CN109637682B - Method for reconstructing molten salt reactor fuel - Google Patents

Method for reconstructing molten salt reactor fuel Download PDF

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CN109637682B
CN109637682B CN201811307960.7A CN201811307960A CN109637682B CN 109637682 B CN109637682 B CN 109637682B CN 201811307960 A CN201811307960 A CN 201811307960A CN 109637682 B CN109637682 B CN 109637682B
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uranium
molten salt
fluoride
thorium
metal
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CN109637682A (en
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王鹏
孙理鑫
曹长青
牛永生
胡聪伟
林俊
窦强
李晴暖
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Shanghai Institute of Applied Physics of CAS
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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
    • G21C19/50—Reprocessing of irradiated fuel of irradiated fluid fuel, e.g. regeneration of fuels while the reactor is in operation
    • 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

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  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Electrolytic Production Of Metals (AREA)

Abstract

The invention provides a method for reconstructing fuel of a molten salt reactor, which comprises the following steps: s1, providing molten fluoride molten salt containing uranium tetrafluoride; s2, providing an active metal, and oxidizing the active metal into metal ions in the fluoride fused salt through an oxidation-reduction reaction, and reducing the uranium tetrafluoride into uranium trifluoride; and S3, introducing mixed gas of uranium hexafluoride and inert gas into the fluoride fused salt, so that the uranium hexafluoride and uranium trifluoride perform an oxidation-reduction reaction to generate uranium tetrafluoride, and realizing reconstruction of uranium materials in the fluoride fused salt. Particularly, when the method provided by the invention is used for reconstructing the thorium-based molten salt reactor fuel, the reconstruction of uranium materials and thorium materials can be realized simultaneously. According to the invention, the method for reconstructing the molten salt reactor fuel has the advantages of simple process flow, low equipment cost, no secondary pollution and capability of avoiding the corrosion of equipment pipelines and also considering the reconstruction of available metal thorium.

Description

Method for reconstructing molten salt reactor fuel
Technical Field
The invention relates to the field of molten salt reactor liquid fuel treatment and liquid fuel preparation, in particular to a method for reconstructing molten salt reactor fuel.
Background
The molten salt reactor is one of six candidate reactor types of a fourth generation reactor nuclear energy system, can continuously add fuel and remove generated fission products in the operation process, and has the advantages of less shutdown times and high neutron utilization rate.
Molten salt reactor fuel processing plays an important role in removing fission products, recovering useful fissile material, and improving the economy of the reactor, and the flow includes: (1) separating out nuclear material U (obtained in the form of uranium hexafluoride); (2) recovery from molten salt leaving a uranium separation process sectionCarrier salts (e.g. LiF and BeF)2) (ii) a (3) Mixing the above uranium hexafluoride (UF)6) And carrier salts for fuel reconstitution.
The fuel reconstruction is an important process in a fuel treatment process, the main purpose of the fuel reconstruction is to convert carrier salt and fissile materials (such as U) separated from the fuel salt after the fuel is dumped into the fuel salt directly used for the molten salt reactor, and the recycling of the carrier salt and the usable fissile materials in the fuel salt after the fuel is dumped is realized. Among them, the conversion of U material to uranium tetrafluoride is the focus of molten salt reactor fuel reconstruction.
At present, the reported fuel reconstitution process is proposed by the Oak Ridge national experiment (ORNL) in USA, and the procedure includes UF6Introducing molten uranium tetrafluoride (UF)4) In a carrier salt of (3), so that UF6And uranium tetrafluoride (UF)4) Reaction in carrier salts to form uranium pentafluoride (UF)5) Then, the UF is treated with hydrogen5Reduced to UF4(ii) a Repeating the above uranium hexafluoride (UF)6) Conversion to UF4Until the uranium elements separated from the fuel salt after the heap is completely reconstructed. However, UF from this process5Has strong oxidizing property, and increases the corrosion of pipelines and containers. If gold material or gold plating protection is adopted, the equipment cost is high.
