Metallic uranium obtaining method

FIELD: metallurgy.

SUBSTANCE: metallic uranium obtaining method involves electrolysis of uranium dioxide in the melt of lithium and potassium chlorides in an electrolysis unit with a graphite anode and a metal cathode and release of metallic uranium on the cathode and carbon dioxide on the anode. First, mixtures of uranium dioxide and carbon are prepared in molar ratio of 6:1 and 1:1 by crushing the corresponding powders; the obtained powders are briquetted into pellets. To the anode space of the electrolysis unit, which is formed with a vessel with porous walls, which is arranged in a ceramic melting pot, there loaded are pellets obtained from mixture of uranium dioxide and carbon, and melt of lithium and potassium chlorides. To the cathode space of the electrolysis unit, which is formed with the vessel walls with porous walls and the ceramic melting pot, there loaded is melt of lithium and potassium chlorides and uranium tetrachloride in the quantity of 5-15 wt % of lithium and potassium chlorides. Electrolysis is performed at the electrolyte temperature of 500-600°C, cathode density of current of 0.5-1.5 A/cm2, anode density of current of 0.05-1.5 A/cm2, in argon atmosphere with periodic loading to anode space of pellets of mixture of uranium dioxide and carbon.

EFFECT: current yield of metallic uranium is 80-90% of theoretical.

1 ex

 

A promising fuel for fast reactors is dense uranium-plutonium fuel with a density greater than the density of oxide fuel. For the synthesis of dense fuel, you can use metallic uranium and plutonium. In a prospective NPP nuclear fuel cycle the final products of the reprocessing of irradiated nuclear fuel is metallic uranium and plutonium. Currently, the final products of the reprocessing of irradiated nuclear fuels are the oxides of uranium and plutonium, therefore, for the synthesis of dense fuel required conversion of the oxides of uranium and plutonium in metallic phase.

The invention relates to methods of producing uranium metal for solid fuel power reactors.

Known metallocherpitsy the method of obtaining uranium metal, which consists in the recovery of uranium oxides or halides derived from oxides) metallic calcium or magnesium (V.B. have been Shevchenko, BN. Sudarikov. The technology of uranium. Gosatomizdat, M., 1961, SS-308). The method is inefficient for the production of fuel from power reactors.

The metal can be obtained by electrolysis of molten salts of uranium. The known method the electrolytic production of metallic uranium from molten uranium tetrafluoride or salts of uranium tetrafluoride with what tridom potassium KUF5 (tetrachloride uranium on an industrial scale in this way is not used), placed in molten chlorides of calcium and sodium (V.B. have been Shevchenko, BN. Sudarikov. The technology of uranium. Gosatomizdat, M., 1961, SS-311). Uranium is allocated at the cathode and at the anode aggressive fluorine, which binds the calcium chloride with the liberation of chlorine - aggressive gas, which is necessary to bind chemically neutral connection.

The known method the electrolytic production of uranium metal from uranium oxides (U.S. Patent No. 7638026, IPC SS 3/34, publ. 29.12.2009) prototype. According to the method of spent nuclear fuel in the form of uranium dioxide is mixed with uranium tetrachloride UCl4and placed in the molten LiCl. The lithium chloride may also be in combination with potassium chloride KCl and trichlorides uranium UCl3. Uranium dioxide to uranium tetrachloride is placed in the anode space of the cell, separated from the cathode space by porous partition.

In the method using a metal cathode and a graphite anode, while the cathode gives the uranium, and the anode is carbon dioxide CO2. Carbon dioxide in the process of electrolysis is formed due to the interaction of the anode material or carbon contained in the scrap tablets oxide fuel, oxygen-containing particles of the electrolyte (UO2+). Interaction with the material of the anode leads to the dissolution of the anode and the need hosamani after some time. Scrap tablets does not provide a stable and fast enough carbon in the electrolyte.

Electrolysis bath also contains additional protective cathode, positioned between the anode space and the main cathode (the cathode, which is obtained uranium metal), while the voltage between the anode and the additional cathode provide passage through a porous wall only ions of trivalent uranium, while particles UCl4remain in the anode space. On the secondary cathode is recovered, the tetravalent uranium to trivalent, and the main cathode subsequent recovery of trivalent uranium to U0.

The objective of the invention is to develop an easier way for the electrolytic production of uranium metal from uranium dioxide.

The task is solved by the fact that in a method of producing uranium metal, including the electrolysis of uranium dioxide in molten chlorides of lithium and potassium in the cell with a graphite anode and a metal cathode and isolation of uranium metal at the cathode and carbon dioxide at the anode, pre-prepared mixture of uranium dioxide and carbon in a molar ratio of 6:1 and 1:1 by grinding powder of uranium dioxide powder and carbon black or graphite as carbon to a particle size of 1-10 μm. the ATEM bitteroot obtained powders into tablets weighing 5-10 g

In the anode space of the cell formed by the vessel with porous walls, placed in a ceramic crucible, download the tablets obtained from a mixture of uranium dioxide and carbon in a molar ratio of 6:1, and the melt of lithium chloride and potassium taken in a molar ratio of 3:2, when the mass ratio of uranium dioxide to lithium chloride and potassium 1:1.

In the cathode space of the cell formed by the walls of the vessel with porous walls and a ceramic crucible, download a melt of lithium chloride and potassium at a molar ratio of 3:2 and uranium tetrachloride in the amount of 5-15 wt.% from the chlorides of lithium and potassium.

