Spiral nuclear fuel positioning grillwork based on 3D printing

Abstract

The invention discloses a spiral nuclear fuel positioning grillwork based on 3D printing. The spiral nuclear fuel positioning grillwork comprises grillwork grid units arranged in an array mode and clamping structures arranged in the grillwork grid units. Each grillwork grid unit is composed of fixing modules at the two ends and a grid unit body, and the adjacent grillwork grid units are interconnected through the fixing modules. The grid unit main body adopts a hollow cylinder structure, and the circumferential surface of the grid unit main body is provided with a diversion trench and a spiral linear guide wing; the clamping structure comprises a rigid bulge arranged in the fixing module and a sheet spring with a circular groove, and the fuel rod is inserted into the grid unit of the grillwork, namely in the fixing module and the main body of the grid unit, and forms surface contact fixation with the rigid bulge and the sheet spring; the positioning grillwork has the advantages of being obvious in stirring and mixing effect, good in fluid passing ability, high in supporting rigidity and stable in fixing structure, the whole grillwork adopts a metal 3D printing integrated forming process, the manufacturing period is greatly shortened, the manufacturing cost is remarkably reduced, and the thermal-hydraulic comprehensive performance of the positioning grillwork is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear fuel assemblies, and in particular to a spiral nuclear fuel positioning grid based on 3D printing. Background Art

[0002] As the core functional unit of reactor energy conversion, the structural reliability of nuclear fuel assemblies directly determines the safety and economy of reactor operation. Fuel rods are arranged in a precise array in nuclear reactor fuel assemblies, and spatial constraints and mechanical support are achieved through positioning grids. Under harsh operating conditions such as extreme temperatures, extreme pressures, and high-intensity neutron irradiation, positioning grids are required to maintain the stability of the fuel assembly arrangement to ensure the controllability of the chain reaction. As a key component of the fuel assembly mechanical support system, the positioning grid must simultaneously meet stringent requirements such as structural stability, fluid transmission efficiency of the moderator and coolant, and resistance to radiation damage. Its performance indicators have become a key technical barrier to the development of fourth-generation nuclear energy systems.

[0003] Existing spacer grids, such as the patent application titled "A Spacer Grid for Nuclear Fuel Assemblies Based on 3D Printing" (Publication No. CN112071443A) and the patent application titled "Spacer Grid with Mixing Performance for Nuclear Fuel Assemblies" (Publication No. CN202948731U), generally employ a layered structural design. The inner layer clamps the fuel rods using elastic support units or rigid protrusions, with turbulence-generating components at the edges to optimize heat exchange. The outer support units incorporate guide structures to assist with mixing and assembly. This traditional construction has significant technical limitations. First, the multi-layer composite structure involves dozens of special-shaped components and relies on multi-step stamping and precision welding processes, resulting in high mold development costs and difficult design iterations. Second, the narrow flow channel cross-section (local gaps as small as 1.5 mm) severely restricts coolant flow capacity, creating the risk of local temperature field distortion. Third, the prominent features of the turbulence components and guide structures lead to unbalanced flow field distribution, creating a significant pressure differential between the inside and outside of the grid. Long-term hydraulic loads can easily induce structural deformation.

