U-10zr metal fuel super-high length-diameter ratio pipe extrusion forming method and die

Abstract

This invention relates to the field of fuel element manufacturing technology, specifically disclosing a method and mold for extruding U-10Zr metal fuel ultra-high length-to-diameter ratio tubes. The forming method includes: (1) preparation of extrusion billet: U-10Zr ingots are obtained by vacuum induction melting and annealing of uranium metal ingots and nuclear-grade sponge zirconium, and copper sheets are wrapped around the outer surface of the ingots, with copper blocks at both ends, and then welded to obtain the extrusion billet; (2) extrusion of the extrusion billet: the extrusion billet is heated and kept at a certain temperature and then placed in a preheated extrusion cylinder for extrusion; the extrusion needle in the extrusion cylinder has a multi-section variable diameter structure, the material of the extrusion needle is GH4037, and the material of the extrusion rod is 5CrMnMo with a hardness of HRC50-52. This invention, through the design of the extrusion rod and extrusion needle, produces ultra-high length-to-diameter ratio tubes in one extrusion molding under a certain pressure, with high material utilization and the ability to achieve mass production of tubes.

Description

Technical Field

[0001] This invention relates to the field of fuel element manufacturing technology, and specifically discloses a method and mold for extruding U-10Zr metal fuel ultra-high length-to-diameter ratio tubes. Background Technology

[0002] Nuclear energy, as a clean, efficient, and sustainable energy source, is receiving increasing attention in the context of global energy structure transformation and the dual-carbon strategy. In the development of advanced nuclear energy systems, fast neutron reactors (referred to as "fast reactors") are considered a key technological path to achieving a closed nuclear fuel cycle and improving uranium resource utilization due to their excellent breeding performance and nuclear waste transmutation capabilities. According to my country's three-step nuclear energy development strategy, the research and development of fast reactors and their supporting fuel systems is a core link in achieving the transition from thermal reactors to fast reactors, and then to fusion reactors.

[0003] Metallic fuels are considered one of the most promising candidate fuels for fourth-generation fast reactors (such as sodium-cooled fast reactors) due to their high heavy metal density, excellent thermal conductivity, good neutron economy, and negative reactive feedback characteristics under accident conditions. Among them, the uranium-zirconium alloy (U-Zr) system, especially the U-10Zr alloy containing 10wt% Zr, is widely regarded as the preferred formulation for metallic fuels because of its high melting point, good irradiation behavior, compatibility with cladding materials, and stable body-centered cubic (BCC) γ-phase structure at high temperatures.

[0004] Currently, the preparation of U-10Zr metallic fuel mainly adopts the traditional smelting-casting-machining process: first, high-purity uranium and zirconium raw materials are smelted into alloy ingots under vacuum or inert atmosphere, and then machined into fuel pellets or short tubes of the required size through machining methods such as turning, drilling, and milling. However, this method has low material utilization, high mold consumption, and difficulty in producing ultra-high aspect ratio tubes in a single extrusion molding process, which is not conducive to large-scale production of metallic fuel. Therefore, it is necessary to develop a new manufacturing method that can achieve high efficiency, high consistency, and large-scale production of U-10Zr metallic fuel ultra-high aspect ratio tubes. Summary of the Invention

[0005] This invention provides a method for extruding U-10Zr metal fuel ultra-high length-to-diameter ratio tubes. By designing the extrusion rod, extrusion needle, and extrusion ratio, the molten and cast ingot is heated and kept at a certain pressure to produce ultra-high length-to-diameter ratio tubes in one step. The method has high material utilization and can achieve high-efficiency, high-consistency, and large-scale production of U-10Zr metal fuel tubes.

[0006] This invention is achieved through the following technical solution:

[0007] A method for extruding U-10Zr metallic fuel ultra-high aspect ratio tubes includes the following steps: (1) Preparation of extruded billet: U-10Zr ingots are obtained by vacuum induction melting and annealing of metallic uranium ingots and nuclear-grade sponge zirconium. After annealing, the riser is removed, the oxide scale is removed, and the U-10Zr ingot is machined to the specified size. Copper sheets are coated on the inner and outer surfaces of the U-10Zr ingot. Copper blocks are placed at both ends of the U-10Zr ingot and fixed by welding. The assembled welded ingot is sealed by plugging holes. Then the extruded billet is pressurized with helium and leak-tested to obtain the extruded billet. (2) Extrusion of billet: The extrusion billet is heated to 800-950℃ and held for 0.5-1h. Then it is placed in an extrusion cylinder preheated to 300-400℃ for extrusion. The extrusion speed is 20-35mm / s and the extrusion ratio is 23.73 to obtain U-10Zr metal fuel ultra-high length-to-diameter ratio tube. The extrusion needle in the extrusion cylinder has a multi-segment variable diameter structure. The material of the extrusion needle is GH4037 and the material of the extrusion rod is 5CrMnMo with a hardness of HRC50-52. The multi-segment variable diameter structure can reduce the working section length and improve the tensile strength of the extrusion needle. The thickness deviation of the tube is less than 0.05mm and the material utilization rate (after removing the head and tail) is greater than 80%. The extruded U-10Zr metal fuel ultra-high length-to-diameter ratio tube is machined to remove the inner and outer copper foil while ensuring that the thickness difference of the tube is less than 0.01mm.

[0008] The extrusion needle features a multi-segment variable diameter structure. The gradient diameter increase enhances overall rigidity, significantly reducing the deflection deformation of slender needles, ensuring core hole coaxiality, and preventing tube wall misalignment. Specifically, the thinner section at the needle tip ensures precise forming of the tube's inner diameter; the thicker section of the middle rod strengthens support and absorbs extrusion vibration, preventing needle tip chatter from causing scratches on the inner tube wall; the larger diameter section at the tail precisely matches the extrusion rod flange, increasing the contact area for more uniform pressure transmission, eliminating stress concentration, and adapting to the hardness and force transmission characteristics of the extrusion rod. It also allows for segmented, precise cooling to control the needle tip's operating temperature, prevent softening, reduce thermal shock cracks, and extend mold life.

[0009] The extrusion needle is made of GH4037, which has stable hardness and modulus at high temperatures of 900-950℃. The slender needle tip is resistant to bending deformation and has good coaxiality, ensuring the accuracy of the core hole and the uniformity of the tube wall. It is resistant to thermal shock, wear-resistant and non-stick, and is nuclear-pure grade with no harmful element precipitation. It is also easy to process into fine needle tips, suitable for precision forming of tubes with small inner diameter and ultra-high length-to-diameter ratio, and has a long mold life.

[0010] The extrusion bar is made of 5CrMnMo, which has high static load strength in the working temperature range of 600-800℃, is resistant to creep and thermal fatigue, has stable pressure transmission without deformation, and has a balance of strength and toughness to absorb impact; it is low in cost, has good processing / repairability, and its surface is resistant to oxidation without peeling, making it economical and practical for industrial batch extrusion.

[0011] Both the extrusion needle and the extrusion rod contain no strong neutron-absorbing elements, thus not contaminating the U-10Zr alloy. They are highly compatible with the U-10Zr hot extrusion process, resulting in excellent billet structure after extrusion, which does not affect subsequent strengthening. Furthermore, they allow for smooth demolding, preventing bending and cracking after forming of ultra-high length-to-diameter ratio tubes.

[0012] According to some preferred embodiments, during the preparation of the extruded billet, it is annealed at 1000±10℃ for 4-6 hours.

[0013] According to some preferred embodiments, the thickness of the copper sheet is 1-3 mm, and the thickness of the copper block is 5-20 mm.

[0014] According to some preferred embodiments, the outer diameter of the extruded billet is 50-65 mm.

[0015] According to some preferred embodiments, the extrusion pressure is 15-20 MPa and the length of the extrusion needle is 200 mm.

[0016] According to some preferred embodiments, the U-10Zr metal fuel ultra-high length-to-diameter ratio tube has an outer diameter of 15mm, an inner diameter of 7mm, and a length-to-diameter ratio of 100-120.

[0017] A die for extruding U-10Zr metal fuel ultra-high length-to-diameter ratio tubes is provided. The die is a conical die with a taper of 120°.

