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:
reactor core and available for release to the containment should be based on the maximum full-power operation of the core with, as a minimum, current licensed values for fuel enrichment, fuel burnup, and an assumed core power equal to the currently licensed rated thermal power times the approved core power measurement uncertainty factor (e.g., 1.02). These parameters should be examined to maximize fission product inventory. The period of irradiation should be of sufficient duration to allow the activity of dose-significant radionuclides to reach equilibrium or to reach maximum values.9 The core inventory should be determined using an appropriate isotope generation and depletion computer code. Core inventory factors (curies per megawatt thermal) provided in TID-14844 and used in some analysis computer codes were derived for low-burnup, low-enrichment fuel and should not be used with higher burnup and higher enrichment fuels. The code should model the fuel geometries, material composition, and burnup, and the cross-section libraries used should be applicable to the projected fuel burnup. For the MHA LOCA, all fuel assemblies in the core are assumed to be affected, and the analysis should use the core-average inventory. For DBA events that do not involve the entire core, the fission product inventory of each of the damaged fuel rods is determined by dividing the total core inventory by 9 Note that for some radionuclides, such as cesium-137, equilibrium will not be reached before fuel offload. Thus, the maximum inventory at the end of life should be used. DG-1389, Page 18 the number of fuel rods in the core. To account for differences in power level across the core, the analysis should apply the radial peaking factors from the facility’s core operating limits report or technical specifications in determining the inventory of the damaged rods. The licensee should not adjust the fission product inventory for events postulated to occur during power operations at less