A high safety modular composite fuel element and a method for manufacturing the same

Abstract

The application provides a high-safety modular composite fuel element and a preparation method thereof, and belongs to the technical field of nuclear reactor fuel. The high-safety modular composite fuel element comprises a shell and a fuel filled in the shell. The shell comprises an outer shell and a plurality of fuel shells arranged in the outer shell. The inner part of each fuel shell is provided with at least one cooling pipe along the axial direction, which is used for the circulation of cooling medium. The space between the inner wall of the fuel shell and the outer wall of the cooling pipe is a fuel cavity, which is used for accommodating a fuel filling body. The method comprises the following steps: outer shell preparation and pyrolytic carbon interface treatment, fuel shell additive manufacturing, debinding treatment of the fuel shell, pre-deposition treatment of the fuel shell, fuel filling and packaging, modular assembly and overall densification treatment. Through the above integrated process, the shell and the internal fuel module can be densified cooperatively.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor fuel technology, and relates to the additive manufacturing of ceramic-based fuel elements, specifically to a high-safety modular composite fuel element and its preparation method. Background Technology

[0002] In recent years, to improve the manufacturing efficiency and accident tolerance of advanced nuclear reactors, new nuclear fuel components have gradually developed towards a high degree of integration between fuel and structure. The Transformational Challenge Reactor (TCR) proposed by Oak Ridge National Laboratory in the United States adopts a fuel component design concept that integrates fuel and supporting structure. This allows high-performance silicon carbide (SiC) materials and tri-structure isotropic particulate fuel (TRISO) to be integrated into structurally integrated SiC-TRISO fuel components. This improves the manufacturing efficiency of core components and reduces deployment costs while ensuring safety. At the same time, by using advanced additive manufacturing technology, the core fuel components are given greater design freedom, enabling them to overcome the limitations of traditional manufacturing in terms of geometric dimensions and the formation of complex internal channels, and to achieve the fabrication of integrated fuel components with complex configurations.

[0003] However, in the aforementioned integrated fuel-structure fuel components, traditional independent cladding structures are typically no longer used. The outer structure of the fuel component needs to simultaneously perform multiple functions, including fuel isolation, structural load-bearing, and safety barrier. Due to the brittle fracture characteristics of SiC ceramic materials, their fracture toughness and damage tolerance are limited. Under complex loads, thermal shocks, or accident conditions, cracks are prone to initiation and propagation in the outer structure of the fuel component, posing a potential risk to the structural integrity and operational safety of the component.

[0004] To improve the safety and reliability of SiC-based fuel components, continuous fiber-reinforced SiC-based composites have attracted attention due to their significant toughening effect. However, existing technologies mostly use these composites for single shells or structural components, and there is a lack of a design and fabrication scheme for an integrated fuel cladding structure suitable for highly integrated fuel-structure components. Especially when the fuel component contains complex fuel modules and cooling channels, how to integrate a cladding structure with high toughness and safety barrier functions with the fuel component while meeting the requirements of fuel filling and cooling functions, and how to obtain a dense and uniform overall structure through a reliable densification process, remains an urgent technical problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a high-safety modular composite fuel element and its preparation method, thereby solving the technical problems of insufficient fracture toughness, easy crack propagation, and limited structural integrity and safety reliability under accident conditions in existing SiC-based integrated fuel components during service.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for preparing a high-safety modular composite fuel element, such as Figure 1 As shown, the specific steps include the following:

[0008] Step 1, Outer shell preparation and pyrolytic carbon interface treatment: The outer shell of the high-safety modular composite fuel element is prepared by continuous SiC fiber weaving, and then the outer shell is subjected to pyrolytic carbon interface treatment to form a uniform pyrolytic carbon interface layer on the inner surface of the outer shell.

[0009] Step 2, Additive manufacturing of fuel casing: The fuel casing is prepared using Digital Light Processing (DLP) or Binder Jetting Additive Manufacturing (BJ) technology.

[0010] Step 3: Degrease the fuel casing.

[0011] Step 4: Pre-deposition treatment of the fuel shell: Using trichloromethylsilane as the source gas, hydrogen as the carrier gas, and hydrogen and argon as dilution gases, chemical vapor infiltration pre-deposition treatment is performed on the degreased fuel shell.

[0012] Step 5, fuel filling and sealing: The mixed fuel is filled into the fuel chamber, and then the filling port is sealed with SiC slurry and dried and cured.

