KR20090104460A - Molten salt electrorefiner for recovering actinide elements - Google Patents

Abstract

PURPOSE: A molten salt electrolytic bath for recovering actinide elements is provided to increase a pool cathode processing efficiency of an electro winning process by designing only a structure of a pool cathode crucible and adopting a driving method of a mixer. CONSTITUTION: A molten salt electrolytic bath for recovering actinide elements comprises an outside crucible(103), an inside crucible(104) and a stirrer impeller(108). The outside crucible is formed inside the electrolytic bath. The outside crucible is filled with molten salt. The inside crucible is formed in the partial inside of the outside crucible. A liquid metal(105) is filled inside the inside crucible. The impeller rotates and contacts with the upper side of the liquid metal. The impeller moves uranium dendrite on the upper side of the liquid metal to the outside crucible.

Description

Molten SALT ELECTROREFINER FOR RECOVERING ACTINIDE ELEMENTS for Recovering Actinide Elements

The present invention relates to a dry treatment process of used nuclear fuel, and in particular, in the electrolytic smelting process of molten salt, the liquid metal is used as a cathode to remove uranium dentite generated at the interface between the molten salt and the liquid cathode, thereby quickly removing actinide-based elements. It relates to a liquid cathode structure of a crucible for recovering a large amount in the container.

Pyroprocessing (Pyroprocessing), which has the advantages of high proliferation resistance, simple equipment, and low generation of waste, has been actively studied for the disposal and disposal of spent nuclear fuel. This pyroprocessing process is mainly a method of recovering actinide-based elements by molten salt electrolysis, which converts spent nuclear fuel, which is an oxide, into a metal state (electrolytic reduction), and deposits pure uranium on a solid cathode for separation. It is a process of recovering (electrorefining) elements of uranium and super uranium (TRU) remaining in molten salt by using liquid metal.

In the electrolytic refining process, pure uranium is separated by using a solid cathode.In this case, the pure uranium is recovered in consideration of the purity of electrodeposited uranium, and is recovered until the ratio of Pu / U in the molten salt reaches about 2.5 to 3, and the remaining uranium and ultrauranium elements Fields (actinides) are recovered in the smelting process. However, when recovering actinide-based elements including uranium by using the liquid cathode in the electrolytic smelting process, uranium remaining in the molten salt after the electrolytic refining process forms a uranium dentite, which is a major obstacle to the electrolytic smelting operation.

Liquid metal is a metal that is in a liquid state at the operating temperature. Cadmium (Cd) is mainly used as a liquid metal, and in a cadmium liquid metal, uranium (U) and actinide (TRU; TRansUranic) elements are recovered at similar potentials. Therefore, the separation recovery of pure plutonium (Pu) is impossible. Therefore, this liquid cathode technology has the advantage of high nuclear proliferation resistance. However, when uranium (U) is electrodeposited on the liquid cathode, a solid uranium precipitates at the interface between the liquid cathode and the molten salt and grows into the molten salt in the resin phase. The dendritic uranium growing at the molten salt and the liquid cathode interface is called uranium dentite. The uranium dentite produced on the surface of the liquid metal itself acts as an electrode to preferentially electrodeposit only uranium in the molten salt, thereby reducing the surface area of the liquid metal. Therefore, uranium dentite greatly hinders electrodeposition of other actinide-based elements, greatly reducing the efficiency of the process, and also grows out of the liquid cathode crucible, causing problems such as shorting of the electrolyzer. Therefore, in the liquid cathode electrolytic smelting process, suppressing the production and growth of uranium dentite generated on the surface of the liquid metal has become a core technology of the entire process.

In order to suppress the production of uranium dentite generated on the surface of the liquid metal and to develop a device for preventing growth, many studies have been conducted in the United States and Japan. Pounder, developed at the US Argonne Research Institute, developed a Pounder device that rotates while moving up and down on the liquid metal surface inside the liquid cathode crucible. This device is a device for crushing uranium dentite produced on the surface of liquid cathode and depositing it inside the liquid cathode. However, although the results of several experiments have been reported, the effect is great when the Pu / U ratio in the molten salt is small. It is known to fall.

