A volatile fission product trapping device and method of trapping

Abstract

The present application relates to a kind of volatile fission product trapping device and trapping method generated in spent fuel dry reprocessing, the device includes catalytic reaction device, dryer 1, fixed bed adsorption device 1, liquid adsorption device, dryer 2 and fixed bed adsorption device 2, by simulating effluent including radioactive tritium, carbon 14, iodine 129 and inert gas Kr and Xe, respectively with non-radioactive hydrogen, carbon dioxide, methyl iodine, Kr and Xe mixed gas as simulation gas source, by each component to each substance in mixed gas is classified and coordinated absorption, finally reach the index that the adsorption trapping efficiency of each effluent simulation is not less than 90%, by simulation can realize the high-efficiency adsorption trapping of the volatile radioactive effluent generated in spent nuclear fuel reprocessing process by the device of the present application.

Description

Technical Field

[0001] This invention relates to the field of industrial environmental protection, specifically to a device and method for capturing volatile fission products generated in the dry reprocessing of spent fuel. Background Technology

[0002] As a safe, clean, and efficient energy source, nuclear fission has become an indispensable part of the global electricity supply. However, while nuclear power reactors continuously generate electricity, they also produce spent fuel almost the same mass as the initial fuel each year. Spent fuel reprocessing is a key step in achieving a closed-loop nuclear fuel cycle. It fully utilizes uranium resources and safely and properly manages radioactive waste, which is of great significance for ensuring the sustainable development of nuclear energy.

[0003] Based on the existing structure of spent fuel in pressurized water reactors, unburned UO2 ceramic pellets must first be separated from the corrosion-resistant cladding zirconium tubes before entering the main reprocessing separation cycle. This process is also known as the initial stage of spent fuel processing. High-temperature oxidation volatilization technology, between the shearing and dissolution of spent fuel elements in traditional spent fuel reprocessing, oxidizes the UO2 ceramic pellets in the spent fuel elements into U3O8 powder, achieving separation of the cladding from the fuel pellets. 3 H, 14 C 129 I, 85 Volatile fissile elements such as Xe / Kr are completely or partially removed in gaseous form, and the released gases are then collected and processed centrally through a gas capture system.

[0004] Tritium is a volatile (elemental tritium) or semi-volatile (tritium water) hydrogen isotope. It is a low-energy β-emitter with a half-life of 12.3 years. Once released, it exists in the biological environment as tritium water, making separation and purification extremely difficult. Among all known methods, catalytic oxidation-adsorption for tritium removal is a mature technology with high processing capacity and the ability to remove low concentrations of tritium, and is considered the most promising technology for widespread application in tritium removal and purification. 129 I has a half-life of 1.57 × 10⁻⁶. 5 a, during post-processing 129 Iodine (I) exists primarily as radioactive elemental iodine and radioactive methyliodine. Radioactive methyliodine is a significant radioactive pollutant; when leaked into the atmosphere, it is easily absorbed by the human thyroid gland, causing glandular damage and even thyroid cancer. Currently, iodine removal processes in spent fuel reprocessing plants abroad mainly employ a two-stage filtration process: liquid absorption and solid adsorption. Radioactive carbon is primarily generated from nitrogen mixed in with fuel through neutron activation. It usually exists in the form of carbon dioxide, and therefore can be treated as a volatile substance. The most important isotope of radioactive carbon is... 14C is a low-energy β-emitter with a half-life of 5730 years, posing a significant hazard to internal radiation. 14 CO2 treatment technologies were developed earlier and are now relatively mature. 85 Kr is a β-γ emitter with a half-life of 10.7 years. If released into the atmosphere, it could be inhaled by humans or cause external radiation exposure. 133 Xe has a half-life of 5.24 days, and adsorption separation is a more ideal method for separating Xe / Kr.

