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:
eleased. Radionuclides that should be considered include xenons, kryptons, halogens, cesiums, and rubidiums. B-1.3 The chemical form of radioiodine released from the fuel to the spent fuel pool should be assumed to be 95-percent cesium iodide (CsI), 4.85-percent elemental iodine, and 0.15-percent organic iodide. This regulatory position and those in B-2 utilize, in part, the transport model discussed in Reference B-1 and those contained in Reference B-2. All the gap activity in the damaged rods is assumed to be released over two phases: Phase 1—the instantaneous release from the rising bubbles. Elemental iodine and organic iodine are conservatively assumed to be in vapor form and subsequently decontaminated by passage through the overlying pool of water into the building atmosphere. Phase 2—the protected release of CsI re-evolving as elemental iodine. CsI is conservatively assumed to completely dissociate into the pool water. Because of the low pH of the pool water, CsI (and Phase 1 absorbed elemental iodine and organic iodine within the pool) then slowly re-evolve as elemental iodine into the building atmosphere. 1 These assumptions may also be used in assessing the radiological consequences of a heavy load drop over fuel accident. If the event is postulated to damage all of the rods in the core, the release activity may be based on the core-average gap fractions of Tables 1 and 2 in the main text of the guide, and the radial peaking factor may be omitted. DG-1389, Appendix B, Page B-2 B-1.4 The radioactive material available for release is assumed to be from the assemblies with the peak inventory. The fission product inventory for the peak assembly represents an upper limit value. The inventory should be calculated assuming the maximum achievable operational power history and burnup. These parameters should be examined to maximize fission product inventory. This inventory calculation should include appropriate assembly peaking factors. B-2. Phase 1 Release —