A 3D printing based helical nuclear fuel positioning lattice

Abstract

A kind of spiral nuclear fuel positioning grid based on 3D printing, including the clamping structure being arranged in array including grid cell and being arranged in its inside;Grid cell is constituted by two end fixed module and grid cell main body, adjacent grid cell is interconnected by fixed module;Grid cell main body adopts hollow cylinder configuration, its circumferential surface is provided with flow guide groove and helical line guide wing;Clamping structure includes rigid convex that is arranged in fixed module and thin piece spring with circular recess, fuel rod is inserted in grid cell, i.e. in fixed module and grid cell main body, and forms surface contact with rigid convex and thin piece spring Fixed;The present application has obvious stirring effect, good fluid passability, strong support stiffness and stable fixing structure advantages, overall grid adopts metal 3D printing integrated forming process, manufacturing cycle is greatly shortened, manufacturing cost is significantly reduced, and the thermal hydraulic comprehensive performance of positioning grid is improved.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel assembly technology, and more specifically to a spiral nuclear fuel positioning grid based on 3D printing. Background Technology

[0002] As the core functional unit for energy conversion in a reactor, the structural reliability of nuclear fuel assemblies directly determines the safety and economy of reactor operation. Fuel rods are arranged in a precise array within the fuel assembly, with spatial constraints and mechanical support achieved through a positioning grid. Under harsh conditions of extreme temperature, extreme pressure, and high-intensity neutron radiation, the positioning grid is necessary 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's mechanical support system, the positioning grid must simultaneously meet stringent requirements such as structural stability, fluid transport efficiency of moderators and coolants, and resistance to radiation damage. Its performance indicators have become a key technological barrier in the development of fourth-generation nuclear energy systems.

[0003] Existing positioning grids, such as the patent application titled "A 3D-printed nuclear fuel assembly positioning grid" (publication number: CN112071443A) and the patent application titled "A positioning grid with mixing properties for nuclear fuel assemblies" (publication number: CN202948731U), generally adopt a layered structural design. The inner layer uses elastic support units or rigid protrusions to hold the fuel rods, and its edges are equipped with turbulence generating components to optimize heat exchange. The outer support units are supplemented with guide structures to assist in mixing and assembly. This traditional structure has significant technical limitations: First, the multi-layered composite structure involves dozens of irregularly shaped components, relying on multi-process stamping and precision welding, resulting in high mold development costs and difficulties in design iteration. Second, the narrow flow channel cross-section (local gaps of only 1.5mm) severely restricts the coolant flow capacity, causing the risk of local temperature field distortion. Furthermore, the prominent features of the turbulence components and guide structures lead to an unbalanced flow field distribution, forming a significant pressure difference between the inner and outer sides of the grid, which can easily induce structural deformation under long-term hydraulic loads.

[0004] Even more challenging is the increasing prominence of the engineering adaptability issues of positioning grids in the full lifecycle management of nuclear fuel assemblies. During hoisting operations, precise positioning within millimeter-level gaps is required, but the dimensional tolerances of traditional ramjet guide vanes can easily cause interference between adjacent components. Furthermore, traditional design methods optimize structural mechanics, fluid mechanics, and neutron performance separately, resulting in significant shortcomings in grid performance. For example, thickening the spring structure to enhance clamping force significantly reduces neutron moderation efficiency, while optimizing flow channel design often requires sacrificing the supporting stiffness of the spring structure. These technical bottlenecks severely restrict the development of new nuclear fuel assemblies and urgently require fundamental solutions through structural innovation and breakthroughs in manufacturing processes. Summary of the Invention

