Method for manufacturing a multi-layer nuclear fuel cladding tube

Abstract

The present invention provides a method for manufacturing a multilayer nuclear fuel cladding tube, which includes the following steps: providing a preliminary cladding tube, in which an inner tube with a rod-shaped insert is inserted is arranged in an outer tube; reducing the diameter of the preliminary cladding tube by applying pressure from the outside to the inside of the preliminary cladding tube; and removing the insert from the inner tube by providing a force in the direction in which the insert extends, wherein the inner tube and the outer tube can be formed of metals different from each other.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a multi-layer nuclear fuel cladding tube, and more particularly, to a method for manufacturing a multi-layer nuclear fuel cladding tube using a rod-shaped insert. Background Art

[0002] Generally speaking, nuclear power plants utilize the heat generated by nuclear fission to produce steam, which in turn uses the power of the generated steam to turn turbines to generate electricity. Nuclear power plants incorporate multiple layers of protective barriers to prevent the leakage of radioactive materials and ensure plant safety. Within these barriers, nuclear fuel cladding tubes, a secondary barrier, surround the nuclear fuel pellets, isolating the nuclear fuel that causes nuclear fission from the coolant circulating in the primary system of the nuclear reactor. This prevents fission products produced during nuclear fission from migrating into the primary coolant. Furthermore, the nuclear fuel cladding tubes effectively transfer the heat generated by nuclear fission to the primary coolant.

[0003] Nuclear fuel cladding tubes are easily oxidized due to reaction with water vapor (H2O) at high temperatures, and this oxidation can be limited or prevented by using different materials to manufacture dual-structure nuclear fuel cladding tubes.

[0004] The dual-structure nuclear fuel cladding tube is required to form a tube with no interface between the outer tube and the inner tube. Generally, there is a limit to making the outer tube closely contact the inner tube because the inner tube is insufficient to provide a force to support the pressure applied from the outside to the inside.

[0005] [Prior art literature]

[0006] (Patent Document 1) Korean Patent No. 10-0963472 Summary of the Invention

[0007] Technical issues

[0008] The present disclosure provides a method for manufacturing a multi-layer nuclear fuel cladding tube, wherein the method inserts a rod-shaped insert into an inner tube so that the inner tube closely contacts an outer tube.

[0009] Technical Solutions

[0010] According to an exemplary embodiment, a method for manufacturing a multilayer nuclear fuel cladding tube includes: providing a preliminary cladding tube, in which an inner tube having a rod-shaped insert inserted therein is arranged in an outer tube; reducing the diameter of the preliminary cladding tube by applying pressure from the outside toward the inside of the preliminary cladding tube; and removing the insert from the inner tube by providing a force parallel to the direction in which the insert extends, and the inner tube and the outer tube are formed of metals different from each other.

[0011] The reducing the diameter of the preliminary clad pipe may include arranging a plurality of rolling units each including a plurality of rollers in a longitudinal direction of the preliminary clad pipe so as to move the preliminary clad pipe between the plurality of rollers that are paired with each other.

[0012] The distance between the multiple rollers of each of the multiple rolling units can be reduced in stages in the longitudinal direction of the prepared clad tube, and the pressure applied to the inner side of the prepared clad tube can be gradually increased when the prepared clad tube is moved between the multiple rollers.

[0013] The plurality of rolling units may include: a first rolling unit, wherein the plurality of rollers are arranged in a first direction; and a second rolling unit, wherein the plurality of rollers are arranged in a second direction intersecting the first direction, and the first rolling unit and the second rolling unit may be arranged alternately.

[0014] When the diameter of the preliminary cladding tube is reduced, the insert may provide the inner tube with a reaction force against the pressure.

[0015] The providing the preliminary cladding tube may include: polishing a surface of the insert body or applying a lubricant to the surface of the insert body; and inserting the insert body into the inner tube.

[0016] The insert may have elasticity.

[0017] The insert may be made of a polymer.

[0018] The insert body may have a hardness lower than a hardness of the inner tube.

[0019] The insert may have a hardness of 60 Shore A to 100 Shore D.

[0020] The length of the insert may be greater than the length of each of the inner tube and the outer tube.

[0021] The original diameter of the insert is equal to or smaller than the inner diameter of the inner tube of the prepared cladding tube,

[0022] When reducing the diameter of the preliminary covering tube, the inner diameter of the inner tube may be reduced to be equal to or smaller than the original diameter of the insert.

[0023] The outer tube may have a ductility greater than a ductility of the inner tube.

[0024] Beneficial effects

[0025] In a method for manufacturing a multi-layer nuclear fuel cladding tube according to an exemplary embodiment, when a rod-shaped insert is inserted into an inner tube and pressure is applied from the outside toward the inside of the preliminary cladding tube to reduce its diameter, the insert provides a reaction force to the inner tube against the pressure applied thereto. This allows the inner and outer tubes to be in close contact and fixed to each other, and allows the multi-layer nuclear fuel cladding tube to be manufactured using a single tube without an interface between the inner and outer tubes.

[0026] Furthermore, since the insert has a rod shape, it can be removed from the inner tube by simply applying a force in the direction in which the insert extends. Since the insert is elastic, it can prevent damage to the inner wall of the inner tube. Furthermore, since the insert is made of a polymer, it can have sufficient hardness to provide the inner tube with sufficient reaction force against the pressure applied to the inner side.

