An initial appraisal of the event-tree methodology used in the Angra 1 nuclear power station probabilistic safety assessment

Abstract

The event-tree analyses of the Angra 1 nuclear power plant probabilistic safety assessment were performed by means of the explicit method of event-tree modelling of shared-equipment dependencies, from which some insights were drawn. At first, we discuss in this paper the effects of collapsing equal impact vectors (from the quantification point of view also). The second feature discussed is related to a critical analysis of the dependency matrix concept in view of a counterpart to it—namely, the GO methodology in the context of modelling intersystem dependencies. Finally, we discuss the possibility of using our computerized event-tree analysis methodology for assessing the unavailability of the involved standby safety systems, most of which are recognized to be noncoherent structures.