Separation and recovery method for uranium-containing radioactive waste

Abstract

The invention relates to the technical field of radioactive waste treatment in the nuclear industry, in particular to a uranium-containing radioactive waste separation and recovery method. A vacuum sublimation and low-temperature rectification combined process is adopted, firstly, a mixed working medium is gasified through vacuum sublimation and reduced-pressure heating, then solid UF6 / BrF3 is separated through a multi-stage condensation system, and uncondensed gas is introduced into a cryogenic device to be liquefied and recycled to recover Br2; finally, efficient purification of UF6 and BrF3 is achieved through gradient depressurization rectification by means of the vapor pressure difference of UF6 and BrF3. Through full-sealing process design, radioactive leakage is avoided, no secondary solid waste is generated, the UF6 purity is larger than or equal to 98.8%, and the method is suitable for radioactive hazardous waste treatment of uranium concentration plants and resource recycling of similar mixtures.

Description

Technical Field

[0001] This application relates to the technical field of nuclear industry radioactive waste treatment, and particularly to a method for separating and recovering uranium-containing radioactive waste. Background Art

[0002] During the operation of the uranium enrichment plant cascade system, radioactive deposits generated in equipment and pipelines will lead to a decrease in production capacity. Some enrichment plants use BrF3 as a cleaning agent to clean components such as UF6, BrF3, and Br2 in the waste, which are highly corrosive, explosive, and radioactive. In the prior art:

[0003] 1. Direct metal container temporary storage method: Loading the waste into a metal container for long-term storage causes occupation of the factory area space and risks of Br2 leakage and explosion due to the reaction between UF6 and BrF3, and resource reuse cannot be achieved;

[0004] 2. Sodium fluoride adsorption method: Chemically adsorbing and solidifying BrF3, but the reaction is violent and prone to explosion, and high-temperature desorption (≥300 °C) is required, resulting in a uranium loss rate > 15%, and radioactive solid waste is generated, which requires secondary treatment;

[0005] 3. Single condensation process: Only partially separating Br2 by low-temperature condensation, but it is difficult to separate UF6 and BrF3 due to their similar vapor pressures, and the recovery rate is less than 80%.

[0006] None of the above methods can effectively separate and reuse bromine compounds and UF6, and have high treatment costs and large environmental risks. Therefore, there is an urgent need to develop a safe, efficient, and low-consumption uranium-containing radioactive waste recovery technology. Summary of the Invention

[0007] To solve the above problems, this application provides a method for separating and recovering uranium-containing radioactive waste, realizing the classified purification and resource reuse of Br2, UF6, and BrF3, and reducing energy consumption and environmental risks.

[0008] To achieve the above object, this application adopts the following technical solutions.

[0009] This application provides a method for separating and recovering uranium-containing radioactive waste, including the following steps:

[0010] (1) Vacuum sublimation process:

[0011] ① Reducing pressure and heating: Vaporizing the mixed working fluid container containing UF6, BrF3, and Br2;

[0012] ② Multi-stage condensation: Passing the generated gaseous mixture into a multi-stage condensation system and condensing at a temperature ≤ 4 °C and a pressure ≤ 10 kPa to condense out solid BrF3 and UF6;

[0013] ③ Cold bromine recovery: Pass the uncondensed gas into a cryogenic device for liquefaction and recovery;

[0014] (2) Low-temperature distillation process:

[0015] ④ Fractional distillation: Gradient depressurize and distill the UF6 and BrF3 mixture condensed in step (1). At 0°C to -10°C, the pressure gradient gradually decreases from 2.7 kPa to 1 kPa to separate UF6 gas and solid BrF3.

[0016] Further, in step ①, the heating temperature > 75°C and the pressure is controlled at ≤ 13.4 kPa.

[0017] Even further, in step ①, the heating temperature is 60°C to 80°C and the pressure is 7 kPa to 13.4 kPa.

[0018] Preferably, in step ①, the heating temperature is 75°C and the pressure is 13.4 kPa.

[0019] Further, the multi-stage condensation in step ② includes three-stage condensation:

[0020] The first-stage condensation: temperature 4°C, pressure ≤ 10 kPa;

[0021] The second-stage condensation: temperature -20°C, pressure ≤ 1.5 kPa;

[0022] The third-stage condensation: temperature -40°C, pressure ≤ 0.693 kPa.

