Mother liquor destroying evaporator and spent fuel post-treatment process system

Abstract

The invention discloses a mother liquor destroying evaporator and a spent fuel post-treatment process system, the mother liquor destroying evaporator comprises a circulation loop for mother liquor to circularly flow, and a heating unit and a separation unit which are sequentially communicated with the circulation loop. The heating unit is used for heating mother liquor, a heated gas-liquid mixture flows to the separation unit through the circulation loop, the separation unit is used for carrying out gas-liquid separation on the gas-liquid mixture, and a liquid phase flows back to the heating unit through the circulation loop, so that one-time evaporation and concentration circulation is completed; and the mother liquor refluxed into the heating unit is continuously subjected to next evaporation and concentration circulation. And the analysis unit is used for analyzing the liquid phase in the sampling loop, opening a concentrated feed liquid outlet according to the analysis result of the analysis unit, and discharging the mother liquor after evaporation and concentration circulation. The mother liquor destroying evaporator can destroy oxalic acid in the mother liquor and realize concentration of the mother liquor at the same time, so that the existing process is improved.

Description

Technical Field

[0001] The invention specifically relates to a mother liquid destruction evaporator and a spent fuel post-processing process system. Background Art

[0002] At present, most countries adopt a closed-loop technology route for nuclear fuel treatment, and spent fuel reprocessing is a key link in achieving nuclear fuel recycling. At present, the main processes of typical spent fuel reprocessing in the world all adopt the PUREX process, which mainly includes the head-end process, chemical separation process and tail-end process (including uranium tail and plutonium tail). The plutonium purification system in the chemical separation process purifies and concentrates the recovered liquid to obtain a higher concentration of liquid, and then sends it to the tail end for conversion. In the tail end process, the solution (mainly plutonium nitrate and nitric acid) sent from the purification cycle is further adjusted and acidified, and then an excess of oxalic acid solution is added to convert it into oxalate precipitate. After filtering the precipitate slurry, oxalate filter cake and mother liquor are obtained, and the filter cake is further processed and converted into the final product.

[0003] The remaining mother liquor contains a certain amount of unrecovered metals, which need to be returned to the purification system for recycling. However, the oxalic acid contained in the mother liquor will reduce the distribution coefficient of plutonium in the separation and extraction, so the oxalic acid in the mother liquor needs to be destroyed before returning.

[0004] At present, the existing post-processing facilities mainly use storage tanks as reaction vessels for mother liquor destruction, that is, manganese nitrate is added to the storage tank containing the mother liquor and heated to cause a redox reaction between manganese nitrate and oxalic acid, thereby destroying the oxalic acid in the mother liquor. The destroyed mother liquor is directly returned to the purification cycle.

[0005] However, this process of directly returning the mother liquor to the purification cycle without concentration will cause the mother liquor to run repeatedly in the purification cycle, increase the operating load of the overall device, reduce the purification production capacity, and also cause adverse effects such as large loss of materials to be recovered and high consumption of nitric acid and oxidants. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a mother liquor destruction evaporator and a spent fuel post-processing process system in view of the above-mentioned deficiencies in the prior art. The mother liquor destruction evaporator can destroy oxalic acid in the mother liquor and simultaneously realize the concentration of the mother liquor.

[0007] According to an embodiment of the first aspect of the present invention, a mother liquor destruction evaporator is provided, comprising: a circulation concentration component and a sampling and analysis component. The circulation concentration component is used to perform evaporation and concentration circulation on the mother liquor, and the circulation concentration component comprises a circulation loop, a heating unit and a separation unit. The circulation loop is used for circulating the mother liquor, and the heating unit and the separation unit are connected to the circulation loop in sequence. The heating unit is used to heat the mother liquor to form a gas-liquid mixture, and the gas-liquid mixture flows to the separation unit via the circulation loop. The separation unit is used to perform gas-liquid separation on the gas-liquid mixture, and the separated liquid phase flows back to the heating unit via the circulation loop to complete an evaporation and concentration cycle, and the liquid phase flowing back to the heating unit continues to perform the next evaporation and concentration cycle. The sampling and analysis component comprises a sampling loop and an analysis unit, one end of the sampling loop is connected to the separation unit, and the other end is connected to the circulation loop. The analysis unit is connected to the sampling loop and is used to analyze the liquid phase in the sampling loop. A concentrated liquid outlet is provided at the lower end of the heating unit, and a control valve is provided at the concentrated liquid outlet. The control valve is used to open the concentrated liquid outlet according to the analysis result of the analysis unit to discharge the mother liquid that has completed the evaporation and concentration cycle.

[0008] The oxalic acid mother liquor destruction evaporation concentration process can significantly reduce the processing volume of the oxalic acid mother liquor returned to the purification cycle, optimize the existing process, and reduce equipment investment and operating costs.

[0009] Preferably, the circulation loop includes a connecting pipeline and a reflux pipeline, and the heating unit is also provided with a feed port and a discharge port, wherein the discharge port is located above the feed port, and the position of the feed port is higher than the concentrated liquid outlet; the separation unit includes a separation tank, and the separation tank is provided with a connecting port, a liquid phase outlet and a gas phase outlet, wherein the gas phase outlet is located at the top of the separation tank for gas phase discharge, and the liquid phase outlet is located at the bottom of the separation tank for liquid phase discharge, and the circulation inlet is located between the liquid phase outlet and the gas phase outlet; the discharge port of the heating unit is connected to the connecting port of the separation tank through a connecting pipeline, and the liquid phase outlet of the separation tank is connected to the feed port of the heating unit through a reflux pipeline.

[0010] Preferably, the inner cavity of the separation tank includes a gas phase section, a gas-liquid separation section and a liquid phase section, the gas phase section, the gas-liquid separation section and the liquid phase section are connected in sequence from top to bottom, the gas phase outlet is connected to the gas phase section, the liquid phase outlet and the connecting port are both connected to the liquid phase section, the separation unit also includes a separation tower plate, the separation tower plate is installed in the gas-liquid separation section, and the separation tower plate is used to perform gas-liquid separation on the heated mother liquor.

[0011] Preferably, the sampling circuit includes a first pipeline, a second pipeline and a sampling tank, one end of the first pipeline is connected to the liquid phase section of the separation tank, and the other end is connected to the upper end of the sampling tank, one end of the second pipeline is connected to the lower end of the sampling tank, and the other end is connected to the reflux pipeline; the liquid flow direction in the sampling circuit is consistent with the liquid flow direction in the circulation circuit.

[0012] Preferably, the mother liquor contains oxalic acid, and the circulating concentration component performs an evaporation and concentration cycle on the mother liquor and destroys the oxalic acid in the mother liquor; the analysis unit includes an analyzer and a controller, the analyzer is connected to the sampling tank, the analyzer is used to analyze the density and oxalic acid content of the liquid phase in the sampling loop, and output the density value and oxalic acid content value of the liquid phase; the controller pre-stores a density target value and an oxalic acid content target value, the controller is electrically connected to the analyzer, and is used to receive the density value and oxalic acid content value output by the analyzer, and when the density value is greater than or equal to the density target value and the oxalic acid content value is less than or equal to the oxalic acid content target value, the control valve is controlled to open the concentrated liquid outlet to discharge the mother liquor that has completed the evaporation and concentration cycle.

