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Carbonaceous substances in Oklo reactors—Analogue for permanent deep geologic disposal of anthropogenic nuclear waste

By
David J. Mossman
David J. Mossman
Department of Geography, Mount Allison University, 144 Main Street, Sackville, New Brunswick E4L 1A7, Canada
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François Gauthier-Lafaye
François Gauthier-Lafaye
Centre de Géochemie de la Surface, Centre National de la Recherche Scientifique, 1 rue Blessig, 67084 Strasbourg Cedex, France
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Adriana Dutkiewicz
Adriana Dutkiewicz
School of Geosciences, University of Sydney, Sydney, New South Wales 2006, Australia
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Ralf Brüning
Ralf Brüning
Department of Physics, Mount Allison University, 67 York Street, Sackville, New Brunswick E4L 1E6, Canada
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Published:
January 01, 2008

Abstract

Seventeen known natural nuclear fission reactors sustained criticality in hydrothermally altered low-grade metasedimentary rocks of the Proterozoic Franceville Series ca. 1968 ± 50 Ma. About half of these reactors contain only traces of carbonaceous substances, and in these, fission products including strontium, cesium, rubidium, and boron migrated away from the reactors and were nearly completely lost. The others are rich in carbonaceous substances, particularly solid, partly graphitized bitumen and kerogen, as well as liquid oil in fluid inclusions. In these carbonaceous substance–rich reactors, uranium and fissiogenic isotopes are held in uraninite, which became enclosed in liquid bitumen during criticality and was subsequently fixed when the bitumen solidified. The preservation of liquid oil in fluid inclusions for over two billion years suggests that time is not a parameter that controls petroleum degradation. This is viewed as a potentially important aspect in engineered nuclear waste containment projects. Likewise, because of the hydrophobic qualities of solid bitumen, its inducible plasticity, and its capability of conversion to nonflammability, it deserves serious consideration for use in permanent deep geologic disposal sites. Indications are that at Oklo, Gabon, carbonaceous substances have combined to restrain the migration of radionuclides and limit the extent to which migration occurs. The strength of the Oklo analogue lies in the fact that it represents more extreme conditions than those likely to be met in a deep geologic repository. The carbonaceous substance–rich reactors of Oklo stand as time-tested analogues for anthropogenic nuclear waste containment strategies.

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Contents

GSA Reviews in Engineering Geology

Deep Geologic Repositories

Norbert T. Rempe
Norbert T. Rempe
1403 N. Country Club Circle Carlsbad, New Mexico 88220, USA
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Geological Society of America
Volume
19
ISBN electronic:
9780813758190
Publication date:
January 01, 2008

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