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:
ddress deaeration, flashing, and other air entrainment mechanisms as discussed in GL 2008-01 and in Appendix A to this guide. The NRC developed this RG using insights from operating PWRs and BWRs, and the guide provides common regulatory positions applicable to both PWRs and BWRs. In certain areas, the RG gives separate guidance for PWRs and BWRs based on the design features of currently operating reactors. Adjustments may be necessary for new or advanced PWR or BWR designs whose features differ from those of currently operating reactors. For example, a plant with passive features will need adjustments for pump NPSH, and analyses of PWRs with in-containment refueling water storage tanks may need to draw on both PWR and BWR guidance. Pressurized-Water Reactors In PWRs, the containment emergency sumps serve as water sources to support long-term recirculation for RHR, emergency core cooling, containment cooling, and containment atmosphere cleanup. These water sources, the related pump suction inlets, and the piping between the sources and suction inlets are important safety components. In this guide, the term ECCS implicitly includes the CSS (or similar system), and the sumps or strainers (or both) servicing the ECCS and the CSS are referred to as ECCS sumps or ECCS strainers. DG-1385, Page 9 The design of PWR strainers and their outlets should consider the avoidance of air ingestion, gas void intrusion, flashing, accumulation of air from deaeration, and other undesirable hydraulic effects (e.g., circulatory flow patterns and outlets leading to high head losses). The location and size of the sump outlets within ECCS sumps are important to minimize air ingestion caused by vortexing at the pump suction inlets, because this phenomenon depends on the submergence level and velocity in the outlet piping. Experiments for PWRs have determined that air ingestion and gas void intrusion caused by vortexing at the pump suction inlets can be minimized by following the sump