SiC secondary neutron source cladding tube, manufacturing method thereof and secondary neutron source rod

Abstract

A SiC secondary neutron source cladding tube is configured to be of a multi-layer tubular structure and comprises a tubular SiC fiber braid layer, a cracking carbon interface layer, a SiC coating and an Al2O3 tritium-resistant coating which are sequentially arranged from inside to outside. The SiC secondary neutron source cladding tube has good tritium resistance, high-temperature mechanical property and wear resistance, can effectively reduce tritium emission of a nuclear power plant caused by tritium permeation and diffusion in a reactor secondary neutron source, and improves the safety of the nuclear power plant. The invention further provides a manufacturing method of the SiC secondary neutron source cladding tube and a secondary neutron source rod.

Description

Technical Field

[0001] The invention belongs to the field of nuclear power, and in particular relates to a SiC secondary neutron source cladding tube and a manufacturing method thereof, and a secondary neutron source rod. Background Art

[0002] In the field of nuclear power generation, tritium is one of the key sources of radioactive substances emitted into the surrounding environment during the operation of nuclear power plants. As modern society pays more and more attention to the safety of nuclear power plant operation, how to effectively reduce tritium emissions has become the core content of the important issue of controlling radioactive emissions from nuclear power plants.

[0003] During the operation of a nuclear power plant, tritium mainly comes from the various core components of the reactor during operation. Among them, the Sb-Be pellets inside the secondary neutron source rod are particularly worthy of attention. Under the complex physical effect of neutron irradiation, the Sb-Be pellets will produce a large amount of tritium. As far as the current technical situation is concerned, the cladding of the secondary neutron source is usually made of stainless steel. However, stainless steel has obvious limitations in its tritium barrier performance. Due to this limitation, tritium can penetrate more easily, which directly leads to a significant increase in the tritium content in the primary circuit of a nuclear power plant.

[0004] In order to solve the problem of tritium penetration, in some existing technical solutions, people have tried to set a tritium barrier coating on the surface of the cladding. Theoretically, this is indeed a feasible method. However, most coating materials with tritium barrier properties are ceramic materials. When the ceramic material coating is applied to the metal cladding tube substrate, a series of problems will arise. For example, there is a thermal stress mismatch between the ceramic material and the metal cladding tube substrate, which is caused by the difference in thermal expansion coefficients between the two. Moreover, the ceramic coating is susceptible to corrosion in the complex operating environment of the nuclear power plant, and it is prone to peeling due to various factors for a long time. These problems have seriously affected the actual effect of the tritium barrier coating.

[0005] In summary, developing and providing a secondary neutron source cladding with better tritium resistance is of great significance to nuclear power plants. This will have a positive and far-reaching impact on reducing tritium emissions from nuclear power plants, and help further ensure the safety and environmental friendliness of nuclear power plant operations. Summary of the invention

[0006] The purpose of the present invention is to provide a SiC secondary neutron source cladding tube to reduce tritium emission of the secondary neutron source. The present invention also provides a method for manufacturing the SiC secondary neutron source cladding tube and a secondary neutron source rod.

[0007] According to an embodiment of one aspect of the present invention, a SiC secondary neutron source cladding tube is provided, wherein the SiC secondary neutron source cladding tube is configured as a multi-layer tubular structure, including a SiC fiber braided layer, a cracked carbon interface layer, a SiC coating and an Al2O3 tritium barrier coating which are arranged in sequence from the inside to the outside along the radial direction, wherein the SiC fiber braided layer includes a three-dimensional structure formed by weaving and winding SiC fibers, and the SiC coating is configured as a dense SiC layer without a fiber structure.

[0008] SiC fiber itself has good tritium resistance and a small neutron absorption cross section. Compared with zirconium alloy and other materials, it has better high-temperature mechanical strength, wear resistance and high-temperature stability. Furthermore, unlike components such as control rods, secondary neutron source rods do not require frequent up and down movements during reactor operation. The strength performance of the composite tube woven from SiC fibers can meet the design requirements of secondary neutron source rods. Al2O3 has good corrosion resistance and air tightness, and has better tritium resistance than SiC at the rated operating temperature of a pressurized water reactor; further, Al2O3 and SiC have similar thermal expansion coefficients, which can effectively avoid cracking, peeling and other problems caused by thermal mismatch. The Al2O3 coating can also effectively solve the air tightness problem of the SiC cladding tube, and can also improve the welding performance between the cladding tube and the metal end plug of the secondary neutron source rod.

