WO2014025060A1 - Channel box and fuel assembly provided therewith - Google Patents

Abstract

[Problem] To provide a channel box which has a high dimensional accuracy and is hardly corroded or deformed after prolonged usage, and a fuel assembly equipped with the channel box. [Solution] A channel box (10) configured from a cylindrical body that is formed by combining a plurality of base members (1) comprising a silicon carbide sintered compact. Owing to this structure, the channel box (10) has a high dimensional accuracy and is hardly corroded or deformed after prolonged usage. A fuel assembly equipped with this channel box (10) has an improved reliability.

Description

Channel box and fuel assembly including the same

The present invention relates to a channel box and a fuel assembly including the channel box.

In a boiling water reactor, a plurality of fuel rods filled with uranium fuel (pellet), an upper tie plate and a lower tie plate that hold the upper and lower portions of the fuel rod, a water rod, and a water rod A fuel assembly including a lattice-shaped spacer that is fixed and supports the fuel rods between the upper tie plate and the lower tie plate and a cylindrical channel box that covers the fuel rods and the spacers is stored. A control rod that controls the output of the reactor by adjusting the number of neutrons in the reactor and controlling the reactivity while four fuel assemblies (two vertical and two horizontal) are arranged. The control rod has a cross shape in a cross section perpendicular to the longitudinal direction of the fuel assembly.

Next, the cylindrical channel box constituting the fuel assembly is described in Non-Patent Document 1 ("Fuel Channel Function and Manufacturing Method", Kobe Steel Technique / Vol.53 No.3 (Dec.2003), p. 98. According to page 102), the neutron absorption cross section is small, the radiation damage is small, the impurities that produce induced radioactivity are small, the corrosion resistance to cooling water is excellent, and the usage environment (about 300 ° C) It is described that a zirconium alloy such as Zircaloy is used because it is required to have excellent mechanical properties.

Further, according to Non-Patent Document 1, the inside of the reactor is a radiation environment and a high-temperature underwater environment, and when the channel box used in such an environment is made of a zirconium alloy such as Zircaloy, in addition to uniform corrosion, It is described that nodular corrosion occurs in which a lens-like thick oxide film is discontinuously formed in a thin and uniform oxide film. Also, in the initial stage of use, deformation due to release of residual stress at the time of manufacture of the channel box occurs, and when the service period is extended, deformation due to fast neutron irradiation and creep deformation due to the difference in internal and external pressure of the channel box It is described that it occurs. Various proposals have been made for corrosion and deformation when a zirconium alloy is used (for example, Patent Documents 1 to 4).

A silicon carbide material containing a boron compound composed of boron-11 has been proposed as a constituent member of a nuclear reactor, and specifically, fuel cladding (pellet cladding tube) is described as a constituent member. The use of 11 doped SiC fibers is described (Patent Document 5).

Japanese Patent Laid-Open No. 5-19079 Japanese Patent Publication No.51-4234 JP-A-8-29570 Japanese Patent Laid-Open No. 11-231083 Japanese Patent No. 4751221

Although the boron-11-doped SiC fiber described in Patent Document 5 is suitable for fuel cladding among the components of a nuclear reactor, it has mechanical properties that cover and protect a plurality of fuel rods. It is not suitable for the required cylindrical channel box. Here, it is conceivable to form a silicon carbide sintered body as a channel box that covers and protects a plurality of fuel rods while suppressing corrosion and deformation in a radiation environment and a high-temperature underwater environment.

However, according to Non-Patent Document 1, the channel box has a cylindrical shape with a plate thickness of 2 to 3 mm and an internal size of about 130 mm and a total length of about 4.2 m. 0.07mm, dimensional tolerance of internal dimension is ± 0.25mm, and dimensional tolerance of total length is + 1 / -2mm, which is demanding. In the production of long cylindrical body made of silicon carbide sintered body, Have the following problems.

