A method and system for treating interface contaminants in a mixed clarifier tank

Abstract

This invention relates to a method and system for treating interface contaminants in a mixing and clarification tank, belonging to the field of nuclear fuel reprocessing. The method involves conveying interface contaminants to the final stage mixing and clarification tank via top-tank operation, separating the organic phase, and then returning the liquid containing interface contaminants from the final stage mixing and clarification tank to the organic phase inlet of the first stage mixing and clarification tank. The interface contaminants are dispersed by the agitation of the pump impeller within the mixing and clarification tank, thereby redissolving radioactive materials in the liquid. This invention utilizes in-situ treatment of interface contaminants and recovery of radioactive elements in a mixing and clarification tank, significantly reducing the accumulation of radioactivity in interface contaminants, mitigating radiation damage from organic solvents, and is simple to operate without requiring additional treatment equipment.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel reprocessing, and more specifically to a method and system for treating contaminants at the interface of a mixing clarifier. Background Technology

[0002] In nuclear facilities, mixing and clarification tanks are commonly used for liquid-liquid extraction separation. These tanks typically consist of multiple stages connected in series, each including a mixing chamber and a clarification chamber for multi-stage extraction. For example, in back-extraction, an organic phase is introduced into the mixing chamber of the first-stage mixing and clarification tank through the organic phase inlet, contacting the aqueous feed flowing in from the clarification chamber of the next-stage tank. The mixture is stirred by a pump impeller within the mixing chamber, using the aqueous feed to dissolve and recover radioactive materials from the organic phase. The mixed phase then flows into the clarification chamber of the first-stage tank for sedimentation and stratification. The feed containing recovered radioactive elements exits from the aqueous phase outlet. The organic phase then enters the mixing chamber of the second-stage mixing and clarification tank, where it is again mixed and extracted with the aqueous phase entering from the third-stage clarification chamber. This process continues until the organic phase flows through each stage to the mixing chamber of the final-stage mixing and clarification tank, where it contacts the aqueous feed for extraction. After stratification in the clarification chamber of the final-stage tank, the organic phase exits from the organic phase outlet.

[0003] However, the α, β, and γ rays emitted by radioactive substances in the feed solution cause irradiation degradation of the organic solvent, generating a series of degradation products and complexes. Furthermore, the feed solution contains chemical reagents such as nitric acid and nitrous acid, which can chemically degrade the organic phase and accelerate its irradiation degradation rate. Organic phase degradation products such as DBP (dibutyl phosphate), MBP (monobutyl phosphate), TBP (tributyl phosphate), and H3PO4 react with elements such as zirconium and iron in the feed solution to form stable compounds, resulting in interfacial contaminants. Because the interfacial contaminants have a greater ability to fix radioactive nuclides U and Pu than the feed solution, this leads to the loss of U and Pu. Interfacial contaminants form in each clarification chamber, located between the organic and aqueous phases. Although most of the aqueous and organic phases are discharged from their respective outlets, a portion of the aqueous and organic phases remains, causing the interfacial contaminants to remain in the clarification chamber, trapped between the organic and aqueous phases, and unable to be effectively treated. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the interface contaminants in the mixing clarification tank cause the loss of radioactive elements and cannot be effectively treated, thereby providing a method for treating interface contaminants in the mixing clarification tank and a system for treating interface contaminants in the mixing clarification tank.

[0005] The technical solution of the present invention:

[0006] A method for treating interface contaminants in a mixing clarifier involves first performing a top-tank treatment on the mixing clarifier to discharge the organic phase and the remaining liquid containing interface contaminants sequentially from the last stage mixing clarifier. Then, the liquid containing interface contaminants is returned to the mixing clarifier from the organic phase inlet of the first stage mixing clarifier. The interface contaminants are broken up and dispersed by a pump impeller in the mixing clarifier, which is used to redissolve the radioactive elements adsorbed in the interface contaminants into the liquid.

[0007] The mixing and clarification tank consists of multiple stages connected in series. Each stage of the mixing and clarification tank includes a mixing chamber and a clarification chamber. A pump impeller is installed in each mixing chamber. During the top tank treatment, interface contaminants are transported from the first stage mixing and clarification tank to the last stage mixing and clarification tank through aqueous phase feeding and accumulate therein. During this process, the organic phase is discharged through the organic phase outlet of the last stage mixing and clarification tank.