In addition, the common reactor adopts uranium as fuel, but uranium resources in nature are very limited, and the thorium-based molten salt reactor is characterized in that thorium resources rich in crusta are utilized to replace depleted uranium. However, the above reported fuel reconstitution processes do not allow for the reconstitution of metallic thorium in thorium-based molten salt stacks.
Disclosure of Invention
The invention aims to provide a method for reconstructing fuel of a molten salt reactor, so as to solve the problems that in the prior art, a fuel reconstruction process has the defects that equipment pipelines are easy to corrode, a device is expensive, and reconstruction of available metal thorium is not considered.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for reconstructing fuel of a molten salt reactor is provided, which comprises the following steps: s1, providing molten fluoride molten salt containing uranium tetrafluoride; s2, providing an active metal, and oxidizing the active metal into metal ions in the fluoride fused salt through an oxidation-reduction reaction, and reducing the uranium tetrafluoride into uranium trifluoride; and S3, introducing mixed gas of uranium hexafluoride and inert gas into the fluoride fused salt, so that the uranium hexafluoride and uranium trifluoride perform an oxidation-reduction reaction to generate uranium tetrafluoride, and realizing reconstruction of uranium materials in the fluoride fused salt.
The fluoride fused salt is a mixture of uranium tetrafluoride and at least one of lithium fluoride, beryllium fluoride, sodium fluoride, potassium fluoride, calcium fluoride and zirconium fluoride, for example, LiF-BeF2-UF4、LiF-BeF2-ZrF4-UF4、LiF-CaF2-UF4、LiF-UF4Or LiF-NaF-KF-UF4。
The active metals are: at least one of thorium, zirconium, uranium, and beryllium.
The active metal is in the form of a sheet, plate, rod, granule or powder.
The step S1 specifically includes: and (3) putting the container containing the fluoride fused salt into a high-temperature furnace, and heating to enable the fluoride fused salt to be in a stable molten state. Specifically, the fluoride molten salt is heated to be above the melting point of the molten salt mixture, and the temperature is kept for more than 30min, so that the molten salt is in a uniform flowing state. Preferably, the material of the container is graphite, corundum, nickel or glassy carbon.
The step S2 specifically includes: heating molten salt to desired reaction temperature, adding active metal, heating and stirring to obtain active metal and UF4Oxidation-reduction reaction occurs to generate metal fluoride and uranium trifluoride. The reaction temperature is 550-900 deg.C, preferably 650-850 deg.C.
It should be understood that to enhance the active metal and UF4The contact efficiency in the molten salt can adopt a proper stirring mode and a proper feeding mode according to the shape of the active metal. When the active metal is in the form of flakes, granules or powder, the active metal is directly put into the molten salt and bubbled with an inert gas or mechanically stirred. When the active metal is in the form of a plate orIn the case of a rod, the active metal is inserted below the liquid level of the molten salt without contacting the bottom of the vessel, and the stirring is carried out in such a manner that the active metal rotates or moves clockwise or/and counterclockwise. The inert gas is nitrogen or argon.
The step S2 specifically includes: providing active metal as a negative electrode, graphite or inert metal as a positive electrode, and connecting the negative electrode and the positive electrode by adopting a lead, so that the active metal is subjected to oxidation reaction and dissolved to generate metal ions, and the uranium tetrafluoride generates uranium trifluoride on the positive electrode. Preferably, the temperature of the galvanic reaction is 600 to 750 ℃.
The step S2 specifically includes: providing an active metal as an anode, providing graphite or an inert metal as a cathode, applying forward current to the anode or applying forward voltage between the anode and the cathode, so that the active metal of the anode is subjected to oxidation reaction to dissolve and generate metal ions, and the uranium tetrafluoride is subjected to reduction reaction at the cathode to deposit and generate uranium trifluoride. Preferably, the operation temperature of the electrolysis is 550-650 ℃, and the current density of the cathode is 200-3900A/m2。
In step S2, the graphite and inert metal are preferably in the shape of sheet, plate and rod, which facilitates the connection of the positive electrode or cathode to the power source and the removal from the molten salt, facilitating the separation of the product.
