Instability of U₃Si₂ in pressurized water media at elevated temperatures

Following the Fukushima Daiichi accident, significant efforts from industry and the scientific community have been directed towards the development of alternative nuclear reactor fuels with enhanced accident tolerance. Among the proposed materials for such fuels is a uranium silicide compound (U₃Si₂), which has been selected for its enhanced thermal conductivity and high density of uranium compared to the reference commercial light water reactor (LWR) nuclear fuel, uranium oxide (UO₂). To be a viable candidate LWR fuel, however, U₃Si₂ must also demonstrate that, in the event of this fuel coming in contact with aqueous media, it will not degrade rapidly. In this contribution, we report the results of experiments investigating the stability of U₃Si₂ in pressurized water at elevated temperatures and identify the mechanisms that control the interaction of U₃Si₂ under these conditions. Our data indicate that the stability of this material is primarily controlled by the formation of a layer of USiO₄ (the mineral, coffinite) at the surface of U₃Si₂. The results also show that these layers are destabilized at T > 300 °C, leading to the complete decomposition of U₃Si₂ and its pulverization due to its full oxidation to UO₂.