JP7397739B2 - Bonding material, bonding method, and bonding structure - Google Patents

Description

The present invention relates to a bonding material, a method for manufacturing a bonded portion, and a bonded structure.

Silicon carbide (SiC) has excellent corrosion resistance, high thermal conductivity, and is stable up to high temperatures, so it is used for sliding members, sealing materials, heat treatment jigs, and the like. Furthermore, because it has a small thermal neutron absorption cross section, research and development is progressing as a promising material for equipment that makes up the fuel assembly of a nuclear reactor core. A composite material made of SiC as a matrix and reinforced by dispersion of SiC fibers (hereinafter also referred to as "SiC/SiC composite material") exhibits high toughness as a ceramic, and its application as a structural material is being considered.

Generally, a fuel assembly is loaded as reactor fuel into the core of a light water reactor such as a boiling water reactor (BWR) or a pressurized water reactor (PWR). In a fuel assembly, a plurality of nuclear reactor fuel rods (also simply referred to as fuel rods) loaded with uranium fuel are aligned and supported by an upper tie plate and a lower tie plate.

Each reactor fuel rod has a fuel cladding tube approximately 4 m long loaded with uranium fuel pellets, and both ends of which are sealed with end plugs. Fuel cladding tubes and end plugs have traditionally been made of zirconium alloy (zircaloy), which has a small thermal neutron absorption cross section and excellent corrosion resistance. For this reason, fuel cladding tubes and end plugs have excellent neutron economy and have been used safely in a normal nuclear reactor environment.

On the other hand, in light water reactors that use water as a coolant, if an accident occurs in which the cooling water cannot flow into the reactor (a so-called loss of coolant accident), the temperature inside the reactor will rise due to the heat generated by the uranium fuel. High temperature water vapor is generated. Additionally, when the fuel rods are exposed to the cooling water due to a lack of cooling water, the temperature of the fuel rods rises to well over 1000°C, and the zirconium alloy in the fuel cladding tube and water vapor react chemically (the zirconium alloy oxidizes). water vapor is reduced) and hydrogen is produced. Generating a large amount of hydrogen is an event that should be strictly avoided as it could lead to an explosion.

To avoid accidents such as loss of coolant and explosions, modern nuclear reactors have system designs that enhance safety by providing multiple power supplies and cooling systems, such as emergency power supplies and emergency core cooling systems. Further improvements and renovations have been made. Attempts to enhance safety are not limited to system design, but are also being considered for the materials that make up the reactor core.

For example, studies are underway to use ceramics as materials for fuel cladding tubes and end plugs instead of zirconium alloys, which cause hydrogen generation. Among them, SiC is being researched and developed as a promising material for fuel cladding tubes and end plugs because it has excellent corrosion resistance, high thermal conductivity, and small thermal neutron absorption cross section. In addition, the oxidation rate of SiC in a high-temperature steam environment exceeding 1300°C is two orders of magnitude lower than that of zirconium alloy, so even if a loss of coolant accident occurs, hydrogen production can be expected to be significantly reduced.

On the other hand, although SiC is a material with excellent corrosion resistance, consideration must be given to corrosion resistance in a highly oxidizing environment. Although SiC has a low reaction rate, it oxidizes to produce silicon oxide. Silicon oxide is water-soluble, and furthermore, in the presence of moisture, volatile silicon hydroxide is produced, so its function as a protective film may be small depending on the environment.

In SiC/SiC composites, pyrocarbon or boron nitride is used as an interfacial layer between the SiC fibers and the SiC matrix, and the interfacial layer may oxidize prior to the SiC. Additionally, SiC matrices have been formed in a variety of ways. For example, when SiC is sintered using a sintering aid such as an oxide, or when SiC is produced by reacting Si and C, oxides, unreacted Si, or unreacted C may be exposed to the environment and disappear by elution into the environment or oxidation. Elution of silicon oxide from SiC may affect the management and control of plants that employ equipment using SiC. For example, in nuclear power plants, water quality management of cooling water places a heavier load on the purification system than before, which is undesirable and should be reduced. When a SiC/SiC composite material is exposed to the environment and the interfacial layer or SiC matrix that constitutes the material is eroded, it may lose its function as a structural material, which is undesirable and should be prevented.

Next, many of the devices including fuel rods are joined structural materials having joints. In many bonding processes, heating is applied to the bonded parts, so in consideration of deterioration due to heating, we need to consider the structure of the bonded parts and the opportunities for appropriate bonding processes (heating) in the series of processes for the target equipment. It is necessary to design a process that incorporates Furthermore, it is necessary to consider the strength, corrosion resistance, etc. of the bonding material and the reaction layer between the bonding material and the base material. Bonding materials and bonding methods for SiC with a high melting point include brazing using Si, Si alloy, oxide, etc., diffusion bonding using Mo, Ti, etc., reaction sintering method, liquid phase sintering method, or chemical vapor deposition. Bonding using SiC formed by the method is being considered. Among these bonding materials, some of Si, Si alloys, Mo, SiC, and oxides have problems in corrosion resistance against high-temperature, high-pressure pure water, and it is undesirable for them to come in direct contact with the liquid, so it is necessary to prevent Should.

Diffusion bonding requires high temperature and high pressure to be applied to the SiC base material in order to obtain an airtight and strong joint. It also serves as a gas seal and is not desirable for bonding where airtightness is required.

As a joining technique by brazing, the technique described in Patent Document 1 is known. Patent Document 1 describes a technique for sealing a fuel rod cladding tube made of a SiC composite material, regardless of the design structure of the fuel rod cladding tube. The cladding preferably has a sealed SiC end plug, and a technique is described in which it is further sealed by internal brazing and an external final SiC coating.

