RU2681331C1 - Method of metal uranium production - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to the production of metallic uranium. Method includes mixing uranium tetrafluoride with metallic calcium, taken with an excess of stoichiometric amount, loading the mixture into the reactor and initiating smelting with the help of a lower electric fuse. Mixture is loaded in layers with a decrease in excess calcium at the loading height, that in the lower loading layer is at least 15 % and in the last surface loading layer at least 5 %. In the process of loading the mixture is compacted with a specific pressure of 10–15 kg/cm².

EFFECT: it is obtained the production of rough uranium ingots without local slag inclusions and an increase in the yield of uranium into the ingot.

3 cl, 1 tbl, 1 ex

Description

The invention relates to the nuclear industry and chemical technology of uranium and inorganic substances and can be used to produce metallic uranium.

Uranium can be obtained by electrolysis of molten salts of alkaline earth metal chlorides and uranium dioxide.

A known method of producing metallic uranium, including the electrolysis of uranium dioxide in a molten lithium chloride and potassium chloride at a temperature of 500-600 ° C in an electrolytic cell with a graphite anode and a metal cathode and the allocation of metallic uranium at the cathode (RF patent No. 2497979, IPC C25C 3/34 (2006.01 ) С22В 60/02 (2006.01), publ. 10.11.2013). The disadvantage of this method is the use of aggressive reagents (lithium and potassium chlorides) at high temperatures and the formation of toxic and aggressive elemental chlorine during electrolysis, which greatly complicates the hardware design of the process.

One of the main methods for producing metallic uranium is the method of calcium thermal reduction of uranium tetrafluoride.

There is a known method of producing uranium by reducing uranium tetrafluoride, by which compressed briquettes from a mixture of uranium tetrafluoride and calcium chips are loaded into the reactor, the reactor with the charge is washed with pure argon, the reaction is excited by electric fuse, and the ingot is cooled in argon medium (Yu.N. Sokursky, Y. M. Sterlin “Uranium and its alloys”, M., Atomizdat, 1971 p. 33). The disadvantage of this method is the need for an additional preliminary briquetting of a mixture of uranium tetrafluoride and calcium chips and a low yield of crude uranium.

There is also a known method of producing metallic uranium, which is used to prepare a mixture of uranium tetrafluoride and calcium, fill the mixture without briquetting in a crucible, which is filled with argon and initiate melting with an electric fuse (Fundamentals of Metallurgy Vol. 5, Moscow, 1968, Metallurgy, p. 72). This method has inherent disadvantages characteristic of metallothermal smelting processes with an upper electric valve. At the upper fuse, the obtained drops of uranium flow down through a cold charge, transferring heat and interacting with oxygen and nitrogen of the air located in the pores of the charge, which leads to an increase in the uranium content in the slag (up to 10%) and, accordingly, a decrease in the output of uranium in the ingot ( less than 95%).

A known method of producing metallic crude uranium, comprising mixing uranium tetrafluoride and uranium chips with metallic calcium, initiating smelting with an electric fuse in argon medium in a graphite reactor that is preheated to a temperature of 200-600 ° C (RF patent No. 2154691, IPC С22В 60/2, 08/20/2000). This method is of interest in the processing of uranium waste in the form of chips formed during the turning of a rough uranium ingot.

The closest solution selected for the prototype is a method for the calcothermal reduction of uranium tetrafluoride, which involves mixing uranium tetrafluoride with excess metal calcium, loading into the reactor and initiating smelting with a lower electric spark (N. S. Turaev, I. I. Zherin “Chemistry and uranium technology ”, Moscow, TsNIIATOMINFORM, 2005, p. 399-401). The disadvantages of the method are the low yield of crude metal uranium (less than 96%) and the high content of uranium in the slag - up to 10%. In addition, after melting, there is a problem of mechanical (using a chisel) separation of slag from the metal.

The objective of the invention and the technical result achieved by using the invention is the production of crude uranium ingots without local slag inclusions, increasing the output of uranium in the ingot and simplifying the process of separating the uranium ingot from the slag.

The problem is solved in that in a method for producing metallic uranium, comprising mixing uranium tetrafluoride with calcium metal taken in excess of a stoichiometric amount, loading the mixture into the reactor and initiating smelting with a lower electric spark plug, according to the invention, the mixture is loaded in layers with decreasing calcium excess over the loading height , which is at least 15% in the lower loading layer and at least 5% in the last surface loading layer, and the mixture is compacted during the loading process.

In particular cases of the invention:

- as calcium using granular calcium with a grain size of 1.0-3.0 mm;

- a mixture of uranium tetrafluoride and calcium is compacted in a reactor with a specific pressure of 10-15 kg / cm ² ;

- a tungsten rod is used as an electric fuse.

