) or, even, a component represented by multiple different FT modules which appear in mutually exclusive sequences of failures (Section 7). However, none of the underlying basic events was involved in any common cause failure (CCF) group of basic events. (In other words, none of those failures or failure modes was shared by another components.) We will now broaden the discussion to the component-level risk importance measures for the components which are involved in a CCF group (which is, many times, the case with most of components in a PRA model). We start, in this section, with discussing the impact of CCF on risk importance of component which is presented in the FT structure by a single basic event.