Double-layer cladding nuclear fuel rod and preparation method thereof

Abstract

The invention discloses a double-layer cladding nuclear fuel rod and a preparation method thereof.The preparation method comprises the steps that S1, a metal cladding with one closed end is loaded into a SiC composite cladding tube with one closed end, and the outer surface of the metal cladding is in close fit with the inner surface of the SiC composite cladding tube; s2, loading the nuclear fuel pellet and the first pressure spring into the metal cladding; s3, a metal end plug is connected to the open end of the metal cladding in a sealed mode, and a metal fuel rod is formed; s4, a second pressure spring and a heat insulation block are arranged in the SiC composite cladding tube to abut against the metal fuel rod; and S5, the SiC end plug is sealed at the open end of the SiC composite cladding tube in a matched mode. The double-layer cladding nuclear fuel rod disclosed by the invention has the characteristics of corrosion resistance and high air tightness, can effectively resist a hydrothermal corrosion environment under a normal operation working condition and an accident working condition, and meanwhile, effectively reduces the risk of releasing fission gas; the overall reliability of the fuel rod is high.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear fuel, and in particular to a double-clad nuclear fuel rod and a preparation method thereof. Background Art

[0002] Silicon carbide (SiC) has become a candidate material for new fuel cladding due to its high melting point, small neutron absorption cross section, high temperature stability, high mechanical strength, good neutron irradiation stability, corrosion resistance, and low hydrogen production rate when reacting with water at high temperature. The use of SiC cladding material can effectively increase the response time to loss of coolant accidents and the operating temperature of the core, which is of great significance in the safe use of nuclear power and improving efficiency. In order to solve the inherent brittleness of SiC, SiC fiber reinforced SiC (SiC f / SiC) composite materials are toughened. SiC f / SiC composite cladding is a new cladding material that is expected to replace the existing Zr alloy.

[0003] At present, the preparation scheme of SiC cladding materials includes a two-layer structure of an outer SiC fiber braided layer and an inner SiC single layer, or a three-layer structure design including a SiC fiber braided layer and two inner and outer SiC single layers, or a metal coating is further applied on the outer layer based on the above design. The preparation methods of SiC composite cladding include nano-impregnation transient liquid phase (NITE) method, chemical vapor infiltration (CVI) method, precursor impregnation cracking (PIP) method and reactive infiltration (RI) method. Among them, the NITE method has high process conditions and cannot produce meter-level SiC cladding materials with performance that meets the requirements at this stage; the SiC composite cladding prepared by the RI method is prone to a large amount of residual Si, which cannot meet the water environment requirements required for the service of the SiC cladding; the SiC composite cladding prepared by the CVI method and the PIP method has a large number of pore defects inside, which cannot meet the airtightness requirements of the nuclear fuel cladding.

[0004] In order to solve the problem of SiC cladding airtightness, both domestic and foreign countries have proposed the design of adding metal cladding tubes inside the SiC cladding. However, the existing technology uses SiC cladding directly outside the metal zirconium alloy tube. f / SiC composite materials, or the method of making the inner and outer tubes of the metal-SiC cladding fit tightly through high-temperature plastic deformation. Under high temperature conditions, the mutual reaction between SiC and Zr intensifies, making it easier to corrode the zirconium alloy tube. And the interface layer between SiC and Zr is prone to produce brittle byproducts, thereby reducing its reliability. Moreover, the above designs are only for the cladding tube structure, and do not solve the problem of welding and packaging of silicon carbide-metal cladding tubes with metal and SiC end plugs, nor do they have specific fuel rod design solutions.

[0005] In order to ensure the overall airtightness of the fuel rod, the outermost SiC fThe temperature during welding of the SiC composite cladding and the SiC end plug is relatively high, usually requiring welding at temperatures above 1500°C, which will cause significant thermal effects such as melting or irreversible phase change on the spring and the metal cladding tube, causing the spring to fail and the metal cladding tube to lose its original performance. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a double-clad nuclear fuel rod and a preparation method thereof.

[0007] The technical solution adopted by the present invention to solve the technical problem is: to provide a method for preparing a double-clad nuclear fuel rod, comprising the following steps:

[0008] S1. Installing a metal cladding tube with one end closed into a SiC composite cladding tube with one end closed, and making the outer surface of the metal cladding tube closely fit with the inner surface of the SiC composite cladding tube by low temperature deformation;

[0009] S2, loading the nuclear fuel pellets and the first compression spring into the metal cladding tube from the open end of the metal cladding tube;

[0010] S3, sealingly connecting a metal end plug to the open end of the metal cladding tube to close it, wherein the metal end plug, the metal cladding tube, the nuclear fuel pellets and the first compression spring together form a metal fuel rod;

[0011] S4, inserting a second compression spring and a heat insulation block into the SiC composite cladding tube from the open end of the SiC composite cladding tube, abutting against the metal fuel rod;

[0012] S5. Sealingly connect a SiC end plug to the open end of the SiC composite cladding tube.

[0013] Preferably, the length of the metal fuel rod is shorter than the length of the SiC composite cladding tube.

[0014] Preferably, in step S1, the low-temperature deformation method includes: providing a ductile coating on the outer surface of the metal cladding tube, and low-temperature treatment to reduce the outer diameter of the metal cladding tube; restoring the temperature to room temperature to expand the outer diameter of the metal cladding tube to fit closely with the inner surface of the SiC composite cladding tube.

[0015] Preferably, the temperature of the low temperature treatment is: -200°C to -50°C; the coating is made of at least one of metal zirconium, metal niobium, silicon steel, and cracked carbon; the thickness of the coating is 5μm to 50μm.

[0016] Preferably, the metal cladding tube and the metal end plug are each made of at least one of zirconium and its alloys, tantalum and its alloys, niobium and its alloys, molybdenum and its alloys, iron-chromium-aluminum alloys, and stainless steel.

[0017] Preferably, the SiC composite cladding tube comprises a SiC fiber braided layer and a SiC single-substance layer composited on the inner side and / or the outer side of the SiC fiber braided layer.

[0018] Preferably, the insulation block is made of at least one of ceramic, glass fiber, rock wool, calcium silicate and aluminum silicate.

[0019] Preferably, step S1 comprises:

[0020] Providing a metal clad tube and two metal end plugs, and sealingly connecting one of the metal end plugs to one end of the metal clad tube to form a metal clad tube with one end closed;

[0021] Providing two SiC composite cladding tubes and two SiC end plugs, and sealingly connecting one of the SiC end plugs to one end of the SiC composite cladding tube to form a SiC composite cladding tube with one end closed;

[0022] Another of the metal end plugs is fitted at the open end of the metal cladding tube in step S3, and another of the SiC end plugs is fitted at the open end of the SiC composite cladding tube in step S5.

[0023] The present invention provides another method for preparing a double-clad nuclear fuel rod, comprising the following steps:

[0024] S1. preparing metal fuel rods;

[0025] S2, loading the metal fuel rod into the SiC composite cladding tube with one end closed, and making the outer surface of the metal fuel rod closely fit with the inner surface of the SiC composite cladding tube by low temperature deformation;

[0026] S3, inserting a second compression spring and a heat insulation block into the SiC composite cladding tube from the open end of the SiC composite cladding tube, abutting against the metal fuel rod;

[0027] S4. Sealingly connecting a SiC end plug to the open end of the SiC composite cladding tube.

[0028] Preferably, the length of the metal fuel rod is shorter than the length of the SiC composite cladding tube.

[0029] Preferably, step S1 comprises:

[0030] S1.1. Provide a metal clad tube and two metal end plugs, and seal one metal end plug to one end of the metal clad tube to form a metal clad tube with one end open;

[0031] S1.2, inserting the nuclear fuel pellets and the first compression spring into the metal cladding tube from the open end of the metal cladding tube;

[0032] S1.3. Sealingly connect another metal end plug to the open end of the metal cladding tube. The metal end plug, the metal cladding tube, the nuclear fuel core block and the first compression spring together form the metal fuel rod.

[0033] Preferably, the metal cladding tube and the metal end plug are each made of at least one of zirconium and its alloys, tantalum and its alloys, niobium and its alloys, molybdenum and its alloys, iron-chromium-aluminum alloys, and stainless steel.

[0034] Preferably, in step S2, the low-temperature deformation method includes: providing a ductile coating on the outer surface of the metal fuel rod, and reducing the outer diameter of the metal fuel rod by low-temperature treatment; restoring the temperature to room temperature to expand the outer diameter of the metal fuel rod to fit closely with the inner surface of the SiC composite cladding tube.

[0035] Preferably, the temperature of the low temperature treatment is: -200°C to -50°C; the coating is made of at least one of metal zirconium, metal niobium, silicon steel, and cracked carbon; the thickness of the coating is 5μm to 50μm.

[0036] Preferably, the SiC composite cladding tube comprises a SiC fiber braided layer and a SiC single-substance layer composited on the inner side and / or the outer side of the SiC fiber braided layer;

[0037] The heat insulation block is made of at least one of ceramic, glass fiber, rock wool, calcium silicate and aluminum silicate.

[0038] The present invention also provides a double-clad nuclear fuel rod, which is made by the above-mentioned preparation method.

[0039] The beneficial effects of the present invention are as follows: it has a double-layer cladding structure, has corrosion resistance and high air tightness, can effectively resist the hydrothermal corrosion environment under normal operating conditions and accident conditions, and effectively reduces the risk of fission gas release; achieves close fitting of the metal fuel rod and the SiC composite cladding tube by low-temperature deformation, does not produce additional interface products, and avoids irreversible thermal effects on the core block, spring and the metal fuel rod itself during the matching and welding of the fuel rod, thereby improving the overall reliability of the fuel rod and reducing the difficulty of the cladding-end plug welding process; separates the SiC end plug and the metal fuel rod by an insulating block and a compression spring, thereby avoiding irreversible thermal effects on the metal fuel rod during the welding of the SiC end plug, thereby avoiding performance loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0041] Figure 1 The figure is a schematic cross-sectional structure diagram of a double-clad nuclear fuel rod according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0043] like Figure 1 As shown, a double-clad nuclear fuel rod according to an embodiment of the present invention may include a SiC composite cladding and a metal fuel rod assembled in the SiC composite cladding.

[0044] The SiC composite cladding comprises a SiC composite cladding tube 10 and two SiC end plugs 11, and the two SiC end plugs 11 are respectively sealed and connected to the opposite ends of the SiC composite cladding tube 10. The SiC composite cladding tube 10 can further be a two-layer structure or a three-layer structure; for the two-layer structure, the SiC composite cladding tube 10 comprises a SiC fiber braided layer and a SiC single-substance layer compounded on the outside of the SiC fiber braided layer; for the three-layer structure, the SiC composite cladding tube 10 comprises a SiC fiber braided layer and a SiC single-substance layer compounded on the inside and outside of the SiC fiber braided layer.

[0045] The metal fuel rod further comprises a metal cladding tube 20 and two metal end plugs 21, and the two metal end plugs 21 are respectively sealed and connected to the opposite ends of the metal cladding tube 20. The metal fuel rod also comprises a plurality of nuclear fuel pellets 22 and a first compression spring 23, and the plurality of nuclear fuel pellets 22 are assembled in the metal cladding tube 20 along the length direction of the metal cladding tube 20, and the first compression spring 23 abuts between the nuclear fuel pellets 22 and a metal end plug 21.

[0046] Furthermore, the double-clad nuclear fuel rod also includes a second compression spring 12 and a heat-insulating block 13. The second compression spring 12 and the heat-insulating block 13 are assembled in the SiC composite cladding tube 10, wherein the second compression spring 12 abuts between a metal end plug 21 of the metal fuel rod and the heat-insulating block 13, and the heat-insulating block 13 abuts between the second compression spring 12 and a SiC end plug 11.

[0047] A coating is provided between the metal fuel rod and the inner surface of the SiC composite cladding tube 10. The coating is made of a material with good ductility, including at least one of metal zirconium, metal niobium, silicon steel, and cracked carbon. The thickness of the coating is 5 μm to 50 μm. The coating is a metal coating or a non-metallic coating according to the material selection, and its setting method includes at least one of PVD process, laser cladding process, CVD process, and CVI process.

