Solubility and Speciation Results from Over- and Undersaturation Experiments on Neptunium, Plutonium, and Americium in Water from Yucca Mountain Region Well UE-25p {number_sign}1 PDF Download

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Languages : en
Pages : 95

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Book Description
Solubility and speciation are important in understanding aqueous radionuclide transport through the geosphere. Results are compared from solubility and speciation experiments from oversaturation and undersaturation of 237NpO{sub 2{sup +}}, 239Pu{sup 4+}, and 241Am{sup 3+}/Nd{sup 3+} in a modified UE-25p-1 groundwater (from the Yucca Mountain region, Nevada, which is being investigated as a potential high-level nuclear waste disposal site) at 60 C and three pH values (6.0, 7.0, 8.5). In the oversaturation experiments, the solubility-controlling steady-state solids were identified and the speciation and/or oxidation states present in the supernatant solutions were determined. The characterized solids were then reintroduced into fresh solutions of the modified UE-25p-1 groundwater to approach the steady state from undersaturation. For the undersaturation experiments, the solubility-controlling steady-state solids were also identified and the speciation and/or oxidation states present in the supernatant solutions were determined. The Np solubility decreased with increasing pH in both the over- and undersaturation experiments. The steady-state concentrations from the two experiments agreed to within an order of magnitude. Pu concentrations from over- and undersaturation agree very well in the pH 6 and 7 experiments. The pH 8.5 oversaturation experiment resulted in a steady-state concentration one order of magnitude above its undersaturation counterpart. For the Am/Nd solutions, the pH 6 and pH 7 experiments resulted in equivalent steady-state concentrations from both over and undersaturation. The pH 8.5 oversaturation experiment was 100 times more soluble than its undersaturation counterpart. 48 refs.