JP2021024758A - Joining member and joint structure including the same - Google Patents

Abstract

To provide: a joining member which has strength against bending stress applied by vibrations during transportation and operation of a fuel assembly, and which has airtightness for preventing leakage of radioactive nuclide; and a joint structure including the joining member.SOLUTION: End plugs 12A, 12B, 12C, 22A and 22B are formed by a base material composed of a SiC composite material at least whose surface region is reinforced by SiC fiber. An orientation direction of the SiC fiber, except for the SiC fiber that is inevitable for structure formation, is parallel to a length direction of the base material and parallel to a surface of the base material.SELECTED DRAWING: Figure 4

Description

The present invention relates to a joining member used for a joining portion such as a fuel assembly and a joining structure provided with the joining member.

As an example of a fuel cladding tube joint having excellent corrosion resistance, radiation resistance, joint strength, etc. even in high temperature and high pressure furnace water, Patent Document 1 states that the fuel cladding tube joint has fuel pellets inserted on the inner surface thereof. When sealing the fuel pellet by joining the end plug to the end of the fuel cladding tube whose outer surface comes into contact with the furnace water, both the fuel cladding tube and the end plug are reinforced with silicon carbide fiber reinforced with silicon carbide filaments. It is described that at least the portion of the portion formed of the composite material and in which the fuel cladding tube and the end plug are joined, which is in contact with the furnace water, is directly joined without interposing different materials.

Patent No. 5677184

Silicon carbide (SiC) is used for sliding members, sealing materials, heat treatment jigs, and the like because it not only has excellent corrosion resistance, but also has high thermal conductivity and is stable up to high temperatures.

Furthermore, since the thermal neutron absorption cross section is small, research and development have been progressing in recent years as a promising material for equipment constituting a fuel assembly in a nuclear reactor core. In particular, a composite material reinforced with SiC fibers (hereinafter, also referred to as “SiC composite material”) exhibits high toughness as ceramics, and its application as a structural material is being studied.

Generally, a fuel assembly is loaded as a reactor fuel in the core of a light water reactor such as a boiling water reactor (BWR: Boiling Water Reactor) or a pressurized water reactor (PWR). In this fuel assembly, a plurality of 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 is loaded with uranium fuel pellets in a fuel cladding tube having a length of about 4 m, and both ends thereof are sealed by end plugs.

Zirconium alloy (Zircaloy), which has a small thermal neutron absorption cross section and excellent corrosion resistance, has been used as the material for these fuel cladding tubes and end plugs, and has excellent neutron economy and is used in ordinary nuclear reactors. Has been used safely in the environment.

On the other hand, in a light water reactor that uses water as a coolant, if an accident occurs in which the coolant cannot flow into the reactor (so-called coolant loss accident), the temperature inside the reactor rises due to the heat generated by the uranium fuel. High temperature steam is generated. Further, when the fuel rods are exposed from the cooling water due to lack of cooling water, the temperature of the fuel rods rises and easily exceeds 1000 ° C., and the zirconium alloy constituting the fuel cladding tube is oxidized and water vapor is reduced by a chemical reaction. Hydrogen is produced. Mass generation of hydrogen is an event that should be strictly avoided because it leads to an explosion accident.

In order to avoid accidents such as loss of coolant and explosion, the current nuclear reactor has a system design with enhanced safety, such as installing multiple power supply devices and cooling devices such as emergency power supply and emergency core cooling system. However, in addition, further improvements and renovations have been repeated. Attempts to enhance safety are being studied not only for system design but also for the materials that make up the core.

For example, studies are underway to use ceramics instead of zirconium alloys, which cause hydrogen generation, as materials for fuel cladding tubes and end plugs. Among them, silicon carbide (SiC) has excellent corrosion resistance, high thermal conductivity, and a small thermal neutron absorption cross section, and therefore research and development is progressing as a promising material for fuel cladding tubes and end plugs. Moreover, since the oxidation rate of SiC in a high-temperature steam environment exceeding 1300 ° C. is more than two orders of magnitude lower than that of a zirconium alloy, a significant reduction in hydrogen production can be expected even in the unlikely event of a loss-of-coolant accident. ..

A SiC composite material reinforced with SiC fibers is preferably used as a base material because it is superior in toughness as a structural member as compared with monolithic SiC.

On the other hand, it is known that the SiC composite material has lower strength than the conventional zirconium alloy at the temperature during normal operation. From this, it is necessary to increase the cross-sectional area in order to obtain the same structural strength.

However, parts such as fuel rods constituting the fuel assembly are elaborately designed to maintain the fission reaction at an appropriate neutron flux and cooling water flow rate, and there are restrictions on the dimensions.

In particular, the upper tie rate and the lower tie rate, which align and support fuel rods and water lots (hereinafter referred to as fuel rods, etc.), are provided with holes for allowing cooling water to pass through, and the fuel rods, etc. are fitted. It is not preferable from the viewpoint of securing the structural strength of the tie plate and the amount of cooling water that the size of the holes and the dents is large. Therefore, it is necessary to increase the strength of the end plug that is in direct contact with the tie plate.