[0009] Furthermore, in some embodiments, the inner surface of the SiC fiber braided layer is sequentially provided with a cracked carbon interface layer, a SiC coating and an Al2O3 tritium barrier coating.

[0010] Furthermore, in some embodiments, the SiC fiber braided layer is configured as a tube with a diameter of 7.4 mm-9.6 mm, and the braiding angle of the SiC fiber is 30°-50°.

[0011] Furthermore, in some embodiments, the SiC coating has a thickness of 50 μm-200 μm.

[0012] Furthermore, in some embodiments, the thickness of the Al2O3 tritium barrier coating is 5 μm-20 μm.

[0013] According to another aspect of the present invention, there is provided a method for manufacturing a SiC secondary neutron source cladding tube, which is used to manufacture the SiC secondary neutron source cladding tube provided in any of the aforementioned embodiments, and comprises the following steps:

[0014] Step a): providing SiC fibers, and weaving the SiC fibers around a core rod to form a tubular SiC fiber braided layer;

[0015] Step b): placing the tubular SiC fiber braided layer in a vacuum environment, and depositing a cracked carbon interface layer on the surface of the tubular SiC fiber braided layer using a chemical vapor deposition process;

[0016] Step c): densifying the tubular SiC fiber braided layer by chemical vapor infiltration process;

[0017] Step d): using a chemical vapor deposition process to deposit a SiC coating on the surface of the cracked carbon interface layer;

[0018] Step e): using a magnetron sputtering process to deposit an Al2O3 tritium barrier coating on the surface of the SiC coating to obtain a cladding tube preform;

[0019] Step f): sintering the cladding tube preform to obtain a finished SiC secondary neutron source cladding tube.

[0020] Furthermore, in some embodiments, the step b) is carried out in a chemical vapor deposition furnace, the vacuum environment pressure is 0.1Pa-0.4Pa, the cracking gas raw material is introduced at a gas flow rate of 10sccm-30sccm, and the cracking gas raw material is heated to the cracking temperature of the cracking gas raw material to perform cracking carbon deposition, wherein the cracking gas raw material includes a gas containing an alkyl, alkene or alkynyl group, and the insulation time is 1h-2h.

[0021] Further, in some embodiments, the step c) is carried out in a chemical vapor infiltration furnace, and the densification treatment step is: providing a vacuum environment of 0.1Pa-0.4Pa in the chemical vapor infiltration furnace, using hydrogen as a carrier gas and argon as a dilution / protective gas, introducing a densification gas raw material, and heating to 1000°C-1400°C; wherein the densification gas raw material includes a mixed gas of silicon tetrachloride and methane, trichloromethylsilane or tetramethylsilane, the gas flow rate of the densification gas raw material is 1000sccm-5000sccm, the gas flow rate of hydrogen is 2000sccm-6000sccm, the gas flow rate of argon is 2000sccm-6000sccm, and the insulation time is 5h-10h.

[0022] Further, in some embodiments, the step d) is carried out in a chemical vapor deposition furnace, a vacuum environment of 0.1Pa-0.4Pa is provided in the chemical vapor deposition furnace, hydrogen is used as a carrier gas, argon is used as a dilution / protective gas, a coating gas raw material is introduced, and the temperature is heated to 1000°C-1400°C; wherein the coating gas raw material includes a mixed gas of silicon tetrachloride and methane, trichloromethylsilane or tetramethylsilane, the gas flow rate of the coating gas raw material is 1000sccm-2000sccm, the gas flow rate of hydrogen is 1000sccm-2000sccm, the gas flow rate of argon is 1000sccm-2000sccm, and the insulation time is 5h-10h.