[0048] Preferably, the structures of the two metal end plugs 21 are not completely the same. One metal end plug 21 is used as a first metal end plug, and the boss at one end of the first metal end plug is fitted into one end of the metal cladding tube 20, and the other end of the first metal end plug is fitted outside the end of the metal cladding tube 20, and the outer surface of the other end is flush with or slightly lower than the outer surface of the end of the metal cladding tube 20. The other metal end plug 21 is used as a second metal end plug, which can be integrally fitted into the end of the metal cladding tube 20 opposite to the other end. The coating is provided on the outer surface of the metal cladding tube 20 and the outer surface of the second metal end plug.

[0049] As can be seen from the above, the metal cladding tube 20 of the metal fuel rod forms the first layer of cladding, and the SiC composite cladding tube 10 forms the second layer of cladding, thereby constituting a double-layer cladding of the nuclear fuel rod, that is, the nuclear fuel core block 22 is sealed by the two outer layers of cladding, thereby improving the overall airtightness of the nuclear fuel rod and reducing the risk of fission gas release.

[0050] refer to Figure 1 A method for preparing a double-clad nuclear fuel rod according to an embodiment of the present invention comprises the following steps:

[0051] S1. Provide a metal cladding tube 20 and two metal end plugs 21 matched with the metal cladding tube 20 , and provide two SiC composite cladding tubes 10 and two SiC end plugs 11 matched with the SiC composite cladding tubes 10 .

[0052] A metal end plug 21 is sealed and connected to one end of the metal cladding tube 20 to form a metal cladding tube 20 with one end closed, and a SiC end plug 11 is sealed and connected to one end of the SiC composite cladding tube 10 to form a SiC composite cladding tube 10 with one end closed.

[0053] The metal cladding tube 20 with one end closed is installed into the SiC composite cladding tube 10 with one end closed until the metal end plug 21 at the closed end of the metal cladding tube 20 abuts against the inner surface of the SiC end plug 11 at the closed end of the SiC composite cladding tube 10, that is, it is assembled in place.

[0054] The outer surface of the metal clad tube 20 is closely matched with the inner surface of the SiC composite clad tube 10 by low temperature deformation, which effectively reduces the generation of byproducts at the interface between the metal inner tube and SiC and improves the reliability of the cladding. The specific operation is as follows: a ductile coating is provided on the outer surface of the metal clad tube 20, and the outer diameter of the metal clad tube 20 is reduced by low temperature treatment; the temperature is restored to room temperature, so that the outer diameter of the metal clad tube 20 is expanded and closely matched with the inner surface of the SiC composite clad tube 10.

[0055] The temperature of the low temperature treatment is -200°C to -50°C. The coating is made of a material with good ductility, including at least one of metal zirconium, metal niobium, silicon steel, and cracked carbon. The thickness of the coating is 5μm to 50μm. The coating is a metal coating or a non-metallic coating according to the material selection, and its setting method includes at least one of PVD process, laser cladding process, CVD process, and CVI process.

[0056] Specifically, the metal clad tube 20 and the metal end plug 21 are respectively made of at least one of a powder metallurgy process, a cold rolling forming process, and an extrusion forming process. In terms of materials, the metal clad tube 20 can be made of at least one of zirconium and its alloys, tantalum and its alloys, niobium and its alloys, molybdenum and its alloys, iron-chromium-aluminum alloys, and stainless steel. The metal end plug 21 is made of at least one of zirconium and its alloys, tantalum and its alloys, niobium and its alloys, molybdenum and its alloys, iron-chromium-aluminum alloys, and stainless steel. Since the metal clad tube 20 and the metal end plug 21 are both made of metal materials, the sealing connection of the metal end plug 21 on the end of the metal clad tube 20 can be achieved by welding, and the welding method further includes at least one of a resistance welding process, a laser welding process, a TIG welding process, a brazing process, and an arc welding process.

[0057] SiC composite cladding tube 10 is SiC f / SiC composite cladding tube, comprising a SiC fiber braided layer, and a SiC single-substance layer composited on the inner side and / or outer side of the SiC fiber braided layer. The SiC composite cladding tube 10 is made by at least one of the NITE process, the CVI process, the CVD process, the PIP process, and the RI process; the SiC end plug is made by at least one of the CVD process, the hot pressing sintering process, the SiC additive manufacturing process, and the reaction sintering process.