[0004] What is even more serious is that in the full life cycle management of nuclear fuel assemblies, the problem of engineering adaptability of positioning grids has become more prominent. During the hoisting operation, precise positioning is required within the millimeter-level gap, but the dimensional tolerance of traditional ramjet guide vanes can easily cause interference between adjacent components. In addition, traditional design methods separate and optimize structural mechanics, fluid mechanics, and neutronic performance, resulting in significant shortcomings in grid performance. For example, thickening the spring structure to enhance the clamping force will significantly reduce the neutron moderation efficiency, and optimizing the flow channel design often requires sacrificing the support stiffness of the spring structure. These technical bottlenecks seriously restrict the research and development of new nuclear fuel assemblies and urgently need to be fundamentally resolved through structural innovation and manufacturing process breakthroughs. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned existing structures, the purpose of the present invention is to provide a spiral nuclear fuel positioning grid based on 3D printing, which has the advantages of obvious mixing effect, good fluid permeability, strong support rigidity and stable fixed structure. The overall grid adopts a metal 3D printing integrated molding process, which greatly shortens the manufacturing cycle and eliminates the need for complex assembly processes, significantly reducing manufacturing costs and improving the comprehensive thermal and hydraulic performance of the positioning grid.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A spiral nuclear fuel positioning grid based on 3D printing includes grid grid units arranged in an array and a clamping structure arranged therein; the grid grid units are composed of fixing modules 1 at both ends and a grid unit body 2, and adjacent grid grid units are interconnected through the fixing modules 1; the grid unit body 2 adopts a hollow cylindrical configuration, and its circumferential surface is provided with a guide groove 6 and a spiral guide wing 5; the clamping structure includes a rigid convex 3 and a thin leaf spring 4 with a circular groove arranged inside the fixing module 1, and the fuel rod 7 is inserted into the grid grid unit, that is, in the fixing module 1 and the grid unit body 2, and is fixed in surface contact with the rigid convex 3 and the thin leaf spring 4.

[0008] The guide grooves 6 and the spiral guide wings 5 are arranged in an alternating manner along the circumference. Each grid unit body 2 has multiple guide grooves 6 and multiple spiral guide wings 5 evenly distributed circumferentially. The axes of the guide grooves 6 and the spiral guide wings 5 form an inclination angle with the horizontal plane.

[0009] Adjacent grid unit bodies 2 are configured with an axial rotation phase difference of 45°.

[0010] The positioning grid is integrally formed by a metal additive manufacturing process, and uses a nickel-based high-temperature alloy or a zirconium alloy as a base material.

[0011] The leaf spring 4 and the rigid convex 3 are arranged on the upper edge of the fixing module 1, and a through hole structure is provided at the corresponding position; the internal clamping structures of the upper and lower fixing modules 1 are arranged in the same manner, and the leaf spring 4 and the rigid convex 3 are arranged in the same direction; the outer surface of the leaf spring 4 is provided with an arc groove matching the radial size of the fuel rod 7.

[0012] The central axis of the arc groove on the outer surface of the thin leaf spring 4 forms an angle of 85° with the horizontal direction in the free state, and a hollow structure with a volume share of ≥30% is provided in the middle, dividing the thin leaf spring 4 into a middle stress-bearing area and elastic areas on both sides; the elastic modulus of the middle stress-bearing area is greater than 20N / m.

[0013] The fixed module 1 adopts a composite structure of a hollow cylinder and a regular octagonal prism, and the edges are chamfered; wherein, the grid grid unit located at the corner is fitted with the grid grid units of the two adjacent sides through double walls, the grid grid unit at the side is fitted with the three adjacent grid grid units through three walls, and the grid grid unit in the middle is fitted with the four adjacent grid grid units through four walls.

[0014] When the diameter of the fuel rod 7 is D, the radial spacing between the rigid boss 3 and the axis of the fuel rod 7 is D / 2, and the radial spacing between the leaf spring 4 and the axis in the free state is D / 2-0.25mm; the inner diameter of the grid unit body 2 is D+1.5mm, the wall thickness is 1mm, the center distance between adjacent grid cells is D+3.1mm, the apicocenter distance between the cross-sections of the fixing modules 1 is D / 2+1.8mm, and the radial overlap dimension of adjacent fixing modules 1 is 0.5mm.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. Utilizing integrated metal 3D printing technology, this invention avoids the complex stamping, welding, and assembly processes required for traditional nuclear fuel positioning grid manufacturing, effectively addressing the high costs and difficult iterations associated with traditional multi-mold manufacturing. Using metal additive manufacturing methods such as selective laser melting (SLM), complex features such as leaf springs, flow channels, and helical guide vanes can be fabricated in a single pass, achieving high-precision near-net-shape shapes. This significantly shortens manufacturing cycles and reduces the accumulated multi-stage machining errors associated with traditional processes. It also simplifies post-processing, avoids residual stresses caused by welding and assembly, and significantly improves material utilization and reduces raw material loss.