[0013] Step 6, Modular Assembly: Assemble the outer shell with the pyrolytic carbon interface layer deposited on the inner wall and the encapsulated fuel shell, so that the fuel shell is placed inside the outer shell to form a modular structure.

[0014] Step 7, Overall densification treatment: Using trichloromethylsilane as the source gas, hydrogen as the carrier gas, and hydrogen and argon as dilution gases, the assembled modular structure is subjected to chemical vapor infiltration densification treatment to obtain a high-safety modular composite fuel element.

[0015] The present invention also has the following technical features:

[0016] Specifically, in step one, the deposition conditions for the pyrolytic carbon interface treatment are as follows: using propylene as the carbon source precursor gas, deposition is carried out at 900–1100°C and 3–8 kPa pressure for 40–60 h. Preferably, deposition is carried out at 1000°C and 5 kPa pressure for 50 h.

[0017] Specifically, in step two, the binder spraying forming technology includes: laying SiC powder on the forming platform, selectively spraying binder along a preset path during the printing process, so that the powder is bonded layer by layer to form a fuel shell blank after printing is completed.

[0018] Specifically, in step two, when the binder spray forming technology is used, the mass ratio of SiC powder to binder is (8-12):1; preferably, the mass ratio of SiC powder to binder is 9:1.

[0019] Specifically, in step two, when using binder spray forming technology, the SiC powder particle size is 30μm, and the phase is β phase; the binder is composed of water-based binder C6H. 10 It is composed of O5 and phenolic resin, and the mass ratio of the two is 1:1.

[0020] Specifically, in step two, the printing parameters for the adhesive jetting technology are: printing speed 40–60 mm / s, and printing layer thickness 0.02–0.04 mm. Preferably, the printing speed is 50 mm / s and the printing layer thickness is 0.03 mm.

[0021] Specifically, in step two, the digital light processing photocuring forming technology includes: mixing SiC powder with resin monomers, photoinitiators and dispersants to prepare SiC ceramic slurry; ball milling the slurry to disperse it evenly and then performing photocuring printing to form a fuel shell after printing is completed.

[0022] Specifically, in step two, when using digital light processing photopolymerization technology, the parameters for photopolymerization printing are: slice thickness of 15–25 μm, light intensity of 20–40 mW / cm², and exposure time of 40–80 s. Preferably, the slice thickness is 20 μm, the light intensity is 30 mW / cm², and the exposure time is 60 s.

[0023] Specifically, in step two, when using digital light processing photocuring molding technology, the SiC powder used has an average particle size of 8 μm and a β-phase silicon carbide phase; the resin monomer used is a dual resin monomer system of 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA), wherein the mass fraction of HDDA is 50%; the dispersant used is a dual dispersant of KOS110 and 17000, with a mass ratio of 1:1 and a total dispersant addition of 5 wt.%; the photoinitiator is TPO, and its addition amount is 2 wt.%.

[0024] Specifically, in step two, when digital light processing photopolymerization forming technology is used, the solid content of the SiC ceramic slurry is 35-45 vol%. Preferably, the solid content of the SiC ceramic slurry is 40 vol%.

[0025] Specifically, in step two, when digital light processing photopolymerization molding technology is used, the ball milling time is 2 to 4 hours. Preferably, the ball milling time is 3 hours.

[0026] Specifically, in step three, the degreasing conditions are as follows: heating to 500–600°C at a rate of 0.8–1.2°C / min, holding at that temperature for 4–6 hours, and then cooling at a rate of 2.8–3.2°C / min. Preferably, heating to 550°C at a rate of 1°C / min, holding at that temperature for 5 hours, and then cooling at a rate of 3°C / min.

[0027] Specifically, in step four, the conditions for chemical vapor infiltration pre-deposition are: deposition temperature of 900–1100℃, deposition pressure of 2–5 kPa, and deposition time of 45–55 h. Preferably, the conditions for chemical vapor infiltration pre-deposition are: deposition temperature of 1000℃, deposition pressure of 3 kPa, and deposition time of 50 h.

[0028] Specifically, in step four, the molar ratio of hydrogen to trichloromethylsilane is 9–12:1, the flow rate of the carrier gas hydrogen is 1.5–2.5 L / min, the flow rate of the dilution gas hydrogen is 0.5–1.5 L / min, and the flow rate of the dilution gas argon is 2.5–3.5 L / min. Preferably, the molar ratio of hydrogen to trichloromethylsilane is 11:1, the flow rate of the carrier gas hydrogen is 2 L / min, the flow rate of the dilution gas hydrogen is 1 L / min, and the flow rate of the dilution gas argon is 3 L / min.

