Spiral multi-lobed nuclear fuel element with composite cladding and method for manufacturing the same

Abstract

The present application relates to a spiral multi-lobed nuclear fuel element with a composite cladding and a manufacturing method thereof, the method comprising the following steps: mixing nuclear material particles with metal matrix powder to form a fuel core blank; placing the fuel core blank in a first cladding tube; using a co-extrusion process to form a core rod with the fuel core blank and the first cladding tube; placing the core rod in a second cladding tube, wherein the melting point of the metal material used in the second cladding tube is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube are better than the mechanical properties of the metal material used in the first cladding tube; using a spin rolling process to obtain a spiral multi-lobed fuel rod; and diffusion welding the spiral multi-lobed fuel rod. In this way, on the basis of preparing a spiral multi-lobed nuclear fuel element with a metal matrix by co-extrusion and spin rolling processes, the spiral multi-lobed nuclear fuel element can withstand higher temperatures and have better mechanical properties.

Description

Technical Field

[0001] The present application relates to the technical field of reactor nuclear fuel element design and manufacturing method, and in particular to a spiral multi-lobed nuclear fuel element with a composite cladding and a manufacturing method thereof. Background Art

[0002] Metal-based dispersed fuel elements are widely used in high-power density high-throughput test reactors and compact power reactors due to their good thermal conductivity. Structurally, metal-based fuel elements are mostly plate-shaped or multi-leaf rod-shaped fuel elements. Among them, multi-leaf rod-shaped fuel elements have received a lot of attention due to their good mechanical properties.

[0003] Patents RU2067324C1, RU2125305C1, and RU2416831C1 disclose spiral multi-lobed metal-based rod / tubular nuclear fuel element schemes with different displacer shapes, materials (some containing combustible poisons), and different rib parameters. In patents CN105895178B, CN102947890B and CN102301430B and their related patents (US20130322591A1, US20110255051A1), American Thorium Energy Co., Ltd. announced a fuel assembly scheme with a multi-lobed profile fuel element rod with spiral ribs, and provided a displacer with a square area with a side length of 1.5~3.5mm in the center, a four-lobed spiral fuel element rod with a pitch of 21.5cm and a circumscribed circle center of 12.6mm; American Light Bridge Corporation announced a fuel assembly with self-spacing for CANDU heavy water reactor in patent CN106716546B.

[0004] The inventor of the present application has published in patents CN113470840B and CN113470841B a manufacturing method of first obtaining a cylindrical or tubular fuel rod by co-extrusion, and then obtaining a spiral multi-lobed fuel element by spinning or rolling. In the co-extrusion process, the fuel core blank and the cladding tube are preheated together in a heating furnace as a combined blank and then extruded under a certain pressure. Therefore, the process is suitable for the metal material used in the cladding tube and the metal matrix material of the fuel core blank to be the same metal material with the same or similar thermodynamic properties, wherein the alloy composition and impurity content in the metal material used in the cladding tube and the metal matrix material of the fuel core blank may be slightly different within an acceptable range.

[0005] In view that the commonly used metal-based dispersed fuels are still mainly Al (aluminum)-based or Zr (zirconium)-based, the metal materials used in the commonly used cladding tubes are also mainly Al or Zr, which has certain limitations for some fuel elements that have higher mechanical properties and temperature requirements for the cladding tube materials.

[0006] In summary, in order to broaden the design and application fields of my country's reactor types and make full use of the superior performance of spiral multi-lobed metal-based rod / tubular nuclear fuel elements, it is urgent to propose a spiral multi-lobed fuel element scheme that can withstand higher temperatures and has better mechanical properties and propose a feasible manufacturing method based on the preparation of spiral multi-lobed metal-based fuel elements through co-extrusion and spin-rolling processes. Summary of the invention

[0007] Based on this, it is necessary to provide a spiral multi-lobed nuclear fuel element with a composite cladding that can withstand higher temperatures and has better mechanical properties, and a method for manufacturing the same.

[0008] A method for manufacturing a spiral multi-lobed nuclear fuel element with a composite cladding comprises the following steps:

[0009] Mixing the nuclear material particles with the metal matrix powder to form a fuel core blank, and pre-sintering the fuel core blank;

[0010] Placing the fuel core blank in a first cladding tube, wherein the metal material used in the first cladding tube is the same as the material of the metal matrix powder, and the first cladding tube includes a tube body and two end plates, and the two end plates respectively seal the two ends of the tube body;

[0011] The fuel core blank and the first cladding tube are formed into a core rod by a co-extrusion process, so that the inner circumference of the tube body and the outer circumference of the fuel core blank are metallurgically bonded at the junction, and the two end plates are metallurgically bonded to both ends of the fuel core blank;

[0012] Placing the core rod in a second cladding tube, wherein the melting point of the metal material used in the second cladding tube is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube are better than the mechanical properties of the metal material used in the first cladding tube;

[0013] Inserting two end plugs into two ends of the second cladding tube respectively, and welding the two end plugs to two ends of the second cladding tube respectively, wherein the metal material used for the second cladding tube is the same as the metal material used for the end plugs;

[0014] A spinning process is used to spin-roll the rod-shaped structure formed by connecting the core rod, the second cladding tube and the end plug to obtain a spiral multi-lobed fuel rod, wherein the outer periphery of the spiral multi-lobed fuel rod is configured with a plurality of blades arranged at intervals, each of the blades extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod, and each of the blades contains a portion of the fuel core;

[0015] Diffusion welding is performed on the spiral multi-lobed fuel rod to metallurgically bond the inner circumference of the second cladding tube to the outer circumference of the core rod, and the two end plugs are metallurgically bonded to the two end plates respectively.

[0016] The manufacturing method of the spiral multi-lobed nuclear fuel element with a composite cladding is as follows: nuclear material particles are mixed with metal matrix powder to form a fuel core blank, and the fuel core blank is pre-sintered. The fuel core blank is placed in a first cladding tube, and the first cladding tube includes a tube body and two end plates, and the two end plates respectively seal the two ends of the tube body. The fuel core blank and the first cladding tube are jointly made into a core rod by a co-extrusion process. Since the metal material used in the first cladding tube is the same as the material of the metal matrix powder, when the core rod is co-extruded, the inner circumference of the tube body and the outer circumference of the fuel core blank can be metallurgically bonded at the junction, and the two end plates are metallurgically bonded to the two ends of the fuel core blank. The core rod is placed in a second cladding tube, and two end plugs are respectively inserted into the two ends of the second cladding tube. Since the metal material used in the second cladding tube is the same as the metal material used in the end plugs, the two end plugs can be welded to the two ends of the second cladding tube. The rod-shaped structure formed by connecting the core rod, the second cladding tube and the end plug is spun by a spun rolling process to obtain a spiral multi-lobed fuel rod. The outer periphery of the spiral multi-lobed fuel rod is structured with a plurality of blades arranged at intervals. Each blade extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod, and each blade contains a part of the fuel core. The first cladding tube and the second cladding tube are made of different metal materials. By diffusion welding the spiral multi-lobed fuel rod, the inner circumference of the second cladding tube and the outer circumference of the core rod can be metallurgically bonded at the junction, and the two end plugs are metallurgically bonded to the two end plates respectively, thereby obtaining a spiral multi-lobed nuclear fuel element with a composite cladding (i.e., a composite structure of the first cladding tube and the second cladding tube). Among them, the melting point of the metal material used in the second cladding tube is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube are better than the mechanical properties of the metal material used in the first cladding tube. In this way, on the basis of preparing a spiral multi-lobed nuclear fuel element with a metal base through co-extrusion and spin-rolling processes, the composite cladding structure of the first cladding tube and the second cladding tube enables the spiral multi-lobed nuclear fuel element to withstand higher temperatures and have better mechanical properties, and the process is well controllable and easy to implement.

[0017] In some embodiments, the step of placing the core rod in the second cladding tube comprises:

[0018] Cooling the core rod, and placing the core rod that has shrunk upon cooling in the second cladding tube; and / or,

[0019] The second cladding tube is heated, and the core rod is placed in the second cladding tube which expands due to the heat.

[0020] In some embodiments, the step of placing the core rod in the second cladding tube comprises:

[0021] Applying pressure or tension to the core rod in the axial direction so that the core rod is placed in the second cladding tube;

[0022] And / or, applying pressure or tension to the second cladding tube in the axial direction so that the core rod is placed in the second cladding tube.

[0023] In some embodiments, after the core rod is placed in the second cladding tube, the core rod and the second cladding tube are interference fit.

[0024] In some embodiments, the metal material used for the first cladding tube is pure Al or Al alloy, and the welding temperature when diffusion welding the spiral multi-lobed fuel rod is greater than or equal to 350° C. and less than or equal to 500° C.;

[0025] Alternatively, the metal material used for the first cladding tube is pure Zr or Zr alloy, and the welding temperature when diffusion welding the spiral multi-lobed fuel rod is greater than or equal to 500°C and less than or equal to 700°C.

