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:
nts in which certain pumps take suction from the ECCS strainers before the switchover of other pumps, the NPSHa for these pumps should consider the submergence of the strainers at the time these pumps initiate suction through the strainers. Unless experiments show otherwise, licensees should assume that debris is uniformly distributed over the available strainer surface. 1.3.11.3 Strainer submergence should be adequate to preclude vortexing, sump fluid flashing, and deaeration induced by differential pressure. Vortexing can cause the ingestion of unacceptable quantities of air into the ECCS and CSS pumps, resulting in unacceptable pump performance. If the pressure drop across the strainer and debris bed is large enough, the coolant will flash to steam. For partially submerged strainers, licensees should evaluate the potential for vortex formation internal to the strainer. Deaeration can similarly cause ingested air and unacceptable pump performance. Both deaeration and sump fluid flashing can result in an unacceptable increase in strainer head loss caused by the increased resistance associated with two-phase flow. 1.3.11.4 Licensees should validate the adequacy of ECCS strainer designs through testing applicable to plant-specific conditions. Analytical or empirical head loss correlations should not be used to validate plant-specific debris bed head losses. However, correlations may be useful in conducting scoping evaluations for conditions and debris loads within the range of applicable test data. 1.3.12 Prototypical Head Loss Testing 1.3.12.1 The methodology for predicting the key inputs to head loss testing has been conservatively developed and documented in NEI 04-07, referred to as the guidance report, and its associated SE (Refs. 37 and 38). Additionally, the NRC staff review guidance (Ref. 13) provides a general approach to plant-specific head loss testing. This guidance document discusses the staff positions on various aspects of head loss testing, including