A high thermal conductivity silicon carbide nuclear fuel element and its use

Abstract

This invention belongs to the field of nuclear energy technology and discloses a high thermal conductivity silicon carbide nuclear fuel element and its application. The outer cladding of the element is located on the outermost side of the high thermal conductivity silicon carbide nuclear fuel element, while the innermost side is the inner cladding. End plugs are located at both ends of the high thermal conductivity silicon carbide nuclear fuel element. The end plugs and the inner cladding are tightly fitted with the outer cladding. The nuclear fuel tube is enclosed inside the high thermal conductivity silicon carbide nuclear fuel element and is in close contact with the outer wall of the inner shell of the inner cladding, the inner wall of the outer shell of the outer cladding, and the inner surface of the small step of the end plug. The heat from the nuclear fuel tube is transferred to the inner cladding, the outer cladding, and the end plugs. The cooling medium carries away the heat generated by the nuclear fuel tube from both sides through the inner wall of the inner shell of the inner cladding, the outer wall of the outer shell of the outer cladding, and the outside of the large step of the end plug. This invention avoids the problems of weld seams and poor high-temperature performance of metal cladding tubes in traditional nuclear fuel element fuel cladding and end plug welding, further improving the safety of nuclear reactors.

Description

Technical Field

[0001] This invention belongs to the field of nuclear energy technology, and in particular relates to a silicon carbide nuclear fuel element with high thermal conductivity and its application. Background Technology

[0002] Fuel elements in a nuclear reactor are the smallest components consisting of a nuclear fuel core and a cladding shell. The nuclear fuel core is highly radioactive, and the cladding tube covering it primarily protects the fuel from coolant corrosion while preventing the leakage of radioactive fission products. The selection of materials, manufacturing processes, and reliability of the cladding are crucial to the advancement, economy, and safety of nuclear power. In a nuclear power plant, the fuel cladding serves to prevent the leakage of fission products, isolate the fuel clump from the cooling water (to prevent them from reacting), and dissipate the heat generated by fission; it is the first line of defense for the nuclear power plant. Currently, zirconium and zirconium alloys are the most commonly used materials for nuclear fuel cladding. Traditional nuclear fuel elements are rod-shaped fuel, achieving heat exchange only through contact between the fuel cladding and cooling water. The heat exchange efficiency is limited by the surface area, preventing further increases in the fuel loading.

[0003] Silicon carbide composite materials, due to their low thermal neutron absorption cross section, good high-temperature mechanical properties, and excellent radiation and oxidation resistance, have shown great development potential in the field of nuclear fuel cladding. With the advancement of nuclear power technology, the nuclear power field has placed higher demands on nuclear fuel cladding: longer refueling cycles, higher safety, and a certain degree of accident containment capability. Silicon carbide composite materials, which maintain good strength and radiation resistance at high temperatures, have attracted significant attention in the nuclear fuel research field and may become the preferred cladding material for Generation 4 nuclear reactors.

[0004] Currently, commercial fuel element structures primarily use zirconium alloy cladding to fill nuclear fuel pellets. Over time, radiation damages the metal in terms of hardening, embrittlement, and material expansion. Furthermore, zirconium alloys have poor high-temperature oxidation properties and low high-temperature strength, making them prone to nuclear fuel leakage under dehydration conditions. Additionally, zirconium alloys produce a significant amount of hydrogen under high-temperature steam conditions, increasing the risk of hydrogen explosions. The technology of directly replacing zirconium alloy cladding with silicon carbide tubes faces a series of technical challenges, including the difficulty in manufacturing large-size silicon carbide tubes, insufficient mechanical strength of silicon carbide tubes, and poor reliability of end-plug connections. The use of silicon carbide in nuclear fuel cladding urgently requires an integrated fuel-cladding structure to reduce connections with other dissimilar materials, thereby advancing the use of silicon carbide in cladding. Summary of the Invention

[0005] To overcome the problems existing in related technologies, the present invention discloses a silicon carbide nuclear fuel element with high thermal conductivity and its application. The present invention provides a nuclear fuel element with high thermal conductivity and high safety, featuring a simple manufacturing process and low cost. Compared with existing metal-clad fuel elements, its structure is greatly simplified, and its thermal conductivity and safety performance are significantly improved.

