Manufacturing method of U3Si2-Al plate type fuel assembly

Abstract

The invention discloses a manufacturing method of a U3Si2-Al plate type fuel assembly, and belongs to the field of nuclear power. The method comprises the following steps that a U3Si2 cast ingot is subjected to spheroidizing powdering treatment to obtain U3Si2 raw material powder, the U3Si2 raw material powder is mixed with aluminum powder to obtain mixed powder with U3Si2 evenly distributed, the mixed powder is pressed into a fuel blank, the fuel blank and a cladding are stacked for stitch welding, and then rolling is conducted to obtain a U3Si2-Al plate type fuel assembly finished product. According to the method, the U3Si2 particles subjected to spheroidizing treatment serve as raw materials, the fluidity of powder in the pressing process can be effectively improved, the uniformity of U3Si2 can be improved, meanwhile, the U3Si2-Al interface area is reduced, stress concentration generated by particle edges and corners in the rolling process is reduced, the chemical reaction of U3Si2 and Al is restrained, and therefore the reliability of the plate type fuel is effectively improved, and the service life of the plate type fuel is effectively prolonged.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power, specifically relating to a method for manufacturing a U3Si2-Al plate fuel assembly. Background Technology

[0002] Plate fuel assemblies, with their advantages of compact size and high utilization rate, are widely used in various advanced reactors, including research reactors. Currently, U3Si2-Al plate fuel assemblies are among the most commonly used. Their manufacturing process typically involves mixing U3Si2 powder and Al powder, pressing them into a billet, and then laminating and rolling it into a plate fuel assembly. However, conventional U3Si2 powder has irregular shapes, poor flowability, and low bulk density. During rolling, due to differences in flowability, it easily leads to fuel accumulation at the edges, resulting in uneven irradiation swelling behavior of the fuel assembly and affecting its dimensional stability and structural integrity. Therefore, providing a manufacturing method that optimizes the uniformity of microstructure during the forming process of U3Si2-Al plate fuel assemblies is of positive significance for improving the reliability of plate fuel assemblies. Summary of the Invention

[0003] The purpose of this invention is to provide a method for manufacturing U3Si2-Al plate fuel assemblies, thereby improving the microstructure uniformity of U3Si2-Al plate fuel assemblies.

[0004] According to an embodiment of the present invention, a method for manufacturing a U3Si2-Al plate fuel assembly is provided, the method comprising the following steps:

[0005] Step a): Provide a U3Si2 ingot, and perform spheroidizing and powdering treatment on the U3Si2 ingot to obtain U3Si2 raw material powder;

[0006] Step b): The U3Si2 raw material powder is mechanically mixed with aluminum powder to obtain a mixed powder with uniformly distributed U3Si2;

[0007] Step c): Press the mixed powder into a fuel blank;

[0008] Step d): The fuel blank and the cladding are stacked and welded together, and then rolled to obtain the finished U3Si2-Al plate fuel assembly.

[0009] This method effectively improves the flowability of powder in the billet and enhances rolling performance by spheroidizing U3Si2 powder. At the same time, reducing the sharp edges of U3Si2 particles can reduce micro-stress concentration points and prevent the initiation of cracks or pores during deformation, thus avoiding the starting point of irradiation failure.

[0010] Furthermore, in some embodiments, in step a), the spheroidizing powder preparation method is gas atomization powder preparation.

[0011] Powder prepared by gas atomization powder preparation process naturally forms a near-spherical structure during solidification.

[0012] Furthermore, in some embodiments, in step a), the spheroidizing powder preparation method is as follows: first, the U3Si2 ingot is ground and crushed to obtain primary powder, and then the primary powder is subjected to plasma spheroidizing treatment or self-grinding spheroidizing treatment.

[0013] Furthermore, in some embodiments, step b) further includes a step of sieving the U3Si2 raw material powder, wherein the particle size of the U3Si2 raw material powder obtained by sieving is 50μm-120μm.

[0014] Furthermore, in some embodiments, in step b), the mechanical mixing method is ball milling or shear mixing.

