μ-XANES and X-ray μ-tomography study of oxidation state, morphology and chemistry evolution during nuclear fuel sintering

Nuclear waste management has led to recycling PuO₂ into nuclear fuel (Mixed OXides). Its manufacturing route involves a sintering process. A model is under construction in order to predict the evolution of the sample characteristics during sintering and to improve the sintering conditions. The small scale model aims to simulate grain size and chemistry evolution of μm large samples. In the green state, crystallites are 0.3 μm in size and made either of UO_2+x or of PuO_2-y. After sintering their size is close to 5μm and they have become a solid solution (U,Pu)O_2-z. At high temperature, sintering is governed by diffusion phenomena. Diffusion coefficients vary with point defect concentration. These defects are related to the oxidation state of the cations, the spatial distribution of which can be observed by means of g-X-Ray Absorption Spectroscopy (XAS). μ-XANES (X-Ray Absorption Near Edge Spectroscopy) and μ-X-Ray tomography pre-study experiments carried out at the ESRF (European Synchrotron Radiation Facility) ID22, Grenoble, have shown the ability of these techniques for such samples. It may be used to observe (U, Pu)O_2-z samples chosen along the sintering route, to check simulation validity.