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:
and the pressure suppression pool. Further heat rejection is achieved by the RHR system after the RCS has been sufficiently depressurized. 3. For all current designs of PWRs and BWRs, depressurization of the RCS is a prereq- uisite to the operation of the RHR system in the long-term cooling mode; therefore, it is important that systems or components required to depressurize the RCS be designed to withstand severe postulated accident conditions and be able to perform their intended functions. a. For PWRs, depressurization of the RCS can be achieved by the pressurizer in conjunction with one or more of these components: (1) the main pressurizer spray, (2) the auxiliary pressurizer spray, or (3) the pressurizer relief valves. b. For BWRs, depressurization of the RCS is achieved by dumping steam to either the main condenser or the pressure suppression pool. Steam condensation during the RHR system operation in the steam condensing mode will help depressurize the RCS. 4. For both PWRs and BWRs, following the reactor shutdown and both the initial and the intermediate cooldown periods, long-term cooling is necessary to prevent heat accumulation in the RCS. This function is usually accomplished by the RHR system. In all current plant designs, the RHR system has a lower design pressure than the RCS. In most of these designs it is located largely outside the containment. However, in some plant designs, the RHR system is located inside the containment. C. REGULATORY POSITION 1. FUNCTIONAL The systems necessary to take the reactor from normal operating conditions to cold shutdown, including the RHR system, should satisfy the functional guidance presented below. a. The design should be such that the reactor can be taken from normal operating condi- tions to cold shutdown using only 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