Nuclear fuel element operation head machining method and device and structure before chromizing and nitriding

Abstract

The invention belongs to the technical field of nuclear power, and particularly relates to a nuclear fuel element operation head machining method and device and a structure before chromizing and nitriding. The structure of the operation head before chromizing and nitriding is determined through a large number of design, machining and welding tests, the structure of the welding position is milled after chromizing and nitriding, the influence of a chromizing and nitriding coating on welding and X-ray detection is eliminated, meanwhile, the size of a sodium hole and a marking plane are milled, and the welding quality is improved. And the size precision of the sodium outlet hole and the reading effect of the marking mark are guaranteed, the technical condition requirements are met, the key technology of the chromizing and nitriding workpiece structure and the manufacturing process is achieved, and a technical guarantee is provided for the smooth development and production of the fast reactor nuclear fuel element.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power, and in particular relates to a method and device for processing a nuclear fuel element operating head and a structure before chromizing and nitriding. Background Art

[0002] A fast reactor nuclear power plant is a nuclear power plant that uses fast neutrons to cause nuclear fuel fission reactions. The operating head is a structural component in the demonstration fast reactor nuclear fuel element. In the reactor, the operating head is clamped by a lifting device to perform fuel element loading and unloading operations. The raw material of the operating head is CN-1515 stainless steel. The surface of the operating head needs to be chromized and nitrided locally to prevent the element from self-welding in the pile and increase the wear resistance of the operating head surface. After the full-size processing of the operating head is completed, chromized and nitrided will have the following problems:

[0003] 1. The chromium nitriding layer at the welding position between the operating head and the outer sleeve will affect the subsequent assembly welding process, and defects such as inclusions and pores will appear during welding.

[0004] 2 When X-ray inspection is performed after the operating head is assembled and welded, the chromium nitride layer at the inner hole of the operating head will affect the X-ray inspection results.

[0005] 3. The chromium nitriding layer is somewhat brittle, and dot-peen marking will cause cracking, which will affect the recognition effect of the operating head after marking.

[0006] 4. The operating head will be subjected to high temperature deformation and coating thickening during the chroming and nitriding process, which will cause the size of the sodium outlet hole to be out of tolerance. Summary of the invention

[0007] In order to overcome the problems existing in the related art, a method and device for processing a nuclear fuel element operating head and a structure before chromizing and nitriding are provided.

[0008] According to one aspect of an embodiment of the present disclosure, a method for processing a nuclear fuel element operating head is provided, wherein the method comprises:

[0009] Step 1: For the processing of the sodium outlet hole and marking plane structure of the structure before chromium nitriding, install the CNC indexing head and tailstock tooling on the workbench of the vertical machining center machine tool. The CNC indexing head clamps the top of the operating head after chromium nitriding, and the tailstock top supports the inner hole at the other end of the operating head after chromium nitriding. Use a milling cutter for milling to realize automatic control of the CNC indexing head for indexing, and the tailstock automatically loosens and tightens to realize automatic milling;

[0010] Step 2: Processing of welding structure; install the spindle large through-hole CNC dividing head on the workbench of the horizontal machining center, clamp the middle part of the operating head after chromizing and nitriding, and close the top to the positioning device. The spindle of the horizontal machining center is on the front of the workpiece, and the end mill is used to rotate around the workpiece to mill the hexagonal welding structure and end face, and the inner hole circle is processed by a boring tool, and then the machine tool worktable is rotated, and the forming tool is used to process the bevel groove of the welding structure, which can realize the functions of automated clamping, indexing and processing.

[0011] In a possible implementation, the minimum machining allowance for removing the chromized nitriding coating is determined for the welding structure of the operating head after chromized nitriding, and the coating removal amount after chromized nitriding is not less than .mm;

[0012] The main body material of the sodium hole in the structure before chroming and nitriding is thickened by at least .mm, and the thinnest main body material at the welding point is thickened by at least .mm.

[0013] In a possible implementation, the structure of the welding position is designed to leave a margin before chromizing and nitriding, and the welding process table structure is not processed. After chromizing and nitriding, the welding process table structure is processed to remove the coating.

[0014] In a possible implementation, in step 1, a one-time clamping is adopted for processing, and a CNC dividing head is used for clamping. After each sodium outlet hole is processed, the machine tool program controls the machine tool to automatically rotate and process subsequent sodium outlet holes in sequence.

[0015] In one possible implementation, the sodium hole and marking plane processing tools after chromium nitriding are installed on the machine tool workbench, which is the workbench of a vertical machining center. Automated clamping is used in the processing process, and the tightening and loosening of the tailstock is controlled by the machine tool program. The tailstock is installed on the tailstock guide rail and can move automatically according to the program control.

