A finite element analysis automatic modeling method for nuclear fuel assembly

Abstract

The application provides a nuclear fuel assembly finite element analysis automatic modeling method, and belongs to the technical field of digital model processing. The method comprises the following steps: after an initial geometric model is obtained, pre-processing, shell extraction, and contact feature and welding point feature identification are performed. Then, according to the contact feature and the welding point feature, the finite element model of the nuclear fuel assembly is automatically created with the contact feature and the welding point feature. Based on the above scheme, the initial geometric model is pre-processed, the complex structure, the curved surface structure and the overlapping surface in the model can be simplified, the missing surface can be filled, and the surface splicing is completed. The problem of inaccurate connection relationship caused by incorrect contact surface selection and incorrect contact direction can be avoided. Then, the finite element modeling of the nuclear fuel assembly is performed by using the pre-extracted contact feature and welding point feature, the software can automatically complete the modeling process, and the correction of the model in the pre-processing process can ensure that the built model has sufficient precision.

Description

Technical Field

[0001] This invention generally relates to the field of digital model processing technology, and specifically to an automatic modeling method for finite element analysis of nuclear fuel assemblies. Background Technology

[0002] Nuclear fuel assemblies, as the core components of nuclear reactors, consist of a fuel skeleton, grid assemblies, fuel rods, and upper and lower tube supports. Their complex structure and harsh operating environment make safety paramount. Therefore, accurate finite element modeling and mechanical property analysis of nuclear fuel assemblies are crucial for ensuring their design rationality and operational reliability. In the finite element modeling of nuclear fuel assemblies, the contact relationships of the grid assemblies and the weld connections are key aspects ensuring the accuracy of the model.

[0003] During the modeling process, the fuel rods are held in place by rigid and elastic protrusions, resulting in numerous contact relationships in the model, sometimes reaching tens of thousands. Current common simulation methods rely on manual operations, including manually creating contact elements, assigning contact properties, and creating weld connection elements.

[0004] However, current methods for applying contacts and weld points in modeling and analyzing lattice components present significant problems. For contact application, while some software supports automatic contact generation, issues such as incorrect contact surface selection and incorrect contact direction often lead to inaccurate contact relationships. Manual contact application, on the other hand, is cumbersome, time-consuming, and prone to errors. For weld point application, manual addition is typically required, but with thousands of weld points, the workload is enormous, and omissions or duplicates are common, affecting model accuracy. Summary of the Invention

[0005] In view of the above-mentioned defects or deficiencies in the existing technology, it is desirable to provide an automatic modeling method for finite element analysis of nuclear fuel assemblies.

[0006] This invention provides an automated modeling method for finite element analysis of nuclear fuel assemblies, comprising:

[0007] S1: Obtain the initial geometric model of the nuclear fuel assembly;

[0008] S2: Preprocess the initial geometric model to obtain the first geometric model;

[0009] S3: Perform a shell extraction operation on the first geometric model to obtain a shell element model;

[0010] S4: Identify the contact features and solder joint features of the shell element model; the shell element model includes multiple gate elements, each gate element including rigid protrusions and elastic protrusions; the contact features include rigid protrusion features and elastic protrusion features;

[0011] S5: Automatically create contact features and weld point features for the finite element model of the nuclear fuel assembly based on the contact features and weld point features.

[0012] According to the technical solution provided by the present invention, S2: preprocessing the initial geometric model to obtain a first geometric model includes:

[0013] The initial geometric model is then subjected to model simplification, missing surface repair, surface cutting, overlapping surface processing, and gap stitching in sequence to obtain the first geometric model;

[0014] The surface cutting includes: dividing the surface into multiple geometric shapes;

[0015] The overlapping surface processing includes: merging the overlapping surfaces into a single surface;

[0016] The gap stitching includes: extending two surfaces whose gaps between adjacent surfaces are within a set gap range until the two surfaces intersect.

[0017] According to the technical solution provided by the present invention, the model simplification includes:

[0018] Replace the rounded and chamfered structures of the initial geometric model with right-angle structures;

[0019] Fill the defect holes in the initial geometric model.

[0020] According to the technical solution provided by the present invention, filling the defect holes in the initial geometric model includes:

[0021] In the initial geometric model, all holes with an area smaller than a set area are detected, resulting in multiple defective holes;

[0022] Multiple first sampling points are selected at the edge of the defective hole;

[0023] Multiple reference lines are obtained by connecting adjacent first sampling points with straight lines;

[0024] The polygons formed by the multiple adjacent and coplanar reference lines are filled into planes.

[0025] According to the technical solution provided by the present invention, the maximum distance between the reference line and the edge of the defective hole is within the set gap range along the direction perpendicular to the reference line.

[0026] According to the technical solution provided by the present invention, the repair of the missing surface includes:

[0027] Obtain the surface to be repaired;

[0028] Extend the surface to be repaired until the gap between the surface to be repaired and the adjacent surface is within the set gap range.

[0029] According to the technical solution provided by the present invention, a curved surface is divided into multiple geometric shapes, including:

[0030] Select multiple second sampling points across the entire curved surface;

[0031] Connect adjacent second sampling points to form multiple non-overlapping triangles;

[0032] Multiple adjacent and coplanar triangles are merged into a single face to obtain multiple polygonal shapes;

[0033] Multiple polygonal shapes and the remaining triangular shapes are combined as multiple geometric shapes.

[0034] According to the technical solution provided by the present invention, the shell unit model includes: a grid assembly, fuel rods, and the mid-surface of the rigid protrusions and elastic protrusions on the grid assembly obtained by the shell extraction operation;

[0035] S4: Identify the contact features and solder joint features of the shell unit model, including:

[0036] Establish a global coordinate system;

[0037] Obtain the cell length and cell height in the shell element model; the cell length is perpendicular to the extension direction of the fuel rod; the cell height is parallel to the extension direction of the fuel rod.

[0038] Based on the cell length, the first coordinates of the rigid protrusion and the elastic protrusion in the global coordinate system are calculated.

[0039] Based on the cell length and cell height, the second coordinate of the solder joint in the global coordinate system is calculated.

[0040] Each rigid and elastic protrusion is numbered, and the number is combined with the corresponding first coordinate to form a contact feature;

[0041] Each solder joint is numbered, and the number is combined with the corresponding second coordinate to form the solder joint feature.

[0042] According to the technical solution provided by the present invention, S5: based on the contact features and the weld joint features, automatically create the contact features and weld joint features of the finite element model of the nuclear fuel assembly, including:

[0043] Import the shell element model into the finite element software;

[0044] Assign material properties to the shell element model;

[0045] Based on the contact and solder joint characteristics, the coordinates of the contact points and solder joints are automatically identified in the shell element model, and the contact points and solder joints are automatically created; the contact points include rigid protrusions and elastic protrusions.

[0046] Connect adjacent contact points and solder joints;

[0047] Set contact properties for the contact points; contact properties include: coefficient of friction and contact stiffness;

[0048] Finally, a finite element model of the nuclear fuel assembly was obtained.

[0049] The beneficial effects of this invention are as follows:

[0050] After obtaining the initial geometric model of the nuclear fuel assembly, preprocessing and shell extraction are performed, and contact and weld features are identified. During the modeling process of the nuclear fuel assembly in the finite element software, contact and weld features are automatically created based on these features. Preprocessing the initial geometric model simplifies complex structures (including fillets and chamfers), curved surfaces, and overlapping surfaces, fills in missing surfaces, and completes surface stitching. This avoids inaccurate connection relationships caused by incorrect contact surface selection or incorrect contact direction. Furthermore, using the pre-extracted contact and weld features for finite element modeling of the nuclear fuel assembly allows the software to automatically complete the modeling process. Combined with the corrections made during preprocessing, this ensures that the constructed model has sufficient accuracy. Attached Figure Description

[0051] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0052] Figure 1 This is a flowchart illustrating an automated modeling method for finite element analysis of nuclear fuel assemblies.

[0053] Figure 2 This is a schematic diagram of a lattice frame assembly;

[0054] Figure 3 This is a schematic diagram of a gate element;

[0055] Figure 4 This is a schematic diagram of an uneven, defective hole.

[0056] Among them: 1. Grid assembly; 2. Rigid protrusion; 3. Elastic protrusion; 4. Fuel rod; 5. Grid cell; 6. Defect hole; 7. Filling surface. Detailed Implementation

[0057] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0058] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0059] Please refer to Figure 1 This invention provides an automatic modeling method for finite element analysis of nuclear fuel assemblies, comprising:

[0060] S1: Obtain the initial geometric model of the nuclear fuel assembly;

[0061] The geometric model of the nuclear fuel assembly is imported into geometry processing software (such as SolidWorks, UG, SpaceClaim, DesignModeler, etc.) for preprocessing. The main purpose of preprocessing is to clean and optimize the geometric model to ensure the smooth progress of subsequent steps.

[0062] Establish a global coordinate system; the origin is the center point of the lattice component, the X and Y axes are the length and width directions of the lattice component, and the Z axis is the height direction.

[0063] S2: Preprocess the initial geometric model to obtain a first geometric model, including:

[0064] The initial geometric model is then simplified, missing surfaces are repaired, curved surfaces are cut, overlapping surfaces are processed, and gaps are stitched together in sequence to obtain the first geometric model.

[0065] The imported initial geometric model may contain some unnecessary features, such as small fillets, chamfers, and small holes. These features can be simplified without affecting the analysis results, thereby reducing the difficulty of mesh generation and computational load.

[0066] The model simplification includes:

[0067] Replace the rounded and chamfered structures of the initial geometric model with right-angle structures;

[0068] Filling the defect holes in the initial geometric model includes:

[0069] In the initial geometric model, all holes with an area smaller than a set area are detected, resulting in multiple defective holes;

[0070] Specifically, the area of ​​the smallest design hole on the lattice assembly is set to be less than or equal to the area of ​​the smallest design hole on the lattice assembly. For example, the area of ​​the smallest design hole on the lattice assembly is 1 mm². 2 The area can then be set to 1mm. 2 It should be noted that the design holes are necessary structural elements required during the design process, not unnecessary defective holes.

[0071] Multiple first sampling points are selected at the edge of the defect hole; that is, multiple points on the edge of multiple defect holes are selected, and the coordinates of each point in the global coordinate system are obtained.

[0072] By connecting adjacent first sampling points with straight lines, multiple reference lines can be obtained; given the coordinates of two points, the straight line passing through the two points can be calculated.

[0073] The polygons formed by the multiple adjacent and coplanar reference lines are filled into planes.

[0074] Specifically, two adjacent reference lines share a common first sampling point.

[0075] Two adjacent first sampling points are traversed by three reference lines. If the three reference lines are coplanar, then the quadrilateral region enclosed by the four points traversed by these three reference lines can be considered as a single plane (ignoring very minor concavities and convexities). If multiple reference lines are coplanar, then the polygon enclosed by the multiple first sampling points traversed by these multiple reference lines can also be roughly considered as a single plane.

[0076] If all reference lines are coplanar, it means that the defect hole is relatively flat. Therefore, a plane can be used to initially fill the defect hole (only the gaps between the sides of the polygon and the edge of the defect hole remain, and the final filling is completed by the gap stitching step).

[0077] If the multiple polygons formed by the multiple first sampling points are not all coplanar, it indicates that the defect hole is uneven, and the multiple polygons are then filled separately. This ensures that the gaps between the faces formed by the multiple polygons are within a set gap range; then, in the gap-sealing step, the gaps between the multiple polygons are sealed together.

[0078] The above method can fill the defective hole into a flat surface. Figure 4 This is a schematic diagram of the uneven defect hole 6, where the filling surface 7 is a polygon composed of multiple reference straight lines.

[0079] When the defective hole is uneven, that is, when the edges of the defective hole are not coplanar, the above method can divide the uneven defective hole into multiple polygonal planes, thus avoiding the situation of incomplete filling when the defective hole is uneven.

[0080] In some embodiments, the maximum distance between the reference line and the edge of the defect hole is within the set gap range (0.01 mm to 0.02 mm, with both the upper and lower limits of the interval being closed intervals) along a direction perpendicular to the reference line.

[0081] Based on this design, the edges of the polygonal filling surface 7 and the defect hole 6 can meet the conditions for gap stitching, and can then be completed into multiple closed planes through subsequent gap stitching steps.

[0082] The missing surface repair includes:

[0083] Obtain the surface to be repaired; this is generally done by manual input or selection.

[0084] Extend the surface to be repaired until the gap between the surface to be repaired and the adjacent surface is within the set gap range.

[0085] Missing face repair is a built-in function of the software, used to check for missing faces in the geometric model. If missing faces are found, the software's repair tool must be used to fix them to ensure the integrity of the geometric model.

[0086] The surface cutting process includes dividing the surface into multiple geometric shapes; this not only reduces the difficulty of mesh generation but also improves the accuracy of contact area identification.

[0087] Specific steps:

[0088] Multiple second sampling points are selected uniformly across the entire curved surface;

[0089] Connecting multiple adjacent second sampling points to form multiple non-overlapping triangles; in this case, the planar region will form multiple coplanar equilateral triangles, and the regions corresponding to the adjacent and coplanar triangles are planar, otherwise they are curved.

[0090] This roughly divides the entire surface into planar and curved parts; the curved part is then divided into multiple geometric shapes according to triangles; the planar part is treated as a single plane.

[0091] Multiple adjacent and coplanar triangles are merged into a single face to obtain multiple polygonal shapes;

[0092] Multiple polygonal shapes and the remaining triangular shapes are combined as multiple geometric shapes.

[0093] Specifically, surface cutting can cut complex surfaces in a geometric model, decomposing them into simpler geometric shapes. This not only reduces the difficulty of mesh generation but also improves the accuracy of contact point identification.

[0094] The overlapping surface processing includes: merging the overlapping surfaces into a single surface;

[0095] When overlapping surfaces exist in a model, they can affect the accuracy of mesh generation and analysis results. Geometric conflicts can be eliminated by deleting overlapping portions or merging overlapping surfaces using the software's "Boolean operation" function.

[0096] The gap stitching includes: extending two surfaces whose gaps between adjacent surfaces are within a set gap range until the two surfaces intersect.

[0097] In this embodiment, the software's "stitching" operation is used to connect the surfaces on both sides of the gap, making them a continuous whole, thereby avoiding discontinuities or errors during mesh generation.

[0098] In this embodiment, the gap stitching operation, combined with the previous processing methods, can first perform preliminary processing on various structures in the model to make the gaps between adjacent faces small enough. Then, by using gap stitching, more adjacent faces can be stitched together. Compared with the method of processing each other independently, the model preprocessing effect is better.

[0099] S3: Perform a shell extraction operation on the first geometric model to obtain a shell element model;

[0100] Unpacking is an existing technology, and the steps include:

[0101] Set the shelling parameters and select the surfaces to retain: According to the design requirements, select the surfaces to be retained. These surfaces are usually the parts that are connected to the outside or need to maintain the integrity of the structure, such as the mounting surface and mating surface of the parts.

[0102] Specify shell thickness: Determine the thickness value of the shell, which will be applied to the entire model or a specific area. Factors such as the strength, rigidity and manufacturing process of the parts need to be considered to ensure that the shell thickness is reasonable and uniform.

[0103] Set the extraction direction: Determine which direction to start extracting material from. This will affect the shape and internal structure of the shell. Usually, the direction is chosen to be consistent with the main axis of symmetry or the direction of key features of the model.

[0104] To generate the shell feature, click the "OK" or "Generate" button. The software will automatically perform the shelling operation according to the set parameters and generate the corresponding shell feature on the model. At this time, the model will be transformed from a solid into a shell with a hollow structure.

[0105] The advantages of shell extraction are: it significantly reduces the number of elements and nodal degrees of freedom, thus lowering the computational load; at the same time, it can accurately describe the mechanical behavior of thin-walled structures, ensuring simulation accuracy. Shell extraction provides an efficient and accurate foundation for subsequent mesh generation and finite element analysis.

[0106] It should be noted that: Reference Figure 2-3 The shell unit model includes: a grid assembly 1, a fuel rod 4, and the mid-surface of the rigid protrusion 2 and elastic protrusion 3 in the grid cell 5 of the grid assembly 1 obtained by shelling operation.

[0107] By analyzing contact features and their coordinates, it is possible to determine whether each component is in the contact area, thus enabling accurate determination of contact features.

[0108] S4: Identify the contact features and solder joint features of the shell unit model, including:

[0109] When performing coordinate positioning and feature recognition on lattice components, establishing a unified global coordinate system is a crucial prerequisite. Since lattice components generally adopt a 17×17 specification, the center of the lattice component is established as the origin of the global coordinate system, and the three coordinate axes of the global coordinate system are parallel to the length, width, and height directions of the lattice component, respectively.

[0110] Let the cell length be L. Under the global coordinate system, each cell has a unique corresponding coordinate value. For example, the center coordinates of a certain cell are (-8L, -8L, 0); and the center coordinates of its four adjacent cells are (-8L, -7L, 0), (-8L, -9L, 0), (-7L, -8L, 0), and (-9L, -8L, 0), respectively. Therefore, the distance between the center points of adjacent cells is L. Taking the coordinates (-8L, -7L, 0) as an example, -8L is the coordinate along the length direction, -7L is the coordinate along the width direction, and 0 is the coordinate along the height direction. The global coordinate system constructed in this way provides a unified benchmark for subsequent coordinate localization and feature recognition.

[0111] S4-1: Obtain the cell length and cell height in the shell unit model; the cell length is perpendicular to the extension direction of the fuel rod; the cell height is parallel to the extension direction of the fuel rod.

[0112] Based on the cell length, the first coordinates of the rigid protrusion and the elastic protrusion in the global coordinate system are calculated.

[0113] S4-2: Calculate the second coordinate of the solder joint in the global coordinate system based on the cell length and cell height.

[0114] S4-3: Number each rigid protrusion and elastic protrusion, and combine the number with the corresponding first coordinate to form a contact feature;

[0115] Each solder joint is numbered, and the number is combined with the corresponding second coordinate to form the solder joint feature.

[0116] Specifically, in the grid assembly structure, each grid cell is equipped with rigid protrusions and elastic protrusions of the same shape and size but different positions, whose main function is to securely hold the fuel rods.

[0117] Based on this structural characteristic, the rigid and elastic protrusions in each grid cell that are in contact with the fuel rod can be accurately identified and assigned a unique number by using the precise position coordinates of each component.

[0118] For example, the contact features within cell C11 are numbered C11_1, C11_2, C11_3, and C11_4 in a counterclockwise direction, starting from the bottom of the cell, while the surface of the fuel rod within the cell is numbered R11.

[0119] Since all cells in the lattice assembly are of equal size, a traversal loop program is written to sequentially identify the features of rigid and elastic protrusions within each cell. Once the traversal is complete, all contact features of the entire lattice assembly can be obtained.

[0120] This approach lays the foundation for quickly establishing the correspondence between each contact feature and the surface of the fuel rod in subsequent operations.

[0121] Specifically, the grid strips are assembled together by interlocking through assembly slots to form a grid assembly; they are connected by solder joints at the intersections, with a 17×17 grid assembly having as many as 512 solder joints. Taking the identification of one of the intersection solder joints as an example, let the grid height be H, the grid length be L, and the distance between the assembly slots be d, so the coordinates of one solder joint are (L / 2, L / 2, H), and the coordinates of the two points in the assembly slot directly opposite the solder joint are (L / 2, L / 2+d / 2, H) and (L / 2, L / 2-d / 2, H) respectively.

[0122] This allows for precise identification of the weld point location. In the subsequent finite element modeling process, beam connections are established between the weld point and the assembly slot directly opposite it to accurately establish the weld point.

[0123] Further, S5: Based on the contact features and the weld joint features, automatically create the contact features and weld joint features of the finite element model of the nuclear fuel assembly, including:

[0124] Import the shell element model into the finite element software;

[0125] Assign material properties to the shell element model;

[0126] Based on the contact and solder joint characteristics, the coordinates of the contact points and solder joints are automatically identified in the shell element model, and the contact points and solder joints are automatically created; the contact points include rigid protrusions and elastic protrusions.

[0127] Connect adjacent contact points and solder joints;

[0128] Set contact properties for the contact points; contact properties include: coefficient of friction and contact stiffness;

[0129] Finally, a finite element model of the nuclear fuel assembly was obtained.

[0130] Specifically, in the finite element analysis workflow, for shell element models that have already undergone feature processing, it is essential to use the secondary development function of finite element software to automatically identify and create key features (such as contact points and weld points).

[0131] This process effectively reduces the tediousness and errors of manual operation, improving analytical efficiency and accuracy. Detailed steps include:

[0132] Choosing a Development Tool: Different finite element software comes with different secondary development tools and interfaces. For example, Abaqus provides a Python script interface, and ANSYS supports secondary development using APDL (ANSYS Parametric Design Language) or Python. The appropriate development tool must be selected based on the finite element software being used.

[0133] Importing the geometric model: Import the processed and feature-identified geometric model into the finite element software.

[0134] Assigning material properties: Assign different material properties to different components. For example, the cladding material for grid strips and fuel rods is Zr4, and the material property for elastic protrusions is Inconel718.

[0135] Contact point creation: For the identified contact points, based on the corresponding number and coordinates, the secondary development interface of the finite element software is used to call the corresponding contact definition function to create contact pairs and define contact attributes (such as friction coefficient, contact stiffness, etc.).

[0136] Solder joint creation: For the identified solder joints, a beam connection is established between adjacent solder joints to simulate the actual solder joints.

[0137] Based on the above scheme, a more accurate finite element model of nuclear fuel assembly can be obtained. This allows for more accurate analytical conclusions when analyzing the structural weaknesses of actual nuclear fuel assemblies, thus enabling improvements to the actual structural design of nuclear fuel assemblies.

[0138] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention is not limited to the specific combination of the above-described technical features, but also includes other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this invention.

Claims

1. An automatic modeling method for finite element analysis of nuclear fuel assemblies, characterized in that, include: S1: Obtain the initial geometric model of the nuclear fuel assembly; S2: Preprocess the initial geometric model to obtain the first geometric model; S3: Perform a shelling operation on the first geometric model to obtain a shell element model; the shell element model includes: a grid assembly, fuel rods, and the mid-surfaces of rigid protrusions and elastic protrusions on the grid assembly obtained through the shelling operation; S4: Identify the contact features and solder joint features of the shell element model; the shell element model includes multiple gate elements, each gate element including rigid protrusions and elastic protrusions; the contact features include rigid protrusion features and elastic protrusion features; Step S4 includes: Establish a global coordinate system; Obtain the cell length and cell height in the shell element model; the cell length is perpendicular to the extension direction of the fuel rod; the cell height is parallel to the extension direction of the fuel rod. Based on the cell length, the first coordinates of the rigid protrusion and the elastic protrusion in the global coordinate system are calculated. Based on the gate length and gate height, the second coordinate of the solder joint in the global coordinate system is calculated. Each rigid and elastic protrusion is numbered, and the number is combined with the corresponding first coordinate to form a contact feature; Each solder joint is numbered, and the number is combined with the corresponding second coordinate to form the solder joint feature; S5: Automatically create contact features and weld point features for the finite element model of the nuclear fuel assembly based on the contact features and weld point features.

2. The automatic modeling method for finite element analysis of nuclear fuel assemblies according to claim 1, characterized in that, S2: Preprocess the initial geometric model to obtain a first geometric model, including: The initial geometric model is then subjected to model simplification, missing surface repair, surface cutting, overlapping surface processing, and gap stitching in sequence to obtain the first geometric model; The surface cutting includes: dividing the surface into multiple geometric shapes; The overlapping surface processing includes: merging the overlapping surfaces into a single surface; The gap stitching includes: extending two surfaces whose gaps between adjacent surfaces are within a set gap range until the two surfaces intersect.

3. The automatic modeling method for finite element analysis of nuclear fuel assemblies according to claim 2, characterized in that, The model simplification includes: Replace the rounded and chamfered structures of the initial geometric model with right-angle structures; Fill the defect holes in the initial geometric model.

4. The automatic modeling method for finite element analysis of nuclear fuel assemblies according to claim 3, characterized in that, Filling the defect holes in the initial geometric model includes: In the initial geometric model, all holes with an area smaller than a set area are detected, resulting in multiple defective holes; Multiple first sampling points are selected at the edge of the defective hole; Multiple reference lines are obtained by connecting adjacent first sampling points with straight lines; The polygons formed by the multiple adjacent and coplanar reference lines are filled into planes.

5. The automatic modeling method for finite element analysis of nuclear fuel assemblies according to claim 4, characterized in that, Along a direction perpendicular to the reference line, the maximum distance between the reference line and the edge of the defective hole is within the set gap range.

6. The automatic modeling method for finite element analysis of nuclear fuel assemblies according to claim 2, characterized in that, The missing surface repair includes: Obtain the surface to be repaired; Extend the surface to be repaired until the gap between the surface to be repaired and the adjacent surface is within the set gap range.

7. The automatic modeling method for finite element analysis of nuclear fuel assemblies according to claim 2, characterized in that, The surface is divided into multiple geometric shapes, including: Select multiple second sampling points across the entire curved surface; Connect adjacent second sampling points to form multiple non-overlapping triangles; Multiple adjacent and coplanar triangles are merged into a single face to obtain multiple polygonal shapes; Multiple polygonal shapes and the remaining triangular shapes are combined as multiple geometric shapes.

8. The automatic modeling method for finite element analysis of nuclear fuel assemblies according to claim 1, characterized in that, S5: Based on the contact features and the weld joint features, automatically create the contact features and weld joint features of the finite element model of the nuclear fuel assembly, including: Import the shell element model into the finite element software; Assign material properties to the shell element model; Based on the contact and solder joint characteristics, the coordinates of the contact points and solder joints are automatically identified in the shell element model, and the contact points and solder joints are automatically created; the contact points include rigid protrusions and elastic protrusions. Connect adjacent contact points and solder joints; Set contact properties for the contact points; contact properties include: coefficient of friction and contact stiffness; Finally, a finite element model of the nuclear fuel assembly was obtained.

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