WO2003063178A1 - Procede de reduction electrolytique - Google Patents

Procede de reduction electrolytique Download PDF

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Publication number
WO2003063178A1
WO2003063178A1 PCT/JP2003/000496 JP0300496W WO03063178A1 WO 2003063178 A1 WO2003063178 A1 WO 2003063178A1 JP 0300496 W JP0300496 W JP 0300496W WO 03063178 A1 WO03063178 A1 WO 03063178A1
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Prior art keywords
fuel
oxide fuel
oxide
anode
electrolytic reduction
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PCT/JP2003/000496
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English (en)
Japanese (ja)
Inventor
Masaki Kurata
Tadashi Inoue
Hirokazu Ota
Kensuke Kinoshita
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Central Research Institute Of Electric Power Industry
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Priority to JP2003562947A priority Critical patent/JPWO2003063178A1/ja
Publication of WO2003063178A1 publication Critical patent/WO2003063178A1/fr

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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
    • G21C19/42—Reprocessing of irradiated fuel
    • G21C19/44—Reprocessing of irradiated fuel of irradiated solid fuel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies

Definitions

  • the term "spent oxide fuel” refers to, for example, light water reactor spent fuel, light water reactor M ⁇ X spent fuel, fast reactor spent fuel, MOX fuel recovered by the Purex method, accelerator driven reactor, etc.
  • Various fuels in the form of oxides related to the nuclear power industry such as spent oxide fuels such as oxide fuels used in next-generation reactors, and oxide targets used for transmutation of long-lived radionuclides, etc. This is a concept that includes general aspects such as chemicals, reagents, and waste.
  • metallic lithium is added as a reducing agent to a molten salt composed of lithium chloride or lithium salt and potassium chloride, and the spent oxide fuel is chemically reduced by the molten salt containing the reducing agent.
  • process waste such as lithium oxide generated by the oxidation-reduction reaction and using metallic lithium.
  • the fuel component ⁇ ramptonium is the carrier of the electric charge, so that these fuel components are eluted into the molten salt during the electrolytic refining, and Remains in the molten salt after the completion of the electrolytic refining treatment.
  • peripheral treatment such as TRU (transuranium element) recovery and waste salt treatment on the molten salt, which complicates the work process.
  • the recovery rate is only about 99% at the highest, resulting in waste.
  • the potential difference between the anode and the cathode for desorbing oxygen is about 1.92.7 V if only the theoretical reduction potential is set.
  • the molten salt, the electrical resistance (IR drop) of the electrode, and the oxidation It is also necessary to consider the decrease in free energy of formation due to the dissolution of calcium hydroxide in the molten salt. Therefore, about the upper limit of the anode and cathode potential difference to co becomes about 2.
  • 7V without 3. 3 3. 5V is a theoretical reduction potential of oxidative Rushiumu
  • the lower limit is the theoretical reduction potential of T I_ ⁇ 2 It becomes 2.5 V instead of 1.9 V.
  • the potential difference between the anode and the cathode is set to an optimal value determined between the equipment conditions, etc., between 2.83.2 V, and electrolysis is performed at a constant voltage.
  • the spent oxide fuel to be treated by the present invention contains 0.130 wt% of fission products which are impurities in addition to the fuel component.
  • the theoretical reduction potentials of the oxides of these components are various values as shown in Table 2.
  • the spent oxide fuel contains various concentrations of oxides of each element.
  • elements such as chalcogens and halogens do not conduct electricity in solid form. Also, since some of these fission products are localized, it is assumed that the electric conductivity in the raw materials is heterogeneous and difficult to control.
  • an object of the present invention is to provide a method for electrolytic reduction of a spent oxide fuel and a simple dry reprocessing method which do not require peripheral treatment such as TRU recovery and waste salt treatment while increasing the recovery rate of fuel components. I do.