Special Publication No. 2017-515094 (especially abstract)

By the way, Ti has excellent corrosion resistance. Therefore, Ti is considered suitable as a brazing material. However, the melting point of Ti is high and it is difficult to use a bonding material made of Ti alone. Therefore, Patent Document 1 describes a brazing material containing Ti and Cr (paragraph 0029), and the melting point of the brazing material can be lowered by containing Cr. However, according to studies conducted by the present inventors, it has been found that the corrosion resistance of the joining material, which is the brazed portion, may be reduced by including Cr.

The problem to be solved by the present invention is to provide a bonding material that is easy to construct and has excellent corrosion resistance, a method for manufacturing a bonded portion, and a bonded structure.

The bonding material of the present invention is a bonding material for bonding a first SiC member and a second SiC member, and is characterized in that it contains Ti in a proportion of 44% by mass or more and less than 100% by mass, and the remainder consists of Cr and unavoidable impurities. shall be. Other solving means will be described later in the mode for carrying out the invention.

According to the present invention, it is possible to provide a bonding material that is easy to construct and has excellent corrosion resistance, a method for manufacturing a bonded portion, and a bonded structure.

FIG. 3 is a schematic cross-sectional view showing a joint. FIG. 7 is a schematic cross-sectional view showing a joint portion of another embodiment. It is a flowchart which shows the manufacturing method of a joint part. FIG. 3 is a schematic cross-sectional view showing a method of manufacturing a joint. It is a flowchart which shows the manufacturing method of the joint part of another embodiment. FIG. 7 is a schematic cross-sectional view showing a method of manufacturing a joint according to another embodiment. FIG. 7 is a schematic cross-sectional view showing a method of manufacturing a joint according to another embodiment. FIG. 7 is a schematic cross-sectional view showing a method of manufacturing a joint according to another embodiment. . FIG. 2 is a schematic cross-sectional view of a fuel rod for BWR, which is an example of a joined structure. FIG. 9 is a cross-sectional view of FIG. 9; 10 is an enlarged view of the joint between the fuel cladding tube and the end plug shown in FIG. 9. FIG. It is a cross-sectional schematic diagram of the fuel rod for PWR which is an example of the joint structure of another embodiment. FIG. 7 is a schematic cross-sectional view of a water rod that is an example of a joint structure according to another embodiment. FIG. 7 is a schematic cross-sectional view of a fuel channel box that is an example of a joint structure according to another embodiment. FIG. 7 is a schematic diagram showing an example of a vertical cross-sectional view of a fuel assembly for BWR, which is an example of a joint structure of another embodiment. 16 is a sectional view taken along the line AA in FIG. 15. FIG. FIG. 3 is a schematic diagram of a fuel assembly for PWR, which is an example of a joint structure according to another embodiment. FIG. 7 is a schematic cross-sectional view showing a cell for BWR, which is an example of a bonded structure according to another embodiment. FIG. 7 is a schematic cross-sectional view showing a PWR cell that is an example of a bonded structure according to another embodiment. It is a graph showing evaluation results of melting start temperature and corrosion resistance of bonding materials with different Ti concentrations.

The present invention will be described below, but the present invention is not limited to the following contents, and can be implemented with arbitrary modifications within a range that does not significantly impair the effects of the present invention. The present invention can be implemented by combining different embodiments. In the following description, the same members in different embodiments will be denoted by the same reference numerals, and overlapping explanations will be omitted.

FIG. 1 is a schematic cross-sectional view showing the joint portion 8. As shown in FIG. The joining section 8 includes a first SiC member 1a (base material), a second SiC member 1b (base material), and a joining material 2 (joining member) for joining the first SiC member 1a and the second SiC member 1b. It is preferable that the first SiC member 1a and the second SiC member 1b are each a base material containing SiC as a main component. The main component in this specification is the component that exhibits the highest proportion among the constituent components. The first SiC member 1a and the second SiC member 1b are each made of a SiC/SiC composite material.

However, the first SiC member 1a and the second SiC member 1b are not limited to the SiC/SiC composite material, and it is sufficient that at least the bonding surfaces 1a1 and 1b1 with the bonding material 2 are made of SiC. In such an example, for example, a SiC layer may be formed on the surface of any fiber-reinforced material to be bonded to the bonding material 2 by vapor deposition or the like.

The bonding material 2 contains Ti in a proportion of 44% by mass or more and less than 100% by mass, and the remainder contains Cr and unavoidable impurities. By including Ti and Cr in this concentration, the melting point of the joining material 2 can be lowered than the melting point of Ti alone, making it easier to construct, and the corrosion resistance of the joining material 2 can be improved. Unavoidable impurities include, for example, Fe, Ni, and the like. The bonding material 2 includes a Ti--Cr alloy in which at least a portion of Ti and Cr are alloyed.

The concentration of Ti may be determined depending on the particularly desired performance of the bonding material 2. The bonding material 2 can contain Ti in a proportion of 44% by mass or more and 70% by mass or less. By including Ti at this concentration, the melting point of the bonding material 2 can be particularly low, making it easy to construct, and suppressing the thermal influence on the first SiC member 1a and the second SiC member 1b during construction. On the other hand, the bonding material 2 can also contain Ti in a proportion of 70% by mass or more and less than 100% by mass. By including Ti at this concentration, the composition of the bonding material 2 can be made close to 100% by mass of Ti, and the corrosion resistance of the bonding material 2 can be made to be close to the corrosion resistance in the case of 100% by mass of Ti. Preferably, by setting the Ti concentration to 90% by mass or less, the melting start temperature can be lowered.

The joining material 2 is a brazed portion 2c that joins the first SiC member 1a and the second SiC member 1b. By providing the brazed portion 2c, it is possible to reduce air bubbles at the joint portion between the first SiC member 1a and the second SiC member 1b and improve adhesion. The brazed portion 2c is formed by, for example, applying a brazing material to at least one of the joint surfaces 1a1 and 1b1 of the first SiC member 1a and the second SiC member 1b, and heat-treating the first SiC member 1a and the second SiC member 1b in a butt state. It is formed.