First, the molding of a molded body that becomes a long cylindrical body can be obtained by processing a molded body obtained by an extrusion molding method or a cold isostatic pressing method into a desired shape. However, ceramics as well as silicon carbide sintered bodies are prone to cracking if the binder used as a molding aid is not sufficiently removed during firing, and warping or deformation is likely to occur if the degree of shrinkage is partially different. Is. In addition, since it is long, it is not easy to handle, is more likely to be warped and deformed, and becomes a defective product due to partial cracks. Therefore, a long tube made of a silicon carbide sintered body is used. It was difficult to obtain a shape. Further, in order to satisfy the dimensional tolerance described above, it is necessary to perform processing such as polishing on the silicon carbide sintered body, but it is extremely difficult to process the inner surface of a particularly long cylindrical body. It was.

The present invention has been devised to solve the above problems, and provides a channel box that is excellent in dimensional accuracy and that is less likely to be corroded or deformed by long-term use, and a fuel assembly including the channel box. It is for the purpose.

The channel box of the present invention is characterized by comprising a cylindrical body in which a plurality of base materials made of a silicon carbide sintered body are combined.

The fuel assembly of the present invention is characterized by including the channel box having the above-described configuration.

The channel box of the present invention has excellent dimensional accuracy and can reduce corrosion and deformation due to long-term use.

Further, according to the fuel assembly of the present invention, the channel box of the present invention is excellent in dimensional accuracy and has little corrosion and deformation due to long-term use, so that it can be used stably over a long period of time. Thus, a highly reliable fuel assembly can be obtained.

An example of the channel box of this embodiment is shown, (a) is a top view, (b) is a front view. The other example of the channel box of this embodiment is shown, (a) is a top view, (b) is a front view. The other example of the channel box of this embodiment is shown, (a) is a top view, (b) is a front view. The other example of the channel box of this embodiment is shown, (a) is a top view, (b) is a front view. The other example of the channel box of this embodiment is shown, (a) is a top view, (b) is a front view. The other example of the channel box of this embodiment is shown, (a) is a top view, (b) is a front view, (c) is a side view. The other example of the channel box of this embodiment is shown, (a) is a top view, (b) is a front view, (c) is a side view. The other example of the channel box of this embodiment is shown, (a) is a top view, (b) is a side view, (c) is a side view. The other example of the channel box of this embodiment is shown, (a) is a top view, (b) is a front view. Another example of the channel box of the present embodiment is shown, (a) is a plan view, (b) is a cross-sectional view taken along line C-C 'in (a). Another example of the channel box of the present embodiment is shown, (a) is a plan view, (b) is a sectional view taken along line DD ′ in (a), and (c) is in (b). It is an enlarged view of the E section. The It is a schematic diagram which shows an example of the combination of the base materials which comprise the channel box of this embodiment. It is a schematic diagram which shows the other example of the combination of the base materials which comprise the channel box of this embodiment. It is a schematic diagram which shows the other example of the combination of the base materials which comprise the channel box of this embodiment. It is a schematic diagram which shows the other example of the combination of the base materials which comprise the channel box of this embodiment.

Hereinafter, an example of the channel box of the present embodiment will be described in detail with reference to the drawings. 1A and 1B show an example of a channel box according to the present embodiment, in which FIG. 1A is a plan view and FIG. 1B is a front view. In the following description, when not limited to the structure shown in the specific figure, the channel box and the base material may be described without reference numerals.

The channel box 10 of the present embodiment is formed of a cylindrical body obtained by combining a plurality (1a, 1b) of base materials 1 made of a silicon carbide sintered body. Thus, since the base material 1 is made of a silicon carbide-based sintered body, the neutron absorption cross-sectional area is small, the radiation damage is small, the impurities that generate induced radioactivity are small, and the corrosion resistance to cooling water is excellent. And satisfying the performance required for the channel box 10 such as excellent mechanical properties in the use environment (about 300 ° C.). In addition, since the cylindrical body is formed by combining the base materials 1a and 1b, the portion corresponding to the inner surface of the channel box 10 can be easily processed before the base materials 1a and 1b are combined. Because it can, it can meet strict dimensional tolerances. Therefore, the channel box 10 having excellent dimensional accuracy and less corrosion and deformation due to long-term use can be obtained.

