Activated carbon modification method suitable for different high-temperature accident working conditions of reactor

Abstract

The invention discloses an activated carbon modification method applicable to different high-temperature accident working conditions of a reactor. The method comprises the following steps: S1, hydrophobic modification of activated carbon: spraying a high-boiling-point super-hydrophobic material-perfluorodecyl trimethoxysilane solution on activated carbon fibers; s2, impregnating and modifying the activated carbon, namely impregnating and modifying the activated carbon with high hydrophobicity by using hexamethylenetetramine HMTA with a high boiling point; s3, performing chemical adsorption modification on the activated carbon: spraying a composite material mixed with Al (OH) 3, SiO2-C, SiO2-Cu0 and SiO2-Ag0 as a flame retardant aqueous solution onto the surface of the activated carbon fiber; and step S4, drying the modified activated carbon solution at a low temperature of 60-85 DEG C. The modified activated carbon can effectively adsorb iodine-131 and other radionuclides and hydrogen generated under different high-temperature accident working conditions, the safety of a reactor is improved, and the modified activated carbon has great market application prospects.

Description

Technical Field

[0001] This invention relates to the modification technology of radioactive gas adsorbent materials, and in particular to a method for modifying activated carbon suitable for different high-temperature accident conditions in reactors. Background Technology

[0002] With the widespread adoption of passive safety technologies, the activated carbon adsorption unit in the AP1000 unit can continue to operate even in the event of a power outage. However, during an accident, the system is in a high-temperature environment, where the adsorption capacity of activated carbon for radioactive iodine, such as gaseous I-131 and Xe-133, is significantly reduced. Furthermore, activated carbon is prone to irreversible structural damage in radiation environments. Therefore, it is necessary to ensure that activated carbon retains its ability to adsorb radioactive iodine at high temperatures.

[0003] Existing technologies mainly include the following improvements: improving the radiation resistance of activated carbon by introducing radiation-resistant coatings or doping stabilizers; improving the iodine adsorption capacity of activated carbon by impregnation with KI; improving physical formability by adding binders; and periodically replacing the adsorbent. However, these improvements are either complex in process, the KI impregnating agent is prone to volatilization and inactivation at high temperatures, or they sacrifice the porosity of activated carbon leading to performance degradation, or they artificially increase the complexity of accident handling. Therefore, it is crucial to effectively and conveniently improve the performance of activated carbon under accident conditions and reduce the potential impact on the environment and the health of surrounding residents. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide an activated carbon modification method applicable to different high-temperature accident conditions in reactors.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for modifying activated carbon applicable to different high-temperature accident conditions in reactors, characterized by comprising the following steps: Step S1, hydrophobic modification of activated carbon: Select a high-boiling-point superhydrophobic material—perfluorodecyltrimethoxysilane solution—and spray it onto activated carbon fibers; Step S2, Activated carbon impregnation modification: High-boiling-point hexamethylenetetramine (HMTA) is used to impregnate and modify activated carbon with high hydrophobicity. Step S3, Activated Carbon Chemical Adsorption Modification: A mixture of Al(OH)3 and SiO2-C, SiO2-Cu... 0 SiO2-Ag 0 The composite material was sprayed as a flame retardant aqueous solution onto the surface of activated carbon fiber; Step S4: Dry the modified activated carbon solution at a low temperature of 60℃~85℃.

[0006] A further technical solution of the present invention is that hydrogen adsorption modification is included between steps S3 and S4, specifically by doping an equal mass of copper oxide into activated carbon.

[0007] Compared with the prior art, the present invention has the following characteristics: This invention achieves the adsorption of methyl iodine, hydrogen, etc. under different high-temperature accident conditions in the reactor by using a perfluorodecyltrimethoxysilane solution to hydrophobically modify activated carbon fibers, selecting hexamethylenetetramine (HMTA) to impregnate and modify the activated carbon, and modifying it with flame retardants and copper oxide. This improves the safety of the reactor device and reduces the impact on the surrounding environment during an accident.

[0008] The detailed structure of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0009] Figure 1 This is a flowchart of the activated carbon modification method of the present invention. Detailed Implementation

[0010] Example 1, as Figure 1 As shown, the activated carbon modification method applicable to different high-temperature accident conditions in reactors includes the following steps: Activated carbon in the reactor is mainly used to adsorb radioactive iodine and other aerosol fission products. Radioactive iodine exists in various forms, with methyl iodine being particularly difficult to adsorb. Under normal operating conditions, the temperature inside the containment vessel does not exceed 50°C, at which point the existing modified activated carbon's adsorption capacity for I-131, Xe-133, and Kr-85 meets the requirements. However, activated carbon adsorption is an exothermic process; as the temperature gradually increases, the performance of the activated carbon will significantly decrease. Therefore, when the temperature inside the containment vessel is in the range of 50°C to 150°C under accident conditions, and in the range of 150°C to 200°C under extreme accident conditions, modification of the activated carbon is necessary.