[0015] Furthermore, in some embodiments, in step b), the aluminum powder is pure Al powder or aluminum alloy powder. Before the mechanical mixing, the aluminum powder contains U3Si2 raw material powder with a particle size of less than 50 μm that has been sieved out. The U3Si2 raw material powder added to the aluminum powder does not exceed 15% of the total amount of U3Si2.

[0016] Furthermore, in some embodiments, in step c), the pressing method of the fuel blank is cold isostatic pressing or stamping, and the pressure is held for 30s-60s after reaching the maximum pressure.

[0017] Pressure holding treatment can promote the plastic flow of aluminum powder and enhance the encapsulation and locking effect on U3Si2 particles, thereby improving the strength of the billet without introducing additives or impurities.

[0018] Furthermore, in some embodiments, step d) further includes an annealing process after rolling.

[0019] Furthermore, in some embodiments, in step d), the annealing temperature is 250℃-350℃.

[0020] Furthermore, in some embodiments, in step d), the casing is an aluminum alloy casing. Attached Figure Description

[0021] Figure 1 This is a flowchart of a manufacturing method for a U3Si2-Al plate fuel assembly in one embodiment.

[0022] The purpose of the above figures is to provide a detailed description of the invention so that those skilled in the art can understand the technical concept of the invention, and not to limit the invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0024] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without causing structural conflicts.

[0025] In this article, "multiple" means at least two.

[0026] U3Si2-Al plate fuel assemblies are widely used in research reactors. Currently, the manufacturing process for U3Si2-Al plate fuel assemblies generally employs the following method: First, U3Si2 ingots are obtained through induction melting or arc melting. Then, the U3Si2 ingots are mechanically crushed to obtain powder. The U3Si2 powder is then mixed with aluminum powder, pressed into a billet, and finally laminated and rolled with a cladding to form a plate fuel assembly. However, U3Si2-Al plate fuel assemblies prepared using this method suffer from several drawbacks. The mechanically crushed U3Si2 powder has irregular angular shapes, poor flowability, and low bulk density. During the rolling process, the difference in flowability between the U3Si2 powder and the aluminum matrix easily leads to edge fuel accumulation. Furthermore, during long-term service, the fuel assembly is prone to uneven overall irradiation swelling, posing a serious threat to the dimensional stability and structural integrity of the fuel element. On the other hand, the manufacturing process of plate fuel assemblies requires a high proportion of fine-particle-size U3Si2 powder to improve the flowability of U3Si2-Al billet powder and make it easier to roll. However, the fine-particle U3Si2 powder has a large specific surface area, which increases the contact area between U3Si2 and Al matrix during service. During irradiation, U3Si2 and Al are prone to react, leading to deterioration of irradiation performance.

[0027] To overcome the aforementioned problems of the prior art, embodiments of the present invention provide a method for manufacturing a U3Si2-Al plate fuel assembly. By spheroidizing U3Si2 powder, the powder flowability during the pressing process is improved, the contact area between U3Si2 and Al is reduced, and the microstructure uniformity of the U3Si2-Al plate fuel assembly is improved, thereby improving the reliability and service life of the U3Si2-Al plate fuel assembly under long-term service conditions.

[0028] like Figure 1 As shown, the method includes the following steps:

[0029] First, U3Si2 ingots are provided, and U3Si2 raw material powder is obtained by spheroidizing and pulverizing the U3Si2 ingots.

[0030] Specifically, in different embodiments, an air atomization powder preparation process can be used, or a method can be used to first grind and crush the U3Si2 ingot to obtain primary powder, and then perform plasma spheroidization treatment or self-grinding spheroidization treatment on the primary powder.

[0031] The spheroidized U3Si2 raw material powder is sieved. In a preferred embodiment, the sieved U3Si2 powder with a particle size of 50μm-120μm is mechanically mixed with aluminum powder to obtain a uniformly distributed U3Si2 mixed powder. In different embodiments, mechanical mixing can be performed by ball milling or shear mixing. During the mixing process, an appropriate amount of flow agent can be added to promote uniform powder mixing. The U3Si2 powder with a particle size of less than 50μm obtained from sieving can be added back to the aluminum powder for subsequent processing steps, with the addition amount not exceeding 15% of the total U3Si2 powder. Depending on the design scheme of the plate fuel assembly composition, the aluminum powder can be pure Al powder or aluminum alloy powder.

[0032] The mixed powder is loaded into a mold and pressed into a fuel blank. In different embodiments, the pressing process can employ cold isostatic pressing or stamping. Spheroidized U3Si2 powder can effectively improve the powder's filling density and flowability in the mold, making it easier to press high-uranium-density, low-field-shaped U3Si2-Al plate fuel assemblies.

[0033] In a preferred embodiment, during the pressing process, after the pressure reaches its maximum value, a pressure holding treatment of 30s-60s is performed to promote the plastic flow of aluminum powder, enhance the coating and locking effect of the aluminum matrix on U3Si2 particles, and effectively improve the strength of the blank without introducing other binders, dispersants and other impurities.

[0034] The fuel blank is stacked and assembled with the aluminum cladding and then welded. After hot rolling, the formed plate fuel assembly blank is obtained. The blank is then subjected to short-time bubbling annealing at 250℃-350℃ and cold rolling. After straightening, core positioning and edge milling, the finished U3Si2-Al plate fuel assembly with dimensions meeting the design requirements is obtained.

[0035] Under conventional processes, plate fuel assemblies undergo severe deformation during rolling. The sharp edges of the U3Si2 particles produced by mechanical crushing become microscopic stress concentration points, easily tearing the surrounding Al matrix during deformation and forming microcracks or voids. These defects can easily become the starting point for irradiation failure during reactor core service. The irregular powder morphology of U3Si2 particles easily induces the "dog bone effect" (edge ​​fuel enrichment) during fuel element rolling, leading to anisotropic irradiation swelling behavior, seriously threatening the dimensional stability and structural integrity of the fuel element. This is the fundamental reason why increasing the U3Si2 powder particle size increases processing difficulty. In contrast, the embodiments of this invention employ a spheroidizing treatment method for U3Si2 particles. During rolling, the smooth spherical surface allows the Al matrix to flow smoothly without stress concentration. The spheres themselves, as rigid particles, uniformly transmit stress and deform in tandem with the matrix, fundamentally eliminating the microscopic damage caused by the sharp edges of the U3Si2 particles. The embodiments of the present invention employ a method of spheroidizing U3Si2 particles. During the rolling process, the smooth spherical surface allows the Al matrix to flow smoothly without stress concentration. The spheres themselves, as rigid particles, uniformly transmit stress and deform in tandem with the matrix, fundamentally eliminating the microscopic damage caused by the sharp edges of the U3Si2 particles.

[0036] In a preferred embodiment, the manufacturing process of the U3Si2-Al plate fuel assembly is as follows:

[0037] First, high-purity Si and U are mixed in a stoichiometric ratio and melted in a vacuum induction furnace to obtain U3Si2 ingots. The U3Si2 ingots are crushed and ground to obtain primary powder. The primary U3Si2 powder is then sieved and fed into a plasma spheroidizing device. Argon gas is introduced as a protective gas, and U3Si2 is heated to melt using a high-energy plasma torch. Due to the surface tension of the liquid, the molten U3Si2 naturally forms a near-spherical shape. Under an inert gas atmosphere and rapid cooling conditions, the molten U3Si2 solidifies into spherical U3Si2 particles. The U3Si2 particles are then sieved to obtain U3Si2 raw material powder with a particle size of 50μm-120μm.

[0038] According to the preset uranium density of the plate fuel assembly, U3Si2 raw material powder and pure Al powder are mixed in proportion and placed in a ball mill for 1 hour of low-speed mixing under inert gas protection. An appropriate amount of PVA is added as a lubricant to obtain a uniformly distributed mixed powder of U3Si2.

