Article ID: 24-00456
This paper outlines the methodology and analysis of the at-power Fire Probabilistic Risk Assessment (FPRA) of the Shimane Unit 2 Nuclear Power Plant (BWR). For most BWRs in Japan, the Fire PRA model is in the development phase. The Shimane Unit 2 Nuclear Power Plant is one such plant, for which the FPRA project began in 2018 as a joint effort by The Chugoku Electric Power Company (Chugoku electric) and Hitachi-GE Nuclear Energy. The PRA process followed the EPRI/USNRC Fire PRA Methodology (NUREG/CR-6850, 2005) as main guidance, with various other NUREG documents as supplementary reference. The project was divided into two phases; phase 1 focused on collecting the requisite plant information to develop a conservative initial model for initial quantification, and phase 2, which removed the conservatisms in phase 1 by analyzing the fire scenarios in more detail. This paper provides an analysis of plant features from the perspective of fire PRA elements, focusing on the relative risk mitigation between initial and final quantification for specific compartments of interest. Moving forward, refinement measures will be taken to remove over-conservatism for risk-significant fire scenarios, and the model will be updated to reflect the latest design changes. The effort included plant walkdowns to confirm various as-built plant characteristics. The PRA team, with support from Chugoku Electric, visited the Shimane site a total of four times to collect data regarding plant partitioning, ignition sources, distance between source and target, and control room features. As a key milestone, the project scope also included an online, external review at the end of Quantitative Screening to assess conformance with the ASME/ANS PRA Standard.