[0058] For the sealed connection between the SiC composite cladding tube 10 and the SiC end plug, at least one of the brazing process, precursor welding process, reaction sintering welding process, NITE phase welding process, solid phase diffusion welding process, glass ceramic welding process, and MAX phase welding process can be used.

[0059] S2. Load the nuclear fuel pellets 22 and the first compression spring 23 into the metal cladding tube 20 from the open ends of the SiC composite cladding tube 10 and the metal cladding tube 20 .

[0060] The number and size of the nuclear fuel pellets 22 are set according to actual needs. In the metal cladding tube 20, a plurality of nuclear fuel pellets 22 abut against the inner surface of the metal end plug 21 at the closed end of the metal cladding tube 20, and are arranged in sequence along the length direction of the metal cladding tube 20. The first compression spring 23 is provided at one end of the arranged nuclear fuel pellets 22.

[0061] S3, insert another metal end plug 21 into the SiC composite cladding tube 10 from the open end of the SiC composite cladding tube 10 and seal it to the open end of the metal cladding tube 20, closing the open end of the metal cladding tube 20. The two metal end plugs 21, the metal cladding tube 20, the nuclear fuel pellets 22 and the first compression spring 23 together form a metal fuel rod.

[0062] Before sealing and connecting the metal end plug 21 , helium is filled into the metal cladding tube 20 .

[0063] In the metal fuel rod, the first compression spring 23 abuts between the nuclear fuel pellet 22 and the inner surface of a metal end plug 21 .

[0064] It can be understood that since the metal fuel rod is entirely in the SiC composite cladding tube 10, the length of the metal fuel rod is smaller than the length of the SiC composite cladding tube 10. The outer diameter of the metal fuel rod is equal to or slightly smaller than the inner diameter of the SiC composite cladding tube 10, so as to ensure a tight fit between the two. In the SiC composite cladding tube 10, a spacer cavity is left between the end of the metal fuel rod and the open end of the SiC composite cladding tube 10, and the spacer cavity is used for the subsequent placement of the second compression spring 12 and the heat insulation block 13.

[0065] S4. Install the second compression spring 12 and the heat insulation block 13 into the SiC composite cladding tube 10 from the open end of the SiC composite cladding tube 10 so as to abut against the metal fuel rod.

[0066] The heat insulating block 13 is made of at least one of ceramic, glass fiber, rock wool, calcium silicate and aluminum silicate.

[0067] S5. Sealingly connect another SiC end plug 11 to the open end of the SiC composite cladding tube 10 to obtain a double-cladding nuclear fuel rod.

[0068] The SiC terminal plug 11 is connected under vacuum or atmosphere.

[0069] In combination with the above steps S4 and S5 , in the SiC composite cladding tube 10 , the second compression spring 12 abuts against the outer surface of a metal end plug 21 of the metal fuel rod, and the insulation block 13 is arranged between the second compression spring 12 and the inner surface of the SiC end plug 11 .

[0070] The second compression spring 12 and the heat insulation block 13 act as a separator between the metal fuel rod and the SiC end plug 11, so as to prevent the metal fuel rod and the nuclear fuel core block 22 inside thereof from being subjected to irreversible thermal influence and causing performance loss when the SiC end plug 11 is welded.

[0071] refer to Figure 1 A method for preparing a double-clad nuclear fuel rod according to another embodiment of the present invention comprises the following steps:

[0072] S1. Prepare metal fuel rods.

[0073] The step S1 may specifically include:

[0074] S1.1. Provide a metal clad tube 20 and two metal end plugs 21 matched with the metal clad tube 20, and seal one metal end plug 21 to one end of the metal clad tube 20 to form a metal clad tube 20 with one end open.

[0075] The metal cladding tube 20 and the metal end plug 21 are respectively made of at least one of a powder metallurgy process, a cold rolling forming process, and an extrusion forming process. In terms of materials, the metal cladding tube 20 can be made of at least one of zirconium and its alloys, tantalum and its alloys, niobium and its alloys, molybdenum and its alloys, iron-chromium-aluminum alloys, and stainless steel. The metal end plug 21 is made of at least one of zirconium and its alloys, tantalum and its alloys, niobium and its alloys, molybdenum and its alloys, iron-chromium-aluminum alloys, and stainless steel. Since the metal cladding tube 20 and the metal end plug 21 are both made of metal materials, the sealing connection of the metal end plug 21 on the end of the metal cladding tube 20 can be achieved by welding, and the welding method further includes at least one of a resistance welding process, a laser welding process, a TIG welding process, a brazing process, and an arc welding process.

[0076] S1.2. Install the nuclear fuel pellets 22 and the first compression spring 23 into the metal cladding tube 20 from the open end of the metal cladding tube 20 .

[0077] The number and size of the nuclear fuel pellets 22 are set according to actual needs. In the metal cladding tube 20, a plurality of nuclear fuel pellets 22 abut against the inner surface of the metal end plug 21 at the closed end of the metal cladding tube 20, and are arranged in sequence along the length direction of the metal cladding tube 20. The first compression spring 23 is provided at one end of the arranged nuclear fuel pellets 22.

[0078] S1.3. Another metal end plug 21 is sealed and connected to the open end of the metal cladding tube 20. The metal end plug 21, the metal cladding tube 20, the nuclear fuel pellets 22 and the first compression spring 23 together form a metal fuel rod.

[0079] Before sealing and connecting the metal end plug 21 , helium is filled into the metal cladding tube 20 .

[0080] In the metal fuel rod, the first compression spring 23 abuts between the nuclear fuel pellet 22 and the inner surface of a metal end plug 21 .

[0081] S2. The metal fuel rod is loaded into the SiC composite cladding tube 10 with one end closed, and the outer surface of the metal fuel rod is closely matched with the inner surface of the SiC composite cladding tube 10.

[0082] Before performing step S2, two SiC composite cladding tubes 10 and two SiC end plugs 11 adapted to the SiC composite cladding tubes 10 are provided; one SiC end plug 11 is sealed and connected to one end of the SiC composite cladding tube 10 to form a SiC composite cladding tube 10 with one end closed.

[0083] SiC composite cladding tube 10 is SiC f / SiC composite cladding tube, comprising a SiC fiber braided layer, and a SiC single-substance layer composited on the inner side and / or outer side of the SiC fiber braided layer. The SiC composite cladding tube 10 is made by at least one of the NITE process, the CVI process, the CVD process, the PIP process, and the RI process; the SiC end plug is made by at least one of the CVD process, the hot pressing sintering process, the SiC additive manufacturing process, and the reaction sintering process.

[0084] For the sealed connection between the SiC composite cladding tube 10 and the SiC end plug, at least one of the brazing process, precursor welding process, reaction sintering welding process, NITE phase welding process, solid phase diffusion welding process, glass ceramic welding process, and MAX phase welding process can be used.

[0085] The outer surface of the metal fuel rod is closely matched with the inner surface of the SiC composite cladding tube 10 by low temperature deformation, which effectively reduces the generation of interface byproducts between the metal inner tube and SiC and improves the reliability of the cladding. The specific operation is as follows: a ductile coating is provided on the outer surface of the metal fuel rod, and the outer diameter of the metal fuel rod is reduced by low temperature treatment; the temperature is restored to room temperature, so that the outer diameter of the metal fuel rod is expanded and closely matched with the inner surface of the SiC composite cladding tube 10.

[0086] The temperature of the low temperature treatment is -200°C to -50°C. The coating is made of a material with good ductility, including at least one of metal zirconium, metal niobium, silicon steel, and cracked carbon. The thickness of the coating is 5μm to 50μm. The coating is a metal coating or a non-metallic coating according to the material selection, and its setting method includes at least one of PVD process, laser cladding process, CVD process, and CVI process.

[0087] The length of the metal fuel rod is shorter than that of the SiC composite cladding tube 10. In the SiC composite cladding tube 10, a spacer cavity is left between the end of the metal fuel rod and the open end of the SiC composite cladding tube 10, and the spacer cavity is used to place the second compression spring 12 and the insulation block 13 later.

[0088] S3. Install the second compression spring 12 and the heat insulation block 13 into the SiC composite cladding tube 10 from the open end of the SiC composite cladding tube 10 so as to abut against the metal fuel rod.

[0089] The heat insulation block 13 is made of at least one of ceramic, glass fiber, rock wool, calcium silicate and aluminum silicate.

[0090] S4. Another SiC end plug 11 is sealed and connected to the open end of the SiC composite cladding tube 10 to obtain a double-cladding nuclear fuel rod.

[0091] The SiC terminal plug 11 is connected under vacuum or atmosphere.

[0092] In combination with the above steps S3 and S4, in the SiC composite cladding tube 10, the second compression spring 12 abuts against the outer surface of a metal end plug 21 of the metal fuel rod, and the heat insulation block 13 is arranged between the second compression spring 12 and the inner surface of the SiC end plug 11. The second compression spring 12 and the heat insulation block 13 play a role of separation between the metal fuel rod and the SiC end plug 11, so as to prevent the metal fuel rod and the nuclear fuel pellets 22 inside thereof from being subjected to irreversible thermal influence when the SiC end plug 11 is welded, thereby causing performance loss.

[0093] In some embodiments of the double-clad nuclear fuel rod of the present invention, the inner diameter of the metal cladding tube 20 is 7.3 mm to 13.3 mm, and the outer diameter is 8.0 mm to 14.0 mm; the inner diameter of the SiC composite cladding tube 10 is 8.1 mm to 14.1 mm, and the outer diameter is 9.5 mm to 15.0 mm.

[0094] In other embodiments, the inner diameter of the metal fuel rod (metal cladding tube 20) is 7.2 mm to 13.2 mm, and the outer diameter is 7.9 mm to 13.9 mm; the inner diameter of the SiC composite cladding tube 10 is 8.1 mm to 14.1 mm, and the outer diameter is 9.5 mm to 15.0 mm.

[0095] The double-clad nuclear fuel rod of the present invention has a leakage rate of 1×10 -15 Pa·m 3 / s~1×10 -13 Pa·m 3 / s, with higher air tightness.

[0096] During the service of the double-clad nuclear fuel rods using the present invention, when the nuclear fuel core blocks swell due to radiation, the coating with good ductility between the metal fuel rods and the SiC composite cladding tubes can achieve a good deformation and stress release effect, thereby increasing the overall mechanical strength of the fuel rods, and can improve the reliability of the cladding during operation, as well as the fuel containment capacity under accident conditions.

[0097] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a double-clad nuclear fuel rod, characterized in that: The following steps are involved: S1. Installing a metal cladding tube with one end closed into a SiC composite cladding tube with one end closed, and making the outer surface of the metal cladding tube closely fit with the inner surface of the SiC composite cladding tube by low temperature deformation; S2, loading the nuclear fuel pellets and the first compression spring into the metal cladding tube from the open end of the metal cladding tube; S3, sealingly connecting a metal end plug to the open end of the metal cladding tube to close it, wherein the metal end plug, the metal cladding tube, the nuclear fuel pellets and the first compression spring together form a metal fuel rod; S4, inserting a second compression spring and a heat insulation block into the SiC composite cladding tube from the open end of the SiC composite cladding tube, abutting against the metal fuel rod; S5. Sealingly connect a SiC end plug to the open end of the SiC composite cladding tube.

2. The method for preparing a double-clad nuclear fuel rod according to claim 1, characterized in that: The length of the metal fuel rod is shorter than the length of the SiC composite cladding tube.

3. The method for preparing a double-clad nuclear fuel rod according to claim 1, characterized in that: In step S1, the low-temperature deformation method includes: providing a ductile coating on the outer surface of the metal cladding tube, and low-temperature treatment to reduce the outer diameter of the metal cladding tube; restoring the temperature to room temperature to expand the outer diameter of the metal cladding tube to fit closely with the inner surface of the SiC composite cladding tube.

4. The method for preparing a double-clad nuclear fuel rod according to claim 3, characterized in that: The temperature of the low temperature treatment is -200°C to -50°C; the coating is made of at least one of metal zirconium, metal niobium, silicon steel and cracked carbon; the thickness of the coating is 5μm to 50μm.