Here, the silicon carbide based sintered body is a sintered body containing 80% by mass or more of silicon carbide out of 100% by mass of all the components constituting the silicon carbide based sintered body. As a method for measuring the content, the content of Si may be obtained using an ICP (Inductively-Coupled-Plasma) emission spectroscopic analyzer and converted to SiC.

In addition, in FIG. 1, although the rectangular tube-shaped cylindrical body was shown, cylindrical shape may be sufficient, and in embodiment of this application, a combination is a concept including joining, coupling | bonding, fitting, and fastening.

Next, FIG. 2 and FIG. 3 show another example of the channel box of the present embodiment, (a) is a plan view, and (b) is a front view. The channel boxes 20 and 30 in FIGS. 2 and 3 show a structure in which the number of combined surfaces in the circumferential direction and the longitudinal direction is increased. In such a structure, since each member is small, it is easy to handle at the time of production, and a plurality of substrates having the same shape (for example, the substrates 2a to 2d) may be produced. A substrate can be produced with high efficiency and high yield.

4 and 5 show another example of the channel box of the present embodiment, (a) is a plan view, and (b) is a front view. When the configuration surface in the circumferential direction is shifted as in the channel boxes 40 and 50 in FIGS. 4 and 5, the configuration is combined as compared with the case where the other configuration is the same and the combination surface in the circumferential direction is the same. Further, since the mechanical characteristics in the longitudinal direction of the channel boxes 40 and 50 are improved, the reliability can be enhanced.

6 to 8 show other examples of the channel box of the present embodiment, (a) is a plan view, (b) is a front view, and (c) is a side view. 6-8, the front view of (b) is a view seen from A in (a), and the side view of (c) is a view seen from B in (a).

As in the case of the channel boxes 60, 70, 80 shown in FIGS. 6 to 8, when the combination surface in the longitudinal direction is shifted, the other configuration is the same and the combination surface in the longitudinal direction is the same. Since the mechanical characteristics in the circumferential direction are improved, the reliability can be improved. In addition, the channel box 80 in the example shown in FIG. 8 has a combination surface at the corners in comparison with the examples shown in FIGS. 6 and 7, and the area of the combination surface in the base material 8a and the base material 8b is large. For this reason, for example, when these are bonded, the bonding strength can be increased, so that the channel box 80 with high reliability can be obtained.

Next, FIG. 9 shows another example of the channel box of the present embodiment, (a) is a plan view, and (b) is a front view. As shown in FIG. 9, when each of the base materials 9a to 9d is formed into a cylindrical shape by a single member, the step of combining the circumferential directions can be omitted, and a plurality of the substrates can be combined in the longitudinal direction. It is possible to make the deformation in the circumferential direction less likely to be caused by the member than the cylindrical shape. In addition, since the base materials 9a to 9d constituting the channel box 90 are shorter in individual length than the entire length of the channel box 90, they are easy to handle and the surface inside the channel box 90 is ground. The channel box 90 can be formed easily, with a high yield, and capable of meeting strict dimensional tolerances.

Next, FIG. 10 shows another example of the channel box of the present embodiment, (a) is a plan view, and (b) is a sectional view taken along line C-C ′ in (a). As shown in FIG. 10, it is preferable that a protrusion P is provided in a portion corresponding to the inner surface of the cylindrical body of the base material 10. As described above, when the protruding portion P is provided, only the protruding portion P can be processed to fit within the strict tolerance of the inner dimension of the channel box 100. Further, since the region other than the protruding portion P is thin, the weight of the channel box 100 can be reduced.

Next, FIG. 11 shows another example of the channel box of the present embodiment, (a) is a plan view, (b) is a sectional view taken along line DD ′ in (a), c) is an enlarged view of an E portion in (b). Thus, it is preferable that at least one of the base materials 11 to be combined has a step, and at least a part of the step is a combination surface. In FIG. 11, the base material 11b has a step, and this step is a combined surface. In such a configuration, since the base material 11a can be fitted to the base material 11b, the reliability against vibration can be increased, and only the facing surfaces of the channel box 110 in the longitudinal direction are combined surfaces. For example, when these are bonded together, the bonding strength can be increased.