  • the present invention provides an electrolytic solution in which a spent oxide fuel to be reduced, which is held by a cathode, and an anode are immersed in a molten salt, and a voltage is applied to the cathode and the anode to reduce the oxide fuel.
  • the molten salt is calcium chloride and an oxygen source material is added at the beginning of the operation, and during the operation, oxygen ions released from the oxide fuel by electrolysis serve as charge carriers, and
  • the actual voltage applied between the oxide fuel and the anode should be below the theoretical reduction potential of the oxygen source material and above 1.5 V.
  • the electrolytic reduction treatment can be performed using oxygen ions supplied by the oxygen source material from the initial stage of operation as a charge carrier, and the processing speed Can be accelerated.
  • the oxygen ions released from the oxide fuel act as charge carriers and the gas generated from the anode becomes oxygen or carbon dioxide.
  • the generation of certain chlorine gas can be avoided.
  • examples of the oxygen source material at the beginning of the operation include calcium oxide, lithium oxide, and magnesium oxide, and preferably use calcium oxide or lithium oxide, and more preferably use oxidizing calcium. Applied by adding oxidation power The voltage range can be made larger.
  • the upper limit of the actual voltage applied between the oxide fuel and the anode needs to be lower than or equal to the theoretical reduction potential of the oxygen source material.
  • the upper limit voltage for electrolytic reduction is 2.7 V. If it exceeds this value, the calcium of the calcium oxide will be reduced and deposited.
  • the upper limit of the electrolytic reduction voltage is 2.6 V. If this value is exceeded, lithium will be reduced and deposited, so that the electrolytic reduction of the oxide fuel cannot be continued.
  • the actual voltage applied between the oxide fuel and the anode refers to the molten salt, the electrical resistance of the electrode (IR drop), and the molten salt of the oxygen source material, based on the voltage applied between the electrodes from the DC power supply.
  • the voltage applied by the DC power supply to each electrode is in the range of about 2.0 to 3.2 V in consideration of the IR drop when calcium oxide is added.
  • the voltage application may be controlled from 1.5 V to the theoretical reduction potential of the oxygen source material, for example, from 1.5 V to 2.7 V when calcium oxide is used as the oxygen source material.
  • the voltage may be applied while gradually increasing the voltage, or the potential may be finely raised or lowered in accordance with the progress of the electrolysis, or a constant voltage may be continuously applied. This should be set appropriately considering the shape of the oxide fuel and the concentration of each element. For example, when a voltage is applied while gradually increasing the voltage value, electrolysis is performed at a potential sufficient for electrolytic reduction, and the thermodynamic or electrochemical conditions in the system are reduced. The matter can be kept homogeneous. In addition, by suppressing the reaction rate sufficiently and sufficiently, multi-element oxides can be reduced as expected.
  • the recovered material becomes homogeneous and the conditions for electrolytic reduction can be maintained.
  • the applied voltage is to be finely increased or decreased (oscillated)
  • the potential is oscillated to change the oxygen concentration at the reaction interface, and the same effect as that obtained by stirring can be obtained. This makes it possible to make the system as homogeneous as possible and to maintain a state close to the conditions under which reduction is theoretically established.
  • the potential of the cathode is determined by the potential at which oxygen ions elute from the fuel loaded on the cathode, and the oxygen source material supplied to the molten salt is decomposed and the surface of the fuel such as calcium And the potential to be deposited.
  • the influence on the cathode potential is a change in the oxygen ion elution potential due to a change in the elemental composition in the fuel, and a change in the metal deposition potential in the fuel due to the addition of another oxygen source material.
  • the potential of both electrodes is controlled using the potential of the reference electrode, it is necessary to reduce the difference between the cathode potential and the reference electrode potential.
  • the current value is preferably a current having a current density of 10 to 100 O mA / cm 2 .
  • the potential exceeds the theoretical reduction potential of calcium chloride, and the supply of oxygen cannot keep up with the corrosion of calcium metal on the cathode and corrosion on the anode. It is not preferable because chlorine gas having a property may be generated.