[0006] The technical solution is as follows: A silicon carbide nuclear fuel element with high thermal conductivity, the element comprising: an inner shell covering nuclear fuel, end plugs sealing both ends, an outer shell covering nuclear fuel, and a nuclear fuel tube sealed between the inner shell, the outer shell, and the end plugs;

[0007] The outer cladding is located on the outermost side of the high thermal conductivity silicon carbide nuclear fuel element, and the innermost side is the inner cladding. End plugs are located at both ends of the high thermal conductivity silicon carbide nuclear fuel element. The end plugs and the inner cladding fit tightly with the outer cladding. The nuclear fuel tube is enclosed inside the high thermal conductivity silicon carbide nuclear fuel element and is in close contact with the inner outer wall of the inner cladding, the outer inner wall of the outer cladding, and the inner surface of the small step of the end plug. The nuclear fuel tube is isolated from the external cooling medium. The heat of the nuclear fuel tube is transferred to the inner cladding, the outer cladding, and the end plug. The cooling medium carries away the heat generated by the nuclear fuel tube from both sides through the inner inner wall of the inner cladding, the outer outer wall of the outer cladding, and the outside of the large step of the end plug.

[0008] Furthermore, the inner and outer circumferential dimensions of the inner shell, end plug, outer shell, and nuclear fuel tube are one of the following: cylindrical, rectangular, or hexagonal.

[0009] Furthermore, during the preparation of the cylinder, rectangular cylinder, and hexagonal cylinder, the inner shell, end plug, outer shell, and nuclear fuel tube are integrated into a single unit through a process of blanking, semi-compacting, densification, and connection.

[0010] Furthermore, the preparation of the cylinder, rectangular cylinder, and hexagonal cylinder includes: the inner shell, end plug, outer shell, and nuclear fuel tube are formed by mold pressing or direct printing by additive manufacturing; the blank is sintered into a semi-dense body; it is machined to the set size; after assembly, it is densified and connected by hot isostatic pressing; or the semi-dense body is hot-pressed and sintered into a dense body by hot isostatic pressing, and then connected by sintering and brazing.

[0011] Furthermore, the inner circumferential dimensions of the inner shell, end plug, outer shell, and nuclear fuel tube are achieved by pressing them into solid form and then machining them to achieve the desired shape and size.

[0012] Furthermore, the outer shell, inner shell, and end plug are made of silicon carbide or fiber-reinforced silicon carbide composite ceramic material;

[0013] The nuclear fuel tube is made of silicon carbide composite ceramic material containing nuclear fuel particles, and the nuclear fuel is one or more of uranium and uranium compounds, plutonium and plutonium compounds.

[0014] Furthermore, the height of the high thermal conductivity silicon carbide nuclear fuel element is 50-5000 mm, the outer circumference of the high thermal conductivity silicon carbide nuclear fuel element is 10-35 mm, and the inner circumference is 2-10 mm;

[0015] The inner shell has a thickness of 0.5-5mm; the inner shell has an inner hole, which is a through hole with a size of 2-15mm;

[0016] The outer perimeter of the outer shell is 10-35mm.

[0017] Furthermore, the thickness of the nuclear fuel tube is 0.5-5 mm;

[0018] The outer periphery of the end plug is a double-stepped tubular structure including a large step and a small step. The inner end plug adopts a straight tubular structure with an inner straight tube. The outer dimension of the large step is 10-35mm and the length of the large step is 3-10mm. The outer dimension of the small step is 5-25mm and the length of the small step is 3-10mm. The inner straight tube dimension is 0.5-25mm. The end plug has a hollow inner hole, and the shape and size of the hollow inner hole are consistent with the inner hole of the inner shell.

[0019] Furthermore, the gap between the inner shell, end plug, outer shell, and nuclear fuel tube during assembly is 0.01-0.5 mm;

[0020] The inner wall of the inner shell and the outer wall of the outer shell are both provided with guide vanes, which are evenly distributed on the surface in a spiral shape.

[0021] Another objective of this invention is to provide an application of high thermal conductivity silicon carbide nuclear fuel elements in low-temperature heating of water-cooled reactors, gas-cooled reactors, lead-based reactors, molten salt reactors, and sodium-cooled reactors. In this application, the high thermal conductivity silicon carbide nuclear fuel elements are used to assemble one or more of the elements, and the assembly is carried out by axial stacking or radial arrangement.

