France has been committed to increasing the sustainability of nuclear energy in order to save uranium resources and reduce the amount of waste produced. This approach involves several steps: first, a transition from the plutonium current mono-recycling in pressurized water reactors to a multi-recycling of Pu in the same type of reactors, then in the longer term a multi-recycling of Pu in fast neutron reactors and finally the transmutation of the minor actinides produced under irradiation.
In the context of multi-recycling, current (U,Pu)O2 fuels will be recycled for the manufacture of new fuels, which will then contain a few percent of minor actinides, in particular americium and neptunium. It is therefore important to have a precise knowledge of the properties of the compounds in the (U-Pu-Am-Np-O) systems to improve fabrication processes and evaluate the impact of minor actinides on the behaviour of these reactor fuels, and in particular on the thermal properties at high temperature.
To obtain an optimized thermodynamic model of this complex system, a good description of the ternary and quaternary subsystems is essential. The (U-Pu-O) and (U-Am-O) systems have been revisited in recent years and are relatively well described. On the other hand, there are very few experimental data available on the (Pu-Am-O) system or on the neptunium bearing oxides. It is therefore necessary to get further insight into these systems and to complement the experimental results.
Atomic scale modelling methods (electronic structure calculations, empirical interatomic potentials) yield numerous properties of materials, in particular structural, electronic, mechanical and thermodynamic ones, which are extremely useful for understanding and/or predicting their behaviour under various conditions.
The objective of this project is to apply a combination of atomic scale modelling methods to calculate the structural and thermodynamic properties of compounds of the Uranium-Plutonium-Americium-Neptunium-Oxygen system to improve the description of their phase diagrams, in complement to experimental characterizations. The results will be used to feed thermodynamic models, in particular those of the TAF-ID international database.
The project will be carried out in a dynamic scientific environment at the Fuel Research Department (IRESNE Institute-CEA Cadarache) with, on the one hand the contribution to the development of simulation tools and the use of cutting edge experimental data in the field of fuel irradiation behaviour and on the other hand theoretical work applicable in many other domains. The work will benefit from several collaborations with laboratories from other CEA centres and will be part of a European collaborative project. The work will lead to the participation in national and international conferences and the writing of publications.