FIG. 2 is a schematic cross-sectional view showing a joint portion 8 of another embodiment. The joint portion 8 includes the metal film 3 so as to cover the joint portion 8 . The metal film 3 covers the bonding material 2, the first SiC member 1a, and the second SiC member 1b.

Preferably, the metal film 3 contains at least one of Cr, Ti, or Zr as a main component. When two or more of Cr, Ti, or Zr are included, it is preferable that the sum of Cr, Ti, and Zr is the main component. By providing the metal film 3, the bonding material 2 can be protected, and the reliability of the bonding portion 8 can be further improved compared to the case where it is not protected.

The thickness of the metal film 3 is preferably 10 μm or more and 1000 μm or less. By setting the thickness to 10 μm or more, the protective effect of the bonding material 2 can be fully exhibited. On the other hand, by setting the thickness to 1000 μm or less, when covering the first SiC member 1a and the second SiC member 1b, the adhesion between the first SiC member 1a and the second SiC member 1b can be improved and peeling can be suppressed. The thickness of the metal film 3 can be controlled by the method of forming the metal film 3. For example, when the film is formed by physical vapor deposition (PVD), chemical vapor deposition (CVD), plating, or powder coating, the thickness is 10 μm or more and 100 μm or less, and when the film is formed by thermal spraying or cold spray, the thickness is 100 μm or more and 1000 μm or less. .

A SiC layer (not shown) may be formed on at least the bonding surfaces 1a1 and 1b1 of the surfaces of the first SiC member 1a and the second SiC member 1b. The formation of the SiC layer prevents the sintering aid and the like that may be contained in the first SiC member 1a and the second SiC member 1b from diffusing into the bonding material 2 and the metal film 3, thereby prolonging the performance of the bonding material 2 and the metal film 3. Can be maintained for a period of time.

The composition of the bonding material 2 is determined by processing the bonding material 2 using FIB (Focused Ion Beam) or the like to obtain a cross section, and then performing composition analysis using Auger electron spectroscopy or XPS (X-ray Photoelectron Spectroscopy), or TEM (Transmission Electron Microscography). ope) or It can be identified by structural analysis using XRD (X-ray diffraction).

FIG. 3 is a flowchart showing a method for manufacturing the joint portion 8 (FIG. 1). FIG. 4 is a schematic cross-sectional view showing a method of manufacturing the joint portion 8. As shown in FIG. The joint portion 8 can be manufactured by including a placement step S1 and a heat treatment step S2. In the arrangement step S1 and the heat treatment step S2, at least a load is applied to support the positions of the first SiC member 1a, the second SiC member 1b, and the bonding material 2.

In the placement step S1, a raw material composition having the composition of the bonding material 2 (FIG. 1) is placed between the first SiC member 1a (FIG. 1) and the second SiC member 1b (FIG. 1). Preferably, the raw material composition includes a Ti--Cr alloy containing Ti and Cr each in a proportion of 2 parts of the bonding material. By using such a raw material composition, it is possible to suppress unevenness in the amounts of Ti and Cr deposited on the joint surfaces 1a1 and 1b1 (FIG. 1). In another embodiment, the raw material composition is preferably a mixture of elemental metals each containing Ti and Cr in a proportion of 2 parts of the bonding material. By using such a raw material composition, there is no need to prepare a Ti--Cr alloy in advance, so that the raw material composition can be easily arranged.

The raw material composition is, for example, in the form of a brazing material. For this reason, by attaching the raw material composition to both the joint surfaces 1a1 and 1b1 (at least one joint surface is sufficient) of the first SiC member 1a and the second SiC member 1b, the brazing material layer 4 as the raw material composition, 4 can be formed. Thereby, the brazing material layers 4, 4 can be easily arranged between the first SiC member 1a and the second SiC member 1b.

The raw material composition can be applied, for example, by thermal spraying or cold spraying, in addition to the above-mentioned brazing filler coating. By using such a method that does not require heating or requires a small amount of heating, it is possible to suppress the influence of heat and pressure on the first SiC member 1a and the second SiC member 1b due to adhesion, and to damage can be suppressed.

In the heat treatment step S2, the bonding material 2 is formed by subjecting the first SiC member 1a and the second SiC member 1b to abutment and heat treatment with the brazing material layers 4, 4 arranged. In the heat treatment step S2, the raw material composition is melted, at least a portion of Ti and Cr are alloyed, and the bonding material 2 is formed. Further, by cooling after the heat treatment, the melted joining material 2 is solidified, and the first SiC member 1a and the second SiC member 1b can be joined by the joining material 2. The heat treatment temperature can be, for example, higher than the melting point of the raw material composition and lower than the melting point of Ti. The heat treatment time can be, for example, 1 second or more and 1 hour or less.

FIG. 5 is a flowchart showing a method for manufacturing the joint portion 8 (FIG. 1) of another embodiment. When forming the metal film 3 (FIG. 2), the method for manufacturing the joint portion 8 includes forming the metal film 3 by physical vapor deposition, chemical vapor deposition, plating, powder coating, thermal spraying, or cold spray after the heat treatment step S2. It may also include a metal film forming step S3. Physical vapor deposition is, for example, a sputtering method. The metal film 3 can be formed by the metal film forming step S3, and the reliability of the joint portion 8 can be further improved as described above. The film forming method may be selected depending on the thickness of the metal film 3.

The method for manufacturing the joint portion 8 may include a second heat treatment step S4 for improving the adhesion of the metal film 3 after the metal film forming step S3. In the second heat treatment step S4, a reaction layer (not shown) can be formed by diffusion between the first SiC member 1a (FIG. 2) and the second SiC member 1b (FIG. 2) and the metal film 3 (FIG. 2), and the metal film 3. Adhesion can be improved. The second heat treatment step S4 can be performed, for example, at 950° C. or more and 1000° C. or less, and for 10 minutes or more and 1 hour or less (preferably 30 minutes or more and 1 hour or less). Note that when the metal film 3 is formed by chemical vapor deposition, thermal spraying, or cold spraying, the reaction layer can be formed by heat input or mechanical mixing during the film forming process without performing the second heat treatment step S4.

