Power modulation galvanometer laser welding method and device for zirconium alloy fuel rod

Abstract

The invention belongs to but not limited to the technical field of welding, and discloses a power modulation galvanometer laser welding method and device for a zirconium alloy fuel rod. A laser beam adopts a circular scanning track for welding along a circumferential weld, the power of 36 phase points in the circular scanning track is adjusted, a gradient power mode that the middle is high and the two sides are low is adopted for welding, a molten pool is stirred through the rotating laser beam, flowing of the molten pool is aggravated, gas escape is promoted, and meanwhile in the power modulation mode, the welding speed is increased. The surface energy distribution of the whole molten pool is more uniform, the power of the edge position of the molten pool is reduced, the weld seam undercut degree is reduced, and weld seam surface forming is more uniform. Three welding production procedures are reduced into two welding production procedures, meanwhile, the rotating speed during fuel rod welding is increased, the welding procedures are optimized, and the welding efficiency is improved; in addition, the problem that oxidation color beside an end plug welding circumferential weld is heavy is solved; and the welding seam air hole defect is improved, and the welding quality is improved.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the field of welding technology, and in particular relates to a power modulated galvanometer laser welding method and device for zirconium alloy fuel rods. Background Art

[0002] Zirconium alloys have excellent mechanical properties, resistance to neutron radiation, and resistance to high temperature and high pressure water corrosion. They are widely used in nuclear reactors as cladding materials and end plugs for nuclear fuel rods. Fuel rods are usually composed of upper and lower end plugs, cladding tubes, and internal core blocks. The sealing quality of the end plugs and cladding tubes plays a key role in the safe operation of the fuel rods in the reactor. Therefore, the study of zirconium alloy welding technology has important theoretical significance and application value.

[0003] At present, the sealing welding of zirconium alloy fuel rods mainly adopts TIG welding, laser welding and vacuum electron beam welding. my country mainly adopts TIG welding method in the field of nuclear sealing welding technology, which has high requirements for welding equipment, slow welding speed and low production efficiency. In terms of laser welding technology, my country's research level and application are relatively lacking, and there is a big gap compared with foreign countries. Therefore, it is of great theoretical significance and application value to study a new type of laser sealing welding technology for zirconium alloy fuel rods to improve welding efficiency and welding quality.

[0004] Zirconium alloy has good welding performance, but its high-temperature chemical properties are active. It is very easy to react with hydrogen, oxygen, nitrogen and other gases in the air during welding. When the temperature reaches 300°C, it strongly absorbs hydrogen. When it reaches 400°C, zirconium begins to strongly absorb oxygen. Above 800°C, it strongly absorbs nitrogen, generating brittle compounds such as zirconium oxide (ZrO2), zirconium nitride (ZrN) and zirconium hydride (ZrH2), which sharply reduce the mechanical properties and corrosion resistance of zirconium alloy. In addition, hydrogen and water vapor are easy to enter the molten pool under poor protection conditions. Due to the fast cooling speed of laser welding, hydrogen does not have time to escape, thus forming pores. and hydrogen-induced cracks, which affect the sealing of the weld. At the same time, zirconium alloy is extremely sensitive to oxygen in the welding environment, and oxidation color is easily generated near the weld, which affects the product performance and aesthetics. Careful pretreatment must be performed before welding zirconium alloy, and zirconium alloy presents different colors at different oxidation levels. The degree of contamination in the weld area can usually be determined by the surface color after welding. The zirconium alloy cladding tube and end plug sealing welding require extremely high assembly accuracy, and usually use interference fit to assemble to prevent a small amount of air from existing in the tiny gaps in the assembly area, causing chemical reactions during the zirconium alloy welding process and affecting the weld performance. Therefore, when welding zirconium alloy, the requirements for the welding environment and welding process are extremely strict.

[0005] In view of the above analysis, the technical problems that need to be solved urgently in the prior art are:

[0006] (1) In the actual welding process, the zirconium alloy end plug and the cladding tube nozzle assembly sealing welding area are not cleaned thoroughly, which can easily cause pollution and produce oxidation color;

[0007] (2) The welding process is complicated, the quality inspection steps are cumbersome, and the production efficiency is low;

[0008] (3) Zirconium alloy has active chemical properties at high temperatures and is very easy to react with gases such as hydrogen, oxygen, and nitrogen in the air during welding, affecting the mechanical properties of the welded joint;

[0009] (4) Laser welding cools down quickly, which causes the hydrogen in the molten pool to have no time to escape, thus forming defects such as pores and hydrogen-induced cracks, affecting the sealing of the weld. Summary of the invention

[0010] In view of the problems existing in the prior art, the present invention provides a power modulated galvanometer laser welding method and device for zirconium alloy fuel rods.

