CN111584111B

CN111584111B - Dissolver for spent fuel element and treatment method of dissolving liquid

Info

Publication number: CN111584111B
Application number: CN202010412167.4A
Authority: CN
Inventors: 刘方; 左臣; 郑卫芳; 晏太红; 王辉; 袁中伟; 李传博; 吕洪彬; 刘协春
Original assignee: China Institute of Atomic of Energy
Current assignee: China Institute of Atomic of Energy
Priority date: 2020-05-15
Filing date: 2020-05-15
Publication date: 2022-06-28
Anticipated expiration: 2040-05-15
Also published as: CN111584111A

Abstract

The invention discloses a dissolver for a spent fuel element and a treatment method of a dissolving solution, wherein the dissolver comprises: the shell is internally provided with a cavity, and a dissolving area and a dissolving solution buffer area which are communicated with each other are arranged in the cavity; the process feed port is communicated with the solution buffer zone, and a process raw material for adjusting the valence and/or removing iodine of the spent fuel solution is fed into the solution buffer zone through the process feed port; and the heat preservation device is used for enabling the temperature of the solution buffer zone to meet the preset temperature condition. The technical scheme of the invention can effectively solve the problems that special equipment needs to be additionally arranged outside the dissolver for adjusting the spent fuel dissolving solution liquid in the prior art, the structure is complex, and the operation cost is high.

Description

Dissolver for spent fuel element and treatment method of dissolving liquid

Technical Field

The invention relates to the technical field of spent fuel post-treatment, in particular to a dissolver for a spent fuel element and a treatment method of a dissolving solution.

Background

Spent fuel dissolution is the first chemical treatment process for spent fuel post-treatment. Specifically, the spent fuel elements are crushed and sheared to form short sections, particles, powder and other forms, the solid spent fuel elements in the forms are converted into a solution form through dissolution, qualified dissolved solution is prepared, and qualified feed liquid is prepared for a subsequent chemical separation process. The qualified feed liquid contains a plurality of requirements, such as strict limitation on the concentration of uranium and acid, requirement on the valence state of important nuclide, limitation on the particle size and the amount of micro solid in the solution, and the like. Therefore, the dissolving process is an important starting point of the whole spent fuel chemical treatment process, and lays a foundation for the stable operation of the subsequent chemical separation process.

The spent fuel dissolving solution plays an important role in the extraction effect of the subsequent extraction process and the stable operation of the process, and the spent fuel dissolving solution is subjected to a fine seasoning process before feeding the subsequent extraction process. The "seasoning" process described above generally includes adjusting the price and removing iodine.

Specifically, the valence adjustment is the adjustment of the equivalent state of plutonium and neptunium. Taking the adjustment of the valence state of plutonium as an example, pu (vi) (hexavalent plutonium) generated in the dissolving process needs to be reduced to pu (iv) (tetravalent plutonium), because pu (vi) and pu (iv) have a certain difference in the extraction behavior of the subsequent extraction and separation process, the distribution ratio of plutonium can be increased by reducing plutonium, which is beneficial to increasing the recovery rate of plutonium and achieving a better extraction effect. In the prior art, it is common practice in post-treatment plants to additionally provide a conditioning tank after the dissolver by adding NaNO under thermal conditions₂Or NO₂(N₂O₄) The reagent is used for adjusting the valence state of plutonium.

In addition, a certain process is needed to convert iodide ions in the dissolving solution into volatile simple substance iodine for removal, so that the problems of solvent degradation, organic iodine formation, overproof iodine in uranium plutonium products and the like caused by iodine entering a subsequent process are avoided. In the prior art, it is common practice in post-treatment plants to additionally provide a special iodine-removing apparatus after the dissolver, in which NO is blown in by blowing air after the dissolving solution exits from the dissolver ₂Or addition of non-radioactive KIO₃To reduce the radioactive iodine concentration, thereby achieving iodine removal.

However, in the above prior art, both price adjustment and iodine removal require additional dedicated equipment outside the dissolver for these operations, and the whole system has a complex structure and high running cost.

Disclosure of Invention

The invention mainly aims to provide a dissolver for a spent fuel element and a method for treating a dissolving solution, so as to solve the problems that special equipment needs to be additionally arranged outside the dissolver for regulating the feed liquid of the spent fuel dissolving solution, the structure is complex and the operation cost is high in the prior art.

To achieve the above object, according to one aspect of the present invention, there is provided a dissolver for a spent fuel element, including: the shell is internally provided with a cavity, and a dissolving area and a dissolving solution buffer area which are mutually communicated are arranged in the cavity; the process feed port is communicated with the dissolving solution buffer zone, and a process raw material for adjusting the valence and/or removing iodine of spent fuel dissolving solution is fed into the dissolving solution buffer zone through the process feed port; and the heat preservation device is used for enabling the temperature of the solution buffer zone to meet the preset temperature condition.

Further, the method also comprises the following steps: the tail gas outlet is communicated with the cavity; the tail gas purification system, tail gas purification system's first side and tail gas outlet intercommunication, tail gas purification system's second side and technology feed through mouth intercommunication, obtain nitrogen oxide gas through tail gas purification system purification by tail gas outlet exhaust dissolved tail gas at least part, and nitrogen oxide gas's at least part is let in the solution buffer by technology feed through mouth as the technology raw materials.

Further, the tail gas purification system comprises an iodine adsorption device and/or a gas-liquid separation device.

