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:
ral 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 radioactive iodine in gap (moles), e. NI-129gap—fuel pin nonradioactive iodine in gap (moles), DG-1389, Appendix B, Page B-3 f. KL = mass transfer coefficient—3.66x10-6 m/s (Ref. B-1), and g. pH—bounding design acidity value of the pool. Note: For this approach, Vpool, Spool, KL, and Qrecirc must use consistent units. (For the purpose of calculating concentrations in M (moles/liter), Vpool must be converted to liters.) Calculation Sequence: 1. Calculate amount of iodine (radioactive and nonradioactive) in the fuel pin gap. 2. Calculate volatile iodine fraction in pool. 3. Calculate removal coefficients. 4. Evaluate release as either: a. an overall release (neglecting time), or b. a time-dependent release. Step 1—Calculate amount of iodine in the fuel pin gap. Both the radioactive and nonradioactive iodine in the pool affect the radioactive iodine evolution. The calculations operate on moles so iodine isotope quantities must be converted to moles. For a given mass of iodine, the number of moles of iodine can be calculated from the mass, m, in grams (g) and its atomic weight, M, as: ܰூିଵଷଵ= ൬ ௠಺షభయభ(௚) ெ಺షభయభ൫௚ ௠௢௟ ൗ ൯൰ (Equation B-4) ܰூିଵଶଽ= ൬ ௠಺షభమవ(௚) ெ಺షభమవ൫௚ ௠௢௟ ൗ ൯൰ (Equation B-5) Alternatively, for radioactive materials, the number of moles can be calculated from the activity in becquerels (Bq): ܰூିଵଷଵ= ൬ ஺಺షభయభ൫ௗ௜௦௦ ൗ൯ ఒ಺షభయభ൫ௗ௜௦௔௧௢௠.௦ ൗ ൯൰ (Equation B-6) Activities in curies (Ci) must be converted to becquerel (1 Ci = 3.7x1010 Bq). The radioactive iodine concentration can be found using radiological decay formulas that account for time before fuel movement. If this is