Fluorination-electrolysis synergistic process applied to post-treatment of metal spent fuel

Abstract

The invention relates to a fluorination-electrolysis synergistic process applied to post-treatment of a metal spent fuel, which is characterized in that fluorine gas reacts with the pretreated metal spent fuel under a high-temperature condition, uranium, plutonium and a small amount of fluorinated volatile fission products in the spent fuel are converted into gaseous fluoride to be separated and transferred; and the uranium-plutonium alloy is further prepared by using technologies such as condensation trapping and gaseous fluoride reduction. Meanwhile, fluorinated residues containing a large amount of high-radioactivity and high-heat-release fission elements and minor actinide elements are subjected to electrolytic separation through a villiaumite system, and separation and recovery of the minor actinide elements are achieved. The regeneration and reforming preparation of the metal fuel can be realized on the basis of alloy ingots obtained by a gaseous fluoride reduction process and actinide metal alloys obtained by molten salt electrolysis through injection casting supplementary materials. Compared with the prior art, efficient recovery of uranium and plutonium in the metal spent fuel and deep separation and recovery of minor actinide elements are achieved, the process is simple, and the treatment time is short.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel cycle technology, and in particular to a fluorination-electrolysis synergistic process for the reprocessing of spent metal fuel. Background Technology

[0002] The treatment of spent metal fuel from fast reactors is one of the key bottlenecks in the implementation of the "thermal reactor-fast reactor-fusion reactor" three-step strategy. Traditional aqueous treatment processes have drawbacks such as large volumes of high-level radioactive waste, difficulty in handling fuels with high burnup or short cooling times, and large-scale equipment. Therefore, dry treatment technology capable of handling high-burnup fast breeder reactors has been proposed. Compared with aqueous treatment, it has higher radiation stability, avoids the solvent radiolysis problem in aqueous treatment, and can promptly process spent fuel from pressurized water reactors and high-burnup fast reactors, significantly shortening the fuel cycle time of fast reactors. The system does not introduce neutron moderators, reducing criticality safety risks. The process flow is shorter and the equipment is more compact, making dry treatment facilities smaller and allowing for co-location with the reactor. Furthermore, the dry treatment process generates less waste, which is in a solid form that is easy to handle and dispose of, resulting in better economic efficiency.

[0003] Internationally, the main dry reprocessing technology for spent metallic fuel is molten salt electrolysis. This technology can be traced back to the 1980s when Argonne National Laboratory (ANL) in the United States developed a molten salt electrolysis refining process for processing spent metallic fuel from its experimental breeder reactor, EBR-II. Its principle is based on the difference in redox potential between actinide elements (such as uranium and plutonium) and fragmented elements in a molten salt system, achieving separation through potential control. However, practical experience has shown that this technology still suffers from problems such as the similar chemical properties of actinide / lanthanide elements, poor separation capability, severe molten salt corrosion, and batch operation limitations. Fluorination volatilization technology is another dry reprocessing process proposed internationally. By fluorinating spent fuel into volatile gases, it achieves efficient separation of uranium, plutonium, and fission products. It has significant advantages such as simple process, continuous scale-up operation, and high lanthanum-actinium separation coefficient. It is mainly used in the reprocessing of oxide and fluoride spent fuels. However, further technical breakthroughs are needed in high-temperature corrosion resistant materials, plutonium hexafluoride stability, and engineering scale-up. In addition, it cannot deeply separate long-lived actinides from fluorination residues. Summary of the Invention

[0004] The purpose of this invention is to provide a fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels, which achieves efficient recovery of uranium and plutonium and deep separation and recovery of minor actinides from spent metal fuels, and the process is simple and has a short processing time.

