Radioactive iodine and compound trapping method

Abstract

The invention discloses a method for trapping radioactive iodine and compounds thereof. The trapping method comprises the following steps: acquiring molten salt in a molten state; introducing tail gas containing radioactive iodine and compounds thereof into the fused salt, and enabling the tail gas to be in full contact with the fused salt and react with the fused salt; after the reaction is completed, separating iodine-containing products captured in the molten salt; new fused salt is supplemented into the fused salt from which the iodine-containing product is separated, the fused salt in the molten state is obtained again, and the steps are repeated. According to the trapping method, after molten salt in a molten state is obtained, tail gas containing radioactive iodine and compounds of the radioactive iodine is introduced into the molten salt, and trapping is achieved through the reaction of the iodine and the compounds of the radioactive iodine in the high-temperature molten salt; an iodine-containing product in the reacted molten salt is separated and purified, and the purified molten salt can be continuously used; the trapping method has the advantages of being high in trapping efficiency, low in cost, simple and convenient in process, capable of effectively reducing secondary waste and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of radioactive waste treatment, and particularly to a method for capturing radioactive iodine and its compounds. Background Art

[0002] Radioactive iodine (mainly I-129 and I-131) is a long-lived radioactive isotope generated during the operation of nuclear reactors and the reprocessing of nuclear fuels. Due to its long half-life, strong mobility, and easy accumulation in the human thyroid gland, it has become a key concern in nuclear waste management. These radioactive iodine and its compounds are mainly released during the shearing and dissolution of spent fuel elements and exist in the form of radioactive gas waste.

[0003] In related technologies, the main method for capturing radioactive iodine and its compounds is the adsorption method, and about 99% of radioactive iodine is adsorbed and filtered by iodine adsorption filters in the gaseous state. These adsorption filters usually contain materials such as silver-loaded adsorbents, which are expensive and difficult to reuse. Moreover, the types of radioactive iodine and its compounds generated during the reprocessing process are relatively complex, and multiple adsorption materials and equipment are often required, resulting in high design, preparation, and operation costs. And when these iodine adsorption filters are decommissioned, a large amount of secondary solid waste containing radioactive iodine will be generated, further increasing the treatment cost. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art or related technologies.

[0005] In view of this, a method for capturing radioactive iodine and its compounds provided by the present invention directly reacts molten salt with the tail gas containing radioactive iodine and its compounds to achieve efficient capture and separation of radioactive iodine and its compounds such as I-129 and I-131, reduce the dependence on expensive adsorbents, and through the purification and reuse of the molten salt, it can also reduce the generation of secondary radioactive waste liquid and solid waste, enhance the adaptability to high-radiation environments, and provide an efficient, environmentally friendly, and economical solution for radioactive waste treatment.

[0006] Specifically, it includes the following technical solutions:

[0007] An embodiment of the first aspect of the present invention provides a method for capturing radioactive iodine and its compounds, and the capturing method includes the following steps:

[0008] Obtain molten salt;

[0009] Introduce the tail gas containing radioactive iodine and its compounds into the molten salt to make it fully contact and react with the molten salt;

[0010] After the reaction is completed, separate the iodine-containing product captured in the molten salt;

[0011] New molten salt is added to the molten salt after the iodine-containing product is separated, and the molten salt is obtained again, and the above steps are repeated.

[0012] Optionally, obtaining the molten salt in a molten state includes:

[0013] A molten salt composed of an alkali metal hydroxide and / or an alkali metal carbonate is heated.

[0014] Optionally, the alkaline molten salt is an alkali metal hydroxide and / or an alkali metal carbonate, the alkali metal hydroxide is one or more of NaOH, KOH and LiOH, and the alkali metal carbonate is one or more of Na2CO3, K2CO3 and Li2CO3;

[0015] Optionally, the heating temperature is 200°C to 1000°C.

[0016] Optionally, the sufficient contact includes any one or more of stirring, increasing the aspect ratio of the reactor, providing parallel sieve plates, and reducing the flow rate of the tail gas containing radioactive iodine and its compounds.

