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Abstract SU170Full Paper + Presentation
NRC-RES’ Sitewide, All Hazards Level 3 PRA Project: Approach and Results for Multi-Unit Level 1 Risk
The U.S. Nuclear Regulatory Commission (NRC) has performed a full-scope, sitewide Level 3 probabilistic risk assessment (PRA) project (L3PRA project) for a two-unit, pressurized-water reactor reference plant. The scope of this project includes all hazards (internal and external) and all radiological sources on the reference site: 1) two, nearly identical reactors; 2) two, hydraulically connected spent fuel pools (SFPs), and 3) a dry cask storage (DCS) facility. The NRC has published a series of reports documenting the results of all of these PRA efforts.
In addition to the single unit PRAs performed for NRC’s L3PRA project, a previously, never-performed task was added: integrated site risk. In order to develop integrated site risk results, multi-unit PRA (MUPRA) results were developed first.
The MUPRA results were developed using these high-level steps: 1) perform a systematic, sitewide dependency assessment, 2) assign multi-unit (MU) coupling factors for identified MU dependencies, and 3) perform MUCDF calculations.
The approach for performing the sitewide dependency assessment was based on previously published reports by the Electric Power Research Institute (EPRI) and the International Atomic Energy Agency (IAEA). The assessment was performed using a phased approach to address multiple categories of potential MU dependencies. Relevant sitewide (or MU) initiating events were identified first. Other categories of potential MU dependencies were addressed only for those MU initiating events (MUIEs).
Identified potential MU dependencies were assigned generic coupling factors. Single unit cutset reviews informed the assignment of coupling factors. Different types of coupling factors were used in MU core damage frequency (MUCDF) calculations (e.g., MU common cause failure coupling factors, MU seismic hazards correlations).
NRC’s L3PRA project developed at-power, MUCDF estimates for all hazards, both internal and external events. Insights have been developed for these results, such as:
• How does the total MUCDF results compare with total single unit CDF?
• Which hazard(s) produced the largest MUCDF results?
• Which hazard(s) are more likely to involve MU core damage?
• What multi-unit dependencies contribute the most to MUCDF for different hazards?
Keywords: Multi-unit (MU), multi-unit PRA (MUPRA), multi-unit core damage frequency (MUCDF), sitewide dependency assessment
← Check another abstractIn addition to the single unit PRAs performed for NRC’s L3PRA project, a previously, never-performed task was added: integrated site risk. In order to develop integrated site risk results, multi-unit PRA (MUPRA) results were developed first.
The MUPRA results were developed using these high-level steps: 1) perform a systematic, sitewide dependency assessment, 2) assign multi-unit (MU) coupling factors for identified MU dependencies, and 3) perform MUCDF calculations.
The approach for performing the sitewide dependency assessment was based on previously published reports by the Electric Power Research Institute (EPRI) and the International Atomic Energy Agency (IAEA). The assessment was performed using a phased approach to address multiple categories of potential MU dependencies. Relevant sitewide (or MU) initiating events were identified first. Other categories of potential MU dependencies were addressed only for those MU initiating events (MUIEs).
Identified potential MU dependencies were assigned generic coupling factors. Single unit cutset reviews informed the assignment of coupling factors. Different types of coupling factors were used in MU core damage frequency (MUCDF) calculations (e.g., MU common cause failure coupling factors, MU seismic hazards correlations).
NRC’s L3PRA project developed at-power, MUCDF estimates for all hazards, both internal and external events. Insights have been developed for these results, such as:
• How does the total MUCDF results compare with total single unit CDF?
• Which hazard(s) produced the largest MUCDF results?
• Which hazard(s) are more likely to involve MU core damage?
• What multi-unit dependencies contribute the most to MUCDF for different hazards?
Keywords: Multi-unit (MU), multi-unit PRA (MUPRA), multi-unit core damage frequency (MUCDF), sitewide dependency assessment