Review of thermal conductivity and heat transfer in UO$sub 2$

The theories of heal transfer in insulators are viewed and discussed relevant to UO/sub 2/. As the rate of heat transfer from a reactor core is determined largely by the thermal conductivity of the fuuel, this coefficient is of paramount importance in improving the efficiency of an installation. There is no theoretical basis to expect small or moderate chemical additions to increase the thermal conductivity of UO/sub 2 when the oxide is classed as an insulator. Large additions of a phase having a high thermal conductivity have been found to increase the net conductivity. Such systems were two phase and had poor sintering cjaracterostocs/ cpmsoderomg UO/sub 2 as a potential oxidic semiconducotor, there is possibility of increasing the themnal conductivity by proper doping. Thermal conduction by intrinsic carriers was treated experimentally and theoretically, and the conductiivity values of the two cases do not presently agree, ie., the Wiedemann-Franz law is not obeyed. The extrinsic case such as a doped urements indicate that doping UO/sub 2/ with Y/sup +3/ and Nb/sup +5/ increases the thermal conductivity. These data are sparce; the magnitude of the increase and its dependence upon impurity concentration and temperature have not been determined. (auth