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 use of CAP in determining the NPSHa of safety-related pumps, as discussed in Section B-3, is summarized below. B-9.1 For DBAs, analyses involving CAP should use a value of NPSHreff that includes the uncertainty in the value of NPSHr3% based on vendor testing and installed operation. The effects of motor slip, suction piping configuration, and air content should be included. NPSHreff should be calculated from NPSHr3% as follows: NPSHreff = (1 + uncertainty) NPSHr3% For non-DBAs, NPSHr3% may be used. B-9.2 The maximum flow rate chosen for the NPSHa analysis should be greater than or equal to the flow rate assumed in the safety analyses that demonstrate adequate core and containment cooling. This ensures that the safety analyses and the NPSHa analysis are consistent. If the NPSHa is assumed to equal NPSHr3% (the usual assumption for determining the amount of CAP used), then the flow rate used in the core and containment cooling analyses should also be greater than or equal to the flow rate resulting from a 3-percent decrease in pump TDH. B-9.3 It should be demonstrated conservatively that, for the plant examined, loss of containment integrity from containment venting, Appendix R fire, or other causes cannot occur, or it will occur only after use of CAP is no longer needed. B-9.4 Operator action to control CAP is acceptable. Any operator actions must be approved by the NRC staff as a part of human factors engineering according to 10 CFR 50.34(f)(2)(iii) (Reference B- 12) and included in the appropriate procedures (emergency, abnormal, or other procedures). DG-1385, Appendix B, Page B-25 B-9.5 It is possible that the NPSHa may be less than NPSHreff (LOCA) or NPSHr3% (special event). In this case, operation in this mode is acceptable if appropriate tests are done to demonstrate that the pump will continue to perform its safety function(s). The following conditions should apply: • Predicted operation during the postulated accident below NPSHreff (LOCA) or NPSHr3%