Methodology for Modeling Fire Growth and Suppression Response for Electrical Cabinet Fires in Nuclear Power Plants (NUREG-2230, EPRI 3002016051)

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Publication Information

Manuscript Completed: November 2019
Date Published: June 2020

U.S Nuclear Regulatory Commission Office of Nuclear Regulatory Research (RES) Washington, DC 20555-0001	Electric Power Research Institute (EPRI) 3420 Hillview Avenue Palo Alto, CA 94304-1338
U.S. NRC-RES Project Manager M. Salley	EPRI Project Manager A. Lindeman

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Abstract

During the past decade, modern fire probabilistic risk assessments (FPRAs) have been developed using NUREG/CR-6850 (EPRI 1011989), EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities. The results show that fire can be a significant portion of the overall site risk profile; however, the methodology was never fully piloted before implementation. As a result, further development of the methods has been performed and additional data have been collected and analyzed during the past decade. These improvements have allowed gaps in the methods to be closed and more realistic estimates of risks to be obtained. One aspect of the FPRA methods and data that has not been explicitly reanalyzed is the fire growth timing profile and plant personnel suppression response for electrical cabinet fires. A simplified model of the average time to peak, steady state, and decay is used to model the ignition source's heat release rate profile. For manual suppression credit, a dense collection of electrical ignition sources spanning three decades is used to represent the fire brigade and plant suppression response times.

Recent research efforts have focused on obtaining more detailed information regarding fire incidents at nuclear power plants. This data collection has enabled researchers to obtain more details on the fire attributes, timeline, and plant impact. This report specifically reviewed the available electrical cabinet fire incident data in an effort to update the methodology to better reflect the observed operating experience. Insights from the data review served as the basis for amending portions of the fire modeling and suppression response to more accurately align with operating experience.

The outcome of this work is a revised set of parameters that addresses both the fire growth and the suppression response in the context of fire scenario modeling. The set of electrical cabinet fire events was classified into either a growing or interruptible fire categorization. Interruptible fires are those that have observed ignition but no significant growth for a period of time. Growing fires, on the other hand, experience growth immediately after ignition. Furthermore, the detection-suppression event tree has been updated to better allow for early plant personnel suppression actions. Additional manual non-suppression bins have been added to better reflect the scenario characteristics. The results of this research can be implemented in new and existing FPRAs for a more realistic representation of the scenario progression and suppression end states.

Keywords

Fire events
Fire growth profile
Fire ignition frequency
Fire probabilistic risk assessment (FPRA)
Manual suppression
Non-suppression probability (NSP)