6533b85bfe1ef96bd12bbb6d

RESEARCH PRODUCT

Study of the oxidation mechanisms of Plutonium

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Oxidation is a key point when applied to a material such as plutonium. It is essential to understand the oxidation mechanisms in order to predict and prevent catastrophic oxidation, thus managing the reprocessing cost.The originality of this work lies in the coupling of different experimental techniques : in-situ X-ray diffraction, Photo-electron spectroscopy (XPS), FIB-SEM, Raman spectrometry and X-ray absorption (EXAFS) with numerical techniques : CALPHAD and Reverse Monte Carlo, in order to determine the oxidation mechanisms of the studied alloy : -phase stabilised PuGa 1 at%.Study of oxidation of this alloy at different temperatures and oxygen partial pressures showed the oxidation kinetics consists first of parabolic growth of a Pu2O3-layer, with  and  dimorphism, and is followed by a linear growth of a PuO2-layer.Furthermore, the highlight of anionic scale growth and pressure-dependant oxidation kinetics allowed to conclude, in accordance with Wagner’s model, that interstitial oxygen was the main point-defect causing the scale growth. Its self-diffusion coefficient has been determined by PuO2 self-reduction.Destabilisation of the alloy during the oxidation has been observed at the oxide/substrate interface, with the formation of a layer composed of pure Pu stable phase, highlighting the existence of a gallium diffusion process. This work has shown that gallium diffuses into the PuO2 structure, either in substitution of Pu or in insertion in the octahedral site.Finally, this work has revealed that presence of carbon in the alloy could lead, in certain temperature and pressure conditions, to the formation of an oxycarbide PuCxO1-x, which has a limiting effect on oxidation kinetics.