Japan's Central Research Institute of Electric Power Industry (CRIEPI) has developed a method to improve the amount of uranium deposition without generating dentite by using an agitator that rotates inside the liquid cathode. It was an experiment. In addition, in Japan, uranium dentite growing on the surface of a liquid cadmium cathode is crushed, sheared by a pair of upper and lower rotary blades, or compressed and crushed by a pair of upper and lower moving plates, and then sedimented into the cadmium cathode. Molten salt electrolysis purification apparatus has been developed, but actual performance has not been reported.

However, the phenomenon that uranium dentite is generated in the electrolytic recovery of actinide metal by the liquid cathode is a rate at which the reduction rate of uranium reduced at the molten salt and liquid metal interface is dissolved or crushed into the liquid cathode and settles below the liquid cathode. It occurs when it is larger than. Therefore, the existing methods have a high initial uranium concentration in the molten salt, so if the amount of uranium to be recovered from the liquid cathode is high, the production of uranium dentite cannot be suppressed, and the production and growth rate can only be managed by precipitation by mechanical crushing. There is no fundamental problem. In particular, it becomes more difficult when the amount of uranium dentite is increased.

In other words, the liquid cathode electrolytic smelting process for recovering actinide-based elements from spent nuclear fuel covers the uranium dentite liquid metal interface generated at the interface between the liquid metal (cadmium) and the molten salt, and thus acts as a cathode. Deterioration of the function of the negative electrode causes a problem of reducing the recovery efficiency of other actinide metals.

The present invention has been made to solve the above problems of the prior art, by devising the structure of the liquid cathode crucible and adopting only the stirrer operation to apply only a simple structure and operation method to greatly improve the efficiency of the liquid cathode process of the electrosmelting process Has its purpose.

A first characteristic of the molten salt electrolyzer for recovering actinide-based elements according to the present invention for solving the above problems is an external crucible formed in the electrolytic cell and filled with molten salt in the molten salt-filled electrolytic cell, the outer A stirrer impeller formed on an inner portion of the crucible, the inner crucible having a liquid metal filled therein and rotating in contact with the upper surface of the liquid metal to move the uranium dentite generated on the upper surface of the liquid metal to the outer crucible; Include.

The molten salt electrolyzer includes a cathode lead wire connecting the liquid metal and the cathode of the power supply device, and includes a cathode lead wire connecting the molten salt and the anode of the power supply device. The liquid metal comprises cadmium.

The cathode lead wires penetrate the inside of the cathode shaft made of ceramic material, and the anode lead wires penetrate the interior of the anode wire shaft made of ceramic material.

The stirrer impeller is characterized by rotating by a drive motor.

The container of the external crucible and the container of the liquid metal crucible are formed of an insulating material.

In the molten salt-filled electrolytic cell according to the present invention, a crucible formed inside the electrolytic cell and filled with molten salt, a partition wall partitioning the inside of the crucible into a first space and a second space, and a liquid metal filled in the first space And an agitator impeller for moving the uranium dentite generated on the upper surface of the liquid metal to the second space by rotating in contact with the upper surface of the liquid metal.

The molten salt electrolyzer includes a cathode lead wire connecting the liquid metal and the cathode of the power supply device, and includes a cathode lead wire connecting the molten salt and the anode of the power supply device.

The cathode lead wires penetrate the inside of the cathode shaft made of ceramic material, and the anode lead wires penetrate the interior of the anode wire shaft made of ceramic material.

The molten salt electrolyzer is formed of an insulating material, the anode lead wire is formed of molybdenum or stainless steel, the stirrer impeller is formed of an insulating material. The liquid metal comprises cadmium.

The stirrer impeller is rotated by a drive motor.

The partition wall is formed of an insulating material.

The molten salt electrolyzer for recovering the actinide element according to the present invention configured as described above removes uranium dentite by providing a simple but improved crucible structure in which uranium dentite generated on the surface of the liquid cathode is precipitated to the bottom of the crucible. By maximizing the effect, there is an effect of greatly improving the actinide-based element recovery efficiency and treatment capacity by the liquid cathode.

Hereinafter, with reference to the accompanying drawings will be described specific details and embodiments of the present invention.

The present invention changes the structure of the liquid cathode to remove uranium dentite generated at the liquid cathode molten salt interface. The molten salt electrolytic smelting apparatus of the present invention uses a double crucible structure (see FIG. 2) and an internal split structure (see FIG. 4) as the structure of the liquid cathode while including all the components of the basic electrolytic smelting electrolyzer. This method has the advantage that the structure of the liquid cathode is simple and the structure is simple and the operation method is simple because only the agitator is used.