[0027] Furthermore, since the swaging process is performed by passing the preliminary clad tube through the plurality of rolling units having a stepwise decreasing spacing between rollers, only the diameter of the preliminary clad tube can be reduced while maintaining its shape, and excessive force can be applied to the outer tube and / or inner tube to prevent damage and deformation of the outer tube and / or inner tube. Furthermore, when the plurality of rolling units are configured by alternating first rolling units in which the plurality of rolling units are arranged in the vertical direction and second rolling units in which the plurality of rolling units are arranged in the horizontal direction, the swaging process can be performed while the preliminary clad tube maintains its circular shape without being dented in either the vertical or horizontal direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flow chart illustrating a method for manufacturing a multi-layer nuclear fuel cladding tube according to an exemplary embodiment.

[0029] Figure 2 1 and 2 are views sequentially illustrating a method of manufacturing a multi-layered nuclear fuel cladding tube according to an exemplary embodiment.

[0030] Figure 3 is a diagram for explaining a rotary swaging process according to an exemplary embodiment.

[0031] Figure 4 is a conceptual diagram for explaining a reaction force caused by an insert according to an exemplary embodiment. DETAILED DESCRIPTION

[0032] Hereinafter, specific embodiments will be described in more detail with reference to the accompanying drawings. However, the present invention can be implemented in different forms and should not be considered to be limited to the embodiments described herein. Specifically, these embodiments are provided to make this disclosure thorough and complete and to fully convey the scope of the invention to those skilled in the art. In every possible case, the same reference numbers are used in the description and drawings to refer to the same or similar elements. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. The same reference numbers in the drawings represent the same elements, and their descriptions will therefore be omitted.

[0033] Figure 1 is a flow chart showing a method for manufacturing a multilayer nuclear fuel cladding tube according to an exemplary embodiment, and Figure 2 1 is a diagram sequentially illustrating a method for manufacturing a multilayer nuclear fuel cladding tube according to an exemplary embodiment. Figure 2 (a) is an exploded perspective view of the prepared cladding tube, Figure 2 (b) is a perspective view showing a coupled state of the preliminary cladding tube, and Figure 2 (c) is a perspective view showing a multi-layer nuclear fuel cladding tube.

[0034] Reference Figure 1 and Figure 2 According to an exemplary embodiment, a method for manufacturing a multilayer nuclear fuel cladding tube may include: process S100, providing a preliminary cladding tube 100a, in which an inner tube 110 in which a rod-shaped insert 50 is inserted is set in an outer tube 120; process S200, reducing the diameter of the preliminary cladding tube 100a by applying a pressure F in a direction from the outside to the inside of the preliminary cladding tube 100a; and process S300, removing the insert 50 from the inner tube 110 by providing a force parallel to the direction in which the insert 50 extends.

[0035] First, in process S100, a preliminary clad tube 100a is provided in which the inner tube 110 having the rod-shaped insert 50 inserted therein is disposed in the outer tube 120. The inner tube 110 having the rod-shaped insert 50 may be disposed in the outer tube 120, and thus, the preliminary clad tube 100a in which the insert 50 is inserted into the inner tube 110 may be prepared. Here, the insert 50 may be inserted into the inner tube 110 in a state in which the inner tube 110 is disposed (or inserted) in the outer tube 120, or the insert 50 may be first inserted into the inner tube 110, and then the inner tube 110 into which the insert 50 is inserted may be arranged in the outer tube 120. Furthermore, the plurality of preliminary clad tubes 100a in which the insert 50 is inserted into the inner tube 110 can be prepared by preparing a plurality of preliminary clad tubes 100a in which the inner tube 110 is inserted into the outer tube 120, and then inserting one long insert 50 (or a continuous insert) into the inner tubes 110 of all of the plurality of preliminary clad tubes 100a. That is, the plurality of preliminary clad tubes 100a can be sewn together by one insert 50, and in this case, the insert 50 is inserted into the inner tube 110 in a state in which the inner tube 110 is inserted into the outer tube 120.

[0036] Thereafter, in process S200, the diameter of the preliminary clad tube 100a is reduced by applying pressure F from the outside toward the inside of the preliminary clad tube 100a. By applying pressure F from the outside toward the inside in the radial direction of the preliminary clad tube 100a toward the central axis of the preliminary clad tube 100a, the diameter of the preliminary clad tube 100a is reduced, thereby securely fixing the inner tube 110 and the outer tube 120 to each other. Here, the insert 50 can provide a force supporting the inner tube 110 against the pressure F applied from the outside toward the inside of the preliminary clad tube 100a.

[0037] That is, in the process S200 of reducing the diameter of the preliminary cladding tube 100a, the outer tube 120 and the inner tube 110 can be firmly fixed to each other by the pressure F applied in the direction from the outside to the inside of the preliminary cladding tube 100a and the force of the insert 50 used to support the inner tube 110, and a multi-layer nuclear fuel cladding tube 100 can be manufactured without a recessed portion.

[0038] Thereafter, in process S300, the insert body 50 is removed from the inner tube 110 by applying a force parallel to the direction in which the insert body 50 extends. Since the rod-shaped insert body 50 has a main body, the insert body 50 can be easily removed from the inner tube 110 by applying a force parallel to the direction in which the insert body 50 extends to the insert body 50 and / or the preliminary cladding tube 100a to remove the insert body 50 from the interior of the inner tube 110. Here, the insert body 50 can be removed by pulling or pushing the insert body 50. When removing the insert body 50 by pulling the insert body 50, a pulling force can be applied to the insert body 50 in the direction in which the insert body 50 extends (along the extending direction or parallel to the extending direction), or a pushing force can be applied to the preliminary cladding tube 100a in the direction in which the insert body 50 extends (or parallel to the extending direction). In contrast, when the insert body 50 is removed by pushing the insert body 50 , a pushing force may be applied to the insert body 50 in the extending direction of the insert body 50 , or a pulling force may be applied to the preliminary cladding tube 100 a in the extending direction of the insert body 50 .

