Contribution of ²³⁸U and ²³²TH to radiation dose and risk from fly ash effluent of coal-fired power plants
Date
2010
Authors
Beckfield, Felicity Cunningham, author
Johnson, Thomas, advisor
Woody, Robert, committee member
Volckens, John, committee member
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Abstract
The goal of this project was to determine the activity concentrations of 238U and 232Th emitted from a coal-fired power plant that could potentially impact human health and the environment. The activity concentration of 238U and 232Th in fly ash was used to estimate effluent uranium and thorium. The estimate of effluent activity was then used to model radiation dose and evaluate any associated increase in cancer risk to employees working in the plant and individuals living near the plant. Grab samples of fly ash were obtained and manually fractionated using the soil sizing techniques of sieving and pipetting. The respective samples were counted using alpha spectroscopy to determine the activity concentrations of 238U and 232Th. Whole body dose was calculated using 10 CFR 20 Appendix B annual limits on intake (ALI). The alpha emissions from 238U and 232Th are of particular interest as they are significant contributors to dose in the lungs and other tissues due to their high relative biologic effectiveness and short range. The results of this study indicate that fly ash contains both 238U and 232Th but is not a radioactive substance as defined by the IAEA transportation safety standards and Title 49 of the Code of Federal Regulations. Although the relative concentration of radionuclides in the fly ash of this study is quite low, it is still possible for individuals to receive a measurable dose. Exceeding occupational and public dose limits would require inhalation of approximately 1-1000 kg of fly ash for 232U and approximately 50 g to 20 kg for 232Th. The highest CEDE (ICRP 30) per unit mass incurred by inhalation of fly ash was class W 232Th (1.81 mrem g-1), while class W 238U had the lowest CEDE per unit mass (3.32 prem g-1). The general relationship between activity concentration of 238U and 232Th found using data from radiochemical analysis and particle size suggest that activity concentration increases with increasing particle size. However the relationship between activity concentration and particle size found in the literature suggests that activity concentration increases with decreasing particle size. The accompanying health risk from 238U and 232Th in fly ash is predicted to be less than 10-5 percent.
Description
Covers not scanned.
Print version deaccessioned 2022.
Print version deaccessioned 2022.
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Subject
Fly ash -- Environmental aspects
Radiation -- Dosage