[0011] The present invention is achieved in this way: a power-modulated galvanometer laser welding method for zirconium alloy fuel rods. During power-modulated galvanometer laser welding, the laser beam adopts a circular scanning trajectory to weld along the annular weld. By adjusting the power of 36 phase points in the circular scanning trajectory, a gradient power mode with high power in the middle and low power on both sides is adopted for welding. The rotating laser beam stirs the molten pool to intensify the flow of the molten pool and promote gas escape. At the same time, in the power modulation mode, the energy distribution on the entire molten pool surface is made more uniform, the power at the edge of the molten pool is reduced, the degree of weld undercut is reduced, and the weld surface formation is made more uniform.

[0012] The power-modulated galvanometer laser welding method for zirconium alloy fuel rods comprises the following steps:

[0013] Step 1: Clamp the middle part of the cladding tube on the three-jaw chuck of the middle rotating shaft of the rotating platform, and place the lower end plug welding area in the atmosphere box on the lower end plug side through the middle through hole of the rotating shaft and the rubber sealing ring on the atmosphere box on the lower end plug side;

[0014] Step 2: After loading the core block, spring, gasket and other materials into the cladding tube from the other end of the cladding tube, the cladding tube on the upper end plug side is placed in the atmosphere box on the upper end plug side through the rubber sealing ring on the atmosphere box on the upper end plug side;

[0015] Step 3: introduce argon gas into the atmosphere box on the lower plug side, and the high-pressure argon gas enters the atmosphere box on the upper plug side through the cladding tube connecting the two atmosphere boxes, and continues to ventilate for more than 5 minutes to ensure that the air in the two sealed boxes is completely replaced by argon gas;

[0016] Step 4: Assemble the plug to be welded pre-placed in the sealing box with the cladding tube, and ensure that the gap between the plug to be welded and the cladding tube mouth weld ring after assembly is less than 0.2 mm;

[0017] Step 5: Move the laser welding head so that the ring plug weld to be welded is located in the middle of the laser spot; adjust the height of the rotating platform and place the ring plug weld to be welded at a position where the laser beam defocus is 0 mm;

[0018] Step 6: Set the global power modulation laser control parameters: laser power 0.9 kW, scanning trajectory as a circle, scanning frequency as 100 Hz, scanning amplitude as 0.4 mm;

[0019] Step 7: Change the laser power modulation mode to adjust the 36 phase points of the global power laser within a circular scanning cycle of the galvanometer laser;

[0020] Step 8: During laser welding, welding is performed along the forward direction of the weld using a gradient power mode with high power in the middle and low power on both sides within a circular scanning cycle.

[0021] Furthermore, before welding, acetone is used to carefully clean the zirconium alloy end plug, the inner and outer assembly areas of the cladding tube orifice, and the area within 20-30 mm of the tube wall from the tube orifice to remove surface dirt, oil and other impurities, and then left to air for more than 30 minutes to allow the acetone to completely evaporate.

[0022] Furthermore, before welding, a welding rotating platform and a gas sealing box are placed under the laser welding head.

[0023] Furthermore, the purity of the argon gas introduced in step 3 is 99.999%, the pressure is 0.14-0.16Mpa, and the gas flow rate is 10-15L / min.

[0024] Furthermore, when the lower end plug is welded to the cladding tube, the laser welding head is fixed and the rotating platform rotates clockwise at a speed of 10 r / min, i.e., 6 s / r;

[0025] The lower end plug ring weld is welded for 4 / 3r, that is, when the welding is 8s, the laser output is stopped, the welding rotating platform stops rotating, and the argon gas sealing box continues to be ventilated.

[0026] Furthermore, when the upper end plug is welded to the cladding tube, the laser welding head is fixed and the rotating platform rotates clockwise at a speed of 10 r / min, i.e., 6 s / r;

[0027] The upper plug ring weld was welded for 4 / 3r, that is, the laser output was stopped after 8s of welding, the welding rotating platform stopped rotating, the argon sealing box continued to ventilate for more than 30s, and the ventilation was stopped after the weld cooled to room temperature.

[0028] Another object of the present invention is to provide a fuel rod based on the method, wherein the upper end plug and the lower end plug are interference fit with the cladding tube, respectively assembled at both ends of the cladding tube, and sealed by a girth weld;

[0029] A first cushion block, a core block, a second cushion block, a spring, a third cushion block and a spring are sequentially arranged inside the cladding tube from the upper end to the lower end.

[0030] Furthermore, the upper end plug, the lower end plug and the cladding tube are made of zirconium alloy.

