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:
luated for any safe-shutdown components, including high-/low-pressure interface components. (2) Based in part on current transformer (CT) testing performed at Brookhaven National Laboratory (Ref. 24), the phenomenon involving ignition of a secondary fire from an open-circuited CT secondary circuit is not a concern for a CT used in any low- and medium-voltage applications (i.e., up to and including 15kV primary circuit voltage). (3) A multiple high-impedance faults (MHIFs) analysis is not required when protective devices for the affected circuits are properly coordinated and have been appropriately tested and maintained. IEEE Standard 242, “IEEE Recommended Practices for Protection and Coordination of Industrial and Commercial Power Systems” (Ref. 25), provides detailed guidance on achieving proper coordination. NEI 00-01, Appendix B.1, justifies the elimination of the need to evaluate MHIFs. RG 1.205, Revision 2, Page 23 (4) When evaluating fire-induced hot shorts and MSOs, the following guidance applies to the number and duration of hot shorts to be considered: a. Number of Hot Shorts for Transient Inrush Considerations – If the MSO scenario involves the potential failure of a safe-shutdown power supply resulting from a temporary overload condition caused by multiple, concurrent inrush currents (i.e., an overlapping inrush transient current from multiple separate loads) due to the spurious operation of multiple loads as a result of hot shorts on the control cable for each load, then the MSO does not need to be considered. This is provided that (1) a normal transient inrush current duration exists, (2) the spurious operations are caused by fire damage to control cables for the loads from the power supply of concern, and the loads are otherwise operating correctly 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