[0005] To overcome the shortcomings of the existing structure, the present invention aims to provide a spiral nuclear fuel positioning grid based on 3D printing, which has the advantages of obvious mixing effect, good fluid flow, strong support rigidity and stable fixing structure. The whole grid adopts metal 3D printing integrated molding process, which greatly shortens the manufacturing cycle, eliminates the need for complicated assembly process, significantly reduces manufacturing cost, and improves the thermal and hydraulic comprehensive performance of the positioning grid.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A 3D-printed spiral nuclear fuel positioning grid includes grid units arranged in an array and a clamping structure disposed inside them. The grid unit consists of two fixed modules 1 at both ends and a grid unit body 2. Adjacent grid units are interconnected through the fixed modules 1. The grid unit body 2 adopts a hollow cylindrical structure, and its circumferential surface is provided with a flow guide groove 6 and a spiral guide wing 5. The clamping structure includes a rigid protrusion 3 disposed inside the fixed module 1 and a thin leaf spring 4 with a circular groove. The fuel rod 7 is inserted into the grid unit, that is, inside the fixed module 1 and the grid unit body 2, and forms surface contact with the rigid protrusion 3 and the thin leaf spring 4 for fixation.

[0008] The flow guide 6 and the spiral guide wing 5 are arranged in an alternating pattern along the circumference. Each grid unit body 2 has multiple flow guide 6 and multiple spiral guide wing 5 evenly distributed around its circumference. The axes of the flow guide 6 and the spiral guide wing 5 form an inclined angle with the horizontal plane.

[0009] The adjacent grid cell bodies 2 are configured with a 45° axial rotation phase difference.

[0010] The positioning grid is integrally formed using a metal additive manufacturing process, with nickel-based high-temperature alloys or zirconium alloys as the base material.

[0011] The thin leaf spring 4 and the rigid protrusion 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 way, and the thin leaf spring 4 and the rigid protrusion 3 are arranged in the same direction; the outer surface of the thin leaf spring 4 is provided with an arc groove that matches the radial dimension of the fuel rod 7.

[0012] The central axis of the arc groove on the outer surface of the sheet spring 4 forms an angle of 85° with the horizontal direction in the free state. The middle part is provided with a hollow structure with a volume ratio of ≥30%, which divides the sheet spring 4 into a middle force-bearing area and two elastic areas on both sides; the elastic modulus of the middle force-bearing area is >20N / m.

[0013] The fixing module 1 adopts a composite structure of a hollow cylinder and a regular octagonal prism, with rounded edges. The grid grid unit located at the corner is attached to the grid grid units on the two adjacent sides through double wall surfaces, the grid grid unit on the side is attached to the grid grid units on the three adjacent sides through three wall surfaces, and the grid grid unit in the middle is attached to the grid grid units on the four adjacent sides through four wall surfaces.

[0014] When the diameter of the fuel rod 7 is D, the radial distance between the rigid protrusion 3 and the axis of the fuel rod 7 is D / 2, and the radial distance between the sheet 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 units is D+3.1mm, the center distance between the cross-section of the fixing module 1 is D / 2+1.8mm, and the radial overlap of adjacent fixing modules 1 is 0.5mm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. By employing integrated metal 3D printing technology, this invention avoids the complex processing steps of stamping, welding, and assembly required in the traditional manufacturing of nuclear fuel positioning grids, effectively solving the problems of high cost and difficulty in iteration caused by traditional multi-mold processing. Using metal additive manufacturing methods such as selective laser cladding (SLM), complex feature structures, including sheet springs, flow channels, and helical guide vanes, can be manufactured in a single step, achieving high-precision near-net-shape forming, significantly shortening the manufacturing cycle, reducing the accumulation of multi-stage processing errors in traditional processes, simplifying post-processing procedures, avoiding residual stress problems caused by welding and assembly, and greatly improving material utilization and reducing raw material loss.

[0017] 2. The composite mixing system, consisting of guide channels and helical guide vanes, achieves a lightweight design through a staggered arrangement at a specific angle. Simultaneously, it generates multi-dimensional turbulence in the coolant flow field. The synergistic effect of the helical guide vanes and guide channels induces a stable secondary vortex structure in the circumferential region of the fuel rods, enhancing the turbulence downstream of the grid, effectively reducing local pressure drop losses during fluid flow, and improving the axial heat exchange uniformity of the fuel rods. Furthermore, the octagonal prism configuration of the fixed module's exterior creates approximately square flow channel cross-sections between adjacent grid cells, significantly improving fluid throughput compared to traditional fully enclosed grid structures, thereby enhancing heat exchange efficiency.

[0018] 3. The helical guide vane adopts a seamless structure design integrally formed with the grid unit body, eliminating the stress concentration risk caused by the heat-affected zone of welds in traditional welded mixing vanes, avoiding the risk of mechanical interference, and achieving smooth fluid guidance through continuous helical curved surfaces. While enhancing the overall structural rigidity, it effectively reduces the impact of flow resistance on grid stability. The topology-optimized grid unit body and the prism configuration of the fixed module work synergistically to significantly improve the overall flow field stability and mechanical load-bearing capacity.

[0019] 4. The conformal coupling design of the thin leaf spring and the arc groove optimizes the contact geometry, transforming 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, avoiding clamping failure caused by localized stress concentration and ensuring the long-term clamping stability of the fuel rod under thermal expansion and mechanical vibration conditions. Simultaneously, the double-end constraint layout of the upper and lower fixing modules creates a symmetrical clamping force distribution at both ends of the grid axially, effectively dispersing the stress concentration phenomenon of traditional single-point clamping structures at a single location, reducing the risk of grid fatigue damage, and improving vibration resistance and long-term service reliability. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention.

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

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

[0023] Figure 4 This is a schematic diagram of a grid unit according to an embodiment of the present invention.

[0024] Figure 5 This is a schematic diagram of the grid cell arrangement according to an embodiment of the present invention.

[0025] Figure 6 This is a schematic diagram of the structure of the grid unit body in an embodiment of the present invention.

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

[0027] Figure 8 This is a schematic diagram of the fixing module in an embodiment of the present invention. Detailed Implementation

[0028] The present invention will now be described in detail 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 providing a clearer definition of the scope of protection of the present invention.

[0029] Reference Figures 1-8 A 3D-printed spiral nuclear fuel positioning grid, taking a 5×5 grid structure as an example, includes grid grid units arranged in an array and a clamping structure set inside them; the grid grid unit consists of two 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 flow guide groove 6 and a spiral guide wing 5; the clamping structure includes a rigid protrusion 3 and a thin leaf spring 4 with a circular groove set inside the fixed module 1; the overall length and width of the positioning grid in this embodiment are 63.5mm, the height is 40mm, and it contains a total of 25 grid grid units. The fuel rod 7 is inserted into the grid grid unit and forms surface contact fixation with the rigid protrusion 3 and the thin leaf spring 4.

[0030] Reference Figure 4 The guide channels 6 and the helical guide vanes 5 are arranged in an alternating pattern along the circumference. Each grid unit body 2 has four guide channels 6 and four helical guide vanes 5 evenly distributed around its circumference. The axes of the guide channels 6 and the helical guide vanes 5 form a 45° inclination angle with the horizontal plane. When the coolant flows from bottom to top through the positioning grid, it forms a vortex under the guidance of the helical guide vanes 5, which divides the mainstream coolant into multiple helical flows. The flow direction is controlled by the guide channels 6. The channel constraint effect of the guide channels 6 is used to enhance the intensity of the vortex and form 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 vanes 5 on the outer walls of the two adjacent grid unit bodies 2, thus ensuring the continuity and stability of the fluid channel. At the same time, the spatial arrangement of the adjacent grid units with varying angles forms dislocation complementarity, which makes the vortex disturbance of the adjacent flow channels form a superposition effect, enhancing the overall mixing performance.

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

[0033] Reference Figure 8The thin leaf spring 4 and the rigid protrusion 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 way, and the thin leaf spring 4 and the rigid protrusion 3 are arranged in the same direction, which effectively disperses the stress concentration phenomenon of the traditional single-point clamping structure at a single position. The outer surface of the thin leaf spring 4 is provided with an arc groove that matches the radial dimension of the fuel rod 7. After the thin leaf spring 4 is compressed and deformed by lateral pressure, the arc groove realizes the surface contact between the fuel rod 7 and the thin leaf spring 4, which significantly improves the contact area and stress distribution uniformity.

[0034] Reference Figure 8 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 the working angle variation range is controlled between 0 and 5°. The middle part is provided with a hollow structure with a volume ratio of ≥30%, which divides the thin leaf spring 4 into a middle force-bearing area and two elastic areas on both sides. The middle force-bearing area concentrates the lateral load, while the two elastic areas on both sides provide flexible compensation. The elastic modulus of the middle force-bearing area is >20N / m, which can effectively withstand the lateral compressive stress of the fuel rod 7.

[0035] Reference Figure 8 The fixing module 1 adopts a composite structure of a hollow cylinder and a regular octagonal prism, with rounded edges. The grid grid unit located at the corner is attached to the grid grid units on the two adjacent sides through double walls, the grid grid unit on the side is attached to the grid grid units on the three adjacent sides through three walls, and the grid grid unit in the middle is attached to the grid grid units on the four adjacent sides through four walls. The adjacent grid grid units form a regular flow channel that is approximately square. While achieving a lightweight overall grid structure, it significantly improves fluid flow and thus enhances heat exchange efficiency.

[0036] Reference Figure 1 , Figure 2 and Figure 3 When the diameter of the fuel rod 7 is D, the radial distance between the rigid protrusion 3 and the axis of the fuel rod 7 is D / 2, and the radial distance between the sheet 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 units is D+3.1mm, the 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 difference in radial distance between the rigid protrusion 3 and the sheet spring 4 forms a pre-tight clamping force to ensure the dynamic stability of the fuel rod 7 under thermal expansion and vibration conditions.

[0037] 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 using 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 spiral nuclear fuel positioning grid based on 3D printing, characterized in that: It includes grid cells arranged in an array and a clamping structure inside them; the grid cells are composed of two fixed modules (1) and a grid cell body (2), and adjacent grid cells are interconnected through the fixed modules (1); the grid cell body (2) adopts a hollow cylindrical structure, and its circumferential surface is provided with a flow guide groove (6) and a spiral guide wing (5); the clamping structure includes a rigid protrusion (3) and a thin leaf spring (4) with a circular groove inside the fixed module (1), and the fuel rod (7) is inserted into the grid cells, that is, inside the fixed module (1) and the grid cell body (2), and forms a surface contact fixation with the rigid protrusion (3) and the thin leaf spring (4); The flow guide groove (6) and the spiral guide wing (5) are arranged in an alternating manner along the circumference. Each grid unit body (2) has multiple flow guide grooves (6) and multiple spiral guide wings (5) evenly distributed in the circumference. The axes of the flow guide groove (6) and the spiral guide wing (5) form an inclined angle with the horizontal plane. The adjacent grid cell bodies (2) are configured with a 45° axial rotation phase difference; The positioning grid is integrally formed using metal additive manufacturing process, and uses nickel-based high-temperature alloy or zirconium alloy as the base material. The thin leaf spring (4) and the rigid protrusion (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 structure of the upper and lower fixed modules (1) is arranged in the same way, and the thin leaf spring (4) and the rigid protrusion (3) are arranged in the same direction; the outer surface of the thin leaf spring (4) is provided with an arc groove that matches the radial dimension of the fuel rod (7). The fixed module (1) adopts a composite structure of a hollow cylinder and a regular octagonal prism, with rounded edges. The grid grid unit located at the corner is attached to the grid grid units on the two adjacent sides through double walls, the grid grid unit on the side is attached to the grid grid units on the three adjacent sides through three walls, and the grid grid unit in the middle is attached to the grid grid units on the four adjacent sides through four walls.

2. The spiral nuclear fuel positioning grid according to claim 1, characterized in that: The outer surface of the leaf spring (4) has a circular arc groove with a central axis that forms an angle of 85° with the horizontal direction in a free state. The middle part has a hollow structure with a volume ratio of ≥30%, which divides the leaf spring (4) into a middle force zone and two elastic zones on both sides; the elastic modulus of the middle force zone is >20N / m.

3. The spiral nuclear fuel positioning grid according to claim 1, characterized in that: The diameter of the fuel rod (7) is At that time, the radial distance between the rigid convex (3) and the axis of the fuel rod (7) is The radial distance between the sheet spring (4) and the axis in its free state is... ; Value of inner diameter of grid unit body (2) Wall thickness The center distance between adjacent grid cells is The center distance of the cross-section of the fixed module (1) is... The radial dimension of the overlap between adjacent fixed modules (1) is .

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