[0029] Specifically, in step five, the mixed fuel consists of TRISO particles and SiC matrix powder, with a volume ratio of 4–6:4–6. Preferably, the volume ratio is 5.5:4.5.

[0030] Specifically, in step five, the SiC slurry is composed of silicon carbide powder and deionized water, with a mass ratio of 8 to 12:1. Preferably, the mass ratio is 9:1.

[0031] Specifically, in step five, the drying and curing conditions are: maintaining a temperature of 60–90°C for 18–24 hours. Preferably, maintaining a temperature of 80°C for 20 hours.

[0032] Specifically, in step seven, the conditions for chemical vapor infiltration densification are: deposition temperature of 1100–1300℃, deposition pressure of 8–10 kPa, and deposition time of 135–155 h. Preferably, the deposition temperature is 1200℃, the deposition pressure is 9 kPa, and the deposition time is 150 h.

[0033] Specifically, in step seven, the molar ratio of hydrogen to trichloromethylsilane is 11–13:1, the flow rate of the carrier gas hydrogen is 4–6 L / min, the flow rate of the dilution gas hydrogen is 2–4 L / min, and the flow rate of the dilution gas argon is 4–6 L / min. Preferably, the molar ratio of hydrogen to trichloromethylsilane is 11:1, the flow rate of the carrier gas hydrogen is 5 L / min, the flow rate of the dilution gas hydrogen is 3 L / min, and the flow rate of the dilution gas argon is 5 L / min.

[0034] The present invention also protects a high-safety modular composite fuel element prepared by the method described above, comprising a housing and the fuel filled therein.

[0035] Specifically, the housing includes an outer shell and a plurality of fuel shells disposed inside the outer shell. Each fuel shell has at least one cooling pipe disposed inside along the axial direction for the flow of cooling medium. The space between the inner wall of the fuel shell and the outer wall of the cooling pipe is a fuel cavity for accommodating fuel filler.

[0036] Optionally and preferably, the outer shell is a hollow prism structure, including at least six side walls and an outer shell bottom plate disposed at the end, with the upper end open and the lower end of the outer shell bottom plate disposed; the fuel shell is a hollow prism structure, including at least three side walls and an outer shell bottom plate disposed at the end, with the upper end open and the lower end of the fuel shell bottom plate disposed; the outer shell bottom plate and the fuel shell bottom plate are provided with through holes corresponding one-to-one with the positions of the cooling pipes, and the diameter of the through holes matches the inner diameter of the cooling flow channel.

[0037] Optionally and preferably, the outer shell is a hollow hexagonal prism structure, and the fuel shell is a hollow triangular prism structure; six fuel shells are disposed inside the outer shell, and the six fuel shells are arranged in a circumferential and closely arranged inside the outer shell, with the sidewalls of adjacent fuel shells fitting together to form an array structure; a cooling pipe is coaxially disposed at the center of each fuel shell; the cooling pipe is a hollow circular tube structure.

[0038] Optionally and preferably, the outer shell is a hollow hexagonal prism structure, and the fuel shell is a hollow triangular prism structure; twelve fuel shells are arranged inside the outer shell, with six fuel shells arranged in a circumferential close arrangement inside the outer shell, and the sidewalls of adjacent fuel shells are attached to each other, thereby forming a two-layer array structure; a cooling pipe is coaxially arranged at the center of each fuel shell, and nine cooling pipes are arranged around it; the cooling pipe at the center of the fuel shell is a hollow circular tube structure, and the cooling pipes around it are hollow Y-shaped tube structures.

[0039] Optionally and preferably, the outer shell is a hollow octagonal prism structure, and the fuel shell is a hollow hexagonal prism structure; seven fuel shells are provided inside the outer shell, one of which is located at the center of the outer shell, and the other six fuel shells are evenly distributed along the circumferential direction, with the seven fuel shells closely arranged in a layer; seven cooling pipes are provided inside each fuel shell, one of which is located at the center of the fuel shell, and the other six cooling pipes are evenly distributed along the circumferential direction; the cooling pipes are hollow circular tube structures.

[0040] Compared with the prior art, the present invention has the following technical effects:

[0041] (I) This invention achieves synergistic densification of the shell and internal fuel module through an integrated process of "module filling and packaging - assembly - synchronous deposition of overall CVI". This method not only improves the integrity and density of the structure, but also significantly reduces the risk of failure due to defect accumulation.