[0013] Preferably, the separation tower plate includes a partition; the partition is placed in a horizontal direction, and the edge of the partition is connected to the inner wall of the separation tank, the partition is provided with an air riser and a liquid downcomer, the air riser is located in the middle of the partition, and the liquid downcomer is located at the edge of the partition; the air riser runs through the partition, and is used for allowing the gas phase below the partition to rise and pass through the partition; an upwardly extending overflow weir is provided on one side of the partition, the overflow weir surrounds the liquid downcomer, the overflow weir itself encloses a liquid downcomer channel, and the liquid downcomer channel is connected to the liquid downcomer; the liquid downcomer channel extends in a vertical direction, and the space above the partition is connected to the space below the partition through the liquid downcomer channel, and the liquid downcomer channel is used for allowing the liquid phase generated by condensation above the partition to flow back to the bottom of the partition.

[0014] Preferably, the separation tower plate also includes multiple air risers and multiple bubble caps; the number of the air risers is multiple, and the number of the air risers is the same as the number of the air risers, each air riser corresponds to one air riser, the air riser is connected to the air riser, the number of the bubble caps is the same as the number of the air risers, each bubble cap corresponds to one air riser, and the bubble cap is arranged at the upper end of the air riser.

[0015] Preferably, there are a plurality of separation plates, and the plurality of separation plates are arranged at intervals along the central axis direction of the separation tank, and the downcomers of two adjacent separation plates are staggered.

[0016] Preferably, the position of the discharge port of the heating unit is higher than the position of the liquid phase outlet of the separation tank, and the position of the liquid phase outlet is higher than the position of the feed port of the heating unit.

[0017] Preferably, the mother liquor destruction evaporator further comprises a first feed pipe and a second feed pipe, both of which are connected to the feed port of the heating unit through the reflux pipeline, the first feed pipe is used for introducing the mother liquor, and the second feed pipe is used for introducing the manganese nitrate solution.

[0018] Preferably, the heating unit comprises a first pipe box, a second pipe box and a heat exchange tube, the first pipe box and the second pipe box are arranged at intervals in the vertical direction, the second pipe box is located above the first pipe box, the heat exchange tube is located between the first pipe box and the second pipe box, the heat exchange tube extends in the vertical direction, and the two ends of the heat exchange tube are respectively connected to the first pipe box and the second pipe box. The feed inlet and the concentrated liquid outlet are both connected to the first pipe box, and the discharge port is connected to the second pipe box. The first pipe box is used to receive the mother liquor and the manganese nitrate solution, and mix the mother liquor and the manganese nitrate solution, the heat exchange tube is used to heat the mixed liquid, and the heated mixed liquid enters the separation tank via the second pipe box and the connecting pipeline.

[0019] Preferably, the heating unit is a vertical shell and tube heat exchanger.

[0020] According to an embodiment of the second aspect of the present invention, there is provided a spent fuel post-processing process system, comprising: a plutonium purification device, a plutonium tail device and the above-mentioned mother liquid destruction evaporator. The circulation loop of the mother liquid destruction evaporator is respectively connected to the plutonium purification device and the plutonium tail device, the mother liquid destruction evaporator is used to evaporate and concentrate the mother liquid produced by the plutonium tail device, and destroy the oxalic acid in the mother liquid, and the liquid treated by the mother liquid destruction evaporator is returned to the plutonium purification device to continue to extract and recover plutonium metal.

[0021] Compared with existing treatment processes, this system reduces the processing volume of the return purification cycle, reduces equipment investment and operating costs, and meets the needs of operating large-scale spent fuel reprocessing plants.

[0022] The mother liquor destruction evaporator in the present invention is passed through the mother liquor and manganese nitrate solution into the circulation loop, and the mother liquor and manganese nitrate mixed solution in the circulation loop are heated by the heating unit, so that manganese nitrate and oxalic acid in the mother liquor undergo redox reaction, thereby destroying the oxalic acid in the mother liquor. At the same time, the heating unit forms a thermal siphon effect by steam heating, so that the mother liquor circulates in the circulation loop, the evaporation structure (heating unit) and the separation structure (separation unit), satisfying the catalyst, stirring and heating conditions required for the mother liquor destruction. Further, the heated gas-liquid mixture enters the separation unit, and the separation unit performs gas-liquid separation on the heated gas-liquid mixture, and the gas phase is discharged through the gas phase outlet at the upper end of the separation unit, and the liquid phase is discharged from the liquid phase outlet, and the liquid phase is refluxed to the heating unit via the circulation loop to complete an evaporation and concentration cycle, and the mother liquor refluxed to the first pipe box continues the next evaporation and concentration cycle. By performing an evaporation and concentration cycle on the mother liquor, the concentration of the mother liquor is achieved, that is, the solvent (water) in the mother liquor is evaporated while retaining the target component (such as plutonium metal to be recovered).

[0023] In addition, the mother liquor is always circulating in the separation structure (separation unit) and the evaporation structure (heating unit) during the evaporation and concentration process, and the evaporator is supplemented with additional mother liquor, so the mother liquor state in the separation tank is unstable, which makes it difficult for the staff to directly judge the oxalic acid content of the mother liquor in the circulation loop, and it is also difficult to directly sample and test the mother liquor in the circulation loop. This mother liquor destruction evaporator provides a stable sampling space for the mother liquor by setting an additional sampling loop. One end of the sampling loop is connected to the separation tank of the separation unit, and the other end is connected to the reflux pipeline of the circulation loop. The liquid flow direction in the sampling loop is consistent with the liquid flow direction in the circulation loop. Therefore, the additional sampling loop will not affect the evaporation and concentration cycle of the mother liquor, and at the same time, a stable mother liquor sampling space is provided for the analysis unit. The analysis unit is used to analyze the density and oxalic acid content of the liquid phase in the sampling loop, and when the density of the mother liquor is higher than the target value and the oxalic acid content value is less than or equal to the set target value, the valve is controlled to open to discharge the mother liquor that has completed the evaporation and concentration cycle.

[0024] In summary, the mother liquor destruction evaporator can destroy the oxalic acid in the mother liquor and concentrate the mother liquor by evaporating and concentrating the mother liquor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of a mother liquid destruction evaporator in some embodiments of the present invention;

[0026] Figure 2 Schematic diagram of the structure of the separation tower plate in some embodiments of the present invention.

[0027] In the figure: 1. heating steam inlet; 2. condensate outlet; 3. first feed pipe; 4. second feed pipe; 5. concentrated liquid outlet; 6. gas phase outlet; 7. sampling port; 8. liquid phase outlet; 9. circulation loop; 91. connecting pipeline; 92. reflux pipeline; 10. heat exchange tube; 11. tube sheet; 12. separation tower plate; 13. second pipeline; 14. first pipeline; 15. heating unit; 16. separation tank; 17. sampling tank; 18. downcomer; 19. bubble cap; 20. overflow weir; 21. riser; 22. partition. DETAILED DESCRIPTION

[0028] The following will be combined with the accompanying drawings in the present invention to clearly and completely describe the technical solutions in the invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of the present invention.

[0029] In the description of the present invention, it should be noted that the terms "upper", "lower", "upstream", "downstream" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience and simplification of the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present invention.

[0030] In the description of the present invention, the terms “first”, “second” and “third” are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0031] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connect", "set", "install", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0032] Example 1

[0033] See also Figure 1 The present invention discloses a mother liquor destruction evaporator, comprising: a circulation concentration component and a sampling and analysis component.

