| Summary: | Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2001. === Includes bibliographical references (p. 64-66). === In order to better understand the behavior of thorium breeder reactor fuel in a repository environment, the behavior of thorium oxide was investigated. The kinetics of crystalline thorium oxide dissolution were studied under argon and argon/10% CO2 over a broad pH range in 0.1 M ionic strength NaC1O4 solution. Samples were analyzed for thorium concentration using ICP-AES, ICP-MS, and NAA. Data was fit to a first order kinetics model. The kinetic rate constant under pure argon was 0.0107 ± 0.00123 h-1 for pH 2-3. Under 10% CO2, the rate constant was 0.00511 ± 0.000863 h-1. No kinetics results could be discerned from the data at higher pH. Under argon, solubility at pH greater than 3 was at nm/L levels, three orders of magnitude lower than at pH 3 and below. Under 10% CO2, solubilities decreased from 10 [mu]mol/L at pH 2.06 to 80 nm/Lat pH 3. Thorium oxide powder remnants from each experiment were analysed using XRD, FflR, and BET surface area analysis. Surface area analysis showed a 15% increase in surface area at pH 10 and higher under argon, and a uniform surface area increase of 15 to 30% under 10% CO2. XRD and FfIR spectra showed that the thorium oxide was otherwise identical to the untreated standards. === by Virginia Curran. === S.M.
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