Thermodynamic Modeling of the Phase Composition of Mixed Uranium-Plutonium Mononitride with Impurity Oxygen Under Irradiation to Burnup 140 GW·days/ton and Temperature 900–1400 K

Thermodynamic modeling of the phase composition of mixed uranium-plutonium mononitride with impurity oxygen as a function of burnup and temperature under irradiation by fast neutrons has shown that the accumulation of fission products results in the formation of heterogeneous fuel: a multicomponent solid solution based on uranium-plutonium oxynitride that contains yttrium, zirconium, and lanthanides and separate nitride, oxide, metal, and intermetallides phases as well as alkaline-metal iodides and, apparently, bromides. The change in the content of these phases as a function of burnup to 140 GW·days/ton and temperature 900–1400 K is calculated. The effect of the individual phases formed in the course of irradiation on the effective thermal conductivity of the fuel is evaluated together with the diffusion coefficient of xenon atoms in the fuel kernel.