[0034] The circulating concentration component is used to perform evaporation and concentration cycle on the mother liquid. The circulating concentration component includes a circulating loop 9, a heating unit 15 and a separation unit. The circulating loop 9 is used for circulating the mother liquid. The heating unit 15 and the separation unit are connected to the circulating loop 9 in sequence. The heating unit 15 is used to heat the mother liquid to form a gas-liquid mixture. The heated mother liquid (gas-liquid mixture) flows to the separation unit via the circulating loop 9. The separation unit is used to perform gas-liquid separation on the gas-liquid mixture. The separated liquid phase flows back to the heating unit 15 via the circulating loop 9 to complete an evaporation and concentration cycle. The liquid phase flowing back to the heating unit 15 continues to perform the next evaporation and concentration cycle. The sampling and analysis component includes a sampling loop and an analysis unit. One end of the sampling loop is connected to the separation unit, and the other end is connected to the circulating loop 9. The liquid flow direction in the sampling loop is consistent with the liquid flow direction in the circulating loop 9. The analysis unit is connected to the sampling loop and is used to analyze the liquid phase in the sampling loop. A concentrated liquid outlet 5 is provided at the lower end of the heating unit 15. The concentrated liquid outlet 5 is provided with a control valve. The control valve is used to open the concentrated liquid outlet 5 according to the analysis result of the analysis unit to discharge the mother liquid that has completed the evaporation and concentration cycle.

[0035] It should be noted that the mother liquor destruction evaporator is particularly suitable for evaporating and destroying the mother liquor in the spent fuel reprocessing process, and the application of the mother liquor destruction evaporator can realize the optimized design of the existing process.

[0036] Specifically, the main process of spent fuel reprocessing adopts the PUREX process, which mainly includes the head-end process, chemical separation process and tail-end process (including uranium tail and plutonium tail). Among them, the head-end process refers to cooling the spent fuel in the spent fuel storage pool for a certain period of time (generally not less than 3 to 5 years) to reduce the radioactive activity and heat release rate, and alleviate the technical difficulty of the reprocessing process. Then, the cooled spent fuel is mechanically processed (such as cutting, shelling, etc.) to expose the fuel core blocks for subsequent chemical dissolution.

[0037] The chemical separation process is that the spent fuel pellets are dissolved in acid to form a solution containing uranium, plutonium and fission products. Insoluble residues are removed by clarifying filtration. Then, a solvent extraction process (such as the PUREX process) is used to separate uranium, plutonium and fission products using tributyl phosphate (TBP) as an extractant. This process is usually completed in multiple extraction cycles. The plutonium purification system in the chemical separation process purifies and concentrates the recovered liquid to prepare a higher concentration liquid, which is then sent to the tail end for conversion.

[0038] The tail process further adjusts the price and acidity of the solution sent from the purification cycle, and then adds oxalic acid solution to convert it into oxalate precipitation. The precipitate slurry is filtered to obtain oxalate filter cake and mother liquor, and the filter cake is further processed to convert it into the final product. The remaining mother liquor contains a certain amount of unrecovered metals, which need to be returned to the purification system for recycling again, but the oxalic acid contained in the mother liquor will reduce the distribution coefficient of plutonium in separation and extraction, so the oxalic acid in it needs to be destroyed before returning.

[0039] Existing post-processing facilities all use storage tanks as reaction vessels for mother liquor destruction, and the destroyed mother liquor is directly returned to the purification cycle. This process of directly returning the mother liquor to the purification cycle without concentration will cause the mother liquor to run repeatedly in the purification cycle, increase the operating load of the overall device, reduce the production capacity of purification and concentration, and also cause adverse effects such as high loss of materials to be recovered and high consumption of nitric acid and oxidants. Therefore, before the mother liquor returns to the purification cycle, the oxalic acid in it needs to be destroyed and the mother liquor volume needs to be reduced by evaporation and concentration, so as to reduce the impact of the mother liquor on the purification cycle after it returns.

[0040] Moreover, plutonium liquid has its own particularity, that is, the criticality safety of the liquid must be guaranteed. Specifically, plutonium is a highly radioactive and fissile element, and its liquid may form a critical mass under certain conditions, thereby triggering a chain reaction and radiation accidents. Therefore, when handling plutonium liquid, relevant safety regulations and operating procedures must be strictly followed to ensure that criticality accidents do not occur.

[0041] Oxalic acid and nitric acid in oxalic acid mother liquor are highly corrosive. As evaporation proceeds, nitric acid can increase to 8-10 mol / L. Under such high temperature and high acid conditions, conventional metal materials cannot meet the use requirements.

[0042] Due to the particularity of plutonium-containing liquid, research on its evaporation and concentration is still in its infancy. In response to the above situation, a mother liquor destruction evaporator is designed, which can not only reduce the volume of the mother liquor returned to the purification cycle but also destroy the oxalic acid in the mother liquor, thus meeting the needs of the tail-end process operation.

[0043] See also Figure 1In this embodiment, the circulation loop 9 includes a connecting pipe 91 and a reflux pipe 92, and the heating unit 15 is also provided with a feed port and a discharge port. The position of the discharge port is higher than the feed port, and the position of the feed port is higher than the concentrated liquid outlet 5. The separation unit includes a separation tank 16, and the separation tank 16 is provided with a connecting port, a liquid phase outlet 8 and a gas phase outlet 6. The gas phase outlet 6 is located at the top of the separation tank 16 for gas phase discharge, and the liquid phase outlet 8 is located at the bottom of the separation tank 16 for liquid phase discharge, and the circulation inlet is located between the liquid phase outlet 8 and the gas phase outlet 6. The discharge port of the heating unit 15 is connected to the connecting port of the separation tank 16 through the connecting pipe 91, and the liquid phase outlet 8 of the separation tank 16 is connected to the feed port of the heating unit 15 through the reflux pipe 92.

[0044] The heating unit 15 and the separation tank 16 are connected through the connecting pipe 91 and the reflux pipe 92 to form a circulation loop 9. When the heating unit 15 heats the mother liquid in the circulation loop 9, a siphon effect is generated, driving the mother liquid to circulate in the circulation loop 9, so that the mother liquid circulates in the circulation loop 9, the evaporation structure (heating unit 15) and the separation structure (separation unit), meeting the catalyst, stirring and heating conditions required for the destruction of the mother liquid.

[0045] Furthermore, the mother liquor destruction evaporator also includes a first feed pipe 3 and a second feed pipe 4, both of which are connected to the feed port of the heating unit 15 through a reflux line 92, the first feed pipe 3 is used to introduce the mother liquor, and the second feed pipe 4 is used to introduce the manganese nitrate solution.

[0046] Specifically, the mother liquor destruction evaporator introduces the mother liquor and manganese nitrate solution into the circulation loop 9, and heats the mixed solution of the mother liquor and manganese nitrate in the circulation loop 9 through the heating unit 15, so that the manganese nitrate and the oxalic acid in the mother liquor undergo an oxidation-reduction reaction, thereby destroying the oxalic acid in the mother liquor. At the same time, the heating unit 15 is heated by steam to form a thermal siphon effect, so that the mother liquor circulates in the circulation loop 9, the evaporation structure (heating unit 15) and the separation structure (separation unit), meeting the catalyst, stirring and heating conditions required for mother liquor destruction.

[0047] It should be noted that the siphon effect of the heating process can be understood as the thermal siphon effect, and its principle is mainly based on the changes in the physical properties of the liquid after heating and the natural circulation caused by these changes. The following is a detailed explanation of this principle: Thermosyphon effect principle: When a liquid (such as water) is heated, part of the liquid will vaporize into steam to form a vapor-liquid mixture. In this process, since the density of steam is much smaller than that of liquid water, the overall density of the vapor-liquid mixture will decrease. Due to the decrease in density, the vapor-liquid mixture will produce an upward density difference relative to the surrounding unheated cold liquid. This density difference becomes the main driving force of the thermal siphon effect. Driven by the density difference, the vapor-liquid mixture that expands due to heat and decreases in density will rise and enter a relatively high position (such as a heat exchanger). At the same time, the surrounding cold liquid with a lower temperature and higher density will fill this gap to form a natural circulation flow. In the heat exchanger, the rising vapor-liquid mixture will release heat, and the steam may recondense into liquid and release latent heat. This heat can be used for heating, hot water production or other heat utilization purposes. The cooled liquid then returns to its original location due to gravity and is heated again, forming a continuous cycle.