Next, in fuel rods, airtightness is required for the fuel cladding, end plugs and their joints to prevent fission nuclides from leaking to the outside.

In the chemical vapor deposition method, which is considered to be the mainstream as a method for producing SiC composite materials for nuclear power applications, even if a SiC matrix is filled between SiC fibers, about 20% of voids remain, so that the airtightness is maintained when used as it is. It is necessary to improve the airtightness of the end plug because it does not meet the requirements of.

Various technologies have been developed and proposed to overcome the above-mentioned weaknesses.

For example, in the above-mentioned Patent Document 1, of the portion where the fuel cladding tube and the end plug are joined, the side in contact with the furnace water is directly joined without interposing a different material, and the side not in contact with the furnace water is a different material, for example titanium. It is disclosed that the bonding is made via a mixture of silicon carbide and titanium silicide, or silicon carbide containing aluminum and ittium.

Here, when considering replacing the Zircaloy member of the fuel assembly with a SiC composite material, the SiC composite material is generally weaker than the Zircaloy at the normal operating temperature of the nuclear reactor, so that the member has dimensional restrictions. It is necessary to use a high-strength SiC composite material.

In particular, since the fuel rods and water rods are fitted to the upper tie plate and the lower tie plate having the cooling water flow path holes via the end plugs, the size of the end plugs is restricted. Therefore, it is necessary to use a high-strength SiC composite material for this end plug.

This is because the end plugs are located at both ends of the fuel rods and function as fixed ends at the points of contact with the upper tie plate and lower tie rate, so bending stress is applied due to vibration during transportation and operation. This is because there is a restriction.

On the other hand, in the technique described in Patent Document 1, since the fuel cladding tube and the end plug are both formed of the SiC composite material, the airtightness depends only on the SiC composite material.

Here, the problem of the SiC composite material is to reduce the porosity in the manufacturing method, and the molten metal impregnation method is known as the manufacturing method in which the porosity is 0, but the nuclear power that residual Si is generated. There is a problem that it is not suitable for use.

Further, when the fuel rods are loaded as a fuel assembly, the fuel rods are fitted to the upper tie plate and the lower tie plate via the end plugs, so that the end plugs have a shape to be incorporated into the tie plate. However, the shape of the end plug shown in Patent Document 1 is simple and does not have the characteristic of the shape to be fitted to the tie plate, and there is room for improvement.

Therefore, in view of the above circumstances, an object of the present invention is to provide a joint member having strength against bending stress applied by vibration during transportation or operation of the fuel assembly and airtightness for preventing leakage of radionuclides. The purpose is to provide a bonded structure equipped with the same.

The present invention includes a plurality of means for solving the above problems. For example, at least the surface region is composed of a base material of a SiC composite material reinforced with SiC fibers, and the orientation direction of the SiC fibers. However, except for the SiC fiber, which is unavoidable in terms of structure formation, it is parallel to the length direction of the base material and parallel to the surface of the base material.

According to the present invention, it is possible to provide a bonded structure having strength against bending stress applied by vibration during transportation or operation of a fuel assembly and airtightness for preventing leakage of radionuclides. Issues, configurations and effects other than those mentioned above will be clarified by the description of the following examples.

It is sectional drawing of the boiling water reactor fuel rod which is an example of the junction structure of this invention. It is sectional drawing of the pressurized water reactor fuel rod which is an example of the junction structure of this invention. It is a partial cross-sectional schematic diagram of the water rod which is another example of the joint structure of this invention. Among the joint structures of the present invention, this is the first example showing the structure of the end plug joint and the end plug. This is a second example of the joint structure of the present invention showing the structure of the end plug joint and the end plug. Among the joint structures of the present invention, this is a third example showing the structure of the end plug joint and the end plug. Among the joint structures of the present invention, this is a fourth example showing the structure of the end plug joint and the end plug. It is a schematic diagram which shows an example of the vertical sectional view of the fuel assembly of the boiling water reactor provided with the junction structure of this invention. FIG. 8 is a cross-sectional view taken along the line AA of FIG. It is a schematic diagram which shows an example of the lower tie-rate vertical sectional view in the fuel assembly of the boiling water reactor shown in FIG. It is a schematic diagram of the fuel assembly of the pressurized water reactor provided with the junction structure of this invention. It is sectional drawing which shows the cell of the boiling water reactor provided with the junction structure of this invention. It is a cross-sectional schematic diagram which shows the cell of the pressurized water reactor provided with the junction structure of this invention.

Hereinafter, embodiments of the joining member of the present invention and the joining structure provided with the joining member will be described in more detail with reference to the drawings. In addition, the same reference numerals may be given to members and parts having the same meaning, and duplicate description may be omitted. Further, the present invention is not limited to the embodiments and examples described below, and can be appropriately combined and improved without departing from the technical idea of the invention.

[Joint structure]
First, specific examples of the bonded structure of the present invention will be described in detail with reference to FIGS. 1 to 3.