[0005] The objective of this invention can be achieved through the following technical solutions: This invention provides a fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels, comprising the following steps: S1. Component disassembly and cutting: Disassemble the spent metal fuel assembly to be processed, remove the stainless steel cladding and a small amount of metallic sodium inside the cladding to obtain the spent metal fuel core, and cut the spent metal fuel core into short segments of 3-5cm. S2, Fluorination and Volatilization: The short section of spent metal fuel core prepared in step S1 is placed in a fluorination furnace, and pure fluorine gas or a fluorine-argon mixture is introduced to fluorinate the short section of spent metal fuel core. The reaction yields a gas mixture A and fluorination residue. S3. Condensation and trapping: The gas mixture A obtained in step S2 is introduced into a cold trap, and gas mixture B is obtained by condensation and trapping. S4, Hydrogen Reduction: The gas mixture B collected by condensation in step S3 is heated and vaporized, and then transferred to the hydrogen reduction furnace with argon gas. Subsequently, fluorine gas and hydrogen-argon gas mixture are introduced to carry out hydrogen reduction reaction to convert it into the corresponding solid tetrafluoride. S5, calcium thermal reduction: The solid tetrafluoride obtained in step S4 is mixed evenly with excess calcium chips and pressed into a ball. Then it is placed in a medium frequency induction device, and after vacuuming and purging with argon, calcium thermal reduction reaction is carried out under micro-positive pressure. After the reaction is completed, the alloy ingot is cooled to obtain the alloy ingot. S6. Fluoride Residue Molten Salt Electrolysis: A LiF-NaF-KF ternary eutectic system is selected as the molten salt electrolyte, with liquid cadmium as the cathode and inert graphite as the anode. At a certain melting temperature, the fluoride residue obtained in step S2 is melted in the molten salt electrolyte. Subsequently, by precisely controlling the deposition potential, actinides in the fluoride residue are selectively deposited. The actinides are deposited on the liquid cadmium electrode to form an An-Cd alloy. The An-Cd alloy is then vacuum distilled to separate cadmium, yielding a high-purity actinide metal alloy. S7. Injection Casting: The alloy ingot obtained in step S5 and the high-purity actinide metal alloy obtained in step S6 are transferred to an injection casting furnace; based on the composition ratio of the target recycled metal fuel core and the composition ratio of the alloy ingot and the high-purity actinide metal alloy, the amount of uranium, plutonium, and zirconium metal to be added is determined, and the corresponding amounts of uranium, plutonium, and zirconium metal are added to the injection casting furnace; then, the target recycled metal fuel core is obtained through smelting and injection casting.

[0006] Preferably, in step S1, the spent metal fuel core is a uranium-zirconium spent metal fuel core or a uranium-transuranic-zirconium spent metal fuel core.

[0007] Preferably, in step S2, the fluorination temperature of the fluorination treatment is between 600℃ and 700℃, the fluorination reaction time is 5-10h, and the volume fraction of fluorine in the fluorine-argon mixture is 45-55%.

[0008] More preferably, in step S2, the gas mixture A includes gaseous fluorides of volatile elements and fission gases.

[0009] More preferably, in step S2, the fission gas includes Kr, Xe, I, and H-3.

[0010] More preferably, in step S2, the fluorinated residue includes 45% to 50% rare earth fluorides, 20% to 25% transition metal fluorides, 15% to 20% alkaline earth metal fluorides, 5% to 8% secondary actinide fluorides, and 0.5% to 2% incompletely volatilized UF4 and PuF4.

[0011] Preferably, in step S3, the condensation temperature of the cold trap is -35 to 45°C, and the condensation time is 5 to 10 hours.

[0012] Preferably, in step S3, the gas mixture B is condensed and collected in a cold trap, and the remaining gas that is not condensed enters the tail gas treatment system and selectively absorbs the fission gases Kr, Xe, I, and H-3.

[0013] More preferably, in step S3, the gas mixture B is a partially fluorinated compound mainly composed of uranium and plutonium.

[0014] More preferably, in step S3, the gas mixture B includes UF6, NpF6, PuF6, MoF6, and TcF6.

[0015] Preferably, in step S4, the heating and vaporization treatment is carried out at a temperature of 100-150°C for 2-5 hours; the volume ratio of the fluorine gas and the hydrogen-argon gas mixture is 5%-10%; the volume ratio of hydrogen to argon in the hydrogen-argon gas mixture is 4%-10%; and the hydrogen reduction reaction is carried out at a temperature of 300-600°C for 2-5 hours.

[0016] Preferably, in step S5, the excess calcium scrap refers to the amount of calcium scrap added exceeding the normal stoichiometric ratio by 10% to 50%, the micro-positive pressure is a gauge pressure of 70 to 150 kPa, the reaction temperature of the calcium thermal reduction reaction is 400 to 700°C, and the reaction time is 1 to 5 hours.

