Uranyl minerals as models for storage of spent nuclear fuels

Storage of Spent Nuclear Fuels (SNF) in geological repositories is the favoured method for a number of EU countries. Under moist oxidising conditions, UO2 will likely oxidise to uranyl compounds via a number of phase changes. These have been characterised on the weathering of uranium ores and on the surface of UO2 and SNF [1]. These phases can sorb radionuclides such as neptunium and therefore alter the migration rates into the near-field. We will present our recent work on the characterisation of the unusual mineral studtite, [UO2(η2-O2)(H2O)2].2H2O, using solid-state electrochemistry [2] and X-ray spectroscopy (U L3-EXAFS and High Energy Resolution-XANES) [3] (Figure); both techniques have the potential to give important information on the electronic structure of actinide complexes but are not currently well utilised. We will discuss the use of Eu(III) as a model for Am in the sorption onto the surface of selected minerals, which has directed our efforts in 241Am(III) incorporations. These have been characterized by emission spectroscopy and γ-spectrometry using emission spectroscopy, and the reactions of 237Np(V) with selected mineral phases, studied by multi-element X-ray spectroscopy. ... mehrFigure. U L3-edge HR-XANES spectrum (left) and solid state cyclic voltammogram (right) of studtite.