Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/34—Electrolytic production, recovery or refining of metals by electrolysis of melts of metals not provided for in groups C25C3/02 - C25C3/32
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
  • C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts
• • 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

Definitions

• This invention relates to methods for the production of metals from oxides present in spent nuclear fuels and is particularly applicable to "the production of actinides, specifically uranium. Methods of the present invention can be used in the treatment of irradiated fuels for producing actinides in metallic form suitable for use as feeds in subsequent electrorefining processes.
• molten salts is intended to cover salts such as lithium chloride which, melts at an elevated temperature and also ionic liquids which typically are liquid at room temperature or which melt at a temperature up to about 100°C.
• the Dimitrovgrad SSC-RIAR process makes use of chemical oxidants (chlorine and oxygen gases) to react with powdered uranium dioxide fuel to form higher oxidation state compounds such as UO 2 Cl 2 which are soluble in the molten salt.
• chemical oxidants chlorine and oxygen gases
• UO 2 Cl 2 oxidation state compounds
• the second process developed by the Argonne National Laboratory (ANL) is fundamentally an electrorefining technology which uses direct current to anodically oxidise uranium to form uranium ions in the molten salt electrolyte. At the cathode the uranium is reduced and electrodeposited as dendritic uranium metal.
• the ANL process requires a metal feed. If oxide fuels are to be treated, it is necessary to reduce the uranium oxide (usually UO 2 pellets) to the metal. This reduction process is carried out chemically, using lithium metal in a LiCl or LiCl/KCl molten salt, or a Li/Cd alloy, at 500 to 600°C. Alternatively, a salt transport process can be used involving a Cu-Mg-Ca alloy and molten CaCl 2 salt. However, in both reduction methods the by-products, Li O and CaO respectively, need to be recovered from the molten salt phase by an electrolysis step. .Effectively this means a two stage process.
• a disadvantage of the lithium reduction process for producing a metallic feed from an oxide is the production of Li 2 O by-product. This requires recycle to make the process economic, and this is done by an electrolytic recovery of lithium metal. Hence this is a two stage process, comprising a reduction step followed by a lithium recovery stage.
• the process thereby involves the use of a single electrochemical process to reduce the metal oxide fuel to a metallic form, with oxygen, CO or CO 2 produced as the only by-products.
• the potential of the cathode is maintained and controlled so that only oxygen ionisation occurs and not the deposition of metal (eg Ca) from the cations (eg Ca ions) in the fused salt.
• the oxide comprises an actinide oxide, such as uranium oxide or irradiated uranium oxide.
• an apparatus for performing a process for reducing to metallic form metal oxides comprising an electrochemical cell which comprises a body or housing; a cathode container, and a cathode connector, wherein said body or housing is maintained as the cathode.
• the body or housing of the cell which comprises the apparatus according to the first aspect of the invention is most conveniently maintained as the cathode by the • provision of an electrical connection from a power supply, provided by means of a connector from the cathode terminal to the body or housing of the cell.
• said connector comprises a bolted connection, but this is positioned externally to the cell.
• No bolted or screwed connections are present within the cell, wherein a cathode connector is provided which is affixed to an internal surface of the cell, most preferably the base of the cell, generally by welding.
• said cathode connector comprises a cathode rail.
• the body or housing of the cell is maintained as the cathode, and said cathode is brought into contact with the cathode container by means of the cathode connector.
• contact is made between the cathode container and the cathode connector in order to facilitate the electrolytic process.
• Contact may be most conveniently achieved by means of a simple press connection between the two components.
• the cathode container preferably comprises a basket, such as a mesh basket, or vessel, typically a metal oxide retaining vessel, and - most preferably - comprises an assembly of such baskets or vessels.
• a basket such as a mesh basket, or vessel, typically a metal oxide retaining vessel
• - most preferably - comprises an assembly of such baskets or vessels.
• the oxide is in contact with the cathode container and it is preferred that the cathode is in the form of a mesh basket or, most preferably, an assembly of mesh baskets, with the oxide being contained within the said baskets.
• the anode may be any suitable inert anode, such as carbon.
• a process for reducing to metallic form metal oxides comprising cathodically electrolysing the oxide in the presence of a molten salt electrolyte in an apparatus according to the first aspect of the invention, the potential of the cathode being controlled so as to favour oxygen ionisation over deposition of metal from the cations present in the molten salt.
• the molten salt electrolyte may be any suitable molten salt or mixture of such salts, for instance chloride salts, preferably CaCl 2 and/or BaCl 2 .
• the oxide treated by the process according to the second aspect of the invention comprises an oxide present in spent nuclear fuel.
