Basic research for assessment of geologic nuclear waste repositories: What solubility and speciation studies of transuranium elements can tell us.

摘要

Solubility and speciation data are important in understanding aqueous radionuclide transport through the geosphere. They define the source term for transport retardation processes such as sorption and colloid formation. Solubility and speciation data are useful in verifying the validity of geochemical codes that are part of predictive transport models. Results from solubility and speciation experiments of (sup 237)NpO(sub 2) (sup +), (sup 239)Pu(sup 4+), and (sup 241)Am(sup 3+)/Nd(sup 3+) in J-13 groundwater (from the Yucca Mountain region, Nevada, which is being investigated as a candidate high-level nuclear waste disposal site) at three different temperatures (25(degrees), 60(degrees), and 90(degrees)C) and pH values (6, 7, and 8.5) are presented and compared with published modeling calculations. The comparison results indicate that there is a great need for experimental data on the solubility and speciation of transuranium elements under a wide range of conditions, for example, pH, Eh, temperature, and composition of groundwaters. Additionally, the influence of alpha radiation and the radiolysis of the secondary transuranium solids on solubility and speciation should be studies. Solubility studies and model calculations should be extended to other important long-lived nuclear waste radionuclides such as nickel, zirconium, cadmium, radium, and thorium. 14 refs., 13 figs., 5 tabs.