[0026] In some embodiments, the step of placing the fuel core blank in the first cladding tube comprises:

[0027] Firstly, one of the two end plates is welded to one end of the tube body;

[0028] Then, the fuel core blank is installed into the tube body from the other end of the tube body;

[0029] Then, the other end plate of the two end plates is welded to the tube body.

[0030] In some embodiments, after the step of using the co-extrusion process to form the fuel core blank and the first cladding tube into a core rod, and before the step of using the spin rolling process to spin the rod-shaped structure formed by connecting the core rod, the second cladding tube and the end plug to obtain a spiral multi-lobed fuel rod, the wall thickness of the tube body of the first cladding tube is greater than or equal to 0.1 mm and less than or equal to 0.3 mm; the wall thickness of the second cladding tube is greater than or equal to 0.3 mm and less than or equal to 0.6 mm;

[0031] After the spiral multi-lobed fuel rod is obtained by the spin-rolling process, the wall thickness of the second cladding tube is greater than or equal to 0.2 mm, and the total wall thickness of the tube body of the first cladding tube and the second cladding tube is greater than or equal to 0.3 mm; the total wall thickness of the tube body of the first cladding tube and the second cladding tube is less than or equal to 1 mm.

[0032] In some embodiments, the step of mixing the core material particles with the metal matrix powder to form a fuel core blank comprises: mixing the core material particles with the metal matrix powder to form a tubular fuel core blank, so that a through hole extending in the axial direction is formed in the fuel core blank;

[0033] The step of placing the fuel core blank in the first cladding tube comprises: placing the first inner tube of the tube body in the through hole, placing the fuel core blank in the first outer tube of the tube body, the center of the end plate is provided with an inner hole communicating with the through hole, and the end plate closes the annular opening formed between the end of the first inner tube and the end of the first outer tube;

[0034] The step of using the co-extrusion process to form the fuel core blank and the first cladding tube into a core rod comprises: metallurgically bonding the outer circumference of the first inner tube to the hole wall of the through hole, and metallurgically bonding the first outer tube to the fuel core blank;

[0035] The step of diffusion welding the spiral multi-lobed fuel rod includes: metallurgically bonding the second outer tube of the second cladding tube to the first outer tube, and metallurgically bonding the second inner tube of the second cladding tube to the first inner tube.

[0036] In some embodiments, the step of mixing the nuclear material particles with the metal matrix powder to form a fuel core blank comprises: mixing the nuclear material particles with the metal matrix powder to form a fuel core blank with a displacer mounting hole;

[0037] The step of placing the fuel core blank in the first cladding tube comprises: placing the first inner tube of the tube body in the displacer mounting hole, placing the fuel core blank in the first outer tube of the tube body, the center of the end plate is provided with an inner hole communicating with the displacer mounting hole, and the end plate closes the annular opening formed between the end of the first inner tube and the end of the first outer tube;

[0038] After the step of forming the fuel core blank and the first cladding tube into a core rod by a co-extrusion process and before the step of inserting two end plugs into the two ends of the second cladding tube, the manufacturing method further comprises placing a displacer in the first inner tube;

[0039] The step of diffusion welding the spiral multi-lobed fuel rod includes: metallurgically bonding the second cladding tube to the first outer tube, and metallurgically bonding the displacer to the first inner tube.

[0040] A spiral multi-lobed nuclear fuel element with a composite cladding, comprising:

[0041] The fuel core is a metal-based dispersed fuel core;

[0042] A first cladding tube, wherein the metal material used in the first cladding tube is the same as the metal matrix material in the fuel core, the first cladding tube comprises a tube body and two end plates, the two end plates respectively seal the two ends of the tube body, the tube body covers the outer circumference of the fuel core and is metallurgically bonded to the fuel core, and the two end plates are metallurgically bonded to the two ends of the fuel core;

[0043] Two end plugs are respectively disposed at two ends of the first cladding tube, and the two end plugs are metallurgically bonded to the two end plates respectively; and

[0044] a second cladding tube, wherein the second cladding tube covers the outer circumference of the first cladding tube and is metallurgically bonded to the first cladding tube, the metal material used in the second cladding tube is the same as the metal material used in the end plugs, and both ends of the second cladding tube cover the outer circumferences of the two end plugs and are welded to the two end plugs;

[0045] The melting point of the metal material used in the second cladding tube is higher than that of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube are better than those of the metal material used in the first cladding tube;

[0046] The outer periphery of the spiral multi-lobed nuclear fuel element is constructed with a plurality of blades arranged at intervals, each of the blades extends in a spiral direction around the axial direction of the spiral multi-lobed nuclear fuel element, and each of the blades contains a portion of the fuel core.

[0047] The above-mentioned spiral multi-lobed nuclear fuel element with a composite cladding, the fuel core is a metal-based dispersed fuel core. The first cladding tube includes a tube body and two end plates, and the two end plates respectively seal the two ends of the tube body. Since the metal material used in the first cladding tube is the same as the material of the metal matrix powder, when the fuel core blank and the first cladding tube are jointly made into a core rod by a co-extrusion process, the junction between the inner circumference of the tube body and the outer circumference of the fuel core blank can be metallurgically bonded, and the two end plates are metallurgically bonded to the two ends of the fuel core blank. Since the metal material used in the second cladding tube is the same as the metal material used in the end plug, the two end plugs can be welded to the two ends of the second cladding tube respectively. The rod-shaped structure formed by connecting the core rod, the second cladding tube and the end plug can be spin-rolled by a spin-rolling process to obtain a spiral multi-lobed fuel rod. Since the first cladding tube and the second cladding tube are made of different metal materials, the inner circumference of the second cladding tube and the outer circumference of the core rod can be metallurgically bonded at the junction, and the two end plugs are metallurgically bonded to the two end plates respectively, so as to obtain a spiral multi-lobed nuclear fuel element with a composite cladding (i.e., a composite structure of the first cladding tube and the second cladding tube). Among them, the melting point of the metal material used in the second cladding tube is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube are better than the mechanical properties of the metal material used in the first cladding tube. In this way, on the basis of preparing a spiral multi-lobed nuclear fuel element with a metal base through co-extrusion and spin-rolling processes, the composite cladding structure of the first cladding tube and the second cladding tube enables the spiral multi-lobed nuclear fuel element to withstand higher temperatures and have better mechanical properties, and the process is well controllable and easy to implement.

[0048] In some embodiments, the fuel core is provided with a through hole extending along its axial direction;

[0049] The tube body includes a first inner tube and a first outer tube, the first inner tube is located in the through hole, the outer circumferential surface of the first inner tube is metallurgically bonded to the hole wall of the through hole, and the first outer tube covers the outer circumferential surface of the fuel core and is metallurgically bonded to the fuel core; the center of the end plate is provided with an inner hole connected to the through hole, and the end plate closes the annular opening formed between the end of the first inner tube and the end of the first outer tube.

[0050] The second cladding tube includes a second inner tube and a second outer tube. The second inner tube is located in the first inner tube. The outer circumference of the second inner tube is metallurgically bonded to the inner circumference of the first inner tube. The second outer tube covers the outer circumference of the first outer tube and is metallurgically bonded to the first outer tube.

[0051] In some embodiments, the fuel core is provided with a displacer mounting hole extending along its axial direction;

[0052] The tube body comprises a first inner tube and a first outer tube, the first inner tube is located in the displacer mounting hole, the outer circumference of the first inner tube is metallurgically bonded to the hole wall of the displacer mounting hole, and the first outer tube covers the outer circumference of the fuel core and is metallurgically bonded to the fuel core; the center of the end plate is provided with an inner hole connected to the displacer mounting hole, and the end plate closes the annular opening formed between the end of the first inner tube and the end of the first outer tube;

[0053] A displacer is disposed in the first inner tube and is metallurgically bonded to the displacer; and the second cladding tube covers the outer circumferential surface of the first outer tube and is metallurgically bonded to the first outer tube.

[0054] In some embodiments, the volume ratio of the nuclear fuel in the fuel core is greater than or equal to 10% and less than or equal to 70%.

[0055] In some embodiments, the material used for the second cladding tube is any one of Zr4, N18, N36, stainless steel 304, stainless steel 316 or stainless steel 321. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 A flow chart of a method for manufacturing a spiral multi-lobed nuclear fuel element with a composite cladding according to some embodiments.

[0057] Figure 2 Schematic diagram of the connection structure of the core rod, the end plug and the second cladding tube in some embodiments.

[0058] Figure 3 for Figure 2 Schematic cross-section of the structure shown.

[0059] Figure 4 For Figure 2 Schematic diagram of the structure of a spiral multi-lobed fuel rod obtained by spin rolling the structure shown.

[0060] Figure 5 for Figure 4 Schematic cross-section of the structure shown.

[0061] Figure 6 Schematic diagram of the connection structure of the core rod, the end plug and the second cladding tube in other embodiments.

[0062] Figure 7 for Figure 6 Schematic cross-section of the structure shown.

[0063] Figure 8 For Figure 6 Schematic diagram of the cross-section of a spiral multi-lobed fuel rod obtained by spin rolling the structure shown.