(1) Reactor fuel rods
1 and 2 are schematic cross-sectional views of a reactor fuel rod, which is an example of the joint structure of the present invention.

As shown in FIG. 1, the fuel rod 10 which is an example of the joint structure of the present invention is joined to the fuel cladding tube 11 and both ends of the fuel cladding tube 11, and seals the end portion of the fuel cladding tube 11. It is provided with end plugs 12A and 12B to stop. Of the fuel rods 10, the end plug 12 corresponds to the joining member of the present invention.

The fuel rod 10 shown in FIG. 1 is a fuel rod for a boiling water reactor, and a plurality of fuel pellets 13 are loaded therein.

Further, in the fuel rod 10, in order to fix the fuel pellet 13, one end of the connected fuel pellet 13 is pressed by the plenum spring 15. A space (fuel plenum 16) is formed in the portion where the plenum spring 15 is arranged, in order to accommodate a gas such as xenon or krypton among the radioactive fission products generated by the combustion of the fuel. It is provided.

Further, the fuel rod 10C, which is an example of the joint structure of the present invention shown in FIG. 2, is a fuel rod for a pressurized water reactor, and like the fuel rod 10 shown in FIG. 1, the fuel cladding tube 11C and the fuel rod 10C It is provided with an end plug 12C for sealing the end portion of the fuel cladding tube 11C. Further, in order to fix the fuel pellet 13, one end of the connected fuel pellet 13 is pressed by the plenum spring 15.

The shape of the end plug 12C is different from the shape of the end plugs 12A and 12B shown in FIG. 1, but their roles are the same.

(2) Water rod
FIG. 3 is a schematic partial cross-sectional view of a water rod which is another example of the joint structure of the present invention.

As shown in FIG. 3, the water rod 20 of the present invention is provided at both ends of the circular tube portion 21 which is the main body of the water rod and the circular tube portion 21, and seals the end portions of the circular tube portion 21. It is provided with end plugs 22A and 22B, and is designed so that furnace water enters the inner side of the circular pipe portion 21. Of the water rods 20, the end plugs 22A and 22B correspond to the joining member of the present invention.

[Joining member]
Next, the configuration of the joining member of the present invention will be described with reference to FIGS. 4 to 7. FIG. 4 is a schematic cross-sectional view showing a first example of the joining member of the present invention.

The joining member shown in FIG. 4 is a case of the end plug 12A or the end plug 12B among the above-mentioned end plugs 12A, 12B, 12C, and is joined to the fuel cladding tube 11 at the joint portion 2. Since it is desirable that the end plug 12C has the same configuration as the end plugs 12A and 12B, the description thereof will be omitted below.

The end plugs 12A and 12B have an end plug tip portion 121 composed of a tip center 131, a diameter reduction portion 132, and a tip end portion 133, and an end plug composed of a body wetted portion 112 and a body insertion portion 113. It is composed of a body portion 111 and.

In the joining member of the present invention including the end plugs 12A and 12B, the end plug tip portion 121 is basically fitted with respect to the tie rate, and bending stress is applied to the bending deformation of the fuel rods. Further, in the fuel rod, airtightness is required to confine the gas such as xenon and krypton generated by nuclear fission, and to confine the helium to be sealed at the time of manufacture in order to maintain equilibrium with the external pressure during operation.

Therefore, the end plug body 111 and the end plug tip 121 in the end plugs 12A and 12B of the present invention are made of the base material of the SiC composite material 1 whose surface region is at least reinforced with SiC fibers 3. Further, the orientation direction of the SiC fibers 3 constituting the base material is parallel to the length direction of the base material and parallel to the surface of the base material, except for the SiC fibers which are unavoidable in terms of structure formation.

Of the end plug body 111 of the end plug, it is desirable that the outer peripheral side of the body wetted portion 112 is a SiC composite material 1 reinforced with SiC fibers 3. The central axis is not particularly limited, and may be made of monolithic SiC in order to supplement the guarantee of airtightness. The region to be monolithic SiC can be up to the reduced diameter portion 132 of the end plug tip portion 121.

Further, in order to facilitate the production, the central axis side of the body portion wetted portion 112 may also be made of the SiC composite material 1 reinforced by the SiC fiber 3. In this case, for the purpose of supplementing the guarantee of airtightness, a monolithic SiC layer can be formed on the surface thereof as shown in FIGS. 5 and 7 described later.

Further, among the end plug body 111 of the end plug, the body insertion portion 113 is not particularly limited, and monolithic SiC is similarly provided to the central axis of the body wetted portion 112 in order to supplement the guarantee of airtightness. It can consist of. Similarly, in order to facilitate the production, it can be made of the SiC composite material 1 reinforced by the SiC fiber 3.

Of the end plug tip portion 121 of the end plug, the tip center 131 is preferably, but is not limited to, a SiC composite material 1 in which all the regions thereof are reinforced by the SiC fiber 3.