[0031] Another object of the present invention is to provide a zirconium alloy fuel rod laser welding rotating platform and argon atmosphere welding protection device based on the method, including a welding rotating platform, an upper end plug side atmosphere box and a lower end plug side atmosphere box;

[0032] The welding rotating platform is used to clamp and rotate the fuel rod cladding tube;

[0033] The upper end plug side atmosphere box and the lower end plug side atmosphere box are used to protect the upper and lower end plug ring welds to prevent the weld metal from chemically reacting with gases such as hydrogen, oxygen and nitrogen in the air during welding.

[0034] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0035] First, the purpose of the present invention is to provide a new power modulation galvanometer laser welding method for zirconium alloy fuel rods, which realizes the laser welding of zirconium alloy nuclear fuel rods; and optimizes the laser welding process, reduces the welding process, and improves the welding efficiency;

[0036] The designed welding protection device effectively protects the fuel rod end plug and cladding tube welding area, prevents the girth weld from contacting with oxygen, nitrogen and other gases in the air, and reduces the oxidation color next to the weld;

[0037] The problem of weld porosity defects is solved by power modulation galvanometer laser. In addition, power modulation reduces the energy distribution on both sides of the weld, reduces the tendency of weld undercut, and makes the weld more beautiful.

[0038] The newly designed upper end plug has the same shape and size as the lower end plug. Compared with the general upper end plug, the through hole on the top of the upper end plug is eliminated.

[0039] Compared with the existing TIG welding method, the traditional plugging welding process is eliminated, and the three welding production processes are reduced to two, which optimizes the welding process. At the same time, the rotation speed during fuel rod welding is increased, and the welding efficiency is improved. In addition, the problem of heavy oxidation color near the end plug and the cladding tube ring weld during TIG welding is alleviated, making the weld more beautiful; the weld porosity defect is improved, and the welding quality is improved.

[0040] Second, the expected benefits and commercial value of the technical solution of the present invention after transformation are as follows: the technical solution of the present invention will significantly save production costs after transformation. First, the welding process is reduced, the plugging welding process is eliminated, and the welding efficiency is improved; in addition, the repeated vacuuming and venting steps in traditional TIG welding are avoided, saving time costs, and at the same time, there is no need to use vacuum equipment, reducing equipment procurement and maintenance costs; the oxidation color next to the weld is reduced, making the weld more beautiful;

[0041] The technical solution of the present invention solves the technical problem that people have been eager to solve but have never succeeded in solving: it realizes the laser welding process of zirconium alloy nuclear fuel rods, improves the welding quality and efficiency, makes certain progress in the field of nuclear fuel rod laser welding technology, and narrows the gap with the international advanced level;

[0042] The welding efficiency is improved, the oxidation color beside the weld is reduced, the weld porosity defect problem is improved, and the welding quality of the end plug ring weld is improved.

[0043] Third, the main parameters of the present invention include laser power setting, scanning frequency, scanning trajectory and gas protection setting. Specifically, the average laser power is 3kW, the maximum power is 4kW, the minimum power is 2kW, the power gradient is 50%, the welding scanning trajectory is circular, and the scanning frequency is set to 100Hz. The protective gas uses 99.99% pure argon gas with a flow rate of 10L / min. These parameter designs are based on the thermophysical properties of the welding material and the power regulation requirements, which can effectively control the heat input and achieve stable welding of dissimilar metals such as aluminum alloy and stainless steel.

[0044] The present invention solves the main problems existing in the prior art of welding dissimilar metals. Due to insufficient control of the welding process, the traditional welding method is prone to defects such as weld element segregation, uneven microstructure, weld undercut, pores, cracks, etc. The present invention adopts a galvanometer laser combined with a gradient power mode, and the power is regulated with high power in the middle and low power on both sides along the scanning trajectory. By regulating the energy distribution of the weld, the energy of the weld edge is reduced, the weld undercut is avoided, and the generation of defects such as weld pores and cracks is significantly improved.

[0045] By introducing global power modulation and laser galvanometer control technology, the present invention realizes precise control of laser power during welding, significantly improving the quality of weld formation. Due to the uniform distribution of laser energy on the entire weld surface, the occurrence of undercut and microcracks on the weld edge is effectively suppressed, and the weld joint has good density and uniformity. At the same time, the use of argon gas to protect the molten pool further ensures that the welding area is not oxidized, improving the fatigue resistance and corrosion resistance of the weld. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1It is a flow chart of a power modulated galvanometer laser welding method for zirconium alloy fuel rods provided in an embodiment of the present invention;

[0047] Figure 2 is a diagram of a fuel rod assembly structure provided by an embodiment of the present invention;