[0064] Fig. 9 Schematic diagram of the connection structure of the core rod, the end plug and the second cladding tube in other embodiments.

[0065] Fig.10 for Fig. 9 Schematic cross-section of the structure shown.

[0066] Fig.11 For Fig. 9 Schematic diagram of the cross-section of a spiral multi-lobed fuel rod obtained by spin rolling the structure shown.

[0067] Explanation of the accompanying drawings: 100, spiral multi-lobed fuel rod; 110, fuel core blank; 121, tube body; 1211, first inner tube; 1212, first outer tube; 122, end plate; 130, second cladding tube; 131, second inner tube; 132, second outer tube; 140, end plug; 150, displacer; 101, through hole; 100a, blade. DETAILED DESCRIPTION

[0068] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application 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 application. However, the present application 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 application, so the present application is not limited by the specific embodiments disclosed below.

[0069] In the description of the present application, it should be understood that if the terms "center", "longitudinal", "lateral", "length", "width", "wall thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or position relationship indicated by these terms is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0070] In addition, if the terms "first" or "second" appear, these terms are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, if the term "plurality" appears, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0071] In this application, unless otherwise clearly specified and limited, if the terms "installed", "connected", "connected", "fixed" and the like appear, these terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0072] In the present application, unless otherwise clearly specified and limited, if there is a description that a first feature is "above" or "below" a second feature, etc., or similar descriptions appear, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0073] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. If an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. If any, the terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in this application are for illustrative purposes only and do not represent the only implementation method.

[0074] Please refer to Figure 1 Combination Figures 2 to 5 The present invention provides a method for manufacturing a spiral multi-lobed nuclear fuel element with a composite cladding, comprising the following steps:

[0075] S100: mixing nuclear material particles with metal matrix powder to form a fuel core blank 110, and pre-sintering the fuel core blank 110.

[0076] S200: placing the fuel core blank 110 in a first cladding tube, wherein the metal material used in the first cladding tube is the same as the material of the metal matrix powder. The first cladding tube includes a tube body 121 and two end plates 122, and the two end plates 122 respectively close the two ends of the tube body 121.

[0077] S300: The fuel core blank 110 and the first cladding tube are made into a core rod by a co-extrusion process, so that the inner circumference of the tube body 121 and the outer circumference of the fuel core blank 110 are metallurgically bonded at the junction, and the two end plates 122 are metallurgically bonded to the two ends of the fuel core blank 110. After the core rod is made by the co-extrusion process, the fuel core blank 110 becomes a fuel core body.

[0078] S400: placing the core rod in the second cladding tube 130, wherein the melting point of the metal material used in the second cladding tube 130 is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube 130 are better than the mechanical properties of the metal material used in the first cladding tube.

[0079] S500: inserting two end plugs 140 into both ends of the second cladding tube 130 respectively, and welding the two end plugs 140 to both ends of the second cladding tube 130 respectively, wherein the metal material used in the second cladding tube 130 is the same as the metal material used in the end plugs 140.

[0080] S600: A rolling process is used to roll a rod-shaped structure formed by connecting a core rod, a second cladding tube 130 and an end plug 140 to obtain a spiral multi-lobed fuel rod 100. The outer periphery of the spiral multi-lobed fuel rod 100 is configured with a plurality of blades 100a arranged at intervals, and each blade 100a extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod. During the rolling process, the rolling tool not only squeezes the first cladding tube and the second cladding tube 130, but also squeezes the fuel core, so that the obtained blade 100a contains part of the fuel core.

[0081] Specifically, the specific method of using the spin-rolling process to spin-roll the rod-shaped structure to obtain the spiral multi-lobed fuel rod can be referred to patent CN113470840B of the inventor of the present application, which will not be described in detail.

[0082] S700: Diffusion welding is performed on the spiral multi-lobed fuel rod, so that the inner circumference of the second cladding tube 130 and the outer circumference of the core rod (i.e., the outer circumference of the tube body) are metallurgically bonded at the junction, and the two end plugs 140 are respectively metallurgically bonded to the two end plates 122. When diffusion welding is performed on the spiral multi-lobed fuel rod, it can be placed in a heating furnace, which can be a resistance furnace.

[0083] The manufacturing method of the spiral multi-lobed nuclear fuel element with a composite cladding is as follows: nuclear material particles are mixed with metal matrix powder to form a fuel core blank 110, and the fuel core blank 110 is pre-sintered. The fuel core blank 110 is placed in a first cladding tube, and the first cladding tube includes a tube body 121 and two end plates 122, and the two end plates 122 respectively seal the two ends of the tube body 121. The fuel core blank 110 and the first cladding tube are made into a core rod by a co-extrusion process. Since the metal material used in the first cladding tube is the same as the material of the metal matrix powder, when the core rod is co-extruded, the inner circumference of the tube body 121 and the outer circumference of the fuel core blank 110 can be metallurgically bonded at the junction, and the two end plates 122 are metallurgically bonded to the two ends of the fuel core blank 110. The core rod is placed in a second cladding tube 130, and two end plugs 140 are respectively inserted into the two ends of the second cladding tube 130. Since the metal material used in the second cladding tube 130 is the same as the metal material used in the end plug 140, the two end plugs 140 can be welded to the two ends of the second cladding tube 130. The spin rolling process is used to spin the rod-shaped structure formed by connecting the core rod, the second cladding tube 130 and the end plug 140 to obtain the spiral multi-lobed fuel rod 100. The outer periphery of the spiral multi-lobed fuel rod 100 is structured with a plurality of blades 100a arranged at intervals, each blade 100a extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod 100, and each blade 100a contains a part of the fuel core. The first cladding tube and the second cladding tube 130 are made of different metal materials. By diffusion welding the spiral multi-lobed fuel rod 100, the inner circumference of the second cladding tube 130 and the outer circumference of the tube body 121 can be metallurgically bonded at the junction, and the two end plugs 140 are metallurgically bonded to the two end plates 122 respectively, so as to obtain a spiral multi-lobed nuclear fuel element with a composite cladding (i.e., a composite structure of the first cladding tube and the second cladding tube 130). Among them, the melting point of the metal material used in the second cladding tube 130 is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube 130 are better than the mechanical properties of the metal material used in the first cladding tube. In this way, on the basis of preparing a spiral multi-lobed nuclear fuel element with a metal base through co-extrusion and spin-rolling processes, the composite cladding structure of the first cladding tube and the second cladding tube 130 enables the spiral multi-lobed nuclear fuel element to withstand higher temperatures and have better mechanical properties, and the process is well controllable and easy to implement.

[0084] Combination Figures 1 to 5, the embodiment of the present application provides a spiral multi-lobed nuclear fuel element with a composite cladding, which can be made by the above-mentioned manufacturing method. The spiral multi-lobed nuclear fuel element with a composite cladding includes: a fuel core, a first cladding tube, a second cladding tube 130 and two end plugs 140. The fuel core is a metal-based dispersed fuel core. The metal material used in the first cladding tube is the same as the metal matrix material in the fuel core. The first cladding tube includes a tube body 121 and two end plates 122. The two end plates 122 respectively close the two ends of the tube body 121. The tube body 121 covers the outer circumferential surface of the fuel core and is metallurgically bonded to the fuel core. The two end plates 122 are metallurgically bonded to the two ends of the fuel core. The two end plugs 140 are respectively arranged at the two ends of the first cladding tube, and the two end plugs 140 are metallurgically bonded to the two end plates 122. The second cladding tube 130 covers the outer circumference of the first cladding tube and is metallurgically bonded to the first cladding tube. The metal material used in the second cladding tube 130 is the same as the metal material used in the end plugs 140. The two ends of the second cladding tube 130 cover the outer circumference of the two end plugs 140 and are welded to the two end plugs 140. Among them, the melting point of the metal material used in the second cladding tube 130 is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube 130 are better than the mechanical properties of the metal material used in the first cladding tube. The outer periphery of the spiral multi-lobed nuclear fuel element is structured with a plurality of blades 100a arranged at intervals, each blade 100a extends in a spiral direction around the axial direction of the spiral multi-lobed nuclear fuel element, and each blade 100a contains a part of the fuel core. It can be understood that the fuel core of the spiral multi-lobed nuclear fuel element is obtained from the fuel core blank 110 in the manufacturing process.

