Thermal Conductivity 18 pp 483-484 | Cite as

# The High-Temperature Ex-Reactor Thermal Conductivity of Thoria and Thoria-Urania

Chapter

## Abstract

Thermal conductivity of a material can be determined by the product of thermal diffusivity, heat capacity, and density. Each of these properties is reviewed for ThO
where λ

_{2}and for ThO_{2}-UO_{2}solid solutions, and compared with similar data for UO_{2}. Between room temperature and 2950 K for ThO_{2}and between room temperature and the temperature range 2850–2950 K for the solid solutions (Th_{0.92}U_{0.08})O_{2}to (Th_{0.70}U_{0.30})O_{2,}thermal conductivity of fully dense (Th_{1-M}-U_{M})O_{2}, for M ≤ 0.3, can be expressed by the following fitted equations:$$\begin{array}{l}
1/{\lambda _o}\; = \;A + BT;\\
A = \;1/\left( {46.947\; - \,112.072\;M} \right);\\
B\; = \;0.0001\left( {1.597\; + \,6.736\;M\; - 21.56\;{M^2}} \right)
\end{array}$$

_{o}is the thermal conductivity in W/m·K and M is the mole fraction of UO_{2}. Corrections for porosity (P) are made using the Maxwell-Eucken equation, λ/λ_{o}= (1 - P)/(1 + ßP), with a constant value of 1.15 for the coefficient ß. Since there is no significant electronic contribution to the heat capacity of ThO_{2}, unlike the case for UO_{2}, the thermal conductivity of ThO_{2}continues to decrease with increasing temperature until a solid-solid phase transition at 2950 K is reached, at which point heat capacity and thermal conductivity increase about 50%. Thermal conductivity decreases again above the transition temperature. ThO_{2}-UO_{2}solid solutions also show evidence for phase transitions from enthalpy data and thus show increases in calculated heat capacities and thermal conductivities. The pretransion thermal conductivities of the ThO_{2}-UO_{2}solid solutions are intermediate between those of thoria and urania. Experimentally determined pretransition heat capacities for the solid solutions agree with values calculated from mole averages of ThO_{2}and UO_{2}.Further details of this work may be found in a report: WARD-TM-1530, Dec. 1982, by J. Belle and R.M. Berman.

## Keywords

Phase Transition Thermal Conductivity Solid Solution Heat Capacity Transition Temperature
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## Copyright information

© Purdue Research Foundation 1985