When loading a mixture of uranium tetrafluoride and calcium into the reactor, its layer-by-layer compaction is carried out. This is necessary in order to ensure greater heat dissipation per unit volume of the reactor during the subsequent reaction of calcium thermal reduction of uranium tetrafluoride:

When the mixture’s lower electrozapal is profiled by layer-by-layer profiling of the calcium mixture with a decrease in calcium excess along the loading height from at least 15% in the lower layer of the mixture to at least 5% in the last surface layer of the loading and its compaction, the unreacted excess of calcium melts and, evaporating, rises in the upper, not yet reacted, layers of the mixture, where it interacts with uranium tetrafluoride. On the other hand, calcium vapors rising from the lower layers condense and give off heat to the upper layers, which increases the temperature of the slag (CaF ₂ ) and contributes to its more complete separation from the uranium melt. This allows you to reduce the amount of uranium in the slag and, accordingly, to increase the output of uranium in the ingot. In addition, the total amount of calcium required for the calcium-thermal reduction of uranium tetrafluoride is reduced. A decrease in the excess of calcium in the upper layers and a decrease in its total amount in the mixture leads to a decrease in the calcium content in the slag, which greatly simplifies the separation of the uranium ingot from the slag and also increases the yield of uranium in the ingot.

Going beyond the declared range of calcium content leads to incomplete calcium-thermal reduction of uranium tetrafluoride by reaction (1).

Compaction of the mixture with a specific pressure of 10-15 kg / cm ² approximately corresponds to manual tampering, for example, with a pestle, which is quite sufficient to ensure the necessary density of the mixture and optimal heat release per unit volume of the load during the reaction (1).

The granule size of calcium metal 1.0-3.0 mm is optimal in terms of maximum yield of uranium in the ingot and simplification of the process of separating slag from the ingot.

The use of a tungsten wire or rod to initiate the reaction (1) simplifies the organization of the lower electric fuse and also eliminates the contamination of the rough uranium ingot with the electrode material.

Due to the profiling of the mixture loading by calcium content with a decrease in excess of calcium along the loading height from 15% in the lower layer of the mixture to 5%, its compaction during loading and initiation of melting by the lower electric igniter, more complete separation of slag and uranium is achieved and, as a result, the yield uranium in the ingot up to 98%, and the amount of calcium used to reduce uranium tetrafluoride is reduced. The proposed method is simple to implement - does not provide for preliminary briquetting of the charge and the use of argon, simplifies the separation of slag and uranium ingot.

The method is as follows.

The inner surface of the graphite reactor was coated with technological coating (CaF2). Samples of uranium and calcium tetrafluoride were mixed in a drunk mixer of the “drunk barrel” type for 30 min. Uranium tetrafluoride had a specific bulk density of 2.6-2.7 g / cm ³ . Three 2.5 kg samples (examples No. 1, 2, 5, 7 of the table) and 3.5 kg (examples No. 3, 4, 6) of uranium tetrafluoride mixed with an excess of calcium, given in the table. Before filling the mixture in the center of the reactor was placed a tube for a rod electric valve. A tungsten rod with a diameter of 1.2 mm was used as an electric fuse. The mixture was loaded in small portions (10-20 g) and manually rammed with a pestle with a force of 10-15 kg / cm ² . In order to prevent jamming of the tube during compaction (tamping) of the charge, it was periodically rotated around its axis. This facilitated the removal of the tube from the rammed charge before initiating the lower electric valve. After the initiation of melting, the tungsten rod was immediately removed from the reactor. After cooling the reactor, it was overturned and the metal was separated from the slag. The table shows data on the calcium content of the layers in the mixture of downloads and the results on the output of uranium in the ingot.

The data in the table indicate that an increase in the yield of uranium in the ingot is achieved by layer loading with a decrease in the excess of calcium along the loading height from at least 15% in the lower layer of the mixture to at least 5% in the last surface loading layer (examples No. 1 , 4, 5).

Thus, the method in accordance with the present invention allows to obtain crude uranium ingots without local inclusions of slag, increase the yield of uranium in the ingot and reduce the amount of calcium required for metallurgical processing of uranium tetrafluoride. Uranium metal ingots obtained by the proposed method had easier separation of the metal from the slag and contained less uranium in the slag (less than 3.0%).

Claims (3)

1. A method of producing metallic uranium, comprising mixing uranium tetrafluoride with calcium metal, taken in excess of a stoichiometric amount, loading the mixture into the reactor and initiating melting using a lower electric valve, characterized in that the mixture is loaded in layers with a decrease in excess calcium in terms of loading height, which in the lower loading layer is at least 15% and in the last surface loading layer is at least 5%, while in the process of loading the mixture is compacted with a specific pressure of 10-15 kg / cm ² . 2. The method according to p. 1, characterized in that as calcium using granular calcium with a grain size of 1.0-3.0 mm 3. The method according to p. 1, characterized in that a tungsten rod is used as an electric fuse.