[0016] In a possible implementation, the workbench is a workbench of a horizontal machining center, and the processing tools for the welding positions after chromizing and nitriding are all installed on the workbench.

[0017] In a possible implementation, the welding structure is a hexagonal structure. In order to ensure the relative position accuracy of the processing, it is necessary to adopt a one-time clamping for processing, using a dividing head for clamping. After each welding structure is processed, the machine tool program controls the automatic rotation to process the subsequent welding structures in sequence.

[0018] In a possible implementation, multiple chromium nitriding and post-operation heads are processed in batches, and a positioning device is designed at the left end of each chromium nitriding and post-operation head to ensure that each workpiece is clamped in the same position.

[0019] According to another aspect of an embodiment of the present disclosure, a nuclear fuel element operating head structure before chromium nitriding is provided, wherein the main body material of the sodium outlet hole of the above-mentioned structure before chromium nitriding is thickened by at least .mm, and the thinnest main body material at the welding point is thickened by at least .mm.

[0020] According to another aspect of the embodiment of the present disclosure, a nuclear fuel element operating head processing device is provided, in which a CNC indexing head and a tailstock tooling are installed on a workbench of a vertical machining center machine tool, the CNC indexing head clamps the top of the chromized and nitrided operating head, the tailstock top supports the inner hole at the other end of the chromized and nitrided operating head, and a milling cutter is used for milling to realize automatic control of the CNC indexing head for indexing, and the tailstock is automatically loosened and tightened to realize automatic milling;

[0021] A spindle large through-hole CNC dividing head is installed on the workbench of the horizontal machining center. The middle part of the operating head is clamped after chromizing and nitriding, and the top is close to the positioning device. The spindle of the horizontal machining center is on the front of the workpiece. An end mill is used to rotate around the workpiece to mill the hexagonal welding structure and end face. A boring cutter is used to process the inner hole circle, and then the machine tool worktable is rotated, and a forming cutter is used to process the bevel groove of the welding structure.

[0022] The beneficial effects of the present disclosure are as follows: the present disclosure performs milling of the welding structure after chroming and nitriding, thereby eliminating the influence of the chroming and nitriding coating on welding and X-ray detection, and simultaneously mills the size of the sodium hole and the marking plane, thereby ensuring the size accuracy of the sodium hole and the reading effect of the marking mark, meeting the technical conditions, solving the key technologies of the chroming and nitriding workpiece structure and manufacturing process, and providing technical guarantee for the smooth development and production of the demonstration fast reactor nuclear fuel elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the finished product of the nuclear fuel element operating head.

[0024] Figure 2 Schematic diagram of the operating head before chroming and nitriding.

[0025] Figure 3 Schematic diagram of the design structure of the weld before chroming and nitriding.

[0026] Figure 4 This is a schematic diagram of the tooling for producing sodium holes and marking the surface after chroming and nitriding.

[0027] Figure 5 This is a schematic diagram of the tooling for processing the welding point after chroming and nitriding.

[0028] In the figure:

[0029] 1. Marking plane; 2. Sodium outlet hole; 3. Welding structure;

[0030] 4. Design structure of marking plane and sodium outlet hole before chromizing and nitriding;

[0031] 5. Design structure of welding joint before chromizing and nitriding;

[0032] 6. Welding process table structure; 7. Chromizing and nitriding processing allowance;

[0033] 8. Operating head after chromizing and nitriding; 9. CNC dividing head; 10. Machine tool workbench; 11. Tailstock guide rail; 12. Tailstock; 13. Workbench; 14. Dividing head; 15. Positioning device; DETAILED DESCRIPTION

[0034] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Figure 1 This is a finished schematic diagram of the nuclear fuel element operating head. Figure 2 This is a schematic diagram of the operation head before chromizing and nitriding. Figure 1 As shown, the method includes:

[0036] In the related art, the operating head needs to be coated with a chromium-nitriding coating according to design requirements to increase the wear resistance and anti-self-welding function of the operating head. Welding tests have shown that welding after chromium-nitriding will cause defects such as inclusions and pores in the weld, and the coating will affect X-ray detection.

[0037] For the welding structure 3 of the operating head, the minimum machining allowance for removing the chromized nitriding coating is determined. The coating removal after chromized nitriding is not less than 0.5 mm, which can eliminate the influence of the coating on welding and X-ray detection. Figure 3 The inner hole thickness is increased by 0.5mm, and the thinnest part at the welding point is thickened by 0.5mm.