[0085] The above-mentioned spiral multi-lobed nuclear fuel element with composite cladding has a fuel core body that is a metal-based dispersed fuel core body. The first cladding tube includes a tube body 121 and two end plates 122, and the two end plates 122 respectively seal the two ends of the tube body 121. Since the metal material used in the first cladding tube is the same as the material of the metal matrix powder, when the fuel core blank 110 and the first cladding tube are jointly made into a core rod by a co-extrusion process, the inner circumference of the tube body 121 and the outer circumference of the fuel core blank 110 can be metallurgically bonded at the junction, and the two end plates 122 are metallurgically bonded to the two ends of the fuel core blank 110. Since the metal material used in the second cladding tube 130 is the same as the metal material used in the end plug 140, the two end plugs 140 can be welded to the two ends of the second cladding tube 130 respectively. The rod-shaped structure formed by connecting the core rod, the second cladding tube 130 and the end plug 140 can be spin-rolled by a spin-rolling process to obtain a spiral multi-lobed fuel rod 100. Since the first cladding tube and the second cladding tube 130 are made of different metal materials, the inner circumference of the second cladding tube 130 and the outer circumference of the tube body 121 can be metallurgically bonded at the junction, and the two end plugs 140 are metallurgically bonded to the two end plates 122 respectively, so as to obtain a spiral multi-lobed nuclear fuel element with a composite cladding (i.e., a composite structure of the first cladding tube and the second cladding tube 130). Among them, the melting point of the metal material used in the second cladding tube 130 is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube 130 are better than the mechanical properties of the metal material used in the first cladding tube. In this way, on the basis of preparing a spiral multi-lobed nuclear fuel element with a metal base through co-extrusion and spin-rolling processes, the composite cladding structure of the first cladding tube and the second cladding tube 130 enables the spiral multi-lobed nuclear fuel element to withstand higher temperatures and have better mechanical properties, and the process is well controllable and easy to implement.

[0086] It should be noted that the alloy composition and impurity content of the metal material used in the first cladding tube and the metal matrix material of the fuel core blank may be slightly different within an acceptable range, and they can still be considered to be the same material.

[0087] The mechanical properties of the metal material used in the second cladding tube 130 are better than those of the metal material used in the first cladding tube. The mechanical properties are, for example, strength, which may include tensile strength, yield strength, and the like.

[0088] The above-mentioned spiral multi-leaf nuclear fuel element with a composite cladding is suitable for pressurized water reactors, fast reactors, low-temperature heating reactors, space reactors, boiling water reactors, micro reactors, zero-power reactors, heavy water reactors, power reactors, and marine power reactors, and is particularly suitable for mobile power reactors that require compact layout and have high structural mechanics requirements.

[0089] In step S400, in actual operation, the core rod can be cooled, and the outer diameter of the core rod is reduced after the core rod is cooled and contracted, and the core rod that is cooled and contracted is convenient to be placed in the second cladding tube 130. The second cladding tube 130 can also be heated, and the inner diameter of the second cladding tube 130 is increased after the second cladding tube 130 is heated and expanded, so that the core rod can be placed in the second cladding tube 130 conveniently.

[0090] In step S400, pressure or tension may be applied to the core rod in the axial direction, so that the core rod enters the second cladding tube 130 under the action of pressure or tension. Pressure or tension may also be applied to the second cladding tube 130 in the axial direction, so that the second cladding tube 130 is sleeved on the core rod under the action of pressure or tension.

[0091] In step S400, after the core rod is placed in the second cladding tube 130, the core rod and the second cladding tube 130 are interference fit to ensure reliable fit between the core rod and the second cladding tube 130, and to help maintain pressure between the first cladding tube and the second cladding tube 130 during diffusion welding in step S700.

[0092] After step S300 and before step S400, the outer surface of the core rod may be polished, and the inner surface of the second cladding tube may be ground and pickled.

[0093] In step S700, the welding temperature when diffusion welding is performed on the spiral multi-lobed fuel rod should be greater than the recrystallization temperature of the material used in the first cladding tube. The metal material used in the first cladding tube can be pure Al or Al alloy, and the welding temperature when diffusion welding is performed on the spiral multi-lobed fuel rod should be greater than or equal to 350°C and less than or equal to 500°C. The metal material used in the first cladding tube can also be pure Zr or Zr alloy, and the welding temperature when diffusion welding is performed on the spiral multi-lobed fuel rod should be greater than or equal to 500°C and less than or equal to 700°C.

[0094] In other embodiments, the metal material (ie, the material of the metal matrix powder) used in the first cladding tube may also be other metal powders with high melting points and low absorption cross-sections.

[0095] The volume ratio of the nuclear fuel particles in the fuel core blank 110 is greater than or equal to 10% and less than or equal to 70%.

[0096] The core material in the fuel core blank 110 may be UAl X , U3Si2, U-Mox or δ phase UZr2, U-Pu-Zr particles.

[0097] The nuclear material in the fuel core blank 110 may be UO2 microspheres coated with Nb or other ceramic nuclear fuel microspheres (eg, uranium nitride coated with Nb or uranium carbide coated with Nb or MOX fuel microspheres coated with Nb).

[0098] Nuclear fuel particles can be either low-enriched nuclear materials or high-enriched nuclear materials depending on the reactor type requirements, and the specific distribution can be between 0.71% and 93%.

[0099] The material used for the second cladding tube 130 is any one of Zr4, N18, N36, stainless steel 304, stainless steel 316 or stainless steel 321.

[0100] In other embodiments, the second cladding tube 130 may also be other zirconium alloys or austenitic stainless steels that have been verified by radiation tests, or other metals or alloy materials with high melting points and low absorption cross-sections that have been verified by radiation tests and have relatively high high-temperature mechanical properties.

[0101] The spiral multi-lobed nuclear fuel element with a composite cladding of the present application may be a spiral multi-lobed structure with three lobes, four lobes or more lobes.

[0102] The cross-sectional shape of the blade 100a is a cosine shape or an elliptical arc shape, and may also be other designed shapes.

[0103] The pitch of the blades 100a can be adjusted arbitrarily according to the design scheme. The height and blade shape of each blade 100a are the same, and each blade 100a is distributed at equal angles around the circumference of the spiral multi-blade nuclear fuel element.

[0104] After step S300 and before step S600, the wall thickness of the tube body of the first cladding tube is greater than or equal to 0.1 mm and less than or equal to 0.3 mm. The wall thickness of the second cladding tube 130 is greater than or equal to 0.3 mm and less than or equal to 0.6 mm.

[0105] After the spiral multi-lobed fuel rod is obtained by the spin rolling process, the wall thickness of the second cladding tube 130 is greater than or equal to 0.2 mm, and the total wall thickness of the tube body of the first cladding tube and the second cladding tube 130 is greater than or equal to 0.3 mm. The total wall thickness of the tube body of the first cladding tube and the second cladding tube 130 is less than or equal to 1 mm.

[0106] Several more specific embodiments are described below:

[0107] Please combine Figures 2 to 5 The first embodiment of the present application provides a stainless steel-Zr composite cladding solid Zr-based spiral multi-lobed nuclear fuel element and a manufacturing method thereof. The spiral multi-lobed nuclear fuel element is a 4-lobed type, the blade 100a is a cosine type, the pitch is 200mm, the total length of the fuel area is 500mm, and the diameter of the circumscribed circle is 13.3mm. The manufacturing method of the spiral multi-lobed nuclear fuel element includes the following steps:

[0108] S110: Mix the nuclear material particles with the metal matrix powder to form a fuel core blank 110, and pre-sinter the fuel core blank 110. The nuclear material particles are UO2 microspheres with a Nb coating on the surface and a diameter of 100-150 μm or UZr2 fuel particles with a δ phase having a certain particle size distribution ( 235 U enrichment is 19.75%~60%), the metal matrix powder is Zr2 alloy powder, and the volume proportion of the nuclear material particles in the fuel core blank 110 is greater than or equal to 10% and less than or equal to 40%.

[0109] Specifically, after the nuclear material particles are fully mixed with the metal matrix powder, a solid cylindrical fuel core blank can be made through a pressing process, and the bonding strength of the core blank can be improved through a pre-sintering process.

[0110] S210: placing the fuel core blank 110 in a first cladding tube, wherein the metal material used in the first cladding tube is the same as the material of the metal matrix powder, that is, the first cladding tube is made of Zr2 alloy. The first cladding tube includes a tube body 121 and two end plates 122, and the two end plates 122 respectively close the two ends of the tube body 121.

[0111] In actual operation, one of the two end plates 122 is first welded to one end of the tube body 121. Then the fuel core blank 110 is loaded into the tube body 121 from the other end of the tube body 121. Then the other end plate 122 of the two end plates 122 is welded to the tube body 121. The welding of the end plate 122 and the tube body 121 can be carried out by vacuum electron beam welding. Thus, the fuel core blank 110 can be enclosed in the first cladding tube. It can be understood that the inner diameter of the tube body 121 is substantially the same as the outer diameter of the fuel core blank 110.

[0112] S310: The fuel core blank 110 and the first cladding tube are made into a core rod by a co-extrusion process. Since the metal material used in the first cladding tube is the same as the material of the metal matrix powder, the inner circumference of the tube body 121 and the outer circumference of the fuel core blank 110 can be metallurgically bonded at the junction during the co-extrusion process to form the core rod, and the two end plates 122 can be metallurgically bonded to the two ends of the fuel core blank 110.

[0113] Furthermore, the surface of the core rod may be polished.

[0114] S410: placing the core rod in the second cladding tube 130, wherein the melting point of the metal material used in the second cladding tube 130 is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube 130 are better than the mechanical properties of the metal material used in the first cladding tube.

