JP2010197360A - Method for treating spent oxide fuel and method and device for treating metal oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating spent oxide fuel and a method and a device for treating metal oxide which efficiently treat metal oxide such as spent oxide fuel and recover metal without loss. <P>SOLUTION: The methods and the device include an electrolytic reduction process for electrochemically reducing the spent oxide fuel to uranium metal and transuranic elements and dissolving them in molten metal by holding the spent oxide fuel on the boundary surface between molten salt and the molten metal by the difference in specific gravity and using the latter as a counter electrode to an anode and an electrolytic refining process for electrochemically recovering the uranium metal and the transuranic elements from the molten metal where they are dissolved in the electrolytic reduction process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spent oxide fuel processing method, a processing apparatus, and an oxide processing method, and more particularly, reused as FBR fuel by reducing and purifying spent oxide fuel generated from a light water reactor to metal. The present invention relates to a method for treating a used spent oxide fuel, a method for treating a metal oxide, and a treatment apparatus.

  When the oxide fuel generated from the light water reactor is converted into a metal fuel and reused as an FBR (Fast Breeder Reactor) fuel, the spent oxide fuel is separated from the cladding tube by decoating and reprocessed. At this time, the decoated oxide fuel is pulverized and recovered in the form of granules or powder. When holding the oxide fuel in the granular or powder state in the cathode container and subjecting it to electrolytic reduction, the cathode container is better in reducing efficiency when the aperture ratio is larger, while holding the powder and improving the yield. Need to have a fine mesh structure. In order to eliminate this contradiction, measures have been taken such as once pelletized oxide fuel is again pelletized and subjected to reduction. However, in this case, efficiency reduction due to an increase in the process cannot be denied. There is also a problem that part of the oxide fuel brought into the electrolytic reduction tank diffuses from the cathode container.

  In addition, as a molten salt electrorefining device for recovering uranium and plutonium from spent metal fuel, the spent metal fuel is accommodated in an anode basket, immersed in molten cadmium and dissolved, and this molten cadmium acts as an anode to serve as a cathode. An apparatus for depositing uranium and plutonium is known (for example, see Patent Document 1). However, even in this method, the spent metal fuel is accommodated in the anode basket, so that there is a problem that the number of processes is large.

Japanese Patent Application Laid-Open No. 11-148995

  As described above, in the conventional spent oxide fuel processing, there is a problem that the efficiency decreases due to an increase in the number of steps, and a part of the oxide fuel brought into the electrolytic reduction tank is removed from the cathode container. It has spread and has become a challenge in the metrology management of the reprocessing process.

  The present invention has been made in response to the above-described conventional circumstances, and can be used to efficiently process metal oxides such as spent oxide fuel and can be recovered without loss of metal. It is an object of the present invention to provide an oxide fuel treatment method, a metal oxide treatment method, and a treatment apparatus.

  One aspect of a method for treating a spent oxide fuel according to the present invention is a treatment method of a spent oxide fuel using a molten salt electrolysis method. A step of preparing an electrolytic cell containing two layers and holding a solid anode in the molten salt, and a used oxide fuel are held at the interface between the molten salt of the electrolytic cell and the molten metal by a specific gravity difference. Using the molten metal as a counter electrode of the anode, and electrochemically reducing the spent oxide fuel to metal uranium and transuranium elements and dissolving them in the molten metal; and the electrolytic reduction step And an electrolytic purification step of electrochemically recovering the metal uranium and the transuranium element from the molten metal in which the metal uranium and the transuranium element are dissolved.

  Another aspect of the method for treating spent oxide fuel according to the present invention is a molten metal that dissolves molten salt, metal uranium, and transuranium element in the spent oxide fuel treatment method using a molten salt electrolysis method. And preparing an electrolytic refining tank containing a molten salt and having a cathode made of a solid or liquid metal in the molten salt And holding the spent oxide fuel at the interface between the molten salt of the electrolytic cell and the molten metal by a specific gravity difference, and using the molten metal as a counter electrode of the anode, Electroreduction step of reducing to metal uranium and transuranium element and dissolving in the molten metal, transporting step of transferring the molten metal in which the metal uranium and transuranium element are dissolved to the electrolytic purification tank, and the electrolysis Purification tank A step of using the molten metal in which the transferred metal uranium and the transuranium element are dissolved as an anode and energizing between the cathode and recovering the metal uranium and the transuranium element to the cathode. To do.