[0039] The mixed powder is loaded into a mold and subjected to cold isostatic pressing. When the pressure reaches its maximum, it is held for 30-60 seconds. By utilizing the high fluidity and dense packing of the spheroidized powder, a fuel blank with significantly improved processability is obtained. The surface of the fuel blank is free of cracks and gaps.

[0040] The fuel blank, 6061 aluminum cladding plate, and frame are stacked and assembled according to the structure of a plate fuel assembly, and connected by lap welding to form a whole. Next, lamination hot rolling and foaming annealing are performed, followed by multi-pass cold rolling leveling at room temperature. Short-time annealing at 300℃ can be performed between rolling steps and after rolling to eliminate internal stress, resulting in a U3Si2-Al plate fuel assembly. Because the powder raw material is spherical, the bond between the fuel pellet and the aluminum matrix is ​​tighter, with no delamination or separation. The U3Si2 particles in the U3Si2-Al plate fuel assembly blank are uniformly dispersed, and the blank has good microstructure uniformity.

[0041] Finally, the blanks are straightened, the core is positioned, and the edges are milled to obtain the finished U3Si2-Al plate fuel assembly with dimensions that meet the design requirements.

[0042] In another preferred embodiment, the manufacturing process of the U3Si2-Al plate fuel assembly is as follows:

[0043] First, high-purity Si and U are mixed in a stoichiometric ratio and melted in a vacuum induction furnace to obtain U3Si2 ingots. The U3Si2 ingots are then melted, and the alloy melt is atomized by a high-pressure inert gas spray to form tiny droplets. These U3Si2 droplets are rapidly cooled in an inert atmosphere and naturally form spherical powder. By controlling the atomization pressure and flow rate, spherical U3Si2 particles with a particle size mainly distributed between 50 μm and 120 micrometers can be produced as U3Si2 raw material powder.

[0044] According to the preset uranium density of the plate fuel assembly, U3Si2 raw material powder and pure Al powder are mixed in proportion and placed in a ball mill for 1 hour of low-speed mixing under inert gas protection. An appropriate amount of PVA is added as a lubricant to obtain a uniformly distributed mixed powder of U3Si2.

[0045] The mixed powder is loaded into a mold and subjected to cold isostatic pressing. When the pressure reaches its maximum, it is held for 30-60 seconds. By utilizing the high fluidity and dense packing of the spheroidized powder, a fuel blank with significantly improved processability is obtained. The surface of the fuel blank is free of cracks and gaps.

[0046] The fuel blank, 6061 aluminum cladding plate, and frame are stacked and assembled according to the structure of a plate fuel assembly, and connected by lap welding to form a whole. Next, lamination hot rolling and foaming annealing are performed, followed by multi-pass cold rolling leveling of the plate at room temperature. Short-time annealing at 300°C can be performed between rolling steps and after rolling to relieve internal stress, resulting in a U3Si2-Al plate fuel assembly.

[0047] Because the powdered raw material is spherical, the fuel pellets are more tightly bonded to the aluminum matrix, with no delamination or separation. The U3Si2 particles in the U3Si2-Al plate fuel assembly blank are uniformly dispersed, and the blank has good structural uniformity.

[0048] Finally, the blanks are straightened, the core is positioned, and the edges are milled to obtain the finished U3Si2-Al plate fuel assembly with dimensions that meet the design requirements.

[0049] In yet another preferred embodiment, the manufacturing process of the U3Si2-Al plate fuel assembly is as follows:

[0050] First, high-purity Si and U are mixed in a stoichiometric ratio and melted in a vacuum induction furnace to obtain U3Si2 ingots. The U3Si2 ingots are then mechanically crushed to obtain U3Si2. Subsequently, the U3Si2 is further crushed and classified using an air jet milling process. After self-grinding and spheroidizing treatment, near-spherical U3Si2 particles are obtained, which are used as U3Si2 raw material powder.

[0051] According to the preset uranium density of the plate fuel assembly, U3Si2 raw material powder and pure Al powder are mixed in proportion and placed in a ball mill for 1 hour of low-speed mixing under inert gas protection. An appropriate amount of PVA is added as a lubricant to obtain a uniformly distributed mixed powder of U3Si2.

