In probabilistic safety analysis (PSA) of highly redundant systems common cause failures (CCF) of components in general contribute to a large extent to the systems unavailability. As CCF events are rare events, operating experience of “classes” of components of the same type (like centrifugal pumps or motor operated gate valves) combined from “similar” plants and systems is used to generate CCF data with sufficient statistical quality.

In the German approach, the operating experience of all German nuclear power plants since the beginning of their operation is combined although these plants belong to different types and generations and although maintenance and...