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:
Losses • Short-Term Transport by Blowdown Jet • Long-Term Transport by Recirculation Velocities • Debris Transport by Containment Spray Washdown • Hydraulic Characteristics - Water Level above Sump Outlet - Sump-Outlet Velocity - Air Ingestion - Inlet Losses • Effects of Air Ingestion on NPSHR • Cavitation Potential - Inlet Design - Temperature Effects • Effects of Particulate and Debris Ingestion • Potential of Strainer Blockage • Head Loss across Strainer Is There Adequate NPSH Margin under All Post-LOCA Conditions? • NPSHR • NPSHA DG-1385, Appendix A, Page A-2 A-1 Emergency Core Cooling System Strainer Hydraulic Performance ECCS strainer hydraulic performance is primarily affected by the potential for air ingestion and for flashing or deaeration of the recirculating coolant across ECCS strainer surfaces, including the debris bed, and internal flow restrictions. Air ingestion could occur in several ways, including (1) through vortex formation, (2) through the release of gas dissolved in the recirculating coolant via deaeration after undergoing a pressure drop, and (3) through entrainment with water drainage that splashes down onto, or in the direct vicinity of, the strainer. Flashing could occur if the strainer pressure drop is sufficiently large that the recirculating coolant undergoes a transition to the vapor phase anywhere in the system. Deaeration may occur if the differential pressure across the strainer is large enough to liberate entrained gases from the fluid. These phenomena may be evaluated by considering factors such as the strainer submergence, the strainer approach velocity, the strainer debris bed head loss, the temperature of the recirculating coolant, and the properties of the containment atmosphere. Licensees should perform prototypical testing to ensure that an ECCS strainer is not subject to vortex formation. Consistent with the range of possible plant-specific values, the testing should consider conservatively low