  • the upper limit is 10 O mA / cm 2 . The reaction proceeds even if the current density is less than 1 O mA / cm 2 , but the reaction speed is slow and not suitable for use on an industrial scale.
  • a current density of at least 1 OmAZ cm 2 or more is preferable. In some cases, it is better to reduce the current value in order to reduce oxides to the end. In other words, if the current value is not reduced to the end, there is a possibility that a small amount of calcium will precipitate when the last part of the sample is reduced.Therefore, it is possible to prevent precipitation by reducing the current value.
  • the oxide fuel can be electrolytically reduced.
  • the electrolytic reduction of the oxide fuel can reduce the fuel components and some of the fission products contained therein to metals.
  • Some elements that are not reduced within the potential difference range of the present invention because the reduction potential is not in this range or the electrical conductivity is significantly different from that of uranium oxide are condensed due to the reduction of fuel components.
  • the molten salt component can penetrate into the fuel and dissolve directly in the molten salt, which can be removed. As a result, at least about half (specifically, about 50 to 60%) of fission products can be roughly removed (decontaminated).
  • the applied voltage is the decomposition voltage of the oxygen source material (the potential at which the oxygen source material decomposes and precipitates as calcium on the surface of the oxide fuel).
  • the potential at which the oxygen source material decomposes and precipitates as calcium on the surface of the oxide fuel For example, in the case of calcium oxide, it is the theoretical reduction potential. If the voltage does not exceed a certain 2.7 V, applying the highest voltage at a constant potential will reduce all the target oxides.
  • anions oxygen ions and chloride ions
  • cations calcium ions
  • the present invention is characterized in that only the oxygen ions having the lowest concentration among them are used as charge carriers, and only oxygen gas or carbon dioxide gas is generated. In this case, it is most preferable to control both the current density and the voltage and proceed with the reduction process while confirming that the oxygen ion concentration in the molten salt is kept constant.
  • the recovered material that has been reduced and recovered by remaining on the cathode can be used as a raw material for a metal fuel or a target. That is, the dry simple reprocessing method of the spent oxide fuel of the present invention, An electrolytic reduction step of reducing spent oxide fuel using the electrolytic reduction method according to claim 1 and recovering at least the fuel component reduced in the same place as the reduction processing; and It is provided with an attached salt removal step and a waste salt treatment step as subsequent steps for removal.
  • the oxygen component supplied by the oxygen source material or oxygen in the fuel is used as a charge carrier to perform an electrolytic reduction process, thereby providing a fuel component (used fuel oxide) in the spent oxide fuel loaded on the cathode.
  • Uranium, plutonium, and other actinides can be converted to metal without any elution loss into the molten salt, and can be directly recovered as raw material for nuclear fuel or nuclear fuel.
  • most of the fission products in the spent oxide fuel compounds or mixtures of alkali metals, alkaline earth metals, divalent rare earth elements, chalcogens, halogens, etc.
  • fusible FP can be decontaminated by dissolving it in molten salt.
  • an electrolytic reduction device allows the remaining portion of fission products in spent oxide fuel (compounds or alloys of trivalent rare earth elements, noble metals, transition metals, etc. ) Can be recovered together with fuel components by removing oxygen.
  • the conventional dry reprocessing technology had a problem when peripheral processes such as TRU recovery and waste salt treatment were required.
  • the simple dry reprocessing method of the present invention after the electrolysis, etc. Various oxide fuels can be processed and the fuel components can be recovered by a simple dry process that does not require any processes or peripheral processes such as TRU recovery.
  • the present invention in which electric charges are carried by oxygen ions, since the elution of fuel components (that is, these aluminum and plutonium) into the molten salt is eliminated, a loss may occur in the recovery amount of these fuel components. Absent.
  • the metal can be prevented from being dissolved in the molten salt, and the recovery rate of the fuel component can be increased.
