Molecular simulations of ionizing irradiation of plutonium extractant solutions

The CEA is developing separation processes for the multi-recycling of plutonium in spent nuclar fuel. The preferred technology for separating plutonium is solvent extraction. In solvents, radiolysis phenomena generated by the presence of alpha radiation emitters such as plutonium are numerous. A better understanding of these phenomena is essential to develop and control these processes. The aim of this thesis will be to understand the mechanisms by which organic solutions are damaged by radiolysis, using numerical simulations. On a microscopic scale, the irradiation of matter by alpha particles begins with a deposition of energy in the electron cloud, leading to the excitation or ionization of the molecules in the medium. This process takes place on the attosecond time scale. The energy thus deposited is then dissipated in nuclear vibration modes, leading to the localization of charges on certain molecular fragments, the weakening of chemical bonds or even their rupture, and the production of reactive chemical species. The latter are the precursors of chemical reactions occurring at later times.
To simulate these ultrafast processes on the basis of first principles, we will adopt the Time-Dependent Density Functional Theory (TD-DFT) methods [1]. TD-DFT simulations consist in explicitly propagating in time the evolution of the electronic cloud subjected to a perturbation such as a collision by an alpha particle. These simulations give access to the amount of energy delivered to the system at atomic resolution, and to the dynamics of the electron cloud. Coupling the TD-DFT simulations with the Newtonian molecular dynamics simulations of atomic nuclei, then gives access to the simulation of ultrafast chemistry taking place on femto- and picosecond timescales. Hybrid QM/MM (Quantum Mechanics/Molecular Mechanics) schemes will be used to account for environmental effects (solvent, counter-ions)[1,2]. The PhD student will be trained in a wide range of methods in the field of theoretical chemistry.
The successful candidate will have a good background in physical and/or quantum chemistry, be motivated and hard-working. Previous experience in numerical simulation, acquired for example during Master's research internships, will be an advantage. The thesis will be carried out under the joint supervision of D. Guillaumont (CEA) and A. de la Lande (Université Paris Sud), requiring the PhD candidate to be located for long periods on each of the two sites of CEA Marcoule and Université Paris Sud.

[1] X Wu, JM Teuler, F Cailliez, C Clavague´ra, DR Salahub, A de la Lande, J. Chem. Theor. Comput. 2017,13, 3985-4002.
[2] K. A. Omar, F. A. Korsaye, R. Tandiana, D. Tolu, J. Deviers, X. J. Wu, A. Parise, A. Alvarez-Ibarra, F. Moncada, J. N. Pedroza-Montero, D. Mejía-Rodriguez, N. T. Van-Oanh, F. Cailliez, C. Clavaguéra, K. Hasnaoui, A. de la Lande, European Physical Journal-Special Topics 2023.