It is understood that when the active metal is used as an electrode material in a galvanic cell or electrolysis, the active metal is in the form of a plate, rod, and particle. Depending on the degree of cleaning and oxidation of the metal surface, the metal may be subjected to a cleaning and surface polishing treatment to remove the surface oxide layer and expose the electrode material. And connecting the electrode with a power supply by adopting a proper connection mode according to different electrode shapes. The anode and cathode are generally connected to a power source by an inert wire, or are connected to the power source by a wire after the anode material and the cathode material are fixed by an electrode holder. When the shape (such as particles) of the electrode material is not easy to fix or connect, the electrode material can be wrapped in an inert metal net and fixed on an electrode clamp by winding an inert metal wire, and then connected with a power supply anode by a lead.
The step S3 specifically includes: by melting saltsReducing the temperature to the required reaction temperature, and introducing mixed gas of uranium hexafluoride and inert gas into molten salt in a bubbling manner to enable UF6With UF3By reaction of redox reactions to UF4. The reaction temperature is 500-700 deg.C, preferably 530-600 deg.C. The flow of uranium hexafluoride in the mixed gas is detected by infrared spectroscopy.
In said step S3, to avoid generation of UF4And UF6The reaction produces UF5Control of UF6And the active metal oxidized in step S2. It will be understood that when the active metal is zirconium, UF6And zirconium in a molar ratio of n (UF)6) (Zr) is less than or equal to 2. When the active metal is uranium, UF6With uranium in a molar ratio of n (UF)6) (u) is less than or equal to 2. When the active metal is beryllium, UF6Molar ratio of beryllium to n (UF)6) (Be) is less than or equal to 1. When the active metal is thorium, UF6With the metal thorium in a molar ratio n (UF)6)/n(Th)≤2。
The steps S2, S3 may be operated in a cycle of several times until the recovered uranium hexafluoride is completely converted into uranium tetrafluoride in the molten salt phase.
The steps S1, S2 and S3 are all performed under an inert atmosphere.
The molten salt prepared by the invention can be directly used as fuel salt or used as fuel salt after being uniformly mixed with carrier salt in a molten state.
Particularly, when the method provided by the invention is used for reconstructing the thorium-based molten salt reactor fuel, the reconstruction of uranium materials and thorium materials can be realized simultaneously. The method comprises the following steps: s1, providing molten fluoride molten salt containing uranium tetrafluoride; s2, providing metal thorium, oxidizing the metal thorium into tetravalent thorium ions in molten salt through an oxidation-reduction reaction, and reducing uranium tetrafluoride into uranium trifluoride; and S3, introducing mixed gas of uranium hexafluoride and inert gas into the molten salt, so that the uranium hexafluoride and uranium trifluoride perform an oxidation-reduction reaction to generate uranium tetrafluoride, and realizing the reconstruction of uranium and thorium in the fluoride molten salt.
It should be understood that in the fuel reconfiguration of the thorium-based molten salt reactor, at least one of zirconium, uranium and beryllium may be used together in addition to a sufficient amount of metallic thorium in the step S2.
The loading amount of the fluoride fused salt is that the liquid level height of the fused salt is more than 1.5cm during melting.
The step S2 specifically includes: heating molten salt to required reaction temperature, adding metal thorium, heating and stirring to obtain metal thorium and UF4Fully contact and generate redox reaction to generate metal fluoride and uranium trifluoride. The reaction temperature is 600-900 deg.C, preferably 650-850 deg.C.
It will be appreciated that in order to increase the metals thorium and UF4The contact efficiency in the molten salt can adopt a proper stirring mode and a feeding mode according to the shape of the metal thorium. When the metal thorium is flaky, granular or powder, the metal thorium is directly put into molten salt, and inert gas is adopted for bubbling or mechanical stirring. When the metal thorium is plate-shaped or rod-shaped, the metal thorium is inserted below the liquid level of the molten salt and is not contacted with the bottom of the container, and the stirring mode is that the metal thorium rotates or moves clockwise or/and anticlockwise. The inert gas is nitrogen or argon.