[0005] US Patent Publication US09044737B2 discloses a radioactive iodine adsorbent and a radioactive iodine removal device. It uses a radioactive methyl iodine adsorbent (modified activated carbon) commonly used in nuclear power plants. Specifically, it employs potassium iodide and diethylenetriamine (TEDA) impregnated modified activated carbon as the adsorbent for radioactive methyl iodine. However, TEDA suffers from drawbacks such as high vapor pressure and low flash point, leading to adsorption performance degradation under high humidity conditions. To achieve efficient Xe / Kr capture, various adsorption and separation materials have been developed, including traditional zeolite molecular sieves, porous carbon materials such as activated carbon and carbon molecular sieves, and novel porous materials such as metal-organic frameworks and organic molecular cages that have seen rapid development in recent years. Catalytic oxidation-adsorption detritium removal is a widely used detritium removal process, and a stable and efficient detritium removal catalyst is crucial for its success. The catalyst design determines the efficiency, economy, and feasibility of the detritium removal method. Reaction absorption based on the acid-base neutralization principle is a method for treating... 14 Common methods for CO2 absorption include Ca(OH)2 or Ba(OH)2 slurry or Class I (alkali metal) and Class II (alkaline earth metal) hydroxides.

[0006] Currently, regarding 3 H, 14 C 129 I and 85 There are various methods for capturing fission products such as Kr / Xe, which are complex and involve dispersed and inconvenient equipment. Therefore, there is an urgent need to provide a method and system for capturing volatile fission products generated in the dry reprocessing of spent fuel, so as to achieve continuous adsorption and capture of these fission products. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a device and method for collecting volatile fission products generated during dry reprocessing of spent fuel.

[0008] Specifically, this is achieved through the following technical solution:

[0009] Non-radioactive hydrogen (H2), carbon dioxide (CO2), methyl iodine (CH3I), Kr, and Xe were used as simulated gas sources to simulate radioactive tritium (H2). 3H), carbon ( 14 C), Iodine ( 129 I) and 85 Xe / Kr.

[0010] A volatile fission product collection device includes a gas mixing tank, a catalytic reaction device, a dryer 1, a fixed-bed adsorption device 1, a liquid adsorption device, a dryer 2, and a fixed-bed adsorption device 2 connected in sequence.

[0011] The catalytic reaction device is used to catalytically oxidize H2 to H2O, the dryer 1 is used to absorb the water vapor generated by the catalytic oxidation of H2, the fixed bed adsorption device 1 is used to adsorb CH3I, the liquid adsorption device is used to adsorb CO2, the dryer 2 is used to absorb the moisture carried out by the gas, and the fixed bed adsorption device 2 is used to adsorb Kr and Xe.

[0012] The catalytic reaction device is equipped with a heating device and is filled with a noble metal catalyst, which is alumina solid powder supported on a noble metal. The noble metal catalyst catalytically oxidizes H2 to H2O, and the oxidation conversion rate of H2 is not less than 95%.

[0013] The dryer 1 is a fixed-bed drying device equipped with a heating device. The fixed-bed drying device contains an adsorbent, which is dry silica gel or CaO, and the water vapor absorption efficiency is not less than 90%.

[0014] The fixed-bed adsorption device 1 is equipped with a heating device and a fixed bed, and the fixed bed is filled with a silver-based adsorbent. The adsorption efficiency of CH3I is above 98%. The silver-based adsorbent is one or more of silver zeolite, silver nitrate-impregnated alumina, or silver nitrate-impregnated silica gel.

[0015] The liquid adsorption device is equipped with a gas inlet pipe and a gas outlet pipe, and industrial liquid alkali is installed inside the liquid adsorption device. The outlet of the gas inlet pipe is located in the lower middle part of the industrial liquid alkali. Gas discharged from the fixed bed adsorption device 1 is introduced through the gas inlet pipe to adsorb CO2 in the industrial liquid alkali. The CO2 adsorption efficiency is over 90%.

[0016] The dryer 2 is a fixed-bed drying device equipped with a heating device. The fixed-bed drying device contains an adsorbent, which is dry silica gel or CaO.

[0017] The fixed bed adsorption device 2 is filled with activated carbon or activated carbon fiber.

[0018] Preferably, the catalytic reaction device is a fixed-bed plug flow reactor; the dryer 1 is a fixed-bed drying tower.

[0019] Preferably, the precious metal is one or both of Pd or Pt.

