Film forming device and method for manufacturing fuel cladding tube

Abstract

To provide a film deposition apparatus usable for a longer period of time and a manufacturing method of a fuel cladding tube.SOLUTION: A film deposition apparatus includes: a vacuum chamber; an electrode material that is arranged on a bottom part or an upper most part of the vacuum chamber and can rotate around an axis line extending in a vertical direction; and multiple targets that are made of chromium as a sputtering evaporation source arranged in the axis line direction in an outer peripheral side of a tube material that is arranged on the electrode material or hung from the electrode material, extends in the axis line direction, and is made of a zirconium alloy.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a film forming apparatus and a method for manufacturing a fuel cladding tube. [Background technology]

[0002] In nuclear reactors (light water reactors), fuel rods are formed by placing fuel pellets in fuel cladding tubes, and multiple fuel rods are bundled together to form a fuel assembly. Fuel cladding tubes are generally made of zirconium alloys. However, zirconium alloys are susceptible to oxidation and deformation when exposed to high-temperature steam in the event of an accident, so there is a need for improved accident resistance in these unlikely events. Furthermore, there is a trend toward higher fuel burnup in the future to reduce spent fuel. Therefore, there is a growing demand for improved corrosion resistance and wear resistance of fuel assemblies so that they can withstand long-term use in nuclear reactors.

[0003] Therefore, a technique for forming a chromium coating on the surface of a zirconium alloy has been proposed, as described in Patent Document 1 below, for example. In this technique, the pipe material is covered with a first coating layer containing a metal element and a second coating layer made of chromium that covers the first coating layer. Specific examples of methods used to form the coating include thermal spraying and chemical vapor deposition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2017-517631 Summary of the Invention [Problem to be solved by the invention]

[0005] However, forming a coating by thermal spraying or chemical vapor deposition, as in Patent Document 1, can cause deterioration of the substrate due to thermal and chemical influences, and can also cause cracks and peeling of the coating at grain boundaries.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a film-forming apparatus and a method for manufacturing a fuel cladding tube that can maintain a coating stably for a longer period of time. [Means for solving the problem]

[0007] In order to solve the above-described problems, the film formation apparatus according to the present disclosure includes a vacuum chamber, an electrode material that is arranged at the bottom or the top of the vacuum chamber and is rotatable about an axis extending in a vertical direction, and a plurality of targets made of chromium as sputtering evaporation sources that are placed on or suspended from the electrode material and that extend in the axial direction and are arranged in the axial direction on the outer periphery of a tubular material made of a zirconium alloy. At least a portion of a pair of the targets adjacent to each other in the axial direction overlaps with each other in the axial direction.

[0008] The method for manufacturing a fuel cladding tube according to the present disclosure includes a preparation step of placing a pipe material made of a zirconium alloy extending in an axial direction on an electrode material in a vacuum chamber and placing a plurality of chromium targets in the axial direction on the outer periphery of the pipe material; an etching step of applying a voltage between the electrode material and the vacuum chamber while argon is being supplied into the vacuum chamber; and a coating formation step of applying voltages between the targets and the vacuum chamber and between the electrode material and the vacuum chamber by independent power sources while argon and nitrogen are being supplied into the vacuum chamber, thereby rotating the pipe material around the axis and forming an amorphous coating on the surface of the pipe material. At least a portion of each of the pair of targets adjacent to each other in the axial direction overlaps with each other in the axial direction. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a film forming apparatus and a method for manufacturing a fuel cladding tube that can be used stably for a longer period of time. [Brief explanation of the drawings]

[0010] [Figure 1]1 is a longitudinal cross-sectional view showing a configuration of a fuel cladding tube according to an embodiment of the present disclosure. FIG. [Figure 2] 1 is a cross-sectional view showing a configuration of a fuel cladding tube according to an embodiment of the present disclosure. FIG. [Figure 3] 1 is a schematic cross-sectional view illustrating a configuration of a film forming apparatus according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is an explanatory diagram showing a coating formation step in a method for manufacturing a fuel cladding tube according to an embodiment of the present disclosure. [Figure 5] 1 is a flowchart illustrating steps in a method for manufacturing a fuel cladding tube according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a fuel rod 1, a cladding tube 10 (fuel cladding tube), a method for manufacturing the cladding tube 10, and a film forming apparatus 40 according to an embodiment of the present disclosure will be described with reference to FIGS.

[0012] (Fuel rod configuration) The fuel rod 1 is rod-shaped and arranged with its axis in the vertical direction inside the reactor core. As shown in Fig. 1, the fuel rod 1 has a cylindrical cladding tube 10, a spring 11 housed inside the cladding tube 10, fuel pellets 2, and upper and lower end plugs 12 and 13 provided at both ends.

[0013] The fuel pellets 2 are fissile materials whose main components are, for example, uranium or plutonium, and are used as a heat source for the reactor core. The fuel pellets 2 are molded into cylindrical pellets with a height and diameter of approximately 1 cm. These fuel pellets 2 are filled in the cladding tube 10 in a stacked manner starting from the bottom. The uppermost fuel pellet 2 is pressed downward by a spring 11.

[0014] (Configuration of cladding tube) 2 and 3, the cladding tube 10 includes a cylindrical tube material 31 centered on an axis O and a metal layer 32 (coating) formed on the outer surface of the tube material 31. The tube material 31 is formed of a zirconium alloy. More specifically, the tube material 31 contains zirconium and at least one chemical species selected from tin, niobium, iron, chromium, and oxygen. Even more specifically, the tube material 31 contains 0 to 2 wt. % tin, 0 to 2 wt. % niobium, 0 to 0.4 wt. % iron, 0 to 0.5 wt. % chromium, 0 to 0.2 wt. % oxygen, and zirconium as the balance.

[0015] The metal layer 32 is a coating containing chromium and nitrogen. More specifically, in the metal layer 32, the chromium element containing nitrogen forms an amorphous structure rather than a crystalline structure. Here, the term "amorphous structure" also includes ultrafine crystalline structures close to an amorphous structure. The metal layer 32 is formed on the surface (outer surface) facing the outer periphery of the pipe material 31. It is also possible to provide another coating layer made of pure chromium on the outer periphery of such a metal layer 32. In this case, pure chromium is softer than the metal layer 32, and therefore can follow the expansion of the pipe material 31 when it expands, thereby reducing the possibility of cracks occurring in the coating.

[0016] (Configuration of film formation device) Next, a film forming apparatus 40 for forming the metal layer 32 on the above-mentioned tubular material 31 will be described with reference to Figures 3 and 4. The film forming apparatus 40 has an electrode material 41 that applies a negative potential (bias voltage) to the tubular material 31, a target 42 and a magnet 43 as sputtering evaporation sources, and power supplies 44 and 45. Note that, for the sake of simplicity, the power supplies 44 and 45 are not shown in Figure 3. Also, for the sake of simplicity, only one set of the target 42 and the magnet 43 is shown in Figure 4.

[0017] The negative pole of a power supply 45 is connected to the target 42 and magnet 43 as a sputtering evaporation source. The magnet 43 is provided on the outer periphery of the target 42. More specifically, the magnet 43 is arranged on the outer periphery of the target 42 so that it is the back surface of the target 42 when viewed from the tubular material 31. The magnet 43 may be in contact with the target 42 or may be spaced apart. The surface of the target 42 is exposed toward the tubular material 31. The target 42 is arranged at a radial distance from the outer surface of the tubular material 31.

[0018] A plurality of such sets of targets 42 and magnets 43 are provided in the axial direction O of the tubular material 31. Furthermore, these targets and magnets 43 are arranged at intervals from one another in the circumferential direction when viewed from the axial direction O. More specifically, if the circumferential position of an arbitrary target 42 and magnet 43 is taken as 0° when viewed from the axial direction O, it is desirable that another target 42 and magnet 43 adjacent to it in the axial direction O be provided at a circumferential position 180° apart. Note that these circumferential positions are merely examples and can be changed as appropriate depending on the design and specifications.

[0019] Furthermore, as shown by the dashed lines in Figure 3, at least a portion of the ends in the direction of the axis O of a pair of targets 42 and magnets 43 adjacent to each other in the direction of the axis O overlap with each other in the direction of the axis O. In other words, these pairs of targets 42 and magnets 43 overlap with each other in the direction of the axis O. Furthermore, the targets 42 and magnets 43 located on both ends in the direction of the axis O extend beyond the ends of the tubular material 31 in the direction of the axis O. In other words, both ends of the tubular material 31 are covered by the targets 42 and magnets 43 from the radially outer side.

[0020] The electrode material 41, which applies a negative potential (bias voltage) to the tubular material 31, is in the form of a plate that contacts the tubular material 31 from below. Alternatively, the electrode material 41 can be placed on top, and the tubular material 31 can be fixed by hanging it from the electrode material 41. The electrode material 41 is rotatable around its own central axis (axis line O). By rotating the electrode material 41, a coating is formed sequentially in the circumferential direction on the surface of the tubular material 31. Alternatively, the electrode material 41 may be fixed and the target 42 may be rotated around the central axis of the electrode material 41.

[0021] (Fuel cladding tube manufacturing method) Next, a method for manufacturing a fuel cladding tube will be described with reference to Figures 4 and 5. As shown in Figure 5, this manufacturing method includes a preparation step S1, an etching step S2, and a coating formation step S3.

[0022] In the preparation step S1, the above-mentioned tubular material 31 is prepared and placed on an electrode material 41. In this state, the tubular material 31 is placed in a vacuum chamber 46. Furthermore, a target 42 made of chromium is placed on the outer periphery of the tubular material 31, and a magnet 43 is placed on the outer periphery of the target 42 so that it is on the back side of the target 42 when viewed from the tubular material 31.

[0023] Following the preparation step S1, an etching step S2 is carried out. In this step, while argon is being supplied into the vacuum chamber, a negative potential (bias voltage) is applied to the tube material 31 (electrode material 41) with respect to the vacuum chamber 46 by supplying power from the power source 44. This causes the argon in the vacuum chamber 46 to become a plasma state, and argon ions (Ar + By setting the magnitude of this bias voltage to 300 V or more, the argon ions are strongly irradiated onto the tubular material 31, and the surface of the tubular material 31 is etched and cleaned.

[0024] Next, a film forming step S3 is performed. In this step, while argon and nitrogen are supplied into the vacuum chamber, a negative potential is applied to the target 42 with respect to the vacuum chamber 46 by the power supply 45. The application of the potential and the magnetic field action of the magnet 43 turn the vicinity of the surface of the target 42 into a high-concentration argon plasma, and argon ions (Ar + ) irradiation causes the chromium element of the target to be released by sputtering. At the same time, a negative potential (bias voltage) relative to the vacuum chamber 46 is applied to the tube material 31 (electrode material 41) by power supply from the power source 44. At this time, the partial pressure of argon is set to 0.1 Pa or less, more preferably 0.01 Pa or more and 0.1 Pa or less. The partial pressure of nitrogen is set to a range of more than 0 Pa and 0.06 Pa or less. The temperature inside the vacuum chamber 46 is set to 150°C or more and 200°C or less. Note that, as will be described in detail later, if the bias voltage is 150 V or more, the chromium will crystallize, making it impossible to obtain an amorphous metal layer 32.

[0025] Under these conditions, as shown in FIG. 4, nitrogen molecules collide with electrons (plasma electrons) emitted by the plasma in the vacuum chamber 46 to form nitrogen ions (N + ) is formed on the surface of the tube material 31. At the same time, chromium (Cr) released by sputtering is deposited on the surface of the tube material 31, and argon ions (Ar) are electrically deposited on the surface of the tube material 31 by the bias voltage. + ), nitrogen ions (N + ) is attracted to the chromium element (Cr) and the nitrogen element (N) is supplied while energy is imparted to the chromium element (Cr) being deposited, thereby forming a metal layer 32 with an amorphous structure.

[0026] (Action and effect) Here, conventionally, thermal spraying or chemical vapor deposition has been used to form the metal layer 32 on the pipe material 31. However, simply forming a coating by thermal spraying or chemical vapor deposition can cause deterioration of the substrate due to thermal or chemical influences. Furthermore, there is a risk of the coating cracking or peeling at the grain boundaries. Therefore, the present embodiment employs the above-described configuration and method.

[0027] According to the above-described configuration, a coating of amorphous nitrogen and chromium can be formed on the surface of the tube material 31. This makes it possible to obtain a uniform coating structure with no microscopic boundaries, unlike, for example, when a coating of crystallized chromium nitride is formed. As a result, even if the tube material 31 expands or deforms due to long-term use, the coating follows and suppresses the deformation, thereby further extending the life of the cladding tube 10.

[0028] Furthermore, since multiple targets 42 arranged in the direction of the axis O are provided, a uniform coating can be formed without unevenness in thickness even on a long tubular material 31 having a large dimension in the direction of the axis O. Conversely, if one large target 42 is used for a long tubular material 31, the internal resistance of the target 42 may cause unevenness in the potential difference between the target 42 and the vacuum chamber 46. However, by forming a film using multiple small targets 42 as described above, unevenness in the potential difference is eliminated, and the thickness of the metal layer 32 can be maintained uniform throughout the entire extension length of the tubular material 31.

[0029] Furthermore, the multiple targets 42 are arranged at intervals from one another in the circumferential direction when viewed from the direction of the axis O. With this configuration, the dimensions of the targets 42 can be reduced compared to, for example, a case in which a cylindrical target 42 is used that covers the entire circumferential area of ​​a pipe material. This reduces the manufacturing cost of the device. In particular, by reducing the size of the targets 42, the volume and dimensions of the vacuum chamber 46 that covers them from the outer periphery can also be reduced. This makes it possible to achieve further cost reductions.

[0030] In addition, by avoiding the enlargement of the target 42 in this manner, for the same reasons as described above, unevenness in the potential difference between the vacuum chamber 46 and the target 42 is eliminated, making it possible to maintain a more uniform film thickness of the metal layer 32 throughout the entire extension length of the tube material 31.

[0031] Furthermore, in the above configuration, at least a portion of the ends of a pair of adjacent targets 42 in the direction of the axis O overlap with each other in the direction of the axis O. Here, sufficient plasma density cannot be ensured at both ends of the target 42 in the direction of the axis O, resulting in a reduced amount of chromium element released by sputtering. It is known that the thickness of the coating (metal layer 32) tends to be small at these ends. However, because the pair of targets 42 overlap with each other at both ends of the target 42 in the direction of the axis O, the chromium element released by the pair of targets 42 in the sputtering is superimposed, and a synergistic effect ensures a sufficient amount of chromium element. As a result, the thickness can be ensured even at these ends, making it possible to obtain a coating with a desired thickness.

[0032] Furthermore, the above manufacturing method allows for the formation of an amorphous nitrogen and chromium coating on the surface of the pipe material 31. This makes it possible to obtain a coating structure that has no microscopic boundaries, i.e., no grain boundaries or lattice defects that weaken its ability to conform to deformation, unlike when, for example, a coating of crystallized chromium nitride is formed. As a result, even if, for example, the pipe material 31 expands or deforms, the coating can easily conform to the deformation, and the life of the cladding tube 10 can be maintained even longer.

[0033] The above describes the embodiments of the present disclosure. It should be noted that various changes and modifications can be made to the above-described configurations and methods without departing from the spirit and scope of the present disclosure. For example, in the above-described embodiments, a configuration and method for forming a film while the tubular material 31 rotates around the axis O in conjunction with the rotation of the electrode material 41 has been described. However, as long as the dimensional constraints of the vacuum chamber 46 allow, it is also possible to adopt a configuration in which the tubular material 31 moves back and forth in the direction of the axis O while the electrode material 41 is rotated.

[0034] In the above embodiment, an example has been described in which the multiple targets 42 and magnets 43 are arranged at circumferential intervals of 180° from one another. However, the circumferential intervals are not limited to the above, and the multiple targets 42 and magnets 43 can also be arranged in a spiral shape from one side to the other in the direction of the axis O. With such a configuration, the same effects as those described above can be obtained.

[0035] <Additional Notes> The film forming apparatus 40 and the method for manufacturing the fuel cladding tube (cladding tube 10) described in each embodiment can be understood, for example, as follows.

[0036] (1) A film forming apparatus 40 according to a first embodiment includes a vacuum chamber 46, an electrode material 41 disposed at the bottom or top of the vacuum chamber 46 and rotatable about an axis O extending in the vertical direction, and a plurality of targets 42 made of chromium as sputtering evaporation sources disposed on or suspended from the electrode material 41, extending in the direction of the axis O, and arranged in the direction of the axis O on the outer periphery of a tube material 31 made of a zirconium alloy.

[0037] According to the above configuration, a coating of amorphous nitrogen and chromium can be formed on the surface of the tubular material 31. This makes it possible to obtain a coating structure free of grain boundaries and lattice defects. Furthermore, since multiple targets 42 are provided arranged in the direction of the axis O, a uniform coating can be formed without unevenness in film thickness even on a long tubular material with a large dimension in the direction of the axis O.

[0038] (2) A film forming apparatus 40 according to a second aspect is the film forming apparatus 40 of (1), in which the targets 42 are arranged at intervals in the circumferential direction when viewed from the axis O direction.

[0039] According to the above configuration, the size of the target 42 can be reduced compared to when using a target 42 that covers the entire circumferential area of ​​the tubular material 31, thereby reducing the manufacturing cost of the device.

[0040] (3) The film forming apparatus 40 according to the third aspect is the film forming apparatus 40 of (1) or (2), in which the multiple targets 42 are arranged at 180° intervals in the circumferential direction when viewed from the direction of the axis O.

[0041] According to the above configuration, it is possible to avoid an increase in the size of the target 42, and therefore it is possible to reduce the manufacturing cost of the device.

[0042] (4) The film forming apparatus 40 according to the fourth aspect is a film forming apparatus 40 according to any one of aspects (1) to (3), in which at least a portion of a pair of the targets 42 adjacent to each other in the direction of the axis O overlaps with each other in the direction of the axis O.

[0043] According to the above configuration, the pair of targets 42 overlap each other at both ends in the direction of the axis O of the target 42, where the thickness of the coating tends to be small. This ensures the film thickness even at these ends, making it possible to obtain a coating having a desired film thickness.

[0044] (5) A manufacturing method of a fuel cladding tube (cladding tube 10) according to the fifth aspect includes a preparation step S1 in which a tube material 31 made of a zirconium alloy extending in the direction of axis O is placed on an electrode material 41 in a vacuum chamber 46, and multiple targets 42 made of chromium are placed on the outer periphery of the tube material 31 in the direction of axis O; an etching step S2 in which a voltage is applied between the electrode material 41 and the vacuum chamber 46 while argon is being supplied into the vacuum chamber 46; and a coating formation step S3 in which a voltage is applied between the target 42 and the vacuum chamber 46 and between the electrode material 41 and the vacuum chamber by independent power sources while argon and nitrogen are being supplied into the vacuum chamber 46, and the tube material 31 is rotated around the axis O to form an amorphous coating on the surface of the tube material 31.

[0045] According to the above method, a coating of amorphous nitrogen and chromium can be formed on the surface of the tubular material 31. This makes it possible to obtain a coating structure free of grain boundaries and lattice defects. Furthermore, since multiple targets 42 arranged in the direction of the axis O are used, a coating can be formed uniformly without unevenness in film thickness even on a long tubular material 31 having a large dimension in the direction of the axis O. [Explanation of symbols]

[0046] 1 fuel rod 2 fuel pellets 10 Cladding tube (fuel cladding tube) 11 Spring 12 Upper end plug 13 Lower end plug 31 Piping material 32 Metal layer 40 Film deposition equipment 41 Electrode material 42 Target 43 Magnet 44 Power supply 45 Power supply 46 Vacuum Chamber O axis

Claims

1. a vacuum chamber; an electrode material disposed at the bottom or top of the vacuum chamber and rotatable about an axis extending in a vertical direction; and a plurality of targets made of chromium as sputtering evaporation sources disposed on or suspended from the electrode material, the electrode material extending in the axial direction, and arranged in the axial direction on the outer periphery of a tube made of a zirconium alloy; A film forming apparatus in which a pair of the targets adjacent to each other in the axial direction at least partially overlap each other in the axial direction.

2. The film deposition apparatus according to claim 1 , wherein the plurality of targets are arranged at intervals in the circumferential direction when viewed from the axial direction.

3. 3. The film deposition apparatus according to claim 1, wherein the plurality of targets are arranged at intervals of 180 degrees in the circumferential direction when viewed from the axial direction.

4. The method includes a preparation step of placing a tubular material made of a zirconium alloy extending in the axial direction on an electrode material in a vacuum chamber, and placing a plurality of chromium targets in the axial direction on the outer periphery of the tubular material; an etching step of applying a voltage between the electrode material and the vacuum chamber while argon is being supplied into the vacuum chamber; and a coating step of applying voltages between the target and the vacuum chamber and between the electrode material and the vacuum chamber by independent power sources while argon and nitrogen are being supplied into the vacuum chamber, and rotating the tubular material around the axis to form an amorphous coating on the surface of the tubular material. A method for manufacturing a fuel cladding tube, wherein a pair of the axially adjacent targets at least partially overlap each other in the axial direction.

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