[0115] Specifically, the metal material used for the second cladding tube 130 may be austenitic stainless steel that has been verified by irradiation testing, such as 321 stainless steel.

[0116] The inner diameter of the second cladding tube 130 is interference fit with the outer diameter of the core rod, and specifically, a base hole H7 / s6 fit can be used. Specifically, the core rod can be cooled so that the core rod shrinks when it is cold, thereby reducing the outer diameter, so that it is convenient to place the core rod that has shrunk when it is cold in the second cladding tube 130. When the temperature of the core rod returns to room temperature, the outer diameter of the core rod can be restored to its outer diameter at room temperature, so that it can be interference fit with the second cladding tube 130. Specifically, the core rod can be shrunk by a freezer, ice water, or liquid nitrogen.

[0117] S510: insert two end plugs 140 into both ends of the second cladding tube 130 respectively, and weld the two end plugs 140 to both ends of the second cladding tube 130 respectively, wherein the metal material used in the second cladding tube 130 is the same as the metal material used in the end plugs 140. The welding between the end plugs 140 and the second cladding tube 130 may be performed by vacuum electron beam welding.

[0118] After step S310 and before step S610, the wall thickness of the tube body of the first cladding tube is 0.1 mm; the wall thickness of the tube body of the second cladding tube 130 is greater than or equal to 0.3 mm and less than or equal to 0.6 mm.

[0119] S610: A spin-rolling process is used to spin-roll a rod-shaped structure formed by connecting a core rod, a second cladding tube 130 and an end plug 140 to obtain a spiral multi-lobed fuel rod 100. The outer periphery of the spiral multi-lobed fuel rod 100 is structured with a plurality of blades 100a arranged at intervals. Each blade 100a extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod, and each blade 100a contains a portion of the fuel core.

[0120] Specifically, the specific method of using the spin-rolling process to spin-roll the rod-shaped structure to obtain the spiral multi-lobed fuel rod can be referred to patent CN113470840B of the inventor of the present application, which will not be described in detail.

[0121] After spinning, the wall thickness of the first cladding tube and the second cladding tube 130 at various positions along the circumferential direction is uneven. After the spiral multi-lobed fuel rod 100 is obtained by spinning, the wall thickness of the thinnest part of the tube wall of the second cladding tube 130 is greater than or equal to 0.2 mm.

[0122] S710: Diffusion welding is performed on the spiral multi-lobed fuel rod, so that the inner circumference of the second cladding tube 130 and the outer circumference of the core rod are metallurgically bonded at the junction, and the two end plugs 140 are respectively metallurgically bonded to the two end plates 122. Specifically, the spiral multi-lobed fuel rod can be placed in a resistance furnace for diffusion welding, and the welding temperature during diffusion welding should be higher than the recrystallization temperature of the first cladding tube, that is, higher than the recrystallization temperature of the Zr2 alloy in this embodiment, greater than or equal to 500°C and less than or equal to 700°C, and the welding temperature is kept for 1 to 4 hours.

[0123] Please combine Figures 2 to 5 The second embodiment of the present application provides a method for manufacturing a stainless steel-Al composite cladding solid Al-based spiral multi-lobed nuclear fuel element. The spiral multi-lobed nuclear fuel element is a 4-lobed type, the blade 100a is a cosine type, the pitch is 200mm, the total length of the fuel area is 500mm, and the diameter of the circumscribed circle is 13.3mm. The method for manufacturing the spiral multi-lobed nuclear fuel element includes the following steps:

[0124] S120: Mix the core material particles with the metal matrix powder to form a fuel core blank 110, and pre-sinter the fuel core blank 110. The core material particles are UAl with a certain particle size distribution. X or U3Si2 fuel particles ( 235 U enrichment is 19.75%~92%), the metal matrix powder is Al alloy powder, and the volume proportion of the nuclear material particles in the fuel core blank 110 is greater than or equal to 20% and less than or equal to 45%.

[0125] Specifically, after the nuclear material particles are fully mixed with the metal matrix powder, a solid cylindrical fuel core blank can be made through a pressing process, and the bonding strength of the core blank can be improved through a pre-sintering process.

[0126] S220: placing the fuel core blank 110 in a first cladding tube, wherein the metal material used in the first cladding tube is the same as the material of the metal matrix powder, that is, the first cladding tube is made of Al alloy. The first cladding tube includes a tube body 121 and two end plates 122, and the two end plates 122 respectively close the two ends of the tube body 121. In this embodiment, the material used in the first cladding tube is X8001 or 6061-O Al alloy.

[0127] In actual operation, one of the two end plates 122 is first welded to one end of the tube body 121. Then the fuel core blank 110 is loaded into the tube body 121 from the other end of the tube body 121. Then the other end plate 122 of the two end plates 122 is welded to the tube body 121. The welding of the end plate 122 and the tube body 121 can be carried out by vacuum electron beam welding. Thus, the fuel core blank 110 can be enclosed in the first cladding tube. It can be understood that the inner diameter of the tube body 121 is substantially the same as the outer diameter of the fuel core blank 110.

[0128] S320: The fuel core blank 110 and the first cladding tube are made into a core rod by a co-extrusion process. Since the metal material used in the first cladding tube is the same as the material of the metal matrix powder, the inner circumference of the tube body 121 and the outer circumference of the fuel core blank 110 can be metallurgically bonded at the junction during the co-extrusion process to form the core rod, and the two end plates 122 can be metallurgically bonded to the two ends of the fuel core blank 110.

[0129] Furthermore, the surface of the core rod may be polished.

[0130] S420: placing the core rod in the second cladding tube 130, wherein the melting point of the metal material used in the second cladding tube 130 is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube 130 are better than the mechanical properties of the metal material used in the first cladding tube.

[0131] Specifically, the metal material used for the second cladding tube 130 may be austenitic stainless steel that has been verified by irradiation testing, such as 304 stainless steel.

[0132] The inner diameter of the second cladding tube 130 is interference fit with the outer diameter of the mandrel, and specifically, the base shaft system P7 / h6 can be used for the fit. Specifically, the second cladding tube 130 can be heated in a heating furnace to expand it, so that the inner diameter of the second cladding tube 130 increases, thereby facilitating the placement of the mandrel into the heat-expanded second cladding tube 130. When the temperature of the second cladding tube 130 returns to room temperature, the inner diameter of the second cladding tube 130 can be restored to its inner diameter at room temperature, so that it can be interference fit with the mandrel.

[0133] S520: insert two end plugs 140 into both ends of the second cladding tube 130 respectively, and weld the two end plugs 140 to both ends of the second cladding tube 130 respectively, wherein the metal material used in the second cladding tube 130 is the same as the metal material used in the end plugs 140. The welding between the end plugs 140 and the second cladding tube 130 can be performed by argon arc welding.

[0134] After step S320 and before step S620, the wall thickness of the tube body of the first cladding tube is 0.15 mm, and the wall thickness of the tube body of the second cladding tube 130 is greater than or equal to 0.3 mm and less than or equal to 0.4 mm.

[0135] S620: A spin-rolling process is used to spin-roll a rod-shaped structure formed by connecting a core rod, a second cladding tube 130 and an end plug 140 to obtain a spiral multi-lobed fuel rod 100. The outer periphery of the spiral multi-lobed fuel rod 100 is structured with a plurality of blades 100a arranged at intervals. Each blade 100a extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod, and each blade 100a contains a portion of the fuel core.

[0136] Specifically, the specific method of using the spin-rolling process to spin-roll the rod-shaped structure to obtain the spiral multi-lobed fuel rod can be referred to patent CN113470840B of the inventor of the present application, which will not be described in detail.

[0137] After spinning, the wall thickness of the first cladding tube and the second cladding tube 130 at various positions along the circumferential direction is uneven. After the spiral multi-lobed fuel rod 100 is obtained by spinning, the wall thickness of the thinnest part of the tube wall of the second cladding tube 130 is greater than or equal to 0.2 mm.

[0138] S720: Diffusion welding is performed on the spiral multi-lobed fuel rod, so that the inner circumference of the second cladding tube 130 and the outer circumference of the core rod are metallurgically bonded at the junction, and the two end plugs 140 are respectively metallurgically bonded to the two end plates 122. Specifically, the spiral multi-lobed fuel rod can be placed in a resistance furnace for diffusion welding, and the welding temperature during diffusion welding should be higher than the recrystallization temperature of the first cladding tube, that is, higher than the recrystallization temperature of the Al alloy in this embodiment, greater than or equal to 350°C and less than or equal to 500°C, and the welding temperature is kept for 1 to 4 hours.

[0139] exist Figures 2 to 5 In the illustrated embodiment, the fuel pellet 110 and the fuel core body are solid structures.

[0140] refer to Figures 6 to 8 In some embodiments, the fuel core is provided with a through hole 101 extending along its axial direction. That is, the fuel core is a tubular structure.