[0052] The mixed powder is loaded into a mold and subjected to cold isostatic pressing. When the pressure reaches its maximum, it is held for 30-60 seconds. By utilizing the high fluidity and dense packing of the spheroidized powder, a fuel blank with significantly improved processability is obtained. The surface of the fuel blank is free of cracks and gaps.

[0053] The fuel blank, 6061 aluminum cladding plate, and frame are stacked and assembled according to the structure of a plate fuel assembly, and connected by lap welding to form a whole. Next, lamination hot rolling and foaming annealing are performed, followed by multi-pass cold rolling leveling of the plate at room temperature. Short-time annealing at 300°C can be performed between rolling steps and after rolling to relieve internal stress, resulting in a U3Si2-Al plate fuel assembly.

[0054] Because the powdered raw material is spherical, the fuel pellets are more tightly bonded to the aluminum matrix, with no delamination or separation. The U3Si2 particles in the U3Si2-Al plate fuel assembly blank are uniformly dispersed, and the blank has good structural uniformity.

[0055] Finally, the blanks are straightened, the core is positioned, and the edges are milled to obtain the finished U3Si2-Al plate fuel assembly with dimensions that meet the design requirements.

[0056] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the technical features involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a U3Si2-Al plate fuel assembly, characterized in that, Includes the following steps: Step a): Provide a U3Si2 ingot, and perform spheroidizing and powdering treatment on the U3Si2 ingot to obtain U3Si2 raw material powder; Step b): The U3Si2 raw material powder is mechanically mixed with aluminum powder to obtain a mixed powder with uniformly distributed U3Si2; Step c): Press the mixed powder into a fuel blank; Step d): The fuel blank and the cladding are stacked and welded together, and then rolled to obtain the finished U3Si2-Al plate fuel assembly.

2. The method for manufacturing the U3Si2-Al plate fuel assembly according to claim 1, characterized in that, In step a), the spheroidizing powder preparation method is gas atomization powder preparation.

3. The method for manufacturing the U3Si2-Al plate fuel assembly according to claim 1, characterized in that, In step a), the spheroidizing powder preparation method is as follows: first, the U3Si2 ingot is ground and crushed to obtain primary powder, and then the primary powder is subjected to plasma spheroidizing treatment or self-grinding spheroidizing treatment.

4. The method for manufacturing a U3Si2-Al plate fuel assembly according to claim 1, 2, or 3, characterized in that, Step b) further includes a step of sieving the U3Si2 raw material powder, wherein the particle size of the U3Si2 raw material powder obtained by sieving is 50μm-120μm.

5. The method for manufacturing a U3Si2-Al plate fuel assembly according to claim 1, 2, or 3, characterized in that, In step b), the mechanical mixing method is ball milling or shear mixing.

6. The method for manufacturing the U3Si2-Al plate fuel assembly according to claim 4, characterized in that, In step b), the aluminum powder is pure Al powder or aluminum alloy powder. Before the mechanical mixing, the aluminum powder contains U3Si2 raw material powder with a particle size of less than 50 μm that has been sieved out. The U3Si2 raw material powder added to the aluminum powder does not exceed 15% of the total amount of U3Si2.

7. The method for manufacturing a U3Si2-Al plate fuel assembly according to claim 1, 2, or 3, characterized in that, In step c), the pressing method of the fuel blank is cold isostatic pressing or stamping, and the pressure is held for 30s-60s after reaching the maximum pressure.

8. The method for manufacturing a U3Si2-Al plate fuel assembly according to claim 1, 2, or 3, characterized in that, In step d), an annealing process is also included after rolling.

9. The method for manufacturing the U3Si2-Al plate fuel assembly according to claim 8, characterized in that, In step d), the annealing temperature is 250℃-350℃.

10. The method for manufacturing a U3Si2-Al plate fuel assembly according to claim 1, 2, or 3, characterized in that, In step d), the cladding is an aluminum alloy cladding.

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