[0023] Further, in some embodiments, the step e) is performed in a magnetron sputtering device, the tubular SiC braided layer processed in the step d) is placed in the magnetron sputtering device, and the vacuum is evacuated to 1×10 -3 Pa-4×10 -3 Pa, use Al with purity not less than 99% as target material, set the shaft speed to 0.4rpm-0.6rpm;

[0024] First, introduce argon gas with a gas flow rate of 100sccm-200sccm, set the bias voltage to 400V-600V, the target power to 0W, the vacuum degree to 0.2Pa-0.4Pa, and the deposition time to 30min-60min;

[0025] Subsequently, argon gas is introduced with a gas flow rate of 100sccm-200sccm; oxygen gas is introduced with a gas flow rate of 10sccm-20sccm, the bias voltage is set to 50V-80V, the target power is 6000W-7000W, the vacuum degree is 0.2Pa-0.4Pa, and the processing time is 15h-60h; and a dense Al2O3 tritium barrier coating is formed on the surface of the SiC coating.

[0026] Furthermore, in some embodiments, in the step f), the sintering step includes: placing the cladding tube preform in an adapted graphite mold, sealing both ends, heating to 1000° C.-1200° C. and maintaining the temperature for 2 h-4 h to complete sintering.

[0027] According to another aspect of the present invention, there is provided a secondary neutron source rod, comprising an end plug, a cladding tube and a core block, wherein the cladding tube adopts the SiC secondary neutron source cladding tube provided in any of the aforementioned embodiments, the end plug is welded at both ends of the cladding tube, and the neutron source core block is enclosed in the cladding tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of a secondary neutron source assembly in one embodiment;

[0029] Figure 2 This is a schematic diagram of the cross-sectional structure of a secondary neutron source rod in one embodiment;

[0030] Figure 3 Schematic diagram of the cross-sectional structure of the SiC secondary neutron source cladding tube in one embodiment.

[0031] 1-secondary neutron source rod; 2a-upper end plug; 2b-lower end plug; 3-neutron source core block; 4-secondary neutron source cladding tube; 5-SiC fiber braided layer; 6-cracking carbon interface layer; 7-SiC coating; 8-Al2O3 tritium barrier coating.

[0032] The purpose of the above embodiments is to explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. For the sake of simplicity, the above drawings only schematically illustrate the structures related to the technical features of the present invention, and do not strictly illustrate the complete structure and all details according to the actual proportion. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0034] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0035] In the description of this article, unless otherwise clearly specified and limited, the technical terms "installed", "connected", "connected" and the like should be understood in a broad sense, for example, it can be a movable connection, a fixed connection or an integral connection. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of this application can be understood according to specific circumstances.

[0036] In the description of this document, terms indicating orientation or positional relationships, such as "up", "down", "left", "right", "horizontal", "vertical", "height", "length", and "width", are intended to accurately describe the embodiments and simplify the description, but are not intended to limit the parts or structures involved to have a specific orientation, be installed or operate in a specific orientation, and should not be construed as a limitation on the embodiments in this document.

[0037] In the description of this article, the terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order or primary and secondary relationship of the described technical features. In the description of this article, the meaning of "plurality" is at least two.

[0038] As a clean, efficient and sustainable energy source, nuclear power is an important choice for addressing climate change and achieving carbon neutrality. As the attention to the safety performance of nuclear power increases, how to reduce the total amount of radioactive emissions from nuclear power plants and reduce environmental impact has become an important issue in the field of nuclear power.

[0039] During the normal operation of nuclear power plants, tritium is the main source of radioactive emissions. Since the half-life of tritium is 12.3 years, its presence in the natural environment will have an impact on the human body and organisms. Therefore, limiting tritium emissions is one of the important directions for improving the safety performance of nuclear power plants.

[0040] There are many sources of tritium during the operation of pressurized water reactor nuclear power plants, such as fission reactions of pellets in fuel rods, neutron capture by combustible poisons and B in the coolant, and activation of Li in the coolant. Sb-Be pellets in the reactor's secondary neutron source will also produce a large amount of tritium under the action of neutron irradiation, while the stainless steel cladding used in the secondary neutron source rods has limited tritium barrier effect, which easily leads to a large amount of tritium penetration and becomes an important source of tritium in the primary coolant. At present, the main solution to improve the tritium barrier performance of stainless steel cladding is to set a coating with good tritium barrier performance on the surface of the stainless steel cladding to achieve the effect of reducing tritium penetration, such as oxide ceramic coatings such as aluminum oxide coatings and titanium oxide coatings. However, there are significant differences in the physical and chemical properties between ceramic coatings and stainless steel cladding tubes. Ceramic coatings applied to the surface of stainless steel under high-temperature irradiation conditions are prone to cracking and peeling due to thermal mismatch.

