Effect of porosity and stoichiometry on the thermal conductivity of uranium dioxide

Measurements have been made using a flash thermal diffusivity technique from 550 to 2500 K on a range of well-characterized materials. Data are reported on specimens of five different porosity levels, samples in which porosity has been redistributed, and specimens, initially of two different porosity levels, oxidized to three different hyperstoichiometries. The data are discussed in the light of current theories, and it is shown that the porosity correction term is temperature-dependent. The conductivity λP at any porosity P over the temperature (T) range 500-1600 K is given by λP (W m−1 K−1) = [0·0433+0·355P + (2·01+1·47P) × 10−4T]−1. This temperature-dependent porosity correction is shown to be related to total porosity, and it is suggested that this is due to additional vacancy scattering. An expression is derived for the additional phonon scattering due to interstitial oxygen atoms up to small hyperstoichiometry levels. Finally, the deviation from linearity at high temperatures is shown to be due to an electronic contribution to the total thermal conductivity.