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:
or (seconds per cubic meter), and R(r, h) is a dimensionless iodine cloud depletion factor which is dependent upon distance from the source, r, and the height of release at the source, h. The value of the depletion factor may be determined using Equation 2, which is a function fitted to conform to plume depletion estimates as provided in the Final Environmental Statement on "as low as practicable". 1 This function is given by R(r,h) = (4.47 x 0-3h + 0.618)[exp{ -(1.06 x 10- 5r)} - exp [-(1.06 x 10 -4r)}]+ exp f-(1.06 x 10-4r)};h<100. (2) In Equation 2, h is the height of radioiodine release and r is the distance from the source, both in meters. Radioiodine present as molecular iodine in the gaseous effluent is deposited from the effluent gases on surfaces via a transfer mechanism with the dimensions of velocity. This is termed deposition velocity, V, and is here given in units of meters per second. Deposition velocities of molecular iodine are reported2 to have been observed to range from approximately 0.01 to 0.03 meter per second. A value of deposition velocity for molecular iodine of 0.015 meter per second has been 1. 42-C2 stated3 to lie within a factor of 5 for most reported observations exclusive of those influenced largely or in part by the airborne presence of methyl iodide. The value of 0.015 meter per second has been chosen, therefore, to represent an appropriate deposition velocity for molecular iodine. The iodine deposited on surface vegetation is not completely retained immediately following deposition. The fraction of deposited iodine that remains on vegetation shortly after deposition is termed the vegetation retention factor and is denoted here as k . Experiments 1 have been conducted to establish the value of this parameter under a variety of conditions. 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