Accident sequences Analysis in a NPP's Electrical System Model using Event Tree Method

This paper analyzes the logical accident scenarios in an electrical system model of a nuclear power plant (NPP) using the coupling of fault tree and event tree analysis methods. An Emergency Power Supply System (EPSS) Benchmark of an NPP is used for validation. The safety functions of the EPSS are identified and their failure probabilities are calculated using fault tree method. The obtained results provide various accident sequences triggered by the loss of the main electric connection of the EPSS and their occurrence frequencies. This methodology ensures an efficient sorting of various accident sequences according to their occurrence frequency and end sates.