Graphite has a special position among all stored radioactive wastes. At present there is no final solution on the problem of disposal of spent graphite in the world. The behavior of radioactive graphite was studied in CuO-NaCl-KCl-Na2CO3-K2CO3 multicomponent melt in argon atmosphere in temperature ranges 373-3273 K by thermodynamic method of modeling. Modeling was made using Terra software, which is designed for the calculation of phase composition, thermodynamic and transport properties of arbitrary systems. The calculations were made using reference database on the properties of individual substances. Thus, graphite burns with the formation of both carbon monoxide and carbon dioxide at 1273 К. Condensed compounds of cesium, chlorine and uranium evaporate at 1573 К. Temperature rise in the system to 1873 К leads to the evaporation of condensed nickel. Condensed strontium oxide converts into a vapor at 2273 К. Condensed compounds of plutonium, potassium and europium evaporate at 2373 К. Condensed beryllium oxide evaporates at 2473 К. Further temperature rise to 2673 К leads to the evaporation of americium (III) oxide. The only vapor-gas phase exists in the temperature range 2673-3273 К in the isolated system.