This report presents a study performed on a set of common-cause failure (CCF) events within the International Common-Cause Failure Data Exchange (ICDE) project. The topic of the study was intersystem dependencies, i.e. events from the operating experience with nuclear power plants where a single CCF mechanism affected components in multiple different systems of the nuclear power plant.
The report also addresses the occurrence of multiple CCF events in only one system with no indications that other systems might also have been affected. These are not ordinarily considered intersystem events but are included in this report as they are considered interesting events since they involve dependencies between CCF groups which are not specifically modelled in a probabilistic risk assessment (PRA). The report is mainly intended for designers, operators and regulators to provide insights into the rare intersystem events in the ICDE database. The insights can give valuable experience to support and improve the modelling of intersystem dependencies in the PRA models and provide intersystem CCF data for quantification purposes.