FIG. 6 is a schematic cross-sectional view showing a method of manufacturing the joint portion 8 (FIG. 1) of another embodiment. In FIG. 6, unlike FIG. 4, a foil-like body 5 of the raw material composition is arranged between the first SiC member 1a and the second SiC member 1b. In addition. In FIG. 6, for convenience of illustration, the thickness of the foil-like body 5 is made larger than the actual size relative to the first SiC member 1a and the second SiC member 1b. By using the foil-like body 5, the amount of the raw material composition arranged can be easily adjusted by adjusting the thickness of the foil-like body 5. The heat treatment step S2 (FIG. 3) is performed with the foil-like body 5 sandwiched between the first SiC member 1a and the second SiC member 1b. The thickness of the foil-like body 5 is, for example, 10 μm or more and 1 mm or less.

The foil-like body 5 can be a Ti--Cr alloy or a mixture of metals molded into a foil shape. Among these, the mixture of metal elements can be a pressed powder foil of Ti and Cr powders blended in a proportion of 2 for the bonding material.

FIG. 7 is a schematic cross-sectional view showing a method of manufacturing the joint portion 8 (FIG. 1) of another embodiment. In FIG. 7, a metal film 6 containing at least one of Ti or Cr is formed on both (or at least one of) the bonding surfaces 1a1 and 1b1. Due to the metal film 6, when the brazing material layer 4 is melted by heat treatment, a bonding interface can be quickly formed with the metal of the metal film 6, and the heat treatment time can be shortened. The metal film 6 can be formed by attaching a raw material containing at least one of Ti or Cr to the bonding surfaces 1a1 and 1b1 by physical vapor deposition, chemical vapor deposition, plating, or powder coating, and then heat-treating the bonded surfaces 1a1 and 1b1.

FIG. 8 is a schematic cross-sectional view showing a method of manufacturing the joint portion 8 (FIG. 1) of another embodiment. The joint portion 8 can also be manufactured by using the foil-like body 5 in place of the brazing material layer 4 shown in FIG. That is, the foil-like body 5, which is the raw material composition, is placed between the bonding surfaces 1a1 and 1b1 on which the metal films 6 are respectively formed. By performing the heat treatment step S2 (FIG. 3) with the foil-like body 5 sandwiched between the first SiC member 1a and the second SiC member 1b, the metal of the metal film 6 can be quickly bonded with the metal of the metal film 6 when the foil-like body 5 is melted. A bonding interface is formed between the two and the heat treatment time can be shortened.

FIG. 9 is a schematic cross-sectional view of a fuel rod 10 for BWR, which is an example of the joined structure 100. The fuel rod 10 is loaded into the core of a nuclear reactor, and includes a fuel cladding tube 11 and end plugs 12 (12a, 12b) that are joined to both ends of the fuel cladding tube 11 and seal the fuel cladding tube 11. , a plurality of fuel pellets 13 are loaded into the fuel cladding tube 11. For example, helium is sealed inside the fuel cladding tube 11 . Both the fuel cladding tube 11 and the end plug 12 are made of a SiC/SiC composite material. The fuel cladding tube 11 and the end plug 12 are joined by a joining material 2 (FIG. 11). In order to fix the fuel pellets 13, one end of the serially loaded fuel pellets 13 is pressed by a plenum spring 15.

FIG. 10 is a cross-sectional view of FIG. 9. The fuel cladding tube 11 has a largely three-layered structure, in which a coating 201 is provided on the outer surface of a circular tube base material 200, and an inner layer 202 is provided on the inner surface. By providing the inner layer 202 on the inner surface of the base material 200, the confinement of fission nuclides can be ensured. Inner layer 202 is a monolithic SiC layer, a metal layer, or a stack of monolithic SiC and metal layers. By providing the innermost metal layer, damage caused by interaction with fuel pellets can be suppressed. Furthermore, by providing a coating 201 (a coating containing at least one of Cr, Ti, and Zr as a main component) on the outer surface of the base material 200, corrosion resistance can be ensured.

FIG. 11 is an enlarged view of the joint 8 between the fuel cladding tube 11 (first SiC member 1a) and the end plug 12a (second SiC member 1b) shown in FIG. In the joint portion 8 , the fuel rod 10 (joint structure 100 ) includes a fuel cladding tube 11 , an end plug 12 , and a joining material 2 , and the joining material 2 joins the fuel cladding tube 11 and the end plug 12 . FIG. 11 does not show the fuel pellets 13, but enlarges the vicinity of the lower end plug 12a.

The end plug 12a includes a body portion 12c and a step portion 12d, and the body portion 12c extends from the step portion 12d formed on the side wall of the end plug 12a toward the tip. The end surface 12d1 of the stepped portion 12d and the open end 11a of the fuel cladding tube 11 abut against each other. The end plug 12a and the fuel cladding tube 11 are made of a bonding material 2a (bonding material 2) that bonds the end surface 12d1 and the open end 11a, and a bonding material 2a (bonding material 2) that bonds the inner wall surface 11b of the fuel cladding tube 11 and the side surface 12c1 of the body portion 12c. Bonding is performed using bonding material 2b (bonding material 2). The joining material 2a extends in the axial direction of the fuel cladding tube 11, and the joining material 2b extends in the radial direction of the fuel cladding tube 11, and these are integrally formed. Therefore, the entire bonding area of the bonding material 2 can be increased, and the bonding strength can be improved. Further, it is desirable that the body portion 12c has a threaded structure between the inner wall surface inside the end plug 12a and the inner wall surface 11b of the fuel cladding tube 11. Even if the thread structure is loose (for example, the peaks and valleys are shallow and the thread pitch is wide), the body portion 12c may separate from the fuel cladding tube 11 and the end plug 12a due to the frictional force between the male thread and the female thread that are screwed together. It is sufficient that the threaded state can be maintained without any problem.

