Oxidation behaviour of USi: an experimental and first principles investigation.

Uranium-containing metallic systems such as USi 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 USi 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 USi 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 USi 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 UO and SiO on the USi{001} surface as well as UO alone on the USi{110} and {111} surfaces. The formation of the peroxo (O) state confirmed the dissociation of molecular oxygen before USi oxidation. Core experimental analyses of the oxidized USi 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.