[0017] 2. The composite mixing system, consisting of guide grooves and helical guide vanes, achieves a lightweight structure through a staggered arrangement at specific inclination angles. It also produces a multi-dimensional turbulence effect on the coolant flow field. The synergistic effect of the helical guide vanes and guide grooves induces the formation of a stable secondary vortex structure in the circumferential area of the fuel rods, enhancing the turbulence effect downstream of the grid, effectively reducing local pressure drop losses during fluid passage, and improving the uniformity of axial heat exchange in the fuel rods. Furthermore, combined with the regular octagonal prism design on the exterior of the fixed module, a regular, approximately square flow channel cross-section is formed between adjacent grid cells. Compared to traditional fully enclosed grid structures, this significantly improves fluid permeability, thereby enhancing heat exchange efficiency.

[0018] 3. The helical guide vanes utilize a weld-free design integrally formed with the main grid unit. This eliminates the stress concentration hazards associated with the heat-affected zone of welds in traditional welded mixing vanes, preventing mechanical interference. The continuous helical surface provides smooth fluid guidance, enhancing overall structural rigidity while effectively reducing the impact of flow resistance on grid stability. The topologically optimized main grid unit and the prismatic configuration of the fixed module synergize to significantly enhance overall flow field stability and mechanical load-bearing performance.

[0019] 4. The surface conformal coupling design of the leaf spring and circular groove optimizes the contact geometry, shifting the contact mode between the fuel rod and the clamping structure from traditional line contact to surface contact. This significantly improves the contact area and stress distribution uniformity, avoids clamping failure caused by localized stress concentration, and ensures the long-term clamping stability of the fuel rods under thermal expansion and mechanical vibration conditions. Furthermore, the double-ended constraint layout of the upper and lower fixing modules creates a symmetrical clamping force distribution at both ends of the grid's axial direction, effectively dispersing the stress concentration at a single location in traditional single-point clamping structures. This reduces the risk of grid fatigue damage and improves vibration resistance and long-term service reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of an embodiment of the present invention.

[0021] Figure 2 2 is a top view of an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of installing fuel rods according to an embodiment of the present invention.

[0023] Figure 4 Schematic diagram of a grid cell according to an embodiment of the present invention.

[0024] Figure 5 Schematic diagram of the arrangement of grid cells in an embodiment of the present invention.

[0025] Figure 6 Schematic diagram of the structure of the grid unit body according to an embodiment of the present invention.

[0026] Figure 7 2 is a top view of the main body of the grid unit according to an embodiment of the present invention.

[0027] Figure 8 Schematic diagram of a fixing module according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and embodiments so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby more clearly defining the protection scope of the present invention.

[0029] Reference Figures 1-8 A spiral nuclear fuel positioning grid based on 3D printing, taking a 5×5 grid structure as an example, includes grid grid units arranged in an array and a clamping structure arranged therein; the grid grid unit is composed of fixed modules 1 at both ends and a grid unit body 2, and adjacent grid grid units are interconnected through the fixed modules 1; the grid unit body 2 adopts a hollow cylindrical configuration, and its circumferential surface is provided with a guide groove 6 and a spiral guide wing 5; the clamping structure includes a rigid convex 3 and a thin leaf spring 4 with a circular groove arranged inside the fixed module 1; the positioning grid in this embodiment has an overall length and width of 63.5 mm and a height of 40 mm, and includes a total of 25 grid grid units. The fuel rods 7 are inserted into the grid grid units and are fixed in surface contact with the rigid convex 3 and the thin leaf spring 4.