[0048] Figure 3 The power modulation mode and heat source distribution diagram provided by the embodiment of the present invention; (a) phase point energy distribution and scanning form of gradient power mode; (b) gradient power heat source distribution diagram;

[0049] Figure 4 (a) a surface morphology diagram of the lower end plug ring weld and (b) a microstructure diagram provided by an embodiment of the present invention;

[0050] Figure 5 (a) a surface morphology image of a sample after corrosion and (b) a morphology image under a scanning electron microscope provided by an embodiment of the present invention;

[0051] Figure 2 Middle: 1. Upper end plug; 2. First gasket; 3. Core block; 4. Second gasket; 5. Third gasket; 6. Spring; 7. Lower end plug; 8. Upper end plug ring weld; 9. Cladding tube; 10. Lower end plug ring weld. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] like Figure 1 As shown, a power modulated galvanometer laser welding method for zirconium alloy fuel rods provided in an embodiment of the present invention comprises the following steps:

[0054] Step 1: Use acetone to carefully clean the zirconium alloy end plug, the inner and outer assembly areas of the cladding tube orifice, and the area within 20 mm to 30 mm of the tube wall from the tube orifice to remove surface dirt, oil and other impurities, and then leave it in the air for more than 30 minutes to allow the acetone to completely evaporate;

[0055] Step 2, placing the welding rotating platform and the gas sealing box under the laser welding head;

[0056] Step 3, clamp the middle part of the cladding tube on the three-jaw chuck of the middle rotating shaft of the rotating platform, and place the lower end plug welding area in the atmosphere box on the lower end plug side through the middle through hole of the rotating shaft and the rubber sealing ring on the atmosphere box on the lower end plug side;

[0057] Step 4, after loading the core block, spring and other materials into the cladding tube from the other end of the cladding tube, the upper plug side cladding tube is placed in the upper plug side atmosphere box through the rubber sealing ring on the upper plug side atmosphere box;

[0058] Step 5, introduce argon gas with a purity of 99.999% and a pressure of 0.14-0.16Mpa into the atmosphere box on the lower end plug side, and set the gas flow rate to 10-15L / min. The high-pressure argon gas enters the atmosphere box on the lower end plug side through the cladding tube connecting the two atmosphere boxes, and continues to ventilate for more than 5 minutes to ensure that the air in the two sealed boxes is completely replaced by argon gas;

[0059] Step 6, assemble the lower end plug pre-placed in the sealing box on the lower end plug side with the cladding tube, and ensure that the gap between the weld seam of the lower end plug and the cladding tube orifice to be welded is less than 0.2 mm after assembly;

[0060] Step 7, move the laser welding head so that the ring weld to be welded is located in the middle of the laser spot;

[0061] Step 8, adjust the height of the rotating platform and place the weld of the lower plug ring to be welded at a position where the laser beam defocus amount is 0 mm;

[0062] Step 9, set the global power modulation laser control parameters: laser power 0.9 kW, set the scanning trajectory to a circle, the scanning frequency to 100 Hz, and the scanning amplitude to 0.4 mm;

[0063] Step 10, changing the laser power modulation mode, and regulating 36 phase points of the global power laser within a circular scanning cycle of the galvanometer laser;

[0064] Step 11, during laser welding, welding is performed in a gradient power mode with high power in the middle and low power on both sides along the forward direction of the weld in a circular scanning cycle;

[0065] Step 12: During welding, the laser welding head is fixed and the rotating platform rotates clockwise at a speed of 10 r / min, i.e., 6 s / r;

[0066] Step 13, welding the lower end plug ring weld for 4 / 3r, that is, stopping the laser output after welding for 8s, stopping the welding rotating platform from rotating, and continuing to ventilate the argon gas sealing box;

[0067] Step 14, assembling the upper end plug pre-placed in the sealing box on the upper end plug side with the cladding tube, ensuring that the gap between the weld seam of the upper end plug and the cladding tube orifice to be welded is less than 0.2 mm after assembly;

[0068] Step 15, moving the laser welding head so that the ring weld to be welded is located in the middle of the laser spot;

[0069] Step 16, welding the upper end plug ring weld using the same welding parameters as the lower end plug ring weld;

[0070] Step 17, welding the upper plug ring weld for 4 / 3r, that is, stop the laser output after 8s of welding, stop the rotation of the welding rotating platform, continue to ventilate the argon gas sealing box for more than 30s, and stop ventilating after the weld cools to room temperature.