A schematic diagram of a liquid cathode electrolytic smelting apparatus using a double crucible liquid cathode (cadmium) structure according to an embodiment of the present invention is shown in FIG. 1. In the electrolytic smelting tank 101, a molten salt 102 in which actinide-based elements are present in the form of chloride is placed, and a cadmium metal 105 acting as a liquid cathode in the center portion of the liquid cathode external crucible 103 installed in the molten salt. Install the inner crucible 104 with the negative electrode. Both the external crucible and the internal crucible are made of ceramic material for insulation.

Referring to FIG. 1, an electrolytic cell 101 is filled with a molten salt 102, and an external crucible 103 is provided inside the electrolytic cell 101. An inner crucible 104 is formed at the center of the outer crucible 103, and the inner crucible 104 is filled with a liquid metal 105, and the outside of the crucible is surrounded by an insulating material.

The inside of the cathode shaft 107 made of a ceramic material penetrates through the liquid cathode lead wire 106 made of molybdenum or stainless steel to contact the liquid metal 105 to act as a cathode. The stirrer impeller 108 made of a ceramic material is attached to the lower portion of the stirrer shaft 109 through which the cathode ray shaft penetrates, and it is installed by adjusting its position to operate at the interface between the liquid cathode 105 and the molten salt 102. Hook the belt 110 to the teeth 111 on the stirrer to connect with the shaft 112 of the stirrer drive motor 113 to rotate the stirrer in accordance with the operation of the motor. The negative electrode connecting portion 114 of the upper portion of the liquid cathode lead wire is connected to the negative electrode of the voltage supply device 115 and the positive electrode connecting portion 116 is connected to the positive electrode of the voltage supply device 115 so that current flows. The anode consists of an anode shaft 117 and an anode lead wire 118.

Referring again to FIG. 1, an agitator impeller 108 is provided on top of the liquid metal 105, which agitates the uranium dentite component on the surface of the liquid metal by rotation of several rotating vanes. It precipitates to the bottom of the outer crucible 103. The stirrer impeller 108 is connected to the bottom of the stirrer shaft 109. In the electrolytic smelting process, a DC voltage supply device 115 for supplying power is provided, the anode of which is connected to the molten salt 102 and the cathode of the voltage supply device 115 is a liquid metal. Connected to 105. The molten salt 102 is connected to the anode of the voltage supply device through the anode lead 118, the anode lead 118 penetrates inside the anode shaft 117. The liquid metal 105 is connected to the cathode of the voltage supply device through the cathode lead wire 106, and the cathode lead wire 106 penetrates inside the cathode shaft 109.

2 is a front view and a cross-sectional view of the liquid cathode structure. Each reference numeral in FIG. 2 is indicated to correspond to a reference numeral of each component of the molten salt electrolyzer of FIG. 1.

A double crucible liquid cathode structure according to an embodiment of the present invention is characterized in that the inner crucible 204 is filled with the liquid metal to the height of the inner crucible and the stirrer impeller 208 is installed on the surface of the liquid metal. The molten salt is filled between the crucible and the external crucible. The stirrer impeller 208 adheres to the liquid cathode surface of the inner crucible and rotates on the molten salt to crush or push the uranium dentite generated at the surface of the liquid cathode to the outside of the inner crucible. At this time, the uranium dentite pushed out of the inner crucible 204 is over the wall of the inner crucible and precipitates to the bottom of the outer crucible 203 filled with molten salt due to the difference in specific gravity. Therefore, new liquid metal is continuously present on the surface of the liquid metal, and the recovery efficiency of actinide metals other than uranium can be increased.

On the other hand, when the actinide elements are electrodeposited on the liquid cathode, the electrodeposited elements are dissolved in the liquid metal, but the undissolved uranium forms the dendrite, and the other elements form the metal and the compound. As described above, the actinide-based element is electrodeposited onto the liquid metal in various forms. Accordingly, the volume of the liquid metal of the inner crucible increases and the volume of the increased liquid metal expands to the liquid metal surface of the inner crucible. On the surface of the liquid metal, liquid metal containing various types of actinide-based elements together with uranium dentite is expanded in volume. At this time, the liquid metal expanded on the surface of the liquid metal of the inner crucible is pushed out of the inner crucible by the rotational movement of the stirrer impeller and settles on the bottom of the outer crucible with the uranium dentite beyond the wall of the inner crucible. Therefore, although there is a difference in concentration of each element, in the inner crucible and the outer crucible, uranium dissolved in the liquid metal and uranium dissolved and pulverized by the stirrer are present together with the liquid metal.