  One aspect of the metal oxide treatment method of the present invention is a metal oxide treatment method for recovering a useful metal from a metal oxide using a molten salt electrolysis method, wherein the useful metal is obtained from the molten salt and the metal oxide. A step of preparing an electrolytic cell that accommodates the molten metal to be dissolved and extracted in two layers; and the metal oxide is held at the interface between the molten metal and the molten salt in the electrolytic cell by a specific gravity difference, and the molten metal As a counter electrode of the anode held in the molten salt, and electrochemically reducing the metal oxide to a useful metal electrochemically, and bringing the useful metal into contact with the molten metal to form the molten metal It is characterized by comprising an extraction step of dissolving and extracting the inside and an electrolytic purification step of recovering the useful metal electrochemically from the molten metal obtained by dissolving and extracting the useful metal.

  One aspect of the metal oxide treatment apparatus of the present invention is a metal oxide treatment apparatus for recovering useful metal from a metal oxide using a molten salt electrolysis method, wherein the useful metal reduced from the metal oxide is used. An electrolytic cell in which a molten metal and a molten salt are contained in two layers and a solid anode is held in the molten salt, and the metal oxide is held at the interface between the molten salt and the molten metal due to a difference in specific gravity. An electrolytic cell for electrochemically reducing the metal oxide to the useful metal by using the molten metal as a counter electrode of the anode and dissolving the metal in the molten metal; and electrochemically processing the metal in the molten metal And an electrolytic refining tank for recovery.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to process metal oxides, such as a used oxide fuel efficiently, the processing method of the used oxide fuel which can collect | recover without losing a metal, metal oxide A processing method and a processing apparatus can be provided.

1 is a longitudinal sectional view showing a configuration of an oxide fuel processing apparatus according to an embodiment of the present invention. The longitudinal cross-sectional view which shows the structure of the electrolytic reduction tank which concerns on one Embodiment of this invention. The longitudinal cross-sectional view which shows the structure of the electrolytic refining tank which concerns on one Embodiment of this invention. The schematic diagram for demonstrating the transfer of the molten cadmium which concerns on one Embodiment of this invention. The longitudinal cross-sectional view which shows the structure of the processing apparatus of the oxide fuel which concerns on other embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view schematically showing a schematic configuration of an oxide fuel processing apparatus according to an embodiment of the present invention, and FIG. 2 is an enlarged longitudinal sectional view showing an electrolytic reduction tank 1 shown in FIG. FIG. 3 is an enlarged longitudinal sectional view of the electrolytic purification tank 9 shown in FIG.

  The present embodiment relates to processing of spent oxide fuel for recovering metal from spent oxide fuel generated from a light water reactor using a molten salt electrolysis method, and includes the following steps. That is, electrolysis in which a metal oxide constituting an oxide fuel is reduced to a metal such as metal uranium (U) or transuranium element (TRU) by a molten salt electrolysis method and dissolved in molten metal (molten cadmium in this embodiment). It is a reduction process and an electrolytic purification process in which U and TRU in molten metal (molten cadmium in the present embodiment) are purified and recovered as metal by electrolytic purification.

  As shown in FIG. 1, the spent oxide fuel treatment apparatus according to this embodiment includes an electrolytic reduction tank 1 and an electrolytic purification tank 9.

  As shown in FIGS. 1 and 2, the electrolytic reduction tank 1 includes an electrolytic tank container 2. In the electrolytic tank container 2, molten cadmium 3 is provided at the lower portion thereof, and molten salt 4 is provided above the molten cadmium 3. Is housed in two layers. In the molten cadmium 3, a current-introducing metal rod 7 whose body is insulated by an insulating tube 6 is inserted, and in the molten salt 4, a solid anode 8 is installed. The solid anode 8 is configured so that the surface area of the portion immersed in the molten salt 4 is sufficiently large. The electrolytic reduction tank 1 is provided with a power source (not shown) for energizing through the current-introducing metal rod 7 and the solid anode 8.

