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  • Organic matter and uraninite from the Oklo natural fission reactors: Natural analogue of radioactive waste containing bitumen and UO(2) irradiated fuel


Spontaneous fission chain reactions occurred two billion years ago in the Oklo sedimentary basin in bitumen-rich sandstones. Studies related to uranium ore deposits have shown that sedimentary organic matter associated with uranium may be altered by irradiation related to the natural decay of (238)U and to the (235)U fission process. This research programme aimed to use the intense irradiation of the organic matter at Oklo to investigate this effect in the case of bitumen matrix for radioactive waste. The investigations focused on the effects of radiation on the chemical structure of organic matter, on the role of the organic matter as reaction buffer and on its ability to trap fission products. The modifications affecting the structure of the organic matter were studied by Specular reflectance Fourier transform micro infrared spectroscopy (micro FTIR). The morphology and texture of bitumens and mineral inclusions were observed by optical microscopy. The combination of petrographic, spectroscopic and isotopic studies allowed the different types of organic matter to be distinguished. The results suggest that the organic matter in the reaction zone has been submitted to thermal alteration and radiolysis, while simultaneously the radiolysis of large amounts of water has produced hydrogenation of aromatic rings.

Additional information

Authors: HOLLIGER P, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR);LOUVAT D, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR);LANDAIS P, Centre national de la recherche scientifique CREGU, Nancy (FR);KRUGE M, Centre national de la recherche scientifique CREGU, Nancy (FR);RUAU O, Centre national de la recherche scientifique CREGU, Nancy (FR)
Bibliographic Reference: EUR 17614 EN (1997) 63pp., FS, ECU 13.50
Availability: Available from the (2)
ISBN: ISBN 92-828-0176-4
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