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:
ommission staff safety evaluation. The limit on sump air or gas ingestion for pumping capacity and the NPSH criteria are applied independently. As stated in NUREG-0897, Revision 1, steady-state air or gas ingestion levels less than 2 percent can also affect NPSH margin. If air or gas ingestion is indicated, then the following relationship can be used to correct the required NPSH from the pump curves for steady-state operating conditions: NPSHrequired(αp < 2%) = NPSHrequired(liquid) × β, where β = 1 + 0.50αp, and αp is the volumetric percentage of air in the fluid at the pump inlet flange. For transient operation, it is not necessary to consider the effect of gas on NPSH if the Table A-2 transient conditions are met, because the conservatism associated with the void fraction Ф adequately covers the short-term effects. For steady-state operation (periods longer than those defined in the table) with voids present at the pump suction, the required NPSH is adjusted as described above. DG-1385, Appendix A, Page A-8 Table A-2 Impact of Ingested Air on Pump Performance (Taken from Staff Safety Evaluation in NEI 09-10, Revision 1a-A) Condition BEP Q Q % Ф for BWR Typical Pumps Ф for PWR Typical Pumps Single-Stage Multistage Stiff Shaft Multistage Flexible Shaft Steady-State Operation 40–120% 0.02 0.02 0.02 0.02 Steady-State Operation <40% or >120% 0.01 0.01 0.01 0.01 Transient Operation 70–120% 0.10 for ≤5 s 0.05 for ≤20 s 0.20 for ≤20 s 0.10 for ≤5 s Transient Operation <70% or >120% 0.05 for ≤5 s 0.05 for ≤20 s 0.05 for ≤20 s 0.05 for ≤5 s Notes: Q = water volumetric flow rate. BEP = best efficiency point. Transient Ф is averaged over the specified time span. Instantaneous Ф is less than 1.7 times the listed value.2 A-4 Criteria for Evaluating Emergency Core Cooling System Strainer Failure The applicable ECCS strainer failure criteria depend on several factors, including submergence and structural strength, and may be pump or system