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:
nuary 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. E-6.5.4 The radioactivity in the secondary water is assumed to become vapor at a rate that is the function of the steaming rate and the partition coefficient.3 A partition coefficient for iodine of 100 may be assumed. The retention of non-iodine particulate radionuclides in the steam generators is limited by the moisture carryover from the steam generators. 3 In this appendix, “partition coefficient” is defined as follows: PC mass of I per unit mass of liquid mass of I per unit mass of gas = 2 2 DG-1389, Appendix E, Page E-6 E-6.6 During periods of steam generator dryout, all primary-to-secondary leakage is assumed to flash to vapor and be released to the environment with no mitigation. Operating experience and analyses have shown that for some steam generator designs, tube uncovery may occur for a short period following any reactor trip (Ref. E-3). If the tubes are uncovered, a portion of the primary-to-secondary leakage will flash and atomize, based on the thermodynamic conditions in the reactor and secondary coolant, and be released to the environment with no mitigation. The potential impact of tube uncovery on the transport model parameters (e.g., flash fraction) needs to be considered. The impact of restoration strategies described in emergency operating procedures for steam generator water levels should be evaluated. DG-1389, Appendix E, Page E-7 APPENDIX E REFERENCES E-1. U.S. Nuclear Regulatory Commission (NRC), “Steam Generator Tube Integrity,” Draft Regulatory Guide DG-1074, December 1998 (ADAMS Accession No. ML003739223).1 E-2. U.S. NRC, “Iodine Behavior in a PWR Cooling System Following a Postulated Steam Generator Tube Rupture Accident,” NUREG-0409, January 1978 (ADAMS Accession No. ML19269F014). E-3. U.S. NRC, “Steam Generator Tube Rupture