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:
se 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 flow. Therefore, licensees should perform an analysis to demonstrate that they have prevented any flashing resulting from a pressure drop at the strainer surface or internal flow restrictions, or that they have analyzed the effects conservatively. A-2 Pump Suction Inlet Hydraulic Performance In addition to the ECCS strainer hydraulic performance, licensees should evaluate the pump suction inlet hydraulic performance. This may be particularly important for partially submerged strainer configurations, vented strainer designs with a free surface above the pump suction inlets, and strainers that could have an interior free surface formed by gas voids caused by accumulated gas from vortexing or deaeration. (See NUREG/CR-6762, “GSI-191 Technical Assessment,” issued August 2002 (Ref. A-2).) Pump suction inlet hydraulic performance (with respect to air ingestion potential) can be evaluated on the basis of submergence level (water depth above the pump suction inlet piping) and necessary pumping capacity (or pipe inlet velocity). The ratio between the water depth above the pipe centerline and the pipe inlet velocity based on the effective pipe flow area can be expressed non- dimensionally as the Froude number (see Figure A-2): Froude number = gs U where g is the acceleration due to gravity, s is the submergence, and U is the pipe inlet velocity. Extensive experiments have shown that the hydraulic performance of pump suction inlets (particularly the potential for air ingestion resulting from vortex formation) is strongly dependent on the Froude number. Perturbations in the geometry of the flow approach path, such as a sharp turn just before the sump, can also influence vortex formation. Where these sharp turns exist, quiescent flume testing may not accurately predict vortex