[0011] Step S1, hydrophobic modification of activated carbon The activated carbon fiber is sprayed with a high-boiling-point superhydrophobic material—perfluorodecyltrimethoxysilane solution—to modify the surface of the activated carbon. Utilizing the hydrolysis and condensation reaction principle of silane coupling agents, silane molecules are chemically bonded to the oxygen-containing functional groups on the surface of the activated carbon, endowing the activated carbon surface with superhydrophobic and superoleophobic properties. This ensures that the activated carbon can maintain excellent hydrophobic performance under high temperature and high humidity environments, thereby achieving good physical adsorption of radioactive methyl iodine, Xe-113, and Kr-85.

[0012] Perfluorodecyltrimethoxysilane, with the molecular formula C13H13F17O3Si, possesses a long carbon chain, giving it stronger hydrophobicity and oleophobicity. This strong hydrophobicity and oleophobicity are particularly important under extreme conditions, helping to protect the surface of activated carbon from moisture and oil. Furthermore, its perfluorocarbon chain is chemically very stable due to the high stability of the CF bond, an important consideration for activated carbon used in extreme chemical environments, as it helps ensure that the modifier does not decompose or become ineffective during use. The chemical structure of perfluorodecyltrimethoxysilane makes it superior in extreme environments, including high-temperature stability and resistance to chemical corrosion, making it more suitable for activated carbon modification under extreme conditions.

[0013] Step S2, Activated carbon impregnation modification Highly hydrophobic activated carbon was modified by impregnation with hexamethylenetetramine (HMTA), a high-boiling-point amine. HMTA is a heterocyclic amine with a strong complexing ability for methyl iodine. Its boiling point is as high as 246°C, and it still has a strong chemical adsorption capacity for methyl iodine under high-temperature accident conditions.

[0014] Step S3, Activated Carbon Chemical Adsorption Modification Under high-temperature accident conditions, the adsorption capacity of activated carbon decreases significantly, and it may even have almost no adsorption capacity for radioactive inert gases Xe-133 and Kr-85. In this situation, the decay heat generated by radioactive decay and the heat generated during adsorption can easily lead to localized overheating, potentially causing the activated carbon to ignite. Therefore, it is necessary to incorporate flame-retardant materials to ensure stable operation of the device. Specifically, this involves mixing Al(OH)3 with SiO2-C and SiO2-Cu... 0 SiO2-Ag 0 The composite material, used as a flame retardant aqueous solution, is sprayed onto the surface of activated carbon fibers, forming a flame-retardant protective layer that completely prevents ignition of the activated carbon. Al(OH)3 and SiO2-C can form a Si-OC ceramic layer under high temperature, isolating oxygen and preventing combustion. Furthermore, copper and silver can directly react with iodine under heating conditions to form copper iodide and silver iodide, increasing the adsorption capacity for I-131 in the chemical adsorption reaction. Due to the high cost of Ag in practical applications, a suitable Ag-Cu ratio is selected based on the application scenario to reduce costs.

[0015] Step S4: Dry the modified activated carbon solution at a low temperature of 60℃~85℃.

[0016] Example 2, applicable to activated carbon modification under different high-temperature accident conditions in reactors, is basically the same as in Example 1, except that hydrogen adsorption modification is included between steps S3 and S4. This is because when a reactor accident occurs and the temperature rises to over 150°C to 200°C or even over 200°C, the zirconium alloy material undergoes a very violent chemical reaction with the high-temperature water vapor. During this reaction, a large amount of hydrogen is inevitably generated, causing the hydrogen concentration in the activated carbon adsorption device and containment vessel to continuously increase. Although the passive hydrogen recombination device can keep the hydrogen concentration below 4% to ensure the nuclear power plant remains in a safe and stable operating state, in extreme situations such as over-design-baseline accidents, the hydrogen concentration will gradually exceed the safe range as it continues to rise, potentially causing hydrogen explosions and other secondary disasters, thus comprehensively affecting the overall safety of the nuclear power plant. By incorporating an equal mass of copper oxide into activated carbon, the characteristic of copper oxide reacting with hydrogen at high temperatures to generate copper can be utilized to reduce the hydrogen concentration and decrease the risk of hydrogen explosion. The generated copper can also significantly enhance the chemical adsorption effect of activated carbon on iodine.

[0017] The above implementation examples reflect the application levels and occasions of the present invention. Any technical solution that achieves the purpose of the present invention by essentially the same means falls within the protection scope of the present invention.

Claims

1. A method for modifying activated carbon applicable to different high-temperature accident conditions in reactors, characterized by: Includes the following steps, Step S1, hydrophobic modification of activated carbon: Select a high-boiling-point superhydrophobic material—perfluorodecyltrimethoxysilane solution—and spray it onto activated carbon fibers; Step S2, Activated carbon impregnation modification: High-boiling-point hexamethylenetetramine (HMTA) is used to impregnate and modify activated carbon with high hydrophobicity. Step S3, Activated Carbon Chemical Adsorption Modification: A mixture of Al(OH)3 and SiO2-C, SiO2-Cu... 0 SiO2-Ag 0 The composite material was sprayed as a flame retardant aqueous solution onto the surface of activated carbon fiber; Step S4: Dry the modified activated carbon solution at a low temperature of 60℃~85℃.

2. The activated carbon modification method applicable to different high-temperature accident conditions in reactors as described in claim 1, characterized in that: in Between steps S3 and S4, hydrogen adsorption modification is also included, specifically by incorporating an equal mass of copper oxide into activated carbon.

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