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:
s available and conditions when offsite power is not available for 72 hours. In an evaluation of safe-shutdown circuits, the availability of uninterrupted power (i.e., offsite power remains available) may affect the ability to control the safe shutdown of the plant by increasing the potential for circuit interactions resulting from fire damage to energized power and control circuits that may result in spurious actuations. Several operating plant licensees have alternative methodologies that rely on intentional disconnection of AC power to specific equipment or to the entire plant as a means to achieve safe shutdown after a fire. The purpose of the self-induced station blackout (SISBO) is to eliminate potential DG-1359, Page 86 spurious actuations that could prevent safe shutdown and allow manual control of required equipment. Some licensees have procedures that cause a SISBO condition to be created as a result of fire effects (e.g., procedures that direct operators to manually trip the credited safe-shutdown EDG in the event of fire damage to circuits of vital EDG support systems). The acceptability of safe-shutdown procedures that voluntarily enter, or otherwise create, a SISBO condition is determined on a case-by-case basis. The ability to cope with a SISBO as part of the post-fire safe-shutdown methodology depends on such issues as time-line logic; assumptions and bases for plant and operator response relative to component realignment; the ability of plant operators to monitor and control plant parameters and align plant components before, during, and after a SISBO has caused control room evacuation and abandonment; and the practicality and reliability of EDG start and load (and restart, if applicable) under post-fire safe-shutdown SISBO conditions. The risk of a SISBO may exceed the actual risk posed by the fire, and the licensee should consider the risk carefully when evaluating the safe-shutdown design and procedures. A plant typically uses this approach to