Document: NRC Regulatory Guide
Document ID: c0dbb594-6262-4b83-96b1-366758ad9676
Document Type: regulatory_guide
Title: Interim Licensing policy on as low as Practicable for Gaseous Radiodine Releases from Light-Water-Cooled Nuclear Power Reactors (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1229/ML12298A137.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.42
CFR Part: 
CFR Title: 

Content:
ditions. Observed values of this parameter range from 0.07 to 0.85.4-15 The value of the vegetation retention factor, ki, selected for use in this guide is 0.3. In addition to the rapid loss of iodine immediately following its deposition, it has been observed that the subsequent rate of removal of the remaining radioiodine from vegetation is greater than that attributable to radiological decay alone. The rate of change of radioiodine on vegetation due to weathering has been shown to be reprsentd =a.... •i, Ia3,10,12,13,16 represented adequately by a first order rate "aw with a recommended16 weathering half-life of 13 days. The model presented here assumes the adequacy of the first order law in calculation and accepts a weathering half-life, Tw, of 13 days. Considering the preceding, the rate of change of radioiodine i on green fodder at the location of interest is given by dpij/dt = klCijV - (Ai + )ij (3) 1. 42-C3 In Equation 3, Pij is the average quantity of radioiodine i present on green fodder (curies per square meter), kI is the vegetation retention factor (dimensionless), C ij is the average air concentration of radioiodine i as 12 (curies per cubic meter), V is the deposition velocity of iodine as 12 (meters per second), X i is the radiological decay constant of radioiodine i (inverse seconds), and X is the weathering decay constant of iodine (inverse W seconds). Integration of Equation 3 with respect to time yields p kC i (1- exp{ -(X. + A )t}] (4) ij xi I w In Equation 4, t represents the time in seconds since the start of radioiodine release. It is here assumed that equilibrium conditions exist and, as a consequence, the exponential term in Equation 4 goes to zero. The average equilibrium areal density of radioiodine i is then given by P klCiljV (5) Wj 0 1.42-C4 where p on vege ij is the quantity of radiolodine i in curies per square meter tation at the location of interest. Annual Infant Thyroid Dose Via Cows Milk Milk cattle pastured on green fodder