Further, it is preferable that the arithmetic average roughness Ra of the roughness curve on the inner surface of the channel box made of a cylindrical body is 1 μm or less. Thereby, at the time of assembling or removing the fuel assembly, the fuel rods or the spacers supporting the fuel rods can be damaged, or the detachment due to the contact between the inner surface of the channel box and the fuel rods or the spacers can be reduced. In the case of the channel boxes 100 and 110 having the structure shown in FIGS. 10 and 11, only the protruding portion P may have the above-described surface properties.

Also, the arithmetic average roughness Ra of the roughness curve on the inner surface of the channel box made of a cylindrical body affects the oxidation of silicon carbide containing 80% by mass or more of the silicon carbide based sintered body. Impurities in the cooling water flowing in the channel box include metal ions, anionic species, and oxidizing radical components. When these impurities adhere to the surface of the silicon carbide sintered body, an oxidation reaction occurs, causing neutron absorption. There is a risk of increasing the cross-sectional area. Therefore, in order to make it difficult for impurities to adhere, the arithmetic mean roughness Ra of the roughness curve on the inner surface of the channel box made of a cylindrical body is preferably smaller, so the arithmetic average roughness Ra of the roughness curve is 0.8 μm. It is preferable that: In such a surface property, since a state with a small neutron absorption cross section can be maintained over a long period of time, it can be regarded as a channel box having excellent corrosion resistance.

The arithmetic mean roughness Ra of the roughness curve may be measured in accordance with JIS B 0601-2001, the measurement length and cut-off value are 5 mm and 0.8 mm, respectively, and a stylus type surface roughness meter is used. In the case of using and measuring, for example, a stylus having a stylus tip radius of 2 μm is applied to the inner surface of the channel box, and the stylus scanning speed is set to 0.5 mm / second. In the present embodiment, the average value of the measured values at the five locations on the inner surface of the channel box adjacent to the spacer is the value of the arithmetic average roughness Ra.

FIG. 12 is a schematic diagram showing an example of a combination of base materials constituting the channel box of the present embodiment. Thus, the area of the combination surface can be increased by inclining the combination surface. For example, when these are bonded, the bonding strength can be increased. A preferable inclination angle θ is, for example, 30 ° or more and 60 ° or less.

In addition, in the combination of channel boxes shown in FIGS. 1 to 12, when the bonding method is used, it is preferable that silicon carbide crystal particles exist in the bonding portion. When silicon carbide crystal particles are present at the joint, even if microcracks are generated at the joint due to exposure to high temperatures, the presence of silicon carbide crystal particles suppresses the progress of microcracks. Therefore, it is possible to suppress a decrease in bonding strength. In order to allow silicon carbide crystal particles to be present in the joint, carbonization may be performed using a paste containing metal silicon powder as a bonding agent, or heat treatment may be performed using a paste containing silicon carbide powder.

In particular, it is preferable that the silicon carbide crystal particles present in the joint have an area ratio of 10 to 50 area% in the cross section of the joint. When the area ratio is 10 area% or more and 50 area% or less, the base materials and the cylindrical bodies can be bonded with high bonding strength, and the bonding strength due to the progress of microcracks when exposed to high temperatures. The decrease can be suppressed.

Here, the area ratio of the silicon carbide crystal particles in the cross section of the joint can be measured using an optical microscope. Specifically, set the range so that the area is 1200 μm ² (the length in the horizontal direction is 40 μm and the length in the vertical direction is 30 μm) at a magnification of 1000 times, and an image in this range is captured by the CCD camera. The image analysis software “A Image-kun” (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.) may be used for analysis by a technique called particle analysis. Here, as setting conditions of this method, the brightness is dark, the binarization method is manual, the threshold value is an index indicating the brightness of the image, and the brightness of each point (each pixel) in the image is set. What is necessary is just to set 0.8 times or more and 2 times or less of the peak value of the histogram shown. A scanning electron microscope may be used instead of the optical microscope.

Also, it is preferable that no pores exist in the joint. When no pores are present, even if a thermal shock is applied to the substrate, cracks starting from the outline of the pores do not occur, so that the reliability against the thermal shock can be improved. The presence / absence of pores in the joint may be determined using a reflected electron image taken with a scanning electron microscope, for example, at a magnification of 150 to 1000 times.

