Double-layer cladded nuclear fuel rod and preparation method therefor

Abstract

A double-layer cladded nuclear fuel rod and a preparation method therefor. The preparation method comprises: step S1, loading a metallic cladding tube (20) with one end closed into a SiC composite cladding tube (10) with one end closed, and making the outer surface of the metallic cladding tube (20) closely fit with the inner surface of the SiC composite cladding tube (10); step S2, loading nuclear fuel pellets (22) and a first compression spring (23) into the metallic cladding tube (20); step S3, sealingly connecting a metal end plug (21) to an open end of the metallic cladding tube (20) to form a metal fuel rod; step S4, loading a second compression spring (12) and heat insulation blocks (13) into the SiC composite cladding tube (10) to abut against the metal fuel rod; and step S5, sealing a SiC end plug (11) in a fit manner at the open end of the SiC composite cladding tube (10). The double-layer cladded nuclear fuel rod has the characteristics of 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, and thus the overall reliability of the fuel rod is high.

Description

Double-layered nuclear fuel rods and their preparation methods Technical Field

[0001] This invention relates to the field of nuclear fuel technology, and in particular to a double-clad nuclear fuel rod and its preparation method. Background Technology

[0002] Silicon carbide (SiC) has become a candidate material for new fuel cladding due to its advantages such as 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 temperatures. The use of SiC cladding materials can effectively increase the response time to loss-of-coolant accidents and the operating temperature of the reactor core, which is of great significance for the safe use and efficiency improvement of nuclear power. To address the inherent brittleness of SiC, fiber-reinforced SiC (SiC fiber-reinforced SiC) can be used. f Toughening of SiC composites. f / SiC composite cladding is a promising new cladding material that can replace existing Zr alloys.

[0003] Currently, SiC cladding material preparation schemes include two-layer structures composed of an outer SiC fiber braided layer and an inner SiC single-element layer, or three-layer structures composed of a SiC fiber braided layer and two SiC single-element layers, or further designs with a metal coating applied to the outer layer. Preparation methods for SiC composite cladding include nano-impregnation transient liquid phase (NITE), chemical vapor infiltration (CVI), precursor impregnation pyrolysis (PIP), and reactive infiltration (RI). Among these, the NITE method has high process requirements and cannot currently produce meter-scale SiC cladding materials with the required performance; the RI method often results in a large amount of residual Si, failing to meet the water environment requirements for SiC cladding service; and the CVI and PIP methods produce SiC composite claddings with numerous internal pores and defects, failing to meet the airtightness requirements of nuclear fuel cladding.

[0004] To address the issue of SiC cladding hermeticity, both domestic and international researchers have proposed designs that incorporate a metal cladding tube inside the SiC cladding. However, current technologies all involve directly depositing SiC cladding outside a zirconium alloy tube. f The composite material of SiC is used, or a method of tightly bonding the inner and outer tubes of the metal-SiC cladding is achieved through high-temperature plastic deformation. However, under high-temperature conditions, the reaction between SiC and Zr intensifies, making the zirconium alloy tube more susceptible to corrosion. Furthermore, the SiC-Zr interface layer is prone to producing brittle byproducts, thus reducing its reliability. Moreover, the above designs only address the cladding tube structure and do not solve the problem of welding and encapsulating the silicon carbide-metal cladding tube with the metal and SiC end plugs, nor do they provide specific fuel rod design solutions.

[0005] To ensure the overall airtightness of the fuel rods, the outermost SiC f The welding temperature between the SiC composite cladding and the SiC end plug is relatively high, usually above 1500℃. This can cause significant thermal effects on the spring and the metal cladding tube, such as melting or irreversible phase transformation, leading to spring failure and loss of the original performance of the metal cladding tube. Summary of the Invention

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

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

[0008] S1. A metal-clad tube with one end closed is inserted into a SiC composite-clad tube with one end closed, and the outer surface of the metal-clad tube is made to fit tightly with the inner surface of the SiC composite-clad tube by low-temperature deformation.

[0009] S2. Insert 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. Seal the metal end plug to the open end of the metal cladding tube to close it. The metal end plug, together with the metal cladding tube, the nuclear fuel pellet and the first compression spring, form a metal fuel rod.

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

[0012] S5. Seal the SiC end plug to the open end of the SiC composite cladding tube.

[0013] Preferably, the length of the metal fuel rod is less 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-clad tube, and reducing the outer diameter of the metal-clad tube by low-temperature treatment; restoring the temperature to room temperature to expand the outer diameter of the metal-clad tube, so as to fit tightly with the inner surface of the SiC composite clad tube.

[0015] Preferably, the temperature of the low-temperature treatment is -200℃ to -50℃; the coating is made of at least one of zirconium metal, niobium metal, silicon steel, and pyrolyzed carbon; and 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 includes a SiC fiber braided layer and a SiC elemental layer composited on the inner and / or outer sides of the SiC fiber braided layer.

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

[0019] Preferably, step S1 includes:

[0020] A metal-clad tube and two metal end plugs are provided, and one of the metal end plugs is sealed to one end of the metal-clad tube to form a metal-clad tube that is closed at one end.

[0021] Two SiC composite clad tubes and two SiC end plugs are provided. One of the SiC end plugs is sealed and connected to one end of the SiC composite clad tube to form a SiC composite clad tube with one end closed.

[0022] Another metal end plug is fitted into the open end of the metal-clad tube in step S3, and another SiC end plug is fitted into the open end of the SiC composite-clad tube in step S5.

[0023] This invention provides another method for preparing double-clad nuclear fuel rods, comprising the following steps:

[0024] S1. Preparation of metal fuel rods;

[0025] S2. The metal fuel rod is inserted into the SiC composite cladding tube that is closed at one end, and the outer surface of the metal fuel rod is made to fit tightly with the inner surface of the SiC composite cladding tube by low-temperature deformation.

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

[0027] S4. A SiC end plug is sealed and connected to the open end of the SiC composite cladding tube.

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

[0029] Preferably, step S1 includes:

[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. Insert 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. Another metal end plug is sealed to the open end of the metal cladding tube, and the metal end plug, together with the metal cladding tube, the nuclear fuel pellet and the first compression spring, forms 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: applying a ductile coating to 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, so as to fit tightly with the inner surface of the SiC composite cladding tube.

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

[0036] Preferably, the SiC composite cladding tube includes a SiC fiber braided layer and a SiC elemental layer composited on the inner and / or outer sides of the SiC fiber braided layer;

[0037] The 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-layered clad nuclear fuel rod, which is prepared by the above-described method.

[0039] The beneficial effects of this invention are as follows: It has a double-layer cladding structure, which has corrosion resistance and high airtightness, effectively resisting the hydrothermal corrosion environment under normal operating conditions and accident conditions, while effectively reducing the risk of fission gas release; it achieves a tight fit between the metal fuel rod and the SiC composite cladding tube through low-temperature deformation, without generating additional interface products, and avoids irreversible thermal effects on the fuel rod assembly and welding process on the fuel block, spring, and metal fuel rod itself, thereby improving the overall reliability of the fuel rod and reducing the difficulty of the cladding-end plug welding process; it uses heat insulation blocks and compression springs to separate the SiC end plug and the metal fuel rod, avoiding irreversible thermal effects on the metal fuel rod during SiC end plug welding, which would cause performance loss. Attached Figure Description

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

[0041] Figure 1 is a schematic cross-sectional view of a double-layered nuclear fuel rod according to an embodiment of the present invention. Detailed Implementation

[0042] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0043] As shown in Figure 1, 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 inside the SiC composite cladding.

[0044] The SiC composite cladding includes a SiC composite cladding tube 10 and two SiC end plugs 11, which are respectively sealed and connected to opposite ends of the SiC composite cladding tube 10. The SiC composite cladding tube 10 can further be a two-layer or three-layer structure; for a two-layer structure, the SiC composite cladding tube 10 includes a SiC fiber braided layer and a SiC elemental layer composited on the outside of the SiC fiber braided layer; for a three-layer structure, the SiC composite cladding tube 10 includes a SiC fiber braided layer and SiC elemental layers composited on the inner and outer sides of the SiC fiber braided layer, respectively.

[0045] The metal fuel rod further includes a metal cladding tube 20 and two metal end plugs 21, which are respectively sealed and connected to opposite ends of the metal cladding tube 20. The metal fuel rod also includes a plurality of nuclear fuel pellets 22 and a first compression spring 23. The plurality of nuclear fuel pellets 22 are assembled inside the metal cladding tube 20 along the length of the metal cladding tube 20, and the first compression spring 23 abuts against 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 insulation block 13. The second compression spring 12 and the heat insulation 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 insulation block 13, and the heat insulation 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. This coating is made of a material with good ductility, including at least one of zirconium metal, niobium metal, silicon steel, and pyrolyzed carbon. The coating thickness is 5 μm to 50 μm. The coating can be a metallic coating or a non-metallic coating depending on the material, and its application method includes at least one of PVD process, laser cladding process, CVD process, and CVI process.

[0048] Preferably, the two metal end plugs 21 have not identical structures. One metal end plug 21 serves as a first metal end plug, which fits into one end of the metal casing tube 20 with a boss at one end. The other end of the first metal end plug fits onto the outer side of the end of the metal casing 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 casing tube 20. The other metal end plug 21 serves as a second metal end plug, which can be integrally fitted into the opposite end of the metal casing tube 20. A coating is applied to the outer surface of the metal casing 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 cladding layer, and the SiC composite cladding tube 10 forms the second cladding layer, thus forming a double cladding layer for the nuclear fuel rod. That is, the nuclear fuel pellet 22 is sealed by the two outer cladding layers, which improves the overall airtightness of the nuclear fuel rod and reduces the risk of fission gas release.

[0050] Referring to Figure 1, a method for preparing an embodiment of the double-clad nuclear fuel rod of the present invention includes the following steps:

[0051] S1. Provide a metal-clad tube 20 and two metal end plugs 21 adapted to the metal-clad tube 20; provide two SiC composite clad tubes 10 and two SiC end plugs 11 adapted to the SiC composite clad tubes 10.

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

[0053] Insert the metal-clad tube 20, which is closed at one end, into the SiC composite clad tube 10, which is closed at the other end, until the metal end plug 21 at the closed end of the metal-clad tube 20 abuts against the inner surface of the SiC end plug 11 at the closed end of the SiC composite clad tube 10, and the assembly is complete.

[0054] By using a low-temperature deformation method, the outer surface of the metal-clad tube 20 is made to fit tightly with the inner surface of the SiC composite-clad tube 10, effectively reducing the generation of by-products at the interface between the metal inner tube and SiC, and improving the reliability of the cladding. The specific operation is as follows: a ductile coating is applied to 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 then restored to room temperature, causing the outer diameter of the metal-clad tube 20 to expand and fit tightly with the inner surface of the SiC composite-clad tube 10.

[0055] The low-temperature treatment temperature is -200℃ to -50℃. The coating is made of a material with good ductility, including at least one of zirconium metal, niobium metal, silicon steel, and pyrolyzed carbon. The coating thickness is 5μm to 50μm. Depending on the material, the coating can be a metallic or non-metallic coating, and its application method includes at least one of PVD, laser cladding, CVD, and CVI processes.

[0056] Specifically, the metal cladding tube 20 and the metal end plug 21 are manufactured using at least one of powder metallurgy, cold rolling, and extrusion molding processes. 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 both the metal cladding tube 20 and the metal end plug 21 are metallic materials, the sealing connection of the metal end plug 21 at the end of the metal cladding tube 20 can be achieved by welding. The welding methods further include at least one of resistance welding, laser welding, TIG welding, brazing, and arc welding.

[0057] SiC composite cladding tube 10 is SiC f The SiC composite cladding tube 10 includes a SiC fiber braided layer and a SiC elemental layer composited on the inner and / or outer sides of the SiC fiber braided layer. The SiC composite cladding tube 10 is manufactured using at least one of the NITE process, CVI process, CVD process, PIP process, and RI process; the SiC end plug is manufactured using at least one of the CVD process, hot pressing sintering process, SiC additive manufacturing process, and 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 following processes can be used: brazing, precursor welding, reaction sintering welding, NITE phase welding, solid-state diffusion welding, glass-ceramic welding, and MAX phase welding.

[0059] S2. The nuclear fuel pellet 22 and the first compression spring 23 are inserted into the metal cladding tube 20 from the open end of the SiC composite cladding tube 10 and the open end of the metal cladding tube 20.

