The use of uranium mononitride as a nuclear fuel is being considered for a number of high temperature applications. In comparison with the most often applied high temperature fuels, UO2 and UC, one finds that UN has a combination of the high melting point of UO2 and the thermal conductivity and high uranium density of UC. However, interest in UN is often dampened by qualitative indications of its low thermal stability and by lack of experimental thermodynamic data. Is is the purpose of this study, therefore, to provide a quantitative measure of the thermal stability of UN and to establish some of its thermodynamic properties.

Uranium carbide shows promise as a fuel material for reactors operating at relatively high temperatures based on its high melting point, high uranium density and high thermal conductivity. Before refined reactor designs can be made, however, good quantitative data on the thermal conductivity at temperatures in excess of 1000C is required. This technical report presents data gathered as part of a continuing study aimed at determining the thermal conductivity of refractory uranium fuels as a function of temperature, density and composition over the temperature range 1000-2200C. At the inception of this program it was felt that an absolute method capable of achieving high temperatures was necessary and that the difficulties encountered in fabricating the large complex specimens needed were justified. The steady state radial heat flow method and apparatus of Rasor and McClelland were therefore chosen. The technical report discusses the experimental equipment and presents results of measurements on three specimens of UC over a temperature range 900 to 1600C. An analysis of the data is made with respect to other physical properties of the material and the measured conductivities are compared with the work of other investigators.