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:
guration include (1) pump cavitation, (2) structural failure, and (3) insufficient water entering the strainer because of head loss caused by debris buildup (i.e., flow starvation). The latter failure mode occurs when water infiltration through a debris bed on the strainer can no longer satisfy the volumetric demands of the pump or pumps taking suction from the strainer. Because the volumes inside and outside the strainer are at equal atmospheric pressures, the only force available to move water through the debris bed is the static pressure head of the water in the pool. DG-1385, Appendix A, Page A-10 Figure A-3b Partially submerged strainer configuration, with containment atmosphere over both the external pool and the strainer internal water surface Numerical simulations confirm that head loss across a debris bed equal to approximately one-half the submerged strainer height can be sufficient to prevent adequate water flow (i.e., the pressure available to move water through the debris bed is approximately the average of the gravitational head at the existing depth of the pool and zero head at the pool surface). For strainers with more complex geometries, the calculation of the pressure available to move water through the debris bed may require more complicated evaluations and additional testing. For all partially submerged strainers, failure is assumed to be reached when one of the following occurs: • Head loss across the debris bed is greater than or equal to NPSH margin. • Head loss across the debris bed is greater than or equal to one-half of the submerged screen height. • Head loss across the debris bed is greater than or equal to the structural limit. When the flow starvation failure criterion is met, the water level on the downstream side of the screen will drop rapidly, and all pumps taking suction from the sump will have insufficient flow for continued operation. After switchover to ECCS recirculation, the configuration may change from partially