[0017] Preferably, in step S5, the alloy ingot includes uranium, plutonium, molybdenum, technetium, and neptunium.

[0018] More preferably, in step S5, uranium and plutonium are the main elements in the alloy ingot, while molybdenum, technetium, and neptunium are minor elements.

[0019] More preferably, in step S5, the content of uranium and plutonium is 95%~97%, and the content of molybdenum, technetium and neptunium is 3%~5%.

[0020] Preferably, in step S6, the molar ratio of LiF, NaF, and KF in the LiF-NaF-KF ternary eutectic system is 43-49:10-14:39-45, and the mass ratio of the fluorinated residue to the LiF-NaF-KF ternary eutectic system is 1%-20%.

[0021] Preferably, in step S6, the melting temperature is 600-700℃, the melting time is 1-5h, the deposition potential is -1 to 1.5V, and the deposition time is 5-10h.

[0022] Preferably, in step S6, the vacuum distillation conditions include: a heating rate of 3~10℃ / min, a distillation temperature of 700~1200℃, and a vacuum pressure of 100Pa~10kPa.

[0023] Preferably, the An-Cd alloy refers to an alloy of actinide elements and cadmium.

[0024] Preferably, in step S6, the high-purity actinide metal alloy includes uranium, neptunium, plutonium, americium, and curium.

[0025] More preferably, in step S6, uranium is the main element in the high-purity actinide metal alloy, while neptunium, plutonium, americium, and curium are minor elements.

[0026] More preferably, in step S6, the high-purity actinide metal alloy contains 50% to 80% uranium and 20% to 50% neptunium, plutonium, americium, and curium.

[0027] Preferably, in step S7, the melting temperature is 1500-1700℃, the melting holding time is 15-25min, and the injection casting refers to injecting the molten metal obtained by melting into a quartz mold under pressure. After cooling to room temperature, the mold is removed, and the target recycled metal fuel core is obtained after the mold is broken.

[0028] Preferably, the fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels comprises several steps: dismantling and cutting of spent metal fuel assemblies, fluorination volatilization, condensation and collection, product reduction (hydrogen reduction, calcium thermal reduction), fluorination slag molten salt electrolysis, and injection casting. The specific process is as follows: Component disassembly and cutting: This process is to separate the metal fuel core from the component. The hot chamber or thick-walled glove is filled with inert gas. The stainless steel cladding and a small amount of metallic sodium inside the cladding are removed using a component disassembly device to obtain the metal fuel core. The metal fuel core is then cut into short segments of 3-5 cm using a single-bar cutting device. Fluorination and volatilization: This process converts uranium and plutonium in the core into a gaseous state through high-temperature fluorination, separating them from fission products. Pure fluorine gas or a fluorine-argon mixture is introduced into a fluorination furnace to fluorinate a short section of the spent metal fuel core. The fluorination temperature is between 600℃ and 700℃. Through the fluorination reaction, U, Np, Pu, Mo, Tc, etc., can be fluorinated into highly volatile fluorides. At the same time, as the core disintegrates, fission gases such as Kr, Xe, I, and H-3 are released. Condensation trapping: After condensation trapping, the main nuclear materials such as UF6, NpF6, and PuF6 and a small amount of fission products are obtained; among them, non-volatile fluorides such as Am, Cm, Sr, Cs, and Zr remain in the solid fluorination residue, and the residue contains a small amount of low-valence fluorides of U, Np, and Pu. Product Reduction: This step reduces the mixed hexafluoride containing uranium, neptunium, plutonium, molybdenum, and technetium collected in the previous step into metal, providing raw materials for the manufacture of recycled metal fuels. It includes two steps: Hydrogen reduction: The hexafluoride collected by the cold trap is heated and transferred to the hydrogen reduction furnace with argon gas. A mixture of fluorine gas and hydrogen-argon gas is introduced for hydrogen reduction. The reaction between fluorine gas and hydrogen gas generates a large amount of heat, which stimulates the hydrogen gas to reduce the hexafluoride and convert it into tetrafluoride. Calcium thermal reduction: Tetrafluoride is uniformly mixed with excess calcium shavings and pressed into a ball, then placed in a crucible. The crucible is placed in a medium-frequency induction device, evacuated and purged with argon, and then heated under a slight positive pressure. The tetrafluoride is reduced to an alloy ingot through the calcium thermal reduction reaction. Fluoride slag molten salt electrolysis: This process utilizes a fluoride salt system to selectively separate and recover the remaining actinides from the fluoride slag. The fluoride slag contains rare earth fluorides, transition metal fluorides, alkaline earth metal fluorides, secondary actinides, and incompletely volatilized UF4 and PuF4, etc. Among these, the secondary actinides Am, Cm, and Pu have significantly higher value than other nuclides; therefore, this step primarily extracts secondary actinides. A LiF-NaF-KF ternary eutectic (FLiNaK) system is selected, with liquid cadmium as the cathode and inert graphite as the anode. The operating temperature is set to 650℃. Through precise potential control, actinides are selectively deposited. The deposited An-Cd alloy is then vacuum distilled to separate cadmium, yielding a high-purity actinide metal alloy, which is then returned to fuel manufacturing. Injection casting: This process involves transferring the alloy ingots obtained from the calcium thermal reduction process and the actinide metal alloys obtained from molten salt electrolysis into the crucible of the injection casting furnace, adding uranium and zirconium metals, adjusting the mass ratio of uranium, plutonium, and zirconium metals to the target ratio, and placing them in a metal fuel vacuum injection casting furnace or a continuous casting furnace to prepare recycled metal fuel rods.