Further, the tail gas treatment system comprises a follow-up tail gas treatment system and a gas distribution device, wherein the gas distribution device is provided with a gas inlet, a first gas outlet and a second gas outlet, the gas inlet is communicated with the second side of the tail gas purification system, the first gas outlet is communicated with the process feed port, and the second gas outlet is communicated with the follow-up tail gas treatment system.

Further, the device also comprises a bubbling device, wherein the process material through port is communicated with the bubbling device, and at least part of the bubbling device is positioned in the solution buffer zone.

Further, the bubbling device comprises a bubbling pipe and a connecting pipe, the connecting pipe is connected between the process feed port and the bubbling pipe, the bubbling pipe is located in the solution buffer zone, a plurality of bubbling holes are formed in the bubbling pipe and are arranged at intervals along the extending direction of the bubbling pipe, and the opening direction of each bubbling hole faces to the bottom wall of the solution buffer zone.

Further, the bubbling pipe is arranged close to the bottom wall of the solution buffer area, and the distances between each position of the bubbling pipe and the bottom wall of the solution buffer area are equal.

Further, still include: a solution outlet which is communicated with the end part of the cavity, and the solution buffer zone is arranged close to the solution outlet; and the flow blocking piece is positioned in the solution buffer zone and close to the solution outlet.

According to another aspect of the invention, a processing method for processing a spent fuel dissolving solution by using the dissolver is provided, and comprises the following steps: step S10: adding a spent fuel element and a solvent into a dissolving zone in a dissolver for dissolving, and enabling a spent fuel dissolving solution generated by dissolving to enter a dissolving solution buffer zone; step S20: enabling the temperature of the solution buffer zone to meet a preset temperature condition; step S30: introducing a process raw material for adjusting the valence and/or removing iodine of the spent fuel solution into the solution buffer zone; step S40: obtaining qualified spent fuel solution; the sequence of step S20 and step S30 is not fixed.

Further, the dissolver further includes an exhaust gas purification system, and step S30 further includes: at least part of dissolved tail gas generated by dissolving the spent fuel element and the solvent is purified by a tail gas purification system to obtain nitrogen oxide gas, and at least part of the nitrogen oxide gas is introduced into a dissolving solution buffer zone as a process raw material for adjusting the valence and/or removing iodine of a spent fuel dissolving solution.

Further, step S20 further includes: enabling the temperature of the solution buffer zone to meet a first preset temperature condition, wherein the first preset temperature condition is that the temperature is greater than or equal to 60 ℃ and less than or equal to 90 ℃; step S30 further includes: and introducing a process raw material for adjusting the price of the spent fuel solution into the solution buffer zone.

Further, step S20 further includes: enabling the temperature of the solution buffer zone to meet a second preset temperature condition, wherein the second preset temperature condition is that the temperature is greater than or equal to 50 ℃ and less than or equal to 90 ℃; step S30 further includes: and introducing a process raw material for removing iodine from the spent fuel solution into the solution buffer zone.

Further, step S20 further includes: enabling the temperature of the solution buffer zone to meet a third preset temperature condition, wherein the third preset temperature condition is that the temperature is greater than or equal to 80 ℃ and less than or equal to 90 ℃; step S30 further includes: and introducing a process raw material for adjusting the valence of the spent fuel solution and removing iodine into the solution buffer zone.

By applying the technical scheme of the invention, the dissolving zone and the dissolving solution buffer zone are arranged in the cavity, the spent fuel element and the solvent are dissolved in the dissolving zone, and the spent fuel dissolving solution generated by dissolving enters the dissolving solution buffer zone. The solution buffer zone is used as a place for implementing a valence adjustment and/or iodine removal process, the temperature of the solution buffer zone meets a preset temperature condition through the heat preservation device, and process raw materials are introduced into the solution buffer zone through the process feed opening, so that the valence adjustment and/or iodine removal of spent fuel solution in the solution buffer zone is realized. The structure fully and reasonably utilizes the inner space of the dissolver, does not need to increase extra special equipment, can realize the further treatment of the spent fuel dissolving liquid while the spent fuel element in the dissolver is dissolved by only adding process raw materials, namely realizes the synchronous completion of dissolving, adjusting the price and removing iodine, thereby simplifying the process of the post-treatment head end of the spent fuel, simplifying the structural equipment and reducing the operation cost. In addition, the solution can be uniformly mixed in the solution buffer zone, solid residues in the solution can be settled as much as possible, and the obtained solution has better quality.

Drawings

Other objects and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings, and will assist in a comprehensive understanding of the invention.

Fig. 1 is a schematic cross-sectional view of a body portion of a dissolver for spent fuel elements according to an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of the lower half of the cartridge of the dissolver of FIG. 1;

FIG. 3 is a schematic top view of the lower half of the case or the like of the dissolver of FIG. 2;

FIG. 4 is a schematic side view of the lower half of the cartridge of the dissolver of FIG. 2;

FIG. 5 is a sectional view taken along A-A of the dissolver of FIG. 2;

FIG. 6 is a sectional view taken along line B-B of the dissolver of FIG. 4;

FIG. 7 is a schematic cross-sectional view of the upper half structure of the lid or the like of the dissolver of FIG. 1;

FIG. 8 is a schematic top view of the upper half of the dissolver of FIG. 7;

fig. 9 is a schematic structural view of a bubbling device of the dissolver of fig. 1;

fig. 10 is a schematic side view of the sparging device of fig. 9;

fig. 11 is a cross-sectional view taken along line C-C of the bubbling device of fig. 9;

fig. 12 is a schematic structural view of the whole (main body portion, gas distribution device, and exhaust gas purification system) of the dissolver of fig. 1; and

fig. 13 is a schematic process flow diagram of a method of treating a dissolution fluid according to one embodiment of the invention.