[0039] Typically, the swaging process is performed in a state where only the inner tube 110 is inserted into the outer tube 120, and the preliminary cladding tube 100a has a hollow tube state. When the swaging process is performed in this manner, when force (or pressure) is applied in the radial direction, the inner tube 110 may not receive uniform force (or energy) and may be concave, thereby manufacturing a concave multi-layer nuclear fuel cladding tube 100.

[0040] In order to solve the above limitations, a method of performing a swaging process in the following manner is also used: using salt (such as KOH) as a filling material and filling the filling material into the inner tube 110, and then melting it and removing the filling material by a solvent (such as water). In this method, people fill the filling material in the form of particles or powder directly into the inner tube 110, and then push the filled inner tube 110 by applying pressure to it using a long rod, thereby increasing its density. As a result, it may not be possible to ensure that the amount of filling material (i.e., salt) inserted into the inner tube 110 is uniform, and reproducibility may not be ensured. In essence, the method using salt as a filling material is not efficient in the swaging process for large-scale production, and is inefficient in terms of time due to its long process time. Therefore, this method is not suitable for the ultimate purpose of a simple and fast swaging process. In particular, after the swaging process, more time is required to remove the condensed filling material. When the filling material is a bulk solid such as particles, the diameter of the inner tube 110 may be reduced, and the inner surface (or inner wall) of the inner tube 110 may be scratched. When a powder-type filling material is used when the inner tube 110 has ductility (or elasticity), the inner tube 110 may be expanded (or deformed) whenever pressure is applied to the filling material to increase the density, and the density of the filling material may vary for each position. In addition, both ends of the preliminary covering tube 100a need to be shielded (or closed) so that the filling material does not escape to the outside during the swaging process. When the two ends of the preliminary covering tube 100a are not firmly sealed, when the internal pressure of the inner tube 110 increases due to the pressure F used to reduce the preliminary covering tube 100, the filling material may escape to the outside by destroying the shielding at both ends of the preliminary covering tube 100a. Furthermore, when both ends of the preliminary cladding tube 100a are very firmly closed, since the preliminary cladding tube 100a is not smoothly compressed, it may not be easy to reduce the diameter of the preliminary cladding tube 100a, or the inner tube 110 and the outer tube 120 may not be in close contact with each other.

[0041] However, since the rod-shaped insert 50 is only pulled or pushed in the exemplary embodiment, the insert 50 can be removed from the inner tube 110 more easily and quickly than in the case where salt is used as a filler material, and the production speed of the multilayer nuclear fuel cladding tube 100 can be increased.

[0042] Here, the inner tube 110 and the outer tube 120 can be formed of different metals (or metal alloys). For example, the inner tube 110 can be made of a zirconium alloy (e.g., Zircaloy-4) and have a hollow tube shape with a housing space (or hollow portion) that accommodates the nuclear fuel pellets when both ends are penetrated in one direction (or longitudinal direction). The inner tube 110 can be inserted into the outer tube 120 and positioned at the innermost portion of the multi-layer nuclear fuel cladding tube 100.

[0043] The outer tube 120 can be made of a metal different from the zirconium alloy of the inner tube 110 (e.g., a metal containing aluminum). The outer tube 120 can be made of a metal with excellent corrosion resistance (e.g., an aluminum alloy such as aluminum, Cr-Al, and FeCrAl) to prevent the inner tube 110 from reacting with high-temperature moisture in a high-temperature, high-pressure atmosphere to generate hydrogen. Furthermore, the nuclear fuel pellets housed in the accommodation space of the inner tube 110 can be protected from high-temperature oxidation, thereby increasing the stability of nuclear operations. Here, the outer tube 120 can have a hollow tube shape with an accommodation space (or hollow portion). When both ends are penetrated in one direction, the inner tube 110 can be inserted and accommodated therein.

[0044] Hydrogen explosions in nuclear power plants are closely related to the oxidizing properties of zirconium. When outer tube 120 is made of a different metal than zirconium to surround the outer portion of inner tube 110, outer tube 120 can have improved oxidation resistance against coolant components. Therefore, in the event of an accident, oxidation and corrosion of inner tube 110 can be prevented.

[0045] Therefore, the multilayer nuclear fuel cladding tube 100 manufactured by utilizing only the advantages of the inner tube 110 and the outer tube 120 can have improved mechanical strength and effectively reduce the risk of accidents caused by high-temperature oxidation. In addition, the inner tube 110 and / or the nuclear fuel contained therein can be protected from the effects of nuclear reactor accidents, thereby enabling stable operation of nuclear power.

[0046] Figure 3 is a diagram for explaining a rotary forging process according to an exemplary embodiment, Figure 3 (a) is a diagram showing a rotary swaging machine including a plurality of rolling units, and Figure 3 (b) is a diagram showing changes in the diameter of the preliminary cladding tube according to the portion.

[0047] Reference Figure 3The process S200 of reducing the diameter of the preliminary clad pipe 100a may include: a process S210 of arranging a plurality of rolling units 210, each including a plurality of rollers 211a, 211b and 212a, in the longitudinal direction of the preliminary clad pipe 100a, so that the preliminary clad pipe 100a moves between the plurality of rollers 211a, 211b and 212a that are paired with each other.