[0018] The technical solution of the present invention has at least the following advantages and beneficial effects: This invention employs an extrusion process to compress and deform a large-diameter extrusion ingot into a small-diameter long tube. Based on a comprehensive stress analysis considering the plastic deformation capacity of the extrusion material, the material extrusion ratio, the dimensions of the extrusion rod and extrusion needle, and the material strength, the extrusion needle is designed as a multi-segment variable-diameter structure. The extrusion needle material is GH4037, the extrusion rod material is 5CrMnMo with a hardness of HRC50-52, and the extrusion ratio is 23.73. This allows for the production of U-10Zr metal fuel ultra-high aspect ratio tubes in a single extrusion process, improving material utilization and achieving high-efficiency, high-consistency, and mass production of tubes. It solves the problems of slender extrusion needles being prone to bending and chattering, leading to uneven wall thickness or even breakage, and the low resistance to eccentric loads of ordinary extrusion rods, making it difficult to produce ultra-high aspect ratio tubes in a single extrusion process. Attached Figure Description

[0019] Figure 1 The process flow diagram of the U-10Zr metal fuel ultra-high length-to-diameter ratio tube extrusion molding method provided by the present invention.

[0020] Figure 2 This is a physical image of the extruded billet provided by the present invention.

[0021] Figure 3This is a schematic diagram of the structure of the mold for extruding U-10Zr metal fuel ultra-high length-to-diameter ratio tubes provided by the present invention.

[0022] Figure 4 This is a physical image of the U-10Zr metal fuel ultra-high length-to-diameter ratio tube provided by the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0024] Example 1 Reference Figure 1 This embodiment provides a method for extruding U-10Zr metallic fuel ultra-high aspect ratio tubes, including the following steps: (1) Preparation of extruded billets: The metal uranium ingot and nuclear-grade sponge zirconium were vacuum induction melted, and then annealed at 1000℃ for 6 hours. After annealing, the riser was removed, the oxide scale was removed, and the ingot was machined to the specified size to obtain U-10Zr ingot. The inner and outer surfaces of the U-10Zr ingot are coated with a 2mm thick copper sheet. 20mm thick copper blocks are placed at both ends of the U-10Zr ingot and fixed by welding. The assembled welded ingot is then sealed with plugging welds. Subsequently, the extruded ingot is subjected to helium pressure testing and leak detection to obtain an extruded ingot with an outer diameter of 65mm. (Refer to...) Figure 2 ; (2) Extrusion of billet: The extrusion billet was heated to 900℃ and held for 1 hour, then placed in an extrusion cylinder preheated to 350℃ for extrusion. The extrusion pressure was 15MPa, the extrusion speed was 25mm / s, and the extrusion ratio was 23.73, resulting in a U-10Zr metal fuel ultra-high length-to-diameter ratio tube with an outer diameter of 15mm, an inner diameter of 7mm, and an aspect ratio of 120. (Refer to...) Figure 4 ; The extrusion needle has a multi-segment variable diameter structure. The material of the extrusion needle is GH4037, and its length is 200mm. The extrusion rod is made of 5CrMnMo with a hardness of HRC50-52. The extrusion die in the extruder is a conical die with a taper of 120°. Figure 3 .

[0025] Example 2 This embodiment provides a method for extruding U-10Zr metallic fuel ultra-high aspect ratio tubes, including the following steps: (1) Preparation of extruded billets: Uranium metal ingots and nuclear-grade sponge zirconium were vacuum induction melted, and then annealed at 990℃ for 4 hours. After annealing, the riser was removed, the oxide scale was removed, and the ingot was machined to the specified size to obtain U-10Zr ingots. The inner and outer surfaces of the U-10Zr ingot are covered with a 1mm thick copper sheet, and 5mm thick copper blocks are placed at both ends of the U-10Zr ingot. After welding and fixing, the assembled welded ingot is plugged and sealed. Then the extruded ingot is pressurized with helium and leak-tested to obtain an extruded ingot with an outer diameter of 50mm. (2) Extrusion of billet: The extrusion billet is heated to 800℃ and held for 0.5h. Then it is placed in an extrusion cylinder preheated to 300℃ for extrusion. The extrusion pressure is 18MPa, the extrusion speed is 20mm / s, and the extrusion ratio is 23.73, to obtain U-10Zr metal fuel ultra-high length-to-diameter ratio tube with an outer diameter of 15mm, an inner diameter of 7mm, and an aspect ratio of 100. The extrusion needle has a multi-section variable diameter structure. The material of the extrusion needle is GH4037, and the length of the extrusion needle is 200mm. The material of the extrusion rod is 5CrMnMo with a hardness of HRC50-52. The extrusion die in the extruder is a conical die with a taper of 120°.