[0020] Preferably, the noble metal catalyst is a Pt-Pd composite supported alumina, wherein the content of Pt is 1-3 wt%, the content of Pd is 2-5 wt%, and the balance is supported alumina.

[0021] Preferably, the silver-based adsorbent is silver nitrate-impregnated silica gel. The specific preparation method of the silver nitrate-impregnated silica gel is as follows: the silica gel is heated at 120-138°C and kept at that temperature for 2.2-3.5 hours. Then, under normal pressure, the silica gel obtained after heating and holding is immersed in a 0.8-1.6 mol / L silver nitrate solution for 1.5-2.5 hours. The liquid is then poured out, and the solid substance obtained is silver-impregnated silica gel. The silver-impregnated silica gel is then dried at 128-135°C for 2.5-3.5 hours to obtain the silver nitrate-impregnated silica gel product.

[0022] Preferably, the activated carbon is coconut shell activated carbon, fruit shell activated carbon, or coal-based activated carbon.

[0023] Preferably, the fixed-bed adsorption device 2 is filled with activated carbon fibers, the single filament diameter of which is 10-20 μm, the average pore size is 1-4 nm, and the specific surface area is 1000-1200 m². 2 / g.

[0024] A method for capturing volatile fission products, using the aforementioned volatile fission product capturing device, includes the following steps:

[0025] (1) A mixture of H2 with a volume concentration of 0.0005–0.20%, CO2 with a volume concentration of 0.50–15.0%, CH3I with a volume concentration of 0.008–2.0%, Xe with a volume concentration of 0.04–4.0%, Kr with a volume concentration of 0.004–0.4%, N2 with a volume concentration of 76–80%, and the remainder being oxygen (the components of which are H2, CO2, CH3I, Xe, and Kr) and a carrier gas is mixed in a mixing tank and then discharged into the catalytic reaction device. The flow rate of the mixed gas is 50–200 mL / min, and the flow rate of the carrier gas is 100–400 mL / min.

[0026] (2) In the catalytic reaction device, the catalytic temperature inside the catalytic reaction device is heated to 150-400°C by a heating device, and the H2 in the gas entering the catalytic reaction device is catalytically oxidized to H2O by the noble metal catalyst filled inside. The amount of the noble metal catalyst is 10-40g. Then the gas after the reaction is discharged and discharged into the dryer 1.

[0027] (3) The temperature inside the dryer 1 is heated to 130-160°C using the heating device installed inside the dryer 1. The H2O in the discharged gas is adsorbed by the adsorbent inside the dryer 1, and then the treated gas is discharged into the fixed bed adsorption device 1.

[0028] (4) The temperature of the fixed bed is heated to 170-200°C by the heating device set in the fixed bed adsorption device 1. The silver-based adsorbent in the fixed bed adsorbs CH3I in the discharged gas, and then the treated gas is discharged into the fixed bed adsorption device 1.

[0029] (5) The gas after step (4) is discharged through the gas inlet pipe of the liquid adsorption device, and CO2 in the gas is adsorbed by industrial liquid alkali, wherein the mass percentage concentration of industrial liquid alkali is 30-48%. Then the treated gas is discharged into dryer 2 through the gas outlet pipe.

[0030] (6) The temperature inside the dryer 2 is heated to 130-160°C using the heating device inside the dryer 2. The H2O in the discharged gas is adsorbed by the adsorbent inside the dryer 2, and then the treated gas is discharged into the fixed bed adsorption device 2.

[0031] (7) Set the adsorption temperature in the fixed bed adsorption device 2 to 0-30℃, and adsorb Kr and Xe in the discharged gas by activated carbon or activated carbon fiber, and then discharge the gas.

[0032] (8) The gas discharged from the fixed bed adsorption device 2 is detected to obtain the gas after the volatile fission products generated in the dry reprocessing of spent fuel are captured.

[0033] Preferably, the adsorbent in the dryer 1 is silica gel, and the amount of silica gel used is 5-20g; the carrier gas is one or more of nitrogen, air, carbon dioxide and helium.

