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:
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 — Initial Gaseous Release and Water Depth An overall iodine decontamination factor (DF) is a function of bubble size and rise time through the water column, both of which are functions of fuel pin pressure. If the water depth is between 19 and 23 feet, an overall effective iodine DF for elemental iodine and organic iodine can be computed based on a best estimate rod pin pressure for the limiting fuel rods in the reactor core at the most limiting time in life. The time period between reactor shutdown and the movement of fuel may be used to compute radioactive decay and less decay power. The limiting pool water temperature near fuel rods and basing the estimate on a full-core offload may be used to determine internal gas temperature and thus pin pressure. For water depths between 19 and 23 feet, an overall iodine DF based on pin pressure is computed as follows: ܦܨூ= 81.046݁଴.ଷ଴ହ൫௧ௗ ൗ൯ (Equation B-1) where: t = bubble rise time (sec), computed as a function of pin pressure, x (psig), as: ݐ(ݏ݁ܿ) = 9.2261݁ି଺ாିସ∗௫ (Equation B-2) d = bubble diameter (cm), computed as a function of pin pressure, x (psig), as: ݀(ܿ݉) = −0.0002 ∗x + 1.0009 (Equation B-3) If the depth of water is not between 19 and 23 feet, the DF will need to be determined on a case-by-case basis. B-3. Phase 2 Release—Re-evolution Release The re-evolution calculation results in a simple exact transient solution. It has the flexibility to consider the effect of potential filtration and other removal mechanisms. The following information is needed: Site-specific and general parameters: a. Vpool—total pool free volume, b. Spool—total pool surface area, c. Qrecirc—volumetric flow of recirculation system (to evaluate effects of filtration), d. NI-131gap—fuel pin