Thermal conductivity of uranium dioxide up to 2900 K from simultaneous measurement of the heat capacity and thermal diffusivity

The thermal diffusivity and heat capacity of uranium dioxide have been meas ured from 500 to 2900 K with an advanced laser-flash technique. These two q uantities were determined simultaneously by means of an accurate numerical fitting of the experimental thermograms. At high temperatures the precision of the method used is much better than that associated with conventional l aser-flash measurements. It was found that the heat capacity continues to i ncrease even at temperatures above the expected lambda transition (2670 K). The inverse of the thermal diffusivity increases linearly with temperature up to 2600 K, whilst at higher temperatures the slope markedly decreases. A new expression for the thermal conductivity as a function of temperature is proposed, which is corroborated by some theoretical considerations on th e underlying heat transport mechanisms. (C) 1999 American Institute of Phys ics. [S0021-8979(99)05902-2].