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:
than 2 percent. DG-1385, Appendix B, Page B-9 The effect of air on required NPSH is included as an uncertainty component of NPSHreff. Licensees should determine a value of NPSHreff applicable to their pumps, considering the effects of pump speed, suction piping configuration, and air contents of pumped water, as described above in (a), (c), and (d), respectively. The NPSHreff should be used to determine the NPSH margin for the DBA NPSH analysis. For special events in BWRs that raise the temperature of the suppression pool (e.g., shutdown after an Appendix R fire, an ATWS, or an SBO), no uncertainty on NPSHr3% is required. NPSHa may also be calculated using realistic (rather than conservative) assumptions. It is possible that the NPSHa may be less than NPSHreff. In this case, it is acceptable to allow operation in this mode if tests are performed in which the pump is run in cavitation, and posttest inspection shows acceptable wear and no damage. As stated in a report by Budris, “Technical Report on Task #3 Findings,” dated October 14, 2009 (Ref. B-10), the following conditions should apply: • Predicted operation during the postulated accident below NPSHreff (LOCA) or NPSHr3% (special events) is of limited duration (less than 100 hours). • The tests are conducted on the actual pump, with the same mechanical shaft seal (including flush system), or at least on a pump of the same model, size, impeller diameter, materials of construction, and pump seal/flush system. • The test is conducted at the same speed as at the plant site. • The test is conducted at the actual predicted NPSHa, since testing at a lower NPSHa can actually reduce, rather than increase, the cavitation erosion rate in some cases. • The test duration is for the time during which NPSHa is predicted to be less than NPSHreff (LOCA) or NPSHr3% (special event). • The flow rate and discharge head remain above the values necessary to provide adequate core and containment cooling. B-5 Cavitation