High-thermal-conductivity silicon carbide nuclear fuel element and application thereof

Abstract

The invention belongs to the technical field of nuclear energy, and discloses a high-thermal-conductivity silicon carbide nuclear fuel element and application thereof. An outer cladding of the element is located on the outermost side of the high-thermal-conductivity silicon carbide nuclear fuel element, an inner cladding is arranged on the innermost side, end plugs are arranged at the two ends of the high-thermal-conductivity silicon carbide nuclear fuel element, the end plugs and the inner cladding are in close fit with the outer cladding, and a nuclear fuel pipe is sealed in the high-thermal-conductivity silicon carbide nuclear fuel element. The inner shell outer wall of the inner cladding shell, the outer shell inner wall of the outer cladding shell and the inner face of the small step of the end plug are tightly attached, and heat of the nuclear fuel pipe is transferred to the inner cladding shell, the outer cladding shell and the end plug. A cooling medium passes through the inner shell inner wall of the inner cladding shell, the outer shell outer wall of the outer cladding shell and the outside of the large step of the end plug, and takes away heat generated by the nuclear fuel pipe from the two sides. The problems that welding seams exist in welding of a fuel cladding and an end plug of a traditional nuclear fuel element and the high-temperature performance of a metal cladding pipe is poor are solved, and the safety of a nuclear reactor is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear energy, and in particular relates to a high thermal conductivity silicon carbide nuclear fuel element and application thereof. Background Art

[0002] The fuel element in a nuclear reactor is the smallest component consisting of a nuclear fuel core and a nuclear cladding. The nuclear fuel core is highly radioactive. The main function of the cladding tube covering the nuclear fuel core is to protect the nuclear fuel from corrosion by the coolant while preventing the radioactive nuclear fission products from spilling out. The selection of materials, manufacturing process and reliability are of great significance to the advancement, economy and safety of the nuclear power field. In a nuclear power plant, the fuel cladding is responsible for preventing the leakage of fission products, isolating the fuel blocks and cooling water (to prevent the two from reacting), and transferring the heat energy generated by fission. It is the first safety barrier of the nuclear power plant. At present, the materials commonly used for nuclear fuel cladding are mainly zirconium and zirconium alloys. Traditional nuclear fuel elements are rod-shaped nuclear fuels, which only achieve the purpose of heat exchange through the contact between the fuel outer cladding and the cooling water. The heat exchange efficiency is limited by the surface area, and the loading amount of nuclear fuel cannot be further increased.

[0003] Silicon carbide composite materials have shown great development potential in the field of nuclear fuel cladding due to their low thermal neutron absorption cross section, good high-temperature mechanical properties, good radiation resistance and oxidation resistance. With the advancement of nuclear power technology, the nuclear power field has put forward higher requirements for nuclear fuel cladding: longer refueling cycle, higher safety, and the ability to accommodate accidents to a certain extent. Silicon carbide composite materials have the ability to maintain good strength and radiation resistance at high temperatures, and have received great attention in the field of nuclear fuel research. They may become the preferred cladding material for the fourth-generation nuclear reactor.

[0004] At present, the structure of commercial fuel elements is mainly composed of zirconium alloy cladding filled with nuclear fuel pellets. As time goes by, radiation causes damage to the metal in terms of hardening, embrittlement and material expansion. In addition, zirconium alloy has poor high-temperature oxidation performance and low high-temperature strength, which can easily cause nuclear fuel leakage under dehydration conditions. Zirconium alloy produces a large amount of hydrogen under high-temperature water vapor conditions, which can easily cause hydrogen explosions. The technology of using silicon carbide tubes to directly replace zirconium alloy claddings has a series of technical difficulties, such as the difficulty in preparing large-sized silicon carbide tubes, insufficient mechanical strength of silicon carbide tubes, and poor reliability of end plug connections. The use of silicon carbide materials in nuclear fuel claddings urgently requires a structure that integrates fuel and cladding to reduce the connection with other heterogeneous material components, thereby promoting the use of silicon carbide materials in claddings. Summary of the invention

[0005] In order to overcome the problems existing in the related art, the disclosed embodiments of the present invention provide a high thermal conductivity silicon carbide nuclear fuel element and its application. The present invention provides a high thermal conductivity and high safety nuclear fuel element, with a simple process route and low cost. Compared with the existing metal cladding fuel element, the structure is greatly simplified, and the thermal conduction efficiency and safety performance are significantly improved.