[0048] In this embodiment, the mother liquor is driven to circulate in the circulation loop 9 through the thermal siphon effect, thereby naturally achieving a stirring effect. Therefore, the mother liquor destruction evaporator can achieve stirring of the mother liquor without providing a stirring unit.

[0049] In this embodiment, the heating unit 15 includes a first pipe box, a second pipe box and a heat exchange tube 10. The first pipe box and the second pipe box are arranged at intervals in the vertical direction. The second pipe box is located above the first pipe box. The heat exchange tube 10 is located between the first pipe box and the second pipe box. The heat exchange tube 10 extends in the vertical direction. Both ends of the heat exchange tube 10 are connected to the first pipe box and the second pipe box respectively; the feed inlet and the concentrated liquid outlet 5 are both connected to the first pipe box, and the discharge port is connected to the second pipe box; the first pipe box is used to receive the mother liquor and the manganese nitrate solution, and mix the mother liquor and the manganese nitrate solution. The heat exchange tube 10 is used to heat the mixed liquid, and the heated mixed liquid enters the separation tank 16 via the second pipe box and the connecting pipeline 91.

[0050] More specifically, in this embodiment, the heating unit 15 uses a vertical shell and tube heat exchanger. The shell and tube heat exchanger is provided with a heating steam inlet 1, a condensed water outlet 2 and a heat exchange medium pipeline. The two ends of the heat exchange medium pipeline are respectively connected to the heating steam inlet 1 and the condensed water outlet 2. The water vapor enters the heat exchange medium pipeline in the shell and tube heat exchanger through the heating steam inlet 1. The heat exchange medium pipeline surrounds the heat exchange tube 10 and is used to heat the mother liquid in the heat exchange tube 10. After the heating steam absorbs heat from the mother liquid and condenses into water, it is discharged from the shell and tube heat exchanger through the condensed water outlet 2. Moreover, the flow direction of the heating steam in the heat exchange medium pipeline is opposite to the flow direction of the mother liquid in the heat exchange tube 10, so that the heat exchange efficiency of the shell and tube heat exchanger is higher and the mother liquid can be heated quickly.

[0051] In other words, the evaporation structure is composed of a shell and tube heat exchanger, a heat exchange tube 10 is arranged inside the shell and tube heat exchanger, both ends of the heat exchange tube 10 are welded to the tube sheet 11, a heating steam inlet 1 is arranged above the shell side of the shell and tube heat exchanger, a condensed water outlet 2 is arranged below the shell side, a connecting pipe is arranged above the tube side of the vertical shell and tube heat exchanger, a return pipe is arranged below the tube side, a concentrated liquid outlet 5 is arranged at the bottom of the tube side, and a mother liquid inlet (i.e., the inlet of the first feed pipe 3) and a manganese nitrate inlet (i.e., the inlet of the second feed pipe 4) are arranged on the return pipe. The temperature range in the heat exchange tube 10 is 100-120°C, and preferably, the evaporation temperature in the heat exchange tube 10 is maintained at about 100-110°C. Of course, the temperature can be adjusted accordingly with different liquid composition.

[0052] More specifically, the evaporation structure adopts a vertical natural circulation evaporator, which is more conducive to meeting critical safety requirements. It should be noted that, considering the particularity of plutonium liquid, that is, in order to meet the critical safety of plutonium liquid, the diameter of the evaporator is limited, and the processing volume requirements must also be met. The vertical natural circulation evaporator (i.e., shell and tube heat exchanger) has the following advantages over existing storage tank equipment: First, the vertical shell and tube heat exchanger can prevent the accumulation of liquid, and the liquid can circulate naturally during the evaporation process, reducing the accumulation of liquid inside the evaporator, thereby reducing the risk of forming a critical mass. Second, the vertical shell and tube heat exchanger can achieve layered evaporation, that is, each heat exchange tube is separated, which helps to control the local concentration and avoid critical safety problems caused by excessive local concentration.

[0053] In addition, the vertical natural circulation evaporator uses natural convection caused by temperature differences to achieve the evaporation process, without the need for additional power equipment such as pumps or fans, which reduces energy consumption and operating costs, and also reduces safety risks caused by equipment failure. Since it does not rely on external energy, the natural circulation evaporator does not produce additional exhaust gas and wastewater during operation, and is highly environmentally friendly.

[0054] At the same time, the diameter of the evaporation chamber is designed to be ≤400mm (especially within the range of 150-400mm), and the length of the evaporation chamber (i.e. the length of the heat exchange tube) and the diameter are designed to be between 5 and 15. The diameter size of the evaporator is limited by the critical safety risk. To achieve a higher liquid processing capacity under the condition of size limitation, it is necessary to design a suitable tube diameter ratio. Too high a tube diameter ratio causes a large static pressure of the liquid column in the evaporator, resulting in fast circulation of the liquid in the evaporator, low gasification rate, and large pressure loss. Too low a tube diameter ratio leads to a small static pressure of the liquid column, slow circulation of the liquid, high gasification rate, and small pressure loss. A suitable tube diameter ratio can achieve efficient operation of the evaporator and has a certain degree of operational flexibility. In fact, the final size can be determined according to the specific source condition and meet the critical safety requirements. In other words, the diameter of the evaporation chamber determines its internal volume, thereby limiting the amount of plutonium liquid that can be processed simultaneously. A smaller diameter means a smaller volume and less liquid, which helps to reduce the risk of reaching critical mass.

[0055] Exemplarily, the diameter of the evaporation chamber is 150, 200, 250, 300 (mm), and the ratio of the length to the diameter of the evaporation chamber is 5, 10, 15. Taking the evaporation chamber diameter of 200, 300, 400 (mm) and the length to diameter ratio of 10 as an example, at this time, the length of the evaporation chamber is 2000, 3000, 4000 (mm). Taking the evaporation chamber diameter of 200, 300, 400 (mm) and the length to diameter ratio of 15 as an example, at this time, the length of the evaporation chamber is 3000, 4500, 6000 (mm). Preferably, the diameter of the evaporation chamber is 300 (mm), and the tube length to tube diameter ratio is 10. At this time, the length of the evaporation chamber is 3000 (mm). Under this diameter and length, the evaporation chamber and the entire circulation loop can maintain efficient operation, realizing an efficient evaporation and concentration cycle of the mother liquor.

[0056] Further, the position of the discharge port of the heating unit 15 is higher than the position of the liquid phase outlet 8 of the separation tank 16, and the position of the liquid phase outlet 8 is higher than the position of the feed port of the heating unit 15. The advantage of such an arrangement is that by arranging the height positions of the above-mentioned discharge port, liquid phase outlet 8 and feed port in sequence from top to bottom (of course, the discharge port, liquid phase outlet 8 and feed port are not on the same vertical axis), the natural circulation of the mother liquid in the circulation loop 9 can be achieved without the need to rely on external force to achieve the circulation flow of the mother liquid.

[0057] Specifically, under the influence of the thermal siphon effect in the heating unit 15, the mother liquor is subjected to the upward siphon force, and can overcome the gravity and move upward and flow into the separation tank 16. The liquid phase in the separation tank 16 flows downward under the action of gravity, and after passing through the liquid phase outlet 8 and the feed port of the heating unit 15, flows into the first pipe box of the heating unit 15. In the first pipe box, the mother liquor and the manganese nitrate solution are further stirred and mixed, so that the reaction of oxalic acid in the mother liquor can be accelerated.