[0042] (II) In terms of specific materials and processes, the outer shell is made of a continuous SiC fiber woven preform with PyC interface treatment, which can effectively improve its fracture toughness and crack propagation resistance, thereby enhancing the safety margin of the overall structure. The fuel element is formed by additive manufacturing and then reinforced by CVI pre-deposition. This process improves its mechanical stability during loading and assembly, and also ensures the consistency of subsequent overall densification steps.

[0043] (III) The present invention adopts a modular structural design, which decomposes the complex fuel component into an outer shell and at least one internal fuel element. This design significantly reduces the difficulty of integral additive manufacturing, while improving the flexibility of geometric design and manufacturing feasibility.

[0044] (IV) The process route of the present invention has strong scalability and can be adapted to different additive manufacturing routes and different combinations of module quantity / size, and has good engineering promotion value. Attached Figure Description

[0045] Figure 1 This is a flowchart illustrating the fabrication process of a highly safe modular composite fuel element.

[0046] Figure 2 This is a physical image of the high-safety modular composite fuel element prepared in Example 2.

[0047] Figure 3 for Figure 2 A cross-sectional view along the A-A' direction.

[0048] Figure 4 This is a physical image (without outer casing) of the high-safety modular composite fuel element prepared in Example 2.

[0049] Figure 5 This is a schematic diagram of the housing structure of the high-safety modular composite fuel element in Example 3.

[0050] Figure 6 This is a schematic diagram of the housing structure of the high-safety modular composite fuel element in Example 5.

[0051] Figure 7 This is a comparison diagram of the reaction force-displacement relationship of the high-safety modular composite fuel element prepared in Example 2.

[0052] The labels in the diagram represent: 1-outer shell, 2-fuel shell, 3-cooling pipe, 4-fuel chamber.

[0053] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0054] It should be noted that all raw materials used in this invention, unless otherwise specified, are those known in the art. For example, the photosensitive resins (HDDA, TMPTA) and photoinitiator (TPO) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., China; the dispersant KOS110 was purchased from Guangzhou Kangou Shuang Trading Co., Ltd.; and Solsperse™ 17000 was purchased from Lubrizol (formerly Avecia).

[0055] Following the above technical solutions, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0056] Example 1

[0057] This embodiment provides a housing for a highly safe modular composite fuel element, such as... Figures 2 to 4As shown, it includes an outer shell (1) and six fuel housings (2) disposed inside the outer shell (1). The six fuel housings (2) are arranged in a circumferential and close arrangement inside the outer shell (1), with the sidewalls of adjacent fuel housings (2) fitting together to form a single-layer array structure; a cooling pipe (3) is coaxially disposed at the center of each fuel housing (2); the cooling pipe (3) is an axially penetrating hollow tubular structure used for the flow of cooling medium. The space between the inner wall of the fuel housing (2) and the outer wall of the cooling pipe (3) is a fuel cavity (4) used to accommodate the fuel filler.

[0058] As a specific solution of this embodiment, the outer shell (1) is a hollow hexagonal prism structure, including six side walls and an outer shell bottom plate set at the end. The outer shell bottom plate is provided with through holes corresponding to the positions of the cooling pipes (3). The diameter of the through holes matches the inner diameter of the cooling channel so that the cooling medium can enter or flow out of the cooling pipes (3).

[0059] As a specific embodiment, the fuel casing (2) is a hollow triangular prism structure with an open upper end and a fuel casing bottom plate at the lower end. The fuel casing bottom plate has a through hole coaxial with the cooling pipe (3) so that the cooling pipe (3) can pass through the fuel casing (2), and also facilitates fuel filling and subsequent sealing. The shape of the fuel casing (2) is adapted to the inner cavity of the outer casing (1), and its outer side wall is attached to the outer side wall of the adjacent fuel casing (2).

[0060] As a specific solution in this embodiment, the cooling pipe (3) is a hollow circular pipe structure, which is axially arranged along the fuel shell (2) and passes through the corresponding through holes on the bottom plate of the fuel shell and the bottom plate of the outer shell to achieve stable conduction of the cooling medium.