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

[0007] The outer cladding is located at the outermost side of the high thermal conductivity silicon carbide nuclear fuel element, the innermost side is the inner cladding, and the end plugs are arranged at both ends of the high thermal conductivity silicon carbide nuclear fuel element. The end plugs and the inner cladding and the outer cladding are closely matched, and the nuclear fuel tube is enclosed in the interior of the high thermal conductivity silicon carbide nuclear fuel element and is closely attached to the inner shell outer wall of the inner cladding, the outer shell 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 passes through the inner shell inner wall of the inner cladding, the outer shell outer wall of the outer cladding and the outside of the large step of the end plug, and takes away the heat generated by the nuclear fuel tube from both sides.

[0008] Furthermore, the inner and outer circumferences of the inner cladding, end plug, outer cladding and nuclear fuel tube are one of the following: a cylinder, a rectangular cylinder and a hexagonal cylinder.

[0009] Furthermore, when the cylindrical body, rectangular cylindrical body and hexagonal cylindrical body are prepared, the inner cladding, end plug, outer cladding and nuclear fuel tube are formed into a blank, a semi-dense body, densified and connected into one body.

[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, and is machined to a set size by mechanical processing. After assembly, hot isostatic pressing is used to achieve densification and connection, or the semi-dense bodies are hot-pressed and sintered into dense bodies by hot isostatic pressing, and then connected by sintering and brazing.

[0011] Furthermore, the inner circumference dimensions of the inner cladding, the end plug, the outer cladding and the nuclear fuel tube are pressed into a solid state and then mechanically processed to achieve the set 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 made of 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 size of the high thermal conductivity silicon carbide nuclear fuel element is 10-35 mm, and the inner circumference size is 2-10 mm;

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

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

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

[0018] The outer circumference of the end plug is a double-step tubular structure including a large step and a small step. The end plug adopts a straight tube structure with an inner straight tube. The outer dimension of the large step is 10-35mm, the length of the large step is 3-10mm, the outer dimension of the small step is 5-25mm, the length of the small step is 3-10mm, and the dimension of the inner straight tube 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 inner cladding, the end plug, the outer cladding and the nuclear fuel tube have a gap of 0.01-0.5 mm between them when they are assembled;

[0020] The inner wall of the inner shell of the inner enclosure and the outer wall of the outer shell of the outer enclosure are both provided with guide wing plates, and the guide wing plates are spirally and evenly distributed on the surface.

[0021] Another object of the present invention is to provide a high thermal conductivity silicon carbide nuclear fuel element for use in low-temperature heating of water reactors, gas-cooled reactors, lead-based reactors, molten salt reactors, and sodium-cooled reactors. In the application, the high thermal conductivity silicon carbide nuclear fuel elements are assembled individually or in multiples, and axial stacking or radial arrangement is adopted during the assembly.

[0022] Combined with all the above technical solutions, the beneficial effects of the present invention are as follows: the structure of the high thermal conductivity silicon carbide nuclear fuel element includes a silicon carbide outer cladding, a nuclear fuel tube, a silicon carbide inner cladding, and an end plug. Among them, the outer cladding tube, the inner cladding tube, and the end plug are made of silicon carbide or fiber-reinforced silicon carbide composite ceramic materials, and the nuclear fuel tube is a silicon carbide composite ceramic material containing nuclear fuel particles. The outer cladding tube, the inner cladding tube, and the end plug blank are made of fuel-free powder by pressing and sintering; the nuclear fuel tube blank is made of fuel-containing powder by pressing and sintering; the inner cladding tube, the nuclear fuel tube, the outer cladding tube, and the end plug are assembled and connected to form an integrated fuel element. The high thermal conductivity nuclear fuel element provided by the present invention has a simple process route, high thermal conductivity, and excellent inherent safety. Compared with the existing metal cladding fuel elements, it has low production cost, excellent thermal conductivity, and high safety performance.

[0023] The present invention increases the contact area between the nuclear fuel element and the cooling water and improves the heat exchange efficiency through the structural design of the inner and outer double-layer cladding, thereby increasing the loading amount of nuclear fuel when designing the nuclear fuel core, and further improving the economy of the nuclear reactor. The silicon carbide fuel cladding and fuel core body integration process is adopted to avoid the problems of the weld and the poor high temperature performance of the metal cladding tube in the traditional nuclear fuel element fuel cladding and end plug welding, and further improve the safety of the nuclear reactor.

[0024] High thermal conductivity silicon carbide nuclear fuel elements have simple structure and manufacturing process. Compared with existing nuclear fuel elements, they require fewer auxiliary structures and significantly reduce manufacturing and post-processing costs. In addition, they have the advantages of inherent safety and high thermal efficiency. They are particularly suitable for small reactors such as test reactors and heating reactors, expanding the site selection range of reactors.