[0023] Further, the temperature for liquefaction and recovery in step ③ is -105 to -115°C and the pressure is ≤ 50 Pa.

[0024] Preferably, the temperature for liquefaction and recovery is -110°C and the pressure is 50 Pa.

[0025] Further, in the cold bromine recovery process of step ③, the unliquefied residual gas is treated by a gas absorption tower filled with sodium fluoride particles, and the gas residence time ≥ 30 seconds.

[0026] Further, the fractional distillation in step ④ includes three-stage distillation:

[0027] The first-stage distillation: temperature 2 to -6°C, pressure 2.7 to 1.4 kPa;

[0028] The second-stage distillation: temperature 0 to -10°C, pressure 1.8 to 1 kPa;

[0029] The third-stage distillation: temperature 0 to -10°C, pressure 1.6 to 1 kPa.

[0030] Furthermore, the temperature of the fractional distillation in step ④ is -2°C to 0°C, and the pressure is controlled at 1.6 kPa to 2 kPa.

[0031] Preferably, the fractional distillation in step ④ includes three-stage distillation:

[0032] The first-stage distillation: temperature 0°C, pressure 2 kPa;

[0033] The second-stage distillation: temperature 0°C, pressure 1.8 kPa;

[0034] The third-stage distillation: temperature 0°C, pressure 1.6 kPa.

[0035] Further, the low-temperature distillation process in step (2) further includes:

[0036] ⑤ UF6 collection: Condense and collect the gas generated by distillation at -120°C to -80°C to obtain solid UF6;

[0037] ⑥ BrF3 collection: Heat the solid mixture distilled out to 10°C to 25°C to obtain liquid BrF3.

[0038] Further, both the vacuum sublimation process and the low-temperature distillation process are carried out in a closed system, and each device is connected by a pipeline.

[0039] This application first converts the mixture into a mixed gas by vacuum sublimation, and then condenses bromine trifluoride and uranium hexafluoride into solids, while bromine is in a gaseous state. By controlling the temperature and pressure, the solid is prevented from wrapping impurities. At the same time, since bromine is separated from most substances at a relatively high temperature, the mass of substances that need to be cooled is reduced, and the energy consumption is reduced.

[0040] This application uses the low-temperature distillation method to separate bromine trifluoride and uranium hexafluoride, and has the following advantages: ① Bromine trifluoride and uranium hexafluoride in the system are extremely chemically active and prone to reaction and explosion. This method does not introduce new substances into the system, and at the same time, the separation is carried out at low temperature, reducing the risk of leakage and explosion, ensuring the safety of the separation process; and no new radioactive waste will be generated; ② This separation method is based on the physical and chemical properties of the substances themselves. Theoretically, the recovery rates of bromine trifluoride and uranium hexafluoride will be higher than those of traditional separation methods; ③ This method also reduces the difficulty of tail gas treatment, reduces the emissions of tail gas and radioactive substances, and is more environmentally friendly; ④ The main instrument devices of this method are all sealed, and the entire separation process system is in a sealed state, which not only reduces the potential hazard of leakage of hazardous chemicals and radioactive substances, but also reduces the possibility of generating other impurities or even causing an explosion during the reaction.

[0041] Compared with the prior art, the beneficial effects of the present application are as follows: ① High recovery efficiency: the purity of UF6 ≥ 98.8%; ② Strong safety: the pressure in the whole process ≤ 13.4 kPa, with sealed operation to avoid the risk of UF6 decomposition and BrF3 explosion; ③ Excellent environmental protection: no adsorbent or chemical additive in the whole process, and no new radioactive solid waste is generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is the process flow diagram of the separation of uranium-containing radioactive waste in Embodiment 1 of the present application; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the protection scope of the present invention.

