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:
of containment accident pressure (CAP) to ensure adequate suction conditions for these pumps. This appendix refers to the pertinent non-DBAs collectively as “special events.” B-1 Pump Net Positive Suction Head and Cavitation Cavitation is defined as the occurrence of vapor-filled cavities in a liquid (Grist, Cavitation and the Centrifugal Pump: A Guide for Pump Users (Ref. B-1)). In a pumped liquid, cavitation is the formation of vapor-filled cavities in the liquid flow due to a decrease in the local static pressure below its vapor pressure. The formation of vapor cavities and the vapor’s subsequent rapid condensation can damage and adversely affect the operation of a centrifugal pump. Cavitation is nearly always accompanied by the release of gases previously dissolved in the liquid. The first appearance of cavitation is called “cavitation inception.” In pumps, cavitation is most likely to occur at the inlet to the blades of the impeller, where the static pressure is lowest. Cavitation in pumps is undesirable not only because it can alter the flow pattern and thus degrade pump performance, but also because collapsing cavities can cause vibration and mechanical damage to the impeller. Directly related to cavitation is the net positive suction head (NPSH). The NPSH is the difference between the inlet absolute total head (which includes the velocity head in the inlet pipe) and the head equivalent to the vapor pressure of the liquid being pumped. The available NPSH (NPSHa) is defined as the NPSH at the pump inlet. The NPSHa is a function of the flow rate, head loss in the suction piping, liquid temperature, absolute pressure above the liquid surface, and liquid elevation relative to the pump for the system in which the pump is located. The required NPSH (NPSHr) 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