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:
rt-length fuel rod designs. Applicability to future fuel rod designs, including chromium (Cr)-coated zirconium (Zr) cladding, non-Zr claddings, doped UO2 fuel, high-density fuel, and mixed-oxide fuel, will be judged on a 10 The data in this section do not apply to cores containing mixed oxide fuel. DG-1389, Page 19 case-by-case basis. Appendix J provides an acceptable analytical technique for calculating plant-specific or fuel rod design-specific fission product release fractions. For non-LOCA DBAs involving a rapid increase in fuel rod power, such as the BWR control rod drop accident and PWR control rod ejection accident, additional fission product releases may occur as a result of pellet fracturing and grain boundary separation. This transient fission gas release (TFGR) increases the amount of activity available for release into the reactor coolant system for fuel rods that experience cladding breach. The empirical database suggests that TFGR is sensitive to both local fuel burnup and peak radial average fuel enthalpy rise. As a result, separate low-burnup and high-burnup TFGR correlations are provided, as follows: pellet burnup < 50 GWd/MTU TFGR = maximum [ (0.26 * ΔH) – 13) / 100, 0 ] pellet burnup > 50 GWd/MTU TFGR = maximum [ (0.26 * ΔH) – 5) / 100, 0 ] where: TFGR = transient fission gas release, fraction, and ΔH = increase in radial average fuel enthalpy, Δ calories per gram. An investigation into the effect of differences in diffusion coefficients and radioactive decay on fission product transient release concluded that adjustments to the above empirically based correlations are needed for different radionuclides (Ref. 27). For stable, long-lived noble gases (e.g., krypton (Kr)-85) and alkali metals (e.g., cesium-137), the transient fission product release is equivalent to the above burnup-dependent correlations. For volatile, short-lived radioactive isotopes such as halogens (e.g., iodine (I)-131) and xenon (Xe) and Kr noble gases (e.g., Xe-133,