[0058] In this embodiment, the heated gas-liquid mixture enters the separation unit, and the separation unit performs gas-liquid separation on the heated gas-liquid mixture. The gas phase in the gas-liquid mixture is discharged through the gas phase outlet 6 at the upper end of the separation unit, and the liquid phase is discharged from the liquid phase outlet 8. The liquid phase flows back to the heating unit 15 through the circulation loop 9 to complete one evaporation and concentration cycle, and flows back to the mother liquid in the first pipe box to continue the next evaporation and concentration cycle. The mother liquid is concentrated by performing an evaporation and concentration cycle on the mother liquid, that is, the solvent (water) in the mother liquid is evaporated while retaining the target component (such as plutonium metal to be recovered).

[0059] In addition, the mother liquor is always circulating in the separation structure (separation unit) and the evaporation structure (heating unit 15) during the evaporation and concentration process, and the evaporator also has additional mother liquor to supplement, so the mother liquor state in the separation tank 16 is unstable, which makes it difficult for the staff to directly judge the oxalic acid content of the mother liquor in the circulation loop 9, and it is also difficult to directly sample and detect the mother liquor in the circulation loop. This mother liquor destruction evaporator provides a stable sampling space for the mother liquor by additionally setting a sampling loop. One end of the sampling loop is connected to the separation tank 16 of the separation unit, and the other end is connected to the return line 92 of the circulation loop 9. The liquid flow direction in the sampling loop is consistent with the liquid flow direction in the circulation loop 9. Therefore, the additionally set sampling loop will not affect the evaporation and concentration cycle of the mother liquor, and at the same time, a stable mother liquor sampling space is provided for the analysis unit. The analysis unit is used to analyze the density and oxalic acid content of the liquid phase in the sampling loop, and when the density of the mother liquor is higher than the target value and the oxalic acid content value is less than or equal to the set target value, the valve is controlled to open to discharge the mother liquor that has completed the evaporation and concentration cycle.

[0060] In summary, the mother liquor destruction evaporator can destroy the oxalic acid in the mother liquor and concentrate the mother liquor by evaporating and concentrating the mother liquor.

[0061] It should also be noted that oxalic acid and nitric acid in the oxalic acid mother liquor are highly corrosive. As evaporation proceeds, nitric acid can be increased to 8-10 mol / L. Conventional metal materials cannot meet the use requirements under such high temperature and high acid conditions. In this embodiment, the circulation loop, heating unit and separation unit are all made of acid-resistant materials. For example: zirconium, tantalum, titanium alloy, etc.

[0062] In order to achieve gas-liquid separation, in some embodiments, gas-liquid separation can be achieved directly by gravity separation. In the case of gravity separation, after the gas-liquid mixture enters the separation tank 16, due to the density difference between the gas and the liquid, the liquid will be deposited at the bottom of the tank under the action of gravity, while the gas will rise to the top of the tank and be discharged through the gas outlet. However, when gravity separation is directly used, the separation efficiency will be relatively low.

[0063] In this embodiment, the inner cavity of the separation tank 16 includes a gas phase section, a gas-liquid separation section and a liquid phase section, and the gas phase section, the gas-liquid separation section and the liquid phase section are connected in sequence from top to bottom. The gas phase outlet 6 is connected to the gas phase section, and the liquid phase outlet 8 and the connecting port are both connected to the liquid phase section. Figure 1 and Figure 2 The separation unit further includes a separation plate 12, which is installed in the gas-liquid separation section and is used for performing gas-liquid separation on the heated mother liquor.

[0064] Specifically, the part of the inner cavity above the separation tray 12 in the separation tank 16 is the gas phase section; the part of the inner cavity below the separation tray 12 is the liquid phase section; the part of the inner cavity where the separation tray 12 is distributed is the gas-liquid separation section. The separation tray 12 in this embodiment is the bubble cap 19 tray.

[0065] By arranging a separation tray 12 (bubble tray) in the middle and upper part of the separation tank 16, gas-liquid mass transfer can be promoted: the bubble tray is specially designed so that the steam (or gas) can be evenly distributed and pass through the liquid layer in the form of small bubbles, thereby greatly increasing the contact area between the gas and liquid phases, promoting the mass transfer process, and improving the mass transfer efficiency. On the bubble tray, liquid can accumulate and form a liquid layer of a certain thickness, i.e., a liquid seal. This helps to stabilize the operation in the tower, prevent gas short circuit, and ensure that the gas and liquid phases can fully contact. Moreover, the design of the bubble tray enables it to maintain a high operating efficiency within a large load range, i.e., it has a large operating flexibility. This is of great significance for adapting to different process conditions and ensuring stable production.

[0066] like Figure 2 As shown, the separation tower plate 12 (bubble tower plate) includes a partition 22. The partition 22 is placed in the horizontal direction, and the edge of the partition 22 is connected to the inner side wall of the separation tank 16. The partition 22 is provided with a gas riser and a liquid downcomer. The gas riser is located in the middle of the partition 22, and the liquid downcomer is located at the edge of the partition 22. The gas riser runs through the partition 22, and is used for the gas phase below the partition 22 to rise and pass through the partition 22. Among them, the horizontally placed partition 22 divides the space in the tower into multiple levels, so that the gas and liquid can contact and exchange at different levels. A flowing liquid layer of a certain thickness is maintained on each layer of the tower plate, and the gas, driven by the pressure difference, rises from the bottom of the tower to the top of the tower through the liquid layer and the gas riser on each tower plate in turn under the pressure difference.

[0067] An overflow weir 20 extending upward is provided on one side (upper side) of the downcomer port. The overflow weir 20 surrounds the downcomer port. The overflow weir itself encloses a downcomer channel, which is connected to the downcomer port. The downcomer channel extends in the vertical direction. The space above the partition 22 is connected to the space below the partition 22 through the downcomer channel. The downcomer channel is used to allow the liquid phase generated by condensation above the partition 22 to flow back to the bottom of the partition 22. When the depth of the accumulated liquid layer on the partition 22 exceeds the height of the overflow weir 20, the liquid on the partition 22 flows from the downcomer channel to the liquid layer of the separation tray 12 of the next layer. The lower end of the downcomer channel is connected to the downcomer 18, which is used to guide the condensed liquid to flow to the separation tray 12 of the next layer. At the same time, in order to ensure that the purified liquid enters the downcomer 18 through the overflow weir, the upper end of the riser 21 is higher than the upper end of the overflow weir 20.

[0068] The cross section of the above-mentioned downcomer is circular. Of course, it can also be elliptical, rectangular, arc-rectangular or other irregular shapes.

[0069] There are multiple separation plates 12, which are arranged at intervals along the central axis of the separation tank 16, and the distance between the separation plates is set between 300-500 mm, so that the separation and purification effect is optimal, and the downcomers of two adjacent separation plates are staggered. In this embodiment, the number of separation plates 12 is 3-8, and preferably, the number of separation plates 12 is 5. By staggering the downcomers, short-circuiting of the liquid layer can be avoided, so that the liquid phase generated by condensation flows through each separation plate 12 in turn, thereby achieving sufficient mass transfer between gas and liquid.

[0070] In other words, if multiple downcomers are arranged on the same vertical axis, the uppermost liquid phase will directly flow into the liquid phase section at the lower end of multiple separation plates 12 when escaping the overflow weir 20, and sufficient mass transfer cannot be achieved.

