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:
ng filter systems, dual containments, or other engineered safety features may be taken into account. Refer to Appendix A to this guide for guidance on acceptable methods and assumptions for evaluating these mechanisms. H-6.2 The containment should be assumed to leak at the leak rate incorporated in the technical specifications (TSs) at peak accident pressure for the first 24 hours and at 50 percent of this leak rate for the remaining duration of the accident. Peak accident pressure is the maximum pressure defined in the TSs for containment leak testing. Leakage from sub-atmospheric containments is assumed to be terminated when the containment is brought to a sub-atmospheric condition, as defined in TSs. Transport from Secondary System H-7. Assumptions acceptable to the NRC staff related to the transport, reduction, and release of radioactive material in and from the secondary system are as follows: H-7.1 A leak rate equivalent to the primary-to-secondary leak rate limiting condition for operation specified in the TSs should be assumed to exist until shutdown cooling is in operation and releases from the steam generators have been terminated. H-7.2 The density used in converting volumetric leak rates (e.g., gallons per minute) to mass leak rates (e.g., pound mass per hour) should be consistent with the basis of surveillance tests used to show compliance with leak rate TSs. These tests typically are based on cooled liquid. The facility’s instrumentation used to determine leakage typically is located on lines containing cool liquids. In most cases, the density should be assumed to be 1.0 gram per cubic centimeter (62.4 pounds mass per cubic foot). H-7.3 All noble gas radionuclides released to the secondary system are assumed to be released to the environment without reduction or mitigation. H-7.4 The transport model described in Regulatory Positions E-6.5 and E-6.6 of Appendix E to this guide should be used for iodine and particulates. DG-1389, Appendix I, Page I-1