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:
between surveillances or leakage checks. DG-1389, Appendix A, Page A-6 A-4.6 The radioiodine that is postulated to be available for release to the environment is assumed to be 97-percent elemental and 3-percent organic.2 Reduction in release activity by dilution or holdup within buildings, or by ESF ventilation filtration systems, may be credited where applicable. Filter systems used in these applications should be evaluated using the guidance of Regulatory Guide 1.52 (Ref. A-6). A-5. Main Steam Isolation Valve Leakage in Boiling-Water Reactors For BWRs, the main steam isolation valves (MSIVs) have design leakage that may result in a radioactivity release. The licensee should analyze and combine the radiological consequences from postulated MSIV leakage with consequences postulated for other fission product release paths to determine the total calculated radiological consequences from the MHA LOCA. Three methods are presented below to compute aerosol deposition within main steamlines. Each method computes similar removal coefficients suitable for radiological consequences calculations, however, these methods are not valid if credit has been taken for aerosol removal from drywell sprays. The three MSIV leakage models are the: 1. Direct adoption of the SAND 2008-6601 (Ref. A-11) recommendations without scaling “R*- factors;” 2. Re-evaluated AEB 98-03 with multi-group; and 3. Numerical Integration. The following assumptions are acceptable for evaluating the consequences of MSIV leakage: A-5.1 The source of the MSIV leakage should be assumed to be the containment (or drywell)3 activity concentration (see Regulatory Position A-2.1). For new BWR designs or license amendments that propose changes from a referenced design control document, other models of MSIV source concentration will be considered on a case-by-case basis. In general, the concepts used in development of the guidance for BWR Mark I, II, and III plants may be followed as applicable to designs under