[0041] In order to solve the above problems, an embodiment of one aspect of the present invention provides a SiC secondary neutron source cladding tube, such as Figure 3 As shown, the cladding tube adopts a multi-layer tubular structure, the matrix is ​​a SiC fiber braided layer 5, the SiC fiber braided layer 5 includes a three-dimensional structure formed by weaving and winding SiC fibers, and the whole is tubular; the outer side of the SiC fiber braided layer 5 is a cracked carbon interface layer 6, which is formed by cracked carbon deposited on the surface of the SiC fiber braided layer 5; the outer side of the cracked carbon interface layer 6 is a SiC coating 7, which is a dense SiC layer formed by chemical vapor deposition, and the inside of the SiC coating 7 is a dense SiC tissue fiber-free structure; the outer side of the SiC coating 7 is an Al2O3 tritium barrier coating, which is a dense Al2O3 layer formed by magnetron sputtering.

[0042] SiC has good resistance to tritium penetration, and SiC has a small neutron absorption cross-section and good neutron permeability, making it a good choice as a core component structural material. SiC also has good high-temperature mechanical properties, is stable at high temperatures, and does not easily react with water. Moreover, after the secondary neutron source rod is loaded into the reactor, it basically does not move during operation and is usually kept inserted in the fuel assembly guide tube. Therefore, the brittleness of the SiC material itself is acceptable when used as a secondary neutron source cladding tube material. However, although the SiC material itself has good tritium resistance, it is limited by the manufacturing process and macroscopic structure, and the airtightness of the SiC tube is insufficient; moreover, Figure 2 As shown, both ends of the secondary neutron source tube need to be welded with metal end plugs for sealing, but the welding performance of SiC and metal end plugs is poor. Therefore, it is necessary to modify the surface of the SiC material by providing an Al2O3 tritium barrier coating 7.

[0043] The advantage of Al2O3 is that it has good thermal stability and certain mechanical strength, is easy to prepare into a dense coating, and has good corrosion resistance and air tightness. Furthermore, Al2O3 has good tritium resistance (10 -8 molH2 m -1 s -1 MPa -1 / 2 ). At the same time, compared with 304 stainless steel (thermal expansion coefficient 15.98×10 -6 / k) and other metal materials, Al2O3 (thermal expansion coefficient (5.3-5.8) × 10 -6 / k) and SiC (thermal expansion coefficient (4.0-4.8) × 10 -6 / k) have closer thermal expansion properties.

[0044] At the same time, in order to enhance the integrity and air tightness of the SiC braided layer 5, a dense SiC coating 7 is provided outside the SiC braided layer 5. However, the overall brittle tendency of the single SiC component structure is more obvious, and a cracked carbon interface layer 6 needs to be provided between the SiC braided layer 5 and the SiC coating 7 to improve the quasi-ductility of the composite structure composed of the SiC braided layer 5 and the SiC coating 7.

[0045] The SiC secondary neutron source cladding tube provided in the above embodiment can be used to manufacture Figure 1 The secondary neutron source rod 1 in the secondary neutron source assembly is shown in FIG. The structure of the secondary neutron source rod 1 is as follows: Figure 2As shown, it includes an upper end plug 2a and a lower end plug 2b respectively arranged at both ends, and the upper end plug 2a and the lower end plug 2b are fixed at both ends of the secondary neutron source cladding tube 4 by welding, so that a closed structure is formed in the secondary neutron source cladding tube 4, and the secondary neutron source core block 3 (Sb-Be core block) is enclosed in the secondary neutron source cladding tube 4, wherein the upper end plug 2a and the lower end plug 2b can be made of materials with good high temperature mechanical properties and radiation damage resistance such as nickel alloy, zirconium alloy or stainless steel. Al2O3 has better welding performance, and the Al2O3 tritium blocking coating 7 enables a good welding connection to be formed between the upper end plug 2a, the lower end plug 2a and the secondary neutron source cladding tube 4. The secondary neutron source rod 1 has good tritium blocking performance, which can effectively reduce the penetration and diffusion of tritium generated by the secondary neutron source core block 3 under the influence of neutron irradiation into the primary circuit coolant, and reduce the tritium emission brought by the secondary neutron source.

