Title: High temperature measurements and condensed matter analysis of the thermo-physical properties of ThO2
Authors: PAVLOV TSVETOSLAV RUMENOVWANGLE TADEASWENMAN MARKTYRPEKL VACLAVVLAHOVIC LUKAROBBA DAVIDEVAN UFFELEN PAULKONINGS RUDYGRIMES R. W.
Citation: SCIENTIFIC REPORTS vol. 8 p. 5038
Publisher: NATURE PUBLISHING GROUP
Publication Year: 2018
JRC N°: JRC106780
ISSN: 2045-2322
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC106780
DOI: 10.1038/s41598-018-21406-w
Type: Articles in periodicals and books
Abstract: Values are presented for thermal conductivity, specific heat, spectral and total hemispherical emissivity of ThO2 (a potential nuclear fuel material) in a temperature range representative of a nuclear accident - 2000 K to 3050 K. For the first time direct measurements of thermal conductivity have been carried out on ThO2 at such high temperatures, clearly showing the property does not decrease above 2000 K. This could be understood in terms of an electronic contribution (arising from defect induced donor/ acceptor states) compensating the degradation of lattice thermal conductivity. The increase in total hemispherical emissivity and visible/near-infrared spectral emissivity is consistent with the formation of donor/acceptor states in the band gap of ThO2. The electronic population of these defect states increases with temperature and hence more incoming photons (in the visible and near-infrared wavelength range) can be absorbed. A solid state physics model is used to interpret the experimental results. Specific heat and thermal expansion coefficient increase at high temperatures due to the formation of defects, in particular oxygen Frenkel pairs. Prior to melting a gradual increase to a maximum value is predicted in both properties. These maxima mark the onset of saturation of oxygen interstitial sites.
JRC Directorate:Nuclear Safety and Security

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