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:
orm prototypical testing to ensure that an ECCS strainer is not subject to vortex formation. Consistent with the range of possible plant-specific values, the testing should consider conservatively low submergence levels and conservatively high flow rates. If the potential exists for a nonuniform flow distribution among the various modules in a strainer array, a conservatively high flow rate should be used to account for this nonuniformity and ensure that vortexing does not occur. Some work has been performed to determine analytically whether vortex formation will occur under various hydraulic conditions for specific types of strainers; NUREG/CR-2758, “A Parametric Study of Containment Emergency Sump Performance,” issued July 1982 (Ref. A-1), provides details. However, these evaluations were based on empirical data and are not generically applicable. Therefore, licensees should conduct properly scaled testing to determine the potential for vortex formation under plant-specific conditions. In some plant designs, the flowpath upstream of the strainers may cause significant vorticity in the flow approaching the strainers. Computational fluid dynamics simulations may be useful in identifying this situation. If significant, the strainer vortex tests should account for vorticity in the flow upstream of the strainer. Licensees should conduct an analysis to ensure that deaeration (or off-gassing) caused by the pressure drop at the strainer surface, including the debris bed, or at internal flow restrictions does not lead to air void formation within or downstream of the strainer that could adversely affect safety pump performance. The accumulation and transport behavior of air voids inside a strainer is not well understood. Therefore, it is difficult to demonstrate that gas voids 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