JP2011043424A - Nuclear fuel reprocessing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sludge removal device and a nuclear fuel reprocessing system capable of removing simultaneously sludge of particles or an ion component which cannot be removed completely by a centrifugal clarifier. <P>SOLUTION: In the nuclear fuel reprocessing system including a shearing-dissolving process 1, a separation process 5, a refining process 13 and a denitrification process 14, the sludge removal device 4 storing a material chemically bonding to the ion component included in a dissolved liquid flowing out from a dissolution tank 2, and removing the sludge is installed on the downstream side of the dissolution tank 2 in the shearing-dissolving process 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nuclear fuel reprocessing system applied to a melting process of a nuclear fuel reprocessing facility.

  Once fossil fuels such as oil and natural gas are burned, they cannot be used again, but the fuels used in nuclear power plants can be used repeatedly by reprocessing them after combustion.

  Currently, uranium 235 is the main fuel used in Japanese nuclear power plants (light water reactors). When uranium 238 absorbs the neutrons emitted by uranium 235, a part of uranium 238 is changed to plutonium. Therefore, a nuclear fuel reprocessing process has been developed in which unburned uranium 235 and newly generated plutonium are removed by reprocessing and used as new fuel.

  In the nuclear fuel reprocessing facility, various process operations such as spent fuel dissolution process, uranium and plutonium separation process, uranium or plutonium purification process, and denitration process are performed.

In the spent fuel dissolving process, spent nuclear fuel is heated and dissolved with nitric acid. However, the existence of sludge (solid content) composed of FP (fission product) elements which are difficult to dissolve in nitric acid (cladding pieces) and nitric acid of cladding tubes (hulls) of nuclear fuel is known. Further, ions such as Zr and Mo are present in a large amount in the solution, and ions such as Zr and Mo account for about 15 to 20% of the solution, and these chemically react with each other to form zirconium molybdate ( It has also been found to produce a colloidal precipitate called Zr (OH) ₂ Mo ₂ O ₇ (H ₂ O) ₂ ). There is a possibility that these solid contents adhere to the inside of the pipe and block the pipe, and there is a need for a system that removes solids and ions that cause solids generation.

JP 2000-56077 A JP 2002-333497 A

  In the nuclear fuel reprocessing process, spent fuel is dissolved in a dissolution tank, then unnecessary solids are removed with a centrifugal clarifier, and uranium and plutonium are separated in a separation step. However, the sludge separation efficiency in the centrifugal clarifier is about 90%, and the remaining sludge of about 10% fine particles remains in the solution.

  In addition, since the ionic component cannot be removed by the centrifugal clarifier, ions in the solution may chemically react to generate sludge. In view of this, Japanese Patent Application Laid-Open No. 2000-56077 proposes a method in which a metal zirconium piece is inserted into a dissolution tank and deposited on a metal zirconium piece into which unnecessary ions such as Zr and Mo are inserted.

  However, even though unnecessary ions such as Zr and Mo can be removed by this method, it is difficult to remove sludge of about 10% fine particles that could not be separated by a centrifugal clarifier, and about 30 hours to remove ion components. There was a risk of taking time.

  In addition, sludge and the like that could not be removed may adhere to the pipe or the like and block the pipe. Therefore, a nuclear fuel reprocessing system that simultaneously removes sludge and ion components of fine particles that cannot be removed by a centrifugal clarifier is provided.

  The present invention relates to a nuclear fuel reprocessing system comprising a shearing / dissolution process, a separation process, a purification process, and a denitration process, and an ionic component contained in the solution flowing out of the dissolution tank downstream of the dissolution tank in the shearing / dissolution process. And a sludge removal device for removing sludge and containing a material that chemically bonds to the substrate.

