Method for producing a zirconium alloy rod for a nuclear fuel assembly end plug

Abstract

The application discloses a preparation method of a zirconium alloy rod for a nuclear fuel assembly end plug, and comprises the following steps: first, a zirconium alloy forging rod is subjected to machining and lubrication, heated and kept warm, and then extruded, and after extrusion, the extruded rod blank is obtained by sequentially performing straightening and polishing treatment; second, the extruded rod blank is heated and kept warm again, and then subjected to multi-pass hot rolling, and after hot rolling, the hot-rolled rod blank is obtained by centerless peeling; third, the hot-rolled rod blank is subjected to multi-pass pilger two-roll cold rolling to obtain a cold-rolled rod blank; fourth, the cold-rolled rod blank is subjected to vacuum annealing treatment to obtain an annealed rod blank; and finally, the annealed rod blank is subjected to finishing treatment, which sequentially comprises straightening, centerless grinding and degreasing, so that the target product is obtained; and the key parameters such as temperature, holding time and deformation amount of each step are strictly controlled. The preparation method breaks through the key technology of long rod cold rolling, realizes large plastic deformation of the zirconium alloy rod, significantly reduces deformation passes and intermediate heat treatment, and thus breaks through the problems of non-uniform structure, low production efficiency and insufficient product precision and the like existing in the traditional process.

Description

Technical Field

[0001] This invention belongs to the field of zirconium alloy rod processing technology, specifically relating to a method for preparing zirconium alloy rods for nuclear fuel assembly end plugs. Background Technology

[0002] Zirconium alloys are widely used in nuclear reactor fuel elements, such as cladding materials and core structural materials, due to their small thermal neutron absorption cross section, high thermal conductivity, good mechanical properties, good processing performance, and good compatibility with UO2. They also have good corrosion resistance and sufficient thermal strength, especially in high-temperature water and high-temperature steam working environments.

[0003] Zirconium alloy rods are primarily used as end plugs for nuclear reactor fuel assemblies. The end plugs are typically welded to the cladding tubes to ensure a tight seal and prevent the release of radioactive materials into the main circuit during normal operation. The reliability of the assembly during reactor operation largely depends on the quality of the connection between the end plug and the cladding tubes; the performance of the end plug directly impacts the safety, reliability, and economics of the nuclear power plant. Therefore, developing a high-quality zirconium alloy rod manufacturing process that meets the requirements for high-burnup reactor types is of paramount importance.

[0004] Currently, most zirconium alloy bars are prepared using the traditional hot rolling-rotary forging process. Due to the fact that multi-pass hot rolling is prone to defects such as adhesion and folding, there is also the disadvantage of insufficient process controllability, which leads to uneven microstructure of the bar and thus affects the corrosion performance of the material. At the same time, rotary forging has low production efficiency due to the limitation of deformation per pass, and insufficient grain breakage leads to uneven microstructure, which in turn affects the reliability and economy of the components.

[0005] In view of this, the inventors propose a method for preparing zirconium alloy rods for nuclear fuel assembly end plugs to overcome the deficiencies of the prior art. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing zirconium alloy rods for nuclear fuel assembly end plugs. This method combines extrusion, hot rolling, Pilger two-roll cold rolling, vacuum annealing, and finishing. It also strictly controls the relevant parameters of each step (including temperature, holding time, deformation amount, etc.), combining the advantages of both hot and cold working. This method overcomes the key technology of cold rolling long billets, enabling large plastic deformation of zirconium alloy rods and significantly reducing the number of deformation passes and intermediate heat treatments. This overcomes the problems of uneven microstructure, low production efficiency, and poor product precision inherent in traditional processes.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing zirconium alloy rods for end plugs of nuclear fuel assemblies, the method comprising the following steps;

[0009] Step 1: After the zirconium alloy forging bar is machined until the surface is smooth and evenly coated with lubricant, it is heated and kept at a certain temperature and then extruded. After extrusion, it is straightened and polished in sequence to obtain the extruded bar billet.

[0010] Step 2: Heat and hold the extruded billet obtained in Step 1, then perform multi-pass continuous hot rolling. After hot rolling, remove the outer layer using a centerless milling machine to obtain a bright hot-rolled billet.

[0011] Step 3: The bright hot-rolled billet obtained in Step 2 is subjected to multi-pass continuous Pilger two-roll cold rolling to obtain a cold-rolled billet;

[0012] Step 4: Vacuum annealing is performed on the cold-rolled billet obtained in Step 3 to obtain an annealed billet;

[0013] Step 5: The annealed billet obtained in Step 4 is subjected to finishing treatment, which includes straightening, centerless grinding and degreasing, and finally the zirconium alloy finished bar is obtained.

[0014] Furthermore, in step one, when extruding the zirconium alloy forging rod, the heating temperature is set to 600℃~680℃, the holding time is set to 5min~20min, and the extrusion speed is set to 5mm / s~20mm / s.

[0015] Furthermore, in step one, when straightening the extruded bar, the residual heat after extrusion is used for straightening, and the straightness of the extruded bar blank after straightening is required to be ≤5mm / 1000mm; during the polishing process, an abrasive wheel or belt with a mesh of not less than 80 is used for polishing, and the surface roughness Ra of the extruded bar blank after polishing is required to be ≤3.2μm.

[0016] Furthermore, in step two, when heating the extruded billet, a box-type resistance furnace is used, and the heating temperature is set to 620℃~680℃. After the temperature reaches the set temperature, it is held for 30min~50min.

[0017] Furthermore, in step two, when performing multi-pass continuous hot rolling on the extruded billet, the total deformation of the hot rolling is required to be 70% to 90%.

[0018] Furthermore, in step three, when performing multi-pass continuous Pilger two-roll cold rolling on the bright hot-rolled billet, the total deformation of the cold rolling is required to be controlled at 40% to 70%, the cold rolling speed is ≤200 times / min, and the feed rate is ≤3.0mm / time.

[0019] Furthermore, in step three, when performing Pilger two-roll cold rolling on the bright hot-rolled billet, before cold rolling, the two ends of the bright hot-rolled billet are first threaded on a lathe, with internal threads machined on one end and external threads machined on the other end. Then, several bright hot-rolled billets are threaded together to form a long billet that is adapted to the length of the loading rack for continuous cold rolling.

[0020] Furthermore, in step four, when performing vacuum annealing on the cold-rolled billet, a vacuum annealing furnace is used for annealing. The vacuum annealing temperature is 580℃~650℃, the holding time is 2h~4h, and the working vacuum degree is better than 7.5×10⁻⁶. -3 Pa.

[0021] Furthermore, in step five, when straightening the annealed billet, the straightness of the straightened billet is ≤0.5mm / 1000mm.

[0022] Furthermore, in step five, when the annealed billet is subjected to centerless grinding, the amount removed by centerless grinding is 0.1 mm to 0.3 mm, and the surface roughness is ≤0.8 μm.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention provides a method for preparing zirconium alloy rods for nuclear fuel assembly end plugs. The process route of this method is: extrusion → hot rolling → Pilger two-roll cold rolling → vacuum annealing → finishing. Compared with the traditional hot rolling + rotary forging process, the preparation method of this invention combines the advantages of hot and cold working, enabling large plastic deformation of the zirconium alloy rods, significantly reducing the number of deformation passes and intermediate heat treatments, improving the dimensional accuracy and surface quality of the zirconium alloy rods. Simultaneously, the distribution of deformation processes improves production efficiency, avoiding defects such as adhesion and folding that are easily caused by multi-pass hot rolling, and the low production efficiency and incomplete grain breakage leading to uneven microstructure caused by the limitation of deformation per pass in rotary forging. In summary, the zirconium alloy rods prepared by the method of this invention can meet the requirements for use in high burnup reactors.

[0025] 2. The present invention provides a method for preparing zirconium alloy rods for nuclear fuel assembly end plugs. This method first involves extrusion and multi-pass continuous hot rolling. Under the pressure of extrusion and hot rolling, the microstructure of zirconium metal will be adjusted, making its microstructure more uniform and its grains smaller, which is beneficial to improving the mechanical properties of zirconium metal, especially tensile strength and plasticity. Then, the hot-rolled billet is processed by centerless turning to remove the oxide scale on the hot-rolled surface, obtaining a bright hot-rolled billet. This can effectively avoid defects such as folds and pits caused by oxide scale embedding into the surface of the rod during subsequent cold rolling, thereby improving the surface quality of the rod.

[0026] 3. The present invention provides a method for preparing zirconium alloy rods for nuclear fuel assembly end plugs. This method achieves continuous cold rolling by machining internal and external threads on both ends of hot-rolled billets and then connecting several hot-rolled short billets into a long billet. This effectively shortens the loading time of cold-worked billets, simplifies the cold-worked operation process, and improves the production efficiency of the rods. At the same time, the Pilger two-roll cold rolling technology is used to replace the traditional rotary forging technology, which can achieve large plastic deformation, greatly reduce the number of deformation passes, reduce the microstructure difference of the rods, further improve the microstructure uniformity of the rods, and significantly improve the surface quality, dimensional accuracy and production efficiency of the rods. Attached Figure Description

[0027] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart of the method for preparing zirconium alloy rods according to the present invention;

[0030] Figure 2 This is a schematic diagram of the thread processing position structure of a single zirconium alloy cold-rolled bar billet according to the present invention;

[0031] Figure 3 This is a schematic diagram of the present invention connecting several threaded bar blanks into a long bar.

[0032] Figure 4 This is a schematic diagram of the Pilger cold rolling process for preparing zirconium alloy rods according to the present invention.

[0033] Wherein: 1 is external thread; 2 is internal thread; 3 is upper roll; 4 is lower roll; 5 is bar stock. Detailed Implementation

[0034] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses consistent with some aspects of the invention as detailed in the appended claims.

[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] Please see Figure 1 As shown, the present invention provides a method for preparing zirconium alloy rods for nuclear fuel assembly end plugs, the method comprising the following steps:

[0037] Step 1: After the zirconium alloy forging bar is machined until the surface is smooth and evenly coated with lubricant, it is heated and kept at a certain temperature and then extruded. After extrusion, it is straightened and polished in sequence to obtain the extruded bar billet.

[0038] Specifically, when extruding zirconium alloy forged bars, induction heating is used to heat them to 600℃~680℃ and hold them for 5min~20min. Then, they are extruded at an extrusion speed of 5mm / s~20mm / s to obtain extruded billets. The residual heat after extrusion is then used for straightening, and the straightness of the extruded billet after straightening is required to be ≤5mm / 1000mm. Finally, polishing is performed using a grinding wheel or belt with a mesh of not less than 80, and the surface roughness Ra of the extruded billet after polishing is required to be ≤3.2μm.

[0039] Step 2: Heat and hold the extruded billet obtained in Step 1, then perform multi-pass continuous hot rolling. After hot rolling, remove the outer layer using a centerless milling machine to obtain a bright hot-rolled billet.

[0040] Specifically, the heating furnace used during hot rolling is a box-type resistance furnace, and the heating temperature is set to 620℃~680℃. After the temperature reaches the set temperature, it is held for 30min~50min. Then, hot rolling is carried out in no less than 10 passes, and the total deformation of hot rolling is controlled to be 70%~90%.

[0041] Step 3: The bright hot-rolled billet obtained in Step 2 is subjected to multi-pass continuous Pilger two-roll cold rolling to obtain a cold-rolled billet;

[0042] Specifically, the bright hot-rolled bar billet from step two is machined with internal and external threads at both ends using a lathe, such as... Figure 2 As shown, several bright hot-rolled bar billets are then threaded together to form a long bar billet (the length of the long bar billet is determined by the length of the loading rack, such as...). Figure 3 As shown) continuous Pilger two-roll cold rolling (e.g. Figure 4 As shown, the total deformation of cold rolling is controlled at 40% to 70%, the cold rolling speed is ≤200 times / min, the feed rate is ≤3.0mm / time, and after cold rolling, a circular saw is used to cut at the threaded connection to obtain the cold-rolled bar billet.

[0043] Step 4: Vacuum annealing is performed on the cold-rolled billet obtained in Step 3 to obtain an annealed billet;

[0044] Specifically, a vacuum annealing furnace is used for annealing. The vacuum annealing temperature is 580℃~650℃, the holding time is 2h~4h, and the working vacuum degree is better than 7.5×10. -3 Pa.

[0045] Step 5: The annealed billet obtained in Step 4 is subjected to finishing treatment, which includes straightening, centerless grinding and degreasing in sequence, and finally the zirconium alloy finished bar is obtained.

[0046] Specifically, the annealed billet in step four is straightened using a six-roll straightener, and the straightness of the billet after straightening is ≤0.5mm / 1000mm; then the straightened billet is subjected to centerless grinding, and the centerless grinding removes 0.1mm~0.3mm to obtain a finished bar of the set diameter with a surface roughness ≤0.8μm; finally, the bar is degreased and then dried to obtain the finished zirconium alloy bar.

[0047] To further verify the effectiveness of the forging method of the present invention, the inventors conducted the following specific embodiments:

[0048] Example 1 (Preparation of a 10mm diameter zirconium alloy rod)

[0049] 1) After machining and lubricating the zirconium alloy forging bar, it is induction heated to 680℃ and held for 5 minutes, and then extruded at an extrusion speed of 5 mm / s to obtain an extruded bar blank with a diameter of 50 mm. The extruded bar blank is then straightened and polished to obtain a bright extruded bar blank with a diameter of 49 mm, a straightness of ≤3 mm / 1000 mm, and a surface roughness Ra of 2.4 μm.

[0050] 2) The bright extruded billet from step 1) is kept at a resistance furnace temperature of 620℃. The first extruded billet is held at this temperature for 30 minutes and then rolled in 10 passes to a diameter of 19mm. The total hot rolling deformation is approximately 85%. The last extruded billet in the same furnace is held at a resistance furnace temperature for 38 minutes and then rolled in 10 passes to a diameter of 19mm. The heating and holding time difference between the first and last extruded billets is 8 minutes. After hot rolling, the billets are slit to a length of 1500mm. The slitting is done using a centerless milling machine to remove the oxide scale from the surface of the extruded billet, with a peeling amount of 0.5mm, resulting in a bright extruded billet with a diameter of 18.5mm.

[0051] 3) The bright hot-rolled bar billet from step 2) is machined with internal and external threads at both ends using a lathe. The thread size is M10×1.5mm and the length is 25mm. Then, the 7 bar billets are connected by threads to form a long bar billet, which is then subjected to Pilger two-roll cold rolling at a speed of 180 times / min and a feed rate of 3.0mm / roll. The diameter of the cold-rolled bar billet is 10.2mm, and the cold rolling deformation is about 69%. After cold rolling, the threaded connection is cut off using a circular saw to obtain the cold-rolled bar billet.

[0052] 4) The cold-rolled billet from step 3) is annealed in a vacuum annealing furnace at a temperature of 615℃ for 4 hours. The vacuum level during annealing is better than 6×10⁻⁶. -3 Pa, to obtain annealed bar blanks.

[0053] 5) The annealed billet from step 4) is straightened using a six-roll straightener. The straightness of the billet after straightening is better than 0.5mm / 1000mm. The straightened billet is then subjected to centerless grinding, with a removal of 0.2mm, to obtain a finished billet with a diameter of 10mm and a surface roughness of 0.7μm. Finally, the billet is degreased at a temperature of 65℃ for 60min, followed by drying to obtain the finished zirconium alloy billet.

[0054] Example 2 (Preparation of a 10mm diameter zirconium alloy rod)

[0055] 1) After machining and lubrication, the zirconium alloy forged bar is induction heated to 650℃ and held for 8 minutes, and then extruded at an extrusion speed of 13 mm / s to obtain an extruded bar blank with a diameter of 50 mm. The extruded bar blank is then straightened and polished to obtain a bright extruded bar blank with a diameter of 49 mm, a straightness of ≤2.5 mm / 1000 mm, and a surface roughness Ra of 2.2 μm.

[0056] 2) The bright extruded billet from step 1) is kept at a resistance furnace temperature of 660℃. The first extruded billet is held at this temperature for 40 minutes and then rolled in 11 passes to a diameter of 17mm. The total hot rolling deformation is 88%. The last extruded billet in the same furnace is also held at a resistance furnace temperature for 40 minutes and then rolled in 11 passes to a diameter of 17mm. The heating and holding time difference between the first and last extruded billets is 10 minutes. After hot rolling, the billets are slit to a length of 1300mm. The slitting is done using a centerless milling machine to remove the oxide scale from the surface of the extruded billet. The scale removal amount is 0.5mm, resulting in a bright extruded billet with a diameter of 16.5mm.

[0057] 3) The bright hot-rolled bar billet from step 2) is machined with internal and external threads at both ends using a lathe. The thread size is M10×1.5mm and the length is 25mm. Then, the 7 bar billets are connected with internal and external threads to form a long bar billet, which is then subjected to Pilger two-roll cold rolling at a speed of 200 times / min and a feed rate of 2.5mm / roll. The diameter of the cold-rolled bar billet is 10.3mm and the cold rolling deformation is 61%. After cold rolling, the threaded connection is cut off using a circular saw to obtain the cold-rolled bar billet.

[0058] 4) Anneal the cold-rolled billet from step 3) in a vacuum annealing furnace at a temperature of 580℃ for 3 hours. The vacuum level during annealing should be better than 6×10⁻⁶. -3 Pa, to obtain annealed bar blanks.

[0059] 5) The annealed billet from step 4) is straightened using a six-roll straightener. The straightness of the billet after straightening is better than 0.5mm / 1000mm. The straightened billet is then subjected to centerless grinding, with a removal of 0.3mm, to obtain a finished billet with a diameter of 10mm and a surface roughness of 0.6μm. Finally, the billet is degreased at a temperature of 60℃ for 60min, and then dried to obtain the finished zirconium alloy billet.

[0060] Example 3 (Preparation of zirconium alloy rods with a diameter of 8 mm)

[0061] 1) After machining and lubricating, the zirconium alloy forged bar is induction heated to 600℃ and held for 20 minutes. It is then extruded at an extrusion speed of 20 mm / s to obtain an extruded bar blank with a diameter of 50 mm. The extruded bar blank is then straightened and polished to obtain a bright extruded bar blank with a diameter of 49 mm, a straightness of ≤2.3 mm / 1000 mm, and a surface roughness Ra of 2.5 μm.

[0062] 2) The bright extruded billet from step 1) is kept at a resistance furnace temperature of 680℃. The first extruded billet is held at this temperature for 50 minutes and then rolled in 12 passes to a diameter of 15mm. The total hot rolling deformation is 89%. The last extruded billet in the same furnace is also rolled in 12 passes to a diameter of 15mm after being held at a resistance furnace temperature for 40 minutes. The heating and holding time difference between the first and last extruded billets is 10 minutes. After hot rolling, the billets are slit to a length of 1200mm. The oxide scale on the surface of the extruded billet is removed using a centerless milling machine, with a peeling amount of 0.5mm, resulting in a bright extruded billet with a diameter of 14.5mm.

[0063] 3) The bright hot-rolled bar billet from step 2) is machined with internal and external threads at both ends using a lathe. The thread size is M8×1.5mm and the length is 25mm. Then, the six bar billets are connected with internal and external threads to form a long bar billet, which is then subjected to Pilger two-roll cold rolling at a speed of 190 times / min and a feed rate of 2.0mm / roll. The diameter of the cold-rolled bar billet is 8.3mm and the cold rolling deformation is 67%. After cold rolling, the threaded connection is cut off using a circular saw to obtain the cold-rolled bar billet.

[0064] 4) Anneal the cold-rolled billet from step 3) in a vacuum annealing furnace at a temperature of 650℃ for 2 hours. The vacuum level during annealing should be better than 6.5 × 10⁻⁶. -3 Pa, to obtain annealed bar blanks.

[0065] 5) The annealed billet from step 4) is straightened using a six-roll straightener. The straightness of the billet after straightening is better than 0.5mm / 1000mm. The straightened billet is then subjected to centerless grinding, with a removal of 0.3mm, to obtain a finished billet with a diameter of 8mm and a surface roughness of 0.5μm. Finally, the billet is degreased at a temperature of 65℃ for 60min, and then dried to obtain the finished zirconium alloy billet.

[0066] To further verify the effectiveness of the preparation method of the present invention, the finished zirconium alloy rods obtained in Examples 1-3 were subjected to physicochemical sampling and testing. The test results are shown in Tables 1-4 below:

[0067] Table 1 Bar Dimensions

[0068] Diameter error / mm Ellipticity / mm ±0.015 ≤0.02

[0069] Table 2 Uniform corrosion performance of bars after 72 hours

[0070] <![CDATA[Weight gain due to corrosion / mg / dm 2 > Corrosion appearance 15.70-16.69 gray-black

[0071] Table 3 Grain size and low-magnification microstructure of the bars

[0072]

[0073]

[0074] Table 4 Mechanical Properties of Bars

[0075] / Rm / MPa <![CDATA[Rp 0.2 / MPa]]> A / ％ room temperature 524-536 361-373 23.0-24.0 High temperature (315℃) 293-303 149-161 34.5-36.0

[0076] As shown in Tables 1-4, the zirconium alloy rods prepared by the method of this invention have the following advantages: First, high dimensional accuracy, specifically, a diameter error of less than 0.2 mm and an ellipticity of less than 0.02 mm; second, good uniform corrosion resistance, with a corrosion weight gain of only 15.70-16.69 mg / dm³.2 Third, both the longitudinal and cross-sectional dimensions reach grade 11 or higher, and the low-magnification microstructure is free of cracks, folds, pores, shrinkage tails, shrinkage porosity, and non-metallic inclusions; fourth, it possesses good room temperature and high-temperature mechanical properties, specifically at room temperature: its tensile strength (Rm) is greater than 520 MPa, and its yield strength (Rp) is greater than 520 MPa. 0.2 Its tensile strength (Rm) is greater than 360 MPa, and its elongation (A) is greater than 23%; at high temperature (315℃), its tensile strength (Rp) is greater than 290 MPa, and its yield strength (Rp) is greater than 23%. 0.2 The strength (A) is greater than 140 MPa, and the elongation (A) is greater than 34%. It is evident that the zirconium alloy rods prepared by the method of this invention exhibit uniform microstructure and properties, good dimensional accuracy and surface quality, and excellent mechanical properties at both room temperature and high temperature.

[0077] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0078] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing zirconium alloy rods for end plugs of nuclear fuel assemblies, characterized in that, The preparation method includes the following steps: Step 1: After the zirconium alloy forging bar is machined until the surface is smooth and evenly coated with lubricant, it is heated and kept at a certain temperature and then extruded. After extrusion, it is straightened and polished in sequence to obtain the extruded bar billet. In step one, when extruding the zirconium alloy forging rod, the heating temperature is set to 600℃~680℃, the holding time is set to 5min~20min, and the extrusion speed is set to 5mm / s~20mm / s. Step 2: Heat and hold the extruded billet obtained in Step 1, then perform multi-pass continuous hot rolling. After hot rolling, remove the outer layer using a centerless milling machine to obtain a bright hot-rolled billet. In step two, when heating the extruded billet, a box-type resistance furnace is used, and the heating temperature is set to 620℃~680℃. After reaching the set temperature, the temperature is held for 30min~50min. In step two, when performing multi-pass continuous hot rolling on the extruded billet, the total deformation of the hot rolling is required to be 70%~90%. Step 3: The bright hot-rolled billet obtained in Step 2 is subjected to multi-pass continuous Pilger two-roll cold rolling to obtain a cold-rolled billet; In step three, when performing multi-pass continuous Pilger two-roll cold rolling on bright hot-rolled billets, the total deformation of the cold rolling is required to be controlled at 40% to 70%, the cold rolling speed is ≤200 times / min, and the feed rate is ≤3.0mm / time. Before cold rolling, the two ends of the bright hot-rolled billets are threaded on a lathe, with one end having an internal thread and the other end having an external thread. Then, several bright hot-rolled billets are threaded together to form a long billet that is adapted to the length of the loading rack for continuous cold rolling. Step 4: Vacuum annealing is performed on the cold-rolled billet obtained in Step 3 to obtain an annealed billet; In step four, when performing vacuum annealing on the cold-rolled billet, a vacuum annealing furnace is used. The vacuum annealing temperature is 580℃~650℃, the holding time is 2h~4h, and the working vacuum degree is better than 7.5×10⁻⁶. -3 Pa; Step 5: The annealed billet obtained in Step 4 is subjected to finishing treatment, which includes straightening, centerless grinding and degreasing in sequence, and finally the zirconium alloy finished bar is obtained.

2. The method for preparing a zirconium alloy rod for end plugs of nuclear fuel assemblies according to claim 1, characterized in that, In step one, when straightening the extruded billet, the residual heat after extrusion is used for straightening, and the straightness of the extruded billet after straightening is required to be ≤5mm / 1000mm; during polishing, an abrasive wheel or belt with a mesh of not less than 80 is used for polishing, and the surface roughness Ra of the extruded billet is required to be ≤3.2μm after polishing.

3. The method for preparing a zirconium alloy rod for end plugs of nuclear fuel assemblies according to claim 1, characterized in that, In step five, when straightening the annealed billet, the straightness of the straightened billet is ≤0.5mm / 1000mm.

4. The method for preparing a zirconium alloy rod for end plugs of nuclear fuel assemblies according to claim 1, characterized in that, In step five, when the annealed billet is subjected to centerless grinding, the amount removed by centerless grinding is 0.1 mm to 0.3 mm, and the surface roughness is ≤0.8 μm.

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