Cheik Njifon Ibrahim1 Michel Freyss1 Roland Hayn2 Marjorie Bertolus1

1, CEA, St Paul Lez Durance, , France
2, IM2NP / Aix-Marseille Université, Marseille, , France

Electronic structure calculations of actinide based materials have long been challenging due to the complex properties of strongly correlated 5f electrons. The density functional theory (DFT) fails to capture these strong 5f electron correlations which govern, in particular in actinide oxides, various features such as magnetic properties, cation mixed valence and defect charge states. (U,Pu)O2 mixed actinide oxides are currently used in pressurized water reactors and are reference fuels for GEN IV reactors. Therefore, an accurate description of actinide oxide basic properties is essential for nuclear energy applications.
We use here the DFT+U approach and the occupation matrix control scheme (OMC) to model bulk properties of uranium-plutonium mixed oxides as a function of the Pu content using a static approach. Using ab initio molecular dynamics combined with DFT+U and the OMC scheme, we investigate UO2, PuO2 and (U,Pu)O2 bulk properties as a function of temperature in particular thermal expansion and variations of enthalpy of these compounds. This study aims at feeding thermodynamic database and will be extended to complex materials for which only few thermodynamic data are available, such as (U,Pu,Am)O2.