  The dissolved solution flowing out from the dissolution tank in the shearing / dissolving process or the dissolved solution from which the sludge has been removed by the centrifugal clarifier is sent to the sludge removal device, and the solid content that could not be removed by the centrifugal clarifier and unnecessary ion components are chemically bonded. By removing them, it is possible to prevent clogging of the pipes due to sludge and to perform stable nuclear fuel reprocessing.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows roughly the whole structure of the nuclear fuel reprocessing system which concerns on Example 1 to which the sludge removal apparatus is applied. The block diagram which shows roughly the whole structure of the nuclear fuel reprocessing system which concerns on Example 2 to which a sludge removal apparatus is applied. The schematic block diagram which shows an example of the sludge removal apparatus employ | adopted as this invention. The schematic block diagram which shows the other example of the sludge removal apparatus employ | adopted as this invention.

  Embodiments of a nuclear fuel reprocessing system according to the present invention will be described below with reference to the drawings.

(Example 1)
Hereinafter, Example 1 is demonstrated using FIG. FIG. 1 is a schematic block diagram showing the whole when a sludge removal apparatus is combined with a nuclear fuel reprocessing process.

  In FIG. 1, the spent fuel A is cut in the shear / dissolution step 1, and the cut spent fuel A is melted in the melting tank 2. The dissolved spent fuel A is sent to the centrifugal clarifier 3 installed in the shearing / dissolving step 1 to separate the sludge B. The solution C from which the sludge B has been removed by the centrifugal clarifier 3 is sent to the sludge removing device 4, and solids and unnecessary ion components that could not be removed by the centrifugal clarifier 3 are removed.

  The solution C from which the solid content and unnecessary ionic components have been removed in the sludge removing device 4 is sent to the separation step 5 where uranium and plutonium D are separated, and the purity of the separated uranium and plutonium D in the purification step 13 In the denitration process 14, nitric acid is separated and denitrated to obtain uranium and plutonium fuel powder.

  In the above configuration, in order to confirm the sludge separation performance in the centrifugal clarifier 3, a test was performed using a simulated solution.

  A glycerin aqueous solution was used as a simulation liquid, and iron oxide was used as a simulation of sludge. As a result, the sludge separation efficiency in the centrifugal clarifier 3 was about 90%, and the remaining sludge of about 10% fine particles remained in the solution. In addition, since the ionic component cannot be removed by the centrifugal clarifier 3, ions in the solution may chemically react to generate sludge. In the nuclear fuel reprocessing system, unnecessary ion components include ZrO2 + and Zr4 +, and it has been found that these ions become solids according to the following equation.

Zr ⁴⁺ + H ₂ O → ZrO ²⁺ + 2H ⁺ Formula 1
2HMoO ₄ ⁻ + ZrO ²⁺ + 2H ₂ O → Zr (OH) ₂ Mo ₂ O ₇ (H ₂ O) ₂ Formula 2
It is known that zirconium molybdate appearing on the right side of Formula 2 becomes a colloidal precipitate. There is a possibility that these sludges adhere to the pipe wall and cause the pipe to be blocked. Therefore, the solution C from which the sludge has been removed by the centrifugal clarifier 3 is sent to the sludge remover 4, and solids and unnecessary ion components that could not be removed by the centrifugal clarifier 3 are chemically bonded and removed by the sludge remover 4. By doing so, it is possible to prevent pipe clogging due to sludge and to perform stable nuclear fuel reprocessing.

(Example 2)
FIG. 2 is a schematic block diagram showing another embodiment when the sludge removal apparatus is combined with the nuclear fuel reprocessing process. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description of the configuration of those parts is omitted.

  In FIG. 2, the spent fuel A is cut in the shearing / dissolution step 1 and dissolved in the dissolution tank 2. Immediately after the dissolution tank 2, a sludge removal device 4 is installed instead of the centrifugal clarifier 3 shown in FIG. Uranium and plutonium D are separated, purified in a purification step 13 to increase the purity of uranium and plutonium D, and denitrated in a denitration step 14 to separate and denitrate into uranium and plutonium fuel powder.

  In this case, the sludge removing device 4 is configured to be able to process a large volume compared to the sludge removing device 4 of FIG.

