JP2005195462A - Method and device for electrorefining spent nuclear fuel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for electrorefining spent nuclear fuel which make it possible to load the spent nuclear fuel into an anode and recover anode residue and cathode precipitate in a normal operating condition and enable continuous operation and highly efficient treatment. <P>SOLUTION: The device for electrorefining the spent nuclear fuel 8 is equipped with an electrorefining container 2 stored with a molten salt 1 made by melting a salt such as chloride and fluoride at high temperature, the anode shaped like a basket or a perforated container which accommodates the spent nuclear fuel 8 and is submerged in the molten salt 1, a power supply circuit 10 which switches over the energization through the anode, a cathode 5 shaped like a column or a cylinder which is submerged in the molten salt 1 and is horizontally placed on the liquid level of it, a power supply device which passes a current between the anode and the cathode through the molten salt 1, a cathode rotator 6 which rotates the cathode 5 on the central axis and a scraper blade 7 which is in contact with the circumferential face of the cathode and scrapes down the precipitate containing uranium and transuranic elements precipitating on the circumferential face. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to spent nuclear fuel reprocessing, and relates to an electrolytic purification method and apparatus for separating and recovering reusable uranium and transuranium (TRU) by electrolyzing spent nuclear fuel in a molten salt bath.

In the conventional electrorefining of spent nuclear fuel using molten salt, it is a batch-type treatment in units of spent nuclear fuel loaded in the molten salt or in units of cathode deposition, and a continuous scraping mechanism for cathode deposits. Even in the electrolytic purification apparatus having the above, since the collection of the deposits depends on the collection container or the like at the lower part of the apparatus, the batch processing is controlled by the capacity of the collection container. Therefore, it is necessary to take out the electrode from the molten salt for exchanging the electrode and the collection container, and for handling at the time of exchanging, an operation such as lowering the temperature of the heating device is necessary, and there is a problem that the processing efficiency is low ( See Patent Documents 1 and 2 below).
Japanese Patent Laid-Open No. 10-53888 JP-A-10-53889

  The present invention has been made to solve the problems of the prior art, and can be used to load spent nuclear fuel to the anode, recover the anode residue, recover the cathode deposit, etc. in a steady operation state. It is an object of the present invention to provide a method and apparatus for electrolytic purification of spent nuclear fuel that can be operated and has high processing efficiency.

  In order to achieve the above object, the invention of claim 1 is characterized in that an electrolytic vessel for storing a molten salt obtained by melting a salt such as chloride or fluoride at a high temperature and a spent nuclear fuel are accommodated and immersed in the molten salt. A cage-shaped or perforated container-shaped anode, a power supply circuit for switching energization to the anode, a columnar or cylindrical shape, and a lower part is immersed in the molten salt and provided horizontally on the liquid surface of the molten salt A cathode, a power supply device for passing a current between the anode and the cathode through the molten salt, a cathode rotating device for rotating the cathode around a central axis, and the circumferential surface in contact with the circumferential surface of the cathode And a scraping blade for scraping off the precipitates containing the uranium and super uranium elements deposited on the substrate.

According to a second aspect of the present invention, the anode is configured to supply current to the spent nuclear fuel by a rotating current supply shaft having a plurality of arms.
According to a third aspect of the present invention, the cathode includes a stirrer that stirs the molten salt.

According to a fourth aspect of the present invention, the cathode and the scraping blade include a heating device that heats the precipitate.
According to a fifth aspect of the present invention, a slope is provided at the rear part of the scraping blade to collect the deposit scraped off from the cathode in a deposit collecting container.

  In the invention of claim 6, a plurality of cage-like or perforated container-like anodes containing spent nuclear fuel are immersed in a molten salt obtained by melting a salt such as chloride or fluoride at a high temperature, A cylindrical shape is formed by immersing the lower part in the molten salt and rotating a cathode horizontally provided on the surface of the molten salt around a central axis while passing an electric current between the anode and the cathode through the molten salt. The current is applied to the plurality of anodes while flowing, and the precipitates containing uranium and superuranium elements deposited on the circumferential surface of the cathode are scraped off with a scraping blade.

  According to the present invention, the spent nuclear fuel can be loaded to the anode in a steady operation state, the anode residue can be collected, the cathode deposit can be collected, and the like. Purification methods and equipment can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
The spent nuclear fuel electrolytic purification apparatus according to the embodiment of the present invention is installed in an electrolytic vessel 2 for storing a molten salt 1 and an outer peripheral portion of the electrolytic vessel 2 as shown in FIG. Partially melted supported by the electric furnace 3, the cage-shaped or perforated container-shaped anode 4 loaded with the spent nuclear fuel 8 to be processed, and the support provided with the shafts at both ends outside the electrolytic container 2. The cathode 5 is set in a state immersed in the salt 1, the rotating device 6 rotates the cathode 5, and the scraping blade 7 for separating the precipitate from the cathode 5. Although not shown, a DC power supply device connected to the anode 4 and the cathode 5 is provided. With this configuration, useful uranium and TRU are dissolved by electrolytic purification from the spent nuclear fuel 8 loaded on the anode 4 and immersed in the molten salt 1, purified to the cathode 5, and collected by precipitation.