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

[0026] Due to its own characteristics, the preparation and processing of full-length silicon carbide cladding tubes is very difficult, and there is currently no mature and reliable process to achieve it. In addition, there is no mature and reliable process for connecting silicon carbide cladding tubes with end plugs of different materials. In the present 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. The size can be selected according to the level of preparation and processing technology, and the required component group can be assembled into a simple arrangement to achieve the same effect as the full-length cladding tube.

[0027] When silicon carbide tubes are used as thin-walled nuclear cladding tubes with full length, their poor plasticity causes people to doubt the safety of their structural strength. The technical solution of the present invention adopts an integrated molding design of silicon carbide tubes with inner and outer claddings fully covering dispersed nuclear fuel. On the basis of ensuring heat exchange efficiency, the wall thickness of nuclear fuel elements is increased, and the length of a single element can also be reduced, which significantly improves the structural strength of a single element and its safety, thereby enhancing people's confidence in the application of silicon carbide cladding tubes in nuclear fuel elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the description, serve to explain the principles of the present disclosure;

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

[0030] Figure 2 It is a schematic cross-sectional structure diagram of an end plug of a high thermal conductivity silicon carbide nuclear fuel element provided by an embodiment of the present invention;

[0031] In the figure: 1. inner cladding; 2. end plug; 3. outer cladding; 4. nuclear fuel tube; 5. inner wall of inner shell; 6. outer wall of inner shell; 7. inner straight tube; 8. outside; 9. large step; 10. small step; 11. inner surface; 12. outer wall of outer shell; 13. inner wall of outer shell. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0033] The innovation of the present invention lies in: the high thermal conductivity silicon carbide nuclear fuel element of the present invention is formed in an integrated manner using silicon carbide or silicon carbide-rich components, and has a simple structure and reliable connection; the overall wall thickness of the nuclear fuel element is increased, and the modular use method shortens the length of the silicon carbide tube, reduces the requirements for preparation and processing technology, and the structural strength of a single nuclear fuel element is high; heat conduction is carried out on both the inside and outside sides, the heat conduction efficiency is high, and the economy is considerable; it has high inherent safety, and has broad application prospects in small reactors such as test reactors and heating reactors.

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

[0035] Embodiment 1, as Figure 1 As shown, a high thermal conductivity silicon carbide nuclear fuel element provided by an embodiment of the present invention includes: 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 cladding 3, the nuclear fuel tube 4, the inner cladding 1 and the end plug 2 are assembled and connected to form an integral fuel element.

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

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

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

[0040] The 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] Among them, in the high thermal conductivity silicon carbide nuclear fuel element, various structures are connected into a whole, the nuclear fuel tube 4 is encapsulated and wrapped in the middle of the element, and the outer periphery of the outer shell 3, the inner periphery of the inner shell 1, and the outer end surface of the end plug 2 are all in contact with the cooling medium.

[0042] Exemplarily, the outer cladding 3, the inner cladding 1, and the 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] Exemplarily, 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, granular, and liquid fuel;

[0046] Exemplarily, 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 size of 5-15 mm and a thickness of 0.5-5 mm;

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

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

[0050] The end plug 2 is a two-step tubular structure on the outside and a straight tubular structure on the inside. The outer size of the large step 9 is 10-35mm, the outer size of the small step 10 is 5-25mm, and the size of the inner straight tube 7 is 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 dimension of the nuclear fuel tube 4 and the inner dimension of the outer cladding 3 is 0.01-0.5mm;

[0053] Preferably, the outer dimensions of the end plug 2 and the large step 9 are consistent with 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 inner dimensions of the end plug 2 are consistent with the outer dimensions of the inner cladding 1;

[0056] The end plug 2 has a large step 9 with a length of 3-10 mm, and the length of the two large steps 9 plus the length of the outer shell 3 is equal to the length of the inner shell 1;

[0057] The end plug 2 has a small step 10 with a length of 3-10 mm, and the length of the two small steps 10 plus the length of the fuel pipe 4 is equal to the length of the outer shell 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 dimension of the nuclear fuel tube 4 and the inner dimension of the outer cladding 3 is 0.01-0.5mm;

[0060] The length of the inner shell 1 is 50-5000 mm.

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

[0062] Embodiment 3, as Figure 1-Figure 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 cladding 1 coating the nuclear fuel, end plugs 2 sealing both ends, an outer cladding 3 coating the nuclear fuel, and a nuclear fuel tube 4 sealed between the inner cladding 1, the outer cladding 3 and the end plugs 2.

