Advanced waste forms research and development. Annual report

Thermogravimetric analysis on cesium aluminosilicates was performed. Pollucite, CsAlSi2O6, appears to have more than adequate thermal stability for Cs fixation in supercalcine. The possibility of leaving Ru as RuO2 during supercalcine crystallization is being assessed. The apatite solid solution [A/sub ss/] phases used in supercalcine phase formation models have been easily prepared as pure phases. Use of Ca instead of Sr as an alkaline earth additive yields a more stable A/sub ss/ phase. Weight ratios have been optimized for two firing temperatures in terms of soxhlet leachability. However, this is not the preferred approach to supercalcine consolidation. The phase formation models developed for PW-4b-type wastes were routinely applied to PW-7, in spite of several significant composition differences in the latter. Uranium oxide remains as a fluorite structure oxide after supercalcine crystallization, but it does seem to have incorporated either or both CeO2 or ZrO2. Characterization of this F/sub ss/ phase will require further study. Based on observations during several complex compatibility studies, it appears that good overall thermal stability at as high as 12000C might be attainable for nepheline based supercalcine formulations. A thorough literature review of the oxide crystal chemistry of Te has been completed