A methodology for estimating an annual release from a diffuse transuranic source

United States government and industrial facilities that emit radioactive materials into the air are required to comply with the Environmental Protection Agency's (EPA) National Emissions Standards for Hazardous Air Pollutants (NESHAPs), 40 CFR 61 (EPA, 1992). According to the regulations, emissions of radionuclides to the ambient air shall not exceed those amounts that would cause any member of the public to receive, in any year, an effective dose equivalent of 10 mrem/y. The dose to members of the public from radionuclide emissions are to be determined using EPA approved modeling methods which require knowledge of the annual radionuclide releases. NESHAPs provides clear guidance for the determination of annual radionuclide releases from point sources (i.e., facility stacks and vents). However, NESHAPs does not provide sufficient guidance for the determination of radionuclide releases from diffuse or area sources. A methodology was developed to determine an annual airborne radionuclide release from a diffuse source based on data obtained from an aerial gamma-ray survey of transuranic contaminated soils. The diffuse radionuclide release was calculated using corrected surface-contamination concentrations and wind speed dependent resuspension rates. The aerial gamma-ray-survey results were corrected for additional radionuclides found in the contaminant source, radioactive decay, radioactive ingrowth, and resuspendable surface soil thickness. In addition, the results were converted from volumetric to area contamination. Using standard air dispersion models, the release can be used to estimate the dose to a given receptor due to each radionuclide in the source material