  • the recovery rate of fuel components such as uranium and plutonium was at most 99% in the conventional chemical treatment method in order to recover useful nuclear fuel components from spent fuel.
  • a recovery rate of uranium and plutonium of 100% can be achieved in principle.
  • fuel components can be recovered at the same location as the reduction site.
  • long-term! The reduction process is sufficiently possible.
  • the recovered fuel components are not subjected to the complicated post-treatment such as electrolytic refining used in the conventional dry reprocessing method, but are simply removed by the attached salt removal section or attached salt removal step, and the deposit is removed as it is.
  • the meltable FP removed in the molten salt can be provided to a waste salt treatment section or a waste salt treatment process without going through a conventional complicated salt treatment process.
  • FIG. 1 is a schematic diagram showing an embodiment of the electrolytic reduction apparatus of the present invention.
  • Fig. 2 is a flowchart showing one embodiment of a simple dry reprocessing method for spent oxide fuel.
  • Fig. 3 is a graph showing the relationship between the cathode-anode potential difference and the electrolysis step.
  • Fig. 4 shows a micrograph of the recovered material after the reduction and reprocessing test in this example.
  • FIG. 1 shows an embodiment of the electrolytic reduction apparatus 1 of the present invention.
  • the electrolytic reduction device 1 includes a cathode 3 for holding a spent oxide fuel 2 to be reduced, an anode 4, a molten salt 5 into which the spent oxide fuel 2 and the anode 4 are immersed, It is provided with a container 6 for accommodating a salt 5 and a DC power supply 7 for applying a voltage to the cathode 3 and the anode 4 to reduce the spent oxide fuel 2.
  • the molten salt 5 is calcium chloride, and an oxygen source material is added thereto, and the actual voltage applied between the oxide fuel 2 and the anode 4 is 1.5 V. Controlled below the theoretical reduction potential of the source material I am trying to be.
  • the voltage actually applied between the two electrodes is from 0.5 V to 2.7 V, and the free energy generated by the dissolution of the IR drop and the oxygen ion.
  • the drop is about 0.5 V in total
  • the voltage applied by the DC power supply 7 to each of the electrodes 3 and 4 is in the range of about 2.0 to 3.2 V.
  • this value differs depending on the shape, size and interval of each of the electrodes 3 and 4.
  • the fusible FP 13 in the spent oxide fuel 2 can be dissolved and removed in the molten salt 5 for decontamination. Further, oxygen can be removed from the non-meltable FP 14 in the spent oxide fuel 2 and recovered together with the fuel component 12.
  • electrolytic reduction can be performed even in a multi-element system such as nuclear fuel.
  • the spent oxide fuel 2 to be reduced is the spent oxide fuel from a nuclear power plant.
  • the spent oxide fuel 2 is assumed to contain 0.1 to 30 wt% of fission products.
  • the electrolytic reduction device 1 reduces uranium oxide and uranium split oxide contained in the spent oxide fuel 2.
  • the electrolytic reduction treatment is performed as described above, it is preferable to select the same oxygen source material as that of the molten salt 5 in order to avoid a complicated reaction.
  • calcium oxide is used as the oxygen source material as described above. In this case, even if a small amount of metal ions are precipitated due to the progress of the process, there is an advantage that the metal can be dissolved in the molten salt 5 and is immediately removed from the fuel surface.
  • the container 6 containing the molten salt 5 is made of, for example, stainless steel, low carbon steel, or special steel such as titanium.
  • the cathode 3 has a basket 8 made of stainless steel, low carbon steel, or special steel such as titanium.
  • the spent oxide fuel 2 is stored inside the basket 8. Then, the spent oxide fuel 2 is immersed in the molten salt 5 by immersing the entire basket 8 in the molten salt 5.
  • the anode 4 has a body 9 made of carbon and a lead 10 made of platinum or carbon. Since the carbon body 9 is used as the anode 4, carbon dioxide is generated from the anode 4 by electrolytic reduction.