5. The method for preparing a double-clad nuclear fuel rod according to any one of claims 1 to 4, characterized in that: The metal cladding tube and the metal end plug are each made of at least one of zirconium and its alloys, tantalum and its alloys, niobium and its alloys, molybdenum and its alloys, iron-chromium-aluminum alloys, and stainless steel; The SiC composite cladding tube comprises a SiC fiber braided layer and a SiC single-substance layer composited on the inner side and / or the outer side of the SiC fiber braided layer; The heat insulation block is made of at least one of ceramic, glass fiber, rock wool, calcium silicate and aluminum silicate.

6. The method for preparing a double-clad nuclear fuel rod according to any one of claims 1 to 4, characterized in that: Step S1 includes: Providing a metal clad tube and two metal end plugs, and sealingly connecting one of the metal end plugs to one end of the metal clad tube to form a metal clad tube with one end closed; Providing two SiC composite cladding tubes and two SiC end plugs, and sealingly connecting one of the SiC end plugs to one end of the SiC composite cladding tube to form a SiC composite cladding tube with one end closed; Another of the metal end plugs is fitted at the open end of the metal cladding tube in step S3, and another of the SiC end plugs is fitted at the open end of the SiC composite cladding tube in step S5.

7. A method for preparing a double-clad nuclear fuel rod, characterized in that: The following steps are involved: S1. preparing metal fuel rods; S2, loading the metal fuel rod into the SiC composite cladding tube with one end closed, and making the outer surface of the metal fuel rod closely fit with the inner surface of the SiC composite cladding tube by low temperature deformation; S3, inserting a second compression spring and a heat insulation block into the SiC composite cladding tube from the open end of the SiC composite cladding tube, abutting against the metal fuel rod; S4. Sealingly connecting a SiC end plug to the open end of the SiC composite cladding tube.

8. The method for preparing a double-clad nuclear fuel rod according to claim 7, characterized in that: The length of the metal fuel rod is shorter than the length of the SiC composite cladding tube.

9. The method for preparing a double-clad nuclear fuel rod according to claim 7, characterized in that: Step S1 includes: S1.

1. Provide a metal clad tube and two metal end plugs, and seal one metal end plug to one end of the metal clad tube to form a metal clad tube with one end open; S1.2, inserting the nuclear fuel pellets and the first compression spring into the metal cladding tube from the open end of the metal cladding tube; S1.

3. Sealingly connect another metal end plug to the open end of the metal cladding tube. The metal end plug, the metal cladding tube, the nuclear fuel core block and the first compression spring together form the metal fuel rod.

10. The method for preparing a double-clad nuclear fuel rod according to claim 9, characterized in that: The metal cladding tube and the metal end plug are each made of at least one of zirconium and its alloys, tantalum and its alloys, niobium and its alloys, molybdenum and its alloys, iron-chromium-aluminum alloys, and stainless steel.

11. The method for preparing a double-clad nuclear fuel rod according to claim 7, characterized in that: In step S2, the low-temperature deformation method includes: providing a ductile coating on the outer surface of the metal fuel rod, and reducing the outer diameter of the metal fuel rod by low-temperature treatment; restoring the temperature to room temperature to expand the outer diameter of the metal fuel rod to fit closely with the inner surface of the SiC composite cladding tube.

12. The method for preparing a double-clad nuclear fuel rod according to claim 11, characterized in that: The temperature of the low temperature treatment is -200°C to -50°C; the coating is made of at least one of metal zirconium, metal niobium, silicon steel and cracked carbon; the thickness of the coating is 5μm to 50μm.

13. The method for preparing a double-clad nuclear fuel rod according to any one of claims 7 to 12, characterized in that: The SiC composite cladding tube comprises a SiC fiber braided layer and a SiC single-substance layer composited on the inner side and / or the outer side of the SiC fiber braided layer; The heat insulation block is made of at least one of ceramic, glass fiber, rock wool, calcium silicate and aluminum silicate.

14. A double-clad nuclear fuel rod, characterized in that: The double-clad nuclear fuel rod is manufactured by the method for preparing the double-clad nuclear fuel rod described in any one of claims 1 to 6 or any one of claims 7 to 13.

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