Evaluation of Fluorapatite as a Waste-Form Material

Fluorapatite, fluorinated calcium phosphate, has been identified as a potential matrix for the entombment of the zirconium fluoride fission product waste stream from the proposed FLEX process. If the efficacy of fluorapatitebased waste-storage can be demonstrated, then new and potentially more-efficient options for handling and separating high-level wastes, based on fluoride-salt extraction, will become feasible. This proposal will develop a dual-path research project to develop a process to fabricate a synthetic fluorapatite waste form for the ZrF4, FP waste stream, characterize the waste form, examine its performance under environmental conditions, and correlate the behavior of the waste form with natural analogs. Characterization of the material will be accomplished through probing the molecular-scale electronic and geometric structure of the materials in order to relate them to macroscopic properties, with the goal of developing techniques to evaluate and predict the performance of different waste-form materials. Time and funding permitting, other waste forms for the zirconium fluoride, fission product salt waste stream will be examined and benchmarked against the fluorapatite matrix baseline. Work Proposed for Academic Year 2002-2003 (8/02 – 7/03), Goals, and Expected Results: The work in the first year of the project will progress along two parallel paths: Fabrication and Natural Analog Characterization. The Fabrication path, led by the KRI team, will examine and evaluate various techniques for the fabrication of synthetic fluorapatite, will synthesis fluorapatite, and will begin the examination of waste loading and fabrication process factors on the synthetic fluorapatite. The Characterization path, led by the UNLV team, will refine the x-ray spectroscopy techniques currently in use to characterize borosilicate glass for HLW disposal and to examine these ceramic and synthetic mineral waste forms, and then apply these techniques to develop a molecularlevel understanding of natural fluorapatite and other fluorine-bearing natural phases as natural analogs for the waste form. These techniques will also be used to examine the changes in surface chemistry caused by environmental degradation of these materials. Preliminary samples of synthetic fluorapatite from the Fabrication path will also be examined as they are available.