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In Situ Isotopic Analysis of Uraninite Microstructures from the Oklo-Okélobondo Natural Fission Reactors, Gabon

Published online by Cambridge University Press:  21 March 2011

Mostafa Fayek ,
Keld A. Jensen ,
Rodney C. Ewing  and
Lee R. Riciputi
Mostafa Fayek
Affiliation:
Dept. Geol. Sci., University of Tennessee, Knoxville, TN 37996 Chemical Sciences Division, Oak Ridge National Lab, Oak Ridge TN 37831
Keld A. Jensen
Affiliation:
National Institute of Occupational Health, Denmark, DK-2100 Copenhagen
Rodney C. Ewing
Affiliation:
Dept. Nuclear Engineering and Rad. Sci., Univ. Michigan, Ann Arbor MI 48109-2104
Lee R. Riciputi
Affiliation:
Dept. Geol. Sci., University of Tennessee, Knoxville, TN 37996 Chemical Sciences Division, Oak Ridge National Lab, Oak Ridge TN 37831
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Abstract

Uranium deposits can provide important information on the long-term performance of radioactive waste forms because uraninite (UO2+X) is similar to the UO2 in spent nuclear fuel. The Oklo-Okélobondo U-deposits, Gabon, serve as natural laboratory where the long-term (hundreds to billions of years) migration of uranium and other radionuclides can be studied over large spatial scales (nm to km). The natural fission reactors associated with the Oklo- Okélobondo U-deposits occur over a range of depths (100 to 400 m) and provide a unique opportunity to study the behavior of uraninite in near surface oxidizing environments versus more reducing conditions at depth. Previously, it has been difficult to constrain the timing of interaction between U-rich minerals and post-depositional fluids. These problems are magnified because uraninite is susceptible to alteration, it continuously self-anneals radiation damage, and because these processes are manifested at the nm to μm scale. Uranium, lead and oxygen isotopes can be used to study fluid-uraninite interaction, provided that the analyses are obtained on the micro-scale. Secondary ionization mass spectrometry (SIMS) permits in situ measurement of isotopic ratios with a spatial resolution on the scale of a few μm. Preliminary U-Pb results show that uraninite from all reactor zones are highly discordant with ages aaproaching the timing of fission chain reactions (1945±50 Ma) and resetting events at 1180±47 Ma and 898±46 Ma. Oxygen isotopic analyses show that uraninite from reactors that occur in near surface environments (δ18O= −14.4‰ to −8.5‰) have reacted more extensively with groundwater of meteoric origin relative to reactors located at greater depths (μ18O= −10.2‰ to −7.3‰). This study emphasizes the importance of using in situ high spatial resolution analysis techniques for natural analogue studies.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 713: Symposium JJ – Scientific Basis for Nuclear Waste Management XXV , 2002 , JJ8.5
Copyright
Copyright © Materials Research Society 2002

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References

REFERENCES

1. Janeczek, J., Ewing, R.C., Oversby, V.M., Werme, L.O., J. NUCL. MATER. 238: 21–130 (1996).Google Scholar
2. Holliger, P., 8th Internat. Sims Conf. Proc., 719–722 (1991).Google Scholar
3. Gauthier-Lafaye, F., Holliger, P., Blanc, P-L., Geochim. Cosmochim. 60, 4831–4852 (1996).Google Scholar
4. Fayek, M., Kyser, T.K., Can. Min. 35, 627–658 (1997).Google Scholar
5. Fayek, M., Kyser, T.K., Geochim. Cosmochim. 64, 2185–2197 (2000).Google Scholar
6. Fayek, M.et al., Inter. Geol. Rev. 42–2, 163–171 (2000).Google Scholar
7. Fayek, M.et al., Chem Geol., in press (2001).Google Scholar
8. Jensen, K.A., Ewing, R.C., Nuclear Science and Technology Eur 19116 EN, 61–91 (2000).Google Scholar
9. Jensen, K.A., Ewing, R.C., Gsa Bulletin 113, 32–62 (2001).Google Scholar
10. Valley, J.W.et al., Soc. Econ. Geol. Rev. 7 (1997).Google Scholar
11. Holliger, P., Cathelineau, M., Chem. Geol. 70: 173 (1988).Google Scholar
12. Cathelineau, M., Boiron, M.C., Holliger, P., Poty, B., Tectonophyscics 177, 55–79 (1990).Google Scholar
13. Gauthier-Lafaye, F., Weber, F., Econ. Geol. 84, 2267–2285 (1989).Google Scholar
14. Parnell, J., Min Mag 60, 581–593 (1996).Google Scholar
15. Naudet, R., Interdisciplinary Science Reviews 1, (Heyden & Son. London, United Kingdom, 1976), pp. 72–84.Google Scholar
16. Bros, R., Earth. Planet. Sci. Lett. 113, 207–218 (1992).Google Scholar
17. Michaud, V., Mathieu, R., Tech. Rep. No. 98/176 (Commissariat a L'energie Atomique/Dcc/Desd/Sesd, France, 1998).Google Scholar
18. Sere, V., thesis, Universite De Paris VII (1996).Google Scholar
19. Louvat, D., Michaud, V., Maravic, H. von, Nuclear Science and Technology Eur 19137 EN, 427p (1999).Google Scholar
20. Pourcelot, L., Gauthier-Lafaye, F., Nuclear Science and Technology Eur 19116 EN, 93–105 (1998).Google Scholar
21. Louvat, D., Toulhaut, P., Smellie, J., Contract Cce N F12W-CT 91–0071 (Commissariat a L'Energie Atomique/IPSN, France, 1995).Google Scholar
22. , Ludwig, Usgs, Open File Rep. 91–445, 1–42 (1993).Google Scholar
23. Evins, L.Z., J. African Earth Sci., submitted.Google Scholar
24. Evins, L.Z., Chem. Geol., submitted.Google Scholar
25. Rogers, J. Geology 104, 91–107 (1996).Google Scholar