Application of micro-focused HERFD XRF/XAS to map the oxidation state of uranium in billion-year old altered minerals

This proposal aims to develop an understanding of the oxidation state of uranium (U) in natural titanate minerals that are analogues for materials under consideration for the immobilisation of plutonium (Pu). Using a range of natural mineral specimens subject to alteration by natural aqueous processes, we will use U M4-edge HERFD-XANES to underpin the mechanisms of U retention by these minerals over their long (< 1 billion years) lifetimes. Moreover, we will perform novel micro-focused U M4-edge HERFD-XRF oxidation state mapping, taking advantage of the unique capability of this technique to distinguish U oxidation states, to confirm the spatial distribution of U5+ in these minerals. These data are important to predict the long-term stability of synthetic titanate ceramic materials currently under consideration for the immobilisation of the UK’s Pu inventory, which will be disposed of in a geological disposal facility.