Uranium-zirconium (U-Zr) alloys are promising candidate fuel materials for the next generation fast reactors. In reactors, the constituent redistribution induced by the thermal gradient and radiation leads to the formation of various intermetallic phases in the fuels. Such phase evolution can significantly impact the thermal transport properties in fuels. Here a mechanistic model is developed to describe the thermal conductivities of U-Zr binary alloys at a wide range of temperatures and Zr concentrations. Different from other models in literature, this thermal conductivity model is based on the intrinsic and residual thermal resistivities. Thermal resistivities of pure uranium and pure zirconium as a function of temperature are estimated from quantum theories and the coefficients are calibrated from the experimental data. The thermal resistivities of U-Zr alloys of different Zr concentrations are determined by the interpolation between the pure U and Zr metals and a compensating term. This model predicts very reasonable thermal conductivities of U-Zr binary system for a wide range of Zr concentrations and temperatures, and its function forms may be applied to other binary or ternary metallic fuel systems.