  As shown in FIG. 2, a plurality of basket-like or perforated container-like anodes 4 are provided, an anode pulling mechanism 9 that pulls up each anode 4, and a power supply circuit that connects and disconnects the power source for each anode 4. 10 is provided. In this way, a plurality of anodes 4 for loading spent nuclear fuel are installed, each anode is connected to a power source in parallel, and a power supply circuit 10 for connecting and disconnecting the power source is provided for each anode to provide electrolytic treatment for each anode. By shifting the work, it becomes possible to sequentially cut and take out the anode that has been subjected to electrolytic refining, and to supply the spent nuclear fuel to be loaded on the anode without stopping the electrolytic refining and the cladding tube material and oxide remaining on the anode after electrolysis Can be taken out.

  The electrolytic purification apparatus of the present embodiment is also configured to control the continuation and stop of the electrolytic current so that the supply of current to the anode 4 is uniform with respect to the surface of the opposing cathode 5. According to this configuration, the supply of current to the anode 4 can be arbitrarily distributed to each anode by the power supply circuit 10 having a function of connecting and disconnecting the power source for each anode 4, and thus to the cathode 5. It is possible to make the growth of precipitates uniform, improve the current efficiency consumed for electrolytic refining, and prevent obstacles to scraping of the precipitates due to the generation of uneven precipitates on the cathode 5 It becomes possible to do.

  The electrolytic purification apparatus of the present embodiment stirs the spent nuclear fuel using a rotary shaft having a plurality of arms installed in the anode container for supplying current to the spent nuclear fuel installed in the container of the anode 4. You may make it carry out. That is, as shown in FIG. 3, the container-shaped anode 4, the current supply shaft 11 installed therein, the arms 12 provided on the current supply shaft 11, the current supply shaft rotating device 13, and the current supply shaft 11 And a current supply terminal 14 for connecting a power source.

  The spent nuclear fuel loaded on the anode 4 is depleted of uranium and TRU on the surface facing the cathode as the electrolysis progresses, and the current efficiency consumed for the dissolution treatment at the anode decreases. According to this configuration, the anode 4 The spent nuclear fuel is stirred by the arm 12 by rotating the current supply shaft 11 provided in the interior, and a fresh surface to be electrolyzed is always exposed to the cathode 5, so that the spent nuclear fuel loaded on the anode 4 is removed. Electrolytic purification can be performed efficiently.

  The electrolytic purification apparatus of the present embodiment may be provided with water wheel-shaped stirring blades at both ends of a cylindrical cathode, and the molten salt may be stirred using the rotation of the cathode. As shown in FIG. 4, the water turbine-like blades 15 provided on the left and right sides of the cathode 5 coaxially with the cathode 5 are rotated together with the cathode 5 by the cathode rotating device 6 to promote the flow of the molten salt 1 in the electrolytic vessel 2. By keeping the uranium concentration in the molten salt 1 constant at all times, electrolytic purification can be performed without being affected by electrochemical mass transfer in electrolytic purification, and a decrease in electrolytic purification efficiency can be suppressed. Moreover, according to this structure, the molten salt 1 can be stirred without installing a structure between the anode 4 and the cathode 5 facing each other, and the electrode surface can be used efficiently.

  The electrolytic purification apparatus of the present embodiment may also be configured to include a heating device that maintains the cathode surface and the cathode deposit scraping blade portion at a temperature equal to or higher than the melting point of the molten salt. FIG. 4 shows details of the contact portion between the cathode 5 and the scraping blade 7. The cathode deposit deposited on the cathode 5 and pulled up from the molten salt 1 along with the rotation of the cathode 5 is solidified due to a decrease in temperature. Stoppage of cathode rotation due to the solidified molten salt may occur. In the present embodiment, in order to prevent this, the heating element 16 is provided on the cathode 5 and the scraping blade 7. As a result, the surface of the cathode and the surface of the scraping blade are maintained at or above the melting point of the molten salt during scraping to prevent the molten salt from solidifying, and the cathode deposit can be easily scraped off. Moreover, separation of the molten salt from the cathode deposit can be promoted by heating the cathode and the scraping blade.

