EFFECT OF DENSITY ON THERMAL CONDUCTIVITY OF URANIUM DIOXIDE

The thermal conductivity of 82, 86, 91 and 95% theoretical density (T.D.) sintered uranium dioxide has been measured by the radial heat flow technique, between 800 and 2000 °C in an argon atmosphere. The data indicate that use of the simplified Loeb or Maxwell-Eucken equations, or currently recommended modifications of these thermal conductivity-density relationships are not applicable for the temperature, temperature gradient, and density ranges investigated. Thermal conductivity values for uranium dioxide were related to both temperature and density by the equation k=0.0130+{T(0.4848-0.4465D}-1, [W/cm·°C], for temperatures between 800 and 2000 °C and densities between 82% and 95% T.D. (T=temperature in °C, and D=density in fraction of theoretical). The time required for microstructural and/or density changes to occur in oxide fuel elements under irradiation is generally short relative to the total exposure time. Because the thermal conductivity of a typical oxide fuel has been found to be quite dependent on density in this investigation, a model utilizing the relationships derived is described in which thermal conductivity and ∫kdT curves corrected for fuel densification occurring in-reactor can be generated. © 1969.