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:
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 hydraulic design considerations in Appendix A to this guide. NUREG-0897, Revision 1, and NUREG/CR-2758, “A Parametric Study of Containment Emergency Sump Performance,” issued July 1982 (Ref. 16), provide additional technical information relevant to ECCS sump hydraulic performance and original design guidelines. The hydraulic design guidelines in Table A-1 of Appendix A apply to designs that do not have a complete water seal over the strainer or that otherwise could have a free surface inside the strainer volume. For example, the sump design could include a vent, the strainer might not be fully submerged, or a pocket of gas could accumulate inside the strainer. For fully submerged, unvented strainers, licensees should use other analytical or empirical means to evaluate the possibility of vortex formation at the strainer surface. Air or gas voids can also be generated downstream of the strainer surface if dissolved gas comes out of solution within the sump fluid after undergoing a pressure drop across the debris bed on the strainer or across flow restrictions within the ECCS piping. Excessive deaeration resulting from the passage of flow through the debris bed or internal system flow restrictions could significantly increase the head loss and impair pumping performance. A similar increase in head loss could occur if sump fluid flashes to vapor upon undergoing a differential pressure drop at the strainer or inside the ECCS. Both the flashing of sump fluid and the generation of air or gas voids through deaeration should be prevented by providing sufficient strainer submergence relative to the expected pressure drop. In general, flashing across or within the strainer should be avoided. Placement of the ECCS strainers at the lowest floor level practical ensures maximum