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:
s much as 2 grams of iodine per day results in only a 50% reduction in milk radioiodine concentration and that, within a rather large range, the iodine content of a cow's diet has little effect on the radioiodine concentration in milk. It is concluded that under normal agricultural practices, the quantities of iodine ingested by cows have little effect on the iodine transfer coefficients. No allowance is, therefore, provided here to adjust the coefficients based upon this mechanism. The average equilibrium concentrations of radioiodine-131 and -133 may then be calculated using 0.20klv 131,j X 131 + xw h31J (6) and 0.09k1 V 133,j X 133 + xw C13 3 J (7) Under the above considerations, the milk radioiodine equilibrium concentrations of 1-131 and 1-133 relative to air radioiodine equi- librium concentrations are m131,j = 5.58 x 102 C1 3 1 ,j (8) m133,j = 4.10 x 101 C133,j (9) The milk ingestion rate for a child is assumed to be 1 liter per day. The breathing rate used in defining the MPC air values for radioiodine in air is 3 cubic meters per day. Using the fractional thyroid deposi- tion values from human ingestion and inhalation as 0.30 and 0.23, 1. 42-C6 Ii respectively, the daily depositions of radioiodine within the thyroid by milk ingestion and air inhalation are given by: Daily Thyroid Deposit (milk) = (0.30)(l)mij and Daily Thyroid Deposit (inhalation) = (0.23)(3)Cij. The ratio of milk to air thyroid doses for the same air concentration is (0.30) (1) mi i (0.2 3 )( 3 ) Cij (10) These ratios for 1-131 and 1-133 are then 243 and 17.8, respectively. Thus, the calculation of infant thyroid dose via the cow milk pathway may be related directly to those air concentration values provided in 10 CFR Part 20 that correspond to air doses of 1500 millirem per year to an infant's thyroid. These are given below: Nuclide 1-131 1-133 Annual Infant Thyroid Dose Via Cows Milk (mrem) (243) 131,1 )(1500) MPC a (17.8) 133 )(1500). aPC a Alternative representations of the above are: