Oxidation behaviour of U3Si2: an experimental and first principles investigation

Abstract

Uranium-containing metallic systems such as U₃Si₂ are potential Accident Tolerant Fuels (ATFs) for Light Water Reactors (LWRs) and the next generation of nuclear reactors. Their oxidation behaviour, especially in oxygen and water-enriched environments, plays a critical role in determining their applicability in commercial reactors. In this work, we have investigated the oxidation behaviour of U₃Si₂ experimentally and by theoretical computation. The appearance of oxide signatures has been established from X-ray diffraction (XRD) and Raman spectroscopic techniques after oxidation of the solid U₃Si₂ sample in synthetic air (oxygen and nitrogen). We have also studied the changes in the electronic structure as well as the energetics of oxygen interactions on the U₃Si₂ surfaces using first principles calculations in the Density Functional Theory (DFT) formalism. The detailed charge transfer and bond length analyses revealed the preferential formation of mixed oxides of UO₂ and SiO₂ on the U₃Si₂{001} surface as well as UO₂ alone on the U₃Si₂{110} and {111} surfaces. The formation of the peroxo (O₂²⁻) state confirmed the dissociation of molecular oxygen before U₃Si₂ oxidation. Core experimental analyses of the oxidized U₃Si₂ samples have revealed the formation of higher oxides from Raman spectroscopy and XRD techniques. This work is introduced to further a better understanding of the oxidation of U–Si metallic fuel compounds.