Of the end plug tip portion 121 of the end plug, the diameter-reduced portion 132 is preferably, but is not limited to, a SiC composite material 1 in which all the regions thereof are reinforced by the SiC fiber 3.

Further, when the reduced diameter portion 132 is composed of the SiC composite material 1 reinforced by the SiC fiber 3, it is structurally impossible that the orientation direction of the SiC fiber is "parallel to the length direction of the base material". However, it is desirable that it is "parallel to the surface of the substrate".

Of the end plug tip portions 121 of the end plug, the most advanced portion 133 is different from the tip center 131 and the reduced diameter portion 132, and has higher airtightness such as monolithic SiC than the SiC composite material 1 reinforced by the SiC fiber 3. Although it is desirable that the material is composed of a material, the shape is not particularly limited, and the shape is desired to be round on the cutting edge side.

Of the portions constituting the above-mentioned end plug, the portion composed of the SiC composite material 1 preferably has a porosity of less than 5%, and is preferably a liquid phase sintering method SiC / SiC composite material or SiC. It is desirable that it is a fiber binding material.

The "SiC fibers unavoidable in terms of structure formation" in the present invention are SiC fibers necessary for maintaining the SiC fibers in a bundled state, and diameter-reduced portions 132, 232, 332 as necessary as end plugs. It refers to the SiC fiber of the reduced diameter portion or the enlarged diameter portion when the 432 or the enlarged diameter portion is provided.

Further, the "porosity" in the present invention means the "area of the hole portion" / ("SiC fiber 3 constituting the SiC composite material 1 and various types of SiC" when the end plug is observed with a microscope or the like. It shall be defined by "area occupied by materials based on them" + "area of hole portion") x 100 [%].

The structure of the joint portion 2 that joins the end plug body portion 111 and the fuel cladding tube 11 is not particularly limited, and a known configuration can be used.

For example, it is formed by brazing and / or diffusion bonding through a predetermined metal bonding material having a solid phase line temperature of 1200 ° C. or higher, and the outer surface of the bonding portion 2 and the portion adjacent to the outer surface of the bonding portion 2. A part of the outer surface of the fuel cladding tube 11 and the end plugs 12A and 12B is covered with a joint coating made of a predetermined coating metal, and the predetermined metal joint material and the predetermined coating metal are average linearly expanded. The coefficient can be less than 10 ppm / K.

Further, inclined surfaces are formed on the ends of the fuel cladding tube 11 and the end plugs 12A and 12B, and the inclined surfaces are joined with a metal joining material in a state of being in contact with each other, and the joint portion 2 is joined to the body of the end plug body 111. It can be supported by the portion insertion portion 113.

The structure of the end plug is not limited to the form shown in FIG. Hereinafter, examples of other forms will be described with reference to FIGS. 5 to 7. 5 is a schematic cross-sectional view showing a second example of the joining member of the present invention, FIG. 6 is a schematic cross-sectional view showing a third example of the joining member of the present invention, and FIG. 7 is a fourth schematic cross-sectional view of the joining member of the present invention. It is sectional drawing which shows an example.

FIG. 5 shows an end plug tip portion 221 composed of a tip center 231, a diameter reduction portion 232, and a tip end portion 233, and an end plug body portion 211 composed of a body portion wetted portion 212 and a body portion insertion portion 213. The surface of the SiC composite material 1 is in contact with the tip of the end plug 221 and the surface of the SiC composite material 1 reinforced by the SiC fiber 3 constituting the body wetted portion 212 of the end plug body 211. It is covered with a monolithic SiC layer 4 that serves as a liquid surface.

The monolithic SiC layer 4 can be applied to the SiC composite material 1 by a chemical vapor deposition method. Alternatively, a SiC sintered material without SiC fibers can be added when the SiC composite material 1 is fired.

The thickness of the monolithic SiC layer 4 is preferably 20 μm or more for the purpose of functioning to maintain airtightness in combination with the SiC composite material 1.

As for the SiC composite material 1 in FIG. 5, the porosity is preferably less than 5%, but the SiC composite material by the chemical vapor deposition method can be applied.

FIG. 6 shows an end plug tip portion 321 composed of a tip center 331, a diameter reduction portion 332, and a tip end portion 333, and an end plug body portion 311 composed of a body wetted portion 312 and a body insertion portion 313. The surface of the SiC composite material 1, which is an end plug composed of, and is reinforced by the SiC fiber 3 constituting the end plug tip portion 321 and the body portion wetted portion 312 of the end plug body portion 311 is corrosion resistant. It is covered with a metal layer 5.

The corrosion-resistant metal layer 5 is a layer containing at least one of Cr, Ti and Zr as a main component, and its thickness is preferably 5 to 1000 μm. When it is 5 μm or more, the effect of improving the corrosion resistance is enhanced, and when it is 1000 μm or less, the adhesion with the SiC composite material 1 can be ensured and the risk of peeling can be reduced.

For the corrosion resistant metal layer 5, physical vapor deposition (PVD: Physical Vapor Deposition), chemical vapor deposition (CVD), thermal spraying, cold spraying, plating, or powder coating method can be used. Specifically, a sputtering method can be used as the physical vapor deposition.

Further, heat treatment may be performed after the film forming step. By performing the heat treatment, a reaction layer by diffusion can be formed between the formed metal layer and the SiC layer, and the adhesion can be improved. For chemical vapor deposition, thermal spraying and cold spraying, a reaction layer may be formed by heat input or mechanical mixing during the film formation process without heat treatment.

The layer thickness of the corrosion-resistant metal layer 5 can be, for example, 10 μm or more and 100 μm or less for film formation by physical vapor deposition, chemical vapor deposition, plating, or powder coating, and 100 μm or more and 1000 μm or less for film formation by thermal spraying or cold spray. The thickness can be determined based on the required corrosion resistance.

FIG. 7 shows an end plug body portion 421 composed of a tip center 431, a diameter reduction portion 432, and a tip end portion 433, and an end plug body portion 411 composed of a body wetted portion 412 and a body insertion portion 413. The surface of the SiC composite material 1 is monolithic, which is an end plug composed of the above, and is reinforced by the SiC fiber 3 constituting the end plug tip portion 421 and the body portion wetted portion 412 of the end plug body portion 411. It is covered with a SiC layer 4, and the surface of the monolithic SiC layer 4 is covered with a corrosion-resistant metal layer 5 which is a wetted surface containing at least one of Cr, Ti, and Zr as a main component.

The details of the monolithic SiC layer 4 to be formed are the same as those shown in FIG. 5 described above, and can be applied to the SiC composite material 1 by a chemical vapor deposition method. Alternatively, a SiC sintered material without SiC fibers can be added when the SiC composite material 1 is fired. Further, the thickness thereof is preferably 20 μm or more for the purpose of functioning to maintain airtightness in combination with the SiC composite material 1.

The details of the corrosion-resistant metal layer 5 to be formed are the same as those shown in FIG. 6 described above, and the layer contains at least one of Cr, Ti, and Zr as a main component, and its thickness is , 5 to 1000 μm, preferably formed by physical vapor deposition, chemical vapor deposition, thermal spraying, cold spraying, plating or powder coating.

The structure of the fuel cladding tube 11 in FIGS. 4 to 7 and the structure of the fuel cladding tube 11C in FIG. 2 are not particularly limited, but assuming a coolant loss accident, the ceramic material is similarly configured as a base material, for example. It is desirable that the SiC material is, in particular, a SiC composite material reinforced with SiC fibers.

Further, it can be assumed that a known appropriate environment-resistant shielding coating is applied to the inner peripheral side and the outer peripheral side thereof.

(3) Fuel assembly
FIG. 8 is a vertical cross-sectional schematic view showing an example of a vertical cross-sectional view of a fuel assembly of a boiling water reactor, which is a first example provided with the bonded structure of the present invention, and FIG. 9 is a vertical cross-sectional schematic view showing A- It is a cross-sectional view of the A'line.

The fuel assembly 30 shown in FIGS. 8 and 9 is an example of a fuel assembly for a boiling water reactor, and includes an upper tie plate 31, a lower tie plate 32, and the above-mentioned plurality of fuel rods 10 and water rods. 20 is provided, a fuel support grid (spacer) 34 for bundling the fuel rods 10 and the water rod 20, and a channel box 35 for surrounding the fuel rod bundles attached to the upper tie plate 31.

In the fuel assembly 30, both ends of the plurality of fuel rods 10 and the water rod 20 are held by the upper tie rate 31 and the lower tie rate 32. To put it simply, the fuel rods 10 (also called full-length fuel rods), the partial length fuel rods 10A, and the water rods 20 are bundled and housed in a square grid-like channel box 35 having a square tubular cross section. (See FIG. 9).

The cooling water flows into the square tubular channel box 35 from the lower part in FIG. 8 via the orifice of the fuel support fitting and the lower tie plate 32 of the fuel assembly 30, and is heated by the fuel rods 10 and 10A. When it boils, it becomes steam and becomes a gas-liquid two-phase flow.

The full-length fuel rod 10 used in the current commercial boiling water reactor has an effective fuel length of about 3.7 m and a total length of about 4 m.

The partial length fuel rod 10A is a kind of reactor fuel rod, and is a fuel rod having a shorter effective fuel length inside than the fuel rod 10 (full-length fuel rod) and a height that does not reach the upper tie plate 31. It is desirable that the partial length fuel rod 10A also has the same structure as the full length fuel rod 10, and in particular, the end plugs that seal both ends thereof are the same as the end plugs shown in any of FIGS. 4 to 7. It is desirable to have a structure.

A handle 37 is fastened to the upper tie plate 31, and when the handle 37 is lifted, the entire fuel assembly 30 can be pulled up.

In the fuel assembly 30 according to the present invention, the water rod 20 or the channel box 35 may be the same as that of the prior art (water rod or channel box made of zirconium alloy).

However, assuming a loss-of-coolant accident, it is desirable that the end plugs 22A and 22B of the water rod 20 have the same structure as the end plugs 12A and 12B of the fuel rod 10. Further, it is desirable that the circular pipe portion 21 of the water rod 20 has the same configuration as the fuel cladding tubes 11 and 11C.

FIG. 10 is a schematic view showing an example of a vertical sectional view of a lower tie plate in a fuel assembly of a boiling water reactor, which is a first example of a structure having a bonded structure of the present invention.

As shown in FIG. 10, for the purpose of preventing foreign matter from entering the inside of the fuel assembly 30, the lower tie plate 32 supporting the lower end of the full length fuel rod 10, the partial length fuel rod 10A, and the water rod 20 A foreign matter filter 47 is added to the lower surface of the mesh portion 43. As a result, the soundness of the fuel is improved.

The lower tie plate 32 supports the nozzle portion 41 whose flow path gradually expands from the cooling water inlet opening 40 toward the downstream side, the fuel rods 10 and 10A, and the lower ends of the water rod 20, and allows the cooling water to flow in a predetermined flow direction. It has a mesh portion 43 having a plurality of outlet openings 42 that can be passed through, and a peripheral side wall 44 that connects the nozzle portion 41 and the mesh portion 43, and is between the nozzle portion 41 and the mesh portion 43. A cooling water receiving chamber 45 surrounded by a peripheral side wall 44 is formed.

An opening 48 is formed in the nozzle portion 41, and a foreign matter filter 47 provided with hundreds of holes 46 having a small diameter of several mm is attached to the lower surface of the mesh portion 43. Foreign matter contained in the cooling water in the cooling water receiving chamber 45 is captured by the foreign matter filter 47 according to the hole diameter size of the hole 46, and only the cooling water from which the foreign matter has been removed is downstream from the outlet opening 42 (upper tie plate 31). Flow to the side).

FIG. 11 is a schematic view of a fuel assembly of a pressurized water reactor which is a second example of a structure provided with the joint structure of the present invention.

The fuel assembly 50 shown in FIG. 11 is an example of a fuel assembly for a pressurized water reactor, and includes a plurality of fuel rods 10C, a plurality of control rod guide thimbles 51, an in-core instrumentation guide thimble 52, and the like. It is provided with a plurality of support grids (spacers) 53 for bundling and supporting the above, an upper nozzle 54, and a lower nozzle 55.

The upper nozzle 54 and the lower nozzle 55 are constituents of the skeleton of the fuel assembly 50, and at the same time, play a role of positioning the fuel assembly 50 in the core and securing a flow path of the cooling water.

(5) Reactor cell
FIG. 12 is a schematic cross-sectional view showing a cell of a boiling water reactor which is a third example of a structure provided with the bonded structure of the present invention.

As shown in FIG. 12, in the cell 60 of the boiling water reactor, four fuel assemblies 30 shown in FIG. 8 and the like are arranged in a square shape, and a control rod 61 having a cross-shaped cross section is located at the center thereof. It is arranged. In the cell 60, by using the fuel assembly 30 provided with the fuel rods 10 and 10A according to the present invention, an emergency situation (for example, a coolant) can be maintained while maintaining the same long-term reliability as the conventional one under a normal operating environment. It is possible to improve the safety in case of loss accident).

FIG. 13 is a schematic cross-sectional view showing a cell of a pressurized water reactor which is a fourth example of a structure provided with the bonded structure of the present invention.

As shown in FIG. 13, in the cell 70 of the pressurized water reactor, since the control rods are arranged in the fuel assembly 50, the four fuel assemblies 50 are arranged in a square shape as they are. In the cell 70 as well, by using the fuel rods 10C and the fuel assembly 50 according to the present invention, an emergency situation (for example, an accident of loss of coolant) is maintained while maintaining the same long-term reliability as the conventional one under a normal operating environment. ) Can be improved.

<Effect>
The end plugs 12A, 12B, 12C, 22A, and 22B of the above-described embodiment are composed of a base material of a SiC composite material whose surface region is reinforced with SiC fibers, and the orientation direction of the SiC fibers is unavoidable in terms of structure formation. By being parallel to the length direction of the base material and parallel to the surface of the base material except for the SiC fibers, the diameter of the tip of the end plug is reduced in the joining member using the SiC composite material as the base material. It is possible to provide an end plug having sufficient bending stress strength and airtightness to prevent leakage of radioactive nuclei.

Therefore, for example, when used for end plugs of fuel rods 10, 10C, water rods 20, etc., the diameter of the end plug insertion hole in the tie plate is reduced to secure the diameter of the cooling water passage hole and maintain the rigidity of the tie rate. Or can be improved. Furthermore, it is possible to suppress the corrosion of SiC in the reactor water environment.

Further, since the porosity of the SiC composite material is less than 5%, higher airtightness can be ensured when the bonded structure is formed.

Further, by further providing the monolithic SiC layer 4 serving as a liquid contact surface on the surface of the base material, it is possible to secure higher airtightness when the bonded structure is formed.

