Oxygen diffusion in the fluorite-type oxides CeO2, ThO2, UO2, PuO2, and (U, Pu)O2

Abstract

This study evaluates the self-diffusion and chemical diffusion coefficients of oxygen in the fluorite-type oxides CeO2, ThO2, UO2, PuO2, and (U, Pu)O2 using point defect chemistry (oxygen vacancies and interstitials). The self-diffusion coefficient changed in proportion to the 1/n power of oxygen partial pressure, similar to the defect concentration. All parameters used to represent the diffusion coefficients were determined, and the experimental data were accurately stated. The defect formation and migration energies of the oxides were compared, and the change in Frenkel defect concentration was found to affect the high-temperature heat capacities of CeO2 and ThO2. The oxygen chemical diffusion was evaluated in the oxides, excluding the line compound ThO2, and the coefficients increased dramatically around the stoichiometric composition, i.e., the chemical diffusion coefficient was much higher at stoichiometric composition, with the oxygen-to-metal ratio equal to 2.00, than in low oxygen-to-metal oxides. This difference altered the mechanism of the reduction and oxidation processes. In the reduction process, the chemical diffusion control rate was dominant and a new phase with the oxygen-to-metal ratio equal to 2.00 was formed, which then expanded from the surface in the oxidation process from a low oxygen-to-metal ratio to the stoichiometric composition.

A science‐based mixed oxide property model for developing advanced oxide nuclear fuels

“…Kato et al evaluated the temperature dependence of the Frenkel defect concentration and showed a relationship with the oxygen diffusion coefficient. 41 They showed that the effect of the Frenkel defect formation on heat capacity is very small in UO 2 , MOX, and PuO 2 . However, the effect of the electronic defect increase is crucial for evaluating high-temperature heat capacity.…”

Study of the Influence of Doping Efficiency of CeO2 Ceramics with a Stabilizing Additive Y2O3 on Changes in the Strength and Thermophysical Parameters of Ceramics under High-Temperature Irradiation with Heavy Ions

“…In turn, studying the stability of these materials, as well as the search for increasing their stability to radiation damage, is the key to expanding new directions in nuclear energy in the field of electricity production using alternative energy sources. The main goal of this work is to determine the mechanisms of radiation damage in inert matrices of dispersed nuclear fuel based on cerium dioxide [11,12], which is considered to be one of the candidate materials in this direction, as well as to determine the proposed mechanisms for increasing the resistance of these ceramics against radiation damage during hightemperature irradiation through the use of stabilizing additives like yttrium oxide (Y 2 O 3 ), the use of which makes it possible to increase the operating efficiency of inert matrices by reducing the degree of radiation damage under high-dose irradiation [13][14][15]. As is known, cerium dioxide (CeO 2 ) is often used in ceramic materials due to its excellent properties such as high chemical stability, high density, and thermal conductivity.…”