[0029] This invention addresses the development of a novel dry reprocessing route for spent metal fuel, supporting the construction of fast reactor nuclear energy systems for closed-loop spent fuel cycles in my country. It combines the advantages of fluorination volatilization and molten salt electrolysis technologies. Fluorination volatilization achieves rapid volatilization and transfer of uranium and plutonium in large quantities of spent fuel through a simple gas-solid reaction, far exceeding the processing capacity of molten salt electrodeposition. Furthermore, molten salt electrodeposition can further separate and process long-lived actinides that cannot be separated by fluorination volatilization. This invention proposes a fluorination-electrolysis synergistic process route suitable for dry reprocessing of spent metal fuel, providing multiple technological reserves for my country's fast reactor fuel cycle and ensuring the achievement of strategic goals such as minimizing high-level radioactive waste and sustainable utilization of nuclear resources.

[0030] This invention provides a fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels. This process utilizes fluorine gas to react with pre-treated spent metal fuels under high-temperature conditions, converting uranium, plutonium, and small amounts of volatile fluorinated fission products in the spent fuels into gaseous fluorides for separation and transfer. Further, uranium-plutonium alloys are prepared using condensation capture (freezing recovery) and gaseous fluoride reduction techniques for the reforming and regeneration of metal fuels. Simultaneously, fluorinated residues containing large amounts of highly radioactive, highly heat-releasing fission elements and actinides are electrolytically separated using a fluoride salt system, achieving deep separation and recovery of high-level radioactive waste. This invention represents a novel method for the regeneration of spent metal fuels, aiming to provide a more efficient and cleaner technological path for the reprocessing of spent metal fuels in my country, to overcome key technical challenges as soon as possible, and to achieve engineering applications.

[0031] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention provides a fluorination-electrolysis synergistic process for the reprocessing of spent metal fuel. It combines the advantages of fluorination volatilization and molten salt electrolysis, avoids the limitations of a single process, and fluorinates a short section of the spent metal fuel core through fluorination volatilization to quickly achieve the gasification separation and recovery of uranium, plutonium and neptunium. Then, through molten salt electrolysis of the LiF-NaF-KF ternary eutectic system, it accurately separates the more difficult secondary actinides from the fluorination residue. Finally, it simultaneously achieves efficient recovery of uranium and plutonium and deep separation of secondary actinides. The process is simple and the processing time is short.

[0032] (2) On the one hand, this invention utilizes the strong fluorination properties of pure fluorine gas or fluorine-argon mixture to rapidly convert metals such as uranium, plutonium, and neptunium into hexafluoride. Subsequently, after condensation and collection, hydrogen reduction, and calcium thermal reduction, alloy ingots mainly composed of uranium and plutonium can be recovered. Uranium can be rapidly fluorinated into UF6 in a pure fluorine atmosphere at 300°C, and the experimental verification shows that the uranium conversion rate is >99%. At the same time, easily fluorinated metals such as molybdenum can be converted at lower temperatures with a conversion rate >99%, making the process highly feasible. On the other hand, through precise potential control of molten salt electrolysis, the secondary actinides in the fluorination residue can be selectively deposited, and the actinide metal alloy can be obtained after subsequent separation, further improving the overall recovery efficiency and significantly shortening the overall process cycle.