  As shown in FIGS. 1 and 3, the electrolytic purification tank 9 includes an electrolytic purification container 10. In the electrolytic purification vessel 10, molten cadmium 3 transferred from the electrolytic reduction tank 1 is accommodated in the lower part, and molten salt 11 for electrolytic purification is accommodated in the upper part of the molten cadmium 3.

  In the molten cadmium 3, a current introducing metal rod 13 whose body is insulated by an insulating tube 12 is inserted. In the molten salt 11 for electrolytic purification, a solid cathode 14 and a liquid metal cathode 15 acting as a cathode are disposed. In FIG. 1, reference numeral 18 denotes an insulating tube, 19 denotes a current introducing rod for the liquid metal cathode 15, and 23 denotes an insulating container for the liquid metal cathode 15. The electrolytic purification tank 9 is provided with a power source (not shown) for energizing through the current-introducing metal rod 13 and the solid cathode 14 or the liquid metal cathode 15.

  As shown in FIG. 1, a first transfer pipe 29 for transferring molten cadmium 3 from the electrolytic reduction tank 1 to the electrolytic purification tank 9 between the electrolytic reduction tank 1 and the electrolytic purification tank 9, and electrolytic purification Second transfer pipes 27 </ b> A and 27 </ b> B for transferring the molten cadmium 3 from the tank 9 to the electrolytic reduction tank 1 through the holding container 28 are provided. The holding container 28 is for temporarily holding the molten cadmium 3 transferred from the electrolytic purification tank 9 to the electrolytic reduction tank 1 and is capable of heating the molten cadmium 3.

  As shown in FIGS. 1 and 2, when the spent oxide fuel 5 is introduced into the electrolytic cell container 2 of the electrolytic reduction tank 1 in the spent oxide fuel processing apparatus having the above-described configuration, the specific gravity is increased from the molten salt 4. The spent oxide fuel 5 that is heavy and lighter in specific gravity than the molten cadmium 3 is held at the interface between the molten salt 4 and the molten cadmium 3 due to the difference in specific gravity, and thus comes into contact with the molten cadmium 3. The spent oxide fuel 5 may be in the form of granules, powder, or any form.

In this state, when a current is supplied from a power source (not shown) between the metal rod 7 for current introduction inserted into the molten cadmium 3 and the anode 8 held in the molten salt 4, the molten cadmium 3 acting as a cathode. From the spent oxide fuel 5 having the same potential as that of oxygen, oxygen is released by an electrochemical reaction such as UO ₂ + 4e ⁻ → U + 2O ²⁻ and is reduced to a metal.

Since the metal uranium or the like reduced as described above is in contact with the molten cadmium 3, it reacts with the molten cadmium 3 simultaneously with the reduction to form an intermetallic compound such as UCd ₁₁ or PuCd ₁₁ to form the molten cadmium 3. Dissolve in

  Since the above electrolytic reduction always occurs at the interface with the molten cadmium 3, the used oxide fuel 5 that has fallen out of the container is transferred to the electrolytic cell as in the conventional electrolytic reduction in which the spent oxide fuel 5 is held in the container. The yield of the process can be kept high without being unrecoverable while being deposited on the bottom.

  Further, since the spent oxide fuel 5 and the metal are not maintained in a mixed state at the interface of the molten cadmium 3, and the surface of the spent oxide fuel 5 is always facing the anode 8. The time required for diffusion of oxygen into the oxide structure can be shortened, and the reduction rate can be improved. Further, since the fuel component reduced to metal is immediately dissolved in the molten cadmium 3, it is less susceptible to re-oxidation due to oxygen generated at the cathode.

