N. М. Barbin, I. A. Sidash, D. I. Terentyev, S. G. Alekseev.

ABSTRACT

Graphite is used as moderator and reflector of neutrons. In addition, in the construction of reactors, graphite is used as seals and bearings. The mass of graphite in the reactors is 1–2 tons At decommissioning graphite reactors produce large quantities of radioactive graphite waste. Existing methods of treatment of radioactive graphite based on its isolation from the environment. These techniques do not significantly reduce the volume of radioactive graphite waste. Resulting in the reprocessing of irradiated reactor graphite by oxidation of the molten salts can be considered as an alternative method of disposal that reduce the volume of radioactive graphite waste. Thermodynamic modeling of oxidation of radioactive graphite in molten Na2CO3–K2CO3–Sb2O3 in an argon atmosphere. To conduct thermodynamic analysis was used the program complex TERRA. Based on these data, the analysis of the distribution of elements between the condensed and gas phases. The result is that the heating system up to 1073 K leads to the evaporation of condensed compounds of antimony and cesium. The heating system up to 1273 K leads to the evaporation of condensed compounds of potassium, sodium, chlorine. The heating system up to 1373 K leads to the evaporation of condensed compounds of Nickel. The heating system up to 1673 K leads to the evaporation of condensed compounds of uranium, calcium and strontium. The heating system up to 1773 K leads to the evaporation of condensed compounds of plutonium, beryllium, americium and europium. At temperatures above 1773 K, there is only a steam and gas phase.

KEYWORDS:

thermodynamic modeling, radioactive graphite, radionuclides, heating, oxidation, melt, carbonates.

N. М. Barbin, А. М. Kobelev, D. I. Terentyev, S. G. Alekseev.

ABSTRACT:

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.

KEY WORDS:

salt melt, radioactive graphite, radionuclides, oxidation, copper oxide, thermodynamic modeling.

N. М. Barbin, А. М. Kobelev, D. I. Terentyev, S. G. Alekseev.

ABSTRACT:

Graphite has a wide application in nuclear industry today. However, the resource of most uranium-graphite reactors in Russia considering their repair-and-renewal operations will be exhausted next 10–15 years. The processing of high-active graphite is made by flameless oxidation method in molten salts. The present work investigates the behavior of radionuclides at flameless oxidation of radioactive graphite in CuO–NaCl–KCl–Na2CO3–K2CO3 multicomponent melt in water vapor. Thermodynamic method of modeling with Terra software was used in this research. This method is an effective and unique one for studying thermal decomposition, reduction and synthesis at various temperatures. The calculations were made using reference database on the properties of individual substances. Graphite burns with the formation of carbon dioxide, methane and condensed potassium carbonate at 573 К. Condensed compounds of cesium, chlorine and uranium evaporate at 1673 К. Temperature rise in the system to 1973 К leads to the evaporation of condensed compounds of beryllium, calcium and strontium. Condensed europium (III) and plutonium (IV) oxides convert into vapor at 2173 К. Condensed nickel oxide evaporates at 2473 К. Further temperature rise to 2773 К leads to the evaporation of condensed americium (III) oxide. The only vapor-gas phase exists in the temperature range 2773–3273 К in the isolated system.

KEY WORDS:

water vapor, radioactive graphite, radionuclides, oxidation, carbonate-oxide melt, thermodynamic modeling.