Evaporator and PUREX process system

Abstract

The invention discloses an evaporator and a PUREX process system, the evaporator comprises a heating chamber and a separation chamber, the heating chamber is an annular space heating chamber, the annular space heating chamber is provided with a feed liquid inlet and a concentrated liquid outlet, a heating piece is arranged outside the heating chamber, and the hollow part is filled with neutron poison; the bottom of the separation chamber is communicated with the top of the heating chamber, a secondary steam outlet is formed in the top of the separation chamber, and a leacheate inlet is further formed in the separation chamber. The evaporator is simple in structure, large in capacity, long in discharging compartment time, low in operation frequency, high in purification efficiency, capable of meeting critical safety and quite stable in operation, evaporation and concentration of plutonium-containing feed liquid can be achieved, plutonium in a post-treatment plant can be recycled, and plutonium loss is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of spent fuel post-processing, and in particular to an evaporator and a PUREX process system. Background Art

[0002] At present, the spent fuel reprocessing process mainly adopts the PUREX process, which mainly includes the head-end process, the chemical separation process and the tail-end process (including the uranium tail and the plutonium tail). The plutonium-containing liquid (1BP) from the co-decontamination cycle is purified and concentrated by the plutonium purification system in the chemical separation process to prepare a qualified high-concentration plutonium liquid (2BP) to remove the plutonium tail for plutonium conversion. In the plutonium tail-end process, the high-concentration plutonium liquid (2BP) from the plutonium purification system is priced and acidified, and then oxalic acid is added for precipitation. The precipitated slurry is filtered to obtain a plutonium oxalate filter cake and a mother liquor. The mother liquor contains a certain amount of plutonium and needs to be returned to the plutonium purification system for a plutonium purification cycle. However, due to the presence of oxalic acid in the mother liquor, the distribution coefficient of Pu (IV) in the extraction process will be reduced, affecting the plutonium yield.

[0003] Therefore, the oxalic acid in the mother liquor must be destroyed before it is returned to the plutonium purification system for the plutonium purification cycle.

[0004] At present, some plutonium purification circulation systems use reflux extraction schemes, which result in a large retention of plutonium liquid in the system and a large amount of waste liquid. In addition, the mother liquor in the plutonium tail process is destroyed and directly returned to the plutonium purification system for plutonium purification circulation, which will dilute the plutonium concentration of the 1BP plutonium-containing liquid. If an evaporator is added to the above two processes to evaporate and concentrate the plutonium-containing liquid, it can not only simplify the process flow, greatly reduce the amount of waste liquid, and improve the plutonium yield, but also enable the mother liquor to be destroyed by oxalic acid while evaporating and concentrating.

[0005] For the evaporation of plutonium-containing liquid, due to the limitation of criticality safety, the slender natural circulation evaporator is currently commonly used. Although this type of evaporator can meet criticality safety, it is relatively difficult to manufacture and has a small capacity and requires frequent operation. Kettle evaporators are commonly used for evaporation of waste liquid in reprocessing plants. They are simple to manufacture and have a large capacity. However, large processing capacity will make it difficult for ordinary kettle evaporators to meet criticality safety requirements and are not suitable for evaporation of liquid containing more plutonium. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide an evaporator and a PUREX process system in view of the above-mentioned deficiencies in the prior art. The evaporator has a simple structure, a large capacity, a long discharge compartment time, a low operating frequency, a high purification efficiency, and can meet critical safety requirements. The operation is very stable, and the evaporation and concentration of plutonium-containing liquid can be achieved, and plutonium in the reprocessing plant can be recovered to reduce plutonium losses.

[0007] The technical solution of the present invention to solve the above technical problems is:

[0008] According to a first aspect of the present invention, there is provided an evaporator comprising a heating chamber and a separation chamber, wherein:

[0009] The heating chamber is an annular gap heating chamber, which is provided with a feed liquid inlet and a concentrated liquid outlet, a heating element is provided outside the heating chamber, and the hollow part is filled with neutron poison; the bottom of the separation chamber is connected with the top of the heating chamber, the top of the separation chamber is provided with a secondary steam outlet, and the separation chamber is also provided with an eluent inlet.

[0010] Optionally, the width of the annular gap heating chamber is 100 to 200 mm.

[0011] Optionally, the diameter of the separation chamber is greater than 150 mm.

[0012] Optionally, the neutron poison is one or more of boron-containing cement, boron-containing polyethylene and boron-containing resin.

[0013] Optionally, the heating element is a heating ring tube or a heating jacket.

[0014] Optionally, a purification component is provided in the separation chamber, and the purification component is a bubble tower plate.

[0015] Optionally, a demister is also provided in the separation chamber.

