Corrosion and interdiffusion studies of U₃Si₂

U₃Si₂ is a candidate fissile phase for use in accident tolerant fuel systems because of its higher fissile density, higher thermal conductivity when compared to uranium dioxide. It is also expected to have acceptable performance in contact with high temperature water (e.g., a leaker event from breached cladding) and in regards to interaction with different cladding materials. In high temperature water, U₃Si₂ is expected to form a protective SiO₂ coating. However, the resistance of U₃Si₂ to corrosion under light water reactor service conditions has been previously unknown. In this study, the corrosion tests of sintered U₃Si₂ discs were conducted in pressurized water at 300°C in an autoclave. The exposure times to corrosion were 6 hours and 24 hours. Detailed composition and microstructural analysis were carried out using a combination of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Only slight weight change of U₃Si₂ discs can be detected in corrosion tests up to 24 hours. A layered structure of corrosion products formed on U₃Si₂, with a glassy silicon oxide layer at the top followed by a nanocrystalline UO₂ layer, a Sirich oxide layer and then a mixture oxide layer of U and Si. A diffusion couple of U₃Si₂ in contact with Zircaloy-4 has been tested at 800°C up to 100 hours. The resulting microstructure and interdiffusion has been studied with SEM/EDS. Some limited interdiffusion has been observed in these tests, and a layer containing Zr and Si forms between the U₃Si₂ disc and the Zircaloy-4 disc.