[0008] Preferably, during top tank processing, the organic phase feed line is closed to stop the organic phase feeding, the aqueous phase discharge line is closed to stop the aqueous phase discharge, the aqueous phase feed line is kept feeding, and the organic phase discharge line is kept discharging.

[0009] The liquid containing interface contaminants is stirred stage by stage through pump impellers in each mixing chamber.

[0010] The pump impeller has an input power of 600–5000 W / m³. 3 The stirring speed is above 100 rpm, preferably 100 to 800 rpm; the stirring time for each pump impeller is 0.5 to 2 hours.

[0011] During the mixing process of the liquid containing interface contaminants, the aqueous phase feed line, aqueous phase discharge line, organic phase feed line, and organic phase discharge line are all closed.

[0012] After the top tank is completed, the liquid containing interface contaminants is transported from the last stage mixing and clarification tank to the organic phase inlet of the first stage mixing and clarification tank through a fluid conveying device and then returned to the mixing and clarification tank.

[0013] The radioactive elements include U and / or Pu.

[0014] A mixed clarifier interface contaminant treatment system is used in the aforementioned mixed clarifier interface contaminant treatment method, comprising a mixed clarifier, wherein the final stage mixed clarifier is connected to the organic phase inlet of the first stage mixed clarifier via a contaminant return pipeline.

[0015] The mixing and clarification tank consists of multiple stages connected in series; each stage includes a mixing chamber and a clarification chamber; the mixing chamber of the last stage mixing and clarification tank is connected to the aqueous phase feed pipeline, and the clarification chamber of the last stage mixing and clarification tank is connected to the organic phase discharge pipeline; the mixing chamber of the first stage mixing and clarification tank is connected to the organic phase feed pipeline; the clarification chamber of the first stage mixing and clarification tank is connected to the aqueous phase discharge pipeline; the clarification chamber of the last stage mixing and clarification tank is connected to the organic phase feed pipeline of the first stage mixing and clarification tank through the waste return pipeline.

[0016] The fluid conveying device is installed on the waste return pipeline; the fluid conveying device is either a centrifugal pump or a steam jet pump, with a material conveying capacity of 1–10 m³ / h. 3 / h.

[0017] The technical solution of this invention has the following advantages:

[0018] 1. This invention provides a method for treating interface contaminants in a mixing and clarification tank. First, a top tank treatment is performed to separate the organic phase, and the remaining liquid containing interface contaminants is accumulated in the final mixing and clarification tank. Unlike when an organic phase is present, interface contaminants are "confined" at the interface between the organic and aqueous phases and are difficult to treat, since the organic phase has been separated, the liquid obtained after the top tank is mainly composed of the aqueous phase. This allows the interface contaminants to "detach" from the interface. Therefore, during the self-circulation process of returning the liquid containing interface contaminants to the mixing and clarification tank, the high-power pump impeller within the tank easily breaks down and disperses the interface contaminants. This allows radioactive substances containing radioactive elements that are encapsulated, absorbed, or complexed by the interface contaminants to redissolve in the liquid, achieving volume reduction of the interface contaminants and simultaneous recovery of radioactive elements. In summary, this invention utilizes a mixing and clarification tank for in-situ treatment of interface contaminants and recovery of radioactive elements, significantly reducing the accumulation of radioactivity in interface contaminants, mitigating radiation damage from organic solvents, and is simple to operate without requiring additional treatment equipment.

[0019] 2. The mixing and clarification tank is multi-stage. When the top tank is used, the organic phase feed pipeline and the aqueous phase discharge pipeline are closed, while the aqueous phase feed pipeline and the organic phase discharge pipeline are kept open. This allows the oil phase in the clarification chamber of each stage of the mixing and clarification tank to be pushed out through the aqueous phase feed. The oil phase accumulates from the first stage of the mixing and clarification tank to the last stage of the mixing and clarification tank and is finally discharged through the organic phase discharge pipeline connected to the last stage of the mixing and clarification tank, thus separating the organic phase. The remaining interface contaminants are transported from the first stage of the mixing and clarification tank to the last stage of the mixing and clarification tank with the aqueous phase feed liquid and accumulate there. This reduces dead zones for interface contaminants and facilitates centralized sewage discharge.