[0060] The number and size of the nuclear fuel pellets 22 are set according to actual needs. Inside the metal cladding tube 20, several 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 sequentially along the length of the metal cladding tube 20. A 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, thus closing the open end of the metal cladding tube 20. The two metal end plugs 21, together with the metal cladding tube 20, the nuclear fuel pellet 22 and the first compression spring 23, form a metal fuel rod.

[0062] Before sealing the metal end plug 21, helium gas is introduced into the metal sheath tube 20.

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

[0064] Understandably, since the metal fuel rod is entirely contained within the SiC composite cladding tube 10, the length of the metal fuel rod is less 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 to ensure a tight fit between the two. A spacer cavity is provided within the SiC composite cladding tube 10 between the end of the metal fuel rod and the open end of the SiC composite cladding tube 10; this spacer cavity is used for subsequent placement of the second compression spring 12 and the heat insulation block 13.

[0065] S4. Insert 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, and abut against the metal fuel rod.

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

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

[0068] The SiC end plug 11 is connected under vacuum or atmospheric conditions.

[0069] Combining steps S4 and S5 above, inside 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 inner surface of the second compression spring 12 and 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, preventing the metal fuel rod and its internal nuclear fuel pellets 22 from being subjected to irreversible thermal effects during the welding of the SiC end plug 11, thus avoiding performance loss.

[0071] Referring to Figure 1, another embodiment of the preparation method of the double-clad nuclear fuel rod of the present invention includes the following steps:

[0072] S1. Preparation of metal fuel rods.

[0073] Step S1 may specifically include:

[0074] S1.1 Provide a metal-clad tube 20 and two metal end plugs 21 adapted to 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 manufactured using at least one of powder metallurgy, cold rolling, and extrusion molding processes. 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 both the metal cladding tube 20 and the metal end plug 21 are metallic materials, the sealing connection of the metal end plug 21 at the end of the metal cladding tube 20 can be achieved by welding. The welding methods further include at least one of resistance welding, laser welding, TIG welding, brazing, and arc welding.

[0076] S1.2. Insert the nuclear fuel pellet 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. Inside the metal cladding tube 20, several 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 sequentially along the length of the metal cladding tube 20. A 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, together with the metal cladding tube 20, the nuclear fuel pellet 22 and the first compression spring 23, form a metal fuel rod.

[0079] Before sealing the metal end plug 21, helium gas is introduced into the metal sheath tube 20.

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

[0081] S2. Insert the metal fuel rod into the SiC composite cladding tube 10, which is closed at one end, and ensure that the outer surface of the metal fuel rod fits tightly against 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 one-end closed SiC composite cladding tube 10.

[0083] SiC composite cladding tube 10 is SiC f The SiC composite cladding tube 10 includes a SiC fiber braided layer and a SiC elemental layer composited on the inner and / or outer sides of the SiC fiber braided layer. The SiC composite cladding tube 10 is manufactured using at least one of the NITE process, CVI process, CVD process, PIP process, and RI process; the SiC end plug is manufactured using at least one of the CVD process, hot pressing sintering process, SiC additive manufacturing process, and 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 following processes can be used: brazing, precursor welding, reaction sintering welding, NITE phase welding, solid-state diffusion welding, glass-ceramic welding, and MAX phase welding.

[0085] By employing a low-temperature deformation method, the outer surface of the metal fuel rod is made to fit tightly with the inner surface of the SiC composite cladding tube 10, effectively reducing the generation of by-products at the interface between the metal inner tube and SiC, and improving the reliability of the cladding. The specific operation is as follows: a ductile coating is applied to 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 then restored to room temperature, causing the outer diameter of the metal fuel rod to expand and fit tightly with the inner surface of the SiC composite cladding tube 10.

[0086] The low-temperature treatment temperature is -200℃ to -50℃. The coating is made of a material with good ductility, including at least one of zirconium metal, niobium metal, silicon steel, and pyrolyzed carbon. The coating thickness is 5μm to 50μm. Depending on the material, the coating can be a metallic or non-metallic coating, and its application method includes at least one of PVD, laser cladding, CVD, and CVI processes.

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

[0088] S3. Insert 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, and 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. Seal another SiC end plug 11 to the open end of the SiC composite cladding tube 10 to obtain a double-clad nuclear fuel rod.

[0091] The SiC end plug 11 is connected under vacuum or atmospheric conditions.

