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Short description of the work
We have performed X-Ray Absoprtion Near Edge Structure (XANES) Studies on the sodium uranates Na3UO4, Na4UO5 and Na2U2O7 at the Rossendorf Beamline (ROBL, ESRF, Grenoble) under the Talisman framework. We have established the local structure and charge distribution of the uranium cation in those compounds. Na4UO5 and Na2U2O7 present uranium in the oxidation state (VI). In the case of the Na3UO4 compound however, XANES spectra have revealed uranium (VI) and not uranium (V) as expected. This has led us to revisit the compound’s structure and chemical composition, namely Na3.2U0.8O4, by incorporation of 20% excess sodium on the uranium site. Those results have direct consequences from thermodynamics’ perspectives for the fuel-sodium interaction.

 

Short description of the work
EXAFS experiments have been performed at the ROBL beamline on 15-18th june. Data were collected at 15K on nine different uranothorite solid solutions (Th1-xUxSiO4) and also three other additional samples used as standards containing Th4+, U4+ and U6+. The studied compounds were under the form pellets mixed with sugar and sealed in an appropriate teflon holders supplied kindly by Andreas Scheinost Almost all the data were collected in both transmission and fluorescence modes. The use of the fluorescence mode was justified by the low quantities of uranium in our samples. In this run, the studied uranothorite compounds are: USiO4 (as synthesized and purified), ThSiO4 (pure), Th0.2U0.8SiO4 (purified), Th0.5U0.5SiO4 (as synthesized, purified and post dissolution tests) and Th0.8U0.2SiO4 (purified and after the dissolution experiment). A final report will be submitted shortly.
Dr. Adel Mesbah

 

Short description of the work
We have performed the EXAFS measurements of 10 liquid samples at the uranium L3 edge, in fluorescence and transmission detection ([U] ~0.005-0.01M). Those samples were composed of ionic liquid phases in which uranium(VI) had been extracted via tributyl-phosphate or DMDBMA. Data analysis is in progress, it will give us the speciation of uranium in solution, as a function of the extraction conditions.

 

Short description of the work
The work carried out at the KIT-INE Laboratories included the flow through dynamic experiments for elution of U-contaminated sediments from the decantation waste of a U conversion facility (3 columns in total). The eluate was analysed for U, Th, pH and Eh and selected aliquots were analysed for alkalinity, cations and anions. In one of the columns U-233 was injected to investigate the retention of U. Strong retention of U was observed in all the experiments. Solid characterisation of the samples was conducted in parallel, comprising XPS and synchrotron measurements. The synchrotron measurements included bulk and micro analysis by XRF and XANES.

 


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