A liquid cathode electrolytic smelting apparatus using an internal split crucible liquid metal (cadmium) structure according to another embodiment of the present invention is shown in FIG. In the electrolytic smelting tank 301, a molten salt 302 in which actinide-based elements are present in the form of chloride is placed, and the liquid cathode crucible 319 installed in the molten salt is provided with an inner partitioned surface 320 of the liquid cathode crucible. The inside of the liquid cathode is divided into two parts, a large part and a small part. The cadmium metal 305 acting as a liquid cathode is placed in the bulky portion, and the small portion is filled with the molten salt 302 like the outside of the crucible. These crucibles are made of ceramic material for insulation.

The liquid cathode electrolytic smelting apparatus according to another embodiment of the present invention shown in FIG. 3 has the same components as the electrolytic smelting apparatus of FIG. 1 except that the crucible is in the form of internal division. In FIG. 3, the crucible 319 is divided into a first space and a second space, filled with a liquid metal 305 in the first space, and molten salt is present in the second space. The first space and the second space are partitioned by a partition wall 307 made of an insulating material.

The liquid metal acts as a cathode by penetrating the liquid cathode lead wire 306 made of molybdenum or stainless steel through the inside of the cathode ray shaft 307 made of a ceramic material and contacting the liquid metal 305. A ceramic impeller 308 is attached to the lower portion of the stirrer shaft 309 through which the cathode ray shaft penetrates and is installed by adjusting the position to operate at the interface between the liquid cathode 305 and the molten salt 302. Hook the belt 310 to the teeth 311 of the top of the stirrer and is connected to the shaft 312 of the stirrer drive motor 313 to rotate the stirrer in accordance with the operation of the motor. The negative electrode connecting portion 314 of the upper portion of the liquid cathode lead wire is connected to the negative electrode of the voltage supply device 315, and the positive electrode connecting portion 316 is connected to the positive electrode of the voltage supply device 315 to allow current to flow. The anode consists of an anode shaft 317 and an anode lead wire 318.

4 is a front view and a cross-sectional view of the liquid cathode structure. Each reference numeral in FIG. 2 is indicated to correspond to a reference numeral of each component of the molten salt electrolyzer of FIG. 1.

The internally divided crucible-type liquid cathode structure according to another embodiment of the present invention is characterized in that the inner crucible has a height of the inner dividing surface 420 lower than the height of the outer wall of the liquid cathode crucible. It is filled up to the height and the impeller 408 of the stirrer is installed on the surface of the liquid metal, and the liquid metal is not filled in the crucible but the molten salt is filled. The impeller 408 of the stirrer adheres to the liquid metal surface inside the crucible and rotates on the molten salt to crush or push uranium dendrites generated on the surface of the liquid cathode to push the molten salt inside the crucible into the filled portion. At this time, the uranium dentite pushed out into the crucible's inner dividing surface exceeds the dividing surface and precipitates at the bottom of the molten salt-filled portion due to the specific gravity difference. Therefore, new liquid metal is continuously present on the surface of the liquid metal, and the recovery efficiency of actinide-based metals other than uranium can be increased.

On the other hand, when the actinide elements are electrodeposited on the liquid cathode, the electrodeposited elements are dissolved in the liquid metal, but the undissolved uranium forms the dendrite, and the other elements form a compound with the metal. As described above, the actinide group element is electrodeposited onto the liquid metal in various forms. Accordingly, the volume of the liquid metal of the cathode crucible increases and the volume of the increased liquid metal expands to the surface of the liquid metal of the cathode crucible. On the surface of the liquid metal, liquid metal containing various types of actinide elements together with uranium dentite is expanded in volume. At this time, the liquid metal expanded on the surface of the liquid metal of the cathode crucible is pushed to the inner part of the crucible by the rotational movement of the stirrer impeller and settles at the bottom of the crucible of the molten salt portion over the wall of the inner part of the crucible with uranium dentite. Done. Therefore, although there is a difference in concentration of each element, in the inner crucible and the outer crucible, as well as the electrodeposited actinide elements, the dissolved uranium and uranium precipitated by the stirrer are present together with the liquid metal.

