Processing, microstructure, leaching, and long-term stability studies related to titanate high-level waste forms

A process leading to titanate-based waste forms for commercial high-level nuclear waste is described. Radionuclides are fixed on hydrous calcium titanate by ion exchange/sorption reactions and the material is converted to a dense, ceramic form by hot pressing. Transmission electron microscopy-electron microprobe characterization was done to determine the effects of compositional changes and process variations on microstructure. Leaching studies in the range of 22 to 150/sup 0/C and pH 2 to 12 were done to assess the effects of the same variables on leaching behavior. Samples of a reference borosilicate glass waste form were leached under the same conditions to provide a direct comparison between the two waste forms. Lead-ion implantation was used to simulate long-term ..cap alpha..-recoil damage in the crystalline titanate phases. Comparison of ..cap alpha..-recoil damage in natural minerals with damage induced in synthesized samples of the same mineral suggest that Pb-ion implantation is a valid technique for simulating ..cap alpha..-recoil effects. All the titanate phases sustained significant lattice damage at equivalent ..cap alpha..-doses of 1 x 10/sup 19//cm/sup 3/; however, Rutherford backscattering and transmission electron microscopy studies showed that the damage did not result in significant matrix dissolution in these leaching tests.