The step S2 specifically includes: providing metal thorium as a negative electrode, providing graphite or inert metal as a positive electrode, and connecting the negative electrode and the positive electrode by adopting a lead so that the metal thorium is subjected to oxidation reaction and dissolved to generate tetravalent thorium ions, and the uranium tetrafluoride is subjected to reduction reaction on the positive electrode to generate uranium trifluoride. The reaction temperature of the primary battery is 600-700 ℃.
The step S2 specifically includes: providing metallic thorium as an anode, providing graphite or inert metal as a cathode, applying forward current to the anode or applying forward voltage between the anode and the cathode through a direct current power supply or an electrochemical workstation, so that the metallic thorium at the anode undergoes an oxidation reaction to dissolve and generate tetravalent thorium ions, and the uranium tetrafluoride undergoes a reduction reaction at the cathode to deposit and generate uranium trifluoride. The operation temperature of the electrolysis is 550-650 ℃, and the current density of the cathode is 200-3900A/m2。
In said step S2, the graphite and inert metal are preferably in the shape of sheets, plates and rods to facilitate connection of the positive electrode in the galvanic cell or the cathode in the electrolytic cell to the power supply and removal from the molten salt to facilitate product separation.
In said step S2, the UF4To all or part of UF in the molten salt4Is reduced to UF3. Starting UF in dissolved metal thorium and molten salt4Has a molar ratio of n (Th)/n (UF)4)≤1:4。
It is understood that when metallic thorium is used as an electrode material in a galvanic cell or electrolysis, the metallic thorium is in the shape of sheets, plates, rods and particles. And connecting the electrode with a power supply by adopting a proper connection mode according to different electrode shapes. The anode and cathode are generally connected to a power source by an inert wire, or are connected to the power source by a wire after the anode material and the cathode material are fixed by an electrode holder. When the shape (such as particles) of the electrode material is not easy to fix or connect, the electrode material can be wrapped in an inert metal net and fixed on an electrode clamp by winding an inert metal wire, and then connected with a power supply anode by a lead.
The step S3 specifically includes: the part of the fused salt filled in the container during melting meets the condition that the height/diameter ratio is more than 2, and the ventilation pipe of the uranium hexafluoride is inserted below the liquid level of the fused salt and is 1-5 mm away from the bottom of the container. Reducing the temperature of the molten salt to the required reaction temperature, and introducing mixed gas of uranium hexafluoride and inert gas into the molten salt in a bubbling manner to enable UF6With UF3By reacting redox reactions to UF4. The reaction temperature is 500-700 deg.C, preferably 530-600 deg.C. The flow of uranium hexafluoride in the mixed gas is detected by infrared spectroscopy.
In said step S3, the UF3Oxidation of (2) to all or part of UF in the molten salt3Is reduced to UF4. Introduced UF6And the molar ratio of the metal thorium dissolved in step S2 is n (UF)6) The/n (metal thorium) is less than or equal to 2.
The steps S2, S3 may be cycled through a plurality of times until the reconstitution of at least one of the metals thorium and uranium hexafluoride is complete.
In conclusion, according to the method for reconstructing the fuel of the molten salt reactor, F, Li is not actively introduced,Be. Other elements except U and Zr can not generate secondary pollution to the molten salt, so that the liquid fuel salt can be directly obtained after the reaction. By controlling UF6And active metal in a molar ratio of UF6With UF3The reaction is complete and UF is avoided6With UF4The reaction generates UF with strong corrosiveness5Therefore, UF can be inhibited6/UF5Corrosion of metal containers. The method is not only suitable for thorium-based molten salt reactor, but also suitable for other molten salt reactors. When the method is applied to fuel reconstruction of the thorium-based molten salt reactor, reconstruction of the uranium material and the thorium material can be simultaneously realized, and the two purposes are achieved. In addition, the method has the advantages of simple process flow, low equipment cost and simple and convenient operation, and is suitable for large-scale use.
In a word, the invention provides the method for reconstructing the molten salt reactor fuel, which has the advantages of simple process flow, low equipment cost, no secondary pollution and capability of avoiding the corrosion of equipment pipelines and also considering the reconstruction of available metal thorium.
