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Uraninite: a 2 Ga Spent Nuclear Fuel from the Natural FissionReactor at Bangombé in Gabon, West Africa

Published online by Cambridge University Press:  03 September 2012

K. A. Jensen ,
R. C. Ewing  and
F. Gauthier-Lafaye
K. A. Jensen
Affiliation:
Department of Earth Sciences, Aarhus University, DK-8000 Aarhus C, keld@geo.aau.dk
R. C. Ewing
Affiliation:
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131
F. Gauthier-Lafaye
Affiliation:
Centre National de la Recherche Scientifique, Centre de Geochemie de la Surface, 67084 Strasbourg Cedex, France
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Abstract

Uraninites from the Bangombé natural fission reactor (RZB) and “normal”uranium-ore occur as fine veins in the sandstone host-rock as well asaltered, broken, and slightly displaced grains in an illitic matrix, and innodules and veins of solid bitumen. Inclusions of galena, (Y,Gd)-richphosphates, a Pb-oxide and a Ti-oxide? were observed. Uraninites just belowRZB were partially altered to a uranyl-sulfate. Three generations ofuraninite were identified based on their PbO-contents of 8–11.06 wt%, 6 wt%(the largest population), and a younger generation with 3 wt%. The highPb-uraninites may be the precursor to the low Pb-uraninites. Diffusionalloss of Pb is indicated by the presence of a Pb-oxide at the interface tothe uraninites. The behaviour of the metallic fission products, incompatiblewith the uraninite structure, may mimic the behaviour of Pb in theseuraninites. The averaged impurity-content ranges from 4.29 to 6.89 wt%, andconsists mainly of SiO2, TiO2, ZrO2, FeO,CaO, Al2O3 and P2O5. Theaveraged content of Y2O3 and the Ln's is less than0.78 wt% and there is a scattered positive correlation with P2O5. The content of Y + Ln's is generally highestin the uraninites from RZB. Uraninite hydration and the formation of“uranopelite/zippeite” have caused complete loss of Y and the Ln's. Theseelements seems also to be partially lost by weak phosphatiancoffinitization. The analytical results indicate that Y and the Ln's, whichare high yield fission products, may be released from uraninite duringalteration in the presence of P.

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Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 465: Symposium II – Scienfific Basis for Nuclear Waste Management XX , 1996 , 1209
Copyright
Copyright © Materials Research Society 1997

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References

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