[0044] Embodiment 1

[0045] As Figure 1 shown, this embodiment provides a method for separating and recovering uranium-containing radioactive waste, including the following steps:

[0046] (1) Vacuum sublimation process:

[0047] ① Pressure reduction and heating: The radioactive waste containing UF6, BrF3 and Br2 is introduced into a closed container, and the temperature of the cleaning mixed working medium container is controlled at 75 °C and the pressure is 13.4 kPa by electric tracing heating and a vacuum pump regulating valve; the pressure reduction and heating gradually convert the mixture in the container into gas;

[0048] ② Multi-stage condensation: The generated gaseous mixture is introduced into a three-stage condensation system by a vacuum pump for condensation; among them,

[0049] The first-stage condensation: The temperature is 4 °C (cooled by ethylene glycol), the pressure is 10 kPa, and the residence time is 20 minutes to collect the condensate; at this time, UF6 and BrF3 are condensed into solids by cooling, while bromine remains gaseous and will not remain; moreover, the eutectic phenomenon of uranium hexafluoride and bromine trifluoride does not occur at this temperature, which is beneficial to the separation between uranium hexafluoride and bromine trifluoride later;

[0050] The second-stage condensation: The temperature is -20 °C (cooled by ethylene glycol), the pressure is 1.5 kPa, and the residence time is 30 minutes to collect the condensate;

[0051] The third-stage condensation: The temperature is -40 °C (cooled by liquid nitrogen), the pressure is 0.693 kPa, and the residence time is 50 minutes to collect the residue;

[0052] ③ Cold bromine recovery: After passing the uncondensed gas into a cryogenic device, it is liquefied at -110°C and 50 Pa, and Br2 is collected; at this time, the saturated vapor pressure of bromine is 0 Pa, and the gaseous bromine separated in the above process is completely condensed; after the container is completely empty (judged by the pressure gauge), then close the valve of the input pipeline of the cryogenic device, and evacuate other impurity gases (such as HF, O2) into the gas absorption tower with a vacuum pump;

[0053] (2) Low-temperature rectification process:

[0054] ④ Fractional rectification: Gradually reduce the pressure of the condensate in step (1) for rectification. First, pause the vacuum pump and restore the pressure of the three-stage condenser to atmospheric pressure; then, cool the material condensed in the first stage to 0°C, and heat the materials condensed in the second stage and the second stage to 0°C; then start the vacuum pump and adjust the pressure of the container to 2 kPa, 1.8 kPa, and 1.6 kPa respectively; in the container, UF6 will sublime into gas due to the vacuum, while BrF3 remains a solid powder;

[0055] ⑤ UF6 collection: Collect the UF6 gas generated from the three-stage rectification into a UF6 collector at -120°C, and then collect the UF6 gas from the second-stage rectification into the uranium hexafluoride collector at -120°C after passing through the three-stage rectification; finally, collect the UF6 gas from the first-stage rectification in the same way as above;

[0056] The mass percentage of UF6 increases step by step in the three-stage rectification, which means that the content of BrF3 gas in the UF6 gas gradually decreases; at the same time, reducing the pressure is also beneficial to reducing the volatility of the BrF3 solid.

[0057] ⑥ BrF3 collection: Heat the material after the three-stage rectification to 10°C to convert BrF3 from solid to liquid, and then collect it into a BrF3 collector with a pump.

[0058] Example 2

[0059] This example provides a method for separating and recovering uranium-containing radioactive waste, including the following steps:.

[0060] (1) Vacuum sublimation process:

[0061] ① Pressure reduction and heating: Pass the radioactive waste containing UF6, BrF3 and Br2 into a closed container, and use electric tracing heating and a vacuum pump regulating valve to control the temperature of the cleaning mixed working medium container to 80°C and the pressure to 11.5 kPa; the pressure reduction and heating gradually convert the mixture in the container into gas;

[0062] ② Multi-stage condensation: Use a vacuum pump to pass the generated gaseous mixture into a three-stage condensation system for condensation; among them,

[0063] First-stage condensation: The temperature is 4°C (cooled by ethylene glycol), the pressure is 5 kPa, and it stays for 20 minutes to collect the condensate. At this time, UF6 and BrF3 are condensed into solids by cooling, while bromine remains in the gaseous state and does not remain. And at this temperature and below, there will be no eutectic phenomenon between uranium hexafluoride and bromine trifluoride, which is beneficial to the separation between uranium hexafluoride and bromine trifluoride later.