A metal film 3 is formed so as to cover the bonding material 2a extending in the radial direction and exposed on the surface of the fuel cladding tube 11. The metal film 3 contains at least one of Cr, Ti, and Zr as a main component. The metal film 3 can protect the joining material 2 and improve the reliability of the fuel cladding tube 11.

The fuel pellets 13 can be filled into the fuel cladding tube 11 by, for example, filling the fuel pellets 13 from above by joining the lower end plug 12a and not joining the upper end plug 12b (FIG. 9). can. For the end plug 12a to be joined before filling, a SiC film is formed on each joint surface of the fuel cladding tube 11 and the end plug 12a by physical vapor deposition, chemical vapor deposition, thermal spraying, cold spray, plating, powder coating, etc. is preferred. Further, in order to improve adhesion, after film formation, it is preferable to heat the film to 950° C. or more and 1000° C. or less to form the reaction layer by diffusion.

It is preferable to form a SiC film in advance on the end plug 12b (FIG. 9) to be joined after filling. Next, in the case of heat treatment, local heating is preferably performed with a cooling mechanism (not shown) provided in the periphery so that only the vicinity of the bonding surface is heated. However, this heat treatment may be omitted. As mentioned above, when the film is formed by chemical vapor deposition, thermal spraying, or cold spraying, the reaction layer can be formed without heat treatment.

FIG. 12 is a schematic cross-sectional view of a fuel rod 20 for PWR, which is an example of a joined structure 100 of another embodiment. The fuel rod 20 includes a tubular fuel cladding tube 11 , and upper and lower openings (not shown) of the fuel cladding tube 11 are sealed with end plugs 12 . A fuel plenum 16 formed inside the fuel cladding tube 11 is filled with fuel pellets 13, and a plenum spring 15 is disposed above the fuel plenum 16. Although the detailed structure is not illustrated, a joint 8 is also formed in the fuel rod 20. The joint portion 8 joins the fuel cladding tube 11 and the end plug 12 with a joining material 2 (not shown in FIG. 12).

FIG. 13 is a schematic cross-sectional view of a water rod 33 that is an example of a joined structure 100 of another embodiment. The water rod 33 has a water rod body 30 and end plugs 12, 12b connected to upper and lower openings (not shown) of the water rod body 30, respectively, and is designed to allow reactor water to enter inside. . The water rod body 30 is made of a SiC/SiC composite material. Although the detailed structure is not shown, a joint 8 is also formed in the water rod 33. The water rod main body 30 and the end plug 12 are joined by the joining portion 8 using the joining material 2 (not shown in FIG. 13).

FIG. 14 is a schematic cross-sectional view of a fuel channel box 35 that is an example of a joint structure 100 of another embodiment. The fuel channel box 35 is a square tube, and a clip portion 38 is provided at the top. In the example of FIG. 14, the water rod main body 30 includes four L-shaped members 39 (first SiC member 1a, second SiC member 1b) made of SiC/SiC composite material, which are joined by joining material 2 at four locations. be done. However, a structure in which U-shaped members (not shown) are joined with the joining material 2 at two locations may also be used.

FIG. 15 is a schematic diagram showing an example of a vertical cross-sectional view of a fuel assembly 40 for BWR, which is an example of a joint structure 100 of another embodiment. Further, FIG. 16 is a cross-sectional view taken along the line AA in FIG. 15. The fuel assembly 40 includes a fuel rod 10 (see FIG. 9) having a joint 8 (not shown in FIGS. 15 and 16), a water rod 33, and a fuel channel box 35. The fuel assembly 40 thus comprises a joint 8 containing a joint material 2 (not shown in FIGS. 15 and 16).

The fuel assembly 40 includes an upper tie plate 31, a lower tie plate 32, and a plurality of fuel rods 10 and water rods 33 whose ends are held by the upper tie plate 31 and the lower tie plate 32. The fuel assembly 40 also includes a fuel support grid (spacer) 34 that bundles the fuel rods 10 and water rods 33, and a fuel channel box 35 that surrounds the plurality of fuel rods 10 attached to the upper tie plate 31. Fuel rods 10 (also referred to as full-length fuel rods), partial-length fuel rods 36, and water rods 33 are bundled and housed in a square lattice shape in a fuel channel box 35 having a rectangular cylindrical cross section.

The partial length fuel rod 36 is a type of nuclear reactor fuel rod, and is a fuel rod that has a shorter internal effective fuel length than the fuel rod 10 (full length fuel rod) and does not reach the upper tie plate 31 in height. A handle 37 is fastened to the upper tie plate 31, and by lifting the handle 37, the entire fuel assembly 40 can be pulled up.

In the fuel assembly 40, the water rod 33 or the fuel channel box 35 may be the same as the conventional technology (zirconium alloy water rod or fuel channel box), but assuming a coolant loss accident, the water rod 33 or the fuel channel box 35 Preferably, the fuel rods 33 also have the same configuration as the fuel rods 10.

FIG. 17 is a schematic diagram of a fuel assembly 50 for PWR, which is an example of a joined structure 100 of another embodiment. The fuel assembly 50 includes fuel rods 20 (FIG. 12) with joints 8 (not shown in FIG. 17). The fuel assembly 50 thus comprises a joint 8 containing a joint material 2 (not shown in FIG. 17).

The fuel assembly 50 includes a plurality of fuel rods 20, a plurality of control rod guide thimbles 51, an in-core instrumentation guide thimble 52, a plurality of support grids (spacers) 53 that bundle and support them, and an upper nozzle 54. and a lower nozzle 55. The upper nozzle 54 and the lower nozzle 55 are components of the skeleton of the fuel assembly 50, and at the same time play a role in positioning the fuel assembly 50 in the reactor core and ensuring a flow path for cooling water.