[0061] Example 2

[0062] This embodiment provides a method for preparing a high-safety modular composite fuel element. The housing of the element adopts the housing of Embodiment 1, and specifically includes the following steps:

[0063] Step 1, preparation of the outer shell and treatment of the pyrolytic carbon interface:

[0064] The outer shell (1) of Example 1 was prepared by continuous SiC fiber weaving. Then, the outer shell (1) was subjected to pyrolytic carbon (PyC) interface treatment. The PyC interface protective layer is usually prepared by chemical vapor deposition (CVD). The deposition conditions are: deposition in an ultra-high temperature CVI furnace filled with 2001% propylene at 1000°C and 5kPa pressure for 50h, forming a uniform PyC interface layer on the inner surface of the SiC fiber preform.

[0065] Step 2, Additive manufacturing of the fuel casing:

[0066] Six fuel shell (2) blanks were prepared using the DLP process. The process included: mixing SiC powder with resin monomer, photoinitiator and dispersant to prepare SiC ceramic slurry with a solid content of 40 vol%. The slurry was ball-milled for 3 hours to ensure uniform dispersion, and then photocured and printed. The DLP printing parameters were as follows: slice thickness of 20 μm, light intensity of 30 mW / cm², and exposure time of 60 s. After printing, the fuel shell (2) was obtained.

[0067] In this embodiment, the SiC powder used has an average particle size of 8 μm and the phase is β-phase silicon carbide; the resin monomer used is an HDDA–TMPTA dual resin monomer system, wherein the mass fraction of HDDA in (HDDA+TMPTA) is 50%; the dispersant used is a dual dispersant of KOS110 and 17000, with a mass ratio of 1:1 and a total dispersant addition amount of 5 wt.%; the photoinitiator used is TPO, and its addition amount is 2 wt.%.

[0068] Step 3: Degreasing the fuel casing:

[0069] The fuel casing (2) was placed in a muffle furnace and heated to 550°C at a rate of 1°C / min, held for 5 hours, and then cooled at a rate of 3°C / min.

[0070] Step 4: Pre-deposition treatment of the fuel casing:

[0071] The degreased fuel casing underwent chemical vapor infiltration (CVI) pre-deposition treatment. During deposition, trichloromethylsilane was used as the source gas, hydrogen as the carrier gas, and hydrogen and argon as dilution gases. The molar ratio of hydrogen to trichloromethylsilane was 11:1. The deposition temperature was controlled at 1000℃, the flow rate of the carrier gas hydrogen was 2 L / min, the flow rate of the dilution gas hydrogen was 1 L / min, and the flow rate of the dilution gas argon was 3 L / min. The deposition pressure was 3 kPa, and the deposition time was 50 h, facilitating subsequent filling, handling, and assembly. The shell density obtained after the preliminary CVI process was 60-65%.

[0072] Step 5, Fuel Filling and Sealing:

[0073] The mixed fuel was filled into the fuel chamber (4); then, the filling port was sealed with a high solids content of 90wt% SiC slurry (i.e., the mass ratio of silicon carbide powder to deionized water was 9:1), and dried and cured. The curing treatment included heat preservation at 80°C for 20 hours. It should be noted that in actual use, the mixed fuel is a mixture of TRISO particles and SiC matrix powder (volume ratio 5.5:4.5). In this embodiment, zirconia microspheres were used as simulated TRISO particles instead of TRISO particles.

[0074] Step Six, Modular Assembly:

[0075] The PyC-treated outer shell (1) is assembled with six encapsulated fuel shells (2) so that the fuel shells (2) are placed inside the outer shell (1) to form a modular structure. In this embodiment, a 0.05mm assembly gap has been reserved at the assembly joint between the outer shell (1) and the fuel shells (2), as well as between adjacent fuel shells (2), before assembly to facilitate assembly positioning.

[0076] Step 7: Perform chemical vapor infiltration (CVI) densification treatment on the assembled modular structure:

[0077] Step 7, Overall Densification Treatment: The assembled modular structure undergoes chemical vapor infiltration densification treatment. During deposition, trichloromethylsilane is used as the source gas, hydrogen as the carrier gas, and hydrogen and argon as dilution gases. The molar ratio of hydrogen to trichloromethylsilane is 11:1. The deposition temperature is controlled at 1200℃, the flow rate of the carrier gas hydrogen is 5 L / min, the flow rate of the dilution gas hydrogen is 3 L / min, and the flow rate of the dilution gas argon is 5 L / min. The deposition pressure is 9 kPa, and the deposition time is 150 h, achieving overall densification. The density of the SiC matrix after deposition is higher than 85%, resulting in a high-density, high-toughness modular SiC composite fuel.