[0064] Second-stage condensation: The temperature is -20°C (cooled by ethylene glycol), the pressure is 1 kPa, and it stays for 30 minutes to collect the condensate.

[0065] Third-stage condensation: The temperature is -40°C (cooled by liquid nitrogen), the pressure is 0.35 kPa, and it stays for 50 minutes to collect the residue.

[0066] ③ Cold bromine recovery: The uncondensed gas is passed into a cryogenic device and condensed at -115°C and 50 Pa to collect Br2. At this time, the saturated vapor pressure of bromine is 0 Pa, and the gaseous bromine separated in the above process is completely condensed. After the container is completely empty (judged by the pressure gauge), then close the valve of the input pipeline of the cryogenic device, and evacuate other impurity gases (such as HF, O2) into the gas absorption tower with a vacuum pump.

[0067] (2) Low-temperature rectification process:

[0068] ④ Fractional rectification: The condensate from step (1) is rectified by gradually reducing the pressure. First, pause the vacuum pump and restore the pressure of the three-stage condenser to atmospheric pressure. Then, cool the material from the first-stage condensation to -5°C, while heat the materials from the second-stage condensation and the second-stage condensation to -5°C. Then start the vacuum pump and adjust the pressure of the container to 1.7 kPa, 1.5 kPa, and 1.3 kPa respectively. In the container, UF6 will sublimate into gas due to the vacuum, while BrF3 remains a solid powder.

[0069] ⑤ UF6 collection: Collect the UF6 gas generated from the three-stage rectification into a UF6 collector at -120°C. Then, pass the UF6 gas from the second-stage rectification through the three-stage rectification and collect it into a uranium hexafluoride collector at -120°C. Finally, collect the UF6 gas from the first-stage rectification in the same way.

[0070] The mass percentage of UF6 in the three-stage rectification increases step by step, which means that the content of BrF3 gas in the UF6 gas gradually decreases. At the same time, reducing the pressure is also beneficial to reducing the volatility of the BrF3 solid.

[0071] ⑥ BrF3 collection: Heat the material after the three-stage rectification to 10°C to convert BrF3 from solid to liquid, and then collect it into a BrF3 collector with a pump.

[0072] Example 3

[0073] This embodiment provides a method for separating and recovering uranium-containing radioactive waste, including the following steps:.

[0074] (1) Vacuum sublimation process:

[0075] ① Pressure reduction and heating: The radioactive waste containing UF6, BrF3, and Br2 is introduced into a closed container, and the temperature of the cleaning mixed working fluid container is controlled at 60°C and the pressure at 7 kPa by electric tracing heating and a vacuum pump regulating valve; the mixture in the container is gradually converted into gas by pressure reduction and heating;

[0076] ② Multi-stage condensation: The gaseous mixture generated is introduced into a three-stage condensation system by a vacuum pump for segmented condensation; among them,

[0077] First-stage condensation: The temperature is 4°C (No. 1 cold and hot box), the pressure is 10 kPa, and the residence time is 20 minutes to collect the condensate; at this time, UF6 and BrF3 are condensed into solids by cooling, while bromine remains in a gaseous state without residue; and below this temperature, there will be no eutectic phenomenon between uranium hexafluoride and bromine trifluoride, which is conducive to the separation between uranium hexafluoride and bromine trifluoride later;

[0078] Second-stage condensation: The temperature is -20°C (No. 2 cold and hot box), the pressure is 1.5 kPa, and the residence time is 30 minutes to collect the condensate;

[0079] Third-stage condensation: The temperature is -40°C (No. 1 deep cold box), the pressure is 0.693 kPa, and the residence time is 50 minutes to collect the residue;

[0080] ③ Cold bromine recovery: The uncondensed gas is introduced into the No. 2 deep cold box device and condensed at -105°C and 50 Pa to collect Br2; at this time, the saturated vapor pressure of bromine is 0 Pa, and the gaseous bromine separated in the above process is completely condensed; after the container is completely empty (judged by the pressure gauge), then close the valve of the input pipeline of the deep cold device, and evacuate other impurity gases (such as HF, O2) into the gas absorption tower with a vacuum pump;

[0081] (2) Low-temperature rectification process:

[0082] ④ Segmented rectification: The condensate from step (1) is subjected to gradient pressure reduction rectification. First, suspend the vacuum pump and restore the pressure of the three-stage condenser to atmospheric pressure; then, cool the material condensed in the first stage to 0°C, and heat the materials condensed in the second stage and the second stage to 0°C; then start the vacuum pump and adjust the air pressure in the container to 2.0 kPa, 1.8 kPa, and 1.6 kPa respectively; in the container, UF6 will be sublimated into gas due to vacuum, while BrF3 remains as a solid powder;

[0083] ⑤ UF6 Collection: Collect the UF6 gas generated from the three-stage rectification into a UF6 collector at -120°C. Then, pass the UF6 gas from the second-stage rectification through the three-stage rectification and collect it into the uranium hexafluoride collector at -120°C. Finally, collect the UF6 gas from the first-stage rectification in the same way.

[0084] The mass percentage of UF6 in the three-stage rectification increases step by step, which means that the content of BrF3 gas in the UF6 gas gradually decreases. At the same time, reducing the pressure is also beneficial to reducing the volatility of solid BrF3.

[0085] ⑥ BrF3 Collection: Heat the material after the three-stage rectification to 10°C to convert BrF3 from solid to liquid, and then collect it into the BrF3 collector with a pump.

[0086] Comparative Example 1

[0087] This comparative example provides a method for separating and recovering uranium-containing radioactive waste. The difference from Example 1 is that the first-stage condensation temperature in the step ② of segmented condensation is 5°C and the pressure is 11 kPa; the remaining preparation processes and parameters are the same as those in Example 1.

[0088] Comparative Example 2

[0089] This comparative example provides a method for separating and recovering uranium-containing radioactive waste. The difference from Example 1 is that the temperature in the step ④ of segmented rectification is controlled at 5°C; the remaining preparation processes and parameters are the same as those in Example 1.

[0090] Comparative Example 3

[0091] This comparative example provides a method for separating and recovering uranium-containing radioactive waste. The difference from Example 1 is that instead of using the vacuum sublimation process (1) in this application to separate bromine, a wet method is used to separate bromine trifluoride, uranium hexafluoride and bromine. First, cool the mixture as a whole to -110°C, then heat it up to -40°C, and control the pressure at 0.693 kPa to turn bromine into gas to achieve bromine separation, and then perform the low-temperature rectification process in step (2); the remaining preparation processes and parameters are the same as those in Example 1.

[0092] Comparative Example 4

[0093] This comparative example provides a method for separating and recovering uranium-containing radioactive waste. The difference from Example 1 is that instead of using the low-temperature rectification process in step (2) of this application to separate bromine trifluoride and uranium hexafluoride, the separation of bromine trifluoride and uranium hexafluoride is achieved by using the sodium fluoride adsorption method; the remaining preparation processes and parameters are the same as those in Example 1.

[0094] Comparative Example 5

[0095] This comparative example provides a method for separating and recovering uranium-containing radioactive waste, including the following steps:

[0096] (1) Separating bromine trifluoride, uranium hexafluoride, and bromine by the low-temperature method. First, cool the mixture as a whole to -110 °C, then heat it up to -40 °C, and control the pressure at 0.693 kPa to turn bromine into a gas, thereby achieving the separation effect of bromine;

[0097] (2) Then separate bromine trifluoride and uranium hexafluoride by the sodium fluoride adsorption method.

[0098] Use the methods of the examples and comparative examples of this application to treat uranium-containing radioactive waste. The gravimetric method of ASTM C761-2011 "Standard Test Methods for Chemical, Mass Spectrometric, Spectrochemical, Nuclear, and Radiochemical Analysis of Uranium Hexafluoride" and the indirect iodometric titration method are used to detect the collected UF6 and BrF3. The detection data are shown in Table 1.