[0020] 3. By using the pump wheel built into each mixing chamber to circulate and stir multiple times, the recovery rate of radioactive elements and the volume reduction effect of interface contaminants can be improved.

[0021] 4. The pump impeller's input power per unit volume is 600~5000W / m 3 The stirring speed is above 100 rpm, preferably 100–800 rpm; the stirring time for each pump impeller is 0.5–2 hours. When the speed is in the range of 100–800 rpm, the stirring speed can be increased by increasing the pump impeller power to improve the recovery rate of radioactive elements and the volume reduction effect of interface contaminants. The effect tends to stabilize after the speed exceeds 800 rpm.

[0022] 5. The mixing and clarification tank used as a conventional extraction device has a feed liquid inlet and outlet. However, during the step-by-step stirring treatment of the feed liquid containing interface contaminants in the mixing and clarification tank, by closing the water phase inlet, water phase outlet, organic phase inlet and organic phase outlet, there is no feed liquid inlet or outlet, so that the mixing and clarification tank is used solely for treating interface contaminants.

[0023] 7. The present invention provides a mixing and clarification tank interface contaminant treatment system, wherein the organic phase inlet of the final mixing and clarification tank is externally connected to the first mixing and clarification tank via a contaminant return pipeline. This allows the slurry containing interface contaminants accumulated in the final mixing and clarification tank during top tank treatment to be returned to the mixing and clarification tank via the contaminant return pipeline, where it is then agitated by a pump impeller. This system is remotely controllable and meets the requirements for plant cleanliness and personnel radiation protection.

[0024] 8. The fluid conveying device is either a centrifugal pump or a steam jet pump, with a material conveying capacity of 1–10 m³ / h. 3 The system uses a powerful fluid conveying device to deliver liquid materials at a rate of / h, reducing discharge time and downtime. The equipment is reliable, stable, and maintenance-free, minimizing the need for personnel intervention. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a front view schematic diagram of a mixing clarification tank interface contaminant treatment system according to the present invention.

[0027] Reference numerals: 1-Mixing and clarification tank, 11-First stage mixing and clarification tank, 19-Last stage mixing and clarification tank, 2-Fluid conveying device, 3-Organic phase feed line, 4-Aqueous phase discharge line, 5-Organic phase discharge line, 6-Aqueous phase feed line, 7-Sludge return line. Detailed Implementation

[0028] Example 1

[0029] like Figure 1 As shown, a mixing and clarification tank interface sludge treatment system includes a mixing and clarification tank 1, which consists of nine stages connected in series. The final stage mixing and clarification tank 19 is connected to the organic phase inlet of the first stage mixing and clarification tank 11 via a sludge return pipeline 7. Each stage of the mixing and clarification tank includes a mixing chamber and a clarification chamber, with a pump impeller installed in the mixing chamber. The pump impeller's unit volume input power can range from 600 to 5000 W / m. 3 Adjust within the range.

[0030] The mixing chamber of the final stage mixing and clarification tank 19 is connected to the aqueous phase feed line 6, and the clarification chamber of the final stage mixing and clarification tank 19 is connected to the organic phase discharge line 5; the mixing chamber of the first stage mixing and clarification tank 11 is connected to the organic phase feed line 3; the clarification chamber of the first stage mixing and clarification tank 11 is connected to the aqueous phase discharge line 4. The suction port of the sludge return line 7 extends into the clarification chamber of the final stage mixing and clarification tank 19, and the end of the sludge return line 7 is connected to the organic phase feed line 3, so as to connect with the organic phase inlet of the first stage mixing and clarification tank 11.

[0031] The system also includes a fluid conveying device 2, which is installed on the waste return pipeline 7; specifically, the fluid conveying device 2 is a centrifugal pump with a material conveying capacity of 1-10m³. 3 / h.

[0032] The workflow of the above-mentioned interface contaminant treatment system for a mixed clarifier is as follows:

[0033] (1) Top Tank. Close the organic phase feed line 3 to stop the organic phase feed, close the aqueous phase discharge line 4 to stop the aqueous phase discharge, keep the aqueous phase feed line 6 feeding, and keep the organic phase discharge line 5 discharging. Perform top tank treatment on the mixing and clarification tank 1, and transport the interface contaminants from the first-stage mixing and clarification tank 11 to the last-stage mixing and clarification tank 19 and accumulate them in this stage. During this period, the organic phase that settles in the clarification chamber of the last-stage mixing and clarification tank 19 is discharged from the organic phase discharge line 5 to separate the organic phase. When the interface in the clarification chamber of the last-stage mixing and clarification tank 19 reaches the suction port of the contaminant return line 7, the top tank treatment ends, and the aqueous phase feed line 6 and the organic phase discharge line 5 are closed.