Drawings
FIG. 1 is electrodeposition UF in example 1 according to the present invention3XRD pattern of the cathode product;
FIG. 2 is electrodeposition UF in example 1 according to the present invention3XRD pattern of fused salt;
FIG. 3 is UF in example 1 according to the present invention3And UF6XRD pattern of the product of the reaction;
FIG. 4 is a diagram of the metals thorium and UF in example 6 according to the invention4XRD pattern of the reduced product;
FIG. 5 is UF in example 6 according to the present invention3And UF6XRD pattern of the reacted product.
Detailed Description
The present invention will be further described with reference to the following specific examples. It should be understood that the following examples are illustrative only and are not intended to limit the scope of the present invention.
Example 1
1) Melting of molten salt: LiF-BeF is filled in the container2-UF4(the mixture ratio is 66-33-0.6 mole%) molten salt is put into a high-temperature furnace of a glove box. Heating toAnd keeping the temperature at 600 ℃ for more than 30min to ensure that the molten salt is in a stable molten state.
2) Preparing an anode material: and (3) polishing the surface of each surface of the zirconium sheet, and respectively ultrasonically cleaning the zirconium sheet by using deionized water, absolute ethyl alcohol and acetone. The zirconium pieces were dried, transferred to a glove box, and further polished with sandpaper. And fixing the zirconium sheet on the electrode chuck, and connecting the upper end of the electrode chuck with the anode of the direct-current power supply through a lead.
3) Preparation of cathode material: and ultrasonically cleaning the nickel sheet by using deionized water, absolute ethyl alcohol and acetone respectively. And drying the nickel sheet, transferring the dried nickel sheet to a glove box, fixing the dried nickel sheet on an electrode chuck, and connecting the upper end of the electrode chuck with a cathode of a direct current power supply through a lead.
4) Oxidation of metallic zirconium and UF3Generation of (1): applying a 1A current to the anode by using a direct current power supply, wherein the current density of the cathode is 650-900A/cm2. After the electrodeposition is finished, the cathode product and the molten salt are characterized by XRD. XRD results showed that the predominant phase of the cathode product was UF3And Li2BeF4(see FIG. 1), the main phase of the molten salt is Li2BeF4And contains very little UF3Phase (see fig. 2). The mass percentage of U in the product is 58 percent, UF3The yield of (a) was 72%. And putting the obtained cathode product into the molten salt, and keeping the temperature for more than 30 min.
5)UF3Oxidation of (2): cooling the molten salt to 550 deg.C, bubbling UF6. Controlling UF in U reaction process6And the molar ratio n of dissolved Zr (UF)6) (Zr) is less than or equal to 2. XRD of the molten salt sample after the reaction was completed is shown in FIG. 3, and only Li was observed2BeF4And LiUF5Phase, showing UF in molten salt3Is totally UF6Oxidation to UF4. Measured and calculated, UF6The utilization rate of the method is 40 to 70 percent.
Example 2
The specific process steps are as follows:
1) melting of molten salt: LiF-BeF is filled in the container2-ZrF4-UF4(the mixture ratio is 65.0-29.2-5.0-0.83 mole%) molten salt graphite container is put into a high-temperature furnace of a glove box, and the temperature is raisedAnd keeping the temperature for 30min to keep the molten salt in a stable molten state when the temperature reaches 720 ℃.
2) Oxidation of metallic uranium and UF3Generation of (1): adding U particles, U and UF to molten salt4Molar ratio of (n), (U)/n (UF)4) Is 2:9, and after the mixture is stirred and reacted for 5 hours at constant temperature, the main phase of the molten salt sample after the reaction is Li2BeF4And UF3。
3)UF3Oxidation of (2): cooling the molten salt to 550 deg.C, bubbling UF6. Controlling UF in the reaction6And the molar ratio n of dissolved U (UF)6) (u) is less than or equal to 2. Measured, UF in the reaction6The conversion rate of (A) is 50 to 80%.
Example 3
1) Melting of molten salt: LiF-UF is filled in the solution4(the mixture ratio is 74-26 mole%) of the graphite container of the molten salt is put into a glove box and a high-temperature furnace, the temperature is raised to 650 ℃, and the temperature is kept for more than 30min, so that the molten salt is in a stable molten state.