[0141] The tube body 121 includes a first inner tube 1211 and a first outer tube 1212. The first inner tube 1211 is located in the through hole 101. The outer circumference of the first inner tube 1211 is metallurgically bonded to the hole wall of the through hole 101. The first outer tube 1212 covers the outer circumference of the fuel core and is metallurgically bonded to the fuel core. That is, an annular cavity is formed between the first inner tube 1211 and the first outer tube 1212, and the fuel core is placed in the annular cavity between the first inner tube 1211 and the first outer tube 1212.

[0142] An annular opening is formed between the end of the first inner tube 1211 and the end of the first outer tube 1212. An inner hole communicating with the through hole 101 is provided at the center of the end plate 122, that is, the end plate 122 is annular. The end plate 122 closes the annular opening formed between the end of the first inner tube 1211 and the end of the first outer tube 1212. It can be understood that the two end plates 122 respectively close the two annular openings at both ends of the first inner tube 1211 and the second outer tube 1212.

[0143] The second cladding tube 130 includes a second inner tube 131 and a second outer tube 132. The second inner tube 131 is located inside the first inner tube 1211. The outer circumference of the second inner tube 131 is metallurgically bonded to the inner circumference of the first inner tube 1211. The second outer tube 132 covers the outer circumference of the first outer tube 1212 and is metallurgically bonded to the first outer tube 1212. That is, the connection structure between the first cladding tube and the fuel core is located between the second inner tube 131 and the second outer tube 132.

[0144] The spiral multi-lobed nuclear fuel element in this embodiment has a central hole (i.e., the channel inside the second inner tube 131). When the spiral multi-lobed nuclear fuel element is in use, the central hole can be used for coolant to flow.

[0145] Combination Figures 6 to 8 The third embodiment of the present application provides a method for manufacturing a stainless steel-Zr composite cladding Zr-based spiral multi-lobed nuclear fuel element with a central hole. The spiral multi-lobed nuclear fuel element is a 3-lobed type, the blade 100a is a cosine type, the pitch is 300mm, the total length of the fuel area is 600mm, the diameter of the circumscribed circle is 12.6mm, and the inner diameter of the second inner tube 132 is 5mm.

[0146] S130: Mix the core material particles with the metal matrix powder to form a tubular fuel core blank 110, so that a through hole 101 extending in the axial direction is formed in the fuel core blank 110. The core material particles are UMo8 microspheres (the mass percentage of Mo is 8%) with a diameter of 50 μm to 150 μm and a Nb or Zr coating on the surface ( 235 U enrichment is 19.75%~40%), the metal matrix powder is Zr2 alloy powder, and the volume proportion of the nuclear material particles in the fuel core blank 110 is greater than or equal to 10% and less than or equal to 40%.

[0147] Specifically, after the nuclear material particles are fully mixed with the metal matrix powder, a cylindrical fuel core blank can be made through a pressing process, and the bonding strength of the core blank can be improved through a pre-sintering process.

[0148] S230: Place the first inner tube 1211 of the tube body 121 in the through hole 101, and place the fuel core blank 110 in the first outer tube 1212 of the tube body 121, that is, place the fuel core blank 110 in the annular cavity between the first inner tube 1211 and the first outer tube 1212. An inner hole connected to the through hole 101 is provided at the center of the end plate 122, and the end plate 122 closes the annular opening formed between the end of the first inner tube 1211 and the end of the first outer tube 1212. Among them, the metal material used in the first cladding tube is the same as the material of the metal matrix powder, that is, the first cladding tube is made of Zr2 alloy. The first cladding tube includes two end plates 122, and the two end plates 122 respectively close the two annular openings at both ends of the first inner tube 1211 and the first outer tube 1212.

[0149] In actual operation, one of the two end plates 122 is first welded to one end of the first inner tube 1211 and the first outer tube 1212 to close one of the annular openings. Then the fuel core blank 110 is loaded from the other end of the first inner tube 1211 and the first outer tube 1212. Then the other end plate 122 of the two end plates 122 is welded to the other end of the first inner tube 1211 and the first outer tube 1212 to close the other annular opening. The welding of the end plate 122 and the tube body 121 can be vacuum electron beam welding, so that the fuel core blank 110 can be enclosed in the first cladding tube. It can be understood that the inner diameter of the first outer tube 1212 is substantially the same as the outer diameter of the fuel core blank 110, and the outer diameter of the first inner tube 1211 is substantially the same as the inner diameter of the fuel core blank 110.

[0150] S330: The fuel core blank 110 and the first cladding tube are made into a core rod by a co-extrusion process. Since the metal material used in the first cladding tube is the same as the material of the metal matrix powder, the outer circumference of the first inner tube 1211 can be metallurgically bonded to the hole wall of the through hole 101, the first outer tube 1212 can be metallurgically bonded to the fuel core blank 110, and the two end plates 122 can be metallurgically bonded to the two ends of the fuel core blank 110 during the co-extrusion process to make the core rod.

[0151] Furthermore, the surface of the core rod may be polished.

[0152] S430: placing the mandrel in the second cladding tube 130, specifically, placing the mandrel between the second inner tube 131 and the second outer tube 132. The melting point of the metal material used in the second cladding tube 130 is higher than that of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube 130 are better than those of the metal material used in the first cladding tube.

[0153] Specifically, the metal material used for the second cladding tube 130 may be austenitic stainless steel that has been verified by irradiation testing, such as 316 stainless steel.

[0154] The inner diameter of the second outer tube 132 is interference fit with the outer diameter of the mandrel, and the base shaft system P7 / h6 can be selected for the fit. The second outer tube 132 is heated in a heating furnace, so that the second outer tube 132 is heated and expanded, thereby increasing the inner diameter, thereby facilitating the insertion of the mandrel into the second outer tube 132. When the temperature of the second outer tube 132 is reduced to room temperature, the inner diameter of the second outer tube 132 can be restored to its inner diameter at room temperature, thereby being interference fit with the outer diameter of the mandrel.

[0155] The outer diameter of the second inner tube 131 is interference fit with the inner diameter of the mandrel, and the base hole system H7 / s6 can be selected for the fit. Specifically, the second inner tube 131 can be cooled so that the second inner tube 131 shrinks when it is cold, thereby reducing the outer diameter, so as to facilitate placing the second inner tube 131 that shrinks when it is cold in the mandrel. When the temperature of the second inner tube 131 rises to room temperature, the outer diameter of the second inner tube 131 can be restored to its outer diameter at room temperature, so as to be interference fit with the mandrel. Specifically, the second inner tube 131 can be shrunk by a freezer, ice water, or liquid nitrogen.

[0156] S530: insert two end plugs 140 into both ends of the second cladding tube 130 respectively, and weld the two end plugs 140 to both ends of the second cladding tube 130 respectively, wherein the metal material used in the second cladding tube 130 is the same as the metal material used in the end plugs 140. The welding between the end plugs 140 and the second cladding tube 130 may be performed by vacuum electron beam welding.

[0157] After step S330 and before step S630, the wall thickness of the first inner tube and the first outer tube of the first cladding tube is 0.2 mm; the wall thickness of the second inner tube and the second outer tube of the second cladding tube 130 is greater than or equal to 0.3 mm and less than or equal to 0.4 mm.

[0158] S630: A spin-rolling process is used to spin-roll a rod-shaped structure formed by connecting a core rod, a second cladding tube 130 and an end plug 140 to obtain a spiral multi-lobed fuel rod 100. The outer periphery of the spiral multi-lobed fuel rod 100 is structured with a plurality of blades 100a arranged at intervals. Each blade 100a extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod, and each blade 100a contains a portion of the fuel core.

[0159] Specifically, the specific method of using the spin-rolling process to spin-roll the rod-shaped structure to obtain the spiral multi-lobed fuel rod can be referred to patent CN113470840B of the inventor of the present application, which will not be described in detail.

[0160] After spinning, the wall thickness of the first cladding tube and the second cladding tube 130 at various positions along the circumferential direction is uneven. After the spiral multi-lobed fuel rod 100 is obtained by spinning, the wall thickness of the thinnest part of the tube wall of the second cladding tube 130 is greater than or equal to 0.2 mm.

[0161] S730: Diffusion welding is performed on the spiral multi-lobed fuel rods to metallurgically bond the second outer tube 132 to the first outer tube 1212, the second inner tube 131 to the first inner tube 1211, and the two end plugs 140 to the two end plates 122. Specifically, the spiral multi-lobed fuel rods can be placed in a resistance furnace for diffusion welding, and the welding temperature during diffusion welding should be higher than the recrystallization temperature of the first cladding tube, that is, higher than the recrystallization temperature of the Zr2 alloy in this embodiment, greater than or equal to 500°C and less than or equal to 700°C, and the welding temperature is kept for 1 to 4 hours.