FIG. 18 is a schematic cross-sectional view showing a BWR cell 61 that is an example of a bonded structure 100 of another embodiment. The cell 61 includes a fuel assembly 40 (FIGS. 15 and 16) that includes a joint 8 (not shown in FIG. 18). The cell 61 therefore comprises a joint 8 containing a joint material 2 (not shown in FIG. 18).

In the cell 61, four fuel assemblies 40 are arranged in a square shape, and a control rod 41 having a cross-shaped cross section is arranged in the center thereof. By utilizing the fuel rods 10 and fuel assemblies 40, the cell 61 maintains the same long-term reliability as before under normal operating conditions, while improving safety in emergency situations (for example, a loss of coolant accident). can do.

FIG. 19 is a schematic cross-sectional view showing a PWR cell 62 that is an example of a bonded structure 100 of another embodiment. The cell 62 includes a fuel assembly 50 (FIGS. 15 and 16) with a joint 8 (not shown in FIG. 18). The cell 62 therefore comprises a joint 8 containing a joint material 2 (not shown in FIG. 18).

In the cell 60, since the control rods are arranged in the fuel assemblies 50, the four fuel assemblies 50 are arranged in a square shape. By utilizing the fuel rods 20 and fuel assemblies 50, the cell 62 also maintains the same long-term reliability as before under normal operating conditions, while improving safety in emergency situations (for example, a loss of coolant accident). can.

As described above, the bonding material 2, the bonding portion 8, and the bonding structure 100 have not only heat resistance but also corrosion resistance in a highly oxidizing usage environment containing moisture, for example. In addition, since the melting point is lower than that of Ti, bonding can be performed more easily than bonding using Ti. Furthermore, the first SiC member 1a and the second SiC member 1b are not easily damaged during bonding, and can be applied to areas where airtightness is required. For example, in a nuclear power plant, fuel rods, water rods, fuel channel boxes, etc. have heat resistance in the event of an accident, while preventing erosion of the joining material 2 due to high corrosion resistance during normal operation. A fuel assembly with reduced risk of base material damage can be provided.

Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that the present invention is not limited to these examples.

(1) Preparation and evaluation of joints of joint material examples 1 to 13 Test pieces (joint part 8) with multiple types of joint configurations (joint material examples 1 to 13) were manufactured. First, a SiC/SiC composite material was prepared as a base material (first SiC member 1a and second SiC member 1b in FIG. 1), and a SiC layer was formed on the surface of the base material by chemical vapor deposition. As raw materials for the bonding material (bonding material 2 in Figure 1), Cr-Ti alloy powders (bonding material examples 1 to 12) and Ti powder (bonding material example 13) with varying Ti concentrations were used, and these were added to the base material. It was attached to the joint surfaces (joint surfaces 1a1 and 1b1 in FIG. 1) by thermal spraying. Thereafter, the base materials were butted against each other at their ends in an inert gas to raise the temperature.

By measuring the displacement between the two base materials sandwiching the bonding surface, the start and completion of melting of the raw material of the bonding material was detected, and the melting start temperature (melting point) was determined. Specifically, the distance between the base materials, which is the width of the bonding material, becomes longer due to thermal expansion due to temperature rise, but the bonding material becomes fluidized by the start of melting, and the distance becomes shorter. Therefore, the temperature at which such a change in distance occurs was defined as the melting start temperature. Melting was completed at a temperature approximately 50° C. higher than the melting start temperature. Thereafter, the test piece was cooled to room temperature, and the joining material was solidified (brazing joining). The chemical composition of the solidified bonding material was analyzed by energy dispersive X-ray analysis (EDX) to determine the Ti concentration contained therein.

Next, the corrosion resistance of the test piece (joint part 8) joined by the brazing method was evaluated by a high temperature water corrosion test. The test piece was loaded into a pressure vessel equipped with a high-purity water circulation loop, and while circulating high-purity water with a dissolved oxygen concentration of 8 mg/L, the pressure was increased to 8 MPa and the temperature inside the pressure vessel was raised to 288 °C. and held for 500 hours. After holding for 500 hours, the temperature inside the pressure vessel was lowered to room temperature, the pressure vessel was opened, and the test piece was taken out. The presence or absence of corrosion was determined by observing the appearance and cross section of the bonding material of the test piece. The appearance and cross-sectional observation were performed visually and using an electron microscope.

Table 1 summarizes the chemical composition, melting start temperature, and presence or absence of high-temperature water corrosion of the bonding materials. Corrosion was confirmed in Bonding Material Examples 1 and 2 in which the Ti concentration was 24% by mass or less. Specifically, peeling of the bonding material and occurrence of cracks due to corrosion were confirmed. On the other hand, no corrosion was observed in bonding material examples 3 to 12 in which the Ti concentration was 44% by mass or more and less than 100% by mass. Therefore, by setting the Ti concentration in the bonding material to 44% by mass or more and less than 100% by mass, excellent corrosion resistance similar to that of Ti can be exhibited, even though the melting start temperature (melting point) can be lowered due to the inclusion of Cr. I understand.

FIG. 20 is a graph showing evaluation results of melting start temperature and corrosion resistance of bonding materials with varying Ti concentrations. In the plot, ○ indicates corrosion resistance, and × indicates no corrosion resistance. The melting start temperature was minimum when the Ti concentration was 44% by mass or more and 70% by mass or less (ie, around 55%). When the Ti concentration was 70% by mass or more, the melting start temperature increased as the Ti concentration increased, and rose to near the melting point of Ti. Therefore, it was confirmed that by setting the Ti concentration to 44% by mass or more and 70% by mass or less, corrosion can be suppressed and the melting start temperature can be particularly lowered. On the other hand, by setting the Ti concentration to 70% by mass or more and less than 100% by mass, the melting start temperature can be lowered than that of a bonding material with 100% by mass of Ti, the composition can be brought closer to 100% by mass of Ti, and the corrosion resistance can be particularly improved. Conceivable. Preferably, by setting the Ti concentration to 90% by mass or less, the melting start temperature can be lowered.