  • the above-described electrolytic reduction device 1 can be used for a simple dry reprocessing device for spent oxide fuel 2.
  • the simple dry reprocessing device for the spent oxide fuel 2 reduces the spent oxide fuel 2 using the electrolytic reduction device 1, and the cathode residue, ie, fuel, reduced in the same place as the reduction process
  • the dry simple reprocessing device has a basket 8 for collecting the spent oxide fuel 2 that has been subjected to the reduction treatment using the electrolytic reduction device 1. This basket 8 constitutes the electrolytic reduction section 15.
  • the collected basket 8 is transferred to the attached salt removing section 16 which performs a post-process, and separates the fuel component 12 and the attached salt 18 to recover the fuel component 12 as a fuel material.
  • Step 1 Disassemble and shear the previously used oxide fuel 2 (Step 1: S l). Then, the spent oxide fuel 2 is subjected to a decoating / heating treatment (step 2: S 2).
  • Uncoating means breaking the pipe containing the fuel and taking out the inside. There are two methods of this uncoating: heating type and mechanical frame type. In the case of a heating type, a cut is made in the zircaloy cladding tube, then heated, and the contents are expanded to expand the cladding tube. It is to be removed. After the decoating, a heat treatment for evaporating and removing some unnecessary components is performed in some cases. When recovering the fuel component 12 from the zircaloy cladding, the zircaloy cladding can be effectively used by omitting step 2.
  • the spent oxide fuel 2 is subjected to a reduction treatment using an electrolytic reduction method, and at least the fuel component 12 reduced at the same place as the reduction treatment is used.
  • An electrolytic reduction step for recovering the wastewater, and an attached salt removal step and a waste salt treatment step as subsequent steps are provided.
  • the electrolytic reduction step in the vessel 6 of the electrolytic reduction section 15 (electrolytic reduction device 1), chloride water as a melting medium and oxidizing water as an oxygen supply substance are melted at 77 ° C or higher to melt molten salt. Get five. Then, the spent oxide fuel 2 obtained in the pretreatment is accommodated in the basket 8 of the cathode 3 and immersed in the molten salt 5. The anode 4 is also immersed in the molten salt 5. Electrolytic reduction of the spent oxide fuel 2 is performed by connecting a DC power supply 7 to the anode 4 and the cathode 3 and applying a voltage of about 2.0 to 3.2 V (step 3).
  • the transfer of oxygen ions is promoted as the oxygen in the spent oxide fuel 2 is separated into ions in the molten salt 5.
  • oxygen ions dissolved in the spent oxide fuel 2 act as a conductor.
  • Oxygen ions react on the surface of the body 9 of the anode 4 and partly become carbon dioxide. This carbon dioxide is discharged into the gas phase as bubbles 11. Since the body 9 of the anode 4 is worn out, it should be replaced periodically.
  • the fuel component 12 of the spent oxide fuel 2 is reduced to eventually metal. Then, the metal is taken out of the molten salt 5 by pulling up the basket 8.
  • Non-melting of fuel components 1 and fission products in spent oxide fuel 2 by using electrolytic reduction device 1 FP 14 is converted to metal and recovered without loss of elution into molten salt 5 You can (step 4).
  • the adhering salt removal unit 16 removes the adhering salt 18 from the collected materials 12 and 14 by filtering or distilling the adhering salt 18 (step 5), whereby the fuel component 1 4 becomes a raw material for new metallic nuclear fuel (Step 6).
  • Spent oxide fuel 2 has a composition Homogeneous, meltable FP is extruded and becomes porous. Therefore, in the attached salt removing step, the salt remaining in the porous gap is flushed with argon gas or the like under reduced pressure.
  • the concentration of uranium, plutonium, and other actinides in the recovered material differs depending on the target to be treated. Therefore, the concentration of nuclear fuel is adjusted to a predetermined concentration by mixing multiple recovered materials or multiple elements.
