Document: NUREG-0800
Document ID: 8f6b1890-a22c-4287-be74-16d780bad03c
Document Type: srp
Title: Revision 6 – August 2016
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1601/ML16019A127.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
properly isolated in order to avoid either damage by overpressurization or the loss of integrity of the low-pressure system and possible radioactive releases. The residual heat removal system used for cold shutdown conditions when in service becomes an extension of the reactor coolant pressure boundary. General Design Criterion (GDC) 15, “Reactor Coolant System Design,” requires that reactor coolant system and associated auxiliary, control, and protection systems shall be designed with sufficient margin to ensure that the design conditions of the reactor coolant pressure boundary are not exceeded during any condition of normal operation, including anticipated operational occurrences. There have been losses of decay heat removal during nonpower operation incidents and they have been a concern for years. The U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 87-12, “Loss of Residual Heat Removal (RHR) while the Reactor Coolant System (RCS) is Partially Filled,” and GL 88-17, “Loss of Decay Heat Removal” for licensees to perform a systems analysis to avoid these problems. There have been a number of recommendations for accomplishing this aim. Until a more definitive guide is published, the criteria in Part B, below, provide an adequate and acceptable design solution for this concern. B. BRANCH TECHNICAL POSITION The following measures should be incorporated in designs of the interfaces between low- pressure systems and the high-pressure reactor coolant system: 1. At least two valves in series should be provided to isolate any subsystem whenever the primary system pressure is above the pressure rating of the subsystem. 2. For system interfaces where both valves are motor-operated, the valves should have independent and diverse interlocks to prevent both from opening unless the primary system pressure is below the subsystem design pressure. Also, the valve operators should receive a signal to close automatically whenever the primary system