[0022] Combining all the above technical solutions, the beneficial effects of this invention are as follows: The structure of the high thermal conductivity silicon carbide nuclear fuel element includes a silicon carbide outer shell, a nuclear fuel tube, a silicon carbide inner shell, and end plugs. The outer shell tube, inner shell tube, and end plugs are made of silicon carbide or fiber-reinforced silicon carbide composite ceramic material, and the nuclear fuel tube is a silicon carbide composite ceramic material containing nuclear fuel particles. The outer shell tube, inner shell tube, and end plug blanks are made from fuel-free powder through pressing and sintering; the nuclear fuel tube blank is made from fuel-containing powder through pressing and sintering; the inner shell tube, nuclear fuel tube, outer shell tube, and end plugs are assembled and connected to form an integrated fuel element. The high thermal conductivity nuclear fuel element provided by this invention has a simple process route, high thermal conductivity, and excellent inherent safety. Compared with existing metal-clad fuel elements, it has lower manufacturing costs, better thermal conductivity, and higher safety performance.

[0023] This invention, through its double-layer cladding structure, increases the contact area between nuclear fuel elements and cooling water, improving heat exchange efficiency. This allows for increased fuel loading during nuclear fuel core design, further enhancing the economics of the nuclear reactor. The integrated silicon carbide fuel cladding and fuel core process avoids the problems of weld seams and poor high-temperature performance of metal cladding tubes inherent in traditional nuclear fuel element cladding and end plug welding, further improving reactor safety.

[0024] High thermal conductivity silicon carbide nuclear fuel elements have a simple structure and manufacturing process. Compared with existing nuclear fuel elements, they require fewer auxiliary structures, resulting in significantly lower manufacturing and post-processing costs. In addition, they have inherent advantages such as safety and high thermal efficiency, making them particularly suitable for small reactors such as experimental reactors and heated reactors, thus expanding the range of reactor site selection.

[0025] Currently, the technical solutions for silicon carbide core cladding tubes at home and abroad are basically designed based on the concept of adding end plugs to the existing cladding tubes. The technical solution of this invention starts from the characteristics of silicon carbide itself and the existing preparation process, rationally optimizes and combines functional components, and proposes an integrated high thermal conductivity silicon carbide nuclear fuel element based on simple structure and high process maturity. The solution has a high degree of conversion and application.

[0026] Due to its inherent properties, silicon carbide is extremely difficult to manufacture and process in its entirety, and currently there is no mature and reliable process available. Furthermore, there is no mature and reliable technology for connecting silicon carbide cladding tubes to end plugs of dissimilar materials. In this invention, the components involved in the high thermal conductivity silicon carbide nuclear fuel element are all made of silicon carbide or silicon carbide-containing materials. Their sizes can be selected according to the level of manufacturing and processing technology, and they can be simply arranged and assembled into the required element group, achieving the same effect as a full-length cladding tube.

[0027] When silicon carbide tubes are used as thin-walled nuclear cladding tubes throughout their entire length, their poor plasticity raises concerns about their structural strength and safety. The technical solution of this invention employs an integrated molding design for silicon carbide tubes that fully encapsulate dispersed nuclear fuel, both internally and externally. This design increases the wall thickness of the nuclear fuel element while maintaining heat exchange efficiency, and simultaneously reduces the length of individual elements, significantly improving the structural strength of each element and enhancing its safety. This strengthens confidence in the application of silicon carbide cladding tubes in nuclear fuel elements. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure;

[0029] Figure 1 This is a diagram of a high thermal conductivity silicon carbide nuclear fuel element provided in an embodiment of the present invention;

[0030] Figure 2 This is a schematic cross-sectional view of the end plug of a high thermal conductivity silicon carbide nuclear fuel element provided in an embodiment of the present invention.

[0031] In the diagram: 1. Inner shell; 2. End plug; 3. Outer shell; 4. Nuclear fuel tube; 5. Inner wall of the inner shell; 6. Outer wall of the inner shell; 7. Inner straight tube; 8. Outer side; 9. Large step; 10. Small step; 11. Inner surface; 12. Outer wall of the outer shell; 13. Inner wall of the outer shell. Detailed Implementation

[0032] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] The innovation of this invention lies in the following: the high thermal conductivity silicon carbide nuclear fuel element is integrally molded using silicon carbide or silicon carbide-rich components, resulting in a simple structure and reliable connection; it increases the overall wall thickness of the nuclear fuel element, adopts a modular approach, shortens the length of the silicon carbide tube, reduces the requirements for preparation and processing technology, and provides high structural strength for a single nuclear fuel element; it features double-sided thermal conduction, resulting in high thermal conductivity and considerable economic benefits; it also possesses high inherent safety, making it a promising candidate for application in small reactors such as experimental reactors and heated reactors.

