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:
uld be appropriate for any physical restrictions in the systems supplied with coolant from the ECCS sump, including openings in the containment spray nozzles, coolant channel openings in the core fuel assemblies, fuel assembly inlet debris screens, small clearances within system flowpaths (e.g., high-pressure safety injection (HPSI) throttle valves), and pump component clearances such as seals, bearings, and impeller running clearances. The strainer opening sizes also affect clean screen head loss, the accumulation of debris passing through the sump strainer, and the wear of components in the ECCS flowpath. The amount of debris that penetrates or bypasses a strainer DG-1385, Page 8 also depends on the strainer area, the strainer layout, the debris arrival sequence, the concentration of debris at the strainer, and the properties of the fluid field close to the strainer. As noted above, many factors, including plant design and layout, can cause degraded pump performance. The effects of debris blockage of ECCS strainers, sump outlet configurations, and post-LOCA hydraulic conditions (e.g., air ingestion) should be considered in an integrated manner. Small amounts of ingested gas during steady-state pump operation will not lead to severe pumping degradation if the NPSHr from the pump manufacturer’s curve is increased to account for the air ingestion. Thus, it is important to use the combined results of all post-LOCA effects to estimate NPSH margin at the pump inlet. Appendix A to this guide provides information on estimating NPSH margins in ECCS strainer designs in which estimated levels of air or gas ingestion are low (2 percent or less). NUREG-0897, Revision 1, “Containment Emergency Sump Performance: Technical Findings Related to Unresolved Safety Issue A-43,” issued October 1985 (Ref. 14), and NUREG/CR-2792, “An Assessment of Residual Heat Removal and Containment Spray Pump Performance under Air and Debris Ingesting Conditions,” issued September 1982 (Ref.