[0017] Optionally, separating the iodine-containing product captured in the molten salt includes:

[0018] The molten salt in the molten state reaches the capacity limit of capturing iodine;

[0019] The iodine-containing product captured and formed in the molten salt is separated.

[0020] Optionally, the separation comprises: cooling crystallization separation; or

[0021] It evaporates after heating and then condenses and separates.

[0022] Optionally, the fractional cooling crystallization is to reduce the temperature of the molten salt after capturing the iodine-containing product to below 500° C., so that the iodide in the molten salt is precipitated in the form of crystals and then separated;

[0023] The volatilization separation is to increase the temperature of the molten salt after capturing the iodine-containing product to above 700° C., so that the iodine-containing product in the molten salt is volatilized and condensed for collection.

[0024] Optionally, the radioactive iodine and its compounds include one or more of elemental iodine, inorganic iodine or organic iodine compounds.

[0025] Optionally, the capture method is used for the tail gas containing radioactive iodine and its compounds generated in the shearing section, dissolution section, and exhaust treatment section of other treatment processes during nuclear fuel post-processing.

[0026] The capture method of this application has the following beneficial effects:

[0027] 1. This application uses molten salt in a molten state to directly react with the tail gas containing radioactive iodine and its compounds, generating corresponding iodides and iodates, effectively capturing the radioactive iodine and its compounds in the tail gas containing radioactive iodine and its compounds, significantly improving the capture efficiency of radioactive iodine, and the loading amount of molten salt can be directly related to the iodine capture amount, especially suitable for the process requirements of treating tail gas containing a large amount of radioactive iodine;

[0028] 2. This application is applicable to processes such as the shearing section and dissolution section in the nuclear fuel reprocessing process, and can effectively purify and remove radioactive iodine and its compounds in the shearing and dissolution tail gases, providing a feasible and efficient solution for the capture and control of iodine-containing tail gases in this link;

[0029] 3. The capture method of this application has a simple process, can be effectively integrated with the existing nuclear fuel reprocessing process, does not require pretreatment operations such as acid and water removal of the tail gas, can directly introduce the tail gas containing radioactive iodine and its compounds into the molten salt to capture the iodine therein, and simultaneously purify the acidic gases and other impurities in the tail gas containing radioactive iodine and its compounds. Combining with the molten salt purification, separation and reuse operations, it can significantly reduce the generation amount of secondary radioactive waste;

[0030] 4. Compared with the traditional adsorption method, the capture method of this application has higher capture efficiency, larger capacity limit and lower secondary waste generation amount, improving the environmental protection and economy of the treatment process, and is more suitable for industrial application;

[0031] 5. The substance composition in the iodine-containing product separated by this application is single, which is convenient for management and subsequent utilization, can be used to prepare transmutation targets, provides convenience for waste treatment, and reduces the complexity in the end-treatment process.

[0032] The above description is only an overview of the technical solution of this application. In order to be able to understand the technical means of this application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of this application more obvious and understandable, the specific implementation manners of this application are specifically given below. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1A flowchart of the steps of a method for trapping radioactive iodine and its compounds according to an embodiment of the present invention. Detailed implementation manners

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] Before further detailed description of the embodiments of the present invention, the orientation terms involved in the embodiments of the present invention, such as "upper part", "lower part", and "side part", do not have the meaning of limiting the protection scope of the present invention.

[0037] To make the technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0038] Figure 1 A flowchart of the steps of a method for trapping radioactive iodine and its compounds according to an embodiment of the present invention.

[0039] As Figure 1 shown, an embodiment of the present invention provides a method for trapping radioactive iodine and its compounds. The trapping method includes the following steps:

[0040] Step 1, obtaining molten salt;

[0041] Step 2, introducing the tail gas containing radioactive iodine and its compounds into the molten salt to make it fully contact and react with the molten salt;

[0042] Step 3, after the reaction is completed, separating the iodine-containing product trapped in the molten salt;

[0043] Step 4, replenishing new molten salt into the molten salt after separating the iodine-containing product, re-obtaining molten salt in a molten state, and repeating the above steps.

