Document: NRC Regulatory Guide
Document ID: 6f0a99f2-d25a-44e3-b7f2-3286449a9752
Document Type: regulatory_guide
Title: Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant Accident (Rev. 5)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2126/ML21266A185.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.82
CFR Part: 
CFR Title: 

Content:
.......................... B-1 DG-1385, Page 5 B. DISCUSSION Reason for Revision This revision of the guide (Revision 5) addresses new considerations identified since the NRC issued Revision 4 of this guide. These considerations concern the use of CAP in determining the NPSH margin for the ECCS and containment heat removal pumps. This revision also incorporates new information on the effects of debris on long-term core cooling. Specifically, information and references that apply to the evaluation of in-vessel effects are added. This revision applies to both PWR and BWR types of light-water reactors. This revised guide contains information specific to the use of CAP for both older plants and newer reactors licensed under 10 CFR Part 50 and 10 CFR Part 52. Background Long-term recirculation cooling raises four primary safety concerns following a LOCA: (1) LOCA-generated and pre-LOCA debris materials may be transported to the ECCS strainers, the downstream components in the ECCS, the containment spray system (CSS), and the reactor core, resulting in adverse heat transfer, blockage, or wear effects, or some combination of all three, (2) There may be post-LOCA hydraulic effects, particularly air ingestion (e.g., through vortexing or deaeration) and flashing. Gas that may exist in system piping downstream of the strainers could be a concern when recirculation is initiated. Activities in response to Generic Letter (GL) 2008-01, “Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems,” dated January 11, 2008 (Ref. 5), address this issue. (3) The combination of Items (1) and (2) may affect long-term recirculation pump operability (i.e., it may affect NPSH available at the pump inlet). (4) CAP may be used in determining the NPSH margin for the ECCS and containment heat removal pumps. These ECCS safety concerns extend to the CSSs for plants with containment designs in which the CSS draws suction from the water supply used for