[0048] In process S210, the plurality of rolling units 210, each including the plurality of rollers 211a, 211b, and 212a, are arranged in the longitudinal direction of the prepared clad pipe 100a. The prepared clad pipe 100a is moved between the plurality of rollers 211a, 211b, and 212a to reduce the diameter of the prepared clad pipe 100a. The rotary swaging machine 200 compresses the outer portion of the prepared clad pipe 100a using the rollers 211a, 211b, and 212a, thereby reducing the diameter of the prepared clad pipe 100a and increasing the length of the prepared clad pipe 100a through compression and stretching, and reducing the distance (interval) between the inner pipe 110 and the outer pipe 120, so that the inner pipe 110 and the outer pipe 120 are firmly fixed to each other. That is, the rotary swaging machine 200 can increase the length or reduce the diameter of the preliminary clad tube 100a by using the plurality of rollers 211a, 211b, and 212a, and apply pressure F from the outside of the preliminary clad tube 100a, so that the inner tube 110 and the outer tube 120 are in close contact with each other. Here, the rotary swaging machine 200 may include a plurality of rolling units 210 arranged in the longitudinal direction of the preliminary clad tube 100a. Each of the plurality of rolling units 210 may include the plurality of rollers 211a, 211b, and 212a, each forming a pair, and the plurality of rollers 211a, 211b, and 212a, each forming a pair, can symmetrically (or evenly) press the preliminary clad tube 100a from the outside toward the central axis of the preliminary clad tube 100a. Here, the plurality of rolls each forming a pair may be a pair of rolls facing each other, or a roll group in which the plurality of rolls are spaced apart from each other by a predetermined angle with respect to the central axis of the preliminary clad pipe 100a.

[0049] When the multiple rolling units 210 are arranged in the longitudinal direction of the prepared clad tube 100a and the prepared clad tube 100a moves through the multiple rollers 211a, 211b and 212a, the force of the multiple rollers 211a, 211b and 212a that compress the prepared clad tube 100a can compress and stretch the prepared clad tube 100a, thereby increasing the length of the prepared clad tube 100a or reducing the diameter of the prepared clad tube 100a, and the inner tube 110 and the outer tube 120 can be in close contact with each other.

[0050] In addition, the distances between the plurality of rollers 211a, 211b, and 212a in the plurality of rolling units 210 may be gradually reduced along the longitudinal direction of the prepared clad pipe 100a, and in the process (S210) of moving the prepared clad pipe 100a between the plurality of rollers 211a, 211b, and 212a, the pressure F applied to the inner side of the prepared clad pipe 100a may be gradually increased. The plurality of rolling units 210 may be spaced apart from each other based on the longitudinal direction (i.e., one direction) of the prepared clad pipe 100a. Each of the plurality of rolling units 210 includes the plurality of rollers 211a, 211b, and 212a, each of the plurality of rollers 211a, 211b, and 212a forms a pair to contact the outer surface of the prepared clad tube 100a, and the prepared clad tube 100a is located between the plurality of rollers 211a, 211b, and 212a, and when the prepared clad tube 100a moves between the plurality of rollers 211a, 211b, and 212a that form a pair with each other, a pushing pressure F can be applied from the outside to the inside in the radial direction of the prepared clad tube 100a. As the distance between the plurality of rollers 211a, 211b, and 212a decreases in stages, the diameter (or size) of the rollers can also be reduced according to the reduction in the diameter of the prepared clad tube 100a. Figure 3 As shown in (a), the diameter of the first horizontal roller 212a may be smaller than the diameter of the first vertical roller 211a, and the diameter of the second vertical roller 211b may be smaller than the diameter of the first horizontal roller 212a.

[0051] For example, each of the plurality of rollers 211a, 211b, or 212a forming a pair may face and contact the outer surface of the prepared clad pipe 100a based on the prepared clad pipe 100a. When the prepared clad pipe 100a is not disposed between the plurality of rollers 211a, 211b, or 212a forming a pair, since the prepared clad pipe 100a does not move between the plurality of rollers 211a, 211b, or 212a forming a pair, the spacing distance between each of the plurality of rollers 211a, 211b, or 212a may be equal to or smaller than the outer diameter (or external diameter) of the prepared clad pipe 100a, and the plurality of rollers 211a forming a pair disposed at the first position may have a spacing distance equal to or slightly smaller than the external diameter of the prepared clad pipe 100a. Therefore, when the prepared cladding tube 100a passes between the multiple rollers 211a, 211b or 212a that are paired with each other, the diameter of the prepared cladding tube 100a can be reduced, or the inner tube 110 and the outer tube 120 can be brought into close contact with each other by the pressure F applied to the outer surface of the prepared cladding tube 100a from the multiple rollers 211a, 211b or 212a that are paired with each other.

[0052] Here, as Figure 3As shown in (a) of FIG. 2 , the spacing distance between the plurality of rollers 211a, 211b, or 212a of each of the plurality of rolling units 210 may be reduced in stages in the longitudinal direction of the prepared clad pipe 100a. When the positions of the prepared clad pipe 100a passing through each of the plurality of rolling units 210 are classified into A, B, and C (at these positions, the spacing distance between the plurality of rollers 211a, 211b, or 212a is reduced in stages), and the diameters and thicknesses of the positions A, B, and C of the prepared clad pipe 100a are inspected, as shown in FIG. Figure 3 As shown in (b), as the number of the plurality of rolling units 210 through which the preliminary clad pipe 100a passes increases, the diameter of the preliminary clad pipe 100a and / or the diameter (or inner diameter) of the accommodation space of the inner pipe 110 may gradually decrease from D1 to D3. This is because the intervals between the plurality of rollers 211a, 211b, or 212a of each of the plurality of rolling units 210 decrease in stages, the pressure F applied to the preliminary clad pipe 100a gradually increases, and the preliminary clad pipe 100a is deformed by the gradually increasing pressure F, thereby reducing the diameter of the preliminary clad pipe 100a and / or the diameter of the accommodation space of the inner pipe 110. That is, in the process S210 of moving the preliminary cladding pipe 100a between the multiple rollers 211a, 211b or 212a, as the preliminary cladding pipe 100a passes through the multiple rollers 211a, 211b or 212a each having a gradually decreasing spacing distance, the pressure F applied to the inner side of the preliminary cladding pipe 100a may gradually increase.

[0053] Therefore, in an exemplary embodiment, by performing a swaging process to allow the preliminary clad pipe 100a to pass through the plurality of rolling units 210, only the diameter of the preliminary clad pipe 100a can be reduced while maintaining the shape of the preliminary clad pipe 100a, and the interval distance between each of the plurality of rollers 211a, 211b, or 212a, each forming a pair in the plurality of rolling units 210, is reduced in stages. In addition, excessive force is not applied to the outer pipe 120 and / or the inner pipe 110, and the outer pipe 120 and / or the inner pipe 110 are not damaged (or broken) or deformed.

[0054] Here, despite Figure 3 In (a), three rolling units 210 are provided, and each of the rolling units 211 and 212 includes two rollers 211a, 211b, or 212a, but the exemplary embodiment is not limited to the number of each of the rollers 211a, 211b, or 212a and the number of the rolling units 210. For example, the number of each of the rollers 211a, 211b, or 212a and the number of the rolling units 210 may be changed variously. In addition, although Figure 3The diameter of the preliminary cladding tube 100a in (b) is greatly reduced, but this is merely illustrative for explaining the change in diameter. When the preliminary cladding tube 100a is substantially made of a soft (or flexible) material, the diameter of the preliminary cladding tube 100a may be as Figure 3 The outer tube 120 and the inner tube 110 may change as shown in (b), or may decrease according to the elongation of the outer tube 120 and the inner tube 110.

[0055] When referring to Figure 3 (a) further details the method of firmly fixing the outer tube 120 and the inner tube 110 to each other by increasing the close contact force between the outer tube 120 and the inner tube 110 through a swaging process. When the preliminary clad tube 100a passes between the plurality of rollers 211a, 211b, or 212a, the pressure F applied to the preliminary clad tube 100a by the rollers 211a, 211b, or 212a applies pressure F to the inside of the preliminary clad tube 100a. Here, since the insert 50 inserted into the inner tube 110 of the preliminary clad tube 100a fills the accommodation space of the inner tube 110, the inner tube 100 can withstand the pressure F applied thereto. That is, since the insert 50 has the force to support the inner tube 110 against the pressure F applied from the outside, the outer tube 120 and the inner tube 110 can be firmly fixed to each other, so that the inner tube 110 is set at a predetermined position, and the outer tube 120 contracts more than the inner tube 110 due to the external force F and retracts toward the inner tube 110.

[0056] The plurality of rolling units 210 may include: a first rolling unit 211, wherein the plurality of rollers 211a and 211b are arranged in a first direction (e.g., a vertical direction); and a second rolling unit 212, wherein the plurality of rollers 212a are arranged in a second direction (e.g., a horizontal direction) that intersects the first direction. The first rolling unit 211 and the second rolling unit 212 may be arranged alternately. That is, the plurality of rolling units 210 may be configured such that the first rolling unit 211, wherein the plurality of rollers 211a and 211b are arranged in the first direction, and the second rolling unit 212, wherein the plurality of rollers 212a are arranged in the second direction, are arranged alternately.

[0057] The first rolling unit 211 may include the plurality of rollers 211a and 211b arranged in the first direction, and the plurality of rollers 211a and 211b may be arranged outside the prepared clad tube 100a and symmetrically with respect to the prepared clad tube 100a arranged therebetween. For example, a pair of rollers 211a or 211b may be arranged to face each other on both sides of the prepared clad tube 100a arranged therebetween in the first direction, and the pair of rollers 211a or 211b facing each other in the first direction may press the prepared clad tube 100a from both sides in the first direction toward the inside of the prepared clad tube 100a.

[0058] The second rolling unit 212 may include the plurality of rollers 212a arranged in a second direction intersecting the first direction, and the plurality of rollers 212a may be arranged outside the prepared clad tube 100a and symmetrically with respect to the prepared clad tube 100a arranged therebetween. For example, a pair of rollers 212a may be arranged to face each other on both sides of the prepared clad tube 100a arranged therebetween in the second direction, and the pair of rollers 212a facing each other in the second direction may press the prepared clad tube 100a from both sides in the second direction toward the inside of the prepared clad tube 100a.

[0059] Here, the first rolling units 211 and the second rolling units 212 may be alternately arranged.

[0060] When only the first rolling unit 211 or the second rolling unit 212 is arranged in series, the entire preliminary clad tube 100a may not be uniformly compressed (or shrunk) because it is compressed only in one direction (e.g., vertical or horizontal). The entire preliminary clad tube 100a may not maintain its shape (or cross-sectional shape) but may sag in one direction (vertical or horizontal). However, when the first rolling unit 211, in which the plurality of rollers 211a and 211b are arranged in the first direction, and the second rolling unit 212, in which the plurality of rollers 212a are arranged in the second direction, are alternately arranged, the preliminary clad tube 100a may be compressed in the second direction in addition to the first direction, and thus, the preliminary clad tube 100a may be uniformly compressed in all directions (or in both directions). Therefore, the swaging process can be performed while the preliminary clad tube 100a maintains its circular shape rather than sag in one direction (vertical or horizontal).

[0061] Here, the rolling unit 211 or 212 in which the plurality of rollers 211a and 211b are arranged in a vertical direction may be first arranged between the first rolling unit 211 and the second rolling unit 212, and the prepared clad pipe 100a may first enter between the rolling unit 211 or 212 arranged in the vertical direction. When the main diameter (or original diameter) of the insert 50 is smaller than the inner diameter of the inner pipe 110 so that the insert 50 is easily inserted into the inner pipe 110, the insert 50 may be deflected downward due to gravity, and thus it may be difficult to position the insert 50 at the inner center of the inner pipe 110. Here, when no external force (such as pressure or tensile strength) is applied, the main diameter may be the original diameter. In this case, when the first rolling unit 211 or the second rolling unit 212 in which the rolling unit 212 or 211 is set in the horizontal direction first compresses the preliminary cladding tube 100a, since the horizontal width of the inner tube 110 may be reduced, the insert 50 is fixed in a downwardly deviated state, and since the insert 50 is not set at the inner center of the inner tube 110, the preliminary cladding tube 100a may be recessed in one direction.

[0062] However, when the rolling unit 211 or 212 arranged in the vertical direction first compresses the preliminary cladding tube 100a, since the vertical position of the insert 50 coincides (or is aligned) with the inner center of the inner tube, the insert 50 can be arranged at the inner center of the inner tube, and the preliminary cladding tube 100a can maintain a circular shape instead of being concave in one direction.

[0063] Figure 4 is a conceptual diagram for explaining a reaction force caused by an insert according to an exemplary embodiment, Figure 4 (a) is a side sectional view of the prepared cladding tube, and Figure 4 (b) is a cross-sectional view of the prepared cladding tube.

[0064] Reference Figure 4 In the process ( S200 ) of reducing the diameter of the preliminary cladding tube 100 a , the insert 50 may provide a reaction force −F against the pressure F toward the inner tube 110 . The insert 50 may provide a reaction force −F against the pressure F applied to the inner side of the inner tube 110 . As a result, the inner tube 110 and the outer tube 120 may be in close contact with each other, and the multi-layered nuclear fuel cladding tube 100 may include one tube without an interface between the inner tube 110 and the outer tube 120 .

[0065] That is, because the insert 50 fills the accommodation space of the inner tube 110, when the diameter of the preliminary cladding tube 100a decreases (or contracts) due to the pressure F applied to the inside during the swaging process, the insert 50 supports the inner tube 110 and provides a reaction force -F in the radial direction (or outward direction) to resist the pressure F. When the outer tube 120 is compressed toward the inner tube 110 by the pressure F and the inner tube 110 is compressed toward the outer tube 120 by the reaction force -F, the inner tube 110 and the outer tube 120 can be in close contact with each other. In addition, due to the sufficient pressure F and reaction force -F, the inner tube 110 and the outer tube 120 can be in close contact and fixed to each other as a single tube without an interface between them. In addition, although the diameter of the inner tube is hardly changed by the reaction force -F of the insert 50, the outer tube 120 can shrink relatively significantly, and thus the inner tube 110 and the outer tube 120 can be in close contact with each other.

[0066] The process S100 of preparing the preliminary cladding tube may include: a process S110 of polishing the surface of the insert body 50 or applying a lubricant to the surface of the insert body 50 ; and a process S120 of inserting the insert body 50 into the inner tube 110 .

[0067] In process S110, the surface of the insert 50 may be polished or a lubricant may be applied to the surface of the insert 50. The surface of the insert 50 may be polished so that the insert 50 is smoothly inserted into and removed from the inner tube 110, or the lubricant may be applied (spread) on the surface of the insert 50. Here, the method for manufacturing a multi-layer nuclear fuel cladding tube according to an exemplary embodiment may be performed at room temperature (approximately 0° C. to 25° C.), and the lubricant may include easily available cooking oil or lubricating oil (e.g., WD-40) rather than expensive high-temperature lubricants or heat-resistant lubricants.

[0068] In addition, when the surface of the insert body 50 is smoothly polished and a lubricant is applied to the surface of the insert body 50, the inner surface of the inner tube 110 may not be scratched by the rough surface of the insert body 50, and since the friction between the inner surface of the inner tube 110 and the surface of the insert body 50 is reduced, damage and / or deformation of the inner tube 110 may be limited or prevented.

[0069] That is, when the insert body 50 has a rough surface, the inner surface of the inner tube 110 may be scratched by the rough surface of the insert body 50, and the inner tube 110 may be torn or damaged due to friction between the inner surface of the inner tube 110 and the surface of the insert body 50. In addition, defects may be generated in the inner tube 110. However, the above limitations can be solved by polishing the surface of the insert body 50 smoothly or applying a lubricant to the surface of the insert body 50.

[0070] Furthermore, in process S120, the insert body 50 may be inserted into the inner tube 110. After the surface of the insert body 50 is smoothly polished or a lubricant is applied to the surface of the insert body 50, the insert body 50 may be inserted into the inner tube 110 so that the insert body 50 is smoothly inserted into the inner tube 110. In this case, the insert body 50 inserted into the inner tube 110 can be easily detached from the inner tube 110 by the smooth surface of the insert body 50 and / or the lubricant. Here, the inner tube 110 into which the insert body 50 is inserted may be inserted (or disposed) into the outer tube 120 after the insert body 50 is first inserted into the inner tube 110, or the insert body 50 may be inserted into the inner tube 110 disposed (or inserted) in the outer tube 120.

[0071] The insert 50 may have elasticity. During the process ( S200 ) of reducing the diameter of the preliminary cladding tube 100 a , if the insert 50 has elasticity, even if the inner diameter of the inner tube 110 is reduced to less than the original diameter of the insert 50, the insert 50 can be removed from the inner tube 110 by simply applying a force in the extending direction of the insert 50 (i.e., pulling the insert 50). Furthermore, when the diameter of the inner tube 110 is reduced, the elastic insert 50 can apply a buffering force to limit or prevent excessive force from being applied to the inner tube 110, and effectively provide a reaction force -F through its elasticity.

[0072] When the insert 50 has elasticity, the inner wall of the inner tube 110 may not be damaged when inserting and removing the insert 50. In addition, since the elastic force is applied when the entire inner surface of the inner tube 110 contacts the outer surface of the insert 50, when the original diameter of the insert 50 is smaller than the inner diameter of the inner tube 110, the reaction force -F may be almost not applied until the inner diameter of the inner tube 110 is reduced by the difference between the inner diameter of the inner tube 110 and the original diameter of the insert 50. Therefore, when the inner diameter of the inner tube 110 is reduced, the inner surface of the inner tube 110 contacts the outer surface of the insert 50, and the insert 50 can be concentrically arranged with the preliminary cladding tube 100a (i.e., the cross section of the insert forms a concentric axis with the (inner) circumference of the inner tube) and arranged at the center of the inner tube 110. Here, the inner tube 110 and the outer tube 120 can also form a concentric axis, and when a reaction force -F is applied (or provided) in the state where the inner tube 110 and the outer tube 120 form a concentric axis, the inner tube 110 and the outer tube 120 can be firmly fixed to each other, and a multi-layer nuclear fuel cladding tube 100 (including one tube) in which the inner tube 110 and the outer tube 120 form a concentric axis can be manufactured.

[0073] In addition, the insert 50 can be made of a polymer. The insert 50 needs to have sufficient hardness so that the insert 50 is not over-compressed and effectively provides a reaction force -F to the inner tube 110. When the insert 50 is made of a polymer, the insert 50 can have elasticity (or ductility) and also have sufficient hardness due to the high density of particles (or molecules). Therefore, the inner tube can provide sufficient reaction force -F to the pressure F applied to the inside of the inner tube 110. For example, the insert 50 can be made of the following: polyacetal, polyoxymethylene (POM), polyetheretherketone (PEEK), polyamide, nylon (such as nylon 6 / 6), ethylene vinyl acetate (EVA), thermoplastics for glue guns, or rubber.

[0074] In addition, the hardness of the insert 50 may be less than the hardness of the inner tube 110. When the hardness of the insert 50 is greater than the hardness of the inner tube 110, since the diameter of the inner tube 110 decreases due to the pressure F applied to the inside, but the diameter of the insert 50 does not change, the inner diameter of the inner tube may not decrease, thereby increasing the burden on the inner tube 110. Therefore, the inner tube 110 may be damaged, for example, cracks may be generated in the inner tube 110. When the insert 50 has the same hardness as that of the inner tube 110, since the surface of the insert 50 is in close contact with the inner surface of the inner tube 110 by the pressure F applied to the inside, the insert 50 may not be removed, or the insert 50 may be broken when removed.

[0075] Here, the insert 50 may have a hardness of 60 Shore A to 100 Shore D. When the insert 50 has a hardness less than 60 Shore A, since the insert 50 is too soft, the diameter of the insert 50 is reduced and the length of the insert 50 is increased by the pressure F applied to the inside, and the insert 50 may not provide a reaction force −F against the applied pressure F. In addition, since the insert 50 is too soft, when the insert 50 is pulled to remove the insert 50 from the inner tube 110, the insert 50 may be broken.

[0076] However, when the insert 50 has a hardness greater than 100 Shore D, since the insert 50 is too rigid, when the inner tube diameter is reduced, the insert 50 may not be removed, and the inner surface of the inner tube closely contacts the surface of the insert 50. As the brittleness increases, a portion of the insert 50 may break and remain in the inner tube 110. In addition, since the elasticity is weakened, the insert 50 may not provide the reaction force -F caused by its elasticity.

[0077] Furthermore, the length of the insert 50 may be greater than the length of each of the inner tube 110 and the outer tube 120. That is, the insert 50 may have a length greater than the length of the preliminary cladding tube 100a. When the length of the insert 50 is greater than the length of each of the inner tube 110 and the outer tube 120, the insert 50 can be easily removed by pulling the portion of the insert 50 protruding (or exposed) from the preliminary cladding tube 100a. Furthermore, when the diameter of the insert 50 is smaller than the diameter of the inner tube 110, the insert 50 can be positioned at the inner center of the inner tube 110 by supporting the protruding (or exposed) portion, and the swaging process can be performed while the insert 50 is positioned at the inner center of the inner tube 110. Furthermore, when multiple preliminary cladding tubes 100a are sewn together into a single long insert 50 by increasing the length of the insert 50, the swaging process can be performed continuously, and when the insert 50 between the multiple preliminary cladding tubes 100a that have undergone the swaging process is cut, the individually cut insert 50 can be removed from the inner tube 110.