It is to be noted that the drawings are not necessarily drawn to scale but are merely shown in a schematic manner which does not detract from the understanding of the reader.

Description of the reference numerals:

11. a case body; 12. a cover body; 20. a dissolution zone; 30. a buffer zone of a dissolving solution; 40. a material inlet is formed in the process; 50. a tail gas outlet; 61. an iodine adsorption device; 62. a gas-liquid separation device; 70. a gas distribution device; 71. a gas inlet; 72. a first gas outlet; 73. a second gas outlet; 80. a bubbling device; 81. a bubbling tube; 811. bulging holes; 82. a connecting pipe; 90. a dissolved solution outlet; 100. a flow blocking member; 110. a material inlet; 120. a solvent inlet; 130. a waste enclosure outlet; 140. a slag discharge port; 150. a feeding structure.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention. It should be apparent that the described embodiment is one embodiment of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.

Unless defined otherwise, technical or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As shown in fig. 1 to 8, the dissolver for the spent fuel element of the present embodiment includes a housing, a material inlet 110, a solvent inlet 120, a spent casing outlet 130, a slag discharge port 140, a feeding structure 150, a dissolving solution outlet 90, a process feed port 40, and a temperature maintaining device. The shell comprises a box body 11 and a cover body 12 covering the box body 11, a cavity is formed in the shell, a feeding structure 150 is arranged in the cavity, a material inlet 110 is communicated with a first end of the feeding structure 150, a solvent inlet 120 and a waste cladding outlet 130 are communicated with a second end of the feeding structure 150, and a dissolving liquid outlet 90 and a slag discharge port 140 are communicated with the end portion of the cavity close to the first end of the feeding structure 150. The cavity is internally provided with a dissolving area 20 and a dissolving solution buffer area 30 which are communicated with each other. The process feed port 40 is in communication with the solution buffer zone 30. And introducing a process raw material for adjusting the valence of the spent fuel solution and removing iodine into the solution buffer zone 30 through a process material inlet 40. The heat preservation device is used for enabling the temperature of the solution buffer zone 30 to meet a preset temperature condition, and the preset temperature condition is a temperature range required by adjusting the price of the spent fuel solution and removing iodine. The heat preservation device is a heat preservation jacket arranged on the periphery of the bottom of the shell, and the temperature of the solution buffer zone 30 can be controlled by adopting a water bath (steam) or electric heating mode.

As shown in fig. 1, fig. 2, fig. 5, and fig. 12, the dissolver of the present embodiment further includes a flow blocking member 100. The cavity forms a dissolving zone 20 corresponding to the area of the feeding structure 150, and a dissolving solution buffer zone 30 is formed between the end surface of the feeding structure 150 and the dissolving solution outlet 90. A baffle 100 is located within the solution buffer zone 30 and proximate the solution outlet 90. The baffle 100 may enhance the baffling of the liquid from the feed structure 150 to the solution outlet 90, thereby further enhancing the cushioning effect. And the solid residue in the solution is settled as much as possible, and the obtained solution has better quality

In this embodiment, the flow blocking member 100 is a flow blocking plate, two side edges of the flow blocking plate are tightly connected to two side walls of the cavity, and a gap is formed between a bottom edge of the flow blocking plate and a bottom wall of the cavity, so that it is ensured that the solution adjusted by the solution can finally flow out from the solution outlet 90. The above-described manner of partitioning the solution buffer area 30 by the flow blocking member 100 is more simple in structure and easy to process and install. Of course, the manner in which the solution buffer 30 is formed is not limited to this, and in other embodiments not shown in the drawings, the solution buffer may be formed of other structures as long as it is ensured that the solution buffer can communicate with the dissolution region and the solution in the solution buffer can be taken out. For example, the solution buffer zone may be defined by a plurality of enclosing plates, and at least one of the enclosing plates has an overflowing hole. The flow baffle 100 is not limited to a flow baffle, and may be another flow baffle, such as a screen, in other embodiments.

When the dissolver starts to operate, the spent fuel elements enter from the material inlet 110 to the first end of the feeding structure 150 and gradually move to the second end of the feeding structure 150 under the rotation of the feeding structure 150. In this process, the solvent (nitric acid) entering from the solvent inlet 120 is contacted with the spent fuel elements in the feed structure 150 (dissolution zone 20) in a counter-current manner. The soluble pellets or powder in the spent fuel element are dissolved into the nitric acid solution to form a solution, which flows into the cavity and into the solution buffer 30. The insoluble cladding of spent fuel elements moves the second end of the feed structure 150 and exits the spent cladding exit 130.

