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:
down success path, which could cause overfill conditions • small diversion paths from success path flowpath (smaller than the significant diversion paths described above) • multiple separate small diversion paths that, when combined, would lead to core damage, rupture of the primary coolant boundary, or rupture of primary containment • a connection to circuits of equipment where spurious operation would adversely affect the SSCs important to safe shutdown (e.g., residual heat removal (RHR)/reactor coolant system isolation valves) 5.3.2 High-Low Pressure Interface The licensee should evaluate the circuits associated with high-low pressure interfaces for the potential to adversely affect safe shutdown. For example, the RHR system is generally a low-pressure system that interfaces with the high-pressure primary coolant system. Thus, the interface most likely consists of two redundant and independent motor-operated valves. Both of these motor-operated valves and their power and control cables may be subject to damage from a single fire. This single fire could cause the two valves to spuriously open, resulting in an interfacing system loss-of-coolant accident (LOCA) through the subject high-low pressure systems’ interface. To ensure adequate protection of this interface and other high-low pressure interfaces from the effects of a single fire, the licensee should perform an evaluation, as follows: a. Identify each high-low pressure interface that uses redundant, electrically controlled devices (such as two-series motor-operated valves) to isolate or preclude the rupture of any primary coolant boundary. b. For each set of redundant valves, verify that the redundant cabling (power and control) has adequate physical separation, as stated in Regulatory Positions 5.3 or 6.1.1.1 of this guide, as applicable. DG-1359, Page 83 c. Where adequate separation is not provided, demonstrate that fire-induced failures (multiple hot shorts, open circuits, and shorts to ground) of