ABSTRACT
For a proper treatment, dependencies are categorized into intrinsic dependencies and extrinsic dependencies in the report of United States Nuclear Regulatory Commission (USNRC 1998b). In (IAEA 2000) dependencies are divided into 4 types (functional dependencies, physical dependencies, human interaction dependencies and component failure dependencies). Despite the differences in categorization, every kind of dependency should be proper treated in a PRA. For example, the graphic structure of a fault tree is used to handle some of the dependencies among failures (e.g. dependencies of system failures on support electric power failures are included in FTs by including failure of power system components as basic events). For those with logical relationships that cannot be expressed explicitly in FTs or ETs, Common Cause Failure (CCF) analyses are then conducted.