[0044] Among them, the capture method includes first obtaining molten salt, then introducing the tail gas containing radioactive iodine and its compounds into the molten salt, enabling the radioactive iodine and its compounds in the tail gas to fully react with the molten salt at high temperature to form iodine-containing products, effectively capturing the radioactive iodine and its compounds in the tail gas containing radioactive iodine and its compounds, significantly improving the capture efficiency of radioactive iodine such as I-129 and I-131, and then separating the formed iodine-containing product from the molten salt. The molten salt is purified and then replenished with new molten salt for reuse, improving the utilization rate of the alkaline molten salt, reducing production costs, and enhancing economic efficiency. Through the capture method of the present application, the molten salt in a molten state directly reacts with the tail gas containing radioactive iodine and its compounds to generate corresponding iodides and iodates, effectively capturing the radioactive iodine and its compounds in the tail gas containing radioactive iodine and its compounds, significantly improving the capture efficiency of radioactive iodine, and the charging amount of the molten salt can be directly related to the iodine capture amount, especially suitable for the process requirements of treating tail gas containing a large amount of radioactive iodine; applicable to processes such as the shearing section and dissolution section in the nuclear fuel reprocessing process, it can effectively purify and remove the radioactive iodine and its compounds in the shearing and dissolution tail gas, providing a feasible and efficient solution for the capture and control of iodine-containing tail gas in this link; the capture method of the present application has a simple process, can be effectively integrated with the existing nuclear fuel reprocessing process, does not require pretreatment operations such as acid and water removal of the tail gas, and can directly introduce the tail gas containing radioactive iodine and its compounds into the molten salt to capture the iodine therein, and at the same time purify the acidic gas and other impurities in the tail gas containing radioactive iodine and its compounds. Combining the molten salt purification, separation, and reuse operations can significantly reduce the generation amount of secondary radioactive waste; compared with the traditional adsorption method, the capture method of the present application has higher capture efficiency, larger capacity limit, and lower secondary waste generation amount, improving the environmental protection and economic efficiency of the treatment process and being more suitable for industrial application; the iodine-containing product separated by the present application has a single substance composition, which is convenient for management and subsequent utilization, can be used to prepare transmutation targets, provides convenience for waste treatment, and reduces the complexity in the end-treatment process.

[0045] Specifically, in step 1, to obtain molten salt, the molten salt composed of alkali metal hydroxides and / or alkali metal carbonates can be heated. The heating of the molten salt can be carried out by resistance heating, microwave heating or induction heating. Generally, the heating temperature is 200°C to 1000°C, and further, the heating temperature can be 500°C to 700°C. The molten salt can be at least one of alkali metal hydroxides and alkali metal carbonates. The alkali metal hydroxides can be one or more of NaOH (sodium hydroxide), KOH (potassium hydroxide), LiOH (lithium hydroxide), and the alkali metal carbonates can be one or more of Na2CO3 (sodium carbonate), K2CO3 (potassium carbonate), Li2CO3 (lithium carbonate). That is to say, the basic molten salt can be at least one of NaOH, KOH, LiOH, Na2CO3, K2CO3 and Li2CO3. In step 4, replenishing new molten salt to the molten salt after separating the iodine-containing product means that the mass ratio of each chemical component in the molten salt in the molten state is restored to the same as that in step 1, that is, adding molten salt with the same components and proportions as in step 1.

[0046] It should be noted that in the capture method of this application, alkali metal hydroxides and / or alkali metal carbonates are used to capture the tail gas containing radioactive iodine and its compounds. Among them, alkali metal hydroxides and alkali metal carbonates have strong working stability in a high-radiation environment, that is, the two will not affect their chemical properties and iodine capture ability in a high-radiation environment. The operation is simple, easy to maintain, and can also reduce the capture cost and increase the capture amount.

[0047] Specifically, place the molten salt in a reactor for heating to form a molten state; pass the tail gas containing radioactive iodine and its compounds into the bottom of the reaction vessel through a corrosion-resistant pipeline; make the tail gas containing radioactive iodine and its compounds fully contact and react with the molten salt until the reaction is completed.