[0071] The power-modulated galvanometer laser welding method for zirconium alloy fuel rods provided by the present invention combines the global power modulation of the galvanometer laser with atmosphere sealing welding to ensure welding quality and structural stability. During the welding process, the assembly area of ​​the zirconium alloy end plug and the cladding tube is first cleaned with acetone to remove oil and impurities to ensure a clean welding surface. After cleaning, the fuel rods are assembled on the welding rotating platform and the atmosphere sealing box to ensure that the welding area is protected by high-purity argon gas to achieve oxidation-free welding. The continuous introduction of high-pressure argon gas further ensures that the air in the atmosphere box is completely replaced, and the welding process is always under the protection of inert gas to prevent oxidation and improve welding strength.

[0072] During the laser welding process, the laser beam performs a circular scan along the circumferential weld to be welded. The laser power is precisely controlled at 36 phase points within the scanning trajectory, using a gradient power mode with high power in the middle and low power on both sides. This power modulation mode allows the center of the weld to obtain a higher heat input, ensuring the depth of the molten pool and the uniformity of the weld, while reducing the heat input at the edge and the occurrence of weld undercut. During welding, the laser head is fixed and the rotating platform rotates clockwise, so that the circumferential weld to be welded moves synchronously with the laser beam, thereby achieving a uniform welding effect.

[0073] This method uses a combination of a rotating platform and galvanometer laser scanning to produce precisely controlled heat input and molten pool stirring effects. Circular scanning enhances the fluidity of the liquid metal in the molten pool, allowing the gas in the molten pool to escape, effectively preventing the formation of porosity defects. The power modulation mode used in the welding process not only evenly distributes the energy on the surface of the molten pool, but also avoids local overheating of the weld, ensuring the composition uniformity and structural density of the weld joint.

[0074] After welding is completed, argon gas is continuously introduced to cool the weld to room temperature to prevent oxidation of the weld and reduce residual stress in the weld area. This design effectively improves the fatigue resistance and corrosion resistance of the weld and is suitable for high-end manufacturing applications where material stability and structural strength are strictly required. The welding method of the present invention not only ensures the consistency of weld quality, but also improves the stability and service life of zirconium alloy fuel rods in high temperature and high pressure environments.

[0075] The embodiment of the present invention provides a zirconium alloy fuel rod laser welding rotating platform and argon atmosphere welding protection device based on the method, including a welding rotating platform, an upper end plug side atmosphere box and a lower end plug side atmosphere box;

[0076] The welding rotating platform is used to clamp and rotate the fuel rod cladding tube;

[0077] The upper end plug side atmosphere box and the lower end plug side atmosphere box are used to protect the upper and lower end plug ring welds to prevent the weld metal from chemically reacting with gases such as hydrogen, oxygen and nitrogen in the air during welding.

[0078] The specific application field of the present invention is the field of nuclear technology, and the specific products are zirconium alloy nuclear fuel rod end plugs and cladding tube welding. In addition, products involving zirconium alloy component welding in the fields of nuclear industry, medical treatment, chemical industry, etc. can also be welded using this technical solution, such as nuclear reactor control rods, guide tubes and other components; chemical pipelines, valves and storage tanks, etc.

[0079] Figure 2 The fuel rod assembly structure diagram shows that the fuel rod is mainly composed of an upper end plug 1, a lower end plug 7, a cladding tube 9, a pellet 3, a spring 6, a first cushion block 2, a second cushion block 4 and a third cushion block 5. The upper end plug 1, the lower end plug 7 and the cladding tube 9 are made of zirconium alloy. The upper and lower end plugs are interference fit with the cladding tube. They are respectively assembled at both ends of the cladding tube and sealed by a girth weld. The upper end plug girth weld 8 is between the upper end plug 1 and the cladding tube 9, and the lower end plug girth weld 10 is between the lower end plug 7 and the cladding tube 9.

[0080] Figure 3 This is the power modulation mode and heat source distribution diagram. During power modulation galvanometer laser welding, the laser beam adopts a circular scanning trajectory to weld along the ring weld. By adjusting the power of 36 phase points in the circular scanning trajectory, a gradient power mode with high power in the middle and low power on both sides is adopted for welding. The rotating laser beam stirs the molten pool to intensify the flow of the molten pool and promote gas escape. At the same time, in the power modulation mode, the energy distribution on the entire molten pool surface is more uniform, the power at the edge of the molten pool is reduced, the degree of weld undercut is reduced, and the weld surface formation is more uniform.

[0081] Figure 4 This is the surface morphology of the lower ring weld after the lower end plug and the cladding tube are welded. Figure 4 It can be seen that the surface of the girth weld is smooth and flat, there is no undercut, the weld has a silvery white metallic luster, and the cladding tube part next to the weld has a small amount of light yellow oxidation color, which has almost no effect on the weld performance and meets the oxidation color standard. The girth weld was inspected by an X-ray flaw detector. There was no unfused, pores and cracks larger than 0.25mm inside the girth weld of the lower end plug. The cross-section of the girth weld was sampled for metallographic observation. The end plug and the cladding tube were well combined, the microstructure was uniform, the effective weld depth reached more than 90% of the wall thickness, and there were no defects such as pores, cracks and inclusions, which met the welding technical requirements.

[0082] The lower end plug ring weld and the cross section of the lower end plug ring weld are sampled for corrosion test. A water corrosion test is carried out in an acidic aqueous solution at 360℃±10℃ for 72±2 hours. After the test, the corrosion degree of the weld surface is observed and compared with the corrosion degree of the end plug and cladding tube surface. Figure 5 The surface morphology of the sample after corrosion and the morphology under scanning electron microscope. Figure 5 It can be seen that the corrosion degree of the weld is similar to that of the end plug and cladding tube, and no excessive brown corrosion products appear on the surface, which can meet the corrosion resistance requirements of the nuclear fuel cladding tube welding structure.

[0083] The fuel rod assembly structure of the present invention is as follows Figure 2 As shown, it is mainly composed of an upper end plug (1), a lower end plug (7) and a cladding tube (9), all of which are made of zirconium alloy materials to improve their stability in high temperature and corrosive environments. The upper end plug (1) and the lower end plug (7) are respectively assembled at the two ends of the cladding tube (9), connected by interference fit, and sealed with a ring weld. There is an upper end plug ring weld (8) between the upper end plug (1) and the cladding tube (9), and there is a lower end plug ring weld (10) between the lower end plug (7) and the cladding tube (9) to ensure sealing and structural stability. During the welding process, the precise control of laser welding reduces the welding defects caused by traditional welding, thereby improving the overall structural strength and durability of the fuel rod.

[0084] like Figure 3 As shown, in the power modulated galvanometer laser welding process of the present invention, the laser beam performs circular scanning along the annular weld to form a uniform energy distribution. The laser power is precisely adjusted at 36 phase points within the circular scanning trajectory, and a gradient power mode with high power in the middle and gradually decreasing power on both sides is adopted, so that the central area of ​​the weld obtains a higher heat input, while the heat input of the edge area is relatively low. This design reduces the weld edge biting phenomenon caused by overheating of the edge, thereby making the edge of the weld smoother and more uniform, and improving the welding quality and aesthetics.

[0085] During the welding process, the rotating laser beam produces a strong stirring effect in the molten pool. As the laser beam rotates, the liquid metal in the molten pool is constantly stirred, avoiding local overheating and increasing the convection effect in the molten pool. This stirring effect can promote the gas generated during the welding process to escape as quickly as possible, avoid bubbles solidifying in the molten pool, reduce the formation of porosity defects in the weld, and improve the density and strength of the weld. This process is especially important for dissimilar metal welding because it can reduce intermetallic stress while increasing the density of the weld.

[0086] In addition, the power modulation mode also makes the temperature distribution on the surface of the molten pool more uniform, avoiding the thermal stress concentration caused by excessive temperature gradient. The gradient mode of power regulation not only makes the weld structure denser, but also forms an ideal composition transition in the fusion area between metals, reducing the material migration phenomenon in the dissimilar metal weld joint. This uniform temperature control reduces the deformation force on the weld during the cooling and shrinking process, reduces the cracks that appear after welding, and improves the long-term stability of the weld joint.

[0087] The power-modulated laser welding method is particularly suitable for annular welds of slender structural parts (such as fuel rods). It not only controls the distribution of laser power, but also ensures the uniformity of the weld surface morphology and internal structure. In practical applications, this welding process can meet the welding needs of parts with complex shapes and improve production efficiency. In addition, the process parameters of power-modulated laser welding can be flexibly adjusted according to the welding requirements of different parts and materials, and have extremely high industrial application value, especially in the manufacture of precision parts.

[0088] The following are two specific embodiments of the power-modulated galvanometer laser welding method for zirconium alloy fuel rods:

[0089] Example 1: Zirconium alloy end plug welding for nuclear reactor fuel rods

[0090] In the manufacture of nuclear reactor fuel rods, zirconium alloy cladding tubes need to be welded to end plugs and maintain good air tightness and mechanical strength to ensure the safety of fuel rods in high temperature and high pressure environments. Traditional welding methods are prone to defects in the welds, affecting the overall performance of the fuel rods. This embodiment uses power modulated galvanometer laser welding to improve welding quality and efficiency.

[0091] 1. Preparation:

[0092] Use acetone to clean the assembly area of ​​the zirconium alloy cladding tube and the end plug, including the 25mm range inside and outside the tube mouth, to remove surface impurities and oil stains. After cleaning, let it air-dry for 30 minutes to allow the acetone to evaporate completely.

[0093] 2. Welding assembly:

[0094] The zirconium alloy cladding tube is clamped on the three-jaw chuck of the rotating platform so that the middle part of the cladding tube is located on the rotating axis of the rotating platform.

[0095] Install the core block, spring and spacer block from the other end of the cladding tube in sequence. Place the upper and lower end plugs in the atmosphere box respectively, and ensure airtightness through the sealing ring.

[0096] 3. Gas replacement:

[0097] Introduce argon gas into the atmosphere box at the lower end and continue ventilating for 5 minutes to remove the air, ensuring that the upper and lower sealed boxes are filled with high-purity argon gas to avoid oxidation during welding.

[0098] 4. Precision assembly and welding parameter setting:

[0099] Adjust the gap between the cladding tube and the plug to be welded so that the gap between the welds to be welded is kept within 0.2mm. Move the laser welding head so that the weld is located at the center of the laser spot, and adjust the height of the rotating platform so that the laser defocus is 0mm.

[0100] Set the laser parameters: laser power is 0.9 kW, scanning trajectory is circular, scanning frequency is 100 Hz, and scanning amplitude is 0.4 mm.

[0101] 5. Power modulation and welding:

[0102] The laser power modulation mode is set to a gradient mode of "high in the middle and low on both sides" to regulate the 36 phase points of the laser within the circular scanning period of the galvanometer.

[0103] Welding is performed in the forward direction of the weld, and circular galvanometer scanning and power modulation are used to achieve high-quality circumferential welds.

[0104] Result analysis: Through power-modulated galvanometer laser welding, the weld is formed evenly, and the air tightness and strength meet the requirements of nuclear fuel rods. The welding efficiency is increased by about 30%, and the pores and cracks in the welding process are significantly reduced. It has been successfully applied to the manufacture of reactor fuel rods.

[0105] Example 2: Welding of zirconium alloy fuel rods for nuclear power plant spare fuel assemblies

[0106] Nuclear power plants need spare fuel assemblies in daily operation, and the welding of spare fuel assemblies needs to ensure extremely high stability and safety. This embodiment uses power modulated galvanometer laser welding technology to weld the end plugs of zirconium alloy fuel rods.

[0107] 1. Cleaning and preparation:

[0108] Use acetone to clean the zirconium alloy fuel rod end plugs and cladding tubes, especially the welding area and the area 22 mm from the tube wall to the tube mouth, to remove surface oil and impurities. After leaving it in the air for 30 minutes, ensure that the cleaning agent is completely volatilized.

[0109] 2. Assembly positioning:

[0110] Fix the cladding tube on the rotating platform and fix it with a three-jaw chuck so that the axis of the cladding tube coincides with the rotating axis.

[0111] The upper and lower end plug areas are placed in a sealed atmosphere box respectively through rubber sealing rings, and the core block, spring and cushion block are loaded from the upper end of the cladding tube to ensure that the upper and lower end plugs to be welded are tightly matched with the cladding tube.

[0112] 3. Argon replacement:

[0113] High-purity argon is introduced for more than 5 minutes to ensure that the oxygen in the sealed box is completely replaced. The flow rate and pressure are strictly controlled during the argon replacement process to ensure that there is no oxidation reaction during welding.

[0114] 4. Welding parameter setting:

[0115] Move the laser welding head so that the annular weld is located in the center of the laser spot, and adjust the height of the rotating platform to ensure that the laser defocus is 0 mm.

[0116] The power modulation laser control parameters were set as follows: power was 0.9 kW, galvanometer scanning frequency was 100 Hz, scanning amplitude was 0.4 mm, and the scanning trajectory was set to a circle.

[0117] 5. Laser power modulation and welding:

[0118] The laser power is modulated in a gradient mode of "high in the middle and low on both sides", and the power of 36 phase points is regulated.

[0119] During laser welding, as the rotating platform moves, the laser forms a circular galvanometer scan at the weld to ensure uniform weld formation and no welding defects.

[0120] Result analysis: This welding process shows excellent weld forming effect in the welding of fuel rod end plugs, and the weld strength and airtightness meet the requirements of nuclear power plant spare fuel assemblies. The welding efficiency is increased by 25% compared with conventional laser welding, which reduces the occurrence of welding defects and ensures the safety and reliability of fuel rods.

[0121] These two examples demonstrate the effect of applying the power modulation galvanometer laser welding method of zirconium alloy fuel rods in different nuclear power needs. Through power modulation technology and galvanometer scanning, not only the welding efficiency is improved, but also the welding quality is ensured, so that the fuel rods meet the high safety and stability requirements.

