Computed Phase Equilibria and Material Studies for the

Abstract- Neutron absorbing elements are required in the center of advanced CANDU fuel bundle designs that make use of slightly enriched uranium in the surrounding elements. Dysprosia mixed with uranium dioxide is one such absorber that has been used for Low Void Reactivity Fuel (LVRF)[1]. An inert zirconia (with and without yttria) mixture is also being considered as a carrier for the neutron absorbers gadolinium and dysprosium. This quaternary oxide system was modeled from the binary oxide phase diagrams involving zirconia using interpolation methods to estimate the Gibbs energies of the multi-component phases. The model provides the solubility of Ln2O3 (Ln=Y,Gd,Dy) in the cubic structure of ZrO2 as well as the temperature where the cubic phase is expected to melt or decompose into more stable solid phases.