[0033] (3) Compared with a single technology process, the synergistic technology of fluorination and molten salt electrolysis effectively avoids the problems of limited molten salt electrodeposition processing capacity and difficulty in further refining fluorination volatilization residue, improves efficiency and production capacity, and also brings better economic benefits.

[0034] (4) The amount of waste generated by the fluorination volatilization method of the present invention is extremely small. On the one hand, the long-lived nuclides in the fluorination residue are further separated by molten salt electrolysis and converted into recyclable high-purity actinide metal alloys. On the other hand, the cracked gases such as Kr, Xe, I, and H-3 can be selectively absorbed by the cold trap collection and tail gas treatment system. Therefore, the present invention effectively avoids the leakage of radioactive gases, significantly reduces the amount of high-level radioactive waste and waste toxicity, and reduces the difficulty of landfill disposal and the regulatory period.

[0035] (5) The present invention is based on the alloy ingot obtained by the calcium thermal reduction process and the actinide metal alloy obtained by molten salt electrolysis. After injection casting, the metal fuel can be regenerated, realizing a closed loop of spent metal fuel-nucleus separation-fuel regeneration, and improving the utilization rate of nuclear resources. Attached Figure Description

[0036] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0037] This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiment.

[0038] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0039] This invention targets high burnup (burnup depth of 15%~20%) uranium-zirconium or uranium-transuranic-zirconium spent metal fuels, employing a synergistic fluorination + electrolysis process to treat them. It combines the high efficiency of fluorination volatilization in recovering uranium and plutonium with the strong deep separation and recovery capabilities of molten salt electrolysis for actinides, achieving efficient recovery of uranium and plutonium from spent metal fuels and deep separation and recovery of fluorination residues. Spent metal fuels contain dozens of metals, including uranium, plutonium, minor actinides, and numerous fissile elements. Among these, uranium, neptunium, plutonium, molybdenum, and technetium are predominantly present and can react with fluorine gas at high temperatures to form highly volatile fluorides in their high valence states. The thermodynamic data for the reaction of these elements with fluorine gas are shown below. Table 1. Thermodynamic data of the reaction between major elements in spent metallic fuels and fluorine gas (300℃) Data shows that the Gibbs free energy ΔG is less than 0, which theoretically means that the fluorination of these elements can all occur. The change in enthalpy ΔH is higher than the heat released by the fluorination of spent oxide fuels, which has a positive effect on the self-sustaining effect of the reaction. Theoretically, this route is feasible.

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0041] Example 1: High-burnup metal spent fuel treatment In this embodiment, the spent metal fuel assembly to be processed is a U-15Pu-10Zr metal fuel assembly that has reached the end of its service life and has been removed from a fast reactor. It has a long service time and numerous cycles, with an estimated burnup depth of 15%. The U mass percentage is approximately 70%, the Pu percentage is approximately 13.5%, the total fission products percentage is approximately 7.0%, of which approximately 4.7% are solids and approximately 2.3% are gases, and approximately 9% are zirconium. This spent metal fuel is then processed to prepare new U-TRU-10Zr metal fuel. The process flow is as follows: Figure 1 The process includes, in sequence: component disassembly and core shearing; fluorination and volatilization of short sections of the metal fuel core; cryogenic capture of the mixed gaseous fluorides generated by co-fluorination; hydrogen reduction of uranium- and plutonium-based fluorides; calcothermic reduction of solid tetrafluorides; molten salt electrolysis of fluorination residue; and injection casting of recycled metal fuel. The specific preparation process is as follows: (1) Component disassembly: First, the components are disassembled in the component disassembly equipment room. The spent metal fuel components are transported to the component disassembly station in the component disassembly hot chamber via waterway. The operator uses the master and slave manipulators to disassemble the components using the disassembly machine in the hot chamber. Since there is a small amount of metallic sodium in the cladding, the whole process is carried out under the protection of inert gas. After disassembly, the spent metal fuel rods are successfully separated from the components and cladding materials.

[0042] (2) Core cutting: The spent metal fuel core rods are then cut into short segments less than 5 cm long using a hot chamber cutting device and transferred to the next process via the hot chamber transfer channel.