By using the dissolver of the embodiment, the dissolving zone 20 and the dissolving solution buffer zone 30 are arranged in the cavity, the spent fuel element and the solvent are dissolved in the dissolving zone 20, and the spent fuel dissolving solution generated by dissolution enters the dissolving solution buffer zone 30. The solution buffer zone 30 is used as a place for implementing the price adjusting and iodine removing process, the temperature of the solution buffer zone 30 meets the preset temperature condition through the heat preservation device, and the process raw materials are fed into the solution buffer zone 30 through the process feed port 40, so that the price adjustment and iodine removal of the spent fuel solution in the solution buffer zone 30 are realized. Qualified spent fuel solution finally flows out from the solution outlet 90. The structure fully and reasonably utilizes the inner space of the dissolver, does not need to increase extra special equipment, can realize the further treatment of the spent fuel dissolving liquid while the spent fuel element in the dissolver is dissolved by only adding process raw materials, namely realizes the synchronous completion of dissolving, adjusting the price and removing iodine, thereby simplifying the process of the post-treatment head end of the spent fuel, simplifying the structural equipment and reducing the operation cost.

In addition, the buffer 30 is designed for the following main purposes:

first, the buffer space as the solution eliminates the concentration fluctuation of the solution flowing out from the feeding structure 150, so that the flowing out solution maintains a smooth value. The solution flowing out of the feeding structure 150 is influenced by the solid material feeding, the powder in the solid material is dissolved faster, and the concentration of the liquid flowing out of the feeding structure 150 rises along with a short time when the solid material falls into the feeding structure 150 each time. This fluctuation can be eliminated by providing the dissolution buffer 30.

Secondly, the fine powder in the solid material pellets just added partially passes through the liquid outlet on the wrapping shell of the feeding structure 150, and the partially incompletely dissolved powder can be dissolved by the solution buffer zone 30.

It should be noted that the processing process of the spent fuel dissolving solution is a complex and fine process, the qualified spent fuel dissolving solution has certain requirements on the uranium concentration and the acidity, and the adjustment of the uranium concentration and the acidity is actually a problem of the control of the dissolving process. In this embodiment, since the solution buffer 30 provides a buffer for the solution, the solution can be mixed more uniformly, which is advantageous for obtaining a solution with stable uranium and acid concentrations, and it is possible to omit the adjustment process of uranium and acid.

In this embodiment, the process material is introduced into the dissolution buffer 30 through the process material inlet 40 to adjust the valence and remove iodine from the spent fuel dissolution solution, specifically, pu (vi) (hexavalent plutonium) generated in the dissolution process is reduced to pu (iv) (tetravalent plutonium), and I in the dissolution solution is simultaneously reduced to plutonium^-、IO₃ ^-Conversion of ions into I₂It is removed. Of course, in other embodiments, the valency may also be adjusted for other ions, such as neptunium, i.e. neptuniumReducing np (vi) (hexavalent neptunium) to np (v) (pentavalent neptunium); the price of the spent fuel solution alone may be adjusted, or iodine may be removed from the spent fuel solution alone.

In addition, the dissolver of the present embodiment is a continuous dissolver, and the operations of dissolution, price adjustment, iodine removal, solution liquid discharge, feeding of the anti-fuel element, solvent addition and the like of the anti-fuel element can be performed simultaneously. Of course, in another embodiment not shown in the figure, the dissolver may be a batch dissolver, and the process material may be added to the dissolution buffer zone of the batch dissolver to perform the feed liquid adjustment operation.

As shown in fig. 3, 4, 6 to 8, and 12, in the dissolver of the present embodiment, the dissolver further includes an exhaust gas outlet 50 and an exhaust gas purification system. The tail gas outlet 50 is communicated with the cavity, and tail gas generated in the dissolving process of the spent fuel element is discharged from the tail gas outlet 50. The first side of the tail gas purification system is in communication with the tail gas outlet 50 and the second side of the tail gas purification system is in communication with the process feed through 40. The dissolved tail gas discharged from the tail gas outlet 50 is purified by a tail gas purification system to obtain a nitrogen oxide gas, wherein the main components of the nitrogen oxide gas are NO and NO ₂A gas. A part of the nitrogen oxide gas is introduced as a process raw material (process gas) into the solution buffer zone 30 through the process inlet 40. The dissolved tail gas is used as process gas, namely, the dissolved tail gas is partially returned to the dissolver after being purified by the tail gas purification system and is used as a gas source for adjusting the material liquid, and the adjusting price and the iodine removal treatment of the dissolved liquid are carried out, so that the reagent is saved, the whole set of facilities for storing and conveying the reagent are simplified, and the advantages are as follows: 1) greatly simplifying the related reagent feeding equipment; 2) and eliminates the use of NaNO₂The problem of increasing salt content and high level radioactive waste liquid caused by price adjustment; 3) and eliminate N₂O₄The problem of equipment corrosion caused by material supply and storage; 4) and the gas return is favorable for reducing the consumption of dissolved acid and saving the solvent.

It should be noted that the raw material of the valence adjustment and iodine removal process is not limited to the tail gas generated during the dissolution of the spent fuel element, and in other embodiments, a reagent for valence adjustment and iodine removal may be directly and additionally added to the dissolution buffer zone for the dissolution treatment, and the added reagent is the same as the reagent in the conventional treatment method, and is not described herein again.

