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:
eakers, fuses, or similar devices. b. A connection to circuits of equipment would adversely affect the shutdown capability if spuriously operated (e.g., RHR or reactor coolant system isolation valves, automatic depressurization system valves, power-operated relief valves, steam generator atmospheric dump valves, instrumentation, steam bypass). For consideration of spurious actuations, the licensee should evaluate all possible functional failure states; that is, the component could be energized or deenergized by one or more circuit failure modes (i.e., hot shorts, open circuits, and shorts to ground). Therefore, valves could fail open or closed, pumps could fail running or not running, or electrical distribution breakers could DG-1359, Page 87 fail open or closed. For three-phase AC circuits, the probability of getting a hot short on all three phases in the proper sequence to cause spurious actuation of a motor is considered sufficiently low that an evaluation is not required, except for cases involving high- and low-pressure interfaces. For ungrounded DC circuits, if the licensee can show that at least two hot shorts of the proper polarity without grounding are required to cause spurious actuation, no further evaluation is necessary, except for cases involving high- and low-pressure interfaces. Hot short conditions are assumed to exist until action has been taken to isolate the circuit from the fire area or other appropriate actions have been taken to negate the effects of the spurious actuation. c. A common enclosure (e.g., raceway, panel, junction box) with shutdown cables (redundant or alternative) (1) is not electrically protected by circuit breakers, fuses, or similar devices or (2) will allow propagation of the fire into the common enclosure. 5.4.4 Protection of Associated Circuits of Concern The shutdown capability may be protected from the adverse effect of damage to associated circuits of concern by the separation and protection guidelines of Regulatory