As described above with reference to the drawings illustrating a molten salt electrolytic cell for the actinide-based element recovery according to the present invention, the present invention is not limited by the embodiments and drawings disclosed herein, the scope of the technical idea is protected It can be applied within.

1 is a cross-sectional view of a molten salt electrolytic smelting apparatus showing an embodiment of a double crucible liquid cathode structure for recovering actinide-based elements of the present invention;

FIG. 2 shows a double crucible liquid cathode structure designed for uranium dentite removal in the apparatus of FIG.

3 is a cross-sectional view of a molten salt electrolytic smelting apparatus showing an embodiment of a split crucible liquid cathode structure for recovering actinide-based elements of the present invention;

4 is a diagram illustrating an internal split crucible liquid cathode structure designed for uranium dentite removal applied in the apparatus of FIG. 3.

           <Explanation of symbols on main parts of the drawings>

101: molten salt electrolytic smelting tank 102; Molten salt

103; Liquid cathode outer crucible 104: Liquid cathode inner crucible

105: liquid metal 108: stirrer impeller

115: voltage supply device 306: liquid cathode lead wire

318: anode lead wire 320: liquid cathode crucible internal split surface

Claims (19)

In the electrolytic cell filled with molten salt, An external crucible formed inside the electrolytic cell and filled with molten salt; An inner crucible formed at an inner portion of the outer crucible and filled with a liquid metal therein; And A molten salt electrolyzer for recovering actinide-based elements comprising an agitator impeller for moving the uranium dentite produced on the upper surface of the liquid metal to the outer crucible by rotating in contact with the upper surface of the liquid metal. The method according to claim 1, The molten salt electrolyzer comprises a cathode lead wire connecting the liquid metal and the cathode of the voltage supply device. The method according to claim 2, The cathode lead wire is a molten salt electrolyzer for recovering actinide-based elements, characterized in that penetrating through the interior of the cathode shaft of a ceramic material. The method according to claim 1, The molten salt electrolyzer comprises a positive electrode lead wire for connecting the molten salt and the positive electrode of the voltage supply device. The method according to claim 4, The anode lead wire is a molten salt electrolyzer for recovering actinide-based elements, characterized in that penetrating through the interior of the anode wire shaft of a ceramic material. The method according to claim 1, The stirrer impeller is a molten salt electrolyzer for actinide element recovery, characterized in that formed of an insulating material. The method according to claim 1, The molten salt electrolyzer for recovering actinide-based elements, characterized in that the liquid metal comprises cadmium. The method according to claim 1, The stirrer impeller is rotated by a drive motor, molten salt electrolyzer for actinide-based element recovery, characterized in that. The method according to claim 1, The container of the external crucible and the container of the liquid metal crucible are molten salt electrolyzer for recovering actinide-based elements, characterized in that formed of an insulating material. In the electrolytic cell filled with molten salt, A crucible formed inside the electrolytic cell and filled with molten salt; A partition wall dividing the inside of the crucible into a first space and a second space; A liquid metal filled in the first space; And A molten salt electrolyzer for recovering actinide-based elements comprising an agitator impeller for moving the uranium dentite generated on the upper surface of the liquid metal to the second space by rotating in contact with the upper surface of the liquid metal. The method of claim 10, The molten salt electrolyzer comprises a cathode lead wire connecting the liquid metal and the cathode of the voltage supply device. The method according to claim 11, The cathode lead wire is a molten salt electrolyzer for recovering actinide-based elements, characterized in that penetrating through the interior of the cathode shaft of a ceramic material. The method according to claim 11, The molten salt electrolyzer comprises a positive electrode lead wire for connecting the molten salt and the positive electrode of the voltage supply device. The method of claim 13, The anode lead wire is a molten salt electrolyzer for recovering actinide-based elements, characterized in that penetrating through the interior of the anode wire shaft of a ceramic material. The method of claim 10, The stirrer impeller is a molten salt electrolyzer for recovering actinide-based elements, characterized in that formed of an insulating material. The method of claim 10, The molten salt electrolyzer for recovering actinide-based elements, characterized in that the liquid metal comprises cadmium. The method of claim 10, The stirrer impeller is rotated by a drive motor, molten salt electrolyzer for actinide-based element recovery, characterized in that. The method of claim 10, The crucible is a molten salt electrolyzer for recovering actinide-based elements, characterized in that formed of an insulating material. The method of claim 10, The partition wall is a molten salt electrolyzer for recovering actinide-based elements, characterized in that formed of an insulating material.

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