[0078] In this embodiment, a numerical simulation test of crack propagation was conducted on the finally prepared high-safety modular composite fuel element, and the results are as follows: Figure 7 As shown, compared to untoughened fuel elements, fiber-toughened fuel elements exhibit a higher level of reaction force during crack propagation, indicating stronger load-bearing capacity and crack propagation resistance. These results demonstrate that the high-safety modular composite fuel element prepared by this invention possesses high toughness, thereby contributing to improved structural integrity and service safety.

[0079] Example 3

[0080] This embodiment provides a housing for a highly safe modular composite fuel element, such as... Figure 4 As shown, its structure is basically the same as that of Example 1, except that the arrangement, number and shape of the cooling pipes (3) are different; and the number of fuel shells (2) is different.

[0081] As a specific solution of this embodiment, the outer shell (1) is provided with twelve fuel shells (2), and the side walls of every six fuel shells (2) are adjacent to each other and arranged in a close manner as a layer, and the twelve fuel shells (2) are arranged in two layers.

[0082] As a specific embodiment, a cooling pipe (3) is coaxially arranged at the center of each fuel casing (2), and nine cooling pipes (3) are arranged around it.

[0083] As a specific embodiment, the cooling pipe (3) at the center of the fuel casing (2) is a hollow circular pipe structure, and the surrounding cooling pipe (3) is a hollow Y-shaped pipe structure.

[0084] Example 4

[0085] This embodiment provides a method for preparing a high-safety modular composite fuel element. The housing of this element adopts the housing of Embodiment 3, and specifically includes the following steps:

[0086] In this embodiment, step one is completely identical to step one in embodiment 2.

[0087] Step 2, Additive manufacturing of the fuel casing:

[0088] Twelve fuel shell (2) blanks were prepared using the BJ process. The SiC powder used had a particle size of 30 μm, was of the β phase, and accounted for 90% of the mass. The binder accounted for 10% of the mass. The binder was a water-based binder C6H. 10 The O5 and phenolic resin mixed binder has a mass ratio of 1:1. The BJ printing parameters are: printing speed 50 mm / s, printing layer thickness 0.03 mm. Subsequently, the fuel shell (2) is degreased: heating rate 1℃ / min, heated to 550℃ and held for 5h, then cooled at 3℃ / min. At the same time, a 0.05 mm assembly gap is reserved at the assembly joint between the outer shell (1) and the fuel shell (2), as well as between adjacent fuel shells (2).

[0089] In this embodiment, steps three to five are completely identical to steps three to five in embodiment 2.

[0090] Step 6, Modular Assembly: Assemble the hexagonal prism shell treated with PyC with the twelve encapsulated fuel shells (2), so that the fuel shells (2) are placed inside the outer shell (1) to form a modular structure.

[0091] In this embodiment, step seven is completely identical to step seven in embodiment 2.

[0092] Example 5

[0093] This embodiment provides a housing for a highly safe modular composite fuel element, such as... Figure 6As shown, it includes an outer shell (1), inside which are seven fuel shells (2), one of which is located at the center of the outer shell (1), and the other six fuel shells (2) are evenly arranged in the circumferential direction, and the seven fuel shells (2) are closely arranged in a layer; each fuel shell (2) is provided with seven cooling pipes (3), one of which is located at the center of the fuel shell (2), and the other six cooling pipes (3) are evenly arranged in the circumferential direction; the space between the inner wall of the fuel shell (2) and the outer wall of the cooling pipes (3) is the fuel chamber (4).

[0094] As a specific solution of this embodiment, the outer shell (1) is a hollow octagonal prism structure (honeycomb structure), including eighteen side walls and an outer shell bottom plate. The outer shell bottom plate is provided with through holes corresponding to the positions of the cooling pipes (3). The diameter of the through holes matches the inner diameter of the cooling channel so that the cooling medium can enter or flow out of the cooling pipes (3).

[0095] As a specific embodiment, the fuel casing (2) is a hollow hexagonal prism structure, including six side walls. Its upper end is open, and a fuel casing bottom plate is provided at the lower end. The fuel casing bottom plate has through holes that are coaxial with the cooling pipe (3) so that the cooling pipe (3) can pass through the fuel casing (2), and at the same time facilitate fuel filling and subsequent sealing. The shape of the fuel casing (2) is adapted to the inner cavity of the outer casing (1), and its outer side wall is attached to the outer side wall of the adjacent fuel casing (2).