As shown in fig. 12, in the dissolver of the present embodiment, the off-gas purification system includes an iodine adsorption device 61 and a gas-liquid separation device 62. Dissolved tail gas is discharged from a tail gas outlet 50, and the discharged tail gas firstly passes through a gas-liquid separation device 62 to remove most of water vapor in the gas; and then the gas enters an iodine adsorption device 61, the iodine adsorption device 61 is an iodine adsorption column, silver silica gel is filled in the iodine adsorption column, the iodine in the gas can be adsorbed under the high-temperature condition of 100-150 ℃ (preferably about 120 ℃), the adsorption capacity is large, and the selectivity is good. The treated gas contains relatively pure NO and NO as main components ₂A gas. In this embodiment, the gas-liquid separation device 62 is disposed upstream of the iodine adsorption device 61, so that the purification effect is better. Of course, in other embodiments not shown in the drawings, on the premise of ensuring that the dissolved tail gas can be used for price adjustment and iodine removal after treatment, the positions of the gas-liquid separation device and the iodine adsorption device in the tail gas purification system are exchanged, or only the iodine adsorption device or the gas-liquid separation device is included, or other devices capable of tail gas treatment are included. In addition, the specific type of the iodine adsorbing device 61 is not limited thereto, and in other embodiments, the iodine adsorbing device may be other adsorbents using silver ions as an active material, such as silver-attached zeolite; alternatively, other molecular sieves that adsorb iodine, concentrated nitric acid, and the like may be used. The gas-liquid separation device 62 may employ condensation or centrifugal separation, which is a well-established process and will not be described herein.

As shown in fig. 12, in the dissolver of the present embodiment, the dissolver further includes a subsequent off-gas treatment system (not shown in the figure) and a gas distribution device 70. The gas distribution device 70 has a gas inlet 71, a first gas outlet 72 and a second gas outlet 73. The gas inlet 71 is in communication with the second side of the tail gas cleanup system, the first gas outlet 72 is in communication with the process feed through 40, and the second gas outlet 73 is in communication with the subsequent tail gas treatment system. In order to ensure the gas flow, a power device such as a vacuum pump needs to be arranged in the gas path to provide power for gas circulation. Under normal circumstances The gas distribution device 70 is used for distributing purified gas, wherein a part of the purified gas is introduced into the solution buffer zone 30 as process gas from the process material inlet 40, and a part of the purified gas is introduced into a subsequent tail gas treatment system for subsequent treatment. The dissolved tail gas is purified by the tail gas purification system and then is divided into streams, and the dissolved tail gas can be regarded as the tail gas which flows to a subsequent tail gas treatment system to be pretreated, so that the subsequent treatment effect of the part of the tail gas is favorably improved. The subsequent tail gas treatment system can comprise nitric acid regeneration, water washing, alkali washing, a high-efficiency filter, gas heating, AgX zeolite, a filter and the like, wherein the nitric acid regeneration, the water washing and the alkali washing are used for removing NO and NO in gas₂The gas heating and AgX zeolite treatment are used for adsorbing iodine in gas, and the filter and the high-efficiency filter are used for filtering aerosol. The structure and process applied in the subsequent tail gas treatment system are all existing and are not described herein again.

It should be noted that, if the amount of dissolved tail gas is not very different from the amount required by feed liquid adjustment under certain conditions, or an outlet flowing to a subsequent tail gas treatment system is additionally arranged on the shell, the dissolved tail gas discharged from the tail gas outlet can be completely returned to the dissolved solution buffer zone after being purified, and the dissolved tail gas does not need to be shunted, i.e., a gas distribution device does not need to be arranged; or, the gas distribution device is arranged at the upstream of the tail gas purification system, the dissolved tail gas is firstly shunted by the gas distribution device, one part of the dissolved tail gas enters the tail gas purification system for purification, the dissolved tail gas returns to the dissolver after purification, and the other part of the dissolved tail gas directly enters the subsequent tail gas treatment system for subsequent treatment.

As shown in fig. 1 to 6 and 9 to 11, in the dissolver of the present embodiment, the dissolver further includes a bubbling device 80, the process feed port 40 is communicated with the bubbling device 80, the bubbling device 80 includes a bubbling pipe 81 and a connecting pipe 82, the connecting pipe 82 is connected between the process feed port 40 and the bubbling pipe 81, and the bubbling pipe 81 is located in the buffer zone 30 of the dissolving solution. The bubbling device 80 bubbles in the solution buffer area 30, so that stirring can be increased, the dissolution of solid powder in the solution buffer area 30 is promoted, the solution can be uniformly mixed, and the continuous solution with stable discharge concentration can be obtained. In this embodiment, a plurality of bubble holes 811 are arranged on the bubbling tube 81, the plurality of bubble holes 811 are spaced and uniformly arranged along the extending direction of the bubbling tube 81 and form a row, the opening direction of each bubble hole 811 faces the bottom wall of the solution buffer area 30, and each bubble hole 811 gives out air downwards at the same time, so that sufficient dispersion of gas in the solution can be ensured, the utilization rate of process gas is improved, meanwhile, the stirring effect of the solution in the solution buffer area 30 is better, and the structure is easier to process. Of course, the arrangement of the bubbling holes 811 is not limited to this, and in other embodiments not shown in the drawings, the bubbling holes may be arranged in multiple rows, or the opening directions of the respective bubbling holes may be different or partially the same.