[0016] Optionally, the eluent is steam condensate.

[0017] Optionally, a condenser is connected to the secondary steam outlet, and the condensate outlet of the condenser is connected to the eluent inlet through a reflux pipe, so as to condense the steam discharged from the separation chamber in the condenser to obtain steam condensate which is returned to the separation chamber as eluent.

[0018] According to a second aspect of the present invention, there is provided a PUREX process system, comprising a head-end process, a chemical separation process, a tail-end process, and also comprising the above-mentioned evaporator, wherein:

[0019] The feed liquid inlet of the evaporator is connected to the tail-end process, and is used to pass the mother liquid produced in the tail-end process and evaporate and concentrate it to obtain a concentrated liquid; the concentrated liquid outlet of the evaporator is connected to the plutonium purification system in the chemical separation process, and is used to return the concentrated liquid to the plutonium purification system for a plutonium purification cycle.

[0020] Compared with the prior art, the evaporator and PUREX process system of the present invention have

[0021] The following benefits:

[0022] (1) The evaporator has a large capacity, which can be 3 to 6 times that of a natural circulation evaporator. The discharge interval is long, the operation frequency is low, and the concentration multiple can reach 5 to 15 times;

[0023] (2) The heating chamber of the evaporator is an annular gap heating chamber filled with neutron poison. Compared with the commonly used kettle evaporator, it can meet the criticality safety requirements through geometric control and poison control;

[0024] (3) The overall structure of the evaporator adopts a kettle type, which is a kettle evaporator with a simple structure and is easy to process and manufacture;

[0025] (4) Compared with the slender natural circulation evaporator, the large diameter separation chamber is conducive to processing and manufacturing, and can improve the steam purification efficiency.

[0026] (5) The system can evaporate and concentrate plutonium-containing liquid, simplify the process flow, greatly reduce the amount of waste liquid generated, and improve the plutonium yield. The mother liquor can also be destroyed by oxalic acid while evaporating and concentrating. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a vertical view of an evaporator in an embodiment of the present invention;

[0028] Figure 2 4 is a top view of the evaporator in the embodiment of the present invention.

[0029] In the figure: 1-heating chamber; 2-feed liquid inlet; 3-concentrate outlet; 4-separation chamber;

[0030] 5- eluent inlet; 6- secondary steam outlet; 7- bubble cap; 8- weir plate; 9- downcomer;

[0031] 10-tear hole; 11-demister; 12-steam heating loop; 13-steam inlet; 14-non-condensable gas outlet; 15-condensate outlet; 16-neutron poison. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0033] In the process of returning the mother liquor produced in the plutonium tail process of the PUREX process system in the prior art to the plutonium purification system for plutonium purification cycle, the reflux extraction scheme has the problems of large plutonium liquid retention, large amount of waste liquid generated, and dilution of the plutonium concentration of the 1BP plutonium-containing liquid, while the evaporation concentration scheme has the problem of relatively large difficulty in evaporator processing and manufacturing.

[0034] The capacity is small, frequent operation is required, or it is difficult to meet the critical safety requirements. The present invention provides an evaporator that meets the critical safety requirements, including a lower heating chamber and an upper separation chamber, wherein: the heating chamber is an annular gap heating chamber, which is provided with a feed liquid inlet and a concentrate outlet, a heating element for heating the heating chamber is provided outside the heating chamber, and the hollow part is filled with neutron poison to meet the critical safety requirements; the bottom of the separation chamber is connected to the top of the heating chamber, the top of the separation chamber is provided with a secondary steam outlet, and the separation chamber is also provided with an eluent inlet.

[0035] Furthermore, the present invention also discloses a PUREX process system, comprising a head-end process, a chemical separation process, a tail-end process, and the evaporator described above, wherein the feed liquid inlet of the evaporator is connected to the tail-end process, and is used to pass the mother liquor generated in the tail-end process and concentrate it to obtain a concentrated liquid; the concentrated liquid outlet of the evaporator is connected to the plutonium purification system in the chemical separation process, and is used to return the concentrated liquid to the plutonium purification system for a plutonium purification cycle.

[0036] Example 1

[0037] like Figure 1 , Figure 2 As shown, this embodiment discloses an evaporator that meets critical safety requirements, including a heating chamber 1 at the bottom and a separation chamber 4 at the top, wherein:

[0038] The heating chamber 1 is an annular heating chamber with a good geometric shape (e.g., annular, tube-shaped), and is provided with a feed liquid inlet 2 and a concentrated liquid outlet 3. A heating element is provided outside the heating chamber 1, and the heating element heats the heating chamber to evaporate and concentrate the feed liquid in the heating chamber to obtain concentrated liquid and steam. The hollow part of the annular heating chamber is filled with neutron poison 16 to meet criticality safety requirements;

[0039] The bottom of the separation chamber 4 is connected to the top of the heating chamber 1. The top of the separation chamber 4 is provided with a secondary steam outlet 6, and the separation chamber 4 is also provided with an eluent inlet 5 for passing an eluent to purify the steam entering the separation chamber and remove the target product (such as plutonium) entrained therein to improve the yield of the target product.