[0092] Combining steps S3 and S4 above, inside 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 act as a separator between the metal fuel rod and the SiC end plug 11, preventing irreversible thermal effects on the metal fuel rod and its internal nuclear fuel pellets 22 during the welding of the SiC end plug 11, thus avoiding performance loss.

[0093] In some embodiments of the double-clad nuclear fuel rods 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 rods of this invention, after testing, showed a leak rate of 1×10⁻⁶. -15 Pa·m 3 / s ~ 1×10 -13 Pa·m 3 / s, with high airtightness.

[0096] During the service of the double-clad nuclear fuel rods of the present invention, when the nuclear fuel pellets swell due to irradiation, the coating with good ductility between the metal fuel rod and the SiC composite cladding tube can play a good role in stress relief during deformation, increase the overall mechanical strength of the fuel rod, and improve the reliability of the cladding during operation, as well as the fuel containment capacity under accident conditions.

[0097] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a double-layered clad nuclear fuel rod, characterized in that, Includes the following steps: S1. A metal-clad tube with one end closed is inserted into a SiC composite-clad tube with one end closed, and the outer surface of the metal-clad tube is made to fit tightly with the inner surface of the SiC composite-clad tube by low-temperature deformation. S2. Insert the nuclear fuel pellets and the first compression spring into the metal cladding tube from the open end of the metal cladding tube; S3. Seal the metal end plug to the open end of the metal cladding tube to close it. The metal end plug, together with the metal cladding tube, the nuclear fuel pellet and the first compression spring, form a metal fuel rod. S4. Insert the second compression spring and the heat insulation block into the SiC composite cladding tube from the open end of the SiC composite cladding tube, and abut against the metal fuel rod; S5. Seal the SiC end plug to the open end of the SiC composite cladding tube.

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

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

4. The method for preparing a double-layered clad nuclear fuel rod according to claim 3, characterized in that, The temperature of the low-temperature treatment is -200℃ to -50℃; the coating is made of at least one of zirconium metal, niobium metal, silicon steel, and pyrolyzed 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 1-4, 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 includes a SiC fiber braided layer and a SiC elemental layer composited on the inner and / or outer sides of the SiC fiber braided layer. The 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 1-4, characterized in that, Step S1 includes: A metal-clad tube and two metal end plugs are provided, and one of the metal end plugs is sealed to one end of the metal-clad tube to form a metal-clad tube that is closed at one end. Two SiC composite clad tubes and two SiC end plugs are provided. One of the SiC end plugs is sealed and connected to one end of the SiC composite clad tube to form a SiC composite clad tube with one end closed. Another metal end plug is fitted into the open end of the metal-clad tube in step S3, and another SiC end plug is fitted into the open end of the SiC composite-clad tube in step S5.

7. A method for preparing a double-layered clad nuclear fuel rod, characterized in that, Includes the following steps: S1. Preparation of metal fuel rods; S2. The metal fuel rod is inserted into the SiC composite cladding tube that is closed at one end, and the outer surface of the metal fuel rod is made to fit tightly with the inner surface of the SiC composite cladding tube by low-temperature deformation. S3. Insert the second compression spring and the heat insulation block into the SiC composite cladding tube from the open end of the SiC composite cladding tube, and abut against the metal fuel rod; S4. A SiC end plug is sealed and connected to the open end of the SiC composite cladding tube.

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

9. The method for preparing a double-layered 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. Insert 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. Another metal end plug is sealed to the open end of the metal cladding tube, and the metal end plug, together with the metal cladding tube, the nuclear fuel pellet and the first compression spring, forms the metal fuel rod.

10. The method for preparing a double-layered 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-layered clad nuclear fuel rod according to claim 7, characterized in that, In step S2, the low-temperature deformation method includes: applying a ductile coating to 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 so that it fits tightly with the inner surface of the SiC composite cladding tube.

12. The method for preparing a double-layered clad nuclear fuel rod according to claim 11, characterized in that, The temperature of the low-temperature treatment is -200℃ to -50℃; the coating is made of at least one of zirconium metal, niobium metal, silicon steel, and pyrolyzed 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 7-12, characterized in that, The SiC composite cladding tube includes a SiC fiber braided layer and a SiC elemental layer composited on the inner and / or outer sides of the SiC fiber braided layer. The 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, It is prepared by the method described in any one of claims 1-6 or any one of claims 7-13 for double-layered clad nuclear fuel rods.

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