2) Preparing a positive electrode material: and polishing each surface of the beryllium sheet in the glove, and connecting one end of the beryllium sheet after polishing with the electrode chuck.
3) Preparation of anode material: and ultrasonically cleaning the nickel sheet by using deionized water, absolute ethyl alcohol and acetone respectively. The nickel plate was dried, transferred to a glove box and fixed to an electrode chuck.
4) Oxidation of metallic beryllium and UF3Generation of (1): the positive electrode and the negative electrode were inserted into the molten salt, and the positive electrode and the negative electrode were connected by a wire to perform a galvanic reaction. During the reaction, Be and UF4Molar ratio of (n), (Be)/n (UF)4) At 1:6, the main phase of the molten salt is LiU4F17、UF3And Li2BeF4。
5)UF3Oxidation of (2): cooling the molten salt to 550 deg.C, bubbling UF6. Controlling UF in the reaction6And the molar ratio n of dissolved Be (UF)6) (Be) is less than or equal to 1. Measured and calculated, UF6The utilization rate of the method is 45-75 percent.
Example 4
1) Melting of molten salt: LiF-CaF is filled in the container2-UF4(mass percentage)The distribution ratio is 53.7: 42.8: 3.5 wt%) graphite container of molten salt was placed in a high temperature furnace of a glove box. Heating to 600 deg.C, and maintaining the temperature for more than 30min to make the molten salt in stable molten state.
2) Oxidation of metallic thorium and UF3Generation of (1): and (3) heating to 800 ℃, adding the Th particles into the molten salt, and stirring at constant temperature for reaction. Measuring and calculating initial UF in dissolved Th and molten salt after reaction4Molar ratio of (n), (Th)/n (UF)4) Is 1: 4. XRD of the fused salt sample showed the major phase to have Li2BeF4、UF3、Li3ThF7And LiUF5。
3)UF3Oxidation of (2): cooling the molten salt to 550 deg.C, bubbling UF6. Controlling UF6And molar ratio of Th n (UF)6) (Th) is 2, XRD of the molten salt sample after the reaction is finished is shown in figure 2, and only Li is observed2BeF4And LiUF5Phase, showing UF in molten salt3Is totally UF6Oxidation to UF4，UF6The utilization rate of (A) is 60-85%.
Example 5
The specific process steps are as follows:
1) melting of molten salt: LiF-NaF-KF-UF filled with the mixture4(the mixture ratio is 27.9: 11.1: 56: 5 wt%) molten salt, placing the graphite container into a glove box, heating to 650 ℃, and keeping the temperature for more than 30min to enable the molten salt to be in a stable molten state.
2) Preparing a positive electrode material: wrapping the thorium sheet by using a nickel screen, winding one end of a nickel wire with the diameter of 1mm outside the nickel screen, fixing the nickel screen to prevent the nickel screen from scattering, and connecting the other end of the nickel wire with the electrode chuck.
3) Preparation of anode material: and ultrasonically cleaning the nickel sheet by using deionized water, absolute ethyl alcohol and acetone respectively. The nickel plate is dried and then transferred to and fixed on an electrode chuck.
4) Oxidation of metallic thorium and UF3Generation of (1): the positive electrode and the negative electrode were inserted into the molten salt, and the positive electrode and the negative electrode were connected by a wire to perform a galvanic reaction. Measurement of dissolved Th after completion of the reaction and initial UF in molten salt4Molar ratio of (n), (Th)/n (UF)4) Is 1: 4. XRD results showed that the major phase of the product was UF3LiF, KF and NaF.
5)UF3Oxidation of (2): cooling the molten salt to 550 deg.C, bubbling Ar and UF6The mixed gas of (1). During the reaction, UF was controlled6And molar ratio of Th n (UF)6)/n(Th)≤2，UF6The conversion rate of (A) is 30-70%.
Example 6
The specific process steps are as follows:
1) melting of molten salt: LiF-BeF is filled in the container2-UF4(the mixture ratio is 66.5-33-0.5 mole%) of molten salt, placing the graphite container into a high-temperature furnace, heating to 600-700 ℃, and preserving heat for 30min to enable the molten salt to be in a stable molten state.
