Document: NRC Regulatory Guide
Document ID: 666e1303-0170-4974-a7d6-af27eb586524
Document Type: regulatory_guide
Title: Risk-Informed, Performance-Based Fire Protection for Existing Light-Water Nuclear Power Plants (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2104/ML21048A448.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.205
CFR Part: 
CFR Title: 

Content:
and have no potential for power cable fire damage, (3) the load sequencer for the associated power supply is not damaged by the fire such that it may cause multiple loads to simultaneously spuriously start, and (4) target conductors that could spuriously start or energize loads powered from the same power supply are in separate cables. b. Number of Inter-Cable Hot Shorts Regardless of Latching Characteristics or Coping Time – If the MSO requires four or more separate target cables with inter-cable hot shorts, excluding a ground fault equivalent hot short (GFEHS), then the MSO does not need to be considered, regardless of whether the circuits are latching or non-latching. For ungrounded power supplies, a credible GFEHS is significantly more likely than inter-cable hot shorts and as such, is not included in this guidance. Spurious operation(s) for the MSO scenario that can be caused by a GFEHS should be considered unless otherwise limited. Inter-cable failures that can result in a GFEHS cannot be counted as part of this limit of four or more separate inter-cable hot shorts. There is no sustained duration consideration required for this case. c. Number of Non-Latching Hot Shorts with 10-Minute Coping Time Regardless of Circuit Failure Mode – If the MSO requires (1) three or more concurrent fire-induced hot shorts on separate target cables in non-latching circuits and (2) the hot shorts must be sustained for more than 10 minutes to cause a condition that cannot be tolerated (refer to NEI 00-01, Appendix H), then the MSO does not need to be considered, regardless of the conductor hot short failure mode (i.e., intra-cable, inter-cable, or GFEHS). For MSO scenarios that result in conditions that cannot be tolerated for 10 minutes or less, any number of non-latching intra-cable circuit failures should be considered, unless otherwise limited. In addition, for latching fire-induced hot shorts, any number of intra-cable circuit failures should be considered unless