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Study of the heat-transport properties of actinide-based mixed oxides is of importance in nuclear technology. This paper describes laser flash technique studies of the thermal diffusivity and thermal conductivity carried out on thorium-lanthanum mixed oxide solid solutions covering a temperature range from 573 to 1573 K and a compositional range from 0 to 30 mol.% LaO1.5. The thermal diffusivity and thermal conductivity of the solid solutions were found to decrease with increase in lanthanum oxide content or temperature. From the temperature dependence of the thermal conductivity it was noted that heat transport in these materials is by lattice conduction. The variation of the two resistivity terms, namely the defect thermal resistivity and the intrinsic thermal resistivity, as well as their ratio as a function of lanthanum oxide content was examined. Employing the thermal conductivity data, phonon mean-free paths were also obtained as a function of composition and temperature.

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Systematic studies were carried out on the oxidation behaviour of uranium dicarbide in air in the temperature range 25 ~ to 700 ~ employing thermogravlmetry, evolved gas detection Xray diffraction and chemical analysis. The mechanistic aspects were investigated and the oxidation was found to proceed through reaction processes involving oxidation of uranium to ct-UO3 with release of chemically bound carbon, reaction of released carbon leading to the formation of CO 2 which gets liberated stepwise, decomposition of ~-UO 3 to U3Os and oxidation of free carbon to CO2. Examination of the thermoanalytical behaviour of sintered graphite, UO3, mixtures of graphite with UO 3 and with U3Os supported the above findings. John Wiley & Sons, Limited, ChichesterAkad$miai Kiadr, Budapest