2) Oxidation of metallic thorium and UF3Generation of (1): and (3) heating to 800 ℃, adding the Th particles into the molten salt, and stirring at constant temperature for reaction. Measuring and calculating initial UF in dissolved Th and molten salt after reaction4Molar ratio of (n), (Th)/n (UF)4) Is 1: 4. XRD of the fused salt sample is shown in FIG. 4, the main phase has Li2BeF4、UF3、Li3ThF7And LiUF5。
3)UF3Oxidation of (2): cooling the molten salt to 550 deg.C, bubbling UF6. Controlling UF6And molar ratio of Th n (UF)6) (Th) is 2, XRD of the molten salt sample after the reaction is finished is shown in figure 5, and only Li is observed2BeF4And LiUF5Phase, showing UF in molten salt3Is totally UF6Oxidation to UF4，UF6The utilization rate of (A) is 60-85%.
Example 7
1) Melting of molten salt: LiF-BeF is filled in the container2-ZrF4-UF4(the mixture ratio is 65.0-29.2-5.0-0.83 mole%) molten salt, placing the graphite container into a high-temperature furnace, heating to 600-700 ℃, and preserving heat for 30min to enable the molten salt to be in a stable molten state.
2) Preparing a positive electrode material: wrapping the thorium sheet by using a nickel screen, winding one end of a nickel wire with the diameter of 1mm outside the nickel screen, fixing the nickel screen to prevent the nickel screen from scattering, and connecting the other end of the nickel wire with the electrode chuck.
3) Preparation of anode material: and ultrasonically cleaning the nickel sheet by using deionized water, absolute ethyl alcohol and acetone respectively. The nickel plate is dried and then transferred to and fixed on an electrode chuck.
4) Oxidation of metallic thorium and UF3Generation of (1): the positive electrode and the negative electrode were inserted into the molten salt, and the positive electrode and the negative electrode were connected by a wire to perform a galvanic reaction. Measurement of dissolved Th after completion of the reaction and initial UF in molten salt4Molar ratio of (n), (Th)/n (UF)4) Is 1: 4. XRD results showed the product phase to be UF3、Li3ThF7And Li2BeF4。
5)UF3Oxidation of (2): cooling the molten salt to 550 deg.C, bubbling Ar and UF6The mixed gas of (1). During the reaction, UF was controlled6And molar ratio of Th n (UF)6)/n(Th)≤2，UF6The conversion rate of (A) is 30-70%.
Example 8
1) LiF-UF is filled in the solution4(the proportion is 74-26 mole%) of the graphite container of the molten salt is put into a medium-high temperature furnace, the temperature is raised to 600-700 ℃, and the temperature is preserved for 30min to enable the molten salt to be in a stable molten state.
2) Preparing an anode material: wrapping the thorium sheet by using a nickel screen, winding one end of a nickel wire with the diameter of 1mm outside the nickel screen, fixing the nickel screen to prevent the nickel screen from scattering, connecting the other end of the nickel wire with the electrode chuck, and connecting the electrode chuck with the anode of the direct-current power supply through a lead.
3) Preparation of cathode material: and ultrasonically cleaning the nickel sheet by using deionized water, absolute ethyl alcohol and acetone respectively. And (3) drying the nickel sheet, transferring to and fixing on an electrode chuck, and connecting the upper end of the electrode chuck with a direct current power supply cathode through a lead.
4) Oxidation of metallic thorium and UF3Generation of (1): electrodeposition was carried out by applying a current of 1A to the anode using a DC power supply. Measuring dissolved Th and initial UF in molten salt after electrodeposition4Molar ratio of (n), (Th)/n (UF)4) Is 1: 8. XRD results showed the product phase to be UF3And Li2BeF4. The mass percentage of U is 58 percent，UF3The yield of (a) was 72%. And putting the obtained cathode product into the molten salt, and keeping the temperature for more than 30 min.