[0096] As a specific solution in this embodiment, the cooling pipe (3) is a hollow circular pipe structure, which is axially arranged along the fuel shell (2) and passes through the corresponding through holes on the bottom plate of the fuel shell and the bottom plate of the outer shell to achieve stable conduction of the cooling medium.

[0097] Example 6

[0098] This embodiment provides a method for preparing a high-safety modular composite fuel element. The housing of this element adopts the housing of Embodiment 2, and specifically includes the following steps:

[0099] In this embodiment, step one is completely identical to step one in embodiment 2.

[0100] Step 2, Additive manufacturing of the fuel casing:

[0101] Six fuel shell (2) blanks were prepared using the DLP process. The process included: mixing SiC powder with resin monomers, photoinitiators and dispersants to prepare SiC ceramic slurry. The average particle size of the SiC powder used was 8 μm, and the phase was β-phase silicon carbide. The resin monomer used was an HDDA–TMPTA dual resin monomer system, in which the mass fraction of HDDA in (HDDA+TMPTA) was 50%. The dispersant used was a dual dispersant of KOS110 and 17000, with a mass ratio of 1:1 and a total dispersant addition of 5 wt.%. The photoinitiator used was TPO, and its addition amount was 2 wt.%. The solid content of the slurry was 40 vol%. The above slurry was ball-milled for 3 hours to make it uniformly dispersed and then photocured and printed. The DLP printing parameters were: slice thickness of 20 μm, light intensity of 30 mW / cm², and exposure time of 60 s. After printing, the fuel shell (2) was obtained. The fuel casing (2) was then degreased: the heating rate was 1℃ / min, and the temperature was maintained at 550℃ for 5 hours, and then cooled down at 3℃ / min. At the same time, a 0.05mm assembly gap was reserved at the assembly joint between the outer casing (1) and the fuel casing (2), as well as between adjacent fuel casings (2), to facilitate subsequent assembly and positioning.

[0102] In this embodiment, steps three to five are completely identical to steps three to five in embodiment 2.

[0103] Step Six, Modular Assembly:

[0104] The PyC-treated outer shell (1) is assembled with seven encapsulated fuel shells (2) so that the fuel shells (2) are placed inside the outer shell (1) to form a modular structure.

[0105] In this embodiment, step seven is completely identical to step seven in embodiment 2.

Claims

1. A method for preparing a high-safety modular composite fuel element, characterized in that, Specifically, the steps include the following: Step 1, Outer shell preparation and pyrolytic carbon interface treatment: The outer shell of the high-safety modular composite fuel element is prepared by continuous SiC fiber weaving, and then the outer shell is subjected to pyrolytic carbon interface treatment to form a uniform pyrolytic carbon interface layer on the inner surface of the outer shell. Step 2, Additive manufacturing of fuel casing: The fuel casing is prepared using digital light processing photopolymerization forming technology or binder spraying forming technology; Step 3: Degrease the fuel casing; Step 4: Pre-deposition treatment of fuel shell: Using trichloromethylsilane as source gas, hydrogen as carrier gas, and hydrogen and argon as dilution gas, chemical vapor infiltration pre-deposition treatment is performed on the degreased fuel shell. Step 5, fuel filling and sealing: The mixed fuel is filled into the fuel chamber, and then the filling port is sealed with SiC slurry and dried and cured. Step 6, Modular Assembly: Assemble the outer shell with the pyrolytic carbon interface layer deposited on the inner wall and the encapsulated fuel shell, so that the fuel shell is placed inside the outer shell to form a modular structure; Step 7, Overall densification treatment: Using trichloromethylsilane as the source gas, hydrogen as the carrier gas, and hydrogen and argon as dilution gases, the assembled modular structure is subjected to chemical vapor infiltration densification treatment to obtain a high-safety modular composite fuel element.

2. The method for preparing a high-safety modular composite fuel element as described in claim 1, characterized in that, In step one, the deposition conditions for the pyrolytic carbon interface treatment are as follows: using propylene as the carbon source precursor gas, deposition is carried out at 900–1100°C and 3–8 kPa pressure for 40–60 h.

3. The method for preparing a high-safety modular composite fuel element as described in claim 1, characterized in that, In step two, the preparation of the fuel casing using binder spraying forming technology includes: laying SiC powder on the forming platform, selectively spraying binder along a preset path during the printing process, so that the powder is bonded layer by layer to form the casing, and obtaining the fuel casing blank after printing is completed; In step two, the printing parameters for the adhesive spraying forming technology are: printing speed 40-60 mm / s, and printing layer thickness 0.02-0.04 mm.

