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:
n 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 submerged to fully submerged. This can occur for several reasons, including the accumulation of containment spray water, the continued melting of ice condenser reservoirs, and the continued addition of the refueling water storage tank inventory to the containment pool. As the containment pool depth changes during recirculation, the “wetted area” (or submerged area) of the strainers may also change. The wetted area determines the average approach velocity of water that may carry debris and the amount of debris that may accumulate per unit of strainer area. Both of these variables affect head loss. The gravitational head of the containment pool across the strainer also varies with the water level. For cases where the strainer submergence varies with time, the containment pool water level should be calculated as a function of time, and a conservative assessment should be made of debris transport and the accumulation of debris on the strainer. For plants that have systems initiating recirculation for containment spray and ECCS at different times, evaluations should consider the containment pool water level and strainer debris loading appropriately in view of this timing. DG-1385, Appendix A, Page A-11 A-4.3 Vented Submerged Strainers A flow starvation failure mode may occur with vented submerged strainers, as illustrated in Figure A-3(c). The potential for this to occur and the subsequent impact on pump performance should be evaluated in the same manner as for a partially submerged strainer, above. Figure A-3c Vented submerged strainer A-4.4 Partial Suction Line Uncovery Unlike earlier strainer designs, the new generation of suction strainer designs that consist of a series of modules connected by piping may be susceptible to uncovery of piping internal to the