  • the meltable FP 13 in the spent oxide fuel 2 is dissolved and removed in the molten salt 5. This can be discarded as salt waste by carrying out the waste salt treatment process by the waste salt treatment unit 19 (Step 7).
  • chloride is mixed with a solidifying agent and heated to convert it into a stable solid.
  • a heating vessel is used. Chloride changes to a stable chemical form when mixed with a solidifying agent.
  • a solidifying agent for example, Zeolite is used.
  • the non-melting FP14 of the fission products can be reduced at the same time as the peroxidized peroxidized plutonium.
  • the nuclear fuel is a mixed system containing uranium oxide as the main component, and the concentration of each component of the non-melting FP14 is a few percent, and is homogeneously dispersed in the fuel material. This is due to a reduction in activity caused by the homogeneous dissolution of each of the components 14 in pentane metal after reduction, and a change in reduction potential accompanying the reduction.
  • the meltable FP 13 allows the molten salt to penetrate into the fuel by utilizing the condensation phenomenon that occurs when the fuel component 12 is reduced. That is, cracks are generated by the condensation of peran oxide by reduction, and the molten salts 5 penetrate into the raw material through the cracks. As a result, these meltable FPs 13 are dissolved and removed in the molten salt 5.
  • the fuel component 12 recovered according to the present invention decontaminates the meltable FP13, which accounts for the majority of fission products, under the condition that there is no loss of uranium, plutonium, and actinide.
  • it can be used as a raw material for nuclear fuel without peripheral processes such as TRU recovery from molten salt.
  • oxygen ions are not accumulated in the molten salt 5 as compared with the case where the spent oxide fuel 2 is reduced using a chemical reduction reaction, so that the apparatus 1 The size can be reduced.
  • the recovered material can be used as a raw material for a metal fuel or a target without passing through a post-process such as electrolysis. It is extremely effective for the efficient disposal of undetermined spent fuel.
  • the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention.
  • calcium oxide is added to the molten salt 5 as an oxygen supply source material at the beginning of the operation, but the present invention is not limited to this, and oxides soluble in the molten salt 5 such as lithium oxide and magnesium oxide are used. Can be used.
  • the upper limit of the actual voltage applied between the two poles in this case is about 2.6 V.
  • spent oxide fuel 2 of a nuclear power plant is used as an oxide to be subjected to dry reprocessing
  • the present invention is not limited to this.
  • a spent light water reactor MOX fuel And MOX fuel recovered by the Purex method a spent light water reactor MOX fuel And MOX fuel recovered by the Purex method.
  • Zircaloy which is used as a cladding tube in light water reactor fuel, does not affect the process within the range of potential current used in this embodiment, so the fuel rod is sheared in the range of 2 mm to 10 cm to perform electrolytic reduction. By doing so, the used cladding (hull) can be collected together with the fuel. At this time, the ratio of Jil force to fuel is 10 to 20 wt%.
  • target used here means that "fuel” has the role of generating heat to generate power, whereas the amount of heat generated is small and does not contribute much to power generation, but has another role. Means that some or all of the fuel is loaded. For example, long-lived radioactivity can be broken down in a nuclear reactor and converted into short-lived radioactivity that is easy to handle (transmutation). When loaded into a nuclear reactor, this is called a “target” and is distinguished from a “fuel”.
  • a type that collects such so-called nuclear waste and reduces the amount of burning is being studied.
  • nuclear reaction Although neutrons are generated within oneself, such a future nuclear reactor is being studied for a type in which a neutron source is placed outside and the target is aimed at the inside.
  • the reprocessing method of the present invention can be applied to, for example, the reprocessing of a “target” used in such a future nuclear reactor.
  • reagents and wastes at present, they can only be disposed of as garbage, but according to the reprocessing method of the present invention, these can be converted into raw materials for nuclear fuel and the amount of waste can be reduced. .
  • wastes and used targets to which the present invention is applied are all multi-elements containing 0.1 to 3 O wt% of fission products.