[0040] In some embodiments, the overall structure of the evaporator is in the form of a kettle, which is a kettle evaporator, has a simple structure, and is easy to process and manufacture.

[0041] In some embodiments, the width of the annular gap heating chamber is 100-200 mm, but is not limited thereto.

[0042] In some embodiments, the diameter of the separation chamber 4 is greater than 150 mm, but is not limited thereto. Specifically, the steam and eluent in the separation chamber 4 contain very little plutonium, and a larger size can also meet the criticality safety requirements, so the size of the separation chamber 4 can be appropriately increased as needed to reduce the empty tower gas velocity of the steam, increase the residence time, reduce the entrainment of mist and foam, and improve the purification efficiency.

[0043] In some embodiments, the neutron poison 16 is one or more of boron-containing cement, boron-containing polyethylene, and boron-containing resin, but is not limited thereto.

[0044] In some embodiments, the eluent is a steam condensate, but is not limited thereto. Specifically, a condenser (not shown in the figure) may be connected to the secondary steam outlet 5 at the top of the separation chamber 1, and the condensate outlet on the condenser is connected to the eluent inlet 5 through a reflux pipe, and the steam discharged from the separation chamber 4 is condensed in the condenser to obtain a steam condensate, which is then returned to the separation chamber 4 through the reflux pipe as the eluent.

[0045] In some embodiments, the heating element is a steam heating loop 12, the inlet end of the steam heating loop 12 is provided with a steam inlet 13, and the outlet end is provided with a condensate outlet 15, wherein the steam inlet 13 is preferably located at the upper part of the steam heating loop 12, and the condensate outlet 15 is located at the lower part of the steam heating loop 12. In addition, the steam heating loop 12 is further provided with a non-condensable gas outlet 14, which is preferably located at the upper part of the steam heating loop 12 and as far away from the steam inlet 13 as possible, for example, located at the opposite side of the steam inlet 13.

[0046] In some embodiments, the heating element may also be a heating jacket, wherein a heating medium inlet is provided at the upper portion of the heating jacket, and a heating medium outlet is provided at the lower portion, and the heating medium flows through the heating jacket.

[0047] In some embodiments, a purification component is provided in the separation chamber 4, and the purification component is located below the eluent inlet 5. Specifically, the purification component can be a bubble cap tray, but is not limited thereto. After the eluent enters the separation chamber from the eluent inlet, the purification component contacts and transfers mass with the steam in the separation chamber to absorb plutonium and other radioactive elements in the steam; at the same time, a small amount of plutonium contained in the eluent can be returned to the evaporator for evaporation and concentration to improve the recovery rate of plutonium.

[0048] The bubble cap tray in this embodiment has the same or similar structure as the common bubble cap tray on the market, including bubble cap 7, weir plate 8, downcomer 9 and tear hole 10, which will not be described in detail here. In addition, in order to reduce the difficulty of processing, bubble cap 7 can directly use standard bubble cap.

[0049] In some embodiments, a demister 11 is further provided in the separation chamber 4, and the demister 11 is located above the eluent inlet 5, for example, at the top of the separation chamber 4. Specifically, the demister 4 can be a cyclone separator or a baffle demister, but is not limited thereto. By providing a demister, mist entrainment in the steam can be removed, effectively preventing product loss.

[0050] Taking the plutonium-containing liquid as an example, the working process of the evaporator in this embodiment is described in detail as follows:

[0051] The plutonium-containing liquid enters the heating chamber of the evaporator from the liquid inlet 2, and the steam enters the steam heating ring tube 12 from the steam inlet 13 to heat the plutonium-containing liquid in the annular gap heating chamber (the hollow part is filled with boron-containing cement). The steam is condensed and discharged from the condensate outlet 15, and the non-condensable gas is regularly discharged from the non-condensable gas outlet 14. During the heating process, the plutonium-containing liquid is heated to boiling, and the boiling gas-liquid mixture enters the bottom of the separation chamber 4, where the gas-liquid mixture is separated. The separated liquid returns to the heating chamber 1 for re-evaporation and concentration, and the steam enters the bubble plate above the separation chamber 4. The eluent enters the separation chamber 4 from the eluent inlet 5, fills the bubble plate, overflows from the weir plate 8 in the bubble plate, and flows to the next bubble plate through the downcomer 9. The steam contacts the eluent through the bubble plate 7 for mass transfer, recovers the plutonium in the steam, and purifies the radioactivity contained. The steam after mass transfer is removed from the entrained droplets by the demister 11 and is discharged through the secondary steam outlet 6. The discharged steam is condensed to obtain a steam condensate containing a small amount of plutonium. The steam condensate is refluxed back to the separation chamber from the feed liquid inlet as an eluent. The eluent absorbs the plutonium in the steam after contacting and mass transfer with the steam, and returns to the heating chamber through the downcomer 9 and the tear hole 10 to be evaporated and concentrated again, thereby improving the recovery rate of plutonium. The plutonium solution (i.e., the concentrated solution) after evaporation and concentration is discharged from the concentrated solution outlet 3.