[0122] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A power modulated galvanometer laser welding method for zirconium alloy fuel rods, characterized in that: The following steps are involved: Step 1: Clamp the middle part of the cladding tube on the three-jaw chuck of the middle rotating shaft of the rotating platform, and place the lower end plug welding area in the atmosphere box on the lower end plug side through the middle through hole of the rotating shaft and the rubber sealing ring on the atmosphere box on the lower end plug side; Step 2: After the core block, spring and spacer are installed into the cladding tube from the other end of the cladding tube, the cladding tube on the upper end plug side is placed in the atmosphere box on the upper end plug side through the rubber sealing ring on the atmosphere box on the upper end plug side; Step 3: introduce argon gas into the atmosphere box on the lower plug side, and the high-pressure argon gas enters the atmosphere box on the upper plug side through the cladding tube connecting the two atmosphere boxes, and continues to ventilate for more than 5 minutes to ensure that the air in the two sealed boxes is completely replaced by argon gas; Step 4: Assemble the plug to be welded pre-placed in the sealing box with the cladding tube, and ensure that the gap between the plug to be welded and the cladding tube mouth weld ring after assembly is less than 0.2 mm; Step 5: Move the laser welding head so that the ring plug weld to be welded is located in the middle of the laser spot; adjust the height of the rotating platform and place the ring plug weld to be welded at a position where the laser beam defocus is 0 mm; Step 6: Set the global power modulation laser control parameters: laser power 0.9 kW, scanning trajectory as a circle, scanning frequency as 100 Hz, scanning amplitude as 0.4 mm; Step 7: Change the laser power modulation mode to adjust the 36 phase points of the global power laser within a circular scanning cycle of the galvanometer laser; Step 8: During laser welding, welding is performed along the forward direction of the weld using a gradient power mode with high power in the middle and low power on both sides within a circular scanning cycle.

2. The power modulated galvanometer laser welding method for zirconium alloy fuel rods according to claim 1, characterized in that: Before welding, use acetone to carefully clean the zirconium alloy end plug, the inner and outer assembly areas of the cladding tube orifice, and the area within 20-30mm of the tube wall from the tube orifice to remove surface dirt, oil and impurities, and then leave it in the air for more than 30 minutes to allow the acetone to completely evaporate.

3. The power modulated galvanometer laser welding method for zirconium alloy fuel rods according to claim 1, characterized in that: Before welding, the welding rotating platform and the gas sealing box are placed under the laser welding head.

4. The power modulated galvanometer laser welding method for zirconium alloy fuel rods according to claim 1, characterized in that: The purity of the argon gas introduced in step 3 is 99.999%, the pressure is 0.14-0.16Mpa, and the gas flow rate is 10-15L / min.

5. The power modulated galvanometer laser welding method for zirconium alloy fuel rods according to claim 1, characterized in that: When the lower end plug is welded to the cladding tube, the laser welding head is fixed and the rotating platform rotates clockwise at a speed of 10r / min, i.e. 6s / r; The lower end plug ring weld is welded for 4 / 3r, that is, when the welding is 8s, the laser output is stopped, the welding rotating platform stops rotating, and the argon gas sealing box continues to be ventilated.

6. The power modulated galvanometer laser welding method for zirconium alloy fuel rods according to claim 1, characterized in that: When the upper end plug is welded to the cladding tube, the laser welding head is fixed and the rotating platform rotates clockwise at a speed of 10r / min, i.e. 6s / r; The upper plug ring weld was welded for 4 / 3r, that is, the laser output was stopped after 8s of welding, the welding rotating platform stopped rotating, the argon sealing box continued to ventilate for more than 30s, and the ventilation was stopped after the weld cooled to room temperature.

7. A fuel rod according to the method according to any one of claims 1 to 6, characterized in that: The upper end plug, the lower end plug and the cladding tube are interference fit, and are respectively assembled at both ends of the cladding tube and sealed by a girth weld; A first cushion block, a core block, a second cushion block, a spring, a third cushion block and a spring are sequentially arranged inside the cladding tube from the upper end to the lower end.

8. The fuel rod according to claim 7, characterized in that The upper end plug, lower end plug and cladding tube are made of zirconium alloy.

9. A zirconium alloy fuel rod laser welding rotating platform and argon atmosphere welding protection device based on the method according to any one of claims 1 to 6, characterized in that: It includes a welding rotating platform, an upper plug side atmosphere box and a lower plug side atmosphere box; The welding rotating platform is used to clamp and rotate the fuel rod cladding tube; The upper end plug side atmosphere box and the lower end plug side atmosphere box are used to prevent the weld metal from chemically reacting with hydrogen, oxygen and nitrogen in the air when welding the upper and lower end plug ring welds.

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