As shown in fig. 3 to 6 and 9 to 11, in the dissolver of the present embodiment, the bubble tube 81 is disposed near the bottom wall of the dissolving solution buffer 30, the first end of the connection tube 82 penetrates out from the end wall of the housing, the first end of the connection tube 82 is communicated with the process material inlet 40, the connection tube 82 bends downward, and the second end of the connection tube 82 is communicated with the bubble tube 81. The cross section of the bottom wall of the solution buffer area 30 is arc-shaped, the bubbling pipe 81 is set to be a bent pipe, and the shape of the bubbling pipe 81 is also arc-shaped with the same radian, so that the distances between each position of the bubbling pipe 81 and the bottom wall of the solution buffer area 30 are equal, the bubbling pipe 81 can be better close to the bottom wall of the solution buffer area 30, the purpose of bubbling from the bottom of the solution is achieved, the dissolution of solid powder at the bottom of the solution buffer area 30 is promoted, and the effect of uniformly mixing the solution is better. Of course, the shape of the bubble tube 81 is not limited thereto, and in other embodiments not shown in the drawings, the bubble tube may have other shapes, for example, the bubble tube may be a straight rod, or a V-shape formed by two straight rods connected together at an angle. Further, the shape of the connection pipe 82 and the connection position with the connection pipe 82 are not limited thereto, and may be designed according to a specific arrangement environment.

It should be noted that, the specific structure of the bubbling device 80 is not limited thereto, and in other embodiments not shown in the drawings, the bubbling device may be another existing bubbling device, and at least a part of the bubbling device is located in the solution buffer area, which is not described herein again. Even in some embodiments, the bubbling device may not be provided, and the purified gas may be directly introduced into the solution buffer zone through a pipeline.

As shown in fig. 1 to 4, in the dissolver of the present embodiment, the slag discharge port 140 of the dissolver is connected to the side wall of the housing and is communicated to the bottom of the dissolving solution buffer zone 30 through a bent pipe, and the slag discharge port 140 is used for extracting extremely fine solid particles (insoluble residues) in the dissolving solution, and the fine particles can not be discharged from the waste cladding outlet 130 along with the cladding and can flow away along with the dissolving solution. After a period of time, the accumulated solid particles are discharged through the slag discharge outlet 140. The generation of tiny insoluble particles (insoluble residues) during the dissolution process is an inherent common phenomenon in the dissolution of spent fuel, so the dissolver must be designed with consideration for the discharge of the insoluble residues. In this embodiment, the slag tap 140 is introduced from the side wall of the housing, rather than being welded by punching from the bottom wall of the housing, in order to reduce the weld on the bottom surface of the continuous dissolver and reduce the risk of corrosion leakage.

In this embodiment, the UO of the spent fuel element₂The dissolved tail gas of the pellet dissolution is used as the process gas used by the spent fuel dissolving liquid seasoning, the price adjustment is similar to the iodine removal process, and the chemical reactions involved in the process of generating and utilizing the process gas are as follows:

UO₂production of NO and NO by pellet dissolution₂Gas:

UO₂+4HNO₃→UO₂(NO₃)₂+2NO₂+2H₂O (1)

UO₂+2.7HNO₃→UO₂(NO₃)₂+0.7NO+1.3H₂O (2)

NO and NO produced₂The gas can be used as a process gas for adjusting price and removing iodine;

when the temperature meets the first preset temperature condition (namely the temperature is more than or equal to 60 ℃ and less than or equal to 90 ℃), NO₂The gas can reduce the plutonium valence state regulating pu (vi) to pu (iv):

PuO₂ ²⁺+NO₂ ^-+2H⁺→Pu⁴⁺+H₂O+NO₃ ^- (3)

when the temperature meets a second preset temperature condition (namely the temperature is more than or equal to 50 ℃ and less than or equal to 90 ℃), NO₂Can be connected with IO₃ ^-Reducing to elemental iodine, thereby achieving iodine expulsion:

2IO₃ ^-+10NO₂+4H₂O→I₂+8H⁺+10NO₃ ^- (4)

IO₃ ^-+I^-+6H⁺→I₂+3H₂O (5)

introducing NO and NO into nitric acid₂Gas with HNO₃Complex reactions occur, eventually there is an equilibrium of various reaction products, the main reactions being as follows:

2NO₂+H₂O→HNO₃+HNO₂ (6)

3HNO₂→HNO₃+2NO+H₂O (7)

2NO+O₂→2NO₂ (8)

therefore, when the nitrogen oxide gas is introduced into the nitric acid, NO and NO in the system₂、NO₂ ^-And NO₃ ^-Are co-existing at the same time.

As shown in fig. 13, the present application further provides a processing method for processing a spent fuel dissolving solution by using the dissolver, which includes the following steps according to an embodiment of the present application:

step S10: adding a spent fuel element and a solvent into a dissolving zone 20 in a dissolver for dissolving, and enabling a spent fuel dissolving solution generated by dissolving to enter a dissolving solution buffer zone 30;

Step S20: enabling the temperature of the solution buffer zone 30 to meet a third preset temperature condition, wherein the third preset temperature condition is that the temperature is greater than or equal to 80 ℃ and less than or equal to 90 ℃;

step S30: dissolved tail gas generated by dissolving the spent fuel element and the solvent is purified by a tail gas purification system to obtain nitrogen oxide gas, and part of the nitrogen oxide gas is introduced into a solution buffer zone 30 as a process raw material for adjusting the price of the spent fuel solution and removing iodine;

step S40: obtaining qualified spent fuel solution;

wherein the nitrogen oxide gas is mainly NO and NO₂The order of gas, step S20 and step S30 is not fixed.