Further, the surface of the base material is further provided with a monolithic SiC layer 4, and the surface of the monolithic SiC layer 4 is further provided with a corrosion-resistant metal layer 5 serving as a liquid contact surface containing at least one of Cr, Ti and Zr as a main component. As a result, it is possible to secure higher airtightness when the bonded structure is formed, and to obtain a bonded member having high corrosion resistance in, for example, an oxidizing environment containing water, a water vapor environment, or a high temperature water environment.

Further, the surface of the base material is further provided with a corrosion-resistant metal layer 5 serving as a liquid contact surface containing at least one of Cr, Ti and Zr as a main component, whereby, for example, an oxidation environment containing water and water vapor. It can have high corrosion resistance in an environment or a high temperature water environment.

Further, since the SiC composite material is a liquid phase sintering method SiC / SiC composite material or a SiC fiber bonding material, the porosity of the base material portion can be reduced to about several%, and the airtightness can be improved. It is possible to secure it reliably.

Further, since the region other than the surface region of the base material is made of monolithic SiC, the airtightness can be improved when, for example, the fuel rods 10 and 10C are used.

Further, since the region other than the surface region of the base material is also the SiC composite material 1 reinforced with the SiC fiber 3, the end plug can be easily manufactured.

<Example>
Hereinafter, the present invention will be described in more detail with reference to Examples. Of course, the present invention is not limited to these examples.

(1) Preparation of joining member
The end plug-shaped joining member shown in FIG. 4 was produced.

For the SiC fiber, Hynicalon type S (fiber diameter 8 μm) having high crystallinity is used, and the direction of the SiC fiber 3 is the length direction of the end plug 12 and the end except for the SiC fiber which is unavoidable in terms of structure formation. It was arranged so as to be parallel to the surface of the stopper 12.

In the chemical vapor deposition method, in order to bundle the SiC fibers, a part of the SiC fibers was woven in the circumferential direction of the end plug and heated in a gas that produces SiC. In the liquid-phase sintering method, a bundle of SiC fibers is impregnated with a slurry obtained by adding oxide and SiC powder, and after removing the resin component of the slurry by heating, the slurry is packed in a graphite mold and hot-pressed. Sintered at high temperature and high pressure. In the SiC fiber bonding method, a bundle of SiC fibers was impregnated with a sintering aid, packed in a graphite mold, and sintered at high temperature and high pressure by hot pressing. At this time, the porosity inside the SiC composite material was 2% in the liquid phase sintering method, 4% in the SiC fiber bonding method, and 22% in the chemical vapor deposition method.

The sintered SiC composite material was machined and molded into a predetermined shape. The end plug body has a diameter of about 10 mm and a length of about 20 mm, and the end plug tip has a diameter of about 7 mm and a length of about 40 mm.

Next, as shown in FIG. 5, an end plug having a monolithic SiC layer on the outer surface was produced. As the monolithic SiC layer, a monolithic SiC layer having a size of 50 to 200 μm was applied to the end plug formed into the above-mentioned predetermined shape by a chemical vapor deposition method.

In another end plug, when the SiC composite material is sintered by the liquid phase sintering method, a slurry to which oxide and SiC powder are added is applied to the outer surface in advance, and the entire material is sintered by hot pressing. Then, a sintered monolithic SiC layer was formed from the slurry on the outer surface.

After applying the monolithic SiC layer to the outer surface, parts requiring dimensional accuracy, such as the joint and the tip of the end plug that fits with the tie plate, were precisely molded by machining.

Next, as shown in FIG. 6 or 7, an end plug having a corrosion-resistant metal layer on the outer surface was produced. A corrosion-resistant metal layer was formed on the surface of the end plug in which the above-mentioned SiC composite material was used and the monolithic SiC layer was provided on the outer surface. Physical vapor deposition, chemical vapor deposition, thermal spraying and cold spray were used for film formation. The film formed by physical vapor deposition and powder coating was heat-treated in vacuum for each substrate after the film was formed.

In the film formation by physical vapor deposition, a sputtering method was applied, Ar gas was introduced to keep the pressure in the chamber constant at 1.3 Pa, and then the sputtering power was 1.50 kW and the bias voltage was 150 V. By switching the sputter evaporation source (target) of pure Cr, pure Ti, pure Zr and Zr alloy, a multilayer film or a gradient composition layer was formed. In the heat treatment, an oil diffusion pump or a turbo molecular pump is used to heat the active metal such as Ti, Zr, etc. during the heat treatment at 950 to 1000 ° C. for 0.5 to 1 hour in a high vacuum of ^{10 -4 Pa or less.} The oxidation of the film was suppressed. Furthermore, it was confirmed that there was no peeling after the heat treatment.

In the film formation by chemical vapor deposition, the raw material gas was flowed and the film forming portion was locally heated using a laser beam or a heater, or photodecomposition using the laser beam was carried out to perform the chemical vapor deposition. As the raw material gas, Cr (CO) ₆ + H _{2 gas was used when the Cr film was formed, TiCl 2} gas was used when the Ti film was formed _{, and ZrCl 2} gas was used when the Zr film was formed. After forming the Cr layer, a multilayer film was formed by changing the raw material gas and heating conditions.

