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:
ination of debris types that produces the maximum head loss to the sump strainer. At a minimum, licensees should consider the postulated break locations and pipe break characteristics described in the following sections. c. Sections 3.3.3 to 3.3.5 of NEI 04-07, “Pressurized Water Reactor Sump Performance Evaluation Methodology,” issued December 2004 (Ref. 38), the associated SE (Ref. 39), and Section 3.2.1.1 of the URG provide additional guidance on break selection criteria. 1.3.2.1 Licensees should consider breaks where debris is most easily transported to the suction strainer (e.g., breaks in areas with the most direct path to the sump strainer or suppression pool). 1.3.2.2 Licensees should consider a spectrum of breaks, including the breaks with the largest amount and greatest variety of debris within the expected zone of influence (ZOI). 1.3.2.3 Licensees should consider medium and large breaks that can generate and transport enough fiber to form a thin filtering bed and that have the greatest potential ratio of particulate to DG-1385, Page 22 fibrous insulation debris by weight. These breaks could form a thin layer that would subsequently filter sufficient particulate debris to create a relatively high head loss (called the “thin-bed effect”). A “thin bed” is a relatively thin layer of debris on a screen or strainer that has a high particulate-to-fiber ratio and causes a large flow resistance. 1.3.2.4 Licensees should disregard break exclusion zones in their evaluations (i.e., pipe breaks should be postulated in break exclusion zones). 1.3.2.5 Licensees should exclude NRC Branch Technical Position (BTP) 3-4, Revision 2, “Postulated Rupture Locations in Fluid System Piping inside and outside Containment,” issued March 2007 (Ref. 40), as a basis for selecting break locations, because limiting conditions for ECCS strainer performance are not related to the pipe vulnerability issues addressed in BTP 3-4. 1.3.2.6 Licensees should consider locations