[0038] See also Figure 2 and Figure 3 Before chromizing and nitriding, the structure 5 at the welding position is designed to leave a margin without processing the welding process table structure 6, and after chromizing and nitriding, the welding process table structure 6 is processed to remove the coating.

[0039] Design for the structure of the sodium outlet hole 1. Since the size will change due to the addition of coating after chromization and nitriding, according to the test, if the sodium outlet hole 1 is processed first and then chromization and nitriding, it will affect the dimensional accuracy of the sodium outlet hole 1, and there is a risk of causing the product to be scrapped due to dimensional deviation. In order to solve this problem, it is designed to perform fine processing of the sodium outlet hole 1 after chromization and nitriding.

[0040] Design of the marking plane 1 structure. Marking tests have shown that marking on the chromized nitriding coating will damage the integrity of the coating, and the marking is not clear after marking, so the sodium hole 2 and the marking plane 1 are not processed before chromized nitriding. After chromized nitriding, the reserved amount is processed by milling to expose the raw material metal, and the dot-needle process is used for marking. This design method can not only not affect the chromized nitriding process, but also ensure clear identification of the marking.

[0041] See also Figure 4 and Figure 5 The semi-finished product of the operating head is subjected to chromizing and nitriding treatment with the reserved processing allowance to form a chromizing and nitriding operating head 8, which requires further processing to remove the local coating.

[0042] The operating head is designed with 6 sodium outlet holes and 1 structure. In order to ensure the relative position accuracy of the processing, it is necessary to adopt a one-time clamping for processing. The CNC dividing head 9 is used for clamping. After each sodium outlet hole is processed, the machine tool program controls the automatic rotation to process the subsequent sodium outlet holes in turn.

[0043] After chromizing and nitriding, the sodium hole and marking plane processing tooling are all installed on the machine tool workbench 10, and the machine tool workbench 10 is the workbench of the vertical machining center.

[0044] Among them, automatic clamping is adopted in the processing process, and the tightening and loosening of the tailstock 12 are controlled by the machine tool program. The tailstock 12 is installed on the tailstock guide rail 11 and can be automatically moved according to the program control.

[0045] Since the length of the operating head 8 after chroming and nitriding is about 600 mm, in order to ensure the accuracy of clamping the workpiece, a tailstock 12 is required for self-centering support.

[0046] The workbench 13 is a workbench of a horizontal machining center, and the processing tools for the welding positions after chromizing and nitriding are all installed on the workbench 13 .

[0047] The welding structure 3 is a hexagonal structure. In order to ensure the relative position accuracy of the processing, it is necessary to adopt a one-time clamping for processing. The dividing head 14 is used for clamping. After each welding structure 3 is processed, the machine tool program controls the automatic rotation to process the subsequent welding structures 3 in sequence.

[0048] Positioning device 15: Since the operating head 8 needs to be processed in batches after chromizing and nitriding, in order to ensure the clamping consistency of each part, it is necessary to design a positioning device at the left end of the operating head 8 after chromizing and nitriding to ensure that each workpiece is clamped in the same position, so as to ensure the processing accuracy and efficiency of the parts.

[0049] In a possible implementation, a method for processing a nuclear fuel element operating head is provided. After the nuclear fuel element is subjected to chromizing and nitriding treatment, the following steps are used for processing.

[0050] Step 1: Structural processing of the sodium outlet hole 2 and the marking plane 1. Install the CNC dividing head 9 and the tailstock 12 tooling on the workbench 10 of the vertical machining center machine tool. The CNC dividing head 9 clamps the top of the chromized and nitrided operating head 8, and the tailstock 12 top supports the inner hole at the other end of the chromized and nitrided operating head 8. Use a milling cutter for milling to realize automatic control of the CNC dividing head 9 for indexing, and the tailstock 12 is automatically loosened and tightened to realize automatic milling.

[0051] Step 2: Processing of the welding structure 3. Install the spindle large through-hole CNC indexing head 14 on the horizontal machining center worktable 13, clamp the middle of the chromized and nitrided operating head 8, and close the top to the positioning device 15. The spindle of the horizontal machining center is on the front of the workpiece. Use the end milling cutter to rotate around the workpiece to mill the hexagonal welding structure 3 and the end face, use the boring cutter to process the inner hole circle, and then rotate the machine tool worktable 13 90 degrees, and use the forming cutter to process the bevel groove of the welding structure 3, which can realize the functions of automatic clamping, indexing and processing.