  As described above, U and TRU (transuranium elements: plutonium, neptunium, americium, curium, etc.) in the spent oxide fuel 5 reduced to metal in the electrolytic reduction tank 1 are dissolved in the molten cadmium 3, When the concentration of U and TRU in the molten cadmium 3 is saturated, the reduced U and TRU are not dissolved in the molten cadmium 3. For this reason, the molten cadmium 3 is transferred to the electrolytic purification tank 9 through the first transfer pipe 29 in a state where the concentrations of U and TRU in the molten cadmium 3 are saturated or close to saturation. The molten cadmium 3 is transferred by, for example, a transfer pump (not shown) provided in the first transfer pipe 29.

  As shown in FIG. 4, prior to the transfer of the molten cadmium 3 from the electrolytic reduction tank 1 to the electrolytic purification tank 9, the molten cadmium 3 in the electrolytic purification tank 9 from which U and TRU have been separated is transferred to the second transfer pipe. It is transferred to the holding container 28 at 27B. When the transfer of the molten cadmium 3 in which U and TRU are dissolved from the electrolytic reduction tank 1 to the electrolytic purification tank 9 is completed, half of the molten cadmium 3 not containing U and TRU in the holding container 28 is transferred to the second transfer pipe. It is transferred to the electrolytic reduction tank 1 at 27A. By transferring the molten cadmium 3 in this way, electrolytic reduction and electrolytic purification can be continued except for the transfer time, and the operation efficiency of the process can be improved.

  In the electrolytic purification tank 9, the molten cadmium 3 transferred from the electrolytic reduction tank 1 is processed by electrolytic purification. At that time, the molten cadmium 3 is used as an anode, and a current is passed between the anode and the cathode from a power source (not shown) using the solid cathode 14 or the liquid metal cathode 15. Thereby, U and TRU contained in the molten cadmium 3 are recovered as metal in the solid cathode 14 or the liquid metal cathode 15.

  Next, another embodiment will be described with reference to FIG. FIG. 5 schematically shows a vertical cross-sectional schematic configuration of the spent oxide fuel processing apparatus according to the present embodiment. The same reference numerals are given to the configurations corresponding to those in FIG. To do. In this embodiment, the electrolytic reduction and electrolytic purification processes described in the above-described embodiments are to be realized in a single container partitioned by a partition plate.

  As shown in FIG. 5, in this embodiment, the electrolytic reduction tank 1 and the electrolytic purification tank 9 are configured by partitioning a single electrolytic tank container 31 with a partition wall (partition plate) 33, and below the partition plate. A molten metal transfer passage 39 is formed between the bottom plate and the electrolytic reduction tank 1 and the electrolytic purification tank 9 directly. In the electrolytic cell container 31, molten cadmium 3 is accommodated so as to be positioned below, and the partition wall 33 is disposed so as to extend into the molten cadmium 3. Molten cadmium 3 is kept at a constant element concentration on both the electrolytic reduction tank 1 side and the electrolytic purification tank 9 side.

  In the upper part of the molten cadmium 3, a molten salt 35 on the electrolytic reduction tank 1 side and a molten salt 37 on the electrolytic purification tank 9 side are accommodated in a state of being partitioned by a partition wall 33. As the molten salt 35 on the electrolytic reduction side, for example, lithium chloride salt + lithium oxide can be used. Further, as the molten salt 37 on the electrolytic purification tank 9 side, for example, lithium chloride + potassium chloride + uranium chloride can be used. The metal rod 24 for current introduction, the body of which is insulated by the insulating tube 26 and immersed in the molten cadmium 3, is used in both the electrolytic reduction tank 1 and the electrolytic purification tank 9, and as a cathode in the case of electrolytic reduction. In the case of electrolytic purification, it is used as an anode.

  In the present embodiment, a current is passed between the anode 8 and the molten cadmium 3 in a state where the spent oxide fuel is held at the interface between the molten salt 35 and the molten cadmium 3 on the electrolytic reduction tank 1 side due to the specific gravity difference. Then, electrolytic reduction is performed.

