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:
oids generated at or inside the strainer surface through deaeration will not eventually reach the pump suction inlet. Furthermore, excessive deaeration could lead to increases in differential pressure across the strainer because of the presence of two-phase flow. Therefore, licensees should ensure that strainer submergence is sufficient, relative to the strainer head loss and other parameters of interest, to minimize deaeration across the strainer debris bed or internal flow restrictions. If the strainer submergence is not sufficient to ensure zero deaeration under the potential post-LOCA conditions, then licensees should follow the guidance below for increasing the required NPSH to account for gas voids. Air ingestion greater than 2 percent by volume (or 1 percent by volume if the ratio of the flow rate to the best efficiency flow rate is over 120 percent or under 40 percent) should be avoided, to ensure that the pumps perform adequately and to prevent a significant increase in pressure drop across the strainer. Strainers should be designed so that water drainage does not splash down directly onto their surfaces or in their vicinity. Drainage splashing onto a water surface above or directly adjacent to the strainer can cause air entrainment and transport downstream of the ECCS strainer by the recirculation flow. As discussed above, this entrained air could adversely affect the performance of the pumps taking suction from the strainer. For designs in which water drainage near the strainer cannot be avoided, a solid cover plate should be provided so that entrained air is not drawn into the strainer. DG-1385, Appendix A, Page A-3 Licensees should conduct an analysis to ensure that the pressure drop at the strainer surface or at internal flow restrictions does not cause flashing of the recirculating coolant. Head loss tests are typically not conducted at design post-LOCA fluid temperatures, so the strainer tests do not model head loss increases caused by two-phase