[0034] Preferably, the industrial liquid alkali is a sodium hydroxide solution, and the amount of industrial liquid alkali used is 300-1000 mL.

[0035] The technical advantages of this invention are as follows:

[0036] (1) The method and system for capturing volatile fission products generated in the dry reprocessing of spent fuel disclosed in this invention can achieve a gas adsorption and capture efficiency of not less than 90% for simulated radioactive fission products. The catalytic reaction, solid adsorption, and liquid adsorption modules are set independently, which can be disassembled as a whole and the device is easy to maintain; it can meet the pretreatment requirements for capturing radioactive gas flows of different concentrations and volumes, has strong applicability, compact structure and small footprint; at the same time, by setting the parameters of each step in the method, especially the close coordination between each component and each step (that is, each component does not play its own independent role, but affects each other), the adsorption efficiency of each component is greatly improved.

[0037] (2) The hydrogen catalysis of this invention uses alumina solid powder supported by noble metals as the catalyst, which exhibits higher activity at lower temperatures compared to metal oxide catalysts. Using alumina as a support fully supports the active components, ensuring good dispersion and increasing catalyst strength. Furthermore, the hydrophobic alumina support overcomes the influence of water vapor on the catalyst, reducing catalyst cost while ensuring high catalytic activity. Preferably, Pt-Pd supported alumina is used, achieving a hydrogen conversion efficiency of over 95%.

[0038] (3) The Xe / Kr adsorption of the present invention preferably uses activated carbon fiber. Compared with activated carbon, the activated carbon fiber with its specially designed single filament diameter, average pore size, and specific surface area has small and uniform micropore size, simple structure, fast adsorption rate, and easy desorption, making it more suitable for Xe / Kr in the specific composition gas of the present invention. At the same time, this design has a large contact area with the adsorbate, which can achieve uniform contact and adsorption, so that the adsorbent material can be fully utilized. The ultra-micropores in the activated carbon fiber have a high adsorption force for Xe / Kr. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the frame of the volatile fission product collection device of the present invention.

[0040] Wherein: 1-mixing tank, 2-catalytic reaction device, 3-dryer 1, 4-fixed bed adsorption device 1, 5-liquid adsorption device, 6-dryer 2, 7-fixed bed adsorption device 2, 8-gas composition detector, A-mixed gas containing component gas, B-carrier gas. Detailed Implementation

[0041] Example 1

[0042] like Figure 1As shown, the adsorption units are connected sequentially. A mixture of H2, CO2, CH3I, Kr, and Xe is introduced into the component gas end (a mixed gas containing the component gases). The concentrations are: H2 0.001%, CO2 1.50%, CH3I 0.02%, Xe 1.0%, Kr 0.1%, N2 75.96%, and O2 21.42%. The flow rate of the mixed gas is 50 mL / min. High-purity helium is introduced into the carrier gas end at a flow rate of 100 mL / min. After gas mixing, a gas homogeneity test is performed. The outlet gas of the mixing tank is continuously collected at 5-minute intervals. A standard deviation of less than 3% for the concentration of each gas component is considered acceptable. The component gas and carrier gas are mixed in a mixing tank and then introduced into the catalytic reaction device (in this embodiment, it is set as a catalytic reaction furnace), and pass through the dryer 1, adsorption bed 1 (fixed bed adsorption device 1), liquid adsorption device, dryer 2 and adsorption bed 2 (fixed bed adsorption device 2) in sequence.

[0043] The catalytic reactor was set at 150℃ and contained 10g of Pt-Pd supported alumina (Pt content 2%, Pd content 3%). Dryer 1 contained 5g of dry silica gel, and its temperature was controlled at 150℃. Adsorption bed 1 was set at 180℃ and contained silver nitrate-impregnated silica gel. The liquid adsorption device contained 300mL of industrial alkali solution with a concentration of 35%. Dryer 2 contained 5g of dry silica gel. Adsorption bed 2 contained activated carbon fibers with an average pore size of 2nm, and its temperature was controlled at 20℃. After 30 minutes of reaction, the concentrations of H2, CO2, CH3I, Kr, and Xe in the tail gas were measured. H2 was detected using a hydrogen-helium mass spectrometer, CO2 using a laser concentration detector, CH3I using an ECD gas chromatograph, and Kr and Xe using a mass spectrometer.