As described above, corrosion resistance against high temperature water was confirmed when the Ti concentration was 44% by mass or more, and it was found that the melting start temperature can be adjusted by changing the Ti concentration. From the viewpoint of heat resistance, a higher melting start temperature is desirable. On the other hand, the temperature at which a base material containing SiC as a main component causes damage upon heating differs depending on its shape and manufacturing method. For example, since stress concentration tends to occur in bent base materials, it is preferable to perform the work at low temperatures. Therefore, a bonding material whose Ti concentration is adjusted so as not to apply a thermal load can be used as necessary.

(2) Fabrication of joints using different methods of applying raw materials for bonding materials Test pieces were fabricated using a plurality of methods for applying raw materials for bonding materials. First, a base material on which a SiC layer was formed was produced in the same manner as in "(1) Fabrication and evaluation of bonding parts of bonding material examples 1 to 13". Next, a mixed powder of simple metals of Ti and Cr, which was blended in consideration of yield so that the Ti concentration would be 55% by mass after melting, was deposited on the bonding surface of the base material by thermal spraying. When the temperature of the test piece was raised to 1460° C. in an inert gas with the bonding surfaces pressed against each other, the mixed powder melted from the contact surface and was able to bond the base materials together as a bonding material.

On the other hand, in order to prepare another test piece, two base materials each having a SiC layer formed thereon were prepared. Then, 10 sheets of Ti--Cr alloy foil (thickness: 0.01 mm) with a Ti concentration of 55% by mass were stacked and sandwiched between the joint surfaces of the two base materials. When the temperature of the test piece was raised to 1460° C. in an inert gas with the bonding surfaces pressed against each other, the base materials could be bonded to each other using the bonding material formed by the molten foil.

In order to prepare another test piece, a mixed powder of Ti and Cr elemental metals mixed with a Ti concentration of 55% by mass was sandwiched between the two Ti-Cr alloy foils, and then a jig was placed between the two Ti-Cr alloy foils. A compacted powder sheet was produced by applying pressure with a press machine. Then, the produced green compact sheet was sandwiched between the bonding surfaces of the two base materials. When the temperature of the test piece was raised to 1460° C. in an inert gas with the bonding surfaces pressed against each other, the base materials could be bonded to each other using the bonding material formed from the molten compacted powder sheet.

Furthermore, in order to prepare another test piece, a Ti layer (metal film 6) was formed on the bonding surface of the base material by physical vapor deposition using the method described later. After formation, Ti--Cr alloy powder was applied to the joint surface of the base material by thermal spraying. When the temperature of the test piece was raised to 1460° C. in an inert gas with the bonding surfaces pressed against each other, the base materials could be bonded to each other using the bonding material formed from the molten powder.

In place of physical vapor deposition, each method of chemical vapor deposition or powder coating, which will be described later, was used, in place of the Ti layer, a Cr layer (metal film 6) or a reaction layer was formed, and in place of the Ti-Cr alloy powder. Test pieces were prepared in the same manner except that a mixed powder of Ti and Cr metals was thermally sprayed. The reaction layer here is formed by the diffusion that occurs in the second heat treatment step S4, as described with reference to FIG. 5 above. In all test pieces, the base materials could be joined together using the joining material.

A helium permeation test was performed on each of the test pieces prepared above, and it was confirmed that airtightness was ensured between both sides of the test piece containing the bonding material. Therefore, it was confirmed that a joint part that ensured airtightness could be manufactured using various manufacturing methods.

(3) Preparation of a joining member whose surface is covered with a coating A metal covering the entire specimen including the joining material is applied to each of the above test specimens by physical vapor deposition, chemical vapor deposition, thermal spraying, cold spraying, or powder coating. A film (metal film 3) was formed.

In film formation by physical vapor deposition, a sputtering method was applied, and after introducing Ar gas and keeping the chamber internal pressure constant at 1.3 Pa, the film was formed at a sputtering power of 1.50 kW and a bias voltage of 150 V. The evaporation apparatus used was one capable of forming multilayer films and graded composition layers by switching sputter evaporation sources (targets) of pure Cr, pure Ti, pure Zr, and Zr alloys. In the metal film forming step S3 (FIG. 5) and the second heat treatment step S4 (FIG. 5) in which a metal film is formed, a high temperature of 10 ⁻⁴ Pa or less is used using an oil diffusion pump (a turbo molecular pump may be used). It was heated in vacuum at 950° C. or higher and 1000° C. or lower for 0.5 hours or more and 1 hour or less. The second heat treatment step S4 in a high vacuum suppressed oxidation of active metal films such as Ti and Zr. After the heat treatment, it was confirmed that the metal film 3 did not peel off.

In film formation by chemical vapor deposition, chemical vapor deposition was carried out by flowing raw material gas and locally heating the film forming area using laser light. As source gases, Cr(CO) ₆ +H ₂ gas was used to generate the Cr film, TiCl ₂ gas was used to generate the Ti film, and ZrCl ₂ gas was used to generate the Zr film. After forming the Cr layer, a multilayer metal film consisting of a Ti film and a Zr film was formed on the Cr layer by changing the source gas and heating conditions. Note that a multilayer film could be formed even if local heating using a heater or photolysis using laser light was performed instead of local heating using laser light.

In the film formation by thermal spraying, after once purging the air around the area including the joint portion 8, the film was formed by plasma spraying while introducing Ar gas as an inert gas under reduced pressure. By suppressing the oxidation of the raw material powder during the thermal spraying process, an active metal film 3 of Ti, Zr, or Zr alloy could be formed. The raw material powder used was pure Cr, pure Ti, pure Zr, or Zr alloy powder (particle size of 10 μm or more and 60 μm or less), and by changing the raw material powder, a multilayer metal film could be formed. By mixing, a metal film with an intermediate composition (ie, an alloy) could be formed.

