JP2007139761A - Fuel compact and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and inexpensively prevent a fuel compact, a fuel sleeve and a graphite block from being damaged, while preventing a coated fuel particle from being damaged by a stress when pressed. <P>SOLUTION: This fuel compact 10 is formed into a cylindrical body by molding integrally an overcoat fuel particle 12. Chamfers 16 are formed in corner parts 10a of an upper end and a lower end in the cylindrical fuel compact 10. Thickness t, t' of the chamfers 16 are 0.10 mm or more, chamfering angles θ, θ' of chamfers are within 30-60°, and the thickness t, t' of the chamfers 16 are set to make a thickness when a chamfer face contacts with the coated fuel particle 12A serve as an upper limit value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used as a fuel in a nuclear reactor such as a high-temperature gas reactor, and is a coating in which a pyrolytic carbon layer, a silicon carbide layer, or the like is coated on oxides or carbide microspheres (fuel nucleus) of nuclear fuel materials such as uranium and thorium. The present invention relates to a fuel compact formed by dispersing and integrally molding fuel particles in a graphite matrix, and an improvement of the manufacturing method thereof.

  The HTGR is composed of graphite, which has a large heat capacity and good high-temperature soundness, and uses a gas such as helium gas that does not cause a chemical reaction even at high temperatures. Is a nuclear reactor that can extract helium gas with high safety and high exit temperature, and uses high-temperature heat of around 900 ° C in a wide range of fields such as hydrogen production and chemical plants as well as power generation. It is possible to do that.

(Coated fuel particles)
As a fuel for this HTGR, generally, a total of four layers from the first layer to the fourth layer are coated around a fuel core having a diameter of about 350 μm to 650 μm obtained by sintering uranium dioxide, thorium or the like into a ceramic form. The applied coated fuel particles with a diameter of about 500 μm to 1000 μm are used. Specifically, it is the following four coatings.

That is, the innermost first layer, generally called a buffer layer, is a layer made of low-density pyrolytic carbon (PyC) having a density of about 1 g / cm ³ , and stores gaseous fission product (FP) gas. It also has the function of absorbing the swelling of nuclear fuel. The second layer applied on top of this first layer is generally an inner pyrolytic carbon (PyC) layer formed from high density pyrolytic carbon having a density of about 1.8 g / cm ³ and is a gaseous fission. It has a function of holding the gaseous fission product (FP) as a barrier for diffusion of the product (FP). The third layer, called the silicon carbide (SiC) layer, is made of silicon carbide with a density of about 3.2 g / cm ³ and mainly holds the solid fission product as a barrier to the diffusion of the solid fission product. In addition, it has a function as a main strength member of the entire coated fuel particle. The outer pyrolytic carbon layer, which is the outermost fourth layer, is composed of high-density pyrolytic carbon having a density of about 1.8 g / cm ³ , as in the second layer, and is formed into a third layer of silicon carbide by irradiation shrinkage. It has a function of generating a compressive stress to maintain the strength of the entire coated fuel particle under irradiation and to hold a gaseous fission product (FP).

  Such coated fuel particles are generally produced through the following steps. First, the production of fuel nuclei will be described in detail. A dripping stock solution is produced by adding pure water and a thickener to an uranyl nitrate stock solution produced by dissolving uranium oxide powder in nitric acid and stirring. In this case, the thickener is added so that the dropped uranyl nitrate stock solution drops into a true sphere due to its surface tension during dropping. As the thickener, for example, a resin having a property of solidifying under an alkaline condition such as polyvinyl alcohol resin, polyethylene glycol, metroise, and the like can be used. Subsequently, after the dripping stock solution adjusted in this way is cooled to a predetermined temperature to adjust the viscosity, it is dropped into the ammonia aqueous solution by vibrating a dropping nozzle having a small diameter. In this case, the droplet is prevented from being deformed at the time of landing by spraying ammonia gas in the space until the droplet reaches the surface of the aqueous ammonia solution to gel the surface of the droplet.

  The stock solution dropped into the aqueous ammonia solution is converted into ammonium deuterated uranate particles by sufficiently reacting with uranyl nitrate in the aqueous ammonia solution. These ammonium heavy uranate particles are roasted in the atmosphere to form uranium trioxide particles, which are further reduced and sintered to obtain a fuel nucleus composed of high-density ceramic uranium dioxide. Since the particle size and sphericity of the fuel core obtained in this way have a great influence on the production conditions in the subsequent coating process, the fuel core is subjected to particle size selection and sphericity selection by a sieve. Once done, it is sent to the coating process.

Next, in the fuel core coating step, the fuel core is loaded on the fluidized bed, and the coating of the first to fourth layers is sequentially performed by thermally decomposing the coating gas. In this case, specifically, the low-density carbon layer of the first layer is coated on the fuel core by pyrolyzing acetylene (C ₂ H ₂ ) at about 1400 ° C. The high-density pyrolytic carbon layers of the second and fourth layers are coated by pyrolyzing propylene (C ₃ H ₆ ) at about 1400 degrees. The silicon carbide layer as the third layer is formed by thermally decomposing methyltrichlorosilane (CH ₃ SiCl ₃ ) at about 1600 ° C. The coated fuel particles produced in this way are further coated with a graphite matrix material made of graphite powder, a binder, etc. on the surface of the coated fuel particles to form overcoated particles.

(Fuel compact)
When the overcoated coated fuel particles are used as a fuel compact, after the coated fuel particles are dispersed in the graphite matrix material, as shown in FIG. 7, for example, a solid cylindrical shape or a hollow cylindrical shape is used. It is sintered after being press-molded or molded to obtain a fuel compact 10 having a fixed shape shown in FIG. 7A (see, for example, Japanese Patent Laid-Open No. 2000-284084). As shown in FIG. 8, when compressing the coated fuel particles 12, the fuel compact 10 is heated by a die or a punch to soften the phenol resin contained in the graphite matrix material to form a binder. The coated fuel particles 12 are integrally formed.

(Loading into the core)
There are two types of fuel compact 10 formed in this way, a solid cylindrical type and a hollow cylindrical type. In either case, 1) a fixed quantity is put in a fuel sleeve (cylinder) formed of graphite. Either in the form of fuel rods plugged up and down, and loaded into a plurality of insertion ports of a hexagonal column type graphite block of a high temperature gas reactor, or 2) a plurality of hexagonal column type graphite blocks of a high temperature gas reactor Either loaded directly into the insertion port, or finally, a plurality of hexagonal columnar graphite blocks are stacked in a honeycomb array to be loaded into the core as fuel.

(Deficiency of fuel compact)
In this case, when handling the fuel compact 10 such as loading into the fuel sleeