Positioning grillwork clamping structure for reducing transverse vibration of nuclear fuel rod and providing secondary support

Abstract

The invention discloses a spacer grid clamping structure for reducing transverse vibration of a nuclear fuel rod and providing secondary support. The rigid convex unit structures and the spring structures are arranged on the grillwork lattice cells, the rigid convex unit structures are designed in a symmetrical arc shape, and the rigid convex unit structures are provided with drain holes and are in an approximate triangle shape so as to improve the supporting rigidity. The arc-shaped groove formed by the rigid convex unit is geometrically concentric with the fuel rod, so that the fuel rod can form a better binding surface on the rigid convex unit. The radius of the arc-shaped groove is slightly larger than that of the fuel rod to provide a buffer space for swelling of the fuel rod; the spring structure is formed by welding a primary supporting structure and an independent secondary supporting structure which are formed by stamping, the primary supporting structure and the secondary supporting structure are connected through a semicircular welding head and a welding groove, and intervention and supplementary supporting are provided under the condition of high flow speed or at the end of the service life when the fuel rod vibrates intensely.

Description

Technical Field

[0001] The present invention belongs to the field of pressurized water reactor fuel assembly structural design, and specifically relates to a positioning grid clamping structure. By optimizing the rigid convex shape and integrating secondary support springs, the structure effectively suppresses the lateral vibration of nuclear fuel rods, reduces the fretting erosion of the fuel rod grid, and improves the safety of reactor operation. Background Art

[0002] Nuclear fuel rods are the core components of the reactor core and are an important guarantee for the safety and economy of nuclear power plants. Traditional pressurized water reactor nuclear power plants use rod-shaped fuel elements, which are fixed by multiple fuel assembly positioning grids, such as Figure 1 Each grid cell clamps the fuel rods through rigid convex and springs. Each grid cell is a square structure. On each plane, the fuel rods are fixed by a spring and two rigid convex through three-point support, as shown in the figure. Figure 2 As shown in the figure, in the direction perpendicular to the length of the fuel rod (lateral direction), the lateral vibration of the fuel rod is constrained by the stiffness of the spring and the rigid convex, and in the direction along the length of the fuel rod (axial direction), the axial movement of the fuel rod is constrained by friction.

[0003] During pressurized water reactor operation, fuel rods vibrate laterally under the influence of high-velocity coolant, leading to tangential fretting wear between the fuel rod and grid (spring / stem). With increasing irradiation, the grid material suffers microstructural damage from prolonged neutron exposure, causing the grid's clamping force to loosen. This weakened grid support further increases the amplitude of the fuel rod's lateral vibration, exacerbating the fretting wear between the fuel rod and grid. According to IAEA research, fuel rod-grid fretting has been the leading cause of fuel rod failures and leaks over the past two decades, accounting for over 50% of known factors. Therefore, suppressing fuel rod vibration, enhancing the grid's support for the fuel rods, and reducing fretting wear have long been the goals of nuclear industry designers.

[0004] The existing technology mainly disperses the contact force by increasing the contact area between the spring / steel convex and the fuel rod, thereby reducing the abrasion depth. Figure 3 , as shown in Figure 4. However, an excessively large contact area increases the probability of capturing foreign matter, which can lead to more severe "three-body" erosion. Furthermore, bending of the fuel rods can lead to stress concentration, exacerbating fretting erosion.

[0005] Analyzing the mechanism of fuel rod-grid fretting, the root cause of this phenomenon is the lateral vibration of the fuel rods. However, existing technologies are not effective in suppressing fuel rod vibration, and none of them consider how to address the weakened support caused by grid relaxation after deeper irradiation. Summary of the Invention

[0006] The present invention aims to provide a positioning grid clamping structure for reducing the lateral vibration of nuclear fuel rods and providing secondary support, thereby optimizing and enhancing the constraint on the lateral vibration of the fuel rods. At the same time, through the design of secondary support springs, the lateral support function of the grid on the fuel rods is further enhanced, so as to provide sufficient support function for the fuel rods even in the later stages of reactor operation.

[0007] The present invention provides a positioning grid clamping structure for reducing the lateral vibration of nuclear fuel rods and providing secondary support, comprising: a grid element and a rigid convex unit structure and a spring structure arranged thereon:

[0008] The rigid convex unit structure is a symmetrically arranged arc structure. A single unit is provided with an arc groove with an arc radius of 5±0.2mm and a width of 4±0.1mm, and a rigid convex water flow hole is opened.

[0009] The spring structure includes a spring primary support structure and a spring secondary support structure, which are equal in width and connected by welding. The spring primary support structure is stamped and formed on the grid element sheet, and the spring secondary support structure is connected to the spring primary support structure welding head through the spring secondary support structure welding groove.

[0010] In some embodiments of the present invention, the rigid cam unit structure is "approximately triangular" with a span smaller than that of a conventional grid rigid cam, and the span direction is perpendicular to the fuel rod axis to form a high-rigidity support.

[0011] In some embodiments of the present invention, the arcuate groove formed by the rigid convex unit is geometrically concentric with the fuel rod, and the rigid convex radius is slightly larger than the fuel rod radius, allowing the fuel rod to expand radially by ≤1% after irradiation without causing compression to the rigid convex unit structure.

[0012] In some embodiments of the present invention, the thickness of the primary spring support structure is 1.5 mm, and the material may be Inconel alloy with an elastic modulus of 200 GPa. The free end thereof is bent toward the fuel rod to form an elastic support arc surface that provides sufficient contact surface.

[0013] In some embodiments of the present invention, the spring secondary support structure welding groove and the spring primary support structure welding head of the above-mentioned spring secondary support structure are both semicircular structures with a radius of 0.5mm. After welding, a combined support part with a thickness of 3mm is formed, and the weld width is ≤0.3mm.

[0014] In some embodiments of the present invention, the diameter of the rigid convex water flow holes is 1.5-2.0 mm, so as to reduce flow resistance and guide the coolant to evenly flush the surface of the fuel rod.

[0015] In some embodiments of the present invention, the above-mentioned spring primary support structure independently provides support in the early stage of reactor operation. When the fuel rod amplitude exceeds 0.1 mm or the plastic deformation of the spring primary support structure is ≥ 0.1 mm, the spring secondary support structure intervenes and forms a combined support with the spring primary support structure.

[0016] Technical principle:

[0017] (1) Rigid convex design: The symmetrical rigid convex unit structure in the present invention is the main design for restraining the lateral vibration of the fuel rod. A single rigid convex unit structure has an arc-shaped groove, and the arc radius is slightly larger than the radius of the fuel rod. On the one hand, it can buffer and restrain the lateral movement of the fuel rod, and on the other hand, it can avoid excessive squeezing of the rigid convex unit structure when the fuel rod swells. The width of the rigid convex unit structure is 4mm to provide sufficient contact surface between the fuel rod and the rigid convex unit structure, dispersing the force on the surface of the fuel rod. At the same time, the arc-shaped design will also change the direction of the force to avoid concentration. As shown in the attached figure Figure 6 As shown, this symmetrical rigid-convex unit structure design has a smaller span, and the entire structure is "approximately triangular." Therefore, a single rigid-convex unit structure has greater support stiffness and can provide sufficient support force. At the same time, the single rigid-convex unit structure is designed with rigid-convex water flow holes to allow coolant to pass smoothly.

[0018] (2) Spring design: The secondary support spring design in the present invention mainly includes two parts. The first part is a spring secondary support structure formed by directly stamping the grid element sheet. The second part is an independent spring primary support structure. The two parts are of equal width and are connected by welding. The connection method is shown in the attached figure. Figure 9 As shown, a semicircular groove structure with a radius of 0.5mm is formed at the upper and lower ends of the spring secondary support structure by reverse stamping, namely the spring secondary support structure welding groove, and a semicircular spring primary support structure welding head with a radius of 0.5mm is prepared at the upper and lower ends of the spring primary support structure. Welding is performed along the upper and lower seams of the contact surface between the spring secondary support structure welding groove and the spring primary support structure welding head to achieve connection.

[0019] During the early stages of reactor operation and in areas with low coolant flow rates, when fuel rod vibration amplitude is small, the primary spring support structure primarily provides elastic support, constraining fuel rod movement. In areas with higher coolant flow rates, such as near the coolant inlet, fuel rod vibration amplitude is greater, and the primary and secondary spring support structures come into intermittent contact. During these contact periods, the secondary spring support structure provides additional support to the fuel rod, preventing even greater vibration amplitude. Later in reactor operation, the primary spring support structure can experience plastic deformation due to fatigue damage. Combined with the effects of material radiation, this significantly reduces the clamping force and may even lead to fracture. While the secondary spring support structure in the present invention also experiences radiation effects, its plastic deformation is much less than that of the primary spring support structure. The two structures are likely to be in prolonged contact, forming a thicker support spring that provides additional support for the fuel rod, thereby preventing loosening and gaps in the fuel rod-grid clamp and preventing severe vibration and abrasion of the fuel rod. This also reduces the likelihood of fatigue fracture in the primary spring support structure.

[0020] The embodiments of the present invention have at least the following advantages or beneficial effects:

[0021] The arc-shaped symmetrical rigid convex unit involved in the present invention can effectively suppress the lateral vibration of the fuel rod during the operation of the reactor.

[0022] In the present invention, each rigid convex unit is designed to have a smaller span, which can provide higher support rigidity and more sufficient clamping force for the fuel rod;

[0023] The design of the arc-shaped contact surface between the rigid convex unit and the fuel rod involved in the present invention can increase the contact area, disperse the magnitude and direction of the force on the fuel rod, and thus reduce the abrasion behavior;

[0024] The arc-shaped symmetrical rigid convex unit involved in the present invention can reduce the possibility of fuel rod deviation when loading fuel rods, and improve the centering accuracy of the fuel rods in the grid cell;

[0025] The secondary support spring design involved in the present invention can provide more support in high-flow rate areas and high-burnup conditions, thereby preventing grid relaxation from causing a reduction in clamping force or even the appearance of gaps, thereby effectively controlling fuel rod vibration and abrasion.

[0026] The spring secondary support structure involved in the present invention can effectively reduce the risk of fatigue fracture of the spring primary support structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is a schematic diagram of the fuel assembly of the present invention;

[0029] Figure 2 This is a schematic diagram of the fuel rod-grid clamping in the present invention;

[0030] Figure 3 A structural diagram of a spacer grid spring used in the prior art to increase the conformal contact area with the fuel rod;

[0031] Figure 4 A structural diagram of a fuel rod clamping structure and a positioning grid in the prior art;

[0032] Figure 5 A schematic diagram of a single spacer grid element clamping structure of the present invention;

[0033] Figure 6 A top view of the gate element of the present invention;

[0034] Figure 7 A side view of a gate element of the present invention;

[0035] Figure 8 This is a front view of the gate element of the present invention;

[0036] Figure 9 This is a mid-axis cross-sectional view of the gate element of the present invention;

[0037] Figure 10 It is a schematic diagram of the overall structure of the present invention.

[0038] Explanation of the accompanying symbols: 1. Grid element; 2. Rigid convex unit structure; 21. Rigid convex water flow hole; 3. Spring primary support structure; 31. Spring primary support structure welding head; 4. Spring secondary support structure; 41. Spring water flow hole; 42. Spring secondary support structure welding groove; 5. Grid element piece. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0041] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not require further definition or explanation in subsequent drawings.

[0042] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprises" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further limitations, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

[0043] In the description of the embodiments of the present invention, "a plurality of" means at least two.

[0044] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0045] like Figure 1-3 The embodiment of the present invention discloses a positioning grid clamping structure for reducing lateral vibration of nuclear fuel rods and providing secondary support, comprising: a grid element and a rigid convex unit structure and a spring structure provided thereon:

[0046] The rigid convex unit structure is a symmetrically arranged arc structure. A single unit is provided with an arc groove with an arc radius of 5±0.2mm and a width of 4±0.1mm, and a rigid convex water flow hole is opened.

[0047] The spring structure includes a spring primary support structure and a spring secondary support structure, which are equal in width and connected by welding. The spring primary support structure is stamped and formed on the grid element sheet, and the spring secondary support structure is connected to the spring primary support structure welding head through the spring secondary support structure welding groove.

[0048] In some embodiments of the present invention, the rigid cam unit structure is "approximately triangular" with a span smaller than that of a conventional grid rigid cam, and the span direction is perpendicular to the fuel rod axis to form a high-rigidity support.

[0049] In some embodiments of the present invention, the arcuate groove formed by the rigid convex unit is geometrically concentric with the fuel rod, and the rigid convex radius is slightly larger than the fuel rod radius, allowing the fuel rod to expand radially by ≤1% after irradiation without causing compression to the rigid convex unit structure.

[0050] In some embodiments of the present invention, the thickness of the primary spring support structure is 1.5 mm, and the material may be Inconel alloy with an elastic modulus of 200 GPa. The free end thereof is bent toward the fuel rod to form an elastic support arc surface that provides sufficient contact surface.

[0051] In some embodiments of the present invention, the spring secondary support structure welding groove and the spring primary support structure welding head of the above-mentioned spring secondary support structure are both semicircular structures with a radius of 0.5mm. After welding, a combined support part with a thickness of 3mm is formed, and the weld width is ≤0.3mm.

[0052] In some embodiments of the present invention, the diameter of the rigid convex water flow holes is 1.5-2.0 mm, so as to reduce flow resistance and guide the coolant to evenly flush the surface of the fuel rod.

[0053] In some embodiments of the present invention, the above-mentioned spring primary support structure independently provides support in the early stage of reactor operation. When the fuel rod amplitude exceeds 0.1 mm or the plastic deformation of the spring primary support structure is ≥ 0.1 mm, the spring secondary support structure intervenes and forms a combined support with the spring primary support structure.

[0054] Example 1:

[0055] like Figure 1-2 ,5-10 The present invention provides a positioning grid clamping structure for reducing the lateral vibration of nuclear fuel rods and providing secondary support, comprising: a grid element and a rigid convex unit structure and a spring structure provided thereon:

[0056] The rigid convex unit structure is a symmetrically arranged arc structure. A single unit is provided with an arc groove with an arc radius of 5±0.2mm and a width of 4±0.1mm, and a rigid convex water flow hole is opened.

[0057] The spring structure includes a spring primary support structure and a spring secondary support structure, which are equal in width and connected by welding. The spring primary support structure is stamped and formed on the grid element sheet, and the spring secondary support structure is connected to the spring primary support structure welding head through the spring secondary support structure welding groove.

[0058] In this embodiment, the rigid cam unit structure is "approximately triangular" with a span smaller than that of a conventional grid rigid cam, and the span direction is perpendicular to the fuel rod axis to form a high-rigidity support.

[0059] In this embodiment, the arc groove formed by the rigid convex unit is geometrically concentric with the fuel rod, and the rigid convex radius is slightly larger than the fuel rod radius, allowing the fuel rod to expand radially by ≤1% after irradiation without causing compression to the rigid convex unit structure.

[0060] Comparative Example 1:

[0061] Rigid convex structure fabrication: A traditional rigid convex structure is constructed with a flat top contact area and a simple flat plate support at the bottom. The rigid convex body is made of ordinary stainless steel without surface coating. The modular bottom connection interface only has mounting holes, without locating slots or guide pins.

[0062] Nuclear fuel assembly assembly: The rigid boss is mounted on the same grid strip as in the embodiment, and a single spring sheet is used to clamp the fuel rod. The fuel rod is inserted into the grid element to complete the assembly of the nuclear fuel assembly.

[0063] Performance testing: Testing was conducted under the same simulated test conditions as in Example 1. Significant wear was observed in the contact area between the fuel rod and the rigid convex. The fuel rod exhibited significant vibration amplitude, with significant fluctuations when the coolant flow rate varied. This indicates that the conventional rigid convex structure exhibits poor wear and vibration resistance, failing to effectively support the fuel rod, and thus compromising the stability of the nuclear fuel assembly.

[0064] Example 2:

[0065] like Figure 1-2 , 5-10, the difference from Example 1 is that the thickness of the spring primary support structure in this embodiment is 1.5 mm, the elastic modulus is 200 GPa, and its free end is bent toward the fuel rod to form an elastic support arc surface that provides sufficient contact surface.

[0066] In this embodiment, the spring secondary support structure welding groove and the spring primary support structure welding head of the above-mentioned spring secondary support structure are both semicircular structures with a radius of 0.5 mm. After welding, a combined support part with a thickness of 3 mm is formed, and the weld width is ≤0.3 mm.

[0067] In this embodiment, the diameter of the rigid convex water flow holes is 1.5-2.0 mm, so as to reduce flow resistance and guide the coolant to evenly flush the surface of the fuel rod.

[0068] In some embodiments of the present invention, the above-mentioned spring primary support structure independently provides support in the early stage of reactor operation. When the fuel rod amplitude exceeds 0.1 mm or the plastic deformation of the spring primary support structure is ≥ 0.1 mm, the spring secondary support structure intervenes and forms a combined support with the spring primary support structure.