[0052] Compared with the prior art, the evaporator of this embodiment has the following advantages:

[0053] (1) Large capacity, which can be 3 to 6 times that of natural circulation evaporator, long discharge interval, low operation frequency, and concentration multiples of 5 to 15 times;

[0054] (2) The heating chamber of the evaporator is an annular gap heating chamber filled with neutron poison. Compared with the commonly used kettle evaporator, it can meet the criticality safety requirements through geometric control and poison control;

[0055] (3) The overall structure of the evaporator adopts a kettle type, which is a kettle evaporator with a simple structure and is easy to process and manufacture;

[0056] (4) Compared with the slender natural circulation evaporator, the large diameter separation chamber is conducive to processing and manufacturing, and can improve the steam purification efficiency.

[0057] Example 2

[0058] This embodiment discloses a PUREX process system, including a head-end process, a chemical separation process, a tail-end process, and also includes the evaporator described in embodiment 1, wherein:

[0059] The liquid inlet of the evaporator is connected to the tail process, and is used to pass the mother liquid produced in the tail process and evaporate and concentrate it to obtain a concentrated liquid;

[0060] The concentrated liquid outlet of the evaporator is connected to the plutonium purification system in the chemical separation process to return the concentrated liquid to the plutonium purification system for a plutonium purification cycle.

[0061] Compared with the prior art, the PUREX process system of this embodiment can evaporate and concentrate the plutonium-containing liquid, simplify the process flow, greatly reduce the amount of waste liquid generated, and improve the plutonium yield. The mother liquor can also be destroyed by oxalic acid while being evaporated and concentrated. Moreover, since it includes the evaporator described in Example 1, it has all the advantages of the evaporator described in Example 1.

[0062] 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. An evaporator, characterized in that: It comprises a heating chamber (1) and a separation chamber (4), The heating chamber is an annular gap heating chamber, the annular gap heating chamber is provided with a feed liquid inlet (2) and a concentrated liquid outlet (3), a heating element is provided outside the heating chamber, and a hollow part is filled with a neutron poison (16); The bottom of the separation chamber is communicated with the top of the heating chamber, a secondary steam outlet (6) is provided on the top of the separation chamber, and a washing liquid inlet (5) is also provided on the separation chamber.

2. The evaporator according to claim 1, characterized in that The width of the annular gap heating chamber is 100-200 mm.

3. The evaporator according to claim 1, characterized in that The diameter of the separation chamber is greater than 150 mm.

4. The evaporator according to claim 1, characterized in that The neutron poison is one or more of boron-containing cement, boron-containing polyethylene and boron-containing resin.

5. The evaporator according to claim 1, characterized in that The heating element is a heating ring tube (12) or a heating jacket.

6. The evaporator according to any one of claims 1 to 5, characterized in that: A purification component is arranged in the separation chamber, and the purification component is a bubble cap tray.

7. The evaporator according to claim 6, characterized in that The separation chamber is also provided with a demister (11).

8. The evaporator according to claim 7, characterized in that The eluent is steam condensate.

9. The evaporator according to claim 8, characterized in that The secondary steam outlet is connected to a condenser. The condensate outlet of the condenser is connected to the eluent inlet through a reflux pipe, and is used to condense the steam discharged from the separation chamber in the condenser to obtain steam condensate which is returned to the separation chamber as eluent.

10. A PUREX process system, comprising a head-end process, a chemical separation process, and a tail-end process, characterized in that: Also includes the evaporator according to any one of claims 1 to 9, The liquid inlet (2) of the evaporator is connected to the tail process and is used to introduce the mother liquid produced in the tail process and evaporate and concentrate it to obtain a concentrated liquid; The concentrated liquid outlet (3) of the evaporator is connected to the plutonium purification system in the chemical separation process, and is used to return the concentrated liquid to the plutonium purification system for plutonium purification cycle.

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