4. The method for preparing a high-safety modular composite fuel element as described in claim 1, characterized in that, In step two, the preparation of the fuel shell using digital light processing photocuring molding technology includes: mixing SiC powder with resin monomer, photoinitiator and dispersant to prepare SiC ceramic slurry; ball milling the above slurry to disperse it evenly and then performing photocuring printing to form the fuel shell after printing is completed. In step two, the parameters for photopolymerization printing are: slice thickness of 15-25 μm, light intensity of 20-40 mW / cm², and exposure time of 40-80 s; In step two, the ball milling time is 2 to 4 hours.

5. The method for preparing a high-safety modular composite fuel element as described in claim 1, characterized in that, In step three, the degreasing conditions are as follows: heat to 500-600℃ at a rate of 0.8-1.2℃ / min, hold for 4-6 hours, and then cool down at a rate of 2.8-3.2℃ / min. In step four, the conditions for chemical vapor infiltration pre-deposition are: deposition temperature of 900–1100℃, deposition pressure of 2–5 kPa, and deposition time of 45–55 h. In step seven, the conditions for chemical vapor infiltration densification are: deposition temperature of 1100–1300℃, deposition pressure of 8–10 kPa, and deposition time of 135–155 h.

6. A high-safety modular composite fuel element prepared by the preparation method according to any one of claims 1 to 5, comprising a shell and fuel filled inside it; characterized in that: The housing includes an outer shell (1) and a plurality of fuel shells (2) disposed inside the outer shell (1). Each fuel shell (2) has at least one cooling pipe (3) disposed inside along the axial direction for the circulation of cooling medium. The space between the inner wall of the fuel shell (2) and the outer wall of the cooling pipe (3) is a fuel cavity (4) for accommodating fuel filler.

7. The high-safety modular composite fuel element as described in claim 6, characterized in that, The outer shell (1) is a hollow prism structure, including at least six side walls and an outer shell bottom plate disposed at the end, with the upper end open and the lower end of the outer shell bottom plate disposed. The fuel shell (2) is a hollow prism structure, including at least three side walls and an outer shell bottom plate disposed at the end, with the upper end open and the lower end disposed of a fuel shell bottom plate; The bottom plate of the outer shell and the bottom plate of the fuel shell are provided with through holes corresponding to the positions of the cooling pipes (3), and the diameter of the through holes matches the inner diameter of the cooling channel.

8. The high-safety modular composite fuel element as described in claim 6, characterized in that, The outer shell (1) is a hollow hexagonal prism structure, and the fuel shell (2) is a hollow triangular prism structure. Six fuel shells (2) are provided inside the outer shell (1). The six fuel shells (2) are arranged in a circumferential and tightly arranged inside the outer shell (1). The sidewalls of adjacent fuel shells (2) are attached to each other, thus forming an array structure. A cooling pipe (3) is coaxially arranged at the center of each fuel casing (2); the cooling pipe (3) is a hollow circular tube structure.

9. The high-safety modular composite fuel element as described in claim 6, characterized in that, The outer shell (1) is a hollow hexagonal prism structure, and the fuel shell (2) is a hollow triangular prism structure. Twelve fuel shells (2) are provided inside the outer shell (1). Every six fuel shells (2) are arranged in a circumferential close arrangement inside the outer shell (1). The sidewalls of adjacent fuel shells (2) are attached to each other, thus forming a two-layer array structure. Each fuel casing (2) has a cooling pipe (3) coaxially arranged at the center, and nine cooling pipes (3) are arranged around it; the cooling pipe (3) at the center of the fuel casing (2) is a hollow round pipe structure, and the cooling pipes (3) around it are hollow Y-shaped pipe structures.

10. The high-safety modular composite fuel element as described in claim 6, characterized in that, The outer shell (1) is a hollow octagonal prism structure, and the fuel shell (2) is a hollow hexagonal prism structure; seven fuel shells (2) are provided inside the outer shell (1), one of which is located at the center of the outer shell (1), and the other six fuel shells (2) are evenly distributed along the circumferential direction, and the seven fuel shells (2) are closely arranged in a layer; Each fuel casing (2) is provided with seven cooling pipes (3), one of which is located at the center of the fuel casing (2), and the other six cooling pipes (3) are evenly distributed in the circumferential direction; the cooling pipes (3) are hollow circular tubes.

Images