Simulation of the speciation of uranium(VI) and plutonium(IV) in organic phase via classical Molecular Dynamics.

The speciation of uranium(VI) and plutonium(IV) in presence of N,N-dialkylamides has been studied by classical Molecular Dynamics (cMD or MD) combined with EXAFS experimental data. The Lennard Jones 12-6-4 potential has been implemented for the implicit description of polarization effects and dispersion forces inducted by the strongly charged actinide ions. The model allowed the production of the first classical molecular dynamics simulation of Pu(IV) in organic phase, to the author knowledge, and provided a rather good prediction of the distances in the first coordination shell and EXAFS spectra, for both Pu and U complexes. The complex structures with three different monoamides, DEHBA, DEHiBA and MDEHA, have been evaluated and compared. Moreover, the aggregation of uranium complexes has been completely characterized. Eventually, the speciation of Pu(IV) has been studied in presence of nitric acid in organic phase, pointing out the key role of HNO3 in stabilizing plutonium hexanitrate complexes and providing new essential insights in the characterization of actinides extraction via Molecular Dynamics.