Improved Ionic Model of Liquid Uranium Dioxide

TL;DR

This paper introduces an improved ionic model for liquid uranium dioxide that accounts for multiple ionic species and Coulomb interactions, enabling better description of phase equilibrium and evaporation phenomena in chemically active UO2.

Contribution

The paper develops a refined ionic model using a modified Mean Sphere Approximation, incorporating multiple uranium and oxygen ions to accurately describe liquid UO2's phase behavior.

Findings

Model captures non-congruent phase equilibrium.

Enables description of evaporation processes.

Introduces plasma-like state related to oxygen potential.

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 [1]. 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(-). 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 (MSA). 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.