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:
ators, 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 discharge line is used for an ECCS function, the power-operated valve should be opened upon receipt of a safety-injection signal once the reactor coolant pressure has decreased below the ECCS design pressure. (3) Three check valves in series, or (4) Two check valves in series, provided there are design provisions to permit periodic testing of the check valves for leak tightness and the testing is performed at least annually. 3. RHR SYSTEM PRESSURE RELIEF a. To protect the RHR system against accidental overpressurization when it is in opera- tion (not isolated from the RCS), pressure relief in the RHR system should be provided with relieving capacity in accordance with the ASME Boiler and Pressure Vessel Code. The most 1.139-4 limiting pressure transient during the plant operating condition when the RHR system is not isolated from the RCS should be considered when selecting the pressure relieving capacity of the RHR system. For example, during shutdown cooling in a PWR with no steam bubble in the pressuri- zer, inadvertent operation of an additional charging pump should be considered in selecting the design bases. Fluid discharged through the RHR system pressure relief valves should be collected and contained so that a relief valve that is stuck in the open position will not: a. Result in flooding of any safety-related equipment. b. Reduce the capability of the ECCS below that needed to mitigate the consequences of a postulated LOCA. c. Result in a non-isolatable situation in which the water provided to the RCS to maintain the core in a safe condition is discharged outside the containment. If interlocks are provided to automatically close the isolation valves when the RCS pres- sure exceeds the RHR design pressure, adequate relief capacity should be provided during the