The behavior of uranium, americium, and plutonium compounds contained in radioactive graphite during its heating in a mixture of water vapor and oxygen was studied by thermodynamic simulation, which was carried out using the TERRA program at temperatures from 373 to 3073 K to determine possible compounds of radionuclides (U, Am, Pu) during the disposal of radioactive graphite by heating it in a mixture of water vapor and oxygen. Thermodynamic simulation has shown that uranium, plutonium, and americium, which are present in radioactive graphite in the form of impurities during heating in a water vapor–oxygen mixture, when certain temperatures are reached, pass into the gas phase. The main list of reactions is selected and equilibrium constants are derived for the combustion of radioactive graphite in a mixture of water vapor and oxygen.