[0099] Table 1 Detection data of the examples and comparative examples of the present invention

[0100] UF6 purity (%) BrF3 purity (%) <![CDATA[UF6 loss rate (%)]]> Example 1 99.4 98.1 1.89 Example 2 98.8 97.0 2.95 Example 3 99.4 98.3 1.86 Comparative Example 1 99.1 97.5 3.54 Comparative Example 2 98.6 97.2 3.13 Comparative Example 3 96.7 95.2 3.96

[0101] Through the above detection process, it can be obtained that the purity of the product treated by the uranium-containing radioactive waste separation and recovery method of this application: the purity of UF6 ≥ 98.8%, meeting the purity standard of uranium hexafluoride for the uranium enrichment conversion production line, realizing the recycling of uranium hexafluoride, and reducing radioactive solid waste; the purity of BrF3 ≥ 97%, which can be reused as a cleaning agent for uranium hexafluoride solid waste remaining in uranium enrichment conversion production facilities, that is, reducing the management risk of hazardous chemicals and reducing costs; Br2, as an auxiliary solvent for the bromine trifluoride cleaning agent, has a lower purity standard, does not require special detection, and generally the recovered liquid bromine will be further recycled.

[0102] Compared with Example 1, in Comparative Example 1, the first-stage condensation temperature in the step of fractional condensation in step ② was 5°C and the pressure was 11 kPa. The high heating temperature and high pressure resulted in a small amount of bromine being in a liquid state, which would dissolve part of UF6 and BrF3 and remain in the container, affecting the separation effect of subsequent steps and the recovery rate of UF6; in Comparative Example 2, the temperature in the step of fractional distillation in step ④ was too high, all controlled at 5°C, resulting in the ideal gas partial pressure ratio of UF6 and BrF3 being lower than 30, the single-stage separation effect being reduced, and finally the purity of the UF6 product being low, which contained BrF3; in Comparative Example 3, the mixture was first cooled to -110°C as a whole and then heated to -40°C. Bromine was turned into a gas by controlling the pressure of 0.693 kPa to achieve bromine separation, and then the low-temperature distillation process in step (2) was carried out. As a result, it was difficult to completely separate bromine from the solid mixture, there was a problem of solid inclusion, and an additional device for solid pulverization needed to be added. Moreover, the presence of bromine would reduce the separation ability of both UF6 and BrF3 and increase the residual rate of solid waste; in Comparative Example 4, the separation of bromine trifluoride and uranium hexafluoride was achieved by using the sodium fluoride adsorption method, which led to the need to replace the adsorbent regularly, increasing radioactive solid waste. Moreover, due to the influence of the sodium fluoride adsorbent in the separation process, it was difficult to control the purity of the product, reducing the recovery rate of uranium hexafluoride;

[0103] In Comparative Example 5, the existing low-temperature method was used to separate bromine from bromine trifluoride, uranium hexafluoride and bromine. There was solid inclusion in this process, and part of the bromine was wrapped by solid bromine trifluoride and uranium hexafluoride and was difficult to extract, resulting in a poor separation effect of bromine; when using the sodium fluoride adsorption method to separate bromine trifluoride and uranium hexafluoride, the following problems would also exist: ① The particle size distribution of sodium fluoride would affect the adsorption effect. Small particle sizes would be compacted due to the increase in adsorption pressure and limited heat dissipation, affecting the progress of the reaction; for large particle sizes, the diffusion rate of uranium hexafluoride was greater than the reaction rate, resulting in a small adsorption rate; moreover, after the adsorption-desorption cycle process, the particle size distribution of sodium fluoride would change, such as particles becoming powders (which might be introduced into uranium hexafluoride), and the powders being compacted (residual uranium hexafluoride). For the separation effect, the adsorbent needed to be replaced regularly, which increased the cost and generated more radioactive solid waste; ② During high-temperature desorption, about 1.5% of the complex would undergo a decomposition reaction in which U(VI) was reduced to U(V), resulting in a decrease in the adsorbent capacity and loss of uranium. Therefore, the present invention does not directly use sodium fluoride to adsorb and separate the mixture, but uses it as an exhaust gas adsorbent.

