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Crandallites and Coffinite: Retardation of Nuclear Reaction Products at the Bangombé Natural Fission Reactor

Published online by Cambridge University Press:  10 February 2011

K.A. Jensen ,
J. Janeczek ,
R.C. Ewing ,
P. Stille ,
F. Gauthier-Lafaye  and
S. Salah
K.A. Jensen
Affiliation:
University of Aarhus, Department of Earth Sciences, Aarhus, Denmark, keld@geo.aau.dk University of Michigan, Department of Nuclear Engineering and Radiological Sciences & Department of Geological Sciences, Ann Arbor, Michigan, USA
J. Janeczek
Affiliation:
University of Silesia, Faculty of Earth Sciences, Sosnoweic, Poland
R.C. Ewing
Affiliation:
University of Michigan, Department of Nuclear Engineering and Radiological Sciences & Department of Geological Sciences, Ann Arbor, Michigan, USA
P. Stille
Affiliation:
Centre National de la Recherche Scientifique, Centre de Geochimie de la Surface, Strasbourg Cedex, France
F. Gauthier-Lafaye
Affiliation:
Centre National de la Recherche Scientifique, Centre de Geochimie de la Surface, Strasbourg Cedex, France
S. Salah
Affiliation:
Centre National de la Recherche Scientifique, Centre de Geochimie de la Surface, Strasbourg Cedex, France
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Abstract

Various REE-Sr-(Pb)-crandallites, uraninite, and coffinite in the near-field of the 2 Ga old super-gene-altered Bangombé U-deposit and its natural fission reactor (RZB) have been examined. The crandallite minerals may have formed during syncriticality host-rock alteration, continous alteration of phosphates, episodic Pb-loss and/or supergene weathering. Coffinitization with P2O5 and SO4-substitution has occurred immediately below RZB and resulted in extensive loss of U (≤ 46%) and enrichment of Ce (≤ 190%) and Nd (≤ 780%). Additional loss of U during coffinitization also may have occurred due to dissolution. Current alteration under oxidizing conditions has resulted in partial dissolution of uraninite and coffinite and the formation of uranyl phases. Despite supergene alteration, the hydrogeochemistry (3.09 ppt U [235U/238U = 0.7012 to 0.7019%], 4.96 ppt Ce, and 1.92 ppt Nd) suggests a remarkable retardation of lanthanides and depleted uranium by REE-Sr-(Pb)-crandallites, uraninite, coffinite, and uranyl phases at RZB.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 608: Symposium QQ – Scientific Basis for Nuclear Waste Management XXIII , 1999 , 525
Copyright
Copyright © Materials Research Society 2000

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References

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