Development of a Full Scope External Hazard PSA for G\"{o}sgen NPP

In the second phase of the PSASpectrum project, a full scope internal flooding and external hazard PSA was developed for Gösgen nuclear power plant. The PSA encompassed external hazard screening based on the list of potential hazards from the ASAMPSA_E project. Relevant hazards including earthquake, external flooding, airplane crash, strong wind and tornado as well as local man-made hazards and hazards leading to unavailability of the water intake have been evaluated. In addition, relevant combinations of hazards were reviewed. For the screened in-hazards, detailed analysis was performed for all plant operating states. The integration of fragilities for earthquake, wind and tornado was performed using the RiskSpectrum ^\circledR ModelBuilder software. In addition, the human reliability analysis methodology developed in phase 1 of PSASpectrum (internal events) was extended to include effects relevant to internal flooding and external hazards. The hazard analysis was then embedded in the existing full scope internal events model, quantifying the results for Level 1 PSA and Level 2 PSA in a fully coupled model. To achieve acceptable calculation time in combination with accurate results, the newest features of RiskSpectrum ^\circledR PSA such as BDD quantification, mutual exclusivity between basic events and conditional quantification were used. The development of the full scope PSA for Gösgen shows that with modern computing power, modeling a fully coupled, traceable PSA for a nuclear power plant down to the component level is feasible and can provide deep insights in the risk profile of the plant and its systems, structures and components.

Keywords: Probabilistic Safety Analysis, External Hazards, Seismic.