5)UF3Oxidation of (2): cooling the molten salt to 550 deg.C, bubbling UF6. Measurement of UF introduced after the end of the reaction6And molar ratio of dissolved Th n (UF)6)/n(Th)≤2，UF6The conversion rate of (A) is 27 to 68 percent.
The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.

Claims (12)

1. A method of molten salt reactor fuel reconfiguration, comprising the steps of:
s1, providing molten fluoride molten salt containing uranium tetrafluoride;
s2, providing an active metal, and oxidizing the active metal into metal ions in the fluoride fused salt through an oxidation-reduction reaction, and reducing the uranium tetrafluoride into uranium trifluoride; and
s3, introducing mixed gas of uranium hexafluoride and inert gas into the fluoride fused salt, so that the uranium hexafluoride and uranium trifluoride perform an oxidation-reduction reaction to generate uranium tetrafluoride, and reconstructing a uranium material in the fluoride fused salt;
when the active metal used in the step S2 is beryllium, the molar ratio of the uranium hexafluoride introduced in the step S3 to the active metal used in the step S2 is less than or equal to 1; when the active metals used in step S2 are zirconium, uranium and thorium, the molar ratio of the uranium hexafluoride introduced in step S3 to the active metal used in step S2 is 2 or less.
2. The method according to claim 1, wherein the fluoride molten salt is a mixture of uranium tetrafluoride and at least one of lithium fluoride, beryllium fluoride, sodium fluoride, potassium fluoride, calcium fluoride, and zirconium fluoride.
3. The method of claim 1, wherein the reactive metal is: at least one of thorium, zirconium, uranium, and beryllium.
4. The method according to claim 1, wherein the step S1 specifically includes: and (3) putting the container containing the fluoride fused salt into a high-temperature furnace, and heating to enable the fluoride fused salt to be in a stable molten state.
5. The method according to claim 1, wherein the step S2 specifically includes: heating molten salt to desired reaction temperature, adding active metal, heating and stirring to obtain active metal and UF4Oxidation-reduction reaction occurs to generate metal fluoride and uranium trifluoride.
6. The method according to claim 1, wherein the step S2 specifically includes: providing active metal as a negative electrode, graphite or inert metal as a positive electrode, and connecting the negative electrode and the positive electrode by adopting a lead, so that the active metal is subjected to oxidation reaction and dissolved to generate metal ions, and the uranium tetrafluoride generates uranium trifluoride on the positive electrode.
7. The method according to claim 1, wherein the step S2 specifically includes: providing an active metal as an anode, providing graphite or an inert metal as a cathode, applying forward current to the anode or applying forward voltage between the anode and the cathode, so that the active metal of the anode is subjected to oxidation reaction to dissolve and generate metal ions, and the uranium tetrafluoride is subjected to reduction reaction at the cathode to deposit and generate uranium trifluoride.
8. The method according to claim 1, wherein the step S3 specifically includes: reducing the temperature of the molten salt to the desired reaction temperature, mixing the uranium hexafluoride and inert gasPassing gas through the molten salt to allow UF6With UF3By reaction of redox reactions to UF4。
9. The method according to claim 1, wherein the steps S2, S3 are operated in cycles until the recovered uranium hexafluoride is completely converted into uranium tetrafluoride in the molten salt phase.
10. The method of claim 1, when used for thorium-based molten salt reactor fuel reconstruction, comprising the steps of:
a1, providing molten fluoride molten salt containing uranium tetrafluoride;
a2, providing metal thorium, oxidizing the metal thorium into tetravalent thorium ions in molten salt through oxidation-reduction reaction, and simultaneously reducing uranium tetrafluoride into uranium trifluoride; and
a3, introducing mixed gas of uranium hexafluoride and inert gas into the molten salt, so that the uranium hexafluoride and uranium trifluoride perform an oxidation-reduction reaction to generate uranium tetrafluoride, and meanwhile, the uranium material and the thorium material in the fluoride molten salt are reconstructed.
11. The method of claim 10, wherein step a2 further comprises providing at least one of zirconium, uranium, and beryllium simultaneously.
12. The method of claim 10, wherein said steps a2, A3 are operated in cycles until the reconstitution of at least one of the metals thorium and uranium hexafluoride is complete.
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