  The electrolytic purification apparatus of the present embodiment also includes a vibration generator that provides a slope at the rear part of the scraping blade and applies a slight vibration to the slope surface in order to collect the cathode deposit separated from the cathode by the scraping blade. It is good also as a structure. This configuration will be described with reference to FIG. In the present embodiment, the cathode deposit separated from the cathode 5 by the scraping blade 7 is pushed and moved to the rear of the scraping blade 7 as the cathode 5 rotates. Therefore, the cathode deposit separated and collected from the cathode 5 by installing the slope 19 behind the scraping blade 7 is carried out and collected outside the electrolytic vessel 2 through the slope 19. If a recovery container is provided at the rear end of the slope, only the cathode deposit can be recovered continuously without stopping the electrolytic purification. Further, by providing the heating device 17 and the ultrasonic oscillator 18 on the slope 19, it becomes possible to prevent the cathode deposit from adhering to the slope 19 and to positively discharge the cathode deposit.

  According to the method and apparatus for electrolytic purification of spent nuclear fuel according to the present embodiment, the following effects can be obtained. That is, dry reprocessing of spent nuclear fuel using molten salt electrolysis, which has been performed in batch processing so far, can be continuously performed. By enabling continuous processing, the stop time of the electrolytic purification apparatus can be shortened and the processing efficiency can be improved. Moreover, the processing speed of spent nuclear fuel can be improved by improving the anode and cathode structures. At the same time, the anode and cathode can be used continuously, and the amount of waste generated in dry reprocessing can be reduced. Furthermore, the amount of molten salt accompanying the recovered uranium and TRU can be reduced, and the burden on the distillation process for treating uranium and TRU after electrolytic purification is reduced.

The partial cutaway perspective view which shows the basic composition of the electrolytic purification apparatus of the spent nuclear fuel of embodiment of this invention. The perspective view which shows the structure of the anode in the electrolytic purification apparatus of the spent nuclear fuel of embodiment of this invention. 1 is a partially cutaway perspective view showing a configuration for supplying current to an electrolytic purification apparatus for spent nuclear fuel according to an embodiment of the present invention. The partially cutaway perspective view which shows the structure for the cathode and cathode deposit removal in the electrolytic purification apparatus of the spent nuclear fuel of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Molten salt, 2 ... Electrolytic container, 3 ... Electric furnace, 4 ... Anode, 5 ... Cathode, 6 ... Cathode rotation apparatus, 7 ... Scraping blade, 8 ... Used nuclear fuel, 9 ... Anode pulling mechanism, 10 ... Power supply Circuit: 11 ... Current supply shaft, 12 ... Arm, 13 ... Current supply shaft rotating device, 14 ... Current supply terminal, 15 ... Stirrer blade, 16 ... Heating element, 17 ... Slope heating element, 18 ... Ultrasonic oscillator, 19 …slope.

Claims (6)

  An electrolytic container for storing molten salt obtained by melting salt at high temperature, a cage-shaped or perforated container-shaped anode that contains spent nuclear fuel and is immersed in the molten salt, and a power supply circuit that switches energization to the anode A cathode having a columnar shape or a cylindrical shape and a lower portion immersed in the molten salt and provided horizontally on the liquid surface of the molten salt, and a power supply device for passing a current between the anode and the cathode through the molten salt A cathode rotating device that rotates the cathode about a central axis, and a scraping blade that contacts the circumferential surface of the cathode and scrapes the precipitate containing uranium and superuranium elements deposited on the circumferential surface. An apparatus for electrolytic purification of spent nuclear fuel, comprising:   2. The spent nuclear fuel electrolytic purification apparatus according to claim 1, wherein the anode supplies current to the spent nuclear fuel through a rotating current supply shaft having a plurality of arms.   2. The spent nuclear fuel electrolytic purification apparatus according to claim 1, wherein the cathode is provided with a stirrer for stirring the molten salt.   2. The spent nuclear fuel electrolytic purification apparatus according to claim 1, wherein the cathode and the scraping blade include a heating device for heating the precipitate.   The apparatus for electrolytic purification of spent nuclear fuel according to claim 1, further comprising a slope at a rear portion of the scraping blade for collecting the deposit scraped from the cathode in a deposit collecting container. A plurality of cage-shaped or perforated container-shaped anodes containing spent nuclear fuel are immersed in a molten salt obtained by melting a salt at a high temperature, and are formed in a columnar shape or a cylindrical shape, and the lower portion is immersed in the molten salt. While rotating a cathode provided horizontally on the liquid surface of the molten salt around a central axis, a current is passed between the anode and the cathode through the molten salt, and energization to the plurality of anodes is shifted, thereby the cathode A method for electrolytically refining spent nuclear fuel, characterized in that a precipitate containing uranium and a transuranium element precipitated on the circumferential surface is scraped off with a scraping blade.

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