  By setting it as such a system, installation of the centrifugal clarifier 3 can be omitted, pipe | tube obstruction | occlusion etc. by sludge can be prevented, and the stable reprocessing of nuclear fuel can be implemented.

Example 3
FIG. 3 is an example of a sludge removal apparatus employed in the first or second embodiment.

  In FIG. 3, the solution C is supplied from the solution supply pipe 6 that constitutes the sludge removing device 4. The filter medium 15 is filled in the filtration tank 7 in the sludge removing device 4. The filter medium 15 is a fine particle having a diameter capable of forming a flow path capable of collecting sludge of 1 μm or less in the flow path. The filter medium 15 may be any material that is chemically bonded to an ionic component contained in the solution C, and is preferably made of metal zirconium.

  The solution C passes through the filter tank 7 filled with the filter medium 15, so that the sludge in the solution C is collected in the filter tank 7 and the sludge is removed from the solution outlet pipe 8. C is taken out.

Further, unnecessary ion components in the solution C are deposited on the filter medium 15 filled in the filter tank 7. Unnecessary ionic components are ZrO ²⁺ and Zr ⁴⁺ , and sludge generation using these chemical species as a source is generated starting from the surface of the filter medium 15 composed of metal zirconium or zirconium compound composed of the same element, and Contribute to growth.

  If the solution C is continuously supplied into the filtration tank 7 for a certain period of time, sludge accumulates in the filter tank 7 and the pressure loss increases, making it difficult to filter the solution C. In this case, the filled filter medium 15 is washed. The zirconium molybdate deposited on the filter medium 15 filled in the filtration tank 7 is selectively dissolved under the alkaline condition based on the following reaction formula (3).

Zr (OH) ₂ Mo ₂ O ₇ (H ₂ O) ₂ + 4OH ⁻ → 2MoO ₄ ²⁻ + ZrO ₂ .2 (H ₂ O) + 3H ₂ O Formula 3
Accordingly, the cleaning liquid is preferably an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide so that sludge deposited on the surface of the filter medium 15 is also dissolved. The sludge removal device 4 is provided with an alkaline aqueous solution tank 9, and the aqueous alkaline solution is supplied through the aqueous alkaline solution supply pipe 10 from the direction opposite to the direction of supply of the solution C to clean the inside of the filtration tank 7. Then, the cleaning liquid in which the sludge deposited on the surface of the filter medium 15 after cleaning is dissolved is discharged to the cleaning liquid tank 11 installed in the sludge removing device 4.

  By doing in this way, even when sludge accumulates in the filtration tank 7 and it becomes difficult to filter the solution C, the filter medium 15 can be regenerated with the alkaline aqueous solution. Furthermore, the sludge that does not dissolve in the alkaline aqueous solution is also washed by flowing the alkaline aqueous solution from the downstream of the sludge removing device 4 (the direction opposite to the supply direction of the solution C) at a flow rate at which the sludge collected in the filtration tank 7 floats. can do. In addition, since the system including the sludge removal device 4 stops during cleaning, a plurality of sludge removal devices 4 are installed in parallel, and the sludge removal device 4 is switched from the one being cleaned to another sludge removal device 4. To use.

Example 4
FIG. 4 shows another embodiment of the sludge removing apparatus employed in Embodiment 1 or Embodiment 2. In FIG. 4, the same parts as those in FIG. 3 are denoted by the same reference numerals, and description of the structure of those parts is omitted.

  In FIG. 4, the solution C is supplied from the solution supply pipe 6 constituting the sludge removing device 4a. In the system of the sludge removal device 4a, a filter 12 is installed instead of the filter medium 15 of the filter tank 7 shown in the third embodiment.

  The filter 12 has a pore diameter of 1 μm or less. The filter 12 may be made of any material that can chemically bond with the ionic component contained in the solution C, and is preferably a sintered metal filter made of metal zirconium, a zirconium compound, or the like. By passing the solution C through the filter 12, the solid content in the solution C is collected on the filter 12, and the solution C from which the sludge is removed is taken out from the solution outlet pipe 8.