[0071] Further, the separation tray 12 further includes a plurality of risers 21 and a plurality of bubbles 19. The number of the riser ports is multiple, and the number of the riser ports is the same as the number of the riser pipes 21, each riser pipe 21 corresponds to a riser port, the riser pipe 21 is connected to the riser port, the number of the bubbles 19 is the same as the number of the riser pipes 21, each bubble cap 19 corresponds to a riser pipe 21, and the bubble cap 19 is disposed at the upper end of the riser pipe 21. The side wall of the bubble cap 19 is provided with a plurality of gas outlets, the gas outlets penetrate the bubble cap 19, and the plurality of gas outlets are arranged along the circumference of the bubble cap 19.

[0072] The bubble cap 19 on the horizontal partition 22 is designed so that when the rising gas enters the liquid layer through the bubble cap 19, it is dispersed into many tiny bubbles, providing a large number of mass transfer interfaces for the gas-liquid two phases, thereby promoting mass and heat exchange.

[0073] In other words, the separation structure is composed of a separation tank 16, a bubble cap tray is provided at the top of the separation tank 16, a connecting pipe is provided at the bottom of the separation tank 16, a return pipe is provided at the bottom of the separation tank 16, and a steam outlet is provided at the top of the separation tank 16. The bubble cap tray includes a tray (i.e., the above-mentioned partition 22), and a liquid riser (i.e., a gas riser 21), an overflow weir 20, a bubble cap 19, and a downcomer 18 are provided on the tray.

[0074] See also Figure 1 In this embodiment, the sampling circuit includes a first pipeline 14, a second pipeline 13 and a sampling tank 17. One end of the first pipeline 14 is connected to the liquid phase section of the separation tank 16, and the other end is connected to the upper end of the sampling tank 17. One end of the second pipeline 13 is connected to the lower end of the sampling tank 17, and the other end is connected to the return pipeline 92. The liquid flow direction in the sampling circuit is consistent with the liquid flow direction in the circulation circuit 9.

[0075] The sampling loop is connected to the liquid phase section in the separation tank 16, and can more stably guide the liquid phase, thereby forming a stable sampling space, so as to improve the accuracy of the measurement of the analysis unit.

[0076] In other words, the sampling structure is composed of a sampling tank 17, a connecting pipeline is provided at the top of the sampling tank 17, a connecting pipeline is provided at the bottom of the sampling tank 17, and a sampling port 7 is provided at the bottom of the sampling tank 17. The sampling port 7 is connected to the analysis unit.

[0077] Furthermore, the mother liquor contains oxalic acid, and the circulating concentration component performs evaporation and concentration circulation on the mother liquor, while destroying the oxalic acid in the mother liquor. The analysis unit includes an analyzer and a controller, and the analyzer is connected to the sampling tank 17. The analyzer is used to analyze the density and oxalic acid content of the liquid phase in the sampling loop, and output the density value and oxalic acid content value of the liquid phase. The controller pre-stores a density target value (≥1500kg / m 3 ) and the target value of oxalic acid content (<0.1 g / L), the controller is electrically connected to the analyzer to receive the density value and oxalic acid content value output by the analyzer, and when the density value is greater than or equal to the density target value and the oxalic acid content value is less than or equal to the oxalic acid content target value, the control valve is controlled to open the outlet of the concentrated liquid to discharge the mother liquor that has completed the evaporation and concentration cycle. For example, when the density value of the liquid phase is ≥1500 kg / m 3 , and when the oxalic acid content is less than 0.1 g / L, the control valve is controlled to open the outlet of the concentrated liquid to discharge the mother liquid that has completed the evaporation and concentration cycle. Of course, it can be understood that the above-mentioned density target value and oxalic acid content target value need to be determined according to actual working conditions.

[0078] In some embodiments, the controller is configured as a programmable logic controller, and the control valve can be configured as an electric valve. The staff can program the programmable logic controller in advance, so as to realize the automatic control of the electric valve through an automated program. Specifically, the electric valve is electrically connected to the controller, and the controller compares the density value of the liquid phase with the density target value, and the oxalic acid content value with the oxalic acid content target value. When the density value of the liquid phase is greater than or equal to the density target value, and the oxalic acid content value is less than or equal to the oxalic acid content target value, an opening signal is sent to the electric valve, and when the electric valve receives the opening signal, it opens the concentrated liquid outlet 5 to discharge the mother liquor that has completed the evaporation and concentration cycle.

[0079] In some other embodiments, the controller is configured as an interactive computer device, and the controller displays information (including analysis data such as the density value and oxalic acid content value of the liquid phase, the density target value and the oxalic acid content target value) to the staff, and can accept the instructions of the staff. When the density value of the liquid phase is greater than or equal to the density target value, and the oxalic acid content value is less than or equal to the oxalic acid content target value, the staff sends a first signal to the electric valve through the controller, and when the electric valve receives the opening signal, it opens the concentrated liquid outlet 5 to discharge the mother liquor that has completed the evaporation and concentration cycle.

[0080] Of course, in some other embodiments, the control valve can be configured as a manual valve. The staff obtains the analysis data such as the density value, oxalic acid content value, density target value and oxalic acid content target value of the liquid phase through the controller (interoperable computer device), and manually opens the valve to discharge the mother liquor that has completed the evaporation and concentration cycle when the density value of the liquid phase is greater than or equal to the density target value and the oxalic acid content value is less than or equal to the oxalic acid content target value.

[0081] The above-mentioned programmable logic controller, computer equipment, electric valve, and manual valve can all be commercially available existing equipment.

[0082] In summary, in view of the need to concentrate the remaining mother liquor after the precipitation of plutonium oxalate at the plutonium tail in the spent fuel reprocessing process and to destroy it with oxalic acid, this embodiment provides a mother liquor destruction evaporator, which simultaneously achieves the functions of mother liquor concentration and oxalic acid destruction.

[0083] To achieve the above purpose, the technical solution adopted in this embodiment is as follows: a mother liquor destruction evaporator, which includes an evaporation structure (i.e., a heating unit 15), a separation structure (i.e., a separation unit) and a sampling structure (i.e., a sampling and analysis component).

[0084] The working process of this mother liquor destruction evaporator is described as follows:

[0085] Among them, the main function of the evaporation structure (i.e., the heating unit 15) is evaporation concentration and oxalic acid destruction, and the implementation form is a shell and tube heat exchanger. Water vapor enters the shell and tube heat exchanger through the heating steam inlet 1, and is absorbed by the mother liquid and condensed into water and then discharged from the shell and tube heat exchanger through the condensed water outlet 2. When the mother liquid destruction evaporator is running, the concentrated liquid outlet 5 is closed, and the mother liquid continuously enters the shell and tube heat exchanger from the mother liquid inlet, rises and vaporizes along the heat exchange tube 10 under the siphon effect, and enters the separation structure through the connecting pipe. The heat exchange tube 10 is welded to the upper and lower tube sheets 11. The manganese nitrate solution enters the shell and tube heat exchanger from the manganese nitrate solution inlet (i.e., the inlet of the second feed pipe 4) to complete the destruction of oxalic acid. After the detection port detects that the concentrated mother liquor meets the set conditions, the concentrated liquid outlet 5 is opened to discharge the concentrated mother liquor out of the evaporator.

[0086] The main function of the separation structure (i.e., the separation unit) is to separate and purify the evaporated steam. At the same time, in order to enhance its separation and purification capabilities, a separation tray 12 is added to the upper part of the separation tank 16. After the evaporated liquid enters the separation tank 16, the evaporated steam enters the upper part of the separation tank 16, and the unevaporated liquid returns to the evaporation structure through the return pipe to continue evaporation. After gravity separation and purification by the bubble tray (i.e., the separation tray 12), the steam is discharged from the evaporator through the steam outlet. This design recovers the materials in the mother liquor as much as possible and reduces the impact of radioactive substances on subsequent equipment and processes.

[0087] The main function of the sampling structure (i.e., sampling loop) is to provide a stable sampling detection space. The mother liquor circulates in the separation structure and the evaporation structure during the evaporation and concentration process, and the evaporator is supplemented with additional mother liquor, so that the state of the mother liquor in the separation tank 16 is unstable. The additionally arranged sampling structure provides a stable sampling space for the mother liquor. The sampling structure is connected to the separation structure through a connecting pipeline. The sampling port 7 samples and detects the state of the mother liquor.

[0088] The main function of the separation tray 12 is to purify the steam. The purified liquid enters the tray from the downcomer 18, and the riser and overflow weir 20 cooperate to control the liquid level on the tray. The steam passes through the bubble cap 19 from the bottom and contacts the liquid on the tray for mass transfer. The entrained liquid droplets are absorbed into the liquid, and the liquid finally returns to the separation chamber for reheating and circulation.

[0089] In summary, the beneficial effects of this mother liquor destruction evaporator are as follows:

[0090] 1. The use of vertical natural circulation evaporator is more conducive to meeting critical safety requirements. At the same time, the diameter of the evaporation chamber is designed to be ≤400mm, and the ratio of tube length to tube diameter is designed to be between 5 and 15. The final size can be determined according to the specific source item to meet the critical safety requirements.

[0091] 2. Under the thermal siphon effect formed by steam heating, the mother liquor circulates in the evaporation structure and the separation structure, meeting the catalyst, stirring and heating conditions required for mother liquor destruction. The mother liquor destruction evaporator combines mother liquor evaporation and oxalate destruction in the evaporator, replacing the mother liquor destruction tank with the evaporator, reducing equipment investment.

[0092] 3. The separation plate 12 further purifies the evaporated tail gas to reduce the loss of nuclides and radioactive emissions.

[0093] 4. The sampling tank 17 can realize the circulation of the feed liquid, and is used for sampling the evaporation feed liquid, and controlling the evaporation concentration and oxalic acid destruction process.

[0094] Example 2

[0095] See also Figure 1 The present invention also discloses a spent fuel post-processing process system, including: plutonium purification equipment, plutonium tail equipment and the mother liquid destruction evaporator in Example 1.

[0096] Among them, the circulation loop of the mother liquor destruction evaporator is connected to the plutonium purification equipment and the plutonium tail end equipment respectively. The mother liquor destruction evaporator is used to evaporate and concentrate the mother liquor produced by the plutonium tail end equipment, and to destroy the oxalic acid in the mother liquor. The liquid treated by the mother liquor destruction evaporator is returned to the plutonium purification equipment to continue to extract and recover plutonium metal.

[0097] In other words, the mother liquor from the tail end enters the mother liquor destruction evaporator to evaporate and concentrate the mother liquor, and destroy the oxalic acid in the mother liquor. The liquid after treatment in the mother liquor destruction evaporator is returned to the plutonium purification equipment to continue extraction and recovery of plutonium metal.

[0098] It should be noted that the spent fuel reprocessing process system adopts the mother liquor destruction evaporator in Example 1, which reduces the processing volume of the return purification cycle compared with the existing treatment process, reduces equipment investment and operating costs, and meets the needs of operating large-scale spent fuel reprocessing plants.

[0099] It is also necessary to explain the process flow of pan-fuel post-processing:

[0100] First, the plutonium purification equipment is used to purify the recycled liquid generated during the spent fuel reprocessing process to obtain purified liquid.

[0101] The plutonium tail equipment is connected to the plutonium purification equipment, and is used to receive the purified feed liquid and perform price and acid adjustment on the purified feed liquid. After adding oxalic acid, a precipitated product is obtained, which is filtered and dried and roasted to obtain the final product. The remaining mother liquor obtained by filtration contains unrecovered plutonium metal and oxalic acid to be destroyed.

[0102] The mother liquor destruction evaporator is used to evaporate and concentrate the mother liquor and destroy the oxalic acid in the mother liquor. The circulation loop 9 of the mother liquor destruction evaporator is connected to the tail end processing equipment and is used to receive the mother liquor. The heating unit 15 of the mother liquor destruction evaporator is used to heat the mother liquor. The heated mother liquor flows to the separation unit through the circulation loop 9. The separation unit is used to separate the gas and liquid of the heated mother liquor. The liquid phase flows back to the heating unit 15 through the circulation loop 9 to complete an evaporation and concentration cycle. The mother liquor flowing back to the first pipe box continues the next evaporation and concentration cycle until the control valve is opened, and the mother liquor that completes the evaporation and concentration cycle is discharged through the concentrated liquid outlet 5.

[0103] The concentrated liquid outlet 5 of the mother liquid destruction evaporator is connected to the plutonium purification equipment, and the mother liquid that completes the evaporation and concentration cycle is refluxed to the plutonium purification equipment, and the plutonium metal in the mother liquid is further recovered by the plutonium purification equipment.

[0104] It should be noted that the above-mentioned plutonium purification equipment and plutonium tail equipment are a combination of multiple equipment (i.e., a set of equipment), rather than a single equipment. Existing plutonium purification equipment and plutonium tail equipment can be used (i.e., plutonium purification equipment and plutonium tail equipment are existing technologies and will not be repeated here), and the processing capacity can be appropriately reduced. In other words, the main process of spent fuel reprocessing in the prior art adopts a direct return to the purification cycle process (i.e., the mother liquor is obtained after the tail end treatment, and is directly returned to the purification cycle without concentration). This requires the plutonium purification equipment to have a larger volume and a stronger purification cycle processing capacity in order to purify a large amount of mother liquor. However, this will greatly increase the floor space of the entire process system. Similarly, the plutonium tail equipment also needs to have a larger volume, which will also cause the plutonium tail equipment to occupy a larger space.

[0105] Compared with the prior art, the process system in this embodiment adopts the method of evaporation concentration first and then return to the purification cycle process. This can effectively reduce the volume required for plutonium purification equipment and plutonium tail equipment, and thus reduce the floor space of these two sets of equipment. Therefore, compared with the existing treatment process, this system reduces the processing volume of the return purification cycle, reduces equipment investment and operating costs, and meets the needs of large-scale spent fuel reprocessing plants.

[0106] In summary, the spent fuel reprocessing system in this embodiment uses the mother liquor destruction evaporator in Example 1 to evaporate and concentrate the plutonium-containing liquid, which can not only reduce the volume of the mother liquor in the return purification cycle but also destroy the oxalic acid in the mother liquor, thereby reducing the processing volume of the mother liquor in the return purification cycle and reducing equipment investment and operating costs.

[0107] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A mother liquor destruction evaporator, characterized in that: include: Circulation concentration components and sampling and analysis components; The circulating concentration component is used to perform evaporation and concentration circulation on the mother liquid, and the circulating concentration component comprises a circulating loop (9), a heating unit (15) and a separation unit, the circulating loop (9) is used for circulating the mother liquid, and the heating unit (15) and the separation unit are connected to the circulating loop (9) in sequence; The heating unit (15) is used to heat the mother liquid to form a gas-liquid mixture, and the gas-liquid mixture flows to the separation unit via the circulation loop (9). The separation unit is used to perform gas-liquid separation on the gas-liquid mixture. The separated liquid phase flows back to the heating unit (15) via the circulation loop (9) to complete one evaporation and concentration cycle, and the liquid phase flowing back to the heating unit (15) continues to perform the next evaporation and concentration cycle; The sampling and analysis component comprises a sampling circuit and an analysis unit, one end of the sampling circuit is connected to the separation unit, and the other end is connected to the circulation circuit (9), and the analysis unit is connected to the sampling circuit for analyzing the liquid phase in the sampling circuit; A concentrated liquid outlet (5) is provided at the lower end of the heating unit (15), and a control valve is provided at the concentrated liquid outlet (5). The control valve is used to open the concentrated liquid outlet (5) according to the analysis result of the analysis unit to discharge the mother liquid that has completed the evaporation and concentration cycle.