[0034] The high-temperature melting and infiltration technology used in this invention further improves the density of silicon carbide based on molding and sintering. Isostatic pressing technology can effectively eliminate the internal pores of the material to achieve densification. Hot pressing sintering is used to achieve assembly connection. Therefore, the hot isostatic pressing process can achieve seamless connection of silicon carbide-based nuclear fuel elements.

[0035] Example 1, as Figure 1 As shown, an embodiment of the present invention provides a silicon carbide nuclear fuel element with high thermal conductivity, comprising: an inner cladding 1, an end plug 2, an outer cladding 3, and a nuclear fuel tube 4 between the inner cladding 1, the outer cladding 3, and the end plug 2.

[0036] The outer casing 3, nuclear fuel tube 4, inner casing 1, and end plug 2 are combined and connected to form a single fuel element.

[0037] The inner shell 1 is located in the inner layer of the structure;

[0038] Nuclear fuel tube 4 is located in the middle layer of the structure;

[0039] The outer shell 3 is located on the outer layer of the structure;

[0040] End plugs 2 are located at both ends of the column and are embedded in the gap between the inner shell 1 and the outer shell 3.

[0041] Within the high thermal conductivity silicon carbide nuclear fuel element, all structures are connected as a whole, and the nuclear fuel tube 4 is encapsulated and covered in the middle of the element. The outer periphery of the outer shell 3, the inner periphery of the inner shell 1, and the outer end face of the end plug 2 are all in contact with the cooling medium.

[0042] For example, the outer shell 3, inner shell 1, and end plug 2 are made of silicon carbide or fiber-reinforced silicon carbide composite ceramic material;

[0043] The nuclear fuel tube 4 is made of silicon carbide composite ceramic material containing nuclear fuel particles.

[0044] For example, the nuclear fuel includes one or more of uranium and uranium compounds, plutonium and plutonium compounds;

[0045] Preferably, the nuclear fuel includes one or more of block, pellet, and liquid fuels;

[0046] For example, the structure of the high thermal conductivity silicon carbide nuclear fuel element is a cylinder or a polygonal cylinder;

[0047] Preferably, the inner shell 1 is a straight tubular structure with an outer dimension of 5-15mm and a thickness of 0.5-5mm;

[0048] The nuclear fuel tube 4 is a straight tube with an outer dimension of 5-25 mm and a thickness of 0.5-5 mm.

[0049] The outer shell 3 is a straight tubular structure with an outer dimension of 10-35mm and a thickness of 0.5-5mm;

[0050] The end plug 2 has a two-step tubular outer structure and a straight tubular inner structure. The outer dimensions of the large step 9 are 10-35mm, the outer dimensions of the small step 10 are 5-25mm, and the dimensions of the inner straight tube 7 are 0.5-25mm.

[0051] Preferably, the gap between the inner dimension of the nuclear fuel tube 4 and the outer dimension of the inner cladding 1 is 0.01-0.5 mm;

[0052] The gap between the outer dimensions of the nuclear fuel tube 4 and the inner dimensions of the outer casing 3 is 0.01-0.5 mm;

[0053] Preferably, the outer dimensions of the end plug 2 and the large step 9 are the same as the outer dimensions of the outer shell 3;

[0054] The outer dimensions of the end plug 2 and the small step 10 are consistent with the outer dimensions of the fuel pipe 4;

[0055] The end plug 2 has the same inner dimensions as the outer dimensions of the inner shell 1;

[0056] The end plug 2 has a large step 9 with a length of 3-10mm. The length of the two large steps 9 plus the length of the outer shell 3 equals the length of the inner shell 1.

[0057] The end plug 2 has a small step 10 with a length of 3-10mm. The length of the two small steps 10 plus the length of the fuel pipe 4 equals the length of the outer casing 3.

[0058] Preferably, the gap between the inner dimension of the nuclear fuel tube 4 and the outer dimension of the inner cladding 1 is 0.01-0.5 mm;

[0059] The gap between the outer dimensions of the nuclear fuel tube 4 and the inner dimensions of the outer casing 3 is 0.01-0.5 mm;

[0060] The inner shell 1 has a length of 50-5000mm.