• the oxide comprises an actinide oxide, such as uranium oxide or irradiated uranium oxide, or mixed uranium/plutonium oxides.
• the uranium oxide is commonly uranium dioxide.
• the oxide may comprise the oxide of a metal such as zirconium or hafnium.
• the fuel may be first treated mechanically to remove its zircaloy cladding before it is added to the electrolytic cell.
• the zircaloy cladding may be treated with the fuel.
• the fuel may require to be sheared into sections of small length prior to treatment in order to expose the oxide fuel to the molten salt.
• Said oxide may be in any physical form, and this is generally dependent on the particular chemical nature of the spent nuclear fuel and the processing to which the material has previously been subjected.
• the fuel may comprise a powder, an amorphous mass, or a dense solid agglomerate.
• the material may be treated according to the method of the second aspect of the present invention by connection to an electrical circuit such that it serves as the cathode during electrolysis; as previously disclosed, connection to the circuit may be conveniently effected by the use of a cathode basket, into which the material is placed.
• the process provides a single electrochemical process to reduce the metal oxide fuel to a metallic form, with oxygen produced as the only by-product.
• the potential of the cathode is maintained and controlled so that only oxygen ionisation occurs and not the deposition of metal (eg Ca) from the cations (eg Ca ions) in the fused salt.
• the process according to the second aspect of the invention provides a more practical, efficient and financially viable means for the production of metal from oxides.
• the electrical continuity of the system which is provided is effective since all the components are held in the cathodic potential region and are, therefore, metallic in nature.
• an electrolytic cell which has a carbon anode, a mesh basket cathode and a cathode rail connector welded to the base of the cell.
• Irradiated oxide fuel is placed in the mesh basket.
• the electrolyte consists of a molten salt or a mixture of such salts comprising, for example, chloride salts such as CaCl 2 or BaCl 2 .
• a voltage is applied between the cathode and the anode.
• the reaction involves the diffusion of oxygen atoms to the surface of .the solid, followed by ionisation according to the reaction:
• the oxide ions which are produced dissolve in the electrolyte and are transferred to the anode where they are re-oxidised to produce oxygen, CO or CO 2 gases.
• the potential at the cathode may be controlled, via a third reference electrode, to ensure that the reaction occurring at the cathode is oxygen ionisation and not deposition of eg Ca metal from the cations in the fused salt. Electrolysis at elevated temperatures results in an increased rate of oxygen diffusion, thereby also encouraging ionisation rather than metal deposition.
• the irradiated fuel is left in the form of a metallic solid at the cathode.
• This metallic solid which contains fission products, can be removed or used directly as the feed for an electrorefining process. The remaining components of the cell may be re-used immediately without the need for any cleaning.
• the electrolytic ionisation of oxygen and the electrorefining processes are carried out in the same cell and the same salt system. ⁇
• a second cathode, or cathode assembly may be required.
• the advantage of the apparatus and process of the present invention is that they facilitate the performance of an- effectively single stage process which provides advantages over the prior art in terms of practicality, efficiency and cost.
• the process is advantageously used for the treatment of irradiated oxide nuclear fuel, possibly in the form of pellets and, most particularly, is applied to fuels such as uranium oxide, and mixed uranium and plutonium fuels.
• FIG. 1 shows an apparatus according to the first aspect of the invention which comprises a series of electrolytic cells, the bodies and housings of which are, in use, connected by means of cathode rails 1 to cathode baskets 2.
• the cells also comprise anodes 4, surrounded by anode protective sleeves 3, and connected to an electrical supply by means of electrical connections 6, these being protected by insulation shrouds 5.
• the cathode baskets 2 which are equipped with basket handles 8, cooled by means of cooling chambers 7, are loaded with spent nuclear fuel pellets and lowered into the electrolyte 9 to a point at which contact is made with cathode rails 1 and, thereby, with the cell housing, which is maintained as the cathode, thereby allowing processing to commence.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Electrolytic Production Of Metals (AREA)

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Citations (7)

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• 2002
  • 2002-02-28 GB GBGB0204671.2A patent/GB0204671D0/en not_active Ceased
• 2003
  • 2003-02-24 KR KR10-2004-7013442A patent/KR20040093726A/ko not_active Withdrawn
  • 2003-02-24 JP JP2003572043A patent/JP2005519192A/ja active Pending
  • 2003-02-24 US US10/505,262 patent/US20050139474A1/en not_active Abandoned
  • 2003-02-24 WO PCT/GB2003/000792 patent/WO2003073436A1/en not_active Ceased
  • 2003-02-24 AU AU2003207344A patent/AU2003207344A1/en not_active Abandoned
  • 2003-02-24 CN CNA038048892A patent/CN1639803A/zh active Pending
  • 2003-02-24 EP EP03704816A patent/EP1481401B1/en not_active Expired - Lifetime
  • 2003-02-24 RU RU2004127170/06A patent/RU2004127170A/ru not_active Application Discontinuation

Patent Citations (7)

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