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) = [00433+0355P + (201+147P) × 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.

[1]  F. Grønvold,et al.  Thermodynamics of the UO2+x phase I. Heat capacities of UO2.017 and UO2.254 from 300 to 1000 K and electronic contributions , 1970 .

[2]  Robert D. Cowan,et al.  Pulse Method of Measuring Thermal Diffusivity at High Temperatures , 1961 .

[3]  R. Reiswig.  Thermal Conductivity of UO2 to 2100°C , 1961 .

[4]  G. Troup,et al.  Paramagnetic resonance of Fe3+ in benitoite , 1965 .

[5]  L. Goldsmith,et al.  Measurements of the thermal conductivity of uranium dioxide at 670 1270 k , 1973 .

[6]  G. P. Marino.  The porosity correction factor for the thermal conductivity of ceramic fuels , 1971 .

[7]  C. Hinman,et al.  Electrical Conductivity of Uranium Dioxide , 1967 .

[8]  J. Hart,et al.  The electret effect in 1-tetradecanol , 1966 .

[9]  D. Mcelroy,et al.  Thermal Conductivity of Uranium Dioxide from ‐57° to 1100°C by a Radial Heat Flow Technique , 1965 .

[10]  J. A. Cape,et al.  Temperature and Finite Pulse‐Time Effects in the Flash Method for Measuring Thermal Diffusivity , 1963 .

[11]  R. Taylor.  An investigation of the heat pulse method for measuring thermal diffusivity , 1965 .

[12]  D. A. Watt.  Theory of thermal diffusivity by pulse technique , 1966 .

[13]  V. Wheeler.  The diffusion and solubility of hydrogen in uranium dioxide single crystals , 1971 .

[14]  M. J. Wheeler,et al.  The high-temperature thermal conductivity of sintered uranium dioxide , 1968 .

[15]  D. Whitmore.  Excitation Processes in Ceramics and Anomalous Increase in Thermal Conductivity at Elevated Temperatures , 1960 .

[16]  G. R. Horn,et al.  Evolution of uranium dioxide structure during irradiation of fuel rods , 1963 .

[17]  R. J. Jenkins,et al.  Flash Method of Determining Thermal Diffusivity, Heat Capacity, and Thermal Conductivity , 1961 .