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:
standpipe systems may be relied on to provide the primary fire suppression (in lieu of automatic water suppression systems) for cable trays of a single division important to safety that are separated from redundant safety divisions by a fire barrier with a minimum rating of 3 hours and are normally accessible for manual firefighting if all of the following conditions are met: a. The number of equivalent standard 610-mm (24-in.)-wide cable trays (both important to safety and nonsafety related) in a given fire area is six or less. Trays exceeding 610 mm (24 in.) should be counted as two trays; trays exceeding 1,220 mm (48 in.) should be counted as three trays, regardless of tray fill. b. The cabling does not provide instrumentation, control, or power to systems required to achieve and maintain hot shutdown. c. Smoke detectors are provided in the area of these cable routings, and continuous line-type heat detectors are provided in the cable trays. In other areas where overriding design features necessary for nuclear safety prevent the separation of redundant cable systems important to safety by 3-hour-rated fire barriers, or if cable trays are not accessible for manual firefighting, an automatic fire suppression system should protect the cable trays. 4.1.3.4 Electrical Cable Separation Redundant systems used to mitigate the consequences of design-basis accidents, but not necessary for safe shutdown, may be lost to a single exposure fire. However, protection should be provided so that a fire within only one such system will not damage the redundant system. Therefore, the separation guidelines of Regulatory Position 5.3.1.1 of this guide apply only to the electrical cabling needed to support the systems that are used for post-fire safe shutdown. All other redundant Class 1E electrical cables should meet the separation guidelines of RG 1.75. When the electrical cabling is covered by separation criteria required for both post-fire safe shutdown and accident mitigation,