Uranium under reducing conditions - Characterization of aqueous speciation and relevant solid phases
The major purpose of my work is the provision of quality assured thermodynamic data for both tetra- and hexavalent uranium. This shall enable a better assessment of speciation in diluted to highly saline solutions as expected near nuclear waste repositories. Namely, increase conservatism and uncertainties applied so far in long-term safety assessments shall be reduced, and consequently confidence in quantitative modelling. Respective experiments are based on parallel developments in electrochemical and spectroscopic tools being complementary to each other. In such a way difficult to access, systems and conditions should be explored to obtain an integral overview about aqueous uranium chemistry. This especially holds for reducing conditions. Simultaneously, experiments are expected to validate the new speciation methods. My work covers speciation studies by a large set of spectroscopy methods. This set has complementary strengths and provides rather low detection limits, down to 10−4 molar for U (IV) and 10−10 molar molar for U (VI). This will not only promote the characterization of complex system, e.g., encountered in nuclear waste management, but also allow a fingerprinting of unknown substances and mixtures which is more reliable than just being based on only one spectroscopy.
I started to investigate the spectroscopic characteristics of U(IV) and U(VI) in different background media (ClO4−, Cl−, SO42−, PO43−, CO32−)using UV/vis, Fluorimetry and TRLFS. All data (thermodynamic as well as associated ion-ion-interaction parameters) will be implemented into the THEREDA database.
- TLFRS (time resolved laser-induced fluorescence spectroscopy)
- LIPAS (laser-induced photoacoustic spectroscopy)
- ATR FT-IR (attenuated total reflection Fourier-transform infrared spectroscopy)
- EXAFS (extended X-ray absorption fine structure)
This work is embedded into the EDUKEM project, a collaboration with Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Braunschweig) and Karlsruhe Institute of Technology.