  Then, after the concentration of U and TRU in the molten cadmium 3 is increased by electrolytic reduction, the polarity of the molten cadmium 3 is switched to the anode, and the solid cathode 14 or the liquid metal cathode 15 on the electrolytic purification tank 9 side is used as the cathode. Electrolytic purification is performed by passing an electric current between them. Thereby, both electrolytic reduction and electrolytic purification can be carried out in the same tank, the process can be made compact, and the transfer system for the molten cadmium 3 can be omitted.

  In each of the above embodiments, the case where molten cadmium 3 is used as the molten metal has been described. However, the molten metal may be any metal that dissolves useful metals such as U and TRU to be recovered. An alloy such as Mg, Cd—Li, Cd—Mg, or Cu—Mg, or a low melting point metal such as Sb or Pb can be used.

  Moreover, although the said embodiment demonstrated the case where U and TRU were collect | recovered from the used oxide fuel 5, when recovering useful metals from other metal oxides, for example, zirconium oxide, copper oxide, titanium oxide, etc. The same applies to the case of recovering these metals from these oxides.

  In addition, this invention is not limited to the said embodiment, Of course, various deformation | transformation are possible.

  DESCRIPTION OF SYMBOLS 1 ... Electrolytic reduction tank, 2 ... Electrolytic tank container, 3 ... Molten cadmium, 4 ... Molten salt, 5 ... Used oxide fuel, 6 ... Insulating tube, 7 ... Metal rod for electric current introduction, 8 ... Solid anode, 9 ... Electrolytic purification tank, 10 ... Electrolytic purification vessel, 11 ... Molten salt, 12 ... Insulating tube, 13 ... Metal rod for current introduction, 14 ... Solid cathode, 15 ... Liquid metal cathode, 28 ... Holding vessel, 27A, 27B ... Second Transfer pipe, 29 ... 1st transfer pipe.

Claims (15)