[0044] Calculate the adsorption efficiencies of H2, CO2, CH3I, Kr, and Xe. The adsorption rates of each gas are shown in Table 1.

[0045] Example 2

[0046] A mixture of H2, CO2, CH3I, Kr, and Xe is introduced into the component gas phase. The concentrations are: H2 0.20%, CO2 12.0%, CH3I 1.5%, Xe 4.0%, Kr 0.4%, N2 63.88%, and O2 18.02%. The flow rate of the mixture is 150 mL / min. High-purity helium is introduced into the carrier gas phase at a flow rate of 300 mL / min. After the gas mixture is prepared, a uniformity test is performed. The outlet gas of the mixing tank is continuously sampled at 5-minute intervals. The standard deviation of the concentration measurement results for each gas component is less than 3%, which meets the standard. After the component gas and carrier gas are mixed in the mixing tank, they are introduced into the catalytic reactor, passing sequentially through dryer 1, adsorption bed 1, liquid adsorption device, dryer 2, and adsorption bed 2.

[0047] The catalytic reactor was set at 250℃ and contained 30g of Pt-Pd supported alumina (Pt content 2%, Pd content 3%). Dryer 1 contained 20g of dry silica gel, and its temperature was controlled at 150℃. Adsorption bed 1 was set at 180℃ and contained silver nitrate-impregnated silica gel. The liquid adsorption device contained 800mL of industrial alkali solution with a concentration of 35%. Dryer 2 contained 20g of dry silica gel. Adsorption bed 2 contained activated carbon fibers with an average pore size of 2nm, and its temperature was controlled at 20℃. After 30 minutes of reaction, the concentrations of H2, CO2, CH3I, Kr, and Xe in the tail gas were measured. H2 was detected using a hydrogen-helium mass spectrometer, CO2 using a laser concentration detector, CH3I using an ECD gas chromatograph, and Kr and Xe using a mass spectrometer.

[0048] The adsorption efficiencies of H2, CO2, CH3I, Kr, and Xe, as well as the adsorption coefficients of Kr and Xe by activated carbon fiber, were calculated. The adsorption rates of each gas are shown in Table 1.

[0049] Example 3

[0050] A mixture of H2, CO2, CH3I, Kr, and Xe is introduced into the component gas phase. The concentrations are: H2 0.20%, CO2 12.0%, CH3I 1.5%, Xe 4.0%, Kr 0.4%, N2 63.88%, and O2 18.02%. The flow rate of the mixture is 150 mL / min. High-purity helium is introduced into the carrier gas phase at a flow rate of 300 mL / min. After the gas mixture is prepared, a uniformity test is performed. The outlet gas of the mixing tank is continuously sampled at 5-minute intervals. The standard deviation of the concentration measurement results for each gas component is less than 3%, which meets the standard. After the component gas and carrier gas are mixed in the mixing tank, they are introduced into the catalytic reactor, passing sequentially through dryer 1, adsorption bed 1, liquid adsorption device, dryer 2, and adsorption bed 2.

[0051] The catalytic reactor was set at 250℃ and contained 30g of Pt-Pd supported alumina (Pt content 2%, Pd content 3%). Dryer 1 contained 20g of dry silica gel, and the temperature was controlled at 150℃. Adsorption bed 1 was set at 180℃ and contained silver nitrate-impregnated silica gel. The liquid adsorption device contained 800mL of industrial alkali solution with a concentration of 35%. Dryer 2 contained 20g of dry silica gel. Adsorption bed 2 contained coconut shell activated carbon with a particle size of 10-16 mesh, and the temperature of adsorption bed 2 was controlled at 20℃. After 30 minutes of reaction, the concentrations of H2, CO2, CH3I, Kr, and Xe in the tail gas were measured. H2 was detected using a hydrogen-helium mass spectrometer, CO2 using a laser concentration detector, CH3I using an ECD gas chromatograph, and Kr and Xe using a mass spectrometer.

