Document: NRC Regulatory Guide
Document ID: 8e45dce1-e1e7-4415-b1dd-7e2a610e545b
Document Type: regulatory_guide
Title: Fire Protection for Nuclear Power Plants (Rev. 4)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2023/ML20231A835.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.189
CFR Part: 
CFR Title: 

Content:
-01, Revision 4, as having the same meaning as the phrase “the safe-shutdown success path” used in this guide. The post-fire safe-shutdown circuit analysis should address all possible fire-induced failures that could affect the safe-shutdown success path, including multiple spurious actuations. Some licensees have based this analysis on the assumption that multiple spurious actuations will not occur simultaneously or in rapid succession. This is known as the “one-at-a-time” assumption. Cable fire testing performed by the NRC and industry has demonstrated that multiple cable faults occur when cables are exposed to fire. These faults depend on multiple factors, including cable insulation or jacketing materials and cable configurations. The success path SSCs and the components important to safe shutdown should be protected from fire damage so that the capability to shut down the plant safely is ensured; specifically, all spurious actuations that could affect safe-shutdown success path SSCs are required to be protected in accordance with Position 5.3.1.1. The one-at-a-time assumption may still pertain to the protection of components important to safe shutdown as applied per the plant’s licensing basis, using the information in Position 5.3.1.2. However, a safety and technical analysis that demonstrates the assumption’s validity for each application should support the use of this assumption. 5.3.1.1 Protection for the Safe-Shutdown Success Path For the success path of SSCs necessary to achieve and maintain hot-shutdown conditions, fire barriers, physical separation, or automatic suppression should protect redundant systems or components. Except in those circumstances in which alternative or dedicated shutdown systems are required, where equipment or cables (including electrical circuits that could prevent operation or cause maloperation caused by hot shorts, open circuits, or shorts to ground) of redundant success paths necessary to achieve and maintain