[0048] Specifically, the reactor can be a reactor or a crucible. The tail gas containing radioactive iodine and its compounds is introduced into the lower portion of the reactor through a corrosion-resistant pipe to facilitate a full reaction between the tail gas and the molten salt. The corrosion-resistant pipe can be a corundum tube or a 310S stainless steel tube. This allows the tail gas containing radioactive iodine and its compounds to fully contact and react with the molten alkaline molten salt, ultimately forming iodine-containing products (iodide and iodate). The process of the present application is simple and can be integrated with existing nuclear fuel reprocessing processes. No tail gas pretreatment is required, and the shearing section tail gas and the dissolving section tail gas can be directly dissolved in the alkaline molten salt, effectively capturing the iodine in the tail gas. It can also purify the acidic gases and other impurities in the tail gas, reducing the generation of secondary radioactive waste. The acidic gases are purified into salts through an acid-base reaction with the molten salt, while other impurities, including radionuclides, Cs, Sr, Tc, and other volatile and semi-volatile fission products, can be captured.

[0049] Heating the reactor effectively reduces heat loss, lowers energy consumption, and saves electricity costs. Crucibles are typically made of refractory materials such as graphite, alumina, or magnesium oxide, which are stable at high temperatures. They also have good thermal conductivity and resistance to acid and alkali corrosion, making them suitable for high-temperature heating with alkaline molten salts.

[0050] It should be noted that since the corrosion-resistant pipe needs to be inserted into the molten alkaline molten salt, it is necessary for the corrosion-resistant pipe to have good high temperature resistance and corrosion resistance. The tail gas containing radioactive iodine and its compounds includes one or more of elemental iodine, inorganic iodine compounds, and organic iodine compounds.

[0051] In a feasible embodiment, sufficient contact includes at least one of stirring, increasing the reactor height-to-diameter ratio, providing a sieve plate, and reducing the flow rate of the iodine-containing tail gas.

[0052] Stirring refers to installing a stirring rod within the reactor, which is driven by a motor to rotate. This increases the contact area and reaction efficiency between the alkaline molten salt and the tail gas containing radioactive iodine and its compounds, ensuring sufficient contact and reaction between the alkaline molten salt and the iodine-containing tail gas. Increasing the reactor's aspect ratio can extend the gas path and increase contact time. Installing sieve plates, which are perforated, spaced, parallel sieve plates within the reactor, can alter the upward path of bubbles in the molten salt and extend contact time. By reducing the rate at which the tail gas containing radioactive iodine and its compounds enters the alkaline molten salt, the contact time between the tail gas containing radioactive iodine and its compounds and the alkaline molten salt can also be extended, ensuring sufficient contact. Sufficient contact facilitates the full reaction of the tail gas containing radioactive iodine and its compounds and improves the efficiency of forming iodide and iodate after the tail gas reaction. At least one of the above methods is selected to increase sufficient contact between the tail gas and the alkaline molten salt.

[0053] It should be noted that the contact area between the tail gas and the molten salt can also be increased by reducing the bubble volume, so as to improve the mass transfer, reaction or mixing efficiency and ensure the full contact and reaction between the tail gas and the alkaline molten salt.

[0054] In a feasible implementation, separating the iodine-containing product trapped in the molten salt includes:

[0055] Waiting for the molten salt in the molten state to reach the capacity limit for iodine trapping;

[0056] Separating the iodine-containing product formed by trapping in the molten salt.

[0057] Among them, the alkaline molten salt reaching the capacity limit for iodine trapping refers to the capacity limit of the alkaline molten salt in the molten state, and the capacity limit is mainly related to the content of the effective components in the molten salt. Taking the NaOH monocomponent or NaOH-Na2CO3 binary molten salt as an example, the capacity limit is related to the content of the effective components in the molten salt, which refers to the part of the molten salt that can react with iodine. In terms of mole percentage, the capacity limit range is 60 mol% to 80 mol%, and the effective components are alkali metal hydroxides and / or alkali metal carbonates. It can be understood that a safety margin should be left in the molten salt, and there must be sufficient unreacted molten salt to ensure the iodine absorption effect. The reaction situation in the molten salt can be estimated based on information such as the tail gas flux, iodine and acid gas concentrations, and the total amount of alkaline molten salt added to the molten salt.

