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:
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 consideration. A-5.2 The chemical form of radioiodine released to the drywell should be assumed to be 95-percent cesium iodide, 4.85-percent elemental iodine, and 0.15-percent organic iodide. With the exception of elemental and organic iodine and noble gases, fission products should be assumed to be in particulate form. A-5.3 All the MSIVs should be assumed to leak at the maximum leak rate above which the TSs would require declaring the MSIVs inoperable. The leakage should be assumed to continue for the duration of the accident as specified in Table 7 of this guide and should be assigned to steamlines so that the accident dose is maximized. Postulated leakage may be reduced after the first 24 hours, if supported by site-specific analyses, to a value not less than 50 percent of the maximum 2 The 97-percent elemental, 3-percent organic speciation is a conservative deterministic assumption based on the hypothesis that most of the iodine released to the environment will be in elemental form with a small percentage converted to organic as supported in Section 3.5 of NUREG-1465, “Accident Source Terms for Light-Water Nuclear Power Plants,” issued February 1995 (Ref. A-10). 3 Note that for the purpose of this analysis the containment now extends up to the MSIVs which are designated as containment isolation valves. DG-1389, Appendix A, Page A-7 leak rate. Section 5.4 of SAND2008-6601, “Analysis of Main Steam Isolation Valve Leakage in Design Basis Accidents Using MELCOR 1.8.6 and RADTRAD,” issued October 2008 (Ref. A- 11), describes an acceptable model for estimating the 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