[0046] In a preferred embodiment, the secondary neutron source cladding tube 4 provided in the above embodiment can be manufactured by the following method:

[0047] Step a): braiding a tubular SiC fiber braided layer 5 .

[0048] Provide SiC fiber raw materials, specifically, third-generation continuous SiC fibers that meet the requirements of high-purity cubic phase β-SiC, such as Cansas-3303, KD-S, KD-SA and other models, can be used, and SiC fibers can also be prepared by methods such as polymer impregnation pyrolysis (PIP). Based on a glass rod with a diameter of 7.4 mm-9.6 mm, a tubular SiC fiber layer 5 is braided in a winding manner, so that the SiC fibers are braided and wound into a three-dimensional structure, wherein the braiding angle is 30°-50°.

[0049] Step b): Deposition of a cracked carbon interface layer 6 .

[0050] The woven SiC fiber tube is placed in the heating section of a chemical vapor deposition furnace (CVD furnace), the CVD furnace is evacuated to 0.1Pa-0.4Pa, and an alkyl, alkenyl or alkynyl gas containing carbon and hydrogen elements is introduced as a cracking gas raw material, and the gas flow rate is controlled to be 10sccm-30sccm. The CVD furnace is heated to the cracking temperature of the cracking gas raw material (for example, 1000℃-1100℃ for methane and 700℃-900℃ for acetylene), and the dehydrogenation reaction of the introduced cracking gas raw material is promoted, and a cracked carbon (PyC) cross-sectional layer is deposited on the surface of the SiC fiber braided layer 5. The total deposition time (holding time) of the cracked carbon is 1h-2h.

[0051] Step c): Densification of the SiC matrix.

[0052] Chemical vapor infiltration (CVI) is used to achieve densification between the SiC fiber braided layer 5 and the cracked carbon interface layer 6. The SiC fiber tube after cracked carbon deposition is placed in the heating section of the CVI furnace, the CVI furnace is evacuated to 0.1Pa-0.4Pa, trichloromethylsilane, tetramethylsilane or silicon tetrachloride + methane is used as the densification gas raw material, hydrogen is used as the carrier gas, and argon is used as the dilution / protective gas, and is introduced into the CVI furnace, and the temperature is raised to 1000℃-1400℃ for chemical vapor infiltration treatment. As the SiC matrix gradually infiltrates, the gap between the SiC fiber braided layer 5 and the cracked carbon interface layer 6 decreases, the infiltration rate decreases, and the gas flow rate of the densification gas raw material gradually increases from 1000sccm-2000sccm to 3000sccm-5000sccm. The hydrogen flow rate is controlled at 2000sccm-6000sccm, the argon flow rate is 2000sccm-6000sccm, and the infiltration time (insulation time) is 5h-10h.

[0053] Step d): preparing a SiC coating.

[0054] A dense SiC coating 7 is deposited on the densified SiC fiber braided layer 5 and the cracked carbon interface layer 6 by using a CVD process. The SiC fiber tube treated by CVI infiltration is loaded into the heating section of the CVD furnace, and the CVD furnace is evacuated to 0.1Pa-0.4Pa. Trichloromethylsilane, tetramethylsilane or silicon tetrachloride + methane are used as coating gas raw materials, hydrogen is used as carrier gas, and argon is used as dilution / protective gas. They are introduced into the CVD furnace and heated to 1000℃-1400℃ to deposit a dense SiC coating 7 on the surface of the cracked carbon interface layer 6. The gas flow rate of the coating gas raw material is 1000sccm-2000sccm, the hydrogen gas flow rate is 1000sccm-2000sccm, the argon gas flow rate is 1000sccm-2000sccm, and the vapor deposition time (holding time) is 5h-10h. Finally, a SiC coating with a thickness of 50μm-200μm is obtained.

[0055] Step e): preparing an Al2O3 tritium barrier coating.

