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:
sure, or until the temperature of the leakage is less than 100 degrees Celsius (212 degrees Fahrenheit). The release of radioactivity from the unaffected steam generators should be assumed to continue until shutdown cooling is in operation and releases from the steam generators have been terminated. The release of radioactivity from the affected steam generator should be assumed to continue until shutdown cooling is operating and releases from the steam generator have been terminated, or the steam generator is isolated from the environment such that no release is possible, whichever occurs first. E-6.4 All noble gas radionuclides released from the primary system should be assumed to be released to the environment without reduction or mitigation. E-6.5 The transport model described in this section should be used for iodine and particulate releases from the steam generators. Figure E-1 illustrates this model, which is summarized below: DG-1389, Appendix E, Page E-5 Figure E-1. Transport Model E-6.5.1 A portion of the primary-to-secondary leakage will flash to vapor, based on the thermodynamic conditions in the reactor and secondary coolant (bulk water in Figure E-1). For the unaffected steam generators used for plant cooldown, the primary-to-secondary leakage, discussed in Regulatory Position E-6.1, can be assumed to mix with the secondary water without flashing during periods of total tube submergence. E-6.5.2 The leakage in the affected steam generator that immediately flashes to vapor will rise through the secondary water of the steam generator and enter the steam space. Credit may be taken for scrubbing in the generator, using the models in NUREG-0409, “Iodine Behavior in a PWR Cooling System Following a Postulated Steam Generator Tube Rupture Accident,” issued January 1978 (Ref. E-2), during periods of total submergence of the tubes. E-6.5.3 The leakage in the affected steam generator that does not immediately flash is assumed to mix with the secondary water.