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:
e amount of suction head, over vapor pressure, required to prevent more than a 3-percent loss in total head of the first stage of the pump at a specific capacity. The predicted performance of the ECCS and the containment heat removal pumps and their associated strainers should be independent of the calculated increases in containment pressure caused by postulated LOCAs, to ensure reliable operation under a variety of possible accident conditions. For example, if the proper operation of the ECCS or the containment heat removal system depends on containment pressure being above a specified amount, operation of these systems at a containment pressure less than this amount (e.g., resulting from impaired containment integrity or from operation of the containment heat removal systems at too high a rate) could significantly affect the systems’ abilities to accomplish their safety functions. However, for certain operating reactors, some credit for CAP may be necessary to demonstrate that adequate pump NPSH margins exist, that unacceptable deaeration will not occur at the strainer, or that sump fluid will not flash to vapor after undergoing a pressure drop at the strainer. The flashing of sump fluid to vapor should be prevented. ANSI/HI 14.3-2019 specifies a method of accounting for the decrease in NPSHr with an increase in the temperature of the pumped fluid. This method is subject to restrictions specified in the standard that are related to pump-specific performance, the amount of air dissolved in the fluid, and the transient nature of the pressure and temperature of the pumped fluid. Because of the uncertainty in these factors, licensees should avoid taking credit for the reduction in NPSHr that results from the temperature of the pumped fluid. Transient NPSH calculations should be performed to ensure that the most limiting conditions are chosen and that the results are conservative. The calculation of NPSH margin should include head loss caused by debris, by