Multi-unit dynamic PRA

Dynamic Probabilistic Risk Analysis (PRA) methods couple stochastic methods (e.g., RAVEN) with safety analysis codes (e.g., RELAP5-3D) to determine risk associated to complex systems such as nuclear plants. Compared to classical PRA methods, which are based on static logic structures (e.g., Event-Trees, Fault-Trees), they can evaluate with higher resolution the safety impact of timing and sequencing of events on the accident progression. Recently, special attention has been given to nuclear plant sites which consist of multiple units and, in particular, on the safety impact of system dependencies, shared systems and common resources on core damage frequencies. In the literature, classical PRA methods have been employed to model multi-unit sites in a limited number of cases while Dynamic PRA methods have never been applied to analyze a full multi-unit model. This paper presents a PRA analysis of a multi-unit plant using Dynamic PRA methods. We employ RAVEN as stochastic tool coupled with RELAP5-3D. The site under consideration consists of three units (each unit is composed by a reactor and its associated spent fuel pool) while the considered initiating event is a seismic induced station blackout event. This paper describes in detail how the multi-unit site has been constructed and, in particular, how unit dependencies and shared resources are modeled from both a deterministic and stochastic point of view.