Values are reported of specific heat, thermal conductivity and thermal diffusivity of UO2 from 1500 K to 2900 K based on laser flash measurements. Experiment is complemented by the development of solid state physics models that aid in the interpretation of the results. Specific heat is shown to exhibit a smooth maximum at 2715 K ± 100 K, consistent with a competition between two processes - oxygen defect interactions (net attraction) and saturation of oxygen interstitial sites. The specific heat model and measurements show, for the first time that a gradual pre-melting transition is consistent with high temperature literature values – enthalpy increment measurements and independently measured high temperature oxygen defect concentrations. Thermal conductivity exhibits a minimum consistent with: 1) an increase in electronic thermal conductivity via polaron production and mobilization and 2) degradation in lattice thermal conductivity due to phonon - phonon scattering and phonon - defect scattering. It is predicted that the high concentration of oxygen defects should contribute significantly to electrical conductivity and thermal expansion at high temperatures.
PAVLOV Tsvetoslav Rumenov;
WENMAN Mark;
VLAHOVIC Luka;
ROBBA Davide;
KONINGS Rudy;
VAN UFFELEN Paul;
GRIMES R. W.;
2018-01-17
PERGAMON-ELSEVIER SCIENCE LTD
JRC106492
1359-6454,
https://publications.jrc.ec.europa.eu/repository/handle/JRC106492,
10.1016/j.actamat.2017.07.060,
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