In the film formation by thermal spraying, the air around the site including the joint was once purged, and then plasma spraying was performed with Ar gas introduced as an inert gas under reduced pressure. Oxidation of the raw material powder during the thermal spraying process was suppressed, forming an active Ti, Zr or Zr alloy film. As the raw material powder, pure Cr, pure Ti, pure Zr and Zr alloy powder (particle size 10 to 60 μm) was used, and a multilayer film could be formed by switching the raw material powder, and an intermediate composition was formed by mixing the raw material powder. I was able to form a film of.

In the film formation by cold spray, helium was used as the working gas and the raw material powder was sprayed on the film-forming portion. Cold spray is characterized in that the working gas temperature is lower than the melting point of the raw material powder, and it is possible to form a dense film by suppressing oxidation, thermal effects, and thermal stress compared to the thermal spraying method. As the raw material powder, pure Cr, pure Ti, pure Zr and Zr alloy powder (particle size number to 50 μm) was used, and a multilayer film could be formed by switching the raw material powder, and an intermediate composition was formed by mixing the raw material powder. I was able to form a film of.

In the film formation by powder coating, Cr powder is applied to the part including the joint, and then heat treatment is performed at 950 ° C to 1000 ° C, and then Ti, Zr or Zr alloy powder is applied and then heat treatment is performed at 950 ° C to 1100 ° C. Was carried out. In some test pieces, the Cr layer could be thickened by Cr plating after coating with Cr powder and subsequent heat treatment.

1 ... SiC composite material (base material)
2 ... Joint part 3 ... SiC fiber 4 ... Monolithic SiC layer 5 ... Corrosion resistant metal layer 10 ... Full length fuel rod (joint structure)
10A ... Partial length fuel rod (joint structure)
10C ... Fuel rod (joint structure)
11, 11C ... Fuel cladding tube (tubular member)
12, 12A, 12B, 12C, 22A, 22B ... End plug (joining member)
13 ... Fuel pellet 15 ... Plenum spring 16 ... Fuel plenum 20 ... Water rod (joint structure)
21 ... Circular tube (tubular member)
30 ... Fuel assembly (BWR)
31 ... Upper tie plate 32 ... Lower tie plate 34 ... Fuel support grid (spacer)
35 ... Channel box 37 ... Handle 40 ... Cooling water inlet opening 41 ... Nozzle part 42 ... Outlet opening 43 ... Mesh part 44 ... Peripheral side wall 45 ... Cooling water receiving chamber 46 ... Hole 47 ... Foreign matter filter 48 ... Opening 50 ... Fuel assembly (PWR)
51 ... Control rod guide thimble 52 ... Guide thimble for in-core instrumentation 53 ... Support grid (spacer)
54 ... Upper nozzle 55 ... Lower nozzle 60 ... Cell (BWR)
61 ... Control rod 70 ... Cell (PWR)
111, 211, 311, 411 ... End plug body 112, 212, 312, 412 ... Body wetted part 113, 213, 313, 413 ... Body insertion part 121, 221, 321, 421 ... End plug tip 131 , 231,331,431 ... Tip center 132,232,332,432 ... Reduced diameter part 133,233,333,433 ... Cutting edge part

Claims (10)

At least the surface area is composed of a base material of SiC composite material reinforced with SiC fibers.
A joining member characterized in that the orientation direction of the SiC fibers is parallel to the length direction of the base material except for the SiC fibers which are unavoidable in terms of structure formation, and is parallel to the surface of the base material. In the joining member according to claim 1,
A joining member characterized in that the porosity of the SiC composite material is less than 5%. In the joining member according to claim 2,
A joining member characterized in that a monolithic SiC layer serving as a wetted surface is further provided on the surface of the base material. In the joining member according to claim 2,
The surface of the base material is further provided with a monolithic SiC layer, and the surface of the monolithic SiC layer is further provided with a corrosion-resistant metal layer serving as a liquid contact surface containing at least one of Cr, Ti and Zr as a main component. A characteristic joining member. In the joining member according to claim 1,
A bonding member characterized in that the surface of the base material is further provided with a corrosion-resistant metal layer serving as a wetted surface, which is mainly composed of at least one of Cr, Ti and Zr. In the joining member according to claim 2,
A joining member, wherein the SiC composite material is a liquid phase sintering method SiC / SiC composite material or a SiC fiber bonding material. In the joining member according to claim 1,
A joining member characterized in that a region other than the surface region of the base material is made of monolithic SiC. In the joining member according to claim 1,
A joining member characterized in that a region other than the surface region of the base material is also made of a SiC composite material reinforced with SiC fibers. Tubular member and
A joint structure comprising the joint member according to any one of claims 1 to 8, which seals an end portion of the tubular member. The joint structure according to claim 9, wherein the joint structure is either a fuel rod or a water rod constituting a nuclear reactor.

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