In the treatment method of this embodiment, the spent fuel solution is subjected to price adjustment and iodine removal simultaneously, so the temperature of the solution buffer 30 needs to satisfy the third preset temperature condition. Of course, in other embodiments, if only the spent fuel solution is subjected to the price adjustment operation, the temperature of the solution buffer 30 needs to satisfy the first preset temperature condition, where the first preset temperature condition is that the temperature is greater than or equal to 60 ℃ and less than or equal to 90 ℃; if only the spent fuel solution is subjected to the iodine removal operation, the temperature of the solution buffer zone 30 needs to meet a second preset temperature condition, wherein the second preset temperature condition is that the temperature is greater than or equal to 50 ℃ and less than or equal to 90 ℃.

In addition, the dissolved tail gas generated by dissolving the spent fuel element and the solvent is generally only introduced into the solution buffer zone 30, so that the solution regulation of the solution can be better realized. The specific reasons are as follows:

the iodine in the solution is dissolved from the solid pellet into the solution along with the dissolving process, and the dissolving process can generate NO₂. During the dissolving process, most iodine enters the dissolved tail gas, namely NO exists₂Under the dissolving condition of gas, a small part of iodine is remained in the solution, and NO is introduced at the moment₂The effect of the gas is not very pronounced. NO is introduced after the solution flows out of the dissolution zone 20 (i.e. into the solution buffer zone 30)₂Gas, removing a small portion of residual iodine, and simultaneously, lengthening the solution and NO by a solution buffer zone 30₂The reaction time of the gas achieves a higher ratio of iodine removal.

The valence state of plutonium is regulated by passing PuO₂ ²⁺Regulation to Pu⁴⁺。PuO₂ ²⁺Is produced in the high temperature dissolution process, and the proportion is generally smaller. Is favorable for PuO under the conditions of high temperature and high acid₂ ²⁺Formation and stabilization of (a). HNO₂Can convert PuO into₂ ²⁺Reduction to Pu⁴⁺The reaction speed is higher under the high-temperature condition. The reason for adjusting the price of the solution buffer 30 is that the solution buffer 30 is a high-temperature and high-acid region, and NO is added ₂Gas, both to suppress new PuO₂ ²⁺To generate, or to form, PuO by dissolution₂ ²⁺Regulated to Pu⁴ ⁺。

In this example, taking a pilot scale continuous dissolver with a processing capacity of 1kg/h as an example, the generation and return utilization of the tail gas are as follows:

according to the initial²³⁵The main element composition related to the process in 1kg of spent fuel pellets under the conditions of 3.7 percent of U enrichment degree, 37000MWd/tU combustion and 8-year cooling time is listed in Table 1.

TABLE 1

Suppose UO₂Dissolving the materials according to the formulas (1) and (2) in nitric acid, and calculating according to the treatment amount of 1kg/h to obtain NO and NO generated in the dissolving process₂The tail gas velocity is 33L/h and 94L/h respectively.

The proportions of higher valence neptunium and plutonium produced during the dissolution are respectively 40% and 5%, i.e. at a uranium concentration of 300g/L in the dissolution solution, the concentrations of neptunium and plutonium to be adjusted to valence are respectively 0.14g/L and 0.19 g/L. Assuming iodine is totally expressed as IO₃ ^-The iodine concentration in the solution was 0.13 g/L. Theoretical NO required for adjustment of plutonium and deiodination calculated according to formulas (3) and (4) taking adjustment of the valence of plutonium and deiodination as examples₂The flow rate was 0.34L/h. Compared with the theoretical consumption of iodine removal by adjusting the price, the dissolved tail gas is hundreds of times excessive, but NO is in the actual process ₂The utilization rate of the gas is extremely low, and the utilization rate is determined by a plurality of factors such as the dispersion degree of the gas, the reaction time, the liquid retention time and the like, so that the actual gas addition multiple is often determined by experimental verification.

Assuming that the volume of the solution buffer 30 is about 5L, the discharge rate of the solution is 3.2L/h. The average residence time of the dissolution in the dissolution buffer 30 was calculated to be 1.56 h. The temperature of the buffer zone was designed to be 80 to 90 ℃ and the proportion of the return gas was set to return 20L/h of dissolved tail gas to the buffer zone.

Under the above process conditions, i.e. the temperature is preferably 80 ℃, the retention time is 1.56h, NO₂The bubbling rate is 20L/h, and the NpO is adjusted after price₂ ⁺The proportion is increased to 85 percent, and the Pu is⁴⁺The proportion is improved to more than 99 percent. IO in solution₃ ^-Is at a concentration of 10^-4M to 10^-5M is reduced to 10^-7And M. Completely meets the requirements of subsequent treatment processes on feed liquid price adjustment and iodine removal.

The embodiment is an integrated dissolving process for synchronously adjusting feed liquid by utilizing return of dissolved tail gas and continuous dissolution, belongs to the technical field of spent fuel post-treatment-head end treatment, and is applied to the further preparation process of the feed liquid after dissolution of a spent fuel element. It provides a very suitable environment for dissolving liquid seasoning, and can continuously dissolve and simultaneously regulate liquid. Aiming at the characteristics of similar process conditions of adjusting the valence of the dissolved solution and removing iodine, the unique structure of the continuous dissolver is utilized, the valence state is adjusted and iodine in the dissolved solution is removed while continuous and stable dissolution is realized, and the tail gas treatment process is simplified.

