Functional block diagrams and automated construction of event trees

Functional block diagrams are introduced as graphical representations of the function of a system. A functional block provides the output of a system as the outcome of a joint event defined by the inputs to the system and its various states. Functional blocks corresponding to different subsystems are combined together to form a functional block diagram representing the functional characteristics of the combined system. Conversely, a complex system represented by a single functional block is decomposed to constituent components with a corresponding functional block diagram. It is demonstrated that a functional block diagram is an alternative representation of an event-tree corresponding to the outcome space of the underlying joint event. The concept of output space partition is introduced and an algorithm is developed for generating the most compact form of the event-tree consistent with a given partition. This algorithm forms the basis of a technique for the automated construction of an event-tree starting from a developed functional block diagram. This technique is amenable to computerization. Finally, as a demonstration of the technique, the event-trees of a boiling water reactor (BWR) are developed.