In film formation by cold spray, raw material powder was sprayed onto the film formation area using helium as the working gas. Cold spraying is characterized by the working gas temperature being lower than the melting point of the raw material powder, which suppresses oxidation, thermal effects, and thermal stress more than thermal spraying, making it possible to form a dense film. The raw material powders used were pure Cr, pure Ti, pure Zr, and Zr alloy powders (particle size ~50 μm). By changing the raw material powders, a multilayer metal film could be formed. By mixing the raw material powders, a multilayer metal film could be formed. A metal film with an intermediate composition (ie, an alloy) could be formed.

In film formation by powder coating, Cr powder is applied to cover at least the bonding material, and then heat treatment is performed at 950°C or more and 1000°C or less, and then Ti powder is applied and heat treatment is performed at 950°C or more and 1100°C or less. did. This made it possible to form a metal film covering the bonding material. Further, a metal film could be formed in the same manner except that Zr powder or Zr alloy powder was used instead of Ti powder. In some specimens, after application of Cr powder and subsequent heat treatment, it was possible to thicken the Cr layer by Cr plating.

The test pieces prepared above were subjected to the high-temperature water corrosion test described in "(1) Preparation and evaluation of joint portions 8 of joining material examples 1 to 13" above. As a result, no corrosion was observed in any of the test pieces, confirming that the metal film shielded the base material and bonding material from the corrosive environment.

As described above, it has been shown that the bonding material 2, the bonding portion 8, and the bonding structure 100 exhibit high corrosion resistance in an oxidizing environment containing moisture, a steam environment, or a high-temperature water environment.

The embodiments described above are specifically described to help understand the present invention, and the present invention is not limited to having all the configurations described. For example, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Further, some of the configurations of each embodiment can be deleted, replaced with other configurations, or added with other configurations.

10,20 Fuel rod (reactor fuel rod)
1000 Joint structure 11 Fuel cladding tube 11a Open end 12, 12a, 12b End plug 12c Body part 12d Step part 13 Fuel pellet 15 Plenum spring 16 Fuel plenum 1a First SiC member 1a1, 1b1 Joint surface 1b Second SiC member 2, 2a, 2b Bonding material 200 Base material 201 Film 202 Inner layer 2c Brazing portion 3 Metal film 30 Water rod body 31 Upper tie plate 32 Lower tie plate 33 Water rod 34 Fuel support grid 35 Fuel channel box 36 Partial length fuel rod 37 Handle 38 Clip portion 39 Member 4 Brazing material layer 41 Control rod 5 Foil-like body (raw material composition)
40, 50 Fuel assembly 51 Control rod guide thimble 52 In-core instrumentation guide thimble 53 Support grid 54 Upper nozzle 55 Lower nozzle 6 Metal film 60, 61, 62 Cell 8 Joint portion S1 Placement step S2 Heat treatment step S3 Metal film forming step S4 Second heat treatment step

Claims (15)

A joining material for joining a first SiC member and a second SiC member,
Contains Ti in a proportion of 44% by mass or more and less than 100% by mass, and the remainder consists of Cr and inevitable impurities.
A bonding material characterized by: The bonding material according to claim 1, wherein the Ti is contained in a proportion of 44% by mass or more and 70% by mass or less. The bonding material according to claim 1, wherein the Ti is contained in a proportion of 70% by mass or more and less than 100% by mass. The joining material according to any one of claims 1 to 3, wherein the joining material is a brazed portion that joins the first SiC member and the second SiC member. A method for manufacturing a joint, comprising: a first SiC member, a second SiC member, and a joining material for joining the first SiC member and the second SiC member,
A raw material composition having the composition of the bonding material containing Ti in a proportion of 44% by mass or more and less than 100% by mass and the remainder consisting of Cr and unavoidable impurities is placed between the first SiC member and the second SiC member. placement process,
a heat treatment step of forming the bonding material by abutting and heat-treating the first SiC member and the second SiC member with the raw material composition arranged. Claim characterized in that the raw material composition is disposed between the first SiC member and the second SiC member by attaching the raw material composition to at least one of the first SiC member and the second SiC member. 5. The method for manufacturing a joint according to 5. The method for manufacturing a joint according to claim 6, wherein the raw material composition is applied by coating, thermal spraying, or cold spraying. 6. The method for manufacturing a joint according to claim 5, further comprising disposing a foil-like body of the raw material composition between the first SiC member and the second SiC member. The method for manufacturing a joint according to any one of claims 5 to 8, wherein the raw material composition includes a Ti--Cr alloy containing the Ti and the Cr in the respective proportions. The method for manufacturing a joint according to any one of claims 5 to 8, wherein the raw material composition is a mixture of elemental metals containing the Ti and the Cr in the respective proportions. A metal film containing at least one of Cr, Ti, or Zr as a main component is formed by physical vapor deposition, chemical vapor deposition, plating, powder coating, thermal spraying, or cold spray so as to cover the joint part. The method for manufacturing a joint according to any one of claims 5 to 8, comprising a forming step. According to any one of claims 5 to 8, a metal layer containing at least one of Ti and Cr is formed on at least one of the joint surfaces of the first SiC member and the second SiC member. Method of manufacturing joints. A bonded structure having a bonded portion including a first SiC member, a second SiC member, and a bonding material for bonding the first SiC member and the second SiC member,
The bonding material contains Ti in a proportion of 44% by mass or more and less than 100% by mass, and the remainder consists of Cr and inevitable impurities.
A bonded structure characterized by: The bonded structure according to claim 13, further comprising a metal film containing at least one of Cr, Ti, or Zr as a main component so as to cover the bonded portion. The joined structure according to claim 13 or 14, wherein the joined structure is a fuel rod, a fuel channel box, a water rod, or a fuel assembly.

Images