During the irradiation of nuclear fuels up to 10% of the original fissile material (uranium and plutonium) is converted into a wide range of fission products. One particular group of fission-product elements, the transition metals Mo, Tc, Ru, Rh and Pd, are not oxidised at the quite low oxygen potentials existing in the fuels, and are precipitated in the fuel in the form of metallic inclusions. The thermodynamic properties and phase diagram of these alloys are of importance, since the precise composition of these alloys, as a function of radial position can provide important information concerning operating conditions inside a fuel pin. For this reason a thorough reassessment of these systems is under way. This paper reports values of the excess-Gibbs energies of mixing in the MoPd, PdRu and MoRu binary systems, and in the MoPdRu ternary. Calculated sections of the MoPdRu system at selected temperatures are presented.