[0063] The outer cladding 3 is located at the outermost side of the structure, the innermost side is the inner cladding 1, the end plugs 2 are arranged at both ends of the structure, the end plugs 2 and the inner cladding 1 and the outer cladding 3 are tightly matched, the nuclear fuel tube 4 is enclosed inside the structure and close to the outer wall 6 of the inner shell, the inner cladding 1, the outer shell inner wall 13 of the outer cladding 3 and 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 cladding 1, the outer cladding 3 and the end plug 2. The cooling medium takes away the heat generated by the nuclear fuel tube 4 from both sides through the inner shell inner wall 5 of the inner cladding 1, the outer shell outer wall 12 of the outer cladding 3 and the outer surface 8 of the large step 9 of the end plug 2, so as to achieve the purpose of efficient heat exchange.

[0064] Specifically, the inner and outer circumferences of the inner cladding 1, the end plug 2, the outer cladding 3 and the nuclear fuel tube 4 can be cylindrical or rectangular, hexagonal or other polygonal columns. In terms of materials, the outer cladding 3, the inner cladding 1 and the 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 made of one or more of uranium and uranium compounds, plutonium and plutonium compounds.

[0065] When the column structure is prepared, the inner cladding 1, the end plug 2, the outer cladding 3 and the nuclear fuel tube 4 are formed into a whole through the processes of blank, semi-dense body, densification and connection.

[0066] In terms of preparation method, the inner cladding 1, the end plug 2, the outer cladding 3 and the nuclear fuel tube 4 can be formed by mold pressing or direct printing by additive manufacturing. The green body is sintered into a semi-dense body, which is processed to a set size by mechanical processing. After assembly, hot isostatic pressing is used to achieve densification and connection, or the semi-dense bodies are hot-pressed and sintered into dense bodies by hot isostatic pressing, and then connected by sintering, brazing, etc., and the connection interface has good airtightness.

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

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

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

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

[0071] The outer cladding 3 has an appropriate outer circumference size to ensure the placement of the nuclear fuel and the heat exchange efficiency as well as the feasibility of the preparation process. Alternatively, the outer circumference size of the outer cladding 3 can be 10-35 mm.

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

[0073] The end plug 2 has an appropriate size to ensure connection reliability and thermal conductivity. As an option, the outer periphery of the end plug 2 is a double-step tubular structure, and the inner part is a straight tubular structure, the outer size of the large step 9 is 10-35mm, the length of the large step 9 is 3-10mm, the outer size of the small step 10 is 5-25mm, the length of the small step 10 is 3-10mm, and the size of the inner straight tube 7 is 0.5-25mm. In addition, to ensure the circulation of the cooling medium, the end plug 2 has a hollow inner hole, and the shape and size of the hole are consistent with the inner hole of the inner shell 1.

[0074] When assembling the inner cladding 1, the end plug 2, the outer cladding 3 and the nuclear fuel tube 4, the gaps between the components have appropriate sizes to ensure assemblability and thermal conductivity. Alternatively, the assembly gap is 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 fins, the main purpose of which is to accelerate the passage of the cooling medium to improve the heat exchange efficiency. The guide fins are evenly distributed on the surface in a spiral shape, which is beneficial to overall heat dissipation.

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

[0077] Compared with the traditional zirconium alloy cladding assembly in the water reactor, the cladding diameter is 9.5mm and the cladding center spacing is 12.6mm. In the nuclear fuel element of the present invention, the outer circumferential size of the nuclear fuel tube 4 is 5-25mm and the wall thickness is 0.5-5mm. The adjustment of the nuclear fuel loading amount is achieved by selecting a suitable wall thickness. The spacing of the nuclear fuel elements of the present invention can be flexibly adjusted by the design of the assembly structure. The spacing between adjacent nuclear fuel elements in the radial direction can be selected to be 5-15mm, so that the heat conducted from the outer wall of the outer cladding 3 can be taken away when the cooling medium passes through.

[0078] Compared with the traditional zirconium alloy cladding assembly, in which end plugs 2 need to be welded at both ends to seal the nuclear fuel after the cladding is filled with nuclear fuel, the nuclear fuel element of the present invention directly connects the nuclear fuel, the cladding and the end plugs 2 into one body, has a reliable structure and a simple preparation process.

[0079] The high thermal conductivity silicon carbide nuclear fuel element described in the embodiment of the present invention has an overall size that can be flexibly customized 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, and is particularly suitable for small reactors and micro-reactors. Its high safety provides a feasible solution for low-temperature heating reactors.

