Spent fuel storage rack assembly process

Abstract

The present application belongs to the field of assembly method, and particularly relates to a spent fuel storage rack assembly process method. It comprises the following steps: step 1: processing multiple connection width nozzle plate specifications; step 2: making a grid spacing positioning tool; step 3: processing a bottom plate upper storage sleeve group positioning groove; step 4: determining the storage sleeve assembly sequence; step 5: determining the storage sleeve assembly reference and performing assembly and laser welding according to the assembly sequence; and step 6: welding the surrounding plate. The present application has the following remarkable effects: ensuring the gap between the nozzle plate and the square tube, meeting the laser welding requirement; controlling the grid spacing size after assembly; realizing the rapid positioning and assembly of the square tube and the bottom plate; achieving the optimal target of production assembly sequence; ensuring the overall tolerance control requirement; and solving the problem of rack distortion.

Description

Technical Field

[0001] This invention pertains to assembly methods, specifically relating to a process for assembling spent fuel storage racks. Background Technology

[0002] Spent fuel storage racks are core equipment in the nuclear fuel cycle and are widely used in in-reactor storage, intermediate off-reactor storage, and reprocessing plant storage.

[0003] A new high-density spent fuel storage grid designed by a design institute further improves critical safety and mechanical properties, and increases spent fuel loading density. The connection between adjacent storage sleeves of the spent fuel storage grid uses a T-shaped full-penetration weld structure with a sprue plate, resulting in significant welding deformation. Furthermore, the flared top of the square tubes makes positioning difficult. The storage sleeves are welded longitudinally and transversely to the base plate at their bottom ends. The outer perimeter plates of the grid use a full-penetration weld structure and are connected to the storage sleeves with fillet welds, resulting in significant welding deformation and making the entire grid prone to twisting and deformation. The grid spacing tolerance between every two storage sleeves is ±1mm, and the perpendicularity requirement between the storage sleeves and the base plate is 1.6mm, requiring very high dimensional accuracy and making assembly extremely difficult. Therefore, tooling and process design are necessary to ensure the product assembly and welding requirements are met. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a process for assembling spent fuel storage racks.

[0005] This invention is achieved as follows: a method for assembling spent fuel storage racks, comprising the following steps:

[0006] Step 1: Process various widths of sprue plates for connection;

[0007] Step 2: Fabricate the grid pitch positioning fixture;

[0008] Step 3: Machining the positioning groove for storing the sleeve assembly on the base plate;

[0009] Step 4: Determine the assembly sequence of the storage sleeve;

[0010] Step 5: Determine the assembly standards for the storage sleeve and assemble and laser weld it according to the assembly sequence;

[0011] Step 6: Welding of the perimeter plate.

[0012] As described above, in a spent fuel storage rack assembly process, step 1 includes selecting a sprue plate of appropriate width based on the actual dimensions measured after the vertical assembly of the storage sleeve, ensuring that the width of the sprue plate is consistent vertically and that the gap between the sprue plate and the square tube assembly is uniform, thus meeting the requirements for laser welding.

[0013] As described above, in a spent fuel storage grid assembly process, step 2 includes fabricating a positioning fixture according to drawings. The grid spacing tolerance after the positioning fixture is assembled is controlled at ±0.5mm to ensure that the grid spacing between storage sleeves meets the positioning requirements.

[0014] The above-described spent fuel storage grid assembly process further includes, in step 2, assembling a grid spacing positioning fixture at the top of the storage sleeve during vertical grid assembly.

[0015] As described above, in a spent fuel storage rack assembly process, step 3 includes machining a square ring positioning groove for storage sleeve assembly on the top surface of the base plate using a CNC machine tool within the thickness deviation range of the base plate. The machining dimensions of the positioning groove are within the plate thickness tolerance range and are designed not to affect the assembly and post-assembly dimensions of the storage sleeve.

[0016] In the above-described spent fuel storage grid assembly process, step 3 further includes controlling the grid spacing of the lower storage sleeve by means of a shaped ring positioning groove machined on the top plate.

[0017] As described above, in a spent fuel storage grid assembly process, step 4 includes: planning the assembly sequence of each specification of grid storage sleeve in advance according to the laser welding beam stroke, designing an assembly sequence suitable for production, and avoiding situations where a large number of nozzle plates cannot be vertically welded.

[0018] As described above, in the process of assembling a spent fuel storage rack, step 4 further includes the following: if the laser welding stroke is not reachable and the vertical welding of the nozzle plate cannot be avoided in the planning, the nozzle plate and the storage sleeve should be horizontally laser welded in advance. The nozzle plates for horizontal welding should all be selected with a wider specification. After welding is completed, the width should be ground before vertical assembly.

[0019] As described above, in a spent fuel storage grid assembly process, step 5 includes selecting a cross reference near the center of each grid, assembling a cross center as the assembly reference for the remaining storage sleeves, assembling each square tube with the positioning groove on the base plate assembly as the reference, and using a theodolite to check the verticality and straightness of each assembled storage sleeve. Assembly and laser welding must be carried out in sequence according to the planned assembly order.

[0020] As described above, in a spent fuel storage grid assembly process, step 6 includes determining the length of the surrounding plate based on the final assembled external dimensions of the grid plus the welding shrinkage of the surrounding plate welds. After the single piece is assembled, two diagonal welds are welded simultaneously. Each weld is welded in three sections: first the middle section, then the top and bottom sections.

[0021] The significant advantages of this invention are: 1) while ensuring the assembly dimensions of the square tube, selecting a sprue plate of appropriate width ensures the assembly gap between the sprue plate and the square tube, thus meeting the requirements of laser welding.

[0022] 2) The grid spacing positioning fixture was manufactured to meet the grid spacing positioning requirements of the product and control the grid spacing size after assembly.

[0023] 3) The square ring positioning groove machined on the top surface of the base plate enables the rapid positioning and assembly of the square tube and the base plate.

[0024] 4) By combining the laser welding beam travel and planning the assembly sequence of the storage sleeve multiple times, and simulating the product assembly process, no situation arose where the laser welding travel could not be reached. This reduced the number of horizontal welding operations between the storage sleeve and the sprue plate, achieving the optimal goal of the production assembly sequence.

[0025] 5) First, assemble a cross center as the assembly datum, and then assemble the surrounding storage sleeves in sequence using the cross datum. The assembly error is decomposed into regions to ensure the overall tolerance control requirements.

[0026] 6) By determining the length of the enclosure plate by adding the welding shrinkage of the enclosure plate weld to the overall dimensions, and by adopting a reasonable welding sequence and welding method, the welding deformation of the enclosure plate was controlled, thus solving the problem of grid distortion and deformation. Attached Figure Description

[0027] Figure 1 3D schematic diagram of the lattice after assembly;

[0028] Figure 2 Pitch positioning fixture;

[0029] Figure 3 A square ring-shaped process positioning groove on the base plate;

[0030] Figure 4 Schematic diagram of laser welding between storage sleeve and nozzle plate;

[0031] Figure 5 A schematic diagram of a 6x6 grid assembly;

[0032] Figure 6 Cross-shaped center assembly reference;

[0033] In the diagram: 1. Enclosure; 2. Base plate; 3. Machining positioning groove; 4. Sprue plate; 5. Beam; 6. Storage sleeve. Detailed Implementation

[0034] A method for assembling spent fuel storage racks includes the following steps:

[0035] 1) Process various width specifications of sprue plates for connection. Select the appropriate width specification of sprue plate according to the actual size measurement after the vertical assembly of the storage sleeve. This can ensure that the width of the sprue plate is consistent from top to bottom and that the gap between the sprue plate and the square tube assembly is uniform, which meets the requirements of laser welding.

[0036] 2) Fabricate the grid pitch positioning fixture (see Figure 2 The tooling spacing tolerance must be more stringent than the grid spacing dimension. The spacing tolerance after the positioning tooling is assembled is controlled at ±0.5mm to ensure that the spacing between the storage sleeves meets the positioning requirements. When assembling the grid vertically, the spacing positioning tooling is assembled at the top of the storage sleeve.