[0061] Example 2: The high thermal conductivity carbon-based nuclear fuel element described herein is used in water reactors, gas-cooled reactors, molten salt reactors, and lead-based reactors.

[0062] Example 3, as Figures 1-2 As shown, as another embodiment of the present invention, the high thermal conductivity silicon carbide nuclear fuel element of the present invention includes an inner shell 1 covering nuclear fuel, an end plug 2 sealing both ends, an outer shell 3 covering nuclear fuel, and a nuclear fuel tube 4 sealed between the inner shell 1, the outer shell 3, and the end plug 2.

[0063] The outer shell 3 is located on the outermost side of the structure, and the innermost side is the inner shell 1. End plugs 2 are located at both ends of the structure. The end plugs 2 and the inner shell 1 are tightly fitted with the outer shell 3. The nuclear fuel tube 4 is enclosed inside the structure and is close to the outer wall 6 of the inner shell. The inner walls 13 of the inner shell 1 and the outer shell 3, as well as the inner surface 11 of the small step 10 of the end plug 2, are isolated from the external cooling medium. The heat of the nuclear fuel tube 4 is transferred to the inner shell 1, the outer shell 3, and the end plug 2. The cooling medium carries away the heat generated by the nuclear fuel tube 4 from both sides through the inner wall 5 of the inner shell 1, the outer wall 12 of the outer shell 3, and the outer surface 8 of the large step 9 of the end plug 2, achieving the purpose of efficient heat exchange.

[0064] Specifically, the inner and outer circumferences of the inner casing 1, end plug 2, outer casing 3, and nuclear fuel tube 4 can be cylindrical or rectangular, hexagonal, or other polygonal prisms. In terms of materials, the outer casing 3, inner casing 1, and end plug 2 can be made of silicon carbide or fiber-reinforced silicon carbide composite ceramic materials, the nuclear fuel tube 4 can be made of silicon carbide composite ceramic materials containing nuclear fuel particles, and the nuclear fuel 4 can be one or more of uranium and uranium compounds, plutonium and plutonium compounds.

[0065] During the preparation of the cylindrical structure, the inner shell 1, end plug 2, outer shell 3 and nuclear fuel tube 4 are processed into a blank, a semi-compacted body, a compacted body, and then connected into a whole.

[0066] In terms of preparation methods, the inner shell 1, end plug 2, outer shell 3 and nuclear fuel tube 4 can be formed by mold pressing or direct printing by additive manufacturing. The blank is sintered into a semi-dense body, and then machined to the set size by mechanical processing. After assembly, it is densified and connected by hot isostatic pressing. Alternatively, the semi-dense bodies can be hot-pressed and sintered into dense bodies by hot isostatic pressing, and then connected by sintering, brazing and other methods. The connection interface has good airtightness.

[0067] The inner circumferential dimensions of the inner shell 1, end plug 2, outer shell 3, and nuclear fuel tube 4 can be formed by mold pressing or additive manufacturing printing, or they can be pressed into solid form and then machined to achieve the set shape and size.

[0068] In terms of size settings, the height of high thermal conductivity silicon carbide nuclear fuel elements is 50-5000 mm, the outer circumference of high thermal conductivity silicon carbide nuclear fuel elements is 10-35 mm, the inner circumference is 2-10 mm, and other dimensions are set according to the specific shape of high thermal conductivity silicon carbide nuclear fuel elements.

[0069] The inner shell 1 and the outer shell 3 have appropriate thicknesses to ensure structural strength and airtightness, and to facilitate rapid heat transfer with the cooling medium. Alternatively, the thickness of the inner shell 1 and the outer shell 3 can be 0.5-5 mm.

[0070] The inner shell 1 has an appropriate inner bore size to ensure the passage of cooling medium. Alternatively, the inner bore can be a through hole with a size of 2-15 mm.

[0071] The outer casing 3 has appropriate outer circumferential dimensions to ensure efficient placement of nuclear fuel and heat exchange, as well as the feasibility of the manufacturing process. Alternatively, the outer circumferential dimensions of the outer casing 3 can be 10-35 mm.

[0072] The nuclear fuel tube 4 has an appropriate thickness to ensure sufficient nuclear fuel is placed to increase the power of the nuclear reactor. Its thickness and the amount of nuclear fuel filled can be determined according to the fuel loading required by the element, and can be adjusted according to the thickness of the inner cladding 1, the outer cladding 3, and the cooling medium. Alternatively, the thickness can be 0.5-5 mm.

