Atomic Scale Investigation of Americium Bearing Mixed Oxide Compounds

Americium is a chemical element produced by neutron capture in nuclear reactors, whose strong radiotoxicity is a major issue for the management of nuclear waste. One solution envisaged to reduce the amount of americium in the waste is to separate it from the other elements present in the fuel after its stay in the reactor and to re-irradiate in order to transform it into a less radiotoxic element thanks to a transmutation reaction [1].<br/>It is therefore necessary to evaluate the impact of Americium on the behaviour of these reactor fuels, and in particular on the thermal properties at high temperature. This requires, among other things, a very good knowledge of the Uranium-Plutonium-Americium-Oxygen thermodynamic system. For this, a good description of the ternary systems (U-Pu-O), (U-Am-O) and (Pu-Am-O) is a prerequisite. The (U-Pu-O) system has been revisited extensively in recent years and is relatively well described. Much less data is available on the Am-bearing oxides, especially at high temperature [2].<br/>Atomic scale modelling methods are now essential to complement the experimental characterizations of nuclear fuels and get further insight into their properties and behaviour. We will present the results of the investigation of the thermodynamic properties of (U,Am)O₂ as a function of composition and temperature using a combination of state-of-the-art empirical interatomic potentials and electronic structure calculations. We calculated especially enthalpy increments, mixing enthalpies, heat capacity and melting temperatures.<br/>This project has received funding from the Euratom research and training programme 2019-2020 under grant agreement No 945077<br/>References<br/>1 Report on sustainable radioactive-waste-management (2012): http://www.cea.fr/english/Documents/corporate-publications/report-sustainable-radioactive-waste-management.pdf<br/>2 C. Guéneau, A. Chartier, L. Van Brutzel, Thermodynamic and thermophysical properties of the actinide oxides, R. Konings, T. Allen, R. Stoller, S. Yamanaka (Eds.), Comprehensive Nuclear Materials (Vol-II), Elsevier, Amsterdam (2012)