Tonya Vitova

High Energy Resolution X-ray Absorption and Emission Investigations for Actinide Systems
Presenter Tonya Vitova

High energy resolution x-ray absorption spectroscopy (HR-XAS) and inelastic x-ray scattering (IXS) combined with quantum theoretical tools are gaining importance for understanding electronic and coordination structures as well as for speciation investigations of actinide (An) materials [1]. HR-XAS is successfully used to remove spectral broadening by registering the partial fluorescence yield emitted by the sample, thereby yielding highly resolved x-ray absorption near edge structure spectra (HR-XANES), which often display resonant features not observed in conventional XAS [1].

We demonstrate the structural characterization capabilities of these novel techniques by discussing results from both model and complex U and Pu materials [1,2]. For example, we have investigated recently the U redox states of U interacted with magnetite nanoparticles and unambiguously demonstrate that U(V) can exist, along with U(IV) and U(VI), in samples kept under anoxic conditions. This result is of importance for understanding the interaction processes of uranium with corrosion products, which can potentially form in a long term nuclear waste repository.

Understanding the long term behavior of vitrified nuclear waste stored in a long term nuclear waste repository requires a full and detailed characterization of the materials as they are synthesized and during exposure to the environment. Industrial glasses are complex, and we took a simplified separate effect approach to elucidate key properties of a simulated glass. In particular, results from U and Pu oxidation states characterization of U and Pu in simulated glass containing varying U or Pu loadings and a highly active glass sampled from the "Verglasungseinrichtung Karlsruhe" (VEK) vitrification process of reprocessed high level nuclear waste will be presented and discussed.

[1] a) T. Vitova et al., Phys. Rev. B 82 (2010) 235118; b) T. Vitova et al., Journal of Physics: Conference Series 430 (1) (2013), 012117; c) R. Caciuffo et al., Phys. Rev. B 81 (2010) 195104.
[2] a) R. Böhler et al., Journal of Nuclear Materials 448 (2013) 330; b) A. Walshe, Dalton Trans. 43 (2014) 4400; c) H. Damien et al., Chem. Eur. J., 20 (2014) 10431.