Next, FIGS. 13 to 15 are schematic views showing other examples of combinations of base materials constituting the channel box of the present embodiment. In FIG. 13, the example fastened using the fastening member 16 in the location which formed the recessed part in the base materials 13a and 13b is shown. Further, FIG. 14 shows an example in which holes are formed in the base material 14a and the base material 14b, and the insertion member 17 is inserted and joined to these holes. Further, FIG. 15 shows an example in which the fastening member 18 and the insertion member 19 are used. The insertion members 17 and 19 correspond to pins and screws, for example. Further, at least one of the insertion members 17, 19 and the fastening member 18 is preferably made of a silicon carbide sintered body, and particularly preferably made of a silicon carbide sintered body containing silicon carbide fibers. It is.

As described above, the combination of the base materials may be performed not only by using a paste containing metal silicon powder or silicon carbide powder, but also by fastening with a fastening member or joining with a pin. Although not illustrated, fitting by shrink fitting or cold fitting may be performed. Furthermore, joining and fastening, joining and joining, joining and fastening and joining, etc. makes it possible to combine firmly, and even if vibrations such as earthquakes occur, the combination is rarely unraveled, so reliability is easily lost. Can be a non-channel box.

In the channel box of the present embodiment, it is preferable that at least one of the plurality of base materials is made of a silicon carbide sintered body including silicon carbide fibers. A base material made of a silicon carbide sintered body containing silicon carbide fiber has higher toughness than a base material made of a silicon carbide sintered body not containing silicon carbide fiber, so that brittle fracture is less likely to occur. The reliability can be improved because there is little risk of deterioration of the mechanical characteristics. In particular, it is preferable that all of the plurality of base materials are made of a silicon carbide sintered body containing silicon carbide fibers.

Here, the silicon carbide fiber is, for example, a silicon carbide fiber having a diameter of 10 μm to 15 μm. The silicon carbide sintered body containing silicon carbide fibers includes a concept including silicon carbide fibers inside the silicon carbide sintered body and those existing on the surface of the silicon carbide sintered body. It is. The silicon carbide fiber preferably has a specific surface area of 10 m ² / g or more and 50 m ² / g or less. Furthermore, it is preferable that the silicon carbide constituting the silicon carbide fiber has a composition formula of SiC _x (where 1 <x ≦ 1.5).

In the channel box of this embodiment, it is preferable that the inner periphery of the cylindrical body is covered with silicon. In such a configuration, the inner surface of the cylindrical body is less likely to be damaged when the fuel rod or the spacer supporting the fuel rod is attached or removed. Moreover, even if it receives contact with the radioactive contaminant (cladding) contained in the cooling water, it becomes difficult to be damaged. Further, since the melting point of silicon is 1410 ° C., the coating of silicon is not peeled off unless the surface temperature of the inner periphery of the cylindrical body reaches a high temperature of 1400 ° C.

Further, it is preferable that the base material made of the silicon carbide based sintered body contains a boron compound, and boron forming the boron compound is boron-11 (“ ¹¹ B”). With such a configuration, boron-11 (“ ¹¹ B”) is a stable isotope with respect to radiation, and thus activation of the substrate can be suppressed. Further, it is preferable that the bonding portion contains a boron compound.

Here, the boron compound is, for example, at least one of boron oxide, boron hydride, boron hydroxide, boron carbide, boron nitride, boron trichloride and boron trifluoride.

Further, the content of the boron compound contained in the base material composed of the silicon carbide sintered body is 0.5% by mass or more and 2% by mass in terms of boron compound out of 100% by mass of all the components constituting the silicon carbide based sintered body. It is preferable that:

Next, an example of the manufacturing method of the channel box of this embodiment and a fuel assembly provided with this channel box will be described. First, in order to obtain a base material composed of a silicon carbide sintered body, a silicon carbide powder having an average particle diameter (D ₅₀ ) of 0.5 μm or more and 2 μm or less, boron carbide powder as a sintering aid, and carbon source A phenol aqueous solution, or a powder of lignin sulfonate and lignin carboxylate, water, and a dispersant are added, and they are mixed and pulverized into a slurry by using a ball mill, a rotary mill, a vibration mill, a bead mill, or the like.