[0078] In addition, the original diameter of the insert body 50 may be equal to or smaller than the inner diameter of the inner tube 110 of the preliminary cladding tube 100a, and in the process S200 of reducing the diameter of the preliminary cladding tube 100a, the inner diameter of the inner tube 110 may be reduced to be equal to or smaller than the original diameter of the insert body 50. The original diameter of the insert body 50 may be equal to or smaller than the inner diameter of the inner tube 110 of the preliminary cladding tube 100a, so that the insert body 50 can be easily inserted into the inner tube 110. In addition, since the inner diameter of the inner tube 110 is reduced to be equal to or smaller than the original diameter of the insert body 50 in the process S200 of reducing the diameter of the preliminary cladding tube 100a, the reaction force -F caused by the insert body 50 can be sufficiently transmitted to the inner tube 110, and the inner tube 110 and the outer tube 120 can be in close contact and firmly fixed to each other.

[0079] Furthermore, the outer tube 120 may have greater ductility than the inner tube 110. This greater ductility allows the outer tube 120 to closely contact the outer surface of the inner tube 110 during the swaging process, minimizing the separation distance between the outer tube 120 and the inner tube 110 so that the inner tube 110 and the outer tube 120 are in close contact with each other. That is, when the ductility of the outer tube 120 is greater than that of the inner tube 110, when pressure is applied to the preliminary cladding tube 100a, the outer tube 120 may closely contact the outer surface of the inner tube 110. Since the outer tube 120, having greater ductility than the inner tube 110, has a much greater ductility than the inner tube 110, the separation distance from the inner tube 110 can be minimized, and the inner tube 110 and the outer tube 120 may be in close contact and securely fixed to each other.

[0080] Therefore, during the process S200 of reducing the diameter of the preliminary cladding tube 100a, the outer tube 120 may shrink more than the inner tube 110, and become in close contact and fixed to the inner tube 100. As described above, in an exemplary embodiment, when the rod-shaped insert is inserted into the inner tube and pressure is applied from the outside to the inside of the preliminary cladding tube to reduce its diameter, the insert provides a reaction force to the inner tube to resist the pressure applied inside. This allows the inner and outer tubes to be in close contact and fixed to each other, and allows the manufacture of a multilayer nuclear fuel cladding tube using a single tube without an interface between the inner and outer tubes. Furthermore, because the insert has a rod shape, it can be removed from the inner tube by simply applying force in the direction in which the insert extends. If the insert is elastic, it will not damage the inner wall of the inner tube. Furthermore, because the insert is made of a polymer, it has sufficient hardness to provide the inner tube with sufficient reaction force to resist the pressure applied inside. Furthermore, since the rotary swaging process is performed by passing the preliminary clad tube through the plurality of rolling units having rollers spaced apart at intervals that decrease in stages, only the diameter of the preliminary clad tube can be reduced while maintaining its shape, and excessive force can be applied to the outer tube and / or inner tube, thereby preventing damage and deformation of the outer tube and / or inner tube. Furthermore, when the plurality of rolling units are configured by alternating a first rolling unit in which the plurality of rolling units are arranged in a vertical direction with a second rolling unit in which the plurality of rolling units are arranged in a horizontal direction, the rotary swaging process can be performed while the preliminary clad tube maintains a circular shape without being concave in either the vertical or horizontal direction.

[0081] Although exemplary embodiments of the present invention have been described, it should be understood that the present invention should not be limited to these exemplary embodiments, but rather that various changes and modifications may be made by those skilled in the art within the spirit and scope of the present invention as claimed below. Therefore, the true scope of protection of the present invention will be determined by the technical scope of the appended claims.

Claims

1. A method for manufacturing a multilayer nuclear fuel cladding tube, comprising: providing a preliminary cladding tube in which an inner tube having a rod-shaped insert inserted therein is disposed in an outer tube; reducing the diameter of the preliminary cladding tube by applying pressure from the outside toward the inside of the preliminary cladding tube; and removing the insert from the inner tube by applying a force parallel to the direction in which the insert extends, wherein the inner tube and the outer tube are formed of different metals from each other, wherein the insert has elasticity, wherein the original diameter of the insert is equal to or smaller than the inner diameter of the inner tube of the prepared cladding tube, and When reducing the diameter of the preliminary cladding tube, the inner diameter of the inner tube is reduced to be equal to or smaller than the original diameter of the insert.

2. The method of claim 1 , wherein reducing the diameter of the preliminary cladding tube comprises: A plurality of rolling units each including a plurality of rollers are arranged in a longitudinal direction of the prepared clad pipe so that the prepared clad pipe moves between the plurality of rollers that are paired with each other.

3. The method according to claim 2, wherein the distance between the plurality of rollers in each of the plurality of rolling units decreases in stages in the longitudinal direction of the ready-clad tube, and The pressure applied to the inner side of the preliminary clad tube gradually increases while the preliminary clad tube is moved between the plurality of rollers.

4. The method according to claim 2, wherein the plurality of rolling units comprises: a first rolling unit, wherein the plurality of rollers are arranged in a first direction; as well as a second rolling unit, wherein the plurality of rollers are arranged in a second direction intersecting the first direction, The first rolling units and the second rolling units are arranged alternately. 5 . The method according to claim 1 , wherein the insert provides a reaction force to the inner tube against the pressure when reducing the diameter of the preliminary cladding tube.

6. The method of claim 1 , wherein providing the prepared cladding tube comprises: polishing the surface of the insert or applying lubricant to the surface of the insert; as well as The insert body is inserted into the inner tube. The method of claim 1 , wherein the insert is made of a polymer. The method of claim 1 , wherein the insert has a hardness less than that of the inner tube. 9 . The method of claim 8 , wherein the insert has a hardness of 60 Shore A to 100 Shore D.

10. The method of claim 1, wherein the length of the insert is greater than the length of each of the inner tube and the outer tube.

11. The method of claim 1 , wherein the outer tube has a greater ductility than the inner tube.

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