DISTRIBUTION AND SOLUBILITY OF RADIONUCLIDES IN WASTE FORMS FOR DISPOSITION OF PLUTONIUM AND SPENT NUCLEAR FUELS: PRELIMINARY RESULTS

摘要

Funded by the U.S. Department of Energy (DOE) Environment Management Science Program (EMSP), a multi-institutional research team lead by the Pacific Northwest National Laboratory (PNNL) is currently studying structural aspects of radionuclides, their surrogates, and neutron absorbers in several waste forms (glass, ceramics, and vitreous ceramics) structure and how composition and structure of the waste forms and processing conditions (oxidizing versus reducing conditions) affect their partitioning and solubility limits in these waste forms. In this article, the research methodology is first reviewed. Then, preliminary results are presented, which were obtained from studies of i) the effects of glass composition (in terms of Al_2O_3, B_2O_3, and Na_2O) on solubility limits of HfO_2 and Gd_2O_3, ii) the effects of Pu oxidation states on its solubility limit in borosilicate glasses, and iii) the effects of U oxidation states and composition (in terms of Na_2O) on its solubility limit in soda-lime silicate glasses. The most significant finding from the current study is that Pu~(3+) is shown to be more soluble (by at least 150%) than Pu~(4+) in borosilicate glass.