[0056] The dense Al2O3 tritium barrier coating 8 was prepared by magnetron sputtering process. The SiC fiber tube with SiC coating 7 was placed at the center of the rotating shaft of the magnetron sputtering coating equipment and vacuumed to 1×10 -3 Pa-4×10 -3Pa. Use 2 pieces of metal Al as targets (purity: 99.0%-100.0%) and place them in parallel on both sides of the turntable. Set the shaft speed to 0.4-0.6rpm. First, introduce argon gas for sputtering cleaning, with a gas flow rate of 100-200sccm, a bias voltage of 400-600V, a target power of 0W, a gas vacuum of 0.2-0.4Pa, and a time of 30-60min. Then carry out Al2O3 coating deposition, with a gas flow rate of Ar: 100-200sccm, O2: 10-20sccm, a bias voltage of 50-80V, a target power of 6000-7000W, a gas vacuum of 0.2-0.4Pa, and a time of 15-60h. A cladding tube preform with a dense Al2O3 tritium barrier coating 8 of 5μm-20μm deposited on the surface is obtained. Step f): sintering.

[0057] The cladding tube preform is sintered by high-temperature isostatic pressing. The cladding tube preform is loaded into a suitable graphite mold, the two ends are sealed, and the cladding tube is heated to 1000°C-1200°C for 2h-4h to obtain a finished SiC secondary neutron source cladding tube. The finished SiC secondary neutron source cladding tube is machined to obtain a secondary neutron source cladding tube 4 for manufacturing a secondary neutron source rod 1. The graphite sintering mold can prevent SiC from deforming at high temperatures and improve the quality of the finished SiC secondary neutron source cladding tube 4. After high-temperature sintering, the finished secondary neutron source cladding tube 4 has good hardness and wear resistance.

[0058] In different embodiments, during the CVD and CVI treatments, the two ends of the tube body surrounded by the SiC fiber braided layer 5 may be sealed, so that the cracked carbon interface layer 6, the SiC coating 7 and the Al2O3 tritium barrier coating 8 are sequentially formed only on the outside of the SiC fiber braided layer 5. It is also possible not to seal the two ends of the tube body surrounded by the SiC fiber braided layer 5, so that the inside of the SiC fiber braided layer 5 is also Figure 3 As shown, a cracked carbon interface layer 6 and a SiC coating layer 7 can be formed in sequence.

[0059] The SiC secondary neutron source cladding tube provided in the above embodiment has a hydrogen (tritium) permeability coefficient that is 9-13 orders of magnitude lower than that of stainless steel materials, which can effectively reduce the radioactive emissions caused by tritium penetration of the secondary neutron source and improve the safety of nuclear power plants. At the same time, the thermal expansion coefficients of different layers of the SiC and Al2O3 composite structure have good adaptability, and are not prone to cracking, peeling and other problems, which can effectively improve the service life and reliability of the secondary neutron source cladding tube. Furthermore, there is a mature brazing process between the Al2O3 material and the metal material, which reduces the difficulty of manufacturing the secondary neutron source rod.

[0060] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, the optimization or equivalent replacement of the structures or method steps involved, and the combination of implementation methods in different embodiments without conflict of structure and principle, all fall within the protection scope of the present invention.

Claims

1. A SiC secondary neutron source cladding tube, characterized in that: The SiC secondary neutron source cladding tube is configured as a multi-layer tubular structure, including a SiC fiber braided layer, a cracked carbon interface layer, a SiC coating and an Al2O3 tritium barrier coating arranged in sequence from the inside to the outside along the radial direction, wherein the SiC fiber braided layer includes a three-dimensional structure formed by weaving and winding SiC fibers, and the SiC coating is configured as a dense SiC layer without a fiber structure.

2. The SiC secondary neutron source cladding tube according to claim 1, characterized in that: The SiC fiber braided layer is configured as a tube with a diameter of 7.4 mm-9.6 mm, and the braiding angle of the SiC fiber is 30°-50°.

3. The SiC secondary neutron source cladding tube according to claim 1 or 2, characterized in that: The SiC coating has a thickness of 50 μm-200 μm.

4. The SiC secondary neutron source cladding tube according to claim 1 or 2, characterized in that: The thickness of the Al2O3 tritium barrier coating is 5 μm-20 μm.

