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Thermodynamic Stability of Actinide Pyrochlore Minerals in Deep Geologic Repository Environments

Published online by Cambridge University Press:  10 February 2011

Yifeng Wang  and
Huifang Xu
Yifeng Wang
Affiliation:
Sandia National Laboratories, 4100 National Parks Highway, Carlsbad, New Mexico88220. E-mail: ywang@sandia.gov
Huifang Xu
Affiliation:
Department of Earth and Planetary Sciences, The University of New Mexico, Albuquerque, New Mexico87131. E-mail: hfxu@unm.edu
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Abstract

Crystalline phases of pyrochlore (e.g., CaPuTi2O7, CaUTi2O7) have been proposed as a durable ceramic waste form for disposal of high level radioactive wastes including surplus weapons-usable plutonium. In this paper, we use a linear free energy relationship to predict the Gibbs free energies of formation of pyrochlore phases (CaMTi2O7). The Pu-pyrochlore phase is predicted to be stable with respect to PuO2, CaTiO3, and TiO2 at room temperatures. Pu-pyrochlore is expected to be stable in a geologic repository where silica and carbonate components are absent or limited. We suggest that a repository in a salt formation be an ideal environment for disposal of high level, pyrochlore-based ceramic wastes. In such environment, adding CaO as a backfill will make pyrochlore minerals thermodynamically stable and therefore effectively prevents actinide release from these mineral phases

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 608: Symposium QQ – Scientific Basis for Nuclear Waste Management XXIII , 1999 , 367
Copyright
Copyright © Materials Research Society 2000

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References

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