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Element Partitioning in a Pyrochlore-Based Ceramic Nuclear Waste form

Published online by Cambridge University Press:  21 March 2011

R. Gieré ,
C. Hatcher ,
E. Reusser  and
E. C. Buck
R. Gieré
Affiliation:
Earth & Atmospheric Sciences, Purdue University, West Lafayette, IN 47907-1397, USA;giere@purdue.edu
C. Hatcher
Affiliation:
Earth & Atmospheric Sciences, Purdue University, West Lafayette, IN 47907-1397, USA;giere@purdue.edu
E. Reusser
Affiliation:
Mineralogy & Petrography, ETH-Zentrum, CH-8092 Zürich, Switzerland
E. C. Buck
Affiliation:
Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352, USA
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Abstract

Pyrochlore-rich ceramics containing additional zirconolite, brannerite and rutile have been developed for immobilizing excess weapons plutonium. This study reports data for a ceramic containing small amounts of Al and Mo in addition to the major oxide components of Ti, U, Ca, Hf, Gd and Ce. Hafnium and Gd are added as neutron absorbers, Al and Mo represent impurities. Quantitative electron microprobe data demonstrate that UO2 is strongly partitioned into brannerite (45 wt%), which is present as euhedral crystals with inclusions of unreacted UO2. Pyrochlore forms the groundmass and has an average UO2 content of 28 wt%. Zirconolite contains only 15 wt% UO2, but is significantly more effective in accommodating Hf and Gd than both brannerite and pyrochlore. Zirconolite incorporates U together with Hf and Ce in one structural site, whereas brannerite and pyrochlore accommodate U with Gd in a site that is distinct from that occupied by Hf. Incorporation of Gd into zirconolite takes place via a coupled substitution involving Al, thus explaining the high Al2O3 contents (3 wt%). Molybdenum was not detected in the major oxides, and it might be present in the accessory rutile. Although the studied waste form was designed to incorporate Pu, the present dataset is also valuable because immobilization of highly fissile U (e.g., U-233) might need to be considered in the future.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 713: Symposium JJ – Scientific Basis for Nuclear Waste Management XXV , 2002 , JJ2.4
Copyright
Copyright © Materials Research Society 2002

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References

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