The electrolysis is carried out at a temperature of the electrolyte 500-600°C., a cathode current density of 0.5 to 1.5 a/cm2and anodic current density of 0.05-1.5 a/cm2in an argon atmosphere with periodic loading in the anode space of tablets from a mixture of uranium dioxide and carbon in a molar ratio of 1:1.

The method is as follows.

Prepare a mixture of uranium dioxide and carbon. As carbon use graphite powder or carbon black. The carbon powder and powdered uranium dioxide are mixed in a molar ratio of 6:1 or 1:1, i.e. in a sixfold excess of carbon to uranium dioxide or in the stoichiometric ratio of the final reaction interaction: UO2+=U+CO2. The mixture is placed in a ball mill; about swagat grinding the mixture to a particle size of 1-10 μm, when this happens the homogenization of the mixture. The first mixture (a mixture of carbon and uranium dioxide in a molar ratio 6:1) prepare for the first load in the cell, the second mixture (molar ratio 1:1) for subsequent downloads in the electrolysis process. The mixture bitteroot into tablets weighing 5-10 g

The use of carbon mixed with uranium dioxide and grinding the mixture to a particle size of 1-10 μm provides an output of uranium metal current up to 80-90% of theoretical (for comparison: when using particles with a size of 200 μm, the current output is 16-20%).

Tablets first mixture of uranium dioxide with carbon added to the salt mixture composition: lithium chloride - potassium chloride, taken in a molar ratio of 3:2, the mixture of chlorides charge / mass ratio to uranium dioxide 1:1.

The resulting mixture is placed in a vessel with porous walls (in the prototype is a vessel 12, the vessel is placed in a ceramic crucible. In a vessel with porous walls is a graphite anode (anode space of the cell), and in the crucible, outside the vessel, and a metal cathode (cathode space of the cell). The porous walls of the vessel are porous partition separating the anode space of the cell from the cathode space. Porous partition permeable to ions, including ions of uranium (U4+and chloride. Cat is the initial compartment is filled with a mixture of lithium chloride with potassium chloride, taken in a molar ratio of 3:2, to which is added the uranium tetrachloride in the amount of 5-15 wt.% from the mixture of chlorides in the cathode compartment.

The uranium tetrachloride is placed in the cathode space once when you first load cell, the electrolysis process it is produced in the anode space. (Unlike the prototype, in which the process is conducted in the presence of uranium tetrachloride only in the anode space, the proposed method in the presence of uranium tetrachloride in the cathode and anode spaces in the proposed method there is no additional protective cathode that simplifies the way). Consumable in the electrolysis of uranium dioxide and carbon periodically added to the anode compartment at the stoichiometric ratio (in the form of tablets of the second mixture in the anode space is saved sixfold excess carbon from stoichiometry), creating a ratio of a mixture of uranium dioxide with carbon to a mixture of lithium chloride and potassium in the anode space of 1:1.

The cell is placed in a sealed apparatus, vacuum to a residual pressure of 10-2mm Hg, the apparatus is filled with argon, the electrolyte is heated to 500÷600°C, while the melting of the electrolyte. The process is carried out at a temperature of 500÷600°C, cathode current density of 0.5÷1.5 a/cm2, anode current density of 0.05÷1.5 a/cm2. Rising the temperature above 600°C leads to the reduction of uranium due to its dissolution and separation of uranium tetrachloride. At temperatures below 500°C increases the viscosity of the electrolyte, which leads to lower current output.

A graphite anode is a non-consumable element of the cell.

At the anode, and near him, apparently, the chloride ion is oxidized to elemental chlorine which reacts with uranium dioxide and carbon, giving the uranium tetrachloride and carbon dioxide. Carbon dioxide away from the anode space and sent for recycling. Chlorine is an intermediate product and is consumed in the process.

The source of uranium metal, which is deposited on the cathode due to the reduction reaction of U4++4E-=U0is uranium tetrachloride formed from uranium dioxide in the anode space. The accumulation of the metal cathode is removed from unit, remove the metal, the cathode is used again. Metal residue purified from the electrolyte melt in a compact metal and further use in the preparation technology of reactor fuel.

The method of obtaining uranium metal, including the electrolysis of uranium dioxide in molten chlorides of lithium and potassium in the cell with a graphite anode and a metal cathode and isolation of uranium metal at the cathode and carbon dioxide on the anode, wherein the pre-prepared mixture of uranium dioxide and the carbon is in a molar ratio of 6:1 and 1:1 by grinding powder of uranium dioxide powder and carbon black or graphite as carbon to a particle size of 1-10 μm, bitteroot obtained powders into tablets weighing 5-10 g in the anode space of the cell formed by the vessel with porous walls, placed in a ceramic crucible, download the tablets obtained from a mixture of uranium dioxide and carbon in a molar ratio of 6:1, and the melt of lithium chloride and potassium taken in a molar ratio of 3:2, when the mass ratio of uranium dioxide to lithium chloride and potassium 1:1, and in the cathode space of the cell formed by the walls of the vessel with porous walls and a ceramic crucible, download a melt of lithium chloride and potassium at a molar ratio of 3:2 and the uranium tetrachloride in the amount of 5-15 wt.% from the chlorides of lithium and potassium, the electrolysis is carried out at a temperature of the electrolyte 500-600°C., a cathode current density of 0.5 to 1.5 a/cm2, anode current density of 0.05-1.5 a/cm2in an argon atmosphere with periodic loading in the anode space of tablets from a mixture of uranium dioxide and carbon in a molar ratio of 1:1.



 

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