Document: NRC Regulatory Guide
Document ID: 2559e7e3-22aa-4dda-8fee-ac029c2a69e4
Document Type: regulatory_guide
Title: Guidance for Residual Heat Removal
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0407/ML040750334.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.139
CFR Part: 
CFR Title: 

Content:
safety-grade systems that satisfy General Design Criteria I through S. 1.139-3 b. These systems should have suitable redundancy in components and features and suitable interconnection, leak detection and containment, and isolation capabilities to ensure that, for onsite electric power system operation (assuming offsite power is not available) and for offsite electric power system operation (assuming onsite power is not available), the system safety function can be accomplished assuming a single failure. In demonstrating that the system can perform its function assuming a single failure, limited operator action outside the control room would be acceptable if suitably justified. c. The systems should be capable of bringing the reactor to a cold-shutdown condition within 36 hours following shutdown with only offsite power or onsite power available, assuming the most limiting single failure. 2. RHR SYSTEM ISOLATION a. Isolation of the suction side of the RHR system should be provided by at least two power-operated valves in series, with valve positions indicated in the control room. Alarms in the control room should be provided to alert the operator if either valve is open when the RCS pressure exceeds the RHR system design pressure. The valves should have independent diverse interlocks to prevent the valves from being opened unless the RCS pressure is below the RHR system design pressure. Failure of a power supply should not cause any valve to change posi- tion. Independent diverse protective measures should be provided to close any open valve in the event of an increase in the RCS pressure above the RHR system design pressure. b. One of the following should be provided on the discharge side of the RHR system to isolate it from the RCS: (1) The valves, position indicators, alarms, and interlocks described in item a. (2) One or more check valves in series with a normally closed power-operated valve with its position indicated in the control room. If the RHR system