The 1999 International Conference on Strongly Coupled Coulomb Systems

J. Phys. IV France 10 (2000) Pr5-363-Pr5-367
DOI: 10.1051/jp4:2000569

Improved ionic model of liquid uranium dioxide

V. Gryaznov¹, I. Iosilevski², E. Yakub³, V. Fortov⁴, G.J. Hyland⁵ and C. Ronchi<sup>6

1</sup>  Institute of Chemical Physics at Chernogolovka, 142432 Chernogolovka, Russia
²  Moscow Institute of Physics and Technology, State University, 147700 Moscow Region, Russia
³  Odessa State Medical University, Odessa, Ukraine
⁴  High Energy-Density Research Centre of RAS, 127412 Moscow, Russia
⁵  University of Warwick, Coventry CV4 7AL, U.K.
⁶  European Commission, Joint Research Centre, Institute for Transuranium, Karlsruhe, Germany

Abstract
The paper presents a model for liquid uranium dioxide, obtained by improving a simplified ionic model, previously adopted to describe the equation of state of this substance [l]. A "chemical picture" is used for liquid UO₂ of stoichiometric and non-stoichiometric composition. Several ionic species are considered here : U(+5), U(+4), U(+3), O(-2) and O(-1). The ions are described as charged hard-spheres of different diameters. Coulomb interaction of ions is taken into account according to the modified Mean Sphere Approximation. The main result of the new model is the appearance of natural "plasma" equivalent, which, from the theory, is directly related to the definition of oxygen potential in liquid UO_2+x. The features of the model make it possible to describe non-congruent phase equilibrium (and evaporation) in uranium dioxide, as well as other relevant phenomena characterising the phase equilibrium in chemically active matter. First calculation results are discussed.

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