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:
able FGR data up to the licensed burnup of the particular fuel rod design. Because of their relatively short half-lives, the amount of activity associated with volatile radioactive isotopes depends on their rate of production (i.e., fission rate and cumulative yield), rate of release, and rate of decay. Maximum R/B ratios for short-lived isotopes are likely to occur at approximately the maximum exposure at the highest power level (i.e., inflection point in the power operating envelope). J-2.1 NUREG/CR-7003 (PNNL-18490), “Background and Derivation of ANS-5.4 Standard Fission Product Release Model,” issued January 2010 (ADAMS Accession No. ML100130186), provides guidance on using the NRC-endorsed ANS-5.4 release model to calculate short-lived R/B factors. J-2.1.1 For nuclides with half-lives of less than 1 hour, no gap inventories are provided. Because of their rapid decay (relative to the time for diffusion and transport), these nuclides will be bounded by the calculated gap fractions for longer lived nuclides under the headings “Other Noble Gases” and “Other Halogens”. J-2.1.2 For nuclides with half-lives of less than 6 hours, an approved fuel performance code is applied to predict the R/B fraction using Equation 12 in NUREG/CR-7003 and its definitions of terms, as follows: where: R is release rate (atoms-cm-3s-1), B is production rate (atoms-cm-3s-1), S is surface area (cm2), V is volume (cm3), α accounts for precursor enhancement effects and is defined below, nuclide m i nuclide m i m i D V S B R λ α , , ,       =       DG-1389, Appendix J, Page J-4 D is diffusion coefficient (cm2s-1), and λ is half-life (s-1).). J-2.1.3 For nuclides with half-lives of greater than 6 hours, the R/B fraction is predicted by multiplying the fractal scaling factor (Fnuclide) by the predicted Kr-85m R/B using Equation 13 of NUREG/CR-7003, as follows: The R/B fraction for isotope I-132 should be calculated using this fractal equation