Further, unnecessary ionic components in the solution C are deposited on the filter 12. Unnecessary ionic components are ZrO ²⁺ and Zr ⁴⁺ , and sludge generation using these chemical species as a source is generated starting from the surface of the filter 12 composed of metal zirconium or zirconium compound composed of the same element, and Contribute to growth.

  If the solution is continuously supplied to the filter 12 for a certain period of time, the filter 12 is clogged and the pressure loss increases, and the solution C becomes difficult to filter. In this case, the filter 12 is washed. Since the zirconium molybdate deposited on the surface of the filter 12 is selectively dissolved based on the above reaction formula 3 under alkaline conditions, the cleaning solution is preferably an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.

  The sludge removal device 4a is provided with an alkaline aqueous solution tank 9, and the alkaline aqueous solution is supplied from the direction opposite to the supply of the solution C through the alkaline aqueous solution supply pipe 10 to wash the filter 12.

  Then, the cleaning liquid is discharged to a cleaning liquid tank 11 installed in the sludge removing device 4a. By doing in this way, even when sludge accumulates in the filter 12 and it becomes difficult to filter the solution C, the filter 12 can be regenerated with the alkaline aqueous solution.

  Furthermore, the sludge that does not dissolve in the alkaline aqueous solution is also washed by flowing the alkaline aqueous solution from the downstream of the sludge removing device 4a (the direction opposite to the supply direction of the solution C) at a flow rate at which the sludge collected on the filter 12 floats. be able to.

  In addition, since the system including the sludge removal device 4a stops during cleaning, a plurality of sludge removal devices 4a are installed in parallel, and the sludge removal device 4a is switched from the one being cleaned to another sludge removal device 4a. I will use it.

  DESCRIPTION OF SYMBOLS 1 ... Shearing / dissolution process, 2 ... Dissolution tank, 3 ... Centrifugal clarifier 4, 4a ... Sludge removal apparatus, 5 ... Separation process, 6 ... Dissolution supply pipe, 7 ... Filtration tank, 8 ... Dissolution outlet pipe, DESCRIPTION OF SYMBOLS 9 ... Alkaline aqueous solution tank, 10 ... Alkaline aqueous solution supply piping, 11 ... Cleaning liquid tank, 12 ... Filter, 13 ... Purification process, 14 ... Denitration process, 15 ... Filter material, A ... Spent fuel, B ... Sludge, C ... Dissolution Liquid, D ... Uranium and plutonium.

Claims (6)

  In a nuclear fuel reprocessing system consisting of a shearing / dissolution process, separation process, purification process, and denitration process, it chemically binds to ionic components contained in the solution flowing out of this dissolution tank downstream of the dissolution tank in the shearing / dissolution process. A nuclear fuel reprocessing system characterized in that a sludge removal device that contains material and removes sludge is installed.   2. The nuclear fuel reprocessing system according to claim 1, wherein the sludge removing device is installed downstream of a centrifugal clarifier constituting a shearing / dissolving step.   The sludge removing device is configured by filling a filter tank with a filter medium, and the filter medium is filled with a filter medium made of a material that chemically bonds with an ionic component contained in the solution. Item 3. The nuclear fuel reprocessing system according to Item 1 or 2.   3. The atom according to claim 1, wherein the sludge removing device includes a filter, and the filter is formed of a material having a pore diameter of 1 μm or less and chemically bonded to an ionic component contained in the solution. Fuel reprocessing system.   The nuclear fuel reprocessing system according to claim 3 or 4, wherein the material chemically bonded to the ionic component contained in the solution is zirconium or a zirconium compound.   6. The sludge removal apparatus is provided with an alkaline aqueous solution tank for supplying an alkaline aqueous solution for regenerating the filter medium or filter and a cleaning liquid tank for storing a cleaned cleaning liquid. The nuclear fuel reprocessing system according to any one of the preceding claims.

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