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:
etry of the flow approach path, such as a sharp turn just before the sump, can also influence vortex formation. Where these sharp turns exist, quiescent flume testing may not accurately predict vortex formation or behavior. Other nondimensional parameters (e.g., the Reynolds number and the Weber number) are of secondary importance. DG-1385, Appendix A, Page A-4 Figure A-2 Submergence level Pump suction inlet hydraulic performance can be divided into the following categories: a. For zero air ingestion (α) caused by vortexing at the pump suction inlets, there is no need for vortex suppressors or increases in the required NPSH above that from the pump manufacturer’s curves. b. If air ingestion (α) caused by vortexing at the pump suction inlets is 2 percent or 1 percent (depending on flow rate) or less, this is a conservative level at which degradation of pumping capability is not expected, provided that an increase in the required NPSH is accounted for as noted below. c. Vortex suppressors are used to reduce air ingestion caused by vortexing at the pump suction inlets to zero. d. For pressurized-water reactors (PWRs), the correlations in Table A-1 can be used to determine which pump suction inlet designs have ingestion levels of 2 percent or less. Table A-1 applies only to PWR sump screens without a complete water seal (e.g., screens are not fully submerged) and with the sump geometry described in the table. However, it should be noted that most strainers have the potential to generate and accumulate air in the long term, which could lead to the formation of a free surface inside the strainer volume. If long-term generation and accumulation of air cannot be ruled out, licensees should continue to consider the design guidance in Table A-1, even if the strainers are fully submerged. Some plant designs have open or vented sumps downstream of the strainers. Table A-1 also applies in these cases. If the PWR pump suction inlet design deviates significantly from the