[0058] It should be noted that the capacity limit of the molten salt is directly related to the iodine trapping amount. Therefore, the molten salt composed of alkali metal hydroxides and / or alkali metal carbonates is used in this application, which can react with iodine and its compounds. Therefore, this application is suitable for the treatment requirements of a large amount of radioactive iodine-containing tail gas.

[0059] In a feasible implementation, the separation includes: cooling crystallization separation; or

[0060] Condensation separation after heating and volatilization.

[0061] Among them, the reacted alkaline molten salt and the iodine-containing tail gas are discharged into a separation container, and the iodide is separated from the unreacted alkaline molten salt in the separation container. Specifically, separation can be carried out by means of cooling crystallization. The temperature of the substances in the separation container is reduced to below 500 °C, so that the iodides (NaI, KI or NaIO3, KIO3) in the reacted molten salt precipitate in crystal form and then are separated. In this way, the main iodides can precipitate in the form of crystals. Overall cooling or local cooling (cold finger crystallization) can be selected, and then the generated crystals are separated. Or separation can be carried out by means of volatilization separation. The temperature of the substances in the separation container is raised to above 700 °C, so that the main iodides such as NaI, KI or NaIO3, KIO3 in the substances volatilize and then are condensed and collected.

[0062] It should be noted that the separated iodide material has a single composition, which is convenient for management and subsequent utilization. It can be used to prepare transmutation target materials or for subsequent solidification treatment, providing convenience for the treatment of iodine-containing waste and reducing the complexity in the treatment process.

[0063] This application can be used in processes such as the treatment of shear section tail gas in the nuclear fuel reprocessing process. By optimizing the composition of the alkaline molten salt and the operating conditions, radioactive iodine and its compounds in the dissolved tail gas can be effectively purified and removed, and the capture and control of radioactive iodine tail gas are efficiently solved. Among them, the composition of the alkaline molten salt can be alkali metal hydroxide, or alkali metal carbonate, or a mixture of alkali metal hydroxide and carbonate. Compared with the traditional tail gas treatment method, the capture method of this application has a higher capture efficiency. The molten alkaline molten salt has a larger capacity limit and a lower secondary waste generation amount, improving the environmental protection and economy of the iodine-containing tail gas treatment process.

[0064] This application realizes the capture of radioactive iodine and its compounds in the tail gas through a molten alkaline molten salt. Subsequently, the iodine-containing product generated by the capture is separated from the alkaline molten salt by means of cooling crystallization or volatilization condensation, realizing the purification of the captured alkaline molten salt and the management of iodine-containing waste. The separated iodine-containing product crystals can also be used for subsequent applications such as the preparation of transmutation target materials. The purified molten salt can be supplemented with new alkaline molten salt and continue to be used. Further description will be given below in combination with specific embodiments.

[0065] Example 1

[0066] (1) Prepare a small reactor, load a mixture of 100 g of sodium hydroxide and sodium carbonate with a mass ratio of 50:50, and load the mixture into the reactor.

[0067] (2) Heat the small reactor to 600 °C to make the mixture reach a molten state.

[0068] (3) Use air as the carrier gas to introduce the iodine-containing tail gas (in the form of iodine vapor) into a small reactor with a height-to-diameter ratio of 5:1 at a flow rate of 10 mL / min, causing the iodine-containing tail gas to react with the molten salt mixture, and collect the gas discharged from the reactor and measure the iodine content therein.

[0069] (4) React for 6 h. After the ventilation ends, naturally cool to room temperature.

