122 Integrating Insights from the Fire PRA Methodology for Nuclear Power Facilities into the Fire Protection SDP (PSAM-0305)

As a part of the Reactor Oversight Program, the U.S. Nuclear Regulatory Commission (NRC) assesses the risk significance of fire protection inspection findings using the fire protection significance determination process (SDP). NRC's assessment contributes to its response to the identified deficiency. In 2004, NRC published a major revision of the fire protection SDP process to improve the transparency and reproducibility of assessing the risk significance of fire protection inspection findings.

This SDP revision was based upon a fire probabilistic risk assessment (PRA) framework which assesses inspection findings according to more robust fire PRA practices. Many of the improvements in the revised fire protection SDP were derived from the Fire Risk Requantification Study (FRRS), a program performed by the NRC Office of Nuclear Regulatory Research (RES) in conjunction with the Electric Power Research Institute (EPRI). Recently, a state-of-the-art fire PRA methodology, “EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities,” was developed and documented in NUREG/CR-6850 (EPRI 1011989) under this program.

Significant technical improvements in evaluating fire frequency, severity, detection and suppression, and fire damage from the FRRS have been included in the fire protection SDR The SDP also utilizes the FRRS's treatment of high energy arcing faults, and benefits generally from the development of initial fire sizes for various ignition sources from this improved fire PRA methodology. The SDP also benefited significantly from updated methods for the analysis of cable/circuit failure modes and effects. These improvements have resolved several outstanding methodological issues remaining from the Individual Plant Examinations of External Events (IPEEEs), and the fire protection SDP has benefited accordingly. The SDP process, in its initial two phases, is intended to serve as a relatively simple, field-applied, screening analysis tool. Hence, several of these approaches were simplified upon their implementation in the SDP.

This paper compares the approaches used in the fire protection SDP and those used in the FRRS fire PRA methodology. In particular, this comparison highlights the techniques used to simplify the fire PRA methods for implementation in the fire protection SDP. In addition, this paper applies the fire protection SDP and the new fire PRA methodology to illustrative examples of several different fire risk factors that could comprise an analysis of a fire protection inspection finding.