[0069] Comparative Example 2:

[0070] Rigid convex structure fabrication: A rigid convex structure is fabricated with a semi-cylindrical concave contact area at the top and a spherical elastic support module at the bottom using conventional rubber gaskets. The rigid body is made of aluminum alloy and is not coated. The modular bottom connection interface is fixed by welding, without positioning or guiding structures.

[0071] Nuclear fuel assembly: The rigid bosses are mounted on the grid strips, but precise positioning is not possible during the installation process. Ordinary metal springs are used to push the fuel rods, which are then inserted into the grid cells to complete the assembly of the nuclear fuel assembly.

[0072] Performance testing: In a simulation test device, the complex operating conditions of Example 2 were simulated and tested. Post-test inspection revealed that the conventional rubber gasket had aged and deformed, losing its elastic support function. The aluminum alloy rigid body degraded and became brittle under irradiation. The fuel rods were severely worn, and the vibration amplitude could not be stably controlled under complex operating conditions. This indicates that the rigid convex structure has deficiencies in high temperature resistance, radiation resistance, wear resistance, and vibration resistance, and cannot meet the operational requirements of nuclear fuel assemblies.

[0073] In summary, the present invention significantly improves the stability and safety of nuclear fuel rods in reactor operation through the innovative design of rigid convex unit structure and spring structure.

[0074] It will be apparent to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above and that the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present application is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A spacer grid clamping structure for reducing lateral vibration of nuclear fuel rods and providing secondary support, characterized by: include: The grid element (1) and the rigid convex unit structure (2) and spring structure arranged thereon are characterized by: The rigid convex unit structure (2) is a symmetrically arranged arc structure, and a single unit is provided with an arc groove with an arc radius of 5±0.2mm and a width of 4±0.1mm, and is provided with a rigid convex water flow hole (21); The spring structure comprises a spring primary support structure (3) and a spring secondary support structure (4), both of which are of equal width and connected by welding, wherein the spring primary support structure (3) is stamped and formed on the grid element sheet (5), and the spring secondary support structure (4) is connected to the spring primary support structure welding head (31) via the spring secondary support structure welding groove (42).

2. A spacer grid clamping structure for reducing lateral vibration of nuclear fuel rods and providing secondary support according to claim 1, characterized in that: The rigid convex unit structure (2) is in the shape of a "near triangle", with a span smaller than that of a conventional grid rigid convex, and a span direction perpendicular to the axis of the fuel rod.

3. A spacer grid clamping structure for reducing lateral vibration of nuclear fuel rods and providing secondary support according to claim 1, characterized in that: The arc groove formed by the rigid convex unit is geometrically concentric with the fuel rod, and the rigid convex radius is slightly larger than the fuel rod radius, allowing the fuel rod to expand radially by ≤1% after irradiation swelling without causing compression to the rigid convex unit structure (2).

4. A spacer grid clamping structure for reducing lateral vibration of nuclear fuel rods and providing secondary support according to claim 1, characterized in that: The thickness of the spring primary support structure (3) is 1.5 mm, and the free end thereof is bent toward the fuel rod to form an elastic support arc surface that provides a sufficient contact surface.

5. A spacer grid clamping structure for reducing lateral vibration of nuclear fuel rods and providing secondary support according to claim 1, characterized in that: The spring secondary support structure welding groove (42) and the spring primary support structure welding head (31) of the spring secondary support structure (4) are both semicircular structures with a radius of 0.5 mm, and after welding, a combined support portion with a thickness of 3 mm is formed, and the weld width is ≤0.3 mm.

6. A spacer grid clamping structure for reducing lateral vibration of nuclear fuel rods and providing secondary support according to claim 1, characterized in that: The pore diameter of the rigid convex water flow hole (21) is 1.5-2.0 mm.

7. A spacer grid clamping structure for reducing lateral vibration of nuclear fuel rods and providing secondary support according to claim 1, characterized in that: The spring primary support structure (3) independently provides support in the early stage of reactor operation. When the fuel rod amplitude exceeds 0.1 mm or the plastic deformation of the spring primary support structure (3) is ≥ 0.1 mm, the spring secondary support structure (4) intervenes and forms a combined support with the spring primary support structure (3).

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