[0052] Calculate the adsorption efficiencies of H2, CO2, CH3I, Kr, and Xe, as well as the adsorption coefficients of activated carbon for Kr and Xe. The adsorption rates of each gas are shown in Table 1.

[0053] Comparative Example 1

[0054] In this comparative example, the gas concentration and flow rate are the same as in Example 2. Adsorption bed 2 is removed, but other settings are the same as in Example 1. The adsorption efficiencies of H2, CO2, CH3I, Kr, and Xe, as well as the adsorption coefficients of activated carbon for Kr and Xe, are calculated. The adsorption rates of each gas are shown in Table 1.

[0055] Table 1

[0056]

[0057] As shown in Table 1 of the results from the various embodiments and comparative examples, the collection rates of H2, CO2, CH3I, Kr, and Xe using the collection method and device of the present invention can all reach over 90%. In Example 2, the gas concentration and flow rate are higher than in Comparative Example 1, resulting in improved adsorption rates and enhanced adsorption effects for each gas. Compared to Example 2, Example 3 uses coconut shell activated carbon as the adsorbent for Xe / Kr. Under certain adsorption conditions, the adsorption effect of coconut shell activated carbon on xenon / kr is not as good as that of activated carbon fiber. The pore size and micropore volume have a significant impact on the xenon / kr adsorption performance. The ultrapores in activated carbon fiber have a higher adsorption force for xenon / kr, indicating that the adsorption effect of activated carbon fiber preferred in the present invention is more obvious. In Comparative Example 1, no xenon / kr collection unit was set up, but its xenon / kr adsorption rate was still around 2%. This indicates that the various components of the present invention are not independent but have a coordinated effect. In the early adsorption units, some xenon / kr is also adsorbed by dry silica gel or silver nitrate-impregnated silica gel, thus proving the existence of coordinated cooperation between the various components and steps of the present invention.

Claims

1. A method for capturing volatile fission products, characterized in that, The volatile fission product capture device comprises a gas mixing tank, a catalytic reaction unit, a dryer 1, a fixed-bed adsorption unit 1, a liquid adsorption unit, a dryer 2, and a fixed-bed adsorption unit 2 connected in sequence. Non-radioactive H2, CO2, CH3I, Kr, and Xe are used as simulated gas sources to simulate radioactivity. 3 H, 14 C 129 I, 85 Kr and 85 Xe; includes the following steps: (1) A mixture of H2 with a volume concentration of 0.0005~0.20%, CO2 with a volume concentration of 0.50~15.0%, CH3I with a volume concentration of 0.008~2.0%, Xe with a volume concentration of 0.04~4.0%, Kr with a volume concentration of 0.004~0.4%, N2 with a volume concentration of 76~80%, and the remainder being oxygen, is mixed with the carrier gas in a mixing tank and then discharged into the catalytic reaction device. The flow rate of the mixed gas is 50~200 mL / min, and the flow rate of the carrier gas is 100~400 mL / min. (2) In the catalytic reaction device, the catalytic temperature inside the catalytic reaction device is heated to 150~400℃ by a heating device, and the H2 in the gas entering the catalytic reaction device is catalytically oxidized to H2O by the noble metal catalyst filled inside. The amount of the noble metal catalyst is 10~40g. Then the gas after the reaction is discharged and discharged into the dryer 1. The noble metal catalyst is Pt-Pd composite supported alumina solid powder, wherein the content of Pt is 1~3wt%, the content of Pd is 2~5wt%, and the balance is supported alumina. (3) The temperature inside the dryer 1 is heated to 130~160℃ using the heating device installed inside the dryer 1. The dried silica gel inside the dryer 1 is used to adsorb H2O in the discharged gas. The amount of dried silica gel is 5~20g. Then the treated gas is discharged into the fixed bed adsorption device 1. (4) The temperature of the fixed bed is heated to 170~200℃ using the heating device set in the fixed bed adsorption device 1. The silver-based adsorbent in the fixed bed adsorbs CH3I in the discharged gas, and then the treated gas is discharged into the liquid adsorption device. (5) The gas after step (4) is discharged through the gas inlet pipe of the liquid adsorption device, and CO2 in the gas is adsorbed by sodium hydroxide solution. The mass percentage concentration of sodium hydroxide solution is 30~48%, and the amount is 300~1000mL. Then the treated gas is discharged into the dryer 2 through the gas outlet pipe. (6) The temperature inside the dryer 2 is heated to 130~160℃ using the heating device installed inside the dryer 2. The H2O in the discharged gas is adsorbed by the adsorbent inside the dryer 2, and then the treated gas is discharged into the fixed bed adsorption device 2. (7) The fixed bed adsorption device 2 is filled with activated carbon fibers. The diameter of the single filament of the activated carbon fibers is 10~20μm, the average pore size is 1~4nm, and the specific surface area is 1000~1200m². 2 / g; The ultra-micropores in the activated carbon fiber can adsorb Xe / Kr at a high level; The adsorption temperature in the fixed bed adsorption device 2 is set to 0~30℃, and the activated carbon fiber adsorbs Kr and Xe in the discharged gas, and then the gas is discharged. (8) Detect the gas discharged from the fixed bed adsorption device 2.