[0080] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0081] The nuclear fuel element of the present invention has a double-sided heat-conducting column structure that replaces the thin-walled, long-tube metal cladding of the existing fuel assembly, and uses silicon carbide-based materials to coat the nuclear fuel, thereby improving the high-temperature performance of the nuclear fuel element; the structure in which the nuclear fuel is close to the cladding can realize rapid transfer of heat generated by the nuclear fuel to the cladding, and the double-sided heat-conducting structure can realize rapid transfer of heat between the cladding and the cooling medium, thereby improving heat conduction efficiency, avoiding heat accumulation in the nuclear fuel element to cause structural abnormalities, and can significantly improve the economy and safety of the nuclear reactor.

[0082] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered within the protection scope of the present invention.

Claims

1. A high thermal conductivity silicon carbide nuclear fuel element, characterized in that: include: An inner cladding (1) covering the nuclear fuel, end plugs (2) sealing both ends, an outer cladding (3) covering the nuclear fuel, and a nuclear fuel tube (4) sealed between the inner cladding (1), the outer cladding (3) and the end plugs (2); The outer cladding (3) is located at the outermost side of the high thermal conductivity silicon carbide nuclear fuel element, and the inner cladding (1) is located at the innermost side. The end plugs (2) are arranged at both ends of the high thermal conductivity silicon carbide nuclear fuel element. The end plugs (2) and the inner cladding (1) are tightly matched with the outer cladding (3). The nuclear fuel tube (4) is enclosed in the interior of the high thermal conductivity silicon carbide nuclear fuel element and is closely attached to the inner shell outer wall (6) of the inner cladding (1), the outer shell inner wall (13) of the outer cladding (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 cladding (1), the outer cladding (3) and the end plug (2); the cooling medium passes through the inner shell inner wall (5) of the inner cladding (1), the outer shell outer wall (12) of the outer cladding (3) and the outer surface (8) of the large step (9) of the end plug (2), and takes away the heat generated by the nuclear fuel tube (4) from both sides.

2. The high thermal conductivity silicon carbide nuclear fuel element according to claim 1, characterized in that: The inner and outer perimeter dimensions of the inner cladding (1), the end plug (2), the outer cladding (3) and the nuclear fuel tube (4) are one of a cylinder, a rectangular cylinder and a hexagonal cylinder.

3. The high thermal conductivity silicon carbide nuclear fuel element according to claim 2, characterized in that: When preparing the cylindrical body, rectangular cylindrical body and hexagonal cylindrical body, the inner cladding (1), the end plug (2), the outer cladding (3) and the nuclear fuel tube (4) are formed into a blank, a semi-dense body, densified and connected into one body.

4. The high thermal conductivity silicon carbide nuclear fuel element according to claim 3, characterized in that: The preparation of the cylindrical body, rectangular cylindrical body and hexagonal cylindrical body comprises: the inner cladding (1), the end plug (2), the outer cladding (3) and the nuclear fuel tube (4) are formed by die pressing or additive manufacturing direct printing, the blank is sintered into a semi-dense body, processed to a set size by mechanical processing, and then densified and connected by hot isostatic pressing after assembly, 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.

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

6. The high thermal conductivity silicon carbide nuclear fuel element according to claim 1, characterized in that: The outer shell (3), the inner shell (1) and the 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 made of one or more of uranium and uranium compounds, plutonium and plutonium compounds.

7. 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 size of the high thermal conductivity silicon carbide nuclear fuel element is 10-35 mm, and the inner circumference size is 2-10 mm; The inner shell (1) has a thickness of 0.5-5 mm; the inner shell (1) has an inner hole, which is a through hole and has a size of 2-15 mm; The outer circumference size of the outer shell (3) is 10-35 mm.

8. 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 circumference of the end plug (2) is a double-step tubular structure including a large step (9) and a small step (10); the inner portion of the end plug (2) adopts a straight tube structure of an inner straight tube (7); the outer dimension of the large step (9) is 10-35 mm, the length of the large step (9) is 3-10 mm, the outer dimension of the small step (10) is 5-25 mm, the length of the small step (10) is 3-10 mm, and the dimension of the inner straight tube (7) is 0.5-25 mm; 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).

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

10. Application of high thermal conductivity silicon carbide nuclear fuel element in low temperature heating of water reactor, gas-cooled reactor, lead-based reactor, molten salt reactor and sodium-cooled reactor, characterized in that: In application, the high thermal conductivity silicon carbide nuclear fuel elements according to any one of claims 1 to 9 are assembled singly or in plurality, and axial stacking or radial arrangement is adopted in the assembly.

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