[0162] refer to Figures 9 to 11 In some embodiments, the fuel core is provided with a displacer mounting hole extending along its axial direction. The tube body 121 includes a first inner tube 1211 and a first outer tube 1212. The first inner tube 1211 is located in the displacer mounting hole. The outer circumference of the first inner tube 1211 is metallurgically bonded to the hole wall of the displacer mounting hole. The first outer tube 1212 covers the outer circumference of the fuel core and is metallurgically bonded to the fuel core. That is, an annular cavity is formed between the first inner tube 1211 and the first outer tube 1212, and the fuel core is placed in the annular cavity between the first inner tube 1211 and the first outer tube 1212. It should be noted that the displacer mounting hole is a square hole, the first inner tube 1211 is adapted to the displacer mounting hole; it is a square tube, and the first outer tube 1212 is a round tube. Therefore, the contour of the annular cavity is an inner square and an outer circle. An annular opening is formed between the end of the first inner tube 1211 and the end of the first outer tube 1212, and the contour of the annular opening is an inner square and an outer circle.

[0163] The center of the end plate 122 is provided with an inner hole connected to the displacer mounting hole, and the contour shape of the inner hole is the same as the contour shape of the displacer mounting hole. The end plate 122 closes the annular opening formed between the end of the first inner tube 1211 and the end of the first outer tube 1212. It can be understood that the two end plates 122 respectively close the two annular openings at both ends of the first inner tube 1211 and the second outer tube 1212.

[0164] The first inner tube 1211 is provided with a displacer 150. The second cladding tube 130 covers the outer circumference of the first outer tube 1212 and is metallurgically bonded to the first outer tube 1212.

[0165] The fourth embodiment of the present application provides a Zr-Al composite cladding Al-based spiral multi-lobed nuclear fuel element containing a metal displacer and a manufacturing method thereof. The spiral multi-lobed nuclear fuel element is a 4-lobed type, the blade 100a is cosine-shaped, the pitch is 400mm, the total length of the fuel zone is 2000mm, and the diameter of the circumscribed circle is 13.3mm. A metal displacer is arranged inside the spiral multi-lobed nuclear fuel element. The manufacturing method of the spiral multi-lobed nuclear fuel element comprises the following steps:

[0166] S140: Mix the nuclear material particles with the metal matrix powder to form a fuel core blank 110 with a displacer installation hole, and pre-sinter the fuel core blank 110. The nuclear material particles are UAl with a certain particle size distribution. X or U3Si2 fuel particles ( 235 U enrichment is 5% to 60%), the metal matrix powder is Al alloy powder, and the volume proportion of the nuclear material particles in the fuel core blank 110 is greater than or equal to 20% and less than or equal to 40%.

[0167] Specifically, after the nuclear material particles are fully mixed with the metal matrix powder, a fuel core blank with a displacer mounting hole (specifically a square hole) can be made through a pressing process, and the bonding strength of the core blank can be improved through a pre-sintering process.

[0168] S240: Place the first inner tube 1211 of the tube body 121 in the displacer mounting hole, and place the fuel core blank 110 in the first outer tube 1212 of the tube body 121, that is, place the fuel core blank 110 in the annular cavity between the first inner tube 1211 and the first outer tube 1212. An inner hole connected to the displacer mounting hole is provided at the center of the end plate 122, and the end plate 122 closes the annular opening formed between the end of the first inner tube 1211 and the end of the first outer tube 1212. Among them, the metal material used in the first cladding tube is the same as the material of the metal matrix powder, that is, Al alloy is used to make the first cladding tube. The first cladding tube includes two end plates 122, and the two end plates 122 respectively close the two annular openings at both ends of the first inner tube 1211 and the first outer tube 1212.

[0169] In actual operation, one of the two end plates 122 is first welded to one end of the tube body 121. Then the fuel core blank 110 is loaded into the tube body 121 from the other end of the tube body 121. Then the other end plate 122 of the two end plates 122 is welded to the tube body 121. The welding of the end plate 122 and the tube body 121 can be carried out by vacuum electron beam welding. Thus, the fuel core blank 110 can be enclosed in the first cladding tube. It can be understood that the inner diameter of the tube body 121 is substantially the same as the outer diameter of the fuel core blank 110.

[0170] In actual operation, one of the two end plates 122 is first welded to one end of the first inner tube 1211 and the first outer tube 1212 to close one of the annular openings. Then the fuel core blank 110 is loaded from the other end of the first inner tube 1211 and the first outer tube 1212. Then the other end plate 122 of the two end plates 122 is welded to the other end of the first inner tube 1211 and the first outer tube 1212 to close the other annular opening. The welding of the end plate 122 and the tube body 121 can be vacuum electron beam welding, so that the fuel core blank 110 can be enclosed in the first cladding tube. It can be understood that the inner diameter of the first outer tube 1212 is substantially the same as the outer diameter of the fuel core blank 110, and the outer diameter of the first inner tube 1211 is substantially the same as the inner diameter of the fuel core blank 110.

[0171] In this embodiment, the material used for the first cladding tube may be X8001 or 6061-O Al alloy.

[0172] S340: The fuel core blank 110 and the first cladding tube are made into a core rod by a co-extrusion process. Since the metal material used in the first cladding tube is the same as the material of the metal matrix powder, the outer circumference of the first inner tube 1211 can be metallurgically bonded to the hole wall of the through hole 101, the first outer tube 1212 can be metallurgically bonded to the fuel core blank 110, and the two end plates 122 can be metallurgically bonded to the two ends of the fuel core blank 110 during the co-extrusion process to make the core rod.

[0173] S341 : placing the displacer 150 in the first inner tube 1211 .

[0174] Specifically in this embodiment, the material used for the displacer 150 may be Zr4. The displacer 150 is transitionally matched with the first inner tube 1211. A base hole system H7 / n6 transitional match may be used. The displacer 150 may be cooled so that the displacer 150 contracts when cold and the outer diameter is reduced, thereby facilitating the placement of the displacer 150 in the first inner tube 1211. After the temperature of the displacer 150 returns to room temperature, the outer diameter returns to the outer diameter at room temperature, thereby enabling transitional matching with the first inner tube 1211.

[0175] Specifically, the displacer 150 may be cooled by using a freezer, ice water or liquid nitrogen.

[0176] Furthermore, the surface of the core rod may be polished.

[0177] S440: placing the core rod in the second cladding tube 130, wherein the melting point of the metal material used in the second cladding tube 130 is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube 130 are better than the mechanical properties of the metal material used in the first cladding tube. Specifically, the metal material used in the second cladding tube 130 can be Zr4 or M5 or ZIRLO or N36 zirconium alloy.

[0178] The inner diameter of the second cladding tube 130 and the outer diameter of the core rod are interference fit, and specifically, a base shaft system P7 / h6 fit can be adopted. Specifically, air pressure or hydraulic pressure can be used to apply pressure, so that the core rod is placed in the second cladding tube 130.

[0179] S540: insert two end plugs 140 into both ends of the second cladding tube 130 respectively, and weld the two end plugs 140 to both ends of the second cladding tube 130 respectively, wherein the metal material used in the second cladding tube 130 is the same as the metal material used in the end plugs 140. The welding between the end plugs 140 and the second cladding tube 130 may be performed by vacuum electron beam welding.

[0180] After step S310 and before step S610, the wall thickness of the second cladding tube 130 is greater than or equal to 0.3 mm and less than or equal to 0.6 mm; the wall thickness of the first inner tube and the second inner tube of the tube body of the first cladding tube are both 0.1 mm.

[0181] S640: A spin-rolling process is used to spin-roll a rod-shaped structure formed by connecting a core rod, a second cladding tube 130 and an end plug 140 to obtain a spiral multi-lobed fuel rod 100. The outer periphery of the spiral multi-lobed fuel rod 100 is structured with a plurality of blades 100a arranged at intervals. Each blade 100a extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod, and each blade 100a contains a portion of the fuel core.

[0182] Specifically, the specific method of using the spin-rolling process to spin-roll the rod-shaped structure to obtain the spiral multi-lobed fuel rod can be referred to patent CN113470840B of the inventor of the present application, which will not be described in detail.

[0183] S740: Diffusion welding is performed on the spiral multi-lobed fuel rods to metallurgically bond the joint of the displacer 150 and the first inner tube 1211, the joint of the inner circumference of the second cladding tube 130 and the outer circumference of the first outer tube 1212, and the two end plugs 140 are respectively metallurgically bonded to the two end plates 122. Specifically, the spiral multi-lobed fuel rods can be placed in a resistance furnace for diffusion welding, and the welding temperature during diffusion welding should be higher than the recrystallization temperature of the first cladding tube, that is, higher than the recrystallization temperature of the Al alloy in this embodiment, greater than or equal to 350°C and less than or equal to 500°C, and the welding temperature is kept for 1 to 4 hours.