[0070] During the above process, the iodine content is analyzed by means of an ion chromatograph. The capture efficiency of iodine vapor is calculated based on the iodine content in the inlet gas (concentration: 153.6 mg / m 3 ) and the iodine content in the treated tail gas (1.2 mg / m 3 ). The test results show that the one-pass capture efficiency of iodine vapor in the iodine-containing tail gas reaches 99.2% using this scheme.

[0071] Example 2

[0072] (1) Prepare a graphite crucible with a height of 15 cm, and load 100 g of a mixture of potassium hydroxide and potassium carbonate in a mass ratio of 80:20 into the crucible. Place the graphite crucible in a closed reaction device equipped with gas inlets and outlets.

[0073] (2) Use a pit furnace to heat the reaction device to 650 °C, causing the mixture in the graphite crucible (with a height-to-diameter ratio of 6:1) to reach a molten state.

[0074] (3) Use air as the carrier gas to introduce the iodine-containing tail gas (in the form of methyl iodide) into the reaction device at a flow rate of 8 mL / min and introduce it into the bottom of the molten salt, causing the iodine-containing tail gas to fully react with the molten salt, and collect the tail gas and measure the iodine content therein.

[0075] (4) React for 6 h. After the ventilation ends, naturally cool to room temperature.

[0076] During the above process, the iodine content is analyzed by means of an ion chromatograph. The capture efficiency of iodine vapor is calculated based on the iodine content in the inlet gas (concentration: 156.4 mg / m 3 ) and the iodine content in the treated tail gas (0.8 mg / m 3 ). Using this scheme, the one-pass capture efficiency of iodine in the iodine-containing vapor reaches 99.5%.

[0077] Example 3

[0078] (1) Prepare a corundum crucible with a height of 15 cm, and load 100 g of potassium carbonate into the corundum crucible. Place the corundum crucible in a closed reaction device equipped with gas inlets and outlets.

[0079] (2) Use a pit-type muffle furnace to heat the reaction device to 650 °C to make the mixture in the corundum crucible (with a height-to-diameter ratio of 6:1) reach a molten state.

[0080] (3) Use air as a carrier gas to introduce the iodine-containing tail gas (the component is methyl iodide) into the reaction device at a flow rate of 10 mL / min and pass it into the bottom of the molten salt, so that the iodine-containing tail gas fully reacts with the molten salt, and collect the tail gas to measure the iodine content therein.

[0081] (4) React for 6 h. After the ventilation ends, naturally cool to room temperature.

[0082] In the above process, the iodine content is tested and analyzed by means of an ion chromatograph. The capture efficiency of iodine vapor is calculated based on the iodine content in the inlet gas (concentration is 151.7 mg / m 3 ) and the iodine content in the tail gas after treatment (1.4 mg / m 3 ). Using this scheme, the one-pass capture efficiency of iodine in the iodine-containing vapor reaches 99.1%.

[0083] Example 4

[0084] (1) Prepare a graphite crucible with a height of 15 cm and load 100 g of sodium hydroxide into the graphite crucible. Place the graphite crucible into a closed reaction device, and this reaction device is provided with gas inlets and outlets.

[0085] (2) Use a pit-type muffle furnace to heat the reaction device to 650 °C to make the mixture in the graphite crucible (with a height-to-diameter ratio of 6:1) reach a molten state.

[0086] (3) Use air as a carrier gas to introduce the iodine-containing tail gas (the component is methyl iodide) into the reaction device at a flow rate of 8 mL / min and pass it into the bottom of the molten salt, so that the iodine-containing tail gas fully reacts with the molten salt, and collect the tail gas to measure the iodine content therein.

[0087] (4) React for 18 h. After the ventilation ends, by means of cold finger crystallization, locally cool the device to 500 °C and keep it warm for 30 min, then take out the cold finger device and cool to room temperature.

[0088] (5) Separate the molten salt on the cold finger device and conduct characterization and analysis.

[0089] In the above process, the iodine content is tested and analyzed by means of an ion chromatograph.

[0090] For the composition and structure characterization and analysis of the separated iodine-containing product, means such as XRD and scanning electron microscopy are used. For the capture efficiency of iodine vapor, it is calculated based on the iodine content in the inlet gas (concentration is 1032.8 mg / m 3 ) and the iodine content in the tail gas after treatment (7 mg / m 3 ).