Next, in this slurry, as molding aids, celluloses such as methylcellulose and carboxymethylcellulose and their modified products, sugars, starches, dextrins and various modified products thereof, various water-soluble synthetic resins such as polyvinyl alcohol, and vinyl acetate After adding and mixing a synthetic resin emulsion such as gum arabic, casein, alginate, glucomannan, glycerin, sorbitan fatty acid ester, etc., ceramic granules containing silicon carbide as a main component are obtained by spray drying.

Here, the addition amount of boron carbide powder as a sintering aid is, for example, 0.12 mass% or more and 1.4 mass% or less with respect to 100 mass% of silicon carbide powder, and the addition amount of carbon source is, for example, carbonization The powder of lignin sulfonate is 0.2 mass% or more and 2 mass% or less, and the powder of lignin carboxylate is 1 mass% or more and 10 mass% or less with respect to 100 mass% of silicon powder. Moreover, the addition amount of a shaping | molding adjuvant is 1 to 15 mass% with respect to 100 mass% of silicon carbide powder, for example. Moreover, it is preferable that the salt of lignin sulfonate and lignin carboxylate is at least one of lithium, sodium and ammonium.

Before spray drying, coarse impurities and debris are removed by passing through a sieve with a particle size number of 200 described in ASTM E11-61 or a mesh finer than this mesh, and further removed by magnetic force. It is preferable to remove iron and its compounds by a method such as removing iron with an iron machine.

Then, the molded body obtained by press-molding the obtained ceramic granules by a powder pressing method or a cold isostatic pressing method is subjected to cutting as necessary. Next, for example, in a nitrogen atmosphere, the temperature is raised to 450 to 650 ° C. over 10 to 40 hours and held for 2 to 10 hours, and then naturally cooled and degreased. Furthermore, by raising the temperature to 1800 to 2200 ° C. and holding for 1 to 10 hours in an inert gas atmosphere, a substrate having a predetermined shape with a relative density of 90% or more can be obtained. In addition, although it does not specifically limit about inert gas, Since acquisition and handling are easy, it is suitable to use argon and helium.

Here, the particle size described in JIS R 1601-1998 is used to reduce the arithmetic average roughness of the surface of the portion of the base material that becomes the inner surface of the cylindrical body or the protrusion provided on the base material to 1 μm or less. What is necessary is just to grind using the grindstone to which the abrasive | polishing material whose number is 240 or more and 280 or less was fixed, for example.

Next, the case of obtaining a substrate made of a silicon carbide sintered body containing silicon carbide fibers will be described.

First, hundreds to thousands of silicon carbide fibers having a diameter of 10 μm to 15 μm are bundled to form a fiber bundle (yarn), and the fiber bundle is arranged in a two-dimensional or three-dimensional direction to form a sheet or cloth. If necessary, these sheets and cloth are laminated to form a preform with a predetermined shape (fiber preform).

Here, the oxygen content in the silicon carbide fiber is preferably 0.5% by mass or less. When the oxygen content is within this range, even if the silicon carbide fiber is exposed to a high temperature, the mechanical properties are unlikely to deteriorate.

The silicon carbide fiber is preferably coated with a film made of pyrolytic carbon or boron nitride and having a thickness of 0.5 μm or more and 1.5 μm or less by chemical vapor deposition. By adopting such a configuration, the mutual diffusion reaction between silicon carbide powder and silicon carbide fibers contained in the slurry described later is suppressed, and the silicon carbide fibers in the substrate manufacturing process are protected from damage.

A fine silicon carbide powder having an average particle size (D ₅₀ ) of 0.1 μm or more and 10 μm or less, a silicon carbide powder comprising coarse particles having an average particle size (D ₅₀ ) of 50 μm or more and 100 μm or less, and a sintering aid Add boron carbide powder as a carbon source, phenol aqueous solution as a carbon source, or powder of lignin sulfonate and lignin carboxylate, water and a dispersant, and mix using a ball mill, rotary mill, vibration mill, bead mill, etc. Prepare a crushed slurry.

