The influence of particle size on the kinetics of UO2 oxidation in aqueous powder suspensions

Previous studies have indicated that the rate of a heterogeneous liquid–solid reaction depends on the size of the solid particles. It has been suggested that both the pre-exponential factor and the activation energy depend on the particle size. The processes involved in dissolution of UO ₂ have been extensively studied because of their importance for the safety analysis of a future deep repository for spent nuclear fuel and in many of these studies powder suspensions of UO ₂ are used as a model system. Therefore, it is of importance to investigate and quantify the particle size effect on the kinetics of UO ₂ oxidation in order to enable comparison of data from studies on different solid substrates. In this work the influence of particle size on the second order rate constant and on the activation energy of the reaction between MnO 4 - and UO ₂ was studied using aqueous UO ₂ -particle suspensions of four different size distributions. A comparative study of the activation energy for the reaction using a UO ₂ pellet was also performed.