Development and application of an interatomic potential for the investigation of mixed oxide compounds containing Americium
Résumé
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].
This requires, among other things, a very good knowledge of the thermodynamic properties of the Am bearing oxides in order to control the process of manufacturing fuels containing this element and to predict the phases formed under irradiation as a function of the composition and the temperature.
Atomic scale modelling, and in particular, methods using empirical interatomic potentials, is a suitable tool for the calculation of thermodynamic properties to complement experimental characterizations. It requires, however, precise potentials describing the interactions between atoms. A formalism adapted to actinide oxides is that of the n-body potential developed by Cooper, Rushton and Grimes (CRG) for many simple oxides, including UO2, AmO2, PuO2 [2,3] and for the (U,Th)O2 [4] and (U,Pu)O2 mixed oxide [5].
We parameterized a potential for Americium with the oxidation state + III in the CRG formalism and validated it against available experimental data. The potential was then applied to determine thermodynamic properties of (U,Am)O2 as a function of Am content and/or temperature, in particular enthalpy increments, heat capacity and melting temperatures.
References
1 Report on sustainable radioactive-waste-management (2012): http://www.cea.fr/english/Documents/corporate-publications/report-sustainable-radioactive-waste-management.pdf
2 M.W.D. Cooper, M.J.D. Rushton, R.W. Grimes, J. Phys.: Condens. Matter 26, 105401 (2014)
3 Potential Model for Actinide Oxides and their Solid Solutions, http://abulafia.mt.ic.ac.uk/potentials/actinides/v1.2/index.html
4 M.W.D. Cooper, S.T. Murphy, P.C.M. Fossati, M.J.D Rushton, R.W. Grimes, Proc. R. Soc. Lond. A Math. Phys. Sci. 470, 20140427(2014)
5 C. Takoukam-Takoundjou, E. Bourasseau, M. J. D. Rushton, V. Lachet, J. Phys.: Condens. Matter 32, 505702 (2020)