[0034] (2) Feed liquid transportation. Turn on the fluid transportation device 2 and transport the feed liquid containing interface contaminants from the clarification chamber of the last stage mixing and clarification tank 19 through the contaminant return pipeline 7 to the organic phase feed pipeline 3, and return it to the first stage mixing and clarification tank 11; turn off the fluid transportation device 2 after the transportation is completed.

[0035] (3) Pump wheel stirring and dissolving. The material transport action of the pump wheel in the mixing chamber of each mixing and clarification tank 1 is used to make the interface contaminants flow from the first mixing and clarification tank 11 to the last mixing and clarification tank 19 with the material liquid. During this process, the stirring action of the pump wheel is used to redissolve the radioactive elements in the interface contaminants into the material liquid.

[0036] Example 2

[0037] A method for treating interface contaminants in a mixed clarifier tank, employing the mixed clarifier tank interface contaminant treatment system described in Example 1, has the following workflow: The organic phase feed line 3 is shut off, the aqueous phase discharge line 4 is shut off, the aqueous phase feed line 6 is maintained, and the organic phase discharge line 5 is maintained. The mixed clarifier tank 1 is subjected to top-tank treatment to progressively push interface contaminants from the first-stage mixed clarifier tank 11 into the next stage, accumulating until the final stage mixed clarifier tank 19. During this process, the organic phase is discharged from the organic phase discharge line 5. Top-tank treatment ends when the interface of the clarification chamber in the final stage mixed clarifier tank 19 reaches the inlet of the contaminant return line 7. The aqueous phase feed line 6 and the organic phase discharge line 5 are shut off, and the fluid conveying device 2 is turned on to transport the interface contaminants from the final stage mixed clarifier tank 19 to the organic phase feed line 3 and back into the mixed clarifier tank 1. After the transport is completed, the fluid conveying device 2 is shut off. Turn on the pump impeller and adjust its power to maintain a speed of 150–250 rpm. Maintain a stirring time of 0.5–2 hours for each pump impeller stage. This allows the pump impeller in the mixing chamber of each stage of the mixing and clarification tank to break down and disperse the interface contaminants, causing the radioactive elements in the interface contaminants to redissolve in the liquid. After the interface contaminants are transported to the final stage mixing and clarification tank 19 and stirred, turn off the pump impeller. The liquid containing interface contaminants settles and separates in the clarification chamber of the final stage mixing and clarification tank 19, with the top contaminants discharged. The liquid containing dissolved radioactive elements is discharged from the aqueous phase outlet pipe 4, and can be returned to the mixing and clarification tank 1 for recycling via the aqueous phase inlet pipe 6.

[0038] The thickness of the contaminants at the interface of the final stage mixing and clarification tank 19 was measured and reduced from 18-20 mm before stirring to 8-12 mm.

[0039] Example 3

[0040] A method for treating interface contaminants in a mixed clarifier tank, employing the mixed clarifier tank interface contaminant treatment system described in Example 1, has the following workflow: The organic phase feed line 3 is shut off, the aqueous phase discharge line 4 is shut off, the aqueous phase feed line 6 is maintained, and the organic phase discharge line 5 is maintained. The mixed clarifier tank 1 is subjected to top-tank treatment to progressively push interface contaminants from the first-stage mixed clarifier tank 11 into the next stage, accumulating until the final stage mixed clarifier tank 19. During this process, the organic phase is discharged from the organic phase discharge line 5. Top-tank treatment ends when the interface of the clarification chamber in the final stage mixed clarifier tank 19 reaches the inlet of the contaminant return line 7. The aqueous phase feed line 6 and the organic phase discharge line 5 are shut off, and the fluid conveying device 2 is turned on to transport the interface contaminants from the final stage mixed clarifier tank 19 to the organic phase feed line 3 and back into the mixed clarifier tank 1. After the transport is completed, the fluid conveying device 2 is shut off. The pump impellers are turned on, and based on Example 2, the input power of the pump impellers is adjusted to increase the speed of each pump impeller to 350-600 rpm to enhance the stirring intensity. The stirring time for each pump impeller is maintained for 0.5-2 hours. This allows the pump impellers in the mixing chamber of each mixing and clarification tank to break down and disperse the interface contaminants, causing the radioactive elements in the interface contaminants to redissolve in the liquid. After the interface contaminants are transported to the final mixing and clarification tank 19 and stirred, the pump impellers are turned off. The liquid containing interface contaminants settles and separates in the clarification chamber of the final mixing and clarification tank 19. The contaminants at the top are discharged, and the liquid containing dissolved radioactive elements is returned to the mixing and clarification tank 1 for recycling.