2. The mother liquor destruction evaporator according to claim 1, characterized in that: The circulation loop (9) comprises a connecting pipeline (91) and a return pipeline (92). The heating unit (15) is further provided with a feed inlet and a discharge port, wherein the discharge port is located above the feed inlet, and the feed inlet is located higher than the concentrated liquid outlet (5); The separation unit comprises a separation tank (16), the separation tank (16) is provided with a communication port, a liquid phase outlet (8) and a gas phase outlet (6), the gas phase outlet (6) is located at the top of the separation tank (16) for discharging the gas phase, the liquid phase outlet (8) is located at the bottom of the separation tank (16) for discharging the liquid phase, and the circulation inlet is located between the liquid phase outlet (8) and the gas phase outlet (6); The discharge port of the heating unit (15) is connected to the connecting port of the separation tank (16) via a connecting pipe (91), and the liquid phase outlet (8) of the separation tank (16) is connected to the feed port of the heating unit (15) via a reflux pipe (92).

3. The mother liquor destruction evaporator according to claim 2, characterized in that: The inner cavity of the separation tank (16) comprises a gas phase section, a gas-liquid separation section and a liquid phase section, wherein the gas phase section, the gas-liquid separation section and the liquid phase section are sequentially connected from top to bottom. The gas phase outlet (6) is connected to the gas phase section, and the liquid phase outlet (8) and the communication port are both connected to the liquid phase section. The separation unit further comprises a separation plate (12), wherein the separation plate (12) is installed in the gas-liquid separation section, and the separation plate (12) is used to perform gas-liquid separation on the heated mother liquor.

4. The mother liquor destruction evaporator according to claim 3, characterized in that: The sampling circuit comprises a first pipeline (14), a second pipeline (13) and a sampling tank (17); one end of the first pipeline (14) is connected to the liquid phase section of the separation tank (16), and the other end is connected to the upper end of the sampling tank (17). One end of the second pipeline (13) is in communication with the lower end of the sampling tank (17), and the other end is in communication with the return pipeline (92); The flow direction of the liquid in the sampling loop is consistent with the flow direction of the liquid in the circulation loop (9).

5. The mother liquor destruction evaporator according to claim 4, characterized in that: The mother liquor contains oxalic acid, and the circulating concentration component performs evaporation and concentration circulation on the mother liquor and destroys the oxalic acid in the mother liquor; The analysis unit comprises an analyzer and a controller, wherein the analyzer is connected to the sampling tank (17), and is used to analyze the density and oxalic acid content of the liquid phase in the sampling loop, and output the density value and oxalic acid content value of the liquid phase; The controller has a density target value and an oxalic acid content target value pre-stored therein. The controller is electrically connected to the analyzer and is used to receive the density value and the oxalic acid content value output by the analyzer. When the density value is greater than or equal to the density target value and the oxalic acid content value is less than or equal to the oxalic acid content target value, the controller controls the control valve to open the concentrated liquid outlet (5) to discharge the mother liquid that has completed the evaporation and concentration cycle.

6. The mother liquor destruction evaporator according to claim 3, characterized in that: The separation tray (12) includes a partition (22); The partition (22) is placed in a horizontal direction, and the edge of the partition (22) is connected to the inner wall of the separation tank (16). The partition (22) is provided with a gas raising port and a liquid lowering port, wherein the gas raising port is located in the middle of the partition (22), and the liquid lowering port is located at the edge of the partition (22); The gas riser penetrates the partition (22) and is used to allow the gas phase below the partition (22) to rise and pass through the partition (22); An overflow weir (20) extending upward is arranged on one side of the partition plate, the overflow weir surrounds the downcomer port, the overflow weir (20) itself encloses a downcomer channel, and the downcomer channel is connected to the downcomer port; The downcomer channel extends in a vertical direction, and the space above the partition (22) is connected to the space below the partition (22) through the downcomer channel. The downcomer channel is used to allow the liquid phase generated by condensation above the partition (22) to flow back to the bottom of the partition (22).

7. The mother liquor destruction evaporator according to claim 6, characterized in that: The separation tray (12) further comprises a plurality of riser pipes (21) and a plurality of bubble caps (19); The number of the air risers is multiple, and the number of the air risers is the same as the number of the air riser pipes (21), each air riser pipe (21) corresponds to one air riser, and the air riser pipe (21) is in communication with the air riser. The number of the bubble caps (19) is the same as the number of the air risers (21); each bubble cap (19) corresponds to one air riser (21); and the bubble cap (19) is arranged to cover the upper end of the air riser (21).

8. The mother liquor destruction evaporator according to claim 6 or 7, characterized in that: The number of the separation plates (12) is multiple, and the multiple separation plates (12) are arranged at intervals along the central axis direction of the separation tank (16), and the downcomers of two adjacent separation plates are staggered.

9. The mother liquor destruction evaporator according to claim 2, characterized in that: The position of the discharge port of the heating unit (15) is higher than the position of the liquid phase outlet (8) of the separation tank (16), and the position of the liquid phase outlet (8) is higher than the position of the feed port of the heating unit (15).

10. The mother liquor destruction evaporator according to claim 9, characterized in that: It also includes a first feed pipe (3) and a second feed pipe (4), wherein the first feed pipe (3) and the second feed pipe (4) are both connected to the feed port of the heating unit (15) through the reflux pipeline (92). The first feed pipe (3) is used for introducing mother liquor, and the second feed pipe (4) is used for introducing manganese nitrate solution.

11. The mother liquor destruction evaporator according to claim 10, characterized in that: The heating unit (15) comprises a first pipe box, a second pipe box and a heat exchange pipe (10), wherein the first pipe box and the second pipe box are arranged at intervals in a vertical direction, the second pipe box is located above the first pipe box, the heat exchange pipe (10) is located between the first pipe box and the second pipe box, the heat exchange pipe (10) extends in a vertical direction, and both ends of the heat exchange pipe (10) are respectively connected to the first pipe box and the second pipe box; The feed inlet and the concentrated liquid outlet (5) are both connected to the first pipe box, and the discharge port is connected to the second pipe box; The first pipe box is used to receive the mother liquor and the manganese nitrate solution and mix the mother liquor and the manganese nitrate solution. The heat exchange tube (10) is used to heat the mixed liquid. The heated mixed liquid enters the separation tank (16) via the second pipe box and the connecting pipeline (91).

12. The mother liquor destruction evaporator according to claim 1, 2, 9, 10 or 11, characterized in that: The heating unit (15) is a vertical shell and tube heat exchanger.

13. A spent fuel reprocessing process system, characterized in that: It comprises a plutonium purification device, a plutonium tail device and a mother liquid destruction evaporator as claimed in any one of claims 1 to 12; The circulation loop of the mother liquor destruction evaporator is connected to the plutonium purification equipment and the plutonium tail end equipment respectively. The mother liquor destruction evaporator is used to evaporate and concentrate the mother liquor produced by the plutonium tail end equipment, and to destroy the oxalic acid in the mother liquor. The liquid treated by the mother liquor destruction evaporator is returned to the plutonium purification equipment to continue to extract and recover plutonium metal.

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