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Geochemical Behaviour of Uranium in Sedimentary Formations: Insights From a Natural Analogue Study

[+] Author Affiliations
Ulrich Noseck, Thomas Brasser

Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH, Braunschweig, Germany

Vaclava Havlova, Radek Cervinka

Nuclear Research Institute Řež plc, Řež, Czech Republic

Juhani Suksi

University Helsinki, Helsinki, Finland

Paper No. ICEM2009-16340, pp. 839-844; 6 pages
doi:10.1115/ICEM2009-16340
From:
  • ASME 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management
  • ASME 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management, Volume 2
  • Liverpool, UK, October 11–15, 2009
  • Conference Sponsors: Nuclear Engineering Division and Environmental Engineering Division
  • ISBN: 978-0-7918-4408-3 | eISBN: 978-0-7918-3865-X
  • Copyright © 2009 by ASME

abstract

Groundwater data from the natural analogue site Ruprechtov have been evaluated with special emphasis on the uranium behaviour in the so-called uranium-rich clay/lignite horizon. In this horizon in-situ Eh-values in the range of −160 to −280 mV seem to be determined by the SO42−/HS− couple. Under these conditions U(IV) is expected to be the preferential redox state in solution. However, on-site measurements in groundwater from the clay/lignite horizon show only a fraction of about 20% occurring in the reduced state U(IV). Thermodynamic calculations reveal that the high CO2 partial pressure in the clay/lignite horizon can stabilise hexavalent uranium, which explains the occurrence of U(VI). The calculations also indicate that the low uranium concentrations in the range between 0.2 and 2.1μg/l are controlled by amorphous UO2 and/or the U(IV) phosphate mineral ningyoite. This confirms the findings from previous work that the uranium (IV) mineral phases are long-term stable under the reducing conditions in the clay/lignite horizon without any signatures for uranium mobilisation. It supports the current knowledge of the geological development of the site and is also another important indication for the long-term stability of the sedimentary system itself, namely of the reducing geochemical conditions in the near-surface (30m to 60 m deep) clay/lignite horizon. Further work with respect to the impact of changes in redox conditions on the uranium speciation is on the way.

Copyright © 2009 by ASME
Topics: Uranium

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