[0026] Example 3 This embodiment provides a method for extruding U-10Zr metallic fuel ultra-high aspect ratio tubes, including the following steps: (1) Preparation of extruded billets: Uranium metal ingots and nuclear-grade sponge zirconium were vacuum induction melted, and then annealed at 1010℃ for 6 hours. After annealing, the riser was removed, the oxide scale was removed, and the ingot was machined to the specified size to obtain U-10Zr ingots. The inner and outer surfaces of the U-10Zr ingot are covered with a 3mm thick copper sheet, and 20mm thick copper blocks are placed at both ends of the U-10Zr ingot. After welding and fixing, the assembled welded ingot is plugged and sealed. Then, the extruded ingot is pressurized with helium and leak-tested to obtain an extruded ingot with an outer diameter of 55mm. (2) Extrusion of billet: The extrusion billet is heated to 950℃ and held for 0.8h. Then it is placed in an extrusion cylinder preheated to 400℃ for extrusion. The extrusion pressure is 20MPa, the extrusion speed is 35mm / s, and the extrusion ratio is 23.73, resulting in U-10Zr metal fuel ultra-high length-to-diameter ratio tubes with an outer diameter of 15mm, an inner diameter of 7mm, and a length-to-diameter ratio of 110. The extrusion needle has a multi-section variable diameter structure. The material of the extrusion needle is GH4037, and the length of the extrusion needle is 200mm. The material of the extrusion rod is 5CrMnMo with a hardness of HRC50-52. The extrusion die in the extruder is a conical die with a taper of 120°.

[0027] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for extruding U-10Zr metallic fuel ultra-high aspect ratio tubes, characterized in that, Includes the following steps: (1) Preparation of extruded billet: U-10Zr ingots are obtained by vacuum induction melting and annealing of metallic uranium ingots and nuclear-grade sponge zirconium. Copper sheets are coated on the inner and outer surfaces of the U-10Zr ingots. Copper blocks are placed at both ends of the U-10Zr ingots and fixed by welding to obtain extruded billets. (2) Extrusion of billet: The billet is heated to 800-950℃ and held for 0.5-1h. Then it is placed in an extrusion cylinder preheated to 300-400℃ for extrusion. The extrusion speed is 20-35mm / s and the extrusion ratio is 23.73 to obtain U-10Zr metal fuel ultra-high length-to-diameter ratio tube. The extrusion needle in the extrusion cylinder has a multi-section variable diameter structure. The material of the extrusion needle is GH4037, and the material of the extrusion rod is 5CrMnMo with a hardness of HRC50-52.

2. The extrusion molding method for U-10Zr metallic fuel ultra-high aspect ratio tubes according to claim 1, characterized in that, During the preparation of the extruded billet, it is annealed at 1000±10℃ for 4-6 hours.

3. The extrusion molding method for U-10Zr metallic fuel ultra-high aspect ratio tubes according to claim 1, characterized in that, The thickness of the copper sheet is 1-3mm, and the thickness of the copper block is 5-20mm.

4. The extrusion molding method for U-10Zr metallic fuel ultra-high aspect ratio tubes according to claim 1, characterized in that, The outer diameter of the extruded billet is 50-65mm.

5. The extrusion molding method for U-10Zr metallic fuel ultra-high aspect ratio tubes according to claim 1, characterized in that, The extrusion pressure is 15-20MPa, and the length of the extrusion needle is 200mm.

6. The extrusion molding method for U-10Zr metallic fuel ultra-high aspect ratio tubes according to claim 1, characterized in that, The U-10Zr metal fuel ultra-high length-to-diameter ratio tube has an outer diameter of 15mm, an inner diameter of 7mm, and a length-to-diameter ratio of 100-120.

7. A die for extruding U-10Zr metallic fuel ultra-high aspect ratio tubes as described in any one of claims 1-6, characterized in that, The mold is a conical mold with a taper of 120°.

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