[0091] By analyzing the iodine content in the tail gas and the composition and structure of the separated products, the one-pass capture efficiency of iodine in the iodine-containing steam using this solution reaches 99.3%, and the separated iodide is mainly sodium iodide.

[0092] It can be understood that in Examples 1 to 3, the gas inlet time is 6 hours. Therefore, less gas is introduced into the molten salt and less crystallization occurs. Therefore, only the capture efficiency can be calculated, and the analysis of the main components of the crystallization cannot be carried out. In Example 4, the gas inlet time is 18 hours, and more crystallization can be obtained. Therefore, the component analysis of the iodide in the crystallization can be carried out.

[0093] As can be seen from the above examples, the capture method of the present application can effectively capture radioactive iodine and its compounds in the iodine-containing tail gas, significantly improve the capture efficiency of radioactive iodine, and the one-pass capture efficiency reaches more than 99%.

[0094] In the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. The term "plurality" means two or more, unless otherwise clearly defined.

[0095] Those skilled in the art will readily think of other embodiments of the present invention after considering the specification and practicing the present invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include the common general knowledge or conventional technical means in the technical field not disclosed by the present invention. The specification and examples are only regarded as exemplary.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for trapping radioactive iodine and its compounds, characterized in that, The capture method comprises the following steps: obtaining molten salt in a molten state; Passing tail gas containing radioactive iodine and its compounds into the molten salt to fully contact and react with the molten salt; After the reaction is completed, separating the iodine-containing product captured in the molten salt; New molten salt is added to the molten salt after the iodine-containing product is separated, and the molten salt is obtained again, and the above steps are repeated.

2. The method for trapping radioactive iodine and its compounds according to claim 1, wherein The step of obtaining the molten salt comprises: A molten salt composed of an alkali metal hydroxide and / or an alkali metal carbonate is heated.

3. The method for trapping radioactive iodine and its compounds according to claim 2, characterized in that, The alkali metal hydroxide is one or more of NaOH, KOH and LiOH, and the alkali metal carbonate is one or more of Na2CO3, K2CO3 and Li2CO3.

4. The method for trapping radioactive iodine and its compounds according to claim 2, characterized in that, The heating temperature is 200°C to 1000°C.

5. The method for trapping radioactive iodine and its compounds according to claim 1, characterized in that, The sufficient contact includes any one or more of stirring, increasing the reactor height-diameter ratio, setting parallel sieve plates, and reducing the flow rate of the tail gas containing radioactive iodine and its compounds.

6. The method for trapping radioactive iodine and its compounds according to claim 1, characterized in that, The step of separating the iodine-containing product captured in the molten salt comprises: The molten salt in the molten state reaches the capacity limit of capturing iodine; The iodine-containing product captured and formed in the alkaline molten salt is separated.

7. The method for trapping radioactive iodine and its compounds according to claim 6, characterized in that, The separation includes: cooling crystallization separation; or It evaporates after heating and then condenses and separates.

8. The method for trapping radioactive iodine and its compounds according to claim 7, characterized in that, The cooling crystallization is to reduce the temperature of the molten salt after capturing the iodine-containing product to below 500° C., so that the iodide in the molten salt is precipitated in the form of crystals and then separated; The volatilization separation is to increase the temperature of the molten salt after capturing the iodine-containing product to above 700° C., so that the iodine-containing product in the molten salt is volatilized and condensed for collection.

9. The method for trapping radioactive iodine and its compounds according to any one of claims 1 to 8, characterized in that, The tail gas containing radioactive iodine and its compounds includes one or more of elemental iodine, inorganic iodine compounds and organic iodine compounds.

10. The method for trapping radioactive iodine and its compounds according to any one of claims 1 to 8, characterized in that, The capture method is used for the tail gas containing radioactive iodine and its compounds generated in the shearing section, the dissolution section, and the exhaust treatment section in other treatment processes during the nuclear fuel post-processing process.

Images