[0030] Reference Figure 4 The guide grooves 6 and the spiral guide wings 5 are arranged in an alternating manner along the circumferential direction. Four guide grooves 6 and four spiral guide wings 5 are evenly distributed around each grid unit body 2. The axes of the guide grooves 6 and the spiral guide wings 5 form a 45° inclination angle with the horizontal plane. When the coolant flows through the spacer grid from bottom to top, a vortex is formed under the guidance of the spiral guide wings 5, which divides the mainstream coolant into multiple spiral flows. The flow direction is controlled by the guide grooves 6, and the channel constraint effect of the guide grooves 6 is used to enhance the vortex intensity, forming a mixing area around the fuel rods 7.

[0031] Reference Figure 5 The adjacent grid unit bodies 2 are configured with a 45° axial rotation phase difference to avoid interference between the spiral guide wings 5 on the outer walls of the two adjacent grid unit bodies 2, thereby ensuring the continuity and stability of the fluid channel; at the same time, the spatial arrangement of the adjacent grid units with variable angles forms dislocation complementarity, so that the vortex disturbances in the adjacent flow channels form a superposition effect, thereby enhancing the overall mixing performance.

[0032] The positioning grid is integrally formed using a metal additive manufacturing process, preferably using a nickel-based high-temperature alloy or a zirconium alloy as the base material. No secondary assembly is required after forming, thus avoiding assembly errors and residual stresses caused by traditional welding or bolt connections. The high-temperature resistance, corrosion resistance, and high-strength properties of the nickel-based high-temperature alloy or the zirconium alloy ensure the long-term service reliability of the grid under the harsh operating conditions of the reactor.

[0033] Reference Figure 8The leaf spring 4 and the rigid convex 3 are arranged on the upper edge of the fixing module 1, and a through-hole structure is provided at the corresponding position; the internal clamping structure of the upper and lower fixing modules 1 is arranged in the same manner, and the leaf spring 4 and the rigid convex 3 are arranged in the same direction, which effectively disperses the stress concentration phenomenon at a single position of the traditional single-point clamping structure; the outer surface of the leaf spring 4 is provided with an arc groove matching the radial size of the fuel rod 7. After the leaf spring 4 is compressed and deformed by the side pressure, the arc groove realizes the surface contact between the fuel rod 7 and the leaf spring 4, significantly improving the contact area and the uniformity of stress distribution.

[0034] Reference Figure 8 The central axis of the arc groove on the outer surface of the leaf spring 4 forms an angle of 85° with the horizontal direction in the free state, and the working angle variation range is controlled within 0-5°; a hollow structure with a volume share of ≥30% is provided in the middle, dividing the leaf spring 4 into a central force-bearing area and elastic areas on both sides. The central force-bearing area concentrates on bearing lateral loads, while the elastic areas on both sides provide flexible compensation; the elastic modulus of the central force-bearing area is greater than 20N / m, which can effectively withstand the lateral compressive stress of the fuel rod 7.

[0035] Reference Figure 8 The fixed module 1 adopts a composite structure of a hollow cylinder and a regular octagonal prism, and the edges are chamfered; the grid grid units at the corners are bonded to the grid grid units at the two adjacent sides through double walls, the grid grid units at the sides are bonded to the three adjacent grid grid units through three walls, and the grid grid units in the middle are bonded to the four adjacent grid grid units through four walls. Regular flow channels of an approximately square shape are formed between adjacent grid grid units, which significantly improves the fluid permeability while achieving lightweight of the overall grid structure, thereby improving the heat exchange efficiency.

[0036] Reference Figure 1 、 Figure 2 and Figure 3 When the diameter of the fuel rod 7 is D, the radial spacing between the rigid protrusion 3 and the axis of the fuel rod 7 is D / 2, and the radial spacing between the leaf spring 4 and the axis in the free state is D / 2-0.25mm. The inner diameter of the grid unit body 2 is D+1.5mm, the wall thickness is 1mm, the center-to-center distance between adjacent grid units is D+3.1mm, the apico-center distance between the cross-section of the fixing module 1 is D / 2+1.8mm, and the radial overlap dimension of adjacent fixing modules 1 is 0.5mm. The radial spacing difference between the rigid protrusion 3 and the leaf spring 4 creates a pre-tightening clamping force, ensuring the dynamic stability of the fuel rod 7 under thermal expansion and vibration conditions.