  • the recovered fuel is molded into a metal-fueled fast reactor fuel
  • Zirconium can be directly contained in the metal fuel. As a result, it is possible to develop a process that can significantly reduce the amount of light water reactor cladding waste (hull) that has been generated in the past.
  • Electrolytic reduction of simulated spent uranium fuel pellets was performed using the electrolytic reduction device 1 shown in Fig. 1.
  • the simulated spent uranium fuel pellet (oxide fuel) is composed mainly of uranium oxide and has Ce, Nd, Sm, Eu, Ru, Rh, Pd, Mo, Zr, S r and Ba are each contained in 0.5 to lwt%.
  • the size of this oxide fuel sample was about 2 mm in thickness and about 8 mm in diameter.
  • a molten salt was obtained by loading and melting magnesium chloride and calcium oxide in a vessel 6 composed of a crucible made of magnesium.
  • the container 6 may be made of titanium.
  • a simulated spent uranium fuel pellet (containing a total of 1 Owt% of simulated fission products) with a lead of Ta (tantalum) as a cathode 3 and a graphite electrode as an anode 4 were loaded.
  • the anode 4 was made of dense glassy carbon and had a diameter of about 4 mm and a length of about 6 O mm.
  • the anode 4 was surrounded by a shroud made of alumina.
  • the shroud prevents the dispersion of carbon and the diffusion of carbon dioxide gas generated in the molten salt. Stop. It should be noted that magnesia shroud may be used instead of alumina.
  • a Ta wire was connected to the top of the carbon to take electrical leads.
  • the above-mentioned oxide fuel is fastened to the cathode 3 with a Ta wire to take an electrical lead, or placed directly on a Ta mesh basket for conduction.
  • the mesh basket is leaded with Ta wire.
  • Molten salt 5 is composed mainly of C a C 1 2 to about 5 0 g, there subcomponent as calcium oxide (oxygen source materials for supplying the responsible of charge) to (C a O) 0 Obtained by adding 0 l to 5 wt%.
  • calcium oxide oxygen source materials for supplying the responsible of charge
  • C a O oxygen source materials for supplying the responsible of charge
  • a potentiogalvanostat (manufactured by PerkinElmer Inc.) was used as the voltage application device.
  • the reference electrode was loaded with Bi in a Ta wire or a Ta basket, and a small amount of a reducing agent was dissolved therein.
  • the test temperature was set at 850 ° C.
  • the voltage was applied as follows. That is, the surface was reduced by electrolysis at a constant current density (about 50 to 10 O mA / cm 2 ) in the initial stage of reduction.
  • a positive / negative voltage (about 2.0 to 3.0 OV, including the electric resistance of the electrode) was applied between the uranium pellet and the graphite electrode at a constant current of 10 OmA.
  • the voltage was applied using a reference electrode, and the cathode potential and the anode potential were controlled with respect to the potential of the reference electrode. Then continuously monitored as the cathode the anode potential does not exceed the theoretical reduction potential of the molten salt 5, to control the current density to 1 0 O mAZ cm 2, to so that to reduction to the specimen centered galvanostatic electrolysis did. Electrolysis was performed in seven steps with a relaxation time of about 30 minutes set every 30 minutes as shown in Fig. 3, and gradually increasing the voltage value. By setting the relaxation time for each electrolytic treatment step, a small amount of reducing agent component precipitated from molten salt 5
  • Fig. 3 shows a graph showing the relationship between the potential difference between the cathode and the anode and the electrolysis step. From this test result, it was found that even if the applied voltage was not constant, there was no effect on the progress of electrolysis. It can also be seen that setting the relaxation time facilitates the process.
  • the relaxation time is, for example, about 30 minutes for 30 minutes to 2 hours of electrolysis, but this depends on the sample size and the like, and is not necessarily required for a small sample.
  • Oxygen contained in the fuel was eluted as oxygen ions into the molten salt 5 and then released from the anode 4 as a gas.
  • a part of the molten salt was collected and subjected to ICP emission analysis.
