Systems interaction analysis: Concepts and techniques (Part I)

The issue of systems interaction events in nuclear power plants was originally raised because of concern about certain types of dependent failures in nuclear power-plant safety systems. The source of this concern is that the interdisciplinary review process required in designing, constructing, and operating nuclear power-plant systems may not be adequate to ensure that redundant safety systems are truly independent. In fact, some operating events have demonstrated that the current process may not adequately ensure that failures caused by systems interactions will not occur. Part I of this article reviews three of the four types of qualitative analysis techniques that can be used to identify possible systems interactions. [The fourth type of technique will be evaluated in Part II of this article, to be published in Vol. 30(3) of Nuclear Safety.] Each technique, by itself, cannot adequately identify all three types of systems interactions: functional, spatial, and induced-human. Some combination of these techniques is required to perform a systems interaction study adequately or to incorporate the study into a probabilistic risk assessment.