Document: NRC Regulatory Guide
Document ID: 4d46a966-d280-43da-9b03-8b0abe7b29ce
Document Type: regulatory_guide
Title: Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2120/ML21204A065.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.183
CFR Part: 
CFR Title: 

Content:
he volumetric flow rate in the steamline. A-5.4 A reduction in MSIV releases that is caused by holdup and deposition in the main steam piping and main condenser, including the treatment of air ejector effluent by offgas systems, may be credited if the components and piping systems used in the release path are capable of performing their safety function during and following a safe-shutdown earthquake (SSE) and are powered by emergency power sources. These reductions are allowed for steam system piping segments that are enclosed by physical barriers, such as closed valves. The piping segments and physical barriers should either be designed, constructed, and maintained to seismic Category I guidelines as specified in Regulatory Guide 1.29 (Ref. A-12) or be evaluated to be rugged as described in Regulatory Position A-5.5. The amount of reduction allowed will be evaluated on an individual case basis and is to be justified based on the alternative drain pathways established by operating procedures and the potential leakage pathways to the environment. In a safety evaluation dated March 3, 1999, the staff found the Boiling Water Reactor Owners Group (BWROG) technical report (TR), “Safety Evaluation of GE Topical Report, NEDC-31858P, Revision 2, ‘BWROG Report for Increasing MSIV Leakage Limits and Elimination of Leakage Control Systems,’” an acceptable method for direct reference in individual submittals on MSIV leakage, subject to the conditions and limitations described in the safety evaluation (Ref. A-13). For the purposes of DBA radiological consequence analyses, based on the information in the BWROG TR, proposed MSIV leakage limits in excess of 200 standard cubic feet per hour (scfh) per steamline and in excess of 400 scfh for total MSIV leakage will be considered on a case-by-case basis with sufficient justification. The single valve limitation is based on the consideration that leakage in excess of 200 scfh may indicate a substantial valve defect. The total