Determining the Effectiveness, Limitations, and Operator Response for Very Early Warning Fire Detection Systems in Nuclear Facilities – Update to Event Tree Parameters (Alpha and Pi) and Integration of NUREG-2230 Methods – Final Report (NUREG-2180, Supplement 1, EPRI 3002028821)

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Publication Information

Date Published: May 2024

U.S. Nuclear Regulatory Commission  Office of Nuclear Regulatory Research  Washington, DC 20555-0001  U.S. NRC-RES Project Manager G. Taylor

Electric Power Research Institute 3420 Hillview Avenue Palo Alto, CA 94304-1338 U.S. NRC-RES Project Manager G. Taylor A. Lindeman

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Abstract

The methodology for modeling very early warning fire detection (VEWFD) systems is documented in NUREG-2180, Determining the Effectiveness, Limitations, and Operator Response for Very Early Warning Fire Detection Systems in Nuclear Facilities (DELORES-VEWFIRE), issued December 2016. Since issuance of that publication, the Electric Power Research Institute (EPRI) and the U.S. Nuclear Regulatory Commission (NRC) have published fire probabilistic risk assessment (PRA) methods and data updates seeking to increase the realism of selected modeling techniques. In addition, both organizations continue to collect fire event experience data from the U.S. commercial nuclear industry. These data are used for updating fire PRA input parameters and to further inform the development of realistic modeling methods. As such, this report describes updates to the methodology for modeling VEWFD in fire PRAs to (1) reflect the impact of new fire event data on parameters in NUREG-2180 and (2) integrate the models in NUREG-2180 with the methods in NUREG-2230, Methodology for Modeling Fire Growth and Suppression Response for Electrical Cabinet Fires in Nuclear Power Plants, issued in 2020, associated with modeling interruptible fires in electrical cabinets.

One key parameter for determining the non-suppression probability (NSP) for scenarios involving VEWFD systems is the fraction of fire events that have an incipient stage. The incipient phase of a fire refers to a non-flaming start of a potential fire event (often consisting of subcomponent overheating). In NUREG-2180, the alpha parameter, α (the fraction of fires that do not have an incipient stage), was determined based on the results of a review of electrical cabinet fire events in EPRI’s Fire Events Database (FEDB) through 2009.

Recent electrical cabinet fire events have been compiled, and more detailed information regarding fire incidents at nuclear power plants has been collected. Using the new data, the parameter α is updated, starting with the NRC’s existing classification of the fire event data in NUREG-2180, which covered events from 1990 through 2009. The update includes any new information (e.g., corrective action documentation, fire reports) about the fire events compiled after the publication of NUREG-2180. The update to the α parameter also includes 23 new fire events from 2010 through 2014 evaluated during the development of NUREG-2230.

This report also updates the suppression rate used to calculate the parameter π. This parameter represents the enhanced suppression probability in the event tree model. The π factor differs between in-cabinet (π₁) and area-wide (π₂) applications. The π₁ factor is applicable for the incabinet event tree and represents the probability that, given success of the technician/field operator to respond to the VEWFD system alert, suppression has failed to limit the fire damage to the enclosure of origin. The π₂ factor is applicable for the area-wide event tree and represents the probability that, given success of the technician/field operator in the room responsible for the VEWFD system alert, suppression activities fail to prevent damage to PRA targets outside the cabinet. The suppression data for the 2010–2014 events are used to update the enhanced suppression rate for VEWFD area-wide applications (for π₂ in NUREG-2180).

This report also describes a process for crediting the methods in NUREG-2230 for modeling interruptible fires in electrical cabinets within the NUREG-2180 incipient detection framework. The results of this research can be implemented in new and existing fire PRAs for a more realistic representation of the scenario progression and suppression end states.

Keywords

Fire events
Fire incipient stage
Fire probabilistic risk assessment (fire PRA)
Non-suppression probability (NSP)
Very early warning fire detection (VEWFD)
Smoke detection
Aspirated smoke detection
National Fire Protection Association (NFPA) 805
Fire Protection