[0037] 3) Within the thickness deviation range of the base plate, a square ring positioning groove for assembling the storage sleeve is machined on the top surface of the base plate using a CNC machine tool. The machining dimensions of the positioning groove should be such that they do not affect the assembly and post-assembly dimensions of the storage sleeve, within the plate thickness tolerance range. Machining the positioning groove significantly reduces manual assembly errors and shortens assembly time. The grid spacing of the lower storage sleeve is controlled by machining the positioning groove on the top plate.

[0038] 4) According to the laser welding beam path (see...) Figure 4 ), plan in advance the assembly sequence of each specification of storage sleeve, and design an assembly sequence suitable for production ( Figure 5 To avoid situations where a large number of nozzle plates cannot be vertically welded, the plan should avoid situations where vertical welding of nozzle plates is unavoidable. For situations where vertical welding of nozzle plates is unavoidable in the planning, horizontal laser welding of nozzle plates should be carried out in advance. For horizontal welding, wider nozzle plates should be selected. After welding is completed, the width should be ground before vertical assembly.

[0039] 5) Select a cross reference near the center of each grid, and assemble one cross center as the assembly reference for the remaining storage sleeves (see...). Figure 6 Each square tube is assembled based on the groove on the base plate assembly. The verticality and straightness of each storage sleeve are checked with a theodolite. Assembly and laser welding must be carried out in the planned assembly sequence.

[0040] 6) Determine the length of the surrounding plate based on the final assembled external dimensions of the grid and the welding shrinkage of the surrounding plate welds. After the single piece is assembled, the two corresponding welds on the diagonal are welded simultaneously. Each weld is divided into three sections: first weld the middle section, then weld the top and bottom sections.

Claims

1. A spent fuel storage rack assembly process method characterized by, Includes the following steps: Step 1: Process various widths of sprue plates for connection; Step 2: Fabricate the grid pitch positioning fixture; Step 3: Machining the positioning groove for storing the sleeve assembly on the base plate; Step 4: Determine the assembly sequence of the storage sleeve; Step 5: Determine the assembly standards for the storage sleeve and assemble and laser weld it according to the assembly sequence; Step 6: Welding of the enclosure panels; Step 1 includes selecting a sprue plate of appropriate width based on the actual dimensions measured after the vertical assembly of the storage sleeve, ensuring that the width of the sprue plate is consistent vertically and that the gap between the sprue plate and the square tube assembly is uniform, in order to meet the requirements of laser welding. Step 2 includes fabricating a positioning fixture according to the drawings. The grid pitch tolerance of the assembled positioning fixture is controlled at ±0.5mm to ensure that the grid pitch between the storage sleeves meets the positioning requirements. Step 2 further includes assembling a grid spacing positioning fixture at the top of the storage sleeve during the vertical assembly of the grid. Step 3 includes machining a square ring positioning groove for assembling the storage sleeve on the top surface of the base plate using a CNC machine tool within the thickness deviation range of the base plate. The machining dimensions of the positioning groove are determined within the thickness tolerance range so as not to affect the assembly and post-assembly dimensions of the storage sleeve. Step 3 further includes controlling the grid spacing of the lower storage sleeve through a shaped ring positioning groove machined on the top plate; Step 4 includes, according to the laser welding beam travel, planning the assembly sequence of each specification of grid storage sleeve in advance, designing an assembly sequence suitable for production, and avoiding situations where a large number of sprue plates cannot be vertically welded. Step 4 also includes that, in cases where the laser welding stroke is not reachable and vertical welding of the sprue plate cannot be avoided in the planning, the sprue plate and storage sleeve should be horizontally laser welded in advance. For horizontally welded sprue plates, wider sprue plates should be selected. After welding is completed, the width should be ground before vertical assembly. Step 5 includes selecting a cross reference near the center of each grid, assembling a cross center as the assembly reference for the remaining storage sleeves, assembling each square tube with the positioning groove on the base plate assembly as the reference, and using a theodolite to check the verticality and straightness of each assembled storage sleeve. Assembly and laser welding must be carried out in the planned assembly sequence. Step 6 includes determining the length of the surrounding plate based on the final assembled external dimensions of the grid and the welding shrinkage of the surrounding plate welds. After the single piece is assembled, the two diagonal welds are welded simultaneously. Each weld is welded in three sections: first the middle section, then the top and bottom sections.

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