[0037] 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's description 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 spiral nuclear fuel positioning grid based on 3D printing, characterized by: The invention comprises grid grid units arranged in an array and a clamping structure arranged inside the grid grid units; the grid grid units are composed of fixed modules (1) at both ends and a grid unit body (2), and adjacent grid grid units are interconnected through the fixed modules (1); the grid unit body (2) adopts a hollow cylindrical configuration, and its circumferential surface is provided with a guide groove (6) and a spiral guide wing (5); the clamping structure comprises a rigid convex (3) and a thin leaf spring (4) with a circular groove arranged inside the fixed module (1); the fuel rod (7) is inserted into the grid grid unit, that is, in the fixed module (1) and the grid unit body (2), and is fixed in surface contact with the rigid convex (3) and the thin leaf spring (4).

2. The spiral nuclear fuel spacer grid according to claim 1, characterized in that: The guide grooves (6) and the spiral guide wings (5) are arranged in a staggered manner along the circumference; each grid unit body (2) has a plurality of guide grooves (6) and a plurality of spiral guide wings (5) evenly distributed along the circumference; the axes of the guide grooves (6) and the spiral guide wings (5) form an inclination angle with the horizontal plane.

3. The spiral nuclear fuel spacer grid according to claim 2, characterized in that: Adjacent grid unit bodies (2) are configured with a 45° axial rotation phase difference.

4. The spiral nuclear fuel spacer grid according to claim 1, characterized in that: The positioning grid is integrally formed by a metal additive manufacturing process, and uses a nickel-based high-temperature alloy or a zirconium alloy as a base material.

5. The spiral nuclear fuel spacer grid according to claim 1, characterized in that: The thin leaf spring (4) and the rigid convex (3) are arranged on the upper edge of the fixed module (1), and a through hole structure is provided at the corresponding position; the internal clamping structures of the upper and lower fixed modules (1) are arranged in the same manner, and the thin leaf spring (4) and the rigid convex (3) are arranged in the same direction; the outer surface of the thin leaf spring (4) is provided with an arc groove matching the radial size of the fuel rod (7).

6. The spiral nuclear fuel spacer grid according to claim 1, characterized in that: The central axis of the circular arc groove on the outer surface of the thin leaf spring (4) forms an angle of 85° with the horizontal direction in a free state, and a hollow structure with a volume share of ≥30% is provided in the middle, dividing the thin leaf spring (4) into a middle stress-bearing area and elastic areas on both sides; the elastic modulus of the middle stress-bearing area is greater than 20N / m.

7. The spiral nuclear fuel spacer grid according to claim 1, characterized in that: The fixed module (1) adopts a composite configuration of a hollow cylinder and a regular octagonal prism, and the edges are rounded; wherein the grid grid unit located at the corner is fitted with the grid grid units of two adjacent sides through double walls, the grid grid unit at the side is fitted with three adjacent grid grid units through three walls, and the grid grid unit in the middle is fitted with four adjacent grid grid units through four walls.

8. The spiral nuclear fuel spacer grid according to claim 1, characterized in that: When the diameter of the fuel rod (7) is D, the radial spacing between the rigid convex (3) and the axis of the fuel rod (7) is D / 2, and the radial spacing between the leaf spring (4) and the axis in the free state is D / 2-0.25mm; the inner diameter of the grid unit body (2) is D+1.5mm, the wall thickness is 1mm, the center distance between adjacent grid grid units is D+3.1mm, the side-center distance of the cross section of the fixed module (1) is D / 2+1.8mm, and the radial overlapping dimension of adjacent fixed modules (1) is 0.5mm.

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