In a method for treating spent oxide fuel using a molten salt electrolysis method,
Preparing an electrolytic cell containing a molten salt and a molten metal that dissolves metal uranium and a transuranium element in two layers and holding a solid anode in the molten salt;
The spent oxide fuel is held at the interface between the molten salt of the electrolytic cell and the molten metal by a specific gravity difference, and the spent oxide fuel is electrochemically used by using the molten metal as a counter electrode of the anode. An electrolytic reduction step of reducing to metal uranium and transuranium elements and dissolving in the molten metal;
An electrolytic refining step of electrochemically recovering the metal uranium and the transuranium element from the molten metal in which the metal uranium and the transuranium element are dissolved in the electrolytic reduction step. Processing method. The method for treating spent oxide fuel according to claim 1,
In the electrolytic purification step, the molten metal in which the molten uranium and the transuranium element are dissolved is accommodated in an electrolytic purification tank in which a molten salt is accommodated and a cathode made of solid or liquid metal is installed in the molten salt. A method for treating spent oxide fuel, wherein electrolytic purification is performed using the molten metal in which uranium and transuranium elements are dissolved as an anode. In a method for treating spent oxide fuel using a molten salt electrolysis method,
An electrolytic cell in which a molten salt and a molten metal that dissolves metal uranium and a transuranium element are contained in two layers and a solid anode is held in the molten salt; a molten salt that is solid or liquid in the molten salt A step of preparing an electrolytic purification tank provided with a cathode made of metal;
The spent oxide fuel is held at the interface between the molten salt of the electrolytic cell and the molten metal by a specific gravity difference, and the spent oxide fuel is electrochemically used by using the molten metal as a counter electrode of the anode. An electrolytic reduction step of reducing to metal uranium and transuranium elements and dissolving in the molten metal;
A transfer step of transferring the molten metal in which the metal uranium and the transuranium element are dissolved to the electrolytic purification tank;
A step of collecting the metal uranium and the transuranium element at the cathode by energizing between the cathode and the molten metal dissolved in the metal uranium and the transuranium element transferred to the electrolytic purification tank as an anode; A method for treating spent oxide fuel, comprising: In the processing method of the spent oxide fuel of Claim 2 or 3,
The method for treating spent oxide fuel, wherein the molten metal storage part of the electrolytic cell and the molten metal storage part of the electrolytic purification tank are connected by a transfer pipe through a molten metal holding container. In the processing method of the spent oxide fuel of Claim 2 or 3,
The electrolytic bath and the electrolytic refining bath are configured by partitioning a single container with a partition plate, and a molten metal transfer path is formed in the lower portion of the partition plate so as to directly communicate both tanks with the bottom plate. A method for treating spent oxide fuel, comprising: In the processing method of the used oxide fuel of any one of Claims 1-5,
The method for treating spent oxide fuel, wherein the molten metal is at least one selected from the group consisting of Cd, Zn-Mg, Cd-Li, Cd-Mg, Cu-Mg, Sb, and Pb. . In the metal oxide treatment method for recovering useful metals from metal oxides using molten salt electrolysis,
Preparing an electrolytic cell containing a molten salt and a molten metal for dissolving and extracting the useful metal from the metal oxide in two layers;
The metal oxide is held by the specific gravity difference at the interface between the molten metal and the molten salt in the electrolytic cell, and the molten metal is used as a counter electrode of the anode held in the molten salt. An electrolytic reduction process for reducing electrochemically to useful metals;
An extraction step of bringing the useful metal into contact with the molten metal and dissolving and extracting into the molten metal;
And an electrolytic purification step of electrochemically recovering the useful metal from the molten metal obtained by dissolving and extracting the useful metal. In the processing method of the metal oxide of Claim 7,
A method for treating a metal oxide, wherein the metal oxide comprises one or more metal oxides selected from zirconium oxide, hafnium oxide, copper oxide, and titanium oxide. In the processing method of the metal oxide of Claim 7 or 8,
The method for treating a metal oxide, wherein the molten metal is at least one selected from the group consisting of Cd, Zn-Mg, Cd-Li, Cd-Mg, Cu-Mg, Sb and Pb. In a metal oxide processing apparatus for recovering useful metals from metal oxides using a molten salt electrolysis method,
An electrolytic cell in which a molten metal that dissolves the useful metal reduced from the metal oxide and a molten salt are contained in two layers and a solid anode is held in the molten salt, the metal oxide being the molten salt And an electrolytic cell in which the metal oxide is electrochemically reduced to the useful metal and dissolved in the molten metal using the molten metal as a counter electrode of the anode while maintaining the interface between the molten metal and the molten metal. When,
An apparatus for treating metal oxide, comprising: an electrolytic purification tank for electrochemically recovering the metal in the molten metal. In the metal oxide processing apparatus according to claim 10,
The electrolytic refining tank contains a molten salt and the molten metal in which the useful metal is dissolved, and includes a cathode made of a solid or liquid metal installed in the molten salt, and the molten metal in which the useful metal is dissolved An apparatus for treating a metal oxide, wherein the apparatus is configured to perform electrolytic purification using a metal as an anode. The metal oxide processing apparatus according to claim 11, wherein
A first transfer pipe for transferring the molten metal from the molten metal reservoir of the electrolytic cell to the molten metal reservoir of the electrolytic purification tank;
A metal oxide comprising: a second transfer pipe for transferring the molten metal from the molten metal reservoir of the electrolytic refining tank to the molten metal reservoir of the electrolytic tank through a molten metal holding container Processing equipment. The metal oxide processing apparatus according to claim 11, wherein
The electrolytic bath and the electrolytic refining bath are configured by partitioning a single container by a partition plate, and a molten metal transfer path is formed at the lower portion of the partition plate to directly connect both the tanks to the bottom plate. A metal oxide processing apparatus characterized by comprising: In the metal oxide processing apparatus according to any one of claims 10 to 13,
The metal oxide comprises one or more metal oxides selected from zirconium oxide, hafnium oxide, copper oxide, and titanium oxide, or a spent oxide fuel. Processing equipment. In the metal oxide processing apparatus of any one of Claims 10-14,
The metal oxide processing apparatus, wherein the molten metal is at least one selected from the group consisting of Cd, Zn-Mg, Cd-Li, Cd-Mg, Cu-Mg, Sb and Pb.

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