[0104] The separation and recovery of uranium-containing radioactive waste are carried out by vacuum sublimation and low-temperature rectification. First, bromine in the waste is effectively separated by the vacuum sublimation method, that is, by utilizing the characteristics that the melting point of bromine and its saturated vapor pressure at low temperature are higher than those of uranium hexafluoride and bromine trifluoride. Uranium hexafluoride and bromine trifluoride are first condensed, and then the percentage of bromine is increased by stepwise condensation. Finally, the separation of bromine in the mixed waste is achieved at low temperature. Second, uranium hexafluoride is separated from bromine trifluoride step by step by the low-temperature rectification method, and bromine trifluoride is recovered separately, that is, by utilizing the difference in the saturated vapor pressures of uranium hexafluoride and bromine trifluoride. The ratio of the ideal gas partial pressures of the two at low temperature meets the separation requirements. By controlling the temperature and pressure for low-temperature rectification, the separation from uranium hexafluoride and bromine trifluoride is achieved, and the classified recovery of uranium-containing radioactive sediment cleaning waste is realized, enabling the materials and cleaning agents to meet the reuse requirements, which is beneficial to the sustainable development of uranium enrichment plants and realizes the green development of the nuclear industry. This technology can also be applied to the recovery operations of similar mixed wastes.

[0105] The above further describes the present invention with the aid of specific embodiments. However, it should be understood that this specific description should not be construed as a limitation on the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A method for separating and recovering uranium-containing radioactive waste, characterized in that, It includes the following steps: (1) Vacuum sublimation process: ① Decompression heating: Vaporize the mixed working medium containing UF6, BrF3 and Br2; ② Multi-stage condensation: Pass the generated gaseous mixture into a multi-stage condensation system, and carry out condensation at a temperature ≤ 4°C and a pressure ≤ 10 kPa to condense out solid BrF3 and UF6; ③ Cold bromine recovery: Pass the uncondensed gas into a cryogenic device for liquefaction and recovery; (2) Low-temperature rectification process: ④ Stepwise rectification: Carry out gradient pressure reduction rectification on the mixture of UF6 and BrF3 condensed in step (1). At 0°C to -10°C, the pressure gradient is gradually reduced from 2.7 kPa by 1 kPa to separate UF6 gas and solid BrF3.

2. The separation and recovery method of uranium-containing radioactive waste according to claim 1, wherein In step ①, the heating temperature > 75°C, and the pressure is controlled at ≤ 13.4 kPa.

3. The separation and recovery method of uranium-containing radioactive waste according to claim 2, wherein In step ①, the heating temperature is 60°C to 80°C, and the pressure is 7 kPa to 13.4 kPa.

4. The separation and recovery method of uranium-containing radioactive waste according to claim 1, characterized in that, In step ②, the multi-stage condensation includes three-stage condensation: The first-stage condensation: temperature 4°C, pressure ≤ 10 kPa; The second-stage condensation: temperature -20°C, pressure ≤ 1.5 kPa; The third-stage condensation: temperature -40°C, pressure ≤ 0.693 kPa.

5. The method for separating and recovering uranium-containing radioactive waste according to claim 1, wherein In step ③, the temperature for liquefaction and recovery is -105 to -115°C, and the pressure is ≤ 50 Pa.

6. The method for separating and recovering uranium-containing radioactive waste according to claim 1, characterized in that, During the cold bromine recovery process in step ③, the unliquefied residual gas is treated by a gas absorption tower filled with sodium fluoride particles, and the gas residence time ≥ 30 seconds.

7. The method for separating and recovering uranium-containing radioactive waste according to claim 1, characterized in that, In step ④, the stepwise rectification includes three-stage rectification: The first-stage rectification: temperature 2 to -6°C, pressure 2.7 to 1.4 kPa; The second-stage rectification: temperature 0 to -10°C, pressure 1.8 to 1 kPa; The third-stage rectification: temperature 0 to -10°C, pressure 1.6 to 1 kPa.

8. The separation and recovery method of uranium-containing radioactive waste according to claim 1, characterized in that, The low-temperature rectification process in step (2) also includes: ⑤ UF6 collection: Condense and collect the gas generated by rectification at -120°C to -80°C to obtain solid UF6; ⑥ BrF3 collection: Heat the solid mixture rectified to 10°C to 25°C to obtain liquid BrF3.

9. The separation and recovery method of uranium-containing radioactive waste according to claim 1, characterized in that, Both the vacuum sublimation process and the low-temperature rectification process are carried out in a closed system, and each device is connected by pipelines.

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