2. The method for capturing volatile fission products according to claim 1, characterized in that, The mixing tank is used to mix the incoming gases, the catalytic reaction device is used to catalytically oxidize H2 to H2O, the dryer 1 is used to absorb the water vapor catalytically oxidized from H2, the fixed bed adsorption device 1 is used to adsorb CH3I, the liquid adsorption device is used to adsorb CO2, the dryer 2 is used to absorb the moisture carried out by the gas, and the fixed bed adsorption device 2 is used to adsorb Kr and Xe. The catalytic reaction device is equipped with a heating device, and the noble metal catalyst catalytically oxidizes H2 to H2O, with an oxidation conversion rate of H2 of not less than 95%. Dryer 1 is a fixed-bed drying device equipped with a heating device. The fixed-bed drying device contains an adsorbent, which is dry silica gel, and the water vapor absorption efficiency is not less than 90%. The fixed-bed adsorption device 1 is equipped with a heating device and a fixed bed, and the fixed bed is filled with a silver-based adsorbent. The adsorption efficiency of CH3I is over 98%. The silver-based adsorbent is one or more of silver zeolite, silver nitrate-impregnated alumina, or silver nitrate-impregnated silica gel. The liquid adsorption device is equipped with a gas inlet pipe and a gas outlet pipe, and industrial liquid alkali is installed inside the liquid adsorption device. The outlet of the gas inlet pipe is located in the middle and lower part of the industrial liquid alkali. The gas discharged from the fixed bed adsorption device 1 is introduced through the gas inlet pipe to adsorb CO2 in the industrial liquid alkali. The CO2 adsorption efficiency is over 90%. Dryer 2 is a fixed-bed drying device equipped with a heating device. The fixed-bed drying device contains an adsorbent, which is dry silica gel or CaO. The modules for catalytic reaction, solid adsorption, and liquid adsorption are set up independently and can be disassembled as a whole.

3. The method for capturing volatile fission products according to claim 2, characterized in that, The catalytic reaction device is a fixed-bed plug flow reactor; the dryer 1 is a fixed-bed drying tower.

4. The method for capturing volatile fission products according to claim 2, characterized in that, The silver-based adsorbent is silver nitrate-impregnated silica gel. The specific preparation method of the silver nitrate-impregnated silica gel is as follows: the silica gel is heated at 120~138℃ and kept at that temperature for 2.2~3.5h. Then, under normal pressure, the silica gel obtained after heating and holding is immersed in a 0.8~1.6mol / L silver nitrate solution for 1.5~2.5h. The liquid is then poured out, and the solid substance obtained is silver-impregnated silica gel. The silver-impregnated silica gel is then dried at 128~135℃ for 2.5~3.5h to obtain the silver nitrate-impregnated silica gel product.

5. The method for capturing volatile fission products according to claim 2, characterized in that, The carrier gas is one or more of nitrogen, air, carbon dioxide, and helium.

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