Zirconium alloy fuel rod end plug composite welding method and zirconium alloy fuel rod

Abstract

A zirconium alloy fuel rod end plug composite welding method and a zirconium alloy fuel rod, belonging to the field of welding. The zirconium alloy fuel rod end plug composite welding method includes the following steps: splicing the zirconium alloy end plug and the zirconium alloy fuel rod cladding together and fixing them, evacuating the zirconium alloy end plug and providing an inert gas environment; first performing TIG welding on the zirconium alloy end plug and the zirconium alloy fuel rod cladding, while simultaneously providing ultrasonic stirring and electromagnetic stirring; then performing TIG welding on the gas filling holes of the zirconium alloy end plug, while simultaneously providing ultrasonic stirring and electromagnetic stirring; and after welding, polishing and quality inspection of the weld area. This method can effectively eliminate pores in the zirconium alloy weld area, promote uniform distribution of microstructure and composition, and improve weld quality and the corrosion resistance of the weld area.

Description

Technical Field

[0001] The invention belongs to the field of welding, and in particular relates to a zirconium alloy fuel rod end plug composite welding method and a zirconium alloy fuel rod. Background Art

[0002] Zirconium alloys are currently widely used as a structural material for fuel rods in commercial pressurized water reactor nuclear power plants due to their low thermal neutron absorption cross-section, excellent corrosion resistance, high thermal strength, and superior weldability. Fuel rods consist of a tubular fuel rod cladding and end plugs at each end. The end plugs are welded to the fuel rod cladding to securely enclose the fuel pellets. In addition to the welds connecting them to the fuel rod cladding, the end plugs are also equipped with gas injection holes for filling the fuel rods with helium. These holes also need to be plugged after gas injection. Because fuel rods must operate for long periods of time in primary cooling water under high temperature, high pressure, and irradiation, the quality of end plug welding significantly impacts reactor safety. Due to limitations in fuel rod manufacturing processes, end plug welding cannot be performed under vacuum conditions. This results in defects such as pores forming in the zirconium alloy weld structure, significantly negatively impacting weld quality and the corrosion resistance of the welded area. Therefore, providing a zirconium alloy end plug welding method that improves weld quality is of great significance for enhancing reactor fuel safety. Summary of the Invention

[0003] The present invention aims to provide a zirconium alloy fuel rod end plug composite welding method to improve the end plug welding quality. The present invention also provides a zirconium alloy fuel rod.

[0004] According to an embodiment of one aspect of the present invention, a composite welding method for a zirconium alloy fuel rod end plug is provided, wherein the composition of the zirconium alloy fuel rod end plug comprises, by weight, 1.0%-1.5% Sn, 0.18%-0.24% Fe, 0.07%-0.13% Cr, 0.09%-0.16% O, 0.007%-0.012% Si, and the balance is Zr and unavoidable impurities, wherein 0.25% <Fe+Cr<0.37%;

[0005] The method comprises the following steps:

[0006] Step a): providing a zirconium alloy fuel rod cladding, splicing the zirconium alloy fuel rod end plug and the zirconium alloy fuel rod cladding together and fixing them with a clamp, performing exhaust treatment in a vacuum environment, and then providing an inert gas environment;

[0007] Step b): performing TIG welding on the connection position between the zirconium alloy fuel rod cladding and the zirconium alloy fuel rod end plug, and simultaneously providing ultrasonic stirring and electromagnetic stirring to the welding molten pool;

[0008] Step c): performing TIG welding to plug the gas filling hole of the zirconium alloy fuel rod end plug, and simultaneously providing ultrasonic stirring and electromagnetic stirring to the welding molten pool;

[0009] Step d): Grind and quality check the welding area.

[0010] The zirconium alloy used for the end plug rods uses a higher content of Sn, which can reduce the sensitivity of impurities introduced during the cladding-end plug welding process and offset the harmful effects of impurities such as N, C, and Al on the corrosion resistance. At the same time, appropriate contents of Fe and Cr are used. The additional vacancy concentration generated during the pinning welding temperature rise process reduces the exchange of oxygen ions and vacancies during the corrosion process, thereby slowing down the exchange rate and improving the corrosion resistance of the weld. Since the zirconium alloy fuel rod end plug welding process cannot be carried out in a vacuum, it is inevitable that defects such as bubbles will appear in the weld structure using conventional welding methods. However, the present invention has found that when ultrasonic stirring is used to assist welding while gas shielded welding, the cavitation effect is limited to the surface of the molten pool and is insufficient to eliminate pores deep in the zirconium alloy molten pool; when only electromagnetic stirring is used to assist welding, the Lorentz force has a low efficiency in migrating micron-level pores, and large pores are easily formed; using ultrasonic stirring and electromagnetic stirring to assist welding at the same time can effectively eliminate pores and improve welding quality.

[0011] Furthermore, in some embodiments, in step b) and step c), the welding current is controlled to be 50A-60A after the TIG welding arc is started.

[0012] Furthermore, in some embodiments, in step b) and step c), after the TIG welding arc is started, the ultrasonic vibration frequency is set to 30kHz-50kHz, and the amplitude is 15μm; the electromagnetic stirring magnetic field intensity is set to 1mT-10mT, and the frequency is 20Hz-80Hz.

[0013] Furthermore, in some embodiments, in step b) and step c), the current in the arc ending stage of TIG welding is reduced at a rate of 4.5 A / s-5.5 A / s, while the ultrasonic amplitude and electromagnetic field intensity are gradually reduced.

[0014] Furthermore, in some embodiments, in step b) and step c), during the TIG welding process, a two-color infrared thermometer and a PID controller are used to perform closed-loop control on the welding process.

[0015] Furthermore, in some embodiments, in step b) and step c), during the TIG welding process, when the molten pool flow rate is lower than 0.3 m / s, the magnetic field intensity of the electromagnetic stirring is increased.

[0016] Furthermore, in some embodiments, in step a), the inert gas environment is a helium environment of 0.5 MPa-1 MPa, wherein the helium concentration is not less than 99.99%.

[0017] Furthermore, in some embodiments, the composition of the fuel rod cladding includes, by weight, 0.1%-0.5% Nb, 0.3%-0.9% Sn, 0.2%-0.4% Fe, 0.01%-0.3% Cr, 0.09%-0.16% O, and at least one of 0.015%-0.03% Si, 0.01%-0.2% V, and 0.01%-0.06% Ge, with the balance being Zr and unavoidable impurities.

[0018] The cladding material itself should have good corrosion resistance.

[0019] Furthermore, in some embodiments, the inner diameter of the fuel rod cladding is 4 mm-15 mm, the outer diameter of the portion of the fuel rod end plug inserted into the fuel rod cladding is 3.5 mm-15 mm, and the fitting clearance is 0-0.5 mm.

[0020] According to another embodiment of the present invention, there is provided a zirconium alloy fuel rod, comprising a fuel rod cladding and an end plug, which are welded using the zirconium alloy fuel rod end plug composite welding method provided in any of the aforementioned embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a microstructure photograph of the zirconium alloy end plug hole blocking welding area in one embodiment;

[0022] Figure 2 Element distribution diagram of the welding area of ​​zirconium alloy end plugging welding in one embodiment;

[0023] Figure 3 A pair of proportional photos of the zirconium alloy end plugging welding area tissue;

[0024] Figure 4 This is a curve of an embodiment and a proportional corrosion weight gain test;

[0025] Figure 5 This is a photo of a zirconium alloy fuel rod sample in one embodiment.

[0026] 1-air hole; 2-end plug; 3-weld; 4-fuel rod cladding.

[0027] The purpose of the above drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the present invention, and is not intended to limit the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below through specific embodiments with reference to the accompanying drawings.

[0029] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment herein. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor does it limit mutually exclusive independent or alternative embodiments. Those skilled in the art will appreciate that an embodiment herein may be combined with other embodiments as long as no structural conflicts arise.

[0030] In the description herein, "a plurality of" means at least two.

[0031] Pressurized water reactors (PWRs) rely on a chain fission reaction within the uranium oxide fuel pellets in the fuel assembly to generate heat. The primary coolant in the steam generator transfers this heat to the secondary cooling water, generating steam that drives the turbine to produce power. During this process, the fuel rods must be exposed to a high-temperature, high-pressure liquid environment for extended periods, maintaining stable strength and structural integrity to effectively contain the fuel pellets and prevent fission products from leaking into the primary coolant. Therefore, the reliability of the fuel rod cladding is crucial to PWR safety. Zirconium alloys are currently the most commonly used fuel rod cladding material due to their low thermal neutron absorption cross-section, excellent corrosion resistance, and excellent high-temperature mechanical and weldability. During the fuel rod manufacturing process, welding is performed to seal the fuel pellets within the fuel rods. The tubular fuel rod cladding is girth-welded to the upper and lower end plugs. The upper end plug is also equipped with a gas injection port for injecting helium into the fuel rods before closure. The gas injection port is then sealed with a plugging weld. During the welding process, if coarse grains appear in the welding area, the corrosion resistance of the zirconium alloy will be seriously affected; on the other hand, Figure 3 As shown, since welding needs to be performed in a helium atmosphere, direct TIG welding of the zirconium alloy fuel rods is likely to cause pores 1 in the weld structure, affecting the welding quality.

[0032] In order to overcome the above problems, an embodiment of one aspect of the present invention provides a zirconium alloy end plug composite welding method, which can effectively improve the welding quality of the zirconium alloy fuel rod weld structure, avoid defects such as pores, and improve the corrosion resistance of the weld structure.

[0033] In a preferred embodiment, the zirconium alloy fuel rod end plug composite welding process is as follows:

[0034] A end plug is provided. The components of the end plug by weight percentage include: 1.0% - 1.5% of Sn, 0.18% - 0.24% of Fe, 0.07% - 0.13% of Cr, 0.09% - 0.16% of O, 0.007% - 0.012% of Si, and the balance is Zr and inevitable impurities, where 0.25% < Fe + Cr < 0.37%; after the end plug is formed, it is annealed at 550°C - 780°C for 1 h - 8 h to form a fully recrystallized structure, in which there are distributed Zr(Fe,Cr)₂ second phases with an average size of 100 nm - 230 nm. In a preferred embodiment, the components of the fuel rod cladding by weight percentage include: 0.1% - 0.5% of Nb, 0.3% - 0.9% of Sn, 0.2% - 0.4% of Fe, 0.01% - 0.3% of Cr, 0.09% - 0.16% of O, and at least one of 0.015% - 0.03% of Si, 0.01% - 0.2% of V, 0.01% - 0.06% of Ge, and the balance is Zr and inevitable impurities; after the fuel rod cladding is formed, it is annealed at 450°C - 600°C for 1 h - 8 h to form a partially recrystallized structure, in which there are distributed second phases with an average size of 50 nm - 180 nm. According to the different specific components, the types of the second phase particles include Zr(Fe,Nb,Cr)₂, Zr₂(Fe,Nb,Cr), and / or Zr(Fe,Nb,V)₂, Zr₂(Fe,Nb,V), and / or Zr(Fe,Nb,Cr,Ge)₂, Zr₂(Fe,Nb,Cr,Ge).

[0035] The fuel rod cladding and the end plug are cleaned and dried to remove surface oxides, oil stains, dust, etc. The fuel rod cladding and the end plug are spliced together so that the welding surfaces match each other, and a special fixture is used for fixation to prevent deformation or displacement during the welding process. Next, a vacuum pumping process is carried out in a sealed welding chamber to remove the air inside the fuel rod cladding, and then an inert gas is backfilled. In a preferred embodiment, helium with a purity of more than 99.99% and a pressure of 0.7 MPa is backfilled into the welding chamber. After the pressure stability is verified through a pressure stabilization test, subsequent welding operations are carried out.

[0036] Next, welding is performed. First, TIG welding is performed on the connection position between the fuel rod cladding and the end plug. After welding is completed, the air filling hole of the upper end plug is plugged by welding. Specifically, an arc starter specially designed for zirconium alloy fuel rod welding is used to start the arc, overcoming the difficulties of high ionization potential and high excitation potential of helium and ensuring stable arc ignition. After the TIG welding arc is started, the welding current is controlled at 50A-60A; after the arc is started, ultrasonic stirring and electromagnetic stirring are provided to the welding pool area at the same time. In a preferred embodiment, the ultrasonic vibration frequency is set to 30kHz-50kHz, the amplitude is 15μm; the electromagnetic stirring magnetic field strength is set to 1mT-10mT, and the frequency is 20Hz-80Hz. During the welding process, ultrasonic vibration can stir the molten pool, promote the full melting and flow of the metal, and more accurately control the energy input during the welding process; electromagnetic stirring can enhance the convection of the molten pool, transport the inclusions in the molten pool to the edge of the molten pool, effectively eliminate the weld porosity and improve the uniformity of element distribution in the welding area; further, the present invention has found that when ultrasonic stirring is used to assist welding while gas shielded welding, the cavitation effect is limited to the surface of the molten pool and is not enough to eliminate the pores deep in the zirconium alloy molten pool; when only electromagnetic stirring is used to assist welding, the Lorentz force has low efficiency in migrating micron-level pores, and large pores are easily formed; the simultaneous use of ultrasonic stirring and electromagnetic stirring to assist welding can effectively eliminate pores and improve welding quality.

[0037] In a preferred embodiment, a two-color infrared thermometer and a PID controller are used together to implement closed-loop control of the TIG welding process, dynamically adjusting arc length, helium flow rate, and welding speed to achieve precise control of welding parameters. In a further preferred embodiment, when the melt pool flow velocity is detected to be below 0.3 m / s, the magnetic field intensity of the electromagnetic stirring is increased to further refine the grains and promote the removal of bubbles in the melt pool.

[0038] During the arc closing stage, the welding current is reduced at a rate of 5 A / s, and the ultrasonic vibration amplitude and electromagnetic stirring magnetic field intensity are gradually reduced simultaneously to avoid the sudden cooling of the molten pool and the formation of microcracks in the weld.

[0039] After welding is completed, the weld area should be fully cooled for at least 20 seconds. The weld seam is then ground and any areas with excessive surface roughness are ground and trimmed. The quality of the girth weld and plugging weld is inspected through visual inspection, gauge inspection, X-ray testing, corrosion testing, and metallographic sampling.

[0040] In a preferred embodiment, when the welding operation is performed correctly, the macroscopic appearance of the fuel rod welding sample (not full length) is as follows: Figure 5 As shown, a uniform and defect-free weld 3 is formed between the end plug 2 and the fuel rod cladding 4. The plugging weld area in the end plug 2 is as shown in FIG. Figure 1As shown in the figure, the structure is uniform without defects such as pores, gaps, inclusions, etc. The element distribution in the welding area is as follows: Figure 2 As shown, it can be seen that the elements such as N, O, Fe, and Sn are evenly distributed without segregation, and no aggregation occurs at the welding interface.

[0041] The fuel rods provided by the embodiment of the present invention and the comparative example samples using ZIRLO alloy fuel rod cladding and Zr-4 alloy end plugs were placed in a steam environment at 427°C and 10.3 MPa for corrosion for 100 days. The weight gain curves of the samples are shown in FIG. Figure 4 It can be seen that the corrosion resistance of the embodiment is improved by 28.8% compared with the comparative example.

[0042] The hybrid welding method provided by the embodiments of the present invention utilizes the coupling effect of high-frequency ultrasonic stirring and electromagnetic stirring to focus the input energy more closely on the weld area, thereby increasing energy utilization efficiency, improving the dimensional accuracy and weld quality of both end plug ring welding and hole plugging welding, promoting the full flow of molten metal within the weld pool, effectively eliminating bubbles generated during welding, promoting the uniform distribution of elements within the weld area, and reducing post-weld defects such as porosity and cracks. It should be understood that during the welding process, the frequency and amplitude of the ultrasonic vibrations, as well as the magnetic field strength of the electromagnetic stirring, need to be reasonably limited; otherwise, deformation and damage to the material or deflection of the welding arc can occur, leading to welding defects.

[0043] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent replacement of the method steps involved, as well as combination of implementation methods in different embodiments without causing structural or principle conflicts, all fall within the scope of protection of the present invention.

Claims

1. A composite welding method for zirconium alloy fuel rod end plugs, characterized in that: The composition of the zirconium alloy fuel rod end plug includes, by weight, 1.0%-1.5% Sn, 0.18%-0.24% Fe, 0.07%-0.13% Cr, 0.09%-0.16% O, 0.007%-0.012% Si, and the balance is Zr and unavoidable impurities, of which 0.25% <Fe+Cr<0.37%; The zirconium alloy fuel rod end plug composite welding method comprises the following steps: Step a): Providing a zirconium alloy fuel rod cladding, wherein the composition of the fuel rod cladding comprises, by weight, 0.1%-0.5% Nb, 0.3%-0.9% Sn, 0.2%-0.4% Fe, 0.01%-0.3% Cr, 0.09%-0.16% O, and at least one of 0.015%-0.03% Si, 0.01%-0.2% V, and 0.01%-0.06% Ge, with the balance being Zr and unavoidable impurities; splicing the zirconium alloy fuel rod end plug and the zirconium alloy fuel rod cladding together and fixing them with a clamp, performing exhaust treatment in a vacuum environment, and then providing an inert gas environment; Step b): performing TIG welding on the connection position between the zirconium alloy fuel rod cladding and the zirconium alloy fuel rod end plug, and simultaneously providing ultrasonic stirring and electromagnetic stirring to the welding pool. After the TIG welding arc is started, the welding current is controlled to be 50A-60A; after the TIG welding arc is started, the ultrasonic vibration frequency is set to 30kHz-50kHz, and the amplitude is 15μm; the electromagnetic stirring magnetic field strength is set to 1mT-10mT, and the frequency is 20Hz-80Hz; Step c): TIG welding is performed on the gas filling holes of the zirconium alloy fuel rod end plugs, and ultrasonic stirring and electromagnetic stirring are simultaneously provided to the welding pool. After the TIG welding arc is started, the welding current is controlled to be 50A-60A; after the TIG welding arc is started, the ultrasonic vibration frequency is set to 30kHz-50kHz, and the amplitude is 15μm; the electromagnetic stirring magnetic field strength is set to 1mT-10mT, and the frequency is 20Hz-80Hz; Step d): Grind and quality check the welding area.

2. The zirconium alloy fuel rod end plug composite welding method according to claim 1, characterized in that: In the step b) and the step c), the current in the arc ending stage of TIG welding is reduced at a rate of 4.5 A / s to 5.5 A / s, while the ultrasonic amplitude and electromagnetic field intensity are gradually reduced.

3. The zirconium alloy fuel rod end plug composite welding method according to claim 1, characterized in that: In the step b) and the step c), during the TIG welding process, a two-color infrared thermometer and a PID controller are used to perform closed-loop control on the welding process.

4. The zirconium alloy fuel rod end plug composite welding method according to claim 3, characterized in that: In the step b) and the step c), during the TIG welding process, when the molten pool flow rate is lower than 0.3 m / s, the magnetic field intensity of the electromagnetic stirring is increased.

5. The zirconium alloy fuel rod end plug composite welding method according to claim 1, characterized in that: In step a), the inert gas environment is a helium environment of 0.5 MPa-1 MPa, wherein the helium concentration is not less than 99.99%.

6. The zirconium alloy fuel rod end plug composite welding method according to claim 1, characterized in that: The inner diameter of the fuel rod cladding is 4mm-15mm, the outer diameter of the portion of the fuel rod end plug inserted into the fuel rod cladding is 3.5mm-15mm, and the fitting clearance is 0-0.5mm.

7. A zirconium alloy fuel rod comprising a fuel rod cladding and an end plug, characterized in that: The fuel rod cladding and the end plug are welded by the zirconium alloy fuel rod end plug composite welding method according to any one of claims 1 to 6.

Images