5. A method for manufacturing a SiC secondary neutron source cladding tube, characterized in that: Used to manufacture the SiC secondary neutron source cladding tube according to any one of claims 1 to 4, and comprising the following steps: Step a): providing SiC fibers, and weaving the SiC fibers around a core rod to form a tubular SiC fiber braided layer; Step b): placing the tubular SiC fiber braided layer in a vacuum environment, and depositing a cracked carbon interface layer on the surface of the tubular SiC fiber braided layer using a chemical vapor deposition process; Step c): densifying the tubular SiC fiber braided layer by chemical vapor infiltration process; Step d): using a chemical vapor deposition process to deposit a SiC coating on the surface of the cracked carbon interface layer; Step e): using a magnetron sputtering process to deposit an Al2O3 tritium barrier coating on the surface of the SiC coating to obtain a cladding tube preform; Step f): sintering the cladding tube preform to obtain a finished SiC secondary neutron source cladding tube.

6. The method for manufacturing a SiC secondary neutron source cladding tube according to claim 5, characterized in that: The step b) is carried out in a chemical vapor deposition furnace, the vacuum environment pressure is 0.1Pa-0.4Pa, the cracking gas raw material is introduced at a gas flow rate of 10sccm-30sccm, and the cracking gas raw material is heated to the cracking temperature of the cracking gas raw material to perform cracking carbon deposition, wherein the cracking gas raw material includes a gas containing an alkyl, alkenyl or alkynyl group, and the insulation time is 1h-2h.

7. The method for manufacturing a SiC secondary neutron source cladding tube according to claim 5, characterized in that: The step c) is carried out in a chemical vapor infiltration furnace, and the densification treatment step is: providing a vacuum environment of 0.1Pa-0.4Pa in the chemical vapor infiltration furnace, using hydrogen as a carrier gas and argon as a dilution / protective gas, introducing a densification gas raw material, and heating to 1000°C-1400°C; wherein the densification gas raw material includes a mixed gas of silicon tetrachloride and methane, trichloromethylsilane or tetramethylsilane, the gas flow rate of the densification gas raw material is 1000sccm-5000sccm, the gas flow rate of hydrogen is 2000sccm-6000sccm, the gas flow rate of argon is 2000sccm-6000sccm, and the insulation time is 5h-10h.

8. The method for manufacturing a SiC secondary neutron source cladding tube according to claim 5, characterized in that: The step d) is carried out in a chemical vapor deposition furnace, in which a vacuum environment of 0.1Pa-0.4Pa is provided, hydrogen is used as a carrier gas, argon is used as a dilution / protective gas, a coating gas raw material is introduced, and the temperature is heated to 1000°C-1400°C; wherein the coating gas raw material includes a mixed gas of silicon tetrachloride and methane, trichloromethylsilane or tetramethylsilane, the gas flow rate of the coating gas raw material is 1000sccm-2000sccm, the gas flow rate of hydrogen is 1000sccm-2000sccm, the gas flow rate of argon is 1000sccm-2000sccm, and the insulation time is 5h-10h.

9. The method for manufacturing a SiC secondary neutron source cladding tube according to claim 5, characterized in that: The step e) is carried out in a magnetron sputtering device, wherein the tubular SiC braided layer treated in the step d) is placed in the magnetron sputtering device and evacuated to 1×10 -3 Pa-4×10 -3 Pa, use Al with purity not less than 99% as target material, set the shaft speed to 0.4rpm-0.6rpm; First, introduce argon gas with a gas flow rate of 100sccm-200sccm, set the bias voltage to 400V-600V, the target power to 0W, the vacuum degree to 0.2Pa-0.4Pa, and the deposition time to 30min-60min; Subsequently, argon gas is introduced with a gas flow rate of 100sccm-200sccm; oxygen gas is introduced with a gas flow rate of 10sccm-20sccm, the bias voltage is set to 50V-80V, the target power is 6000W-7000W, the vacuum degree is 0.2Pa-0.4Pa, and the processing time is 15h-60h; and a dense Al2O3 tritium barrier coating is formed on the surface of the SiC coating.

10. The method for manufacturing a SiC secondary neutron source cladding tube according to claim 5, characterized in that: In the step f), the sintering step includes: placing the cladding tube preform in a suitable graphite mold, sealing both ends, heating to 1000° C.-1200° C. and keeping the temperature for 2 h-4 h to complete sintering.

11. A secondary neutron source rod, comprising an end plug, a cladding tube and a neutron source pellet, characterized in that: The cladding tube adopts the SiC secondary neutron source cladding tube according to any one of claims 1 to 4, the end plugs are welded at both ends of the cladding tube, and the neutron source pellets are enclosed in the cladding tube.

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