Oxidation of U3Si2: The role of exothermic energy

Uranium silicide (U3Si2) is one of the candidate accident tolerant fuel materials under consideration for adoption in power producing nuclear reactors. The development of this fuel material including the bulk scale manufacturing route, and factors which may affect this route, are still under investigation. One such factor is the influence of oxygen on the material and the consequent release of exothermic energy. This work uses combined thermogravimetric and differential scanning calorimetry (DSC) methods to study oxidation of arc melted U3Si2 material, including ramp tests, isothermal experiments and varying particle sizes. It is found that there is a difference in mass gain profile between fragments and small powder samples, with fragments delivering the same heat load (∼4.6 ± 0.5 kJ.g−1) over a significantly shorter period of time. The measured exothermic heat output is in agreement with thermodynamic modelling once corrections have been made for the presence of elemental silicon in the reaction product. The onset temperature of rapid oxidation also reduces with particle size. Initial reactivities of freshly prepared powder samples during isothermal experiments give appropriate reaction constants, which are used to construct an Arrhenius plot. Supporting DSC data indicate that one of the higher temperature data points (275°C in this instance) had exhibited exothermic energy-induced self-heating and an accelerated rate of reaction. The resultant calculated activation energy from oxidation of freshly prepared U3Si2 powder is approximately 36 kJ.mol−1.