Thermodynamics of rare earth chlorides in LiCl–KCl–CsCl eutectic based melts

E. A. Kharina, R. Yu. Kaychenkova, A. S. Dedyukhin,

A. V. Shchetinskiy, L. F. Yamshchikov, V. A. Volkovich

ABSTRACT

In this paper, the temperature dependences of formal standard potentials of some rare earth metals such as lanthanum, neodymium, praseodymium, gadolinium, holmium and erbium and the thermodynamic characteristics of the formation of their chlorides in molten eutectic mixture of lithium, potassium and cesium chlorides were calculated using the experimental data on determination of their equilibrium potentials.

KEYWORDS:

rare earth metals, melts, chlorides, quasi-standard potentiafls, emf method

DOI: 10.1134/S0235010619010079

Corrosion of various types of stainless steels in chloraluminate melts

V. V. Karpov, A. V. Abramov, K. V. Dedov, A. V. Shak, A. Yu. Zhlyakov,

I. B. Polovov, S. V. Belikov, O. I. Rebrin

ABSTRACT

In the present work the corrosion behavior of 08Kh17T (analogue of AISI 439) ferritic steel, 12Kh13 (analogue of AISI 410) and 16Kh12MVSFBR ferritic-martensitic steels, and AISI 316L (analogue of 03Kh16N15M3), 12Kh18N10T (analogue of AISI 321) and 06KhN28MDT austenitic alloys was studied at 550°C in fused KCl–AlCl3 mixture with the initial AlCl3EtoEKCl ratio of 1.1. The corrosion rates of the studied materials in the KCl–AlCl3 were determined. The corrosion processes in all the studied iron-based steels were caused by the red-ox reactions resulting in dissolution of the most electronegative alloy components (Cr, Fe and Mn), that indicate the electrochemical nature of corrosion phenomena.

KEYWORDS

corrosion, stainless steel, chloraluminate melts, intergranular corrosion, molten salt reactor

DOI: 10.7868/S0235010619010067

On the separation of uranium and zirconium: electrochemical properties of zirconium in 3LiCl–2KCl melt

D. S. Maltsev, V. A. Volkovich, E. V. Raguzina, K. E. Strepetov, A. A. Kozlova, M. N. Soldatova

ABSTRACT

Electrochemical properties of zirconium in lithium and potassium chlorides eutectic melt was studied employing solid (tungsten) and liquid (gallium, indium, zinc) cathodes in temperature range 550–750°С.

KEYWORDS

uranium, zirconium, separation, cyclic voltammetry, chloride melts, deposition potentials

DOI: 10.7868/S0235010619010109

Formation of phosphates of rare earth elements in melts based on the equimolar mixture of sodium and potassium chlorides

A. B. Ivanov, V. V. Sukhikh, V. A. Volkovich, B. D. Vasin, A. V. Chukin

ABSTRACT

Processes taking part during reaction of chlorides of 15 rare earth elements (yttrium, lanthanum and all lanthanides except for promethium) with sodium orthophosphate in the melts based on NaCl–KCl equimolar mixture under inert atmosphere at 750°C. Phase composition and particle size distribution of the phosphates of rare earth elements (REE) formed was determined. The effect of the mole ratio of phosphate to REE on the composition and particle size of the phosphates formed was studied. Conditions required for the quantitative precipitating from the melt individual REE and a mixture of REE imitating the content of rare earth fission products in the spent nuclear fuels arriving for the reprocessing.

KEYWORDS

rare earth elements, chloride melts, phosphates, precipitation, spent nuclear fuels

DOI: 10.7868/S0235010619010055

Activity of lanthanum in zinc-containing alloys: study of La–Zn, La–U–Zn and La–U–Ga–Zn systems

V. A. Volkovich, D. S. Maltsev, E. V. Raguzina, A. S. Dedyukhin, A. V. Shchetinskiy, L. F. Yamshchikov

ABSTRACT

The effect of alloy components on thermodynamic properties of f-elements was studied on the example of zinc-containing alloys. Activity of lanthanum in La–Zn, La–U–Zn and La–U–Ga–Zn systems, and activity of uranium in U–Zn system were determined at 573–1073 K. The effect of second low melting metal (gallium) and second f-element (uranium) on activity of lanthanum in zinc-containing systems was analyzed.

KEYWORDS

lanthanum, uranium, zinc, gallium, alloy, activity, thermodynamics

DOI: 10.7868/S0235010619010225

Thermodynamic analysis of oxidation of radioactive graphite in the melt Na2CO3–K2CO3–Sb2O3 in the carbon dioxide atmosphere

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

ABSTRACT

Currently in the world there are power reactors, reactors for plutonium production and research reactors whose number is more than 100 pieces of Graphite in the above mentioned reactors is used as the reflector, moderator, and also as Fuel cladding. Flameless combustion is a promising method of reducing the amount of solid radioactive waste. Method of flameless combustion is based on the oxidation of TRO in the oxide-carbonate melts and significantly reduces the volume of radioactive graphite. Thermodynamic modeling of oxidation of radioactive graphite in molten Na2CO3–K2CO3–Sb2O3 in an atmosphere of carbon dioxide. To conduct thermodynamic analysis was used the program complex TERRA. Thermodynamic modeling was carried out with initial pressure of one atmosphere, at an initial temperature of 273 K and the final temperature 3273 К. The step change in temperature is 100 K. Based on these data, the analysis of the distribution of elements between the condensed and gas phases. The modelling shows that the carbon disappears at a temperature of 873 K.

The heating of the system up to 1073 K leads to the evaporation of condensed compounds of antimony. The heating system up to 1673 K leads to the evaporation of condensed compounds of potassium, sodium, chlorine, uranium and cesium. The heating system up to 2273 K, leads to evaporation of condensed compounds of nickel. The heating system up to 2573 K leads to the evaporation of condensed calcium compounds, plutonium, beryllium, strontium, americium and europium. At temperatures above 2573 K, there is only a steam and gas phase.

KEYWORDS:

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

Thermodynamic analysis of oxidation of radioactive graphite in the melt Na2CO3–K2CO3–Sb2O3 in the argon atmosphere

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.

Thermodynamic analysis of oxidation of radioactive graphite in multicomponent melt in the inert atmosphere

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.

Thermodynamic analysis of oxidation of radioactive graphite in CuO–NaCl–KCl–Na2CO3–K2CO3 multicomponent melt in water vapor

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.