  • the analysis was performed by dissolving about 0.2 g of the collected salt in 50 cc of 1 N acetic acid and comparing the concentration with a standard sample ranging from 10 ppb to 10 ppm.
  • Fig. 4 shows a photograph of the recovered fuel taken with a scanning electron microscope (JEOL). From this photograph, it was confirmed that cracks had entered the sample center and M ⁇ ⁇ X was completely reduced. In addition, the quantitative analysis of EDX confirmed that the Pu concentration was about 9 to 11 wt% and that the dispersion was homogeneous.
  • the fuel component 12 and the non-melting FP 14 of the spent oxide fuel 2 were reduced and eventually turned into metal.
  • the fuel component 12 and the non-melting FP 14 of the spent oxide fuel 2 could be taken out of the molten salt 5.
  • the fusible FP 13 in the spent oxide fuel 2 was dissolved and removed in the molten salt 5.
  • the relaxation time is set after reduction for a certain period of time, and the thermodynamic conditions in the sample are homogenized, so that not only lanthanum but also plutonium and rare earth elements are evenly distributed. It is possible to reduce.
  • reactions can also occur in parallel, which allows for a more pure sample to be removed. In this test, the central part of the sample was left unreduced to elucidate the behavior of the elements, but in the actual process, the oxide sample was completely reduced by optimizing the sample shape and potential current. I do.

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  • Electrolytic Production Of Metals (AREA)

Abstract

L'invention concerne un procédé de réduction d'un combustible oxyde usé ainsi qu'un procédé d'extraction des composants du combustible, tels que le métal du combustible oxyde, par ce procédé. Ces procédés améliorent le pourcentage d'extraction des composants du combustible et ne requièrent pas l'intervention de traitements périphériques tels que l'extraction TRU et le traitement des sels résiduaires. Le combustible oxyde usé (2) devant être réduit et placé dans une cathode (3) et une anode (4) est trempé dans du sel fondu de chlorure de calcium (5) ayant été enrichi d'un matériau d'alimentation en oxygène au début de l'opération. La tension appliquée entre le combustible oxyde (2) et l'anode (4) est régulée jusqu'au potentiel de réduction théorique du matériau d'alimentation en oxygène et au moins 1,5 V pour réduire le combustible oxyde (2). Lors du fonctionnement, les ions d'oxygène libérés par le combustible oxyde (2) par électrolyse sont utilisés comme porteurs de charge pour favoriser la réduction électrolytique.
PCT/JP2003/000496 2002-01-21 2003-01-21 Procede de reduction electrolytique WO2003063178A1 (fr)

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JP2008013793A (ja) * 2006-07-04 2008-01-24 Korea Atomic Energy Research Inst キャパシター用タンタルまたはニオブ粉末の製造方法
JP2010533792A (ja) * 2007-07-18 2010-10-28 グリーン メタルズ リミテッド ルテニウム酸カルシウム電極材料
JP2015230170A (ja) * 2014-06-03 2015-12-21 株式会社東芝 複合酸化物分離方法
JP2017082264A (ja) * 2015-10-26 2017-05-18 株式会社東芝 ガラス固化体の溶解方法及びその溶解装置

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008013793A (ja) * 2006-07-04 2008-01-24 Korea Atomic Energy Research Inst キャパシター用タンタルまたはニオブ粉末の製造方法
JP4511498B2 (ja) * 2006-07-04 2010-07-28 韓国原子力研究院 キャパシター用タンタルまたはニオブ粉末の製造方法
JP2010533792A (ja) * 2007-07-18 2010-10-28 グリーン メタルズ リミテッド ルテニウム酸カルシウム電極材料
JP2015230170A (ja) * 2014-06-03 2015-12-21 株式会社東芝 複合酸化物分離方法
JP2017082264A (ja) * 2015-10-26 2017-05-18 株式会社東芝 ガラス固化体の溶解方法及びその溶解装置

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