And after apply | coating or impregnating this slurry to a preform (fiber preform), the preform (fiber preform) is degreased by the same method as described above. Next, if necessary, a preform (fiber preform) coated or impregnated with a slurry is laminated, and then heated to 1800-2200 ° C. in an inert gas atmosphere and pressure baked for 1-10 hours. By bonding, a base material having a predetermined shape with a relative density of 90% or more can be obtained. Here, the pressure used in the pressure sintering is, for example, 10 MPa or more and 30 MPa or less.

Next, an example of the combination by joining the base materials will be described. After applying a paste containing each powder of metal silicon, carbon and silicon carbide on at least one surface which is a combination surface of the substrates, the substrates are combined by applying pressure including their own weight. And it apply | coats so that a junction part may be coat | covered from the outer side of a combination surface, and it sets temperature and holding time as 80 to 200 degreeC and 8 to 14 hours, respectively, and dries. After that, heat treatment is performed in an inert gas atmosphere such as argon at a temperature and a holding time of 1400 ° C. or more and 1500 ° C. or less and 30 minutes or more and 90 minutes or less, respectively. Obtainable.

Further, in forming the molded body, a predetermined amount of silicon carbide powder, sintering aid, binder and water were weighed, put into a kneader and kneaded to obtain a clay-like clay. Thereafter, this kneaded material may be used to form a cylindrical molded body by molding with a screw-type extruder equipped with a mold capable of molding a desired shape at the tip. And you may obtain a channel box by the method mentioned above about the process after fabrication. Needless to say, after the cylindrical shaped body is first fired and cut, the portion of the base material that becomes the inner surface of the cylindrical body may be ground and joined.

Further, in order to coat the inner periphery of the cylindrical body with silicon, the substrate or the cylindrical body may be dipped in a solution containing silicon, pulled up, dried, and then heat-treated in an inert gas atmosphere. Note that the heat treatment may be performed at a temperature of 1420 ° C. to 1460 ° C. for 1 hour to 2 hours. It goes without saying that silicon may be applied only to the inner surface of the channel box that will be close to the spacer during attachment or removal.

In addition, as another combination method, a concave portion is formed in the base material and fastened by a fastening member, or a hole is drilled in the base material and joined by a pin, fastening by a fastening member, joining by a pin, or paste is used. What is necessary is just to combine the joined.

Next, as a method of manufacturing the fuel assembly, a fuel rod filled with uranium fuel (pellet), an upper tie plate and a lower tie plate that respectively hold the upper and lower portions of the fuel rod, a water rod, and the water rod A grid-like spacer that is fixed to the upper tie plate and supports the fuel rod between the upper tie plate and the lower tie plate, and the channel box of this embodiment are prepared. Then, for example, fix the spacer to the water rod, attach the water rod to the lower tie plate, insert the fuel rod into the spacer grid, then install the upper tie plate, and finally position the fuel rod and spacer. A fuel assembly can be obtained by covering the portion to be covered with a channel box.

And since the channel box of this embodiment is excellent in dimensional accuracy and has little corrosion and deformation due to long-term use, the fuel assembly including such a channel box is stable over a long period of time. Can be used, and is highly reliable.

1 to 15: Base material 10 to 110: Channel box 16, 18: Fastening member 17, 19: Insertion member

Claims (7)

1. A channel box comprising a cylindrical body in which a plurality of base materials made of a silicon carbide sintered body are combined.
2. The channel box according to claim 1, wherein the base material is formed into a cylindrical shape by a single member.
3. 3. The channel box according to claim 1, wherein the base material includes a protruding portion at a portion corresponding to an inner surface of the cylindrical body.
4. The channel box according to any one of claims 1 to 3, wherein at least one of the substrates to be combined is provided with a step, and at least a part of the step is a combined surface.
5. 5. The channel box according to claim 1, wherein at least one of the plurality of base materials is made of a silicon carbide sintered body including silicon carbide fibers.
6. The channel box according to any one of claims 1 to 5, wherein an inner periphery of the cylindrical body is covered with silicon.
7. A fuel assembly comprising the channel box according to any one of claims 1 to 6.

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