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:
ed October 1985 (Ref. 14), and NUREG/CR-2792, “An Assessment of Residual Heat Removal and Containment Spray Pump Performance under Air and Debris Ingesting Conditions,” issued September 1982 (Ref. 15), provide additional technical findings on NPSH effects on pumps performing the functions of RHR, emergency core cooling, containment cooling, and containment atmosphere cleanup. When air ingestion is 2 percent or less, compensation for its effects may be achieved without redesign if the NPSHa is greater than the NPSHr (as adjusted for the percentage of voiding at the pump inlet). A 2-percent limit on allowed void ingestion was selected because data show that levels above 2 percent can produce significant head degradation. Gas intrusion and accumulation issues in plant safety systems have been an ongoing concern for many years. The NRC issued GL 2008-01 to request that each licensee evaluate its ECCS, decay heat removal system, and CSS for licensing basis, design, testing, and corrective actions for pump response to suction voids. In addition, the NRC requested that licensees demonstrate that the subject safety-related systems comply with the applicable regulatory requirements to ensure that gas void accumulation and transport arising from deaeration or air ingestion, or both, are maintained below the amount that challenges operability of these systems, and that appropriate action is taken when conditions adverse to quality are identified. In general, gas accumulation causes relatively short-term ingestion of larger amounts of gas, while vortexing and deaeration cause longer term ingestion of smaller amounts of gas. Short-term and longer-term gas ingestion are evaluated differently because they have different effects on pump performance. Licensees should evaluate and address deaeration, flashing, and other air entrainment mechanisms as discussed in GL 2008-01 and in Appendix A to this guide. The NRC developed this RG using insights from operating PWRs and BWRs, and