[0073] End plug 2 has appropriate dimensions to ensure connection reliability and thermal conductivity. Alternatively, end plug 2 has a double-stepped tubular outer circumference and a straight tubular inner structure. The outer dimension of the larger step 9 is 10-35 mm, and the length of the larger step 9 is 3-10 mm. The outer dimension of the smaller step 10 is 5-25 mm, and the length of the smaller step 10 is 3-10 mm. The dimensions of the inner straight tube 7 are 0.5-25 mm. In addition, to ensure the flow of cooling medium, end plug 2 has a hollow inner hole, the shape and size of which are consistent with the inner hole of the inner shell 1.

[0074] When assembling the inner casing 1, end plug 2, outer casing 3, and nuclear fuel tube 4, the gaps between each component should be of appropriate size to ensure assemblability and thermal conductivity. Alternatively, the assembly gap can be 0.01-0.5 mm.

[0075] In some embodiments, the inner wall of the inner shell 1 and the outer wall of the outer shell 3 may also be provided with guide vanes. The main purpose is to accelerate the passage of the cooling medium to improve the heat exchange efficiency. The guide vanes are evenly distributed on the surface in a spiral shape, which is beneficial to overall heat dissipation.

[0076] In practical applications, the nuclear fuel elements described in this invention can be used individually or in multiple assembly; the number of nuclear fuel elements assembled depends on the size of the reactor. In terms of assembly method, multiple fuel elements can be stacked axially, arranged radially, or extended in both directions.

[0077] Compared to the traditional zirconium alloy cladding assemblies in water reactors, which have a cladding diameter of 9.5 mm and a center-to-center spacing of 12.6 mm, the nuclear fuel elements of this invention have an outer circumferential dimension of 5-25 mm and a wall thickness of 0.5-5 mm. The amount of nuclear fuel loaded can be adjusted by selecting an appropriate wall thickness. The spacing of the nuclear fuel elements in this invention can be flexibly adjusted through the design of the assembly structure. The radial spacing between adjacent nuclear fuel elements can be selected as 5-15 mm to allow the cooling medium to carry away the heat conducted from the outer wall of the outer cladding 3.

[0078] Compared to traditional zirconium alloy cladding assemblies, where end plugs 2 need to be welded to both ends to seal the nuclear fuel after the cladding is filled with nuclear fuel, the nuclear fuel element of this invention directly connects the nuclear fuel, cladding, and end plugs 2 into one unit, resulting in a reliable structure and a simple manufacturing process.

[0079] The silicon carbide nuclear fuel element with high thermal conductivity described in this invention can be flexibly customized in size and is suitable for reactors of different sizes, such as water reactors, gas-cooled reactors, lead-based reactors, molten salt reactors, and sodium-cooled reactors. It is especially suitable for small reactors and micro reactors. Its high safety provides a feasible solution for cryogenic heating reactors.

[0080] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0081] The nuclear fuel element of this invention features a double-sided heat-conducting column structure that replaces the thin-walled, long-tube metal cladding of existing fuel assemblies. It uses silicon carbide-based material to coat the nuclear fuel, improving the high-temperature performance of the nuclear fuel element. The structure of the nuclear fuel being in close contact with the cladding allows for rapid heat transfer from the nuclear fuel to the cladding. The double-sided heat-conducting structure also enables rapid heat transfer between the cladding and the cooling medium, improving heat conduction efficiency and preventing heat accumulation in the nuclear fuel element that could cause structural abnormalities. This significantly improves the economy and safety of nuclear reactors.

