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:
) depends on the pump design. It is the NPSH value that limits cavitation within the pump to a specified amount (or prevents it entirely). The American National Standards Institute/Hydraulic Institute standard ANSI/HI 14.6-2016, “American National Standard for Rotodynamic Pumps for Hydraulic Performance Acceptance Tests” (Ref. B-2), defines NPSHr as the value of NPSH that results in cavitation sufficient to reduce the pump total dynamic head (TDH) by 3 percent. This guidance will denote this value by NPSHr3%. NPSHr as a function of flow rate is typically obtained by testing the pump in question or a similar pump at the pump vendor’s facility in accordance with ANSI/HI 14.6-2016. Figure B-1 shows the HI constant flow rate test for the determining NPSHr3%. The test begins with a large value of NPSHa in the test loop, which is gradually reduced. The flow rate and the pump speed are held constant. As the test loop NPSHa is reduced, a value of NPSHa is reached at which the pump TDH can no longer be maintained and decreases. The value of NPSHr is the value of the measured NPSHa corresponding to a given measured decrease in the TDH. The value of NPSHr3% corresponds to a TDH 3 percent below the TDH at the higher values of NPSHa for which the TDH is constant. Other quantities could also be DG-1385, Appendix B, Page B-2 obtained (e.g., NPSHr1%). These are the most accurate test methods for determining the NPSHr3% of a pump. For best accuracy, the test should be conducted at the rated speed and impeller diameter, with the NPSHa controlled by a vacuum pump. The NPSH margin is defined as the difference between NPSHa and NPSHr. The NPSH margin should be greater than or equal to zero. Another useful parameter is the NPSH margin ratio, which is defined as the ratio NPSHa/NPSHr. When the suction pressure or the NPSHa is decreased from the value corresponding to cavitation inception, the region of cavitation grows. If the decrease in NPSHa is significant, then noise, cavitation