Combined Electronic Structure and Empirical Potential Study of the AmO_2-x System

One objective of the nuclear industry is to improve its sustainability by increasing the reuse of spent fuel and reducing the amount of final waste and its radiotoxicity. Minor actinides are chemical elements produced by neutron capture in nuclear reactors, whose amount in the waste should be reduced. One solution envisaged, in particular for americium, is to separate it from the rest of the waste and to incorporate it in new fuels, for instance oxide fuels, to be re-irradiated in reactors [1]. It is therefore necessary to know with great accuracy the properties and behaviour of americium oxides which may form in these nuclear fuels.

Multiscale modelling methods are now essential tools to complement experimental characterizations of nuclear fuel materials and get further insight into the mechanisms governing their behaviour. Atomic scale modelling is at the basis of this approach as it enables one to obtain properties of studied systems using a physics-based description.

We will present the results of our investigation combining electronic structure calculations and empirical interatomic potentials to study the properties of the cubic phases of AmO_2-x as a function of temperature and composition (Oxygen over metal ratio). Structural properties, such as lattice parameter, thermal expansion coefficient and density; thermodynamic properties, i.e., enthalpy increment, specific heat capacity and melting temperature, as well as the reduction of AmO₂ in temperature, will be discussed.

This investigation is included in the PATRICIA project, which has received funding from the Euratom research and training programme 2019-2020 under grant agreement No 945077.

References
[1] Report on sustainable radioactive waste management (2012):
http://www.cea.fr/english/Documents/corporate-publications/report-sustainable-radioactive-waste-management.pdf