2, IM2NP / Aix-Marseille Université, Marseille, , France
3, CEA, DAM, DIF, Arpajon, , France
Uranium-plutonium mixed oxide (MOX) fuel with about 25% of Pu content is the reference nuclear fuel for the future Gen IV fast neutron reactor in France. It will be fabricated from spent fuel coming out of the current pressurized water reactors and will, as a consequence, contain a few percent of Am (less of 5%). The high radiotoxicity of Pu makes the MOX fuel difficult to handle experimentally and, consequently, experimental data on this compound are scarce. The main goal of this study is to determine the effect of americium on the properties of the mixed actinide oxide fuel (U, Pu)O2 containing americium in low concentration, by comparison of the results obtained for (U, Pu)O2 to those obtained for (U, Pu, Am)O2.
Electronic structure calculations based on the DFT+U approach are used. The occupation matrix control (OMC) scheme is also used to avoid convergence of the calculations to metastable states. As a first step, we calculate bulk properties and thermodynamic properties (thermal expansion, variation of enthalpy …) of AmO2 as the function of U and J parameters of DFT+U. In order to get insight into the influence of americium on irradiation damage in oxide fuels, the formation and migration energies of points defects (vacancies, interstitial, Schottky defects) calculated in (U, Pu)O2 for various Pu contents are compared to those obtained in (U, Am)O2.