[0052] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for processing a nuclear fuel element operating head, characterized in that: The method comprises: Step 1: For the processing of the sodium outlet hole (2) and the marking plane (1) structure of the structure before chromium nitriding, a numerical control indexing head (9) and a tailstock (12) tooling are installed on the workbench (10) of the vertical machining center machine tool, the numerical control indexing head (9) clamps the top of the operating head (8) after chromium nitriding, and the tailstock (12) supports the inner hole of the other end of the operating head (8) after chromium nitriding. A milling cutter is used for milling to realize automatic control of the numerical control indexing head (9) for indexing, and the tailstock (12) is automatically loosened and tightened to realize automatic milling; Step 2: Processing the welding structure (3); installing a spindle large through-hole CNC indexing head (14) on a horizontal machining center workbench (13), clamping the middle of the chromized and nitrided operating head (8), and pressing the top of the positioning device (15). The spindle of the horizontal machining center is on the front of the workpiece, and a vertical milling cutter is used to rotate around the workpiece to mill the hexagonal welding structure (3) and the end face, and a boring cutter is used to process the inner hole circle, and then the machine tool workbench (13) is rotated 90 degrees, and a forming cutter is used to process the bevel groove of the welding structure (3), which can realize the functions of automatic clamping, indexing and processing.

2. The method according to claim 1, characterized in that: Determine the minimum machining allowance for removing the chromized nitriding coating on the welded structure (3) of the operating head (8) after chromized nitriding, and the coating removal amount after chromized nitriding is not less than 0.5 mm; The bulk material of the sodium outlet hole of the structure before chromizing and nitriding is thickened by at least 0.5 mm, and the thinnest bulk material at the welding point is thickened by at least 0.5 mm.

3. The method according to claim 1, characterized in that: Before chromizing and nitriding, the structure (5) at the welding position is designed to leave a margin without processing the welding process table structure (6), and after chromizing and nitriding, the welding process table structure (6) is processed to remove the coating.

4. The method according to claim 1, characterized in that In step 1, a one-time clamping is adopted for processing, and a numerically controlled dividing head (9) is used for clamping. After each sodium outlet hole is processed, the machine tool program controls the machine tool to automatically rotate and process the subsequent sodium outlet holes in sequence.

5. The method according to claim 1, characterized in that: After chromizing and nitriding, the sodium hole and marking plane processing tooling are installed on a machine tool workbench (10). The machine tool workbench (10) is a workbench of a vertical machining center. In the processing process, automatic clamping is adopted. The tightening and loosening of the tailstock (12) are controlled by the machine tool program. The tailstock (12) is installed on the tailstock guide rail (11) and can be automatically moved according to the program control.

6. The method according to claim 1, characterized in that The workbench (13) is a workbench of a horizontal machining center, and the processing tools for the welding positions after chromizing and nitriding are all installed on the workbench (13).

7. The method according to claim 1, characterized in that The weld structure (3) is a hexagonal structure. In order to ensure the relative position accuracy of the processing, it is necessary to adopt a one-time clamping process for processing. The dividing head (14) is used for clamping. After each weld structure (3) is processed, the machine tool program controls the machine tool to automatically rotate and process the subsequent weld structures (3) in sequence.

8. The method according to claim 1, characterized in that: A plurality of chromized and nitrided operating heads (8) are processed in batches, and a positioning device (15) is designed at the left end of each chromized and nitrided operating head (8) to ensure that each workpiece is clamped in the same position.

9. A nuclear fuel element operating head structure before chromization and nitriding, characterized in that: The main body material of the sodium outlet hole of the structure before chromization and nitriding as described in any one of claims 1 to 8 is thickened by at least 0.5 mm, and the thinnest main body material at the welding point is thickened by at least 0.5 mm.

10. A nuclear fuel element operating head processing device, characterized in that: In the device, a CNC indexing head (9) and a tailstock (12) tooling are installed on a vertical machining center machine tool workbench (10), the CNC indexing head (9) clamps the top of the chromized and nitrided operating head (8), the top of the tailstock (12) supports the inner hole of the other end of the chromized and nitrided operating head (8), and a milling cutter is used for milling to realize automatic control of the CNC indexing head (9) for indexing, and the tailstock (12) is automatically loosened and tightened to realize automatic milling; A spindle large through-hole CNC indexing head (14) is installed on a horizontal machining center worktable (13), the middle of the chromized and nitrided operating head (8) is clamped, and the top is tightly attached to a positioning device (15). The spindle of the horizontal machining center is on the front of the workpiece, and an end mill is used to rotate around the workpiece to mill the hexagonal welding structure (3) and the end face, and a boring cutter is used to process the inner hole circle, and then the machine tool worktable (13) is rotated 90 degrees, and a forming cutter is used to process the inclined surface groove of the welding structure (3).

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