[0082] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A silicon carbide nuclear fuel element with high thermal conductivity, characterized in that, include: The inner shell (1) covering nuclear fuel, the end plugs (2) sealing both ends, the outer shell (3) covering nuclear fuel, and the nuclear fuel tube (4) sealed between the inner shell (1), the outer shell (3) and the end plugs (2); The outer shell (3) is located on the outermost side of the high thermal conductivity silicon carbide nuclear fuel element, and the innermost side is the inner shell (1). End plugs (2) are set at both ends of the high thermal conductivity silicon carbide nuclear fuel element. The end plugs (2) and the inner shell (1) are tightly fitted with the outer shell (3). The nuclear fuel tube (4) is sealed inside the high thermal conductivity silicon carbide nuclear fuel element and is attached to the inner outer wall (6) of the inner shell (1), the outer inner wall (13) of the outer shell (3), and the end plugs (2). The inner surface (11) of the small step (10) of the plug (2) isolates the nuclear fuel tube (4) from the external cooling medium; the heat of the nuclear fuel tube (4) is transferred to the inner shell (1), the outer shell (3) and the end plug (2); the cooling medium carries away the heat generated by the nuclear fuel tube (4) from both sides through the inner wall (5) of the inner shell (1), the outer wall (12) of the outer shell (3) and the outside (8) of the large step (9) of the end plug (2); The inner and outer circumference dimensions of the inner shell (1), end plug (2), outer shell (3) and nuclear fuel tube (4) are one of cylinder, rectangular prism, and hexagonal prism. The preparation of the cylinder, rectangular cylinder and hexagonal cylinder includes: the inner shell (1), end plug (2), outer shell (3) and nuclear fuel tube (4) are formed by mold pressing or additive manufacturing direct printing. The blank is sintered into a semi-dense body, processed to the set size by machining, assembled and then densified and connected by hot isostatic pressing, or the semi-dense body is hot-pressed and sintered into a dense body by hot isostatic pressing, and then connected by sintering and brazing.

2. The high thermal conductivity silicon carbide nuclear fuel element according to claim 1, characterized in that, During the preparation of the cylinder, rectangular cylinder, and hexagonal cylinder, the inner shell (1), end plug (2), outer shell (3), and nuclear fuel tube (4) are integrated into a whole through the processes of blank body, semi-dense body, densification, and connection.

3. The high thermal conductivity silicon carbide nuclear fuel element according to claim 1, characterized in that, The inner circumference dimensions of the inner shell (1), end plug (2), outer shell (3) and nuclear fuel tube (4) are achieved by pressing them into solid form and then machining them to achieve the set shape and size.

4. The high thermal conductivity silicon carbide nuclear fuel element according to claim 1, characterized in that, The outer shell (3), inner shell (1), and end plug (2) are made of silicon carbide or fiber-reinforced silicon carbide composite ceramic material; The nuclear fuel tube (4) is made of silicon carbide composite ceramic material containing nuclear fuel particles, and the nuclear fuel is one or more of uranium and uranium compounds, plutonium and plutonium compounds.

5. The high thermal conductivity silicon carbide nuclear fuel element according to claim 1, characterized in that, The height of the high thermal conductivity silicon carbide nuclear fuel element is 50-5000 mm, the outer circumference of the high thermal conductivity silicon carbide nuclear fuel element is 10-35 mm, and the inner circumference is 2-10 mm; The inner shell (1) has a thickness of 0.5-5mm; the inner shell (1) has an inner hole, which is a through hole with a size of 2-15mm; The outer casing (3) has an outer perimeter dimension of 10-35 mm.

6. The high thermal conductivity silicon carbide nuclear fuel element according to claim 1, characterized in that, The thickness of the nuclear fuel tube (4) is 0.5-5 mm; The outer periphery of the end plug (2) is a double-stepped tubular structure including a large step (9) and a small step (10). The end plug (2) adopts a straight tubular structure with an inner straight tube (7). The outer dimension of the large step (9) is 10-35mm and the length of the large step (9) is 3-10mm. The outer dimension of the small step (10) is 5-25mm and the length of the small step (10) is 3-10mm. The size of the inner straight tube (7) is 0.5-25mm. The end plug (2) has a hollow inner hole. The shape and size of the hollow inner hole are consistent with the inner hole of the inner shell (1).

7. The high thermal conductivity silicon carbide nuclear fuel element according to claim 1, characterized in that, The gap between the inner shell (1), end plug (2), outer shell (3) and nuclear fuel tube (4) during assembly is 0.01-0.5 mm; The inner wall (5) of the inner shell (1) and the outer wall (12) of the outer shell (3) are both provided with guide vanes, which are evenly distributed on the surface in a spiral shape.

8. An application of high thermal conductivity silicon carbide nuclear fuel element in cryogenic heating of water-cooled reactors, gas-cooled reactors, lead-based reactors, molten salt reactors, and sodium-cooled reactors, characterized in that... In application, single or multiple high thermal conductivity silicon carbide nuclear fuel elements as described in any one of claims 1-7 are assembled, with axial stacking or radial arrangement used in the assembly.

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