[0184] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0185] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for manufacturing a spiral multi-lobed nuclear fuel element with a composite cladding, characterized in that: The following steps are involved: Mixing the nuclear material particles with the metal matrix powder to form a fuel core blank, and pre-sintering the fuel core blank; Placing the fuel core blank in a first cladding tube, wherein the metal material used in the first cladding tube is the same as the material of the metal matrix powder, and the first cladding tube includes a tube body and two end plates, and the two end plates respectively seal the two ends of the tube body; The fuel core blank and the first cladding tube are formed into a core rod by a co-extrusion process, so that the inner circumference of the tube body and the outer circumference of the fuel core blank are metallurgically bonded at the junction, and the two end plates are metallurgically bonded to both ends of the fuel core blank; Placing the core rod in a second cladding tube, wherein the melting point of the metal material used in the second cladding tube is higher than the melting point of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube are better than the mechanical properties of the metal material used in the first cladding tube; Inserting two end plugs into two ends of the second cladding tube respectively, and welding the two end plugs to two ends of the second cladding tube respectively, wherein the metal material used for the second cladding tube is the same as the metal material used for the end plugs; A spinning process is used to spin-roll the rod-shaped structure formed by connecting the core rod, the second cladding tube and the end plug to obtain a spiral multi-lobed fuel rod, wherein the outer periphery of the spiral multi-lobed fuel rod is configured with a plurality of blades arranged at intervals, each of the blades extends in a spiral direction around the axial direction of the spiral multi-lobed fuel rod, and each of the blades contains a part of the fuel core; Diffusion welding is performed on the spiral multi-lobed fuel rod to metallurgically bond the inner circumference of the second cladding tube to the outer circumference of the core rod, and the two end plugs are metallurgically bonded to the two end plates respectively.

2. The manufacturing method according to claim 1, characterized in that: The step of placing the core rod in the second cladding tube comprises: Cooling the core rod, and placing the core rod that has shrunk upon cooling in the second cladding tube; and / or, The second cladding tube is heated, and the core rod is placed in the second cladding tube which expands due to the heat.

3. The manufacturing method according to claim 1, characterized in that: The step of placing the core rod in the second cladding tube comprises: Applying pressure or tension to the core rod in the axial direction so that the core rod is placed in the second cladding tube; And / or, applying pressure or tension to the second cladding tube in the axial direction so that the core rod is placed in the second cladding tube.

4. The manufacturing method according to claim 1, characterized in that: After the core rod is placed in the second cladding tube, the core rod and the second cladding tube are interference fit.

5. The manufacturing method according to claim 1, characterized in that: The metal material used for the first cladding tube is pure Al or Al alloy, and the welding temperature when diffusion welding the spiral multi-lobed fuel rod is greater than or equal to 350° C. and less than or equal to 500° C.; Alternatively, the metal material used for the first cladding tube is pure Zr or Zr alloy, and the welding temperature when diffusion welding the spiral multi-lobed fuel rod is greater than or equal to 500°C and less than or equal to 700°C.

6. The manufacturing method according to claim 1, characterized in that: The step of placing the fuel core blank in the first cladding tube comprises: Firstly, welding one of the two end plates to one end of the tube body; Then, the fuel core blank is installed into the tube body from the other end of the tube body; Then, the other end plate of the two end plates is welded to the tube body.

7. The manufacturing method according to claim 1, characterized in that: After the step of using the co-extrusion process to form the fuel core blank and the first cladding tube into a core rod, and before the step of using the spin rolling process to spin the rod-shaped structure formed by connecting the core rod, the second cladding tube and the end plug to obtain a spiral multi-lobed fuel rod, the wall thickness of the tube body of the first cladding tube is greater than or equal to 0.1 mm and less than or equal to 0.3 mm; the wall thickness of the second cladding tube is greater than or equal to 0.3 mm and less than or equal to 0.6 mm; After the spiral multi-lobed fuel rod is obtained by the spin-rolling process, the wall thickness of the second cladding tube is greater than or equal to 0.2 mm, and the total wall thickness of the tube body of the first cladding tube and the second cladding tube is greater than or equal to 0.3 mm; the total wall thickness of the tube body of the first cladding tube and the second cladding tube is less than or equal to 1 mm.

8. The manufacturing method according to claim 1, characterized in that: The step of mixing the core material particles with the metal matrix powder to form a fuel core blank comprises: mixing the core material particles with the metal matrix powder to form a tubular fuel core blank, so that a through hole extending in the axial direction is formed in the fuel core blank; The step of placing the fuel core blank in the first cladding tube comprises: placing the first inner tube of the tube body in the through hole, placing the fuel core blank in the first outer tube of the tube body, the center of the end plate is provided with an inner hole communicating with the through hole, and the end plate closes the annular opening formed between the end of the first inner tube and the end of the first outer tube; The step of using the co-extrusion process to form the fuel core blank and the first cladding tube into a core rod comprises: metallurgically bonding the outer circumference of the first inner tube to the hole wall of the through hole, and metallurgically bonding the inner circumference of the first outer tube to the outer circumference of the fuel core blank; The step of diffusion welding the spiral multi-lobed fuel rod includes: metallurgically bonding the second outer tube of the second cladding tube to the first outer tube, and metallurgically bonding the second inner tube of the second cladding tube to the first inner tube.

9. The manufacturing method according to claim 1, characterized in that: The step of mixing the nuclear material particles with the metal matrix powder to form a fuel core blank comprises: mixing the nuclear material particles with the metal matrix powder to form a fuel core blank with a displacer mounting hole; The step of placing the fuel core blank in the first cladding tube comprises: placing the first inner tube of the tube body in the displacer mounting hole, placing the fuel core blank in the first outer tube of the tube body, the center of the end plate is provided with an inner hole communicating with the displacer mounting hole, and the end plate closes the annular opening formed between the end of the first inner tube and the end of the first outer tube; After the step of forming the fuel core blank and the first cladding tube into a core rod by co-extrusion, and before the step of inserting two end plugs into the two ends of the second cladding tube, the manufacturing method further comprises placing a displacer in the first inner tube; The step of diffusion welding the spiral multi-lobed fuel rod includes: metallurgically bonding the second cladding tube to the first outer tube, and metallurgically bonding the displacer to the first inner tube.

10. A spiral multi-lobed nuclear fuel element with a composite cladding, characterized in that: include: The fuel core is a metal-based dispersed fuel core; A first cladding tube, wherein the metal material used in the first cladding tube is the same as the metal matrix material in the fuel core, the first cladding tube comprises a tube body and two end plates, the two end plates respectively seal the two ends of the tube body, the tube body covers the outer circumference of the fuel core and is metallurgically bonded to the fuel core, and the two end plates are metallurgically bonded to the two ends of the fuel core; Two end plugs are respectively arranged at two ends of the first cladding tube, and the two end plugs are respectively metallurgically bonded to the two end plates; as well as a second cladding tube, wherein the second cladding tube covers the outer circumference of the first cladding tube and is metallurgically bonded to the first cladding tube, the metal material used in the second cladding tube is the same as the metal material used in the end plugs, and both ends of the second cladding tube cover the outer circumferences of the two end plugs and are welded to the two end plugs; The melting point of the metal material used in the second cladding tube is higher than that of the metal material used in the first cladding tube, and the mechanical properties of the metal material used in the second cladding tube are better than those of the metal material used in the first cladding tube; The outer periphery of the spiral multi-lobed nuclear fuel element is constructed with a plurality of blades arranged at intervals, each of the blades extends in a spiral direction around the axial direction of the spiral multi-lobed nuclear fuel element, and each of the blades contains a portion of the fuel core.

11. The spiral multi-lobed nuclear fuel element according to claim 10, characterized in that: The fuel core is provided with a through hole extending along its axial direction; The tube body includes a first inner tube and a first outer tube, the first inner tube is located in the through hole, the outer circumferential surface of the first inner tube is metallurgically bonded to the hole wall of the through hole, and the first outer tube covers the outer circumferential surface of the fuel core and is metallurgically bonded to the fuel core; the center of the end plate is provided with an inner hole connected to the through hole, and the end plate closes the annular opening formed between the end of the first inner tube and the end of the first outer tube. The second cladding tube includes a second inner tube and a second outer tube. The second inner tube is located in the first inner tube. The outer circumference of the second inner tube is metallurgically bonded to the inner circumference of the first inner tube. The second outer tube covers the outer circumference of the first outer tube and is metallurgically bonded to the first outer tube.

12. The spiral multi-lobed nuclear fuel element according to claim 10, characterized in that: The fuel core is provided with a displacer mounting hole extending along its axial direction; The tube body comprises a first inner tube and a first outer tube, the first inner tube is located in the displacer mounting hole, the outer circumference of the first inner tube is metallurgically bonded to the hole wall of the displacer mounting hole, and the first outer tube covers the outer circumference of the fuel core and is metallurgically bonded to the fuel core; the center of the end plate is provided with an inner hole connected to the displacer mounting hole, and the end plate closes the annular opening formed between the end of the first inner tube and the end of the first outer tube; A displacer is disposed in the first inner tube and is metallurgically bonded to the displacer; and the second cladding tube covers the outer circumferential surface of the first outer tube and is metallurgically bonded to the first outer tube.

13. The spiral multi-lobed nuclear fuel element according to claim 10, characterized in that: The volume ratio of the nuclear fuel in the fuel core is greater than or equal to 10% and less than or equal to 70%.

14. The spiral multi-lobed nuclear fuel element according to claim 10, characterized in that: The material used for the second cladding tube is any one of Zr4, N18, N36, stainless steel 304, stainless steel 316 or stainless steel 321.

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