5. Risk Importance of Component Represented by a Single Basic Event not Involved in a CCF Group

At the beginning, we introduce two basic terms which will be used in all considerations to come. Both of them are “events”:

• Failure of component by a considered failure mode, when challenged. (This failure mode is presented in a PRA model by specifically defined single basic event.)

• Occurrence of specified top event representing certain damage state (e.g. reactor core damage).