The framework of this study is the potential use of molten salts in the nuclear industry of the future. Those systems properties have been determined from finite temperature molecular dynamics simulations with a realistic representation of the interatomic interactions (the dipole-polarizable ion model, DIPPIM). Among the quantities that can be obtained from molecular dynamics simulations, structural and dynamic properties hold particular interest for this work : those are mandatory to determine the various molten salts capabilities for being used as coolants in nuclear reactors, or the speciation of fission products in silicate glasses. This work has been particularly focused on the effect of adding small amounts of oxides in a fluorozirconate based molten salt. The formation of molecular ions based on strong Zr–O–Zr bonds results in an important medium-range ordering of the system and in a noticeable slowing of the dynamics of the ions, accompanied by an increase of the viscosity. Keywords Fluoride ionic molten salts, fourth generation nuclear reactor, concentration of oxide, molecular dynamics, computer simulations, structural study, dynamical analysis, viscosity, diffusion, NaF–ZrF4.

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