It should also be noted that, in case of conflict, the embodiments and features of the embodiments of the present invention may be combined with each other to obtain new embodiments.

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and the scope of the present invention is subject to the scope of the claims.

Claims

1. A dissolver for a spent fuel element, comprising:

the shell is internally provided with a cavity, and a dissolving area (20) and a dissolving solution buffer area (30) which are communicated with each other are arranged in the cavity;

the process feed port (40) is communicated with the dissolving solution buffer zone (30), and a process raw material for adjusting the valence and/or removing iodine of spent fuel dissolving solution is fed into the dissolving solution buffer zone (30) through the process feed port (40);

and the heat preservation device is used for enabling the temperature of the solution buffer area (30) to meet a preset temperature condition, and the preset temperature condition is a temperature range required for adjusting the price of the spent fuel solution and removing iodine.

2. The dissolver according to claim 1, further comprising:

a tail gas outlet (50) in communication with the cavity;

tail gas clean-up system, tail gas clean-up system's first side with tail gas outlet (50) intercommunication, tail gas clean-up system's second side with technology feed through mouth (40) intercommunication, by tail gas outlet (50) exhaust dissolves at least partial process tail gas clean-up system purifies and obtains nitrogen oxide gas, nitrogen oxide gas at least part conduct the technology raw materials by technology feed through mouth (40) lets in dissolve liquid buffer (30).

3. A dissolver according to claim 2, characterized in that the tail gas cleaning system comprises an iodine adsorption unit (61) and/or a gas-liquid separation unit (62).

4. The dissolver according to claim 2, further comprising a subsequent off-gas treatment system and a gas distribution device (70), the gas distribution device (70) having a gas inlet (71), a first gas outlet (72) and a second gas outlet (73), the gas inlet (71) communicating with the second side of the off-gas purification system, the first gas outlet (72) communicating with the process feed opening (40), the second gas outlet (73) communicating with the subsequent off-gas treatment system.

5. The dissolver according to claim 1, further comprising a bubbling device (80), wherein the process feed (40) is in communication with the bubbling device (80), and wherein the bubbling device (80) is at least partially located within the solution buffer zone (30).

6. The dissolver according to claim 5, wherein the bubbling device (80) comprises a bubbling pipe (81) and a connecting pipe (82), the connecting pipe (82) is connected between the process feed port (40) and the bubbling pipe (81), the bubbling pipe (81) is located in the solution buffer area (30), a plurality of bubbling holes (811) are arranged on the bubbling pipe (81), the plurality of bubbling holes (811) are arranged at intervals along the extending direction of the bubbling pipe (81), and the opening direction of each bubbling hole (811) faces the bottom wall of the solution buffer area (30).

7. The dissolver according to claim 6, wherein the bubbling tube (81) is disposed close to the bottom wall of the solution buffer zone (30), and the distance between each position of the bubbling tube (81) and the bottom wall of the solution buffer zone (30) is equal.

8. The dissolver according to claim 1, further comprising:

a solution outlet (90) in communication with an end of the cavity, the solution buffer zone (30) being disposed proximate to the solution outlet (90);

a flow barrier (100) located within the solution buffer zone (30) and proximate to the solution outlet (90).

9. A method for treating spent fuel dissolving liquid by using the dissolver according to any one of claims 1 to 8, comprising the following steps:

step S10: adding the spent fuel element and a solvent into a dissolving zone (20) in a dissolver for dissolving, and enabling the spent fuel dissolving solution generated by dissolving to enter a dissolving solution buffer zone (30);

step S20: enabling the temperature of the dissolving solution buffer area (30) to meet a preset temperature condition;

step S30: introducing a process raw material for adjusting the valence and/or removing iodine of spent fuel solution into the solution buffer zone (30);

step S40: obtaining qualified spent fuel solution;

Wherein the step S20 and the step S30 are not fixed in order.

10. The process of claim 9, wherein the dissolver further comprises a tail gas cleanup system,

the step S30 further includes: at least part of dissolved tail gas generated by dissolving the spent fuel element and the solvent is purified by the tail gas purification system to obtain nitrogen oxide gas, and at least part of the nitrogen oxide gas is introduced into the dissolving solution buffer zone (30) as a process raw material for adjusting the price of the spent fuel dissolving solution and/or removing iodine.

11. The processing method according to claim 9,

the step S20 further includes: enabling the temperature of the solution buffer area (30) to meet a first preset temperature condition, wherein the first preset temperature condition is that the temperature is more than or equal to 60 ℃ and less than or equal to 90 ℃;

the step S30 further includes: and introducing a process raw material for adjusting the valence of the spent fuel solution into the solution buffer zone (30).

12. The processing method according to claim 9,

the step S20 further includes: enabling the temperature of the solution buffer area (30) to meet a second preset temperature condition, wherein the second preset temperature condition is that the temperature is greater than or equal to 50 ℃ and less than or equal to 90 ℃;

The step S30 further includes: and introducing a process raw material for removing iodine from the spent fuel solution into the solution buffer zone (30).

13. The processing method according to claim 9,

the step S20 further includes: enabling the temperature of the solution buffer area (30) to meet a third preset temperature condition, wherein the third preset temperature condition is that the temperature is greater than or equal to 80 ℃ and less than or equal to 90 ℃;

the step S30 further includes: and introducing a process raw material for adjusting the valence of the spent fuel solution and removing iodine into the solution buffer zone (30).