[0041] The thickness of the contaminant at the interface of the final stage mixing and clarification tank 19 was measured and reduced from 18-20 mm before stirring to 6-10 mm.

[0042] Application examples

[0043] The interface contaminant treatment method of the mixing clarifier in Examples 2-3 was applied to a TBP / kerosene-UO2(NO3)2-HNO3 system. The U content in the interface contaminants was measured before and after stirring treatment, and the U recovery rate was found to be 65%–80%.

[0044] The recovery rate is calculated as follows: Recovery rate = (U content in interface contaminants before treatment - U content in interface contaminants after treatment) / U content in interface contaminants before treatment.

[0045] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for treating interface contaminants in a mixing clarifier, characterized in that, First, the mixing and clarification tank is treated at the top to discharge the organic phase and the remaining liquid containing interface contaminants from the last stage mixing and clarification tank. The liquid containing interface contaminants is then transported from the last stage mixing and clarification tank to the organic phase inlet of the first stage mixing and clarification tank via a fluid conveying device and returned to the mixing and clarification tank. The interface contaminants are broken up and dispersed by the pump impeller in the mixing and clarification tank, so that the radioactive elements adsorbed in the interface contaminants can be redissolved in the liquid.

2. The processing method according to claim 1, characterized in that, The mixing and clarification tank is composed of multiple stages connected in series. Each stage of the mixing and clarification tank includes a mixing chamber and a clarification chamber. The pump impeller is installed in the mixing chamber of each stage. During the top tank treatment, interface contaminants are gradually transported from the first-stage mixing and clarification tank to the last-stage mixing and clarification tank via aqueous phase feeding and accumulate therein. During this process, the organic phase is discharged through the organic phase outlet of the last-stage mixing and clarification tank.

3. The processing method according to claim 2, characterized in that, The liquid containing interface contaminants is stirred stage by stage through pump impellers in the mixing chambers of each stage of the mixing and clarification tank.

4. The processing method according to claim 2, characterized in that, The pump impeller has a unit volume input power of 600~5000 W / m 3 The stirring speed is above 100 rpm, and the stirring time of each pump impeller is 0.5~2h.

5. The processing method according to claim 4, characterized in that, The pump impeller has a stirring speed of 100~800 rpm.

6. The processing method according to claim 1, characterized in that, The radioactive elements include U and / or Pu.

7. A system for treating interface contaminants in a mixing clarifier tank, characterized in that, The processing method according to any one of claims 1-6 includes a mixing and clarification tank, wherein the final mixing and clarification tank is connected to the organic phase inlet of the first mixing and clarification tank via a sludge return pipeline.

8. The processing system according to claim 7, characterized in that, The mixing and clarification tank consists of multiple stages connected in series; each stage of the mixing and clarification tank includes a mixing chamber and a clarification chamber. The mixing chamber of the last stage mixing and clarification tank is connected to the aqueous phase feed pipeline, and the clarification chamber of the last stage mixing and clarification tank is connected to the organic phase discharge pipeline; the mixing chamber of the first stage mixing and clarification tank is connected to the organic phase feed pipeline; the clarification chamber of the first stage mixing and clarification tank is connected to the aqueous phase discharge pipeline; the clarification chamber of the last stage mixing and clarification tank is connected to the organic phase feed pipeline of the first stage mixing and clarification tank through the waste return pipeline.

9. The processing system according to claim 8, characterized in that, A fluid conveying device is installed on the waste return pipeline; the fluid conveying device is either a centrifugal pump or a steam jet pump, with a liquid conveying capacity of 1–10 m³. 3 / h.

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