[0043] (3) Fluorination and volatilization: The short core section is placed in a fluorination boat and loaded into a fluorination furnace for high-temperature fluorination at 650°C. The atmosphere is a fluorine-argon mixture with a fluorine gas fraction of 50%. After fluorination, the cracking gas and the generated low-boiling-point fluorides are carried into the subsequent process along with the carrier gas. The fluorination slag remains in the fluorination boat for further separation and purification by molten salt electrolysis.

[0044] (4) Condensation and collection: The gaseous material produced by fluorination contains mixed products such as UF6, PuF6, NpF6, MoF6, Kr, Xe, and I, with UF6 being the main component. The main recovered materials, UF6, PuF6, and NpF6, are collected by freezing in a cold trap at approximately -40°C. The remaining gases with lower boiling points flow into the tail gas treatment system, where valuable nuclides such as Kr, I, and H-3 can be selectively adsorbed and recovered.

[0045] (5) Hydrogen reduction: Fluorides such as UF6, PuF6, and NpF6 can be heated and vaporized in the cold trap and carried to the hydrogen reduction furnace by argon gas. At the same time, a hydrogen-argon mixture and pure fluorine gas are introduced into the hydrogen reduction furnace to carry out a reduction reaction, reducing hexafluoride to solid tetrafluoride. The volume ratio of fluorine gas to hydrogen-argon mixture is 5%-10%, and the volume ratio of hydrogen to argon in the hydrogen-argon mixture is 4%-10%.

[0046] (6) Calcium thermal reduction: The tetrafluoride is transferred to the calcium thermal reduction process through the transfer channel, mixed with calcium chips and loaded into a three-piece set. The reduction is ignited using a medium frequency induction furnace. After the reaction is completed and the furnace body is cooled, the alloy ingot is taken out of the furnace and crushed to obtain alloy ingot.

[0047] (7) Molten salt electrolysis: The fluorinated residue contains rare earth fluorides (40%~50%), transition metal fluorides (20%~25%), alkaline earth metal fluorides (15%~20%), actinide fluorides (5%~8%), and incompletely volatilized PuF4 (approximately 1%). Among these, the value of minor actinides is far higher than that of other nuclides, so this step mainly extracts minor actinides. For this purpose, a LiF-NaF-KF ternary eutectic (FLiNaK) system was selected, with liquid cadmium as the cathode and inert graphite as the anode. The operating temperature was set to 650℃. Through precise potential control, actinide metal alloys can be deposited on the liquid cadmium electrode.

[0048] (8) Injection casting: The alloy ingots obtained from the calcium thermal reduction process and the actinide metal alloy obtained from molten salt electrolysis are transferred to the crucible of the injection casting furnace. A very small amount of uranium, plutonium, and zirconium metals are added to the crucible, and the metal mass ratio is adjusted to the target ratio. After the furnace is loaded and the atmosphere is replaced, the melting begins. The melting temperature is increased to 1600℃ and held for 20 minutes. The furnace is then pressurized to inject the molten metal into a quartz mold. After cooling to room temperature, the furnace is opened and the mold is removed. After the mold is broken, a new U-TRU-Zr metal fuel core is obtained.

[0049] In this embodiment, uranium can be rapidly fluorinated to UF6 in a pure fluorine atmosphere at 300°C, and the experimental verification shows that the uranium conversion rate is >99%. At the same time, easily fluorinated metals such as molybdenum can be converted at lower temperatures with a conversion rate >99%, making this process highly feasible.

[0050] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels, characterized in that, Includes the following steps: S1. Component disassembly and cutting: Disassemble the spent metal fuel assembly to be processed, remove the stainless steel cladding and a small amount of metallic sodium inside the cladding to obtain the spent metal fuel core, and cut the spent metal fuel core into short segments of 3-5cm. S2, Fluorination and Volatilization: The short section of spent metal fuel core prepared in step S1 is placed in a fluorination furnace, and pure fluorine gas or a fluorine-argon mixture is introduced to fluorinate the short section of spent metal fuel core. The reaction yields a gas mixture A and fluorination residue. S3. Condensation and trapping: The gas mixture A obtained in step S2 is introduced into a cold trap, and gas mixture B is obtained by condensation and trapping. S4, Hydrogen Reduction: The gas mixture B collected by condensation in step S3 is heated and vaporized, and then transferred to the hydrogen reduction furnace with argon gas. Subsequently, fluorine gas and hydrogen-argon gas mixture are introduced to carry out hydrogen reduction reaction to convert it into the corresponding solid tetrafluoride. S5, calcium thermal reduction: The solid tetrafluoride obtained in step S4 is mixed evenly with excess calcium chips and pressed into a ball. Then it is placed in a medium frequency induction device, and after vacuuming and purging with argon, calcium thermal reduction reaction is carried out under micro-positive pressure. After the reaction is completed, the alloy ingot is cooled to obtain the alloy ingot. S6. Fluoride Residue Molten Salt Electrolysis: A LiF-NaF-KF ternary eutectic system is selected as the molten salt electrolyte, with liquid cadmium as the cathode and inert graphite as the anode. At a certain melting temperature, the fluoride residue obtained in step S2 is melted in the molten salt electrolyte. Subsequently, by precisely controlling the deposition potential, actinides in the fluoride residue are selectively deposited. The actinides are deposited on the liquid cadmium electrode to form an An-Cd alloy. The An-Cd alloy is then vacuum distilled to separate cadmium, yielding a high-purity actinide metal alloy. S7. Injection Casting: The alloy ingot obtained in step S5 and the high-purity actinide metal alloy obtained in step S6 are transferred to an injection casting furnace; based on the composition ratio of the target recycled metal fuel core and the composition ratio of the alloy ingot and the high-purity actinide metal alloy, the amount of uranium, plutonium, and zirconium metal to be added is determined, and the corresponding amounts of uranium, plutonium, and zirconium metal are added to the injection casting furnace; then, the target recycled metal fuel core is obtained through smelting and injection casting.

2. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S1, the spent metal fuel core to be processed is a uranium-zirconium spent metal fuel core or a uranium-transuranic-zirconium spent metal fuel core.

3. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S2, the fluorination temperature of the fluorination treatment is between 600℃ and 700℃, the fluorination reaction time is 5-10h, and the volume fraction of fluorine in the fluorine-argon mixture is 45-55%.

4. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S3, the condensation temperature of the cold trap is -35-45℃, and the condensation time is 5-10h; the gas mixture B is condensed and collected in the cold trap, and the remaining gas that is not condensed enters the exhaust gas treatment system.

5. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S4, the heating and vaporization treatment is carried out at a temperature of 100-150℃ for 2-5 hours; the volume ratio of the fluorine gas and hydrogen-argon gas mixture is 5%-10%; the volume ratio of hydrogen to argon in the hydrogen-argon gas mixture is 4%-10%; and the hydrogen reduction reaction is carried out at a temperature of 300-600℃ for 2-5 hours.

6. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S5, the excess calcium scrap refers to the amount of calcium scrap added exceeding the normal stoichiometric ratio by 10% to 50%, the micro-positive pressure is a gauge pressure of 70 to 150 kPa, the reaction temperature of the calcium thermal reduction reaction is 400 to 700°C, and the reaction time is 1 to 5 hours; the alloy ingot includes uranium, plutonium, molybdenum, technetium, and neptunium.

7. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S6, the molar ratio of LiF, NaF, and KF in the LiF-NaF-KF ternary eutectic system is 43-49:10-14:39-45, and the mass ratio of the fluorinated residue to the LiF-NaF-KF ternary eutectic system is 1%-20%.

8. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S6, the melting temperature is 600-700℃, the melting time is 1-5h, the deposition potential is -1 to 1.5V, and the deposition time is 5-10h.

9. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S6, the vacuum distillation conditions include: a heating rate of 3~10℃ / min, a distillation temperature of 700~1200℃, and a vacuum pressure of 100Pa~10kPa; the high-purity actinide metal alloy includes elements of uranium, neptunium, plutonium, americium, and curium.

10. The fluorination-electrolysis synergistic process for the reprocessing of spent metal fuels according to claim 1, characterized in that, In step S7, the melting temperature is 1500-1700℃, the melting holding time is 15-25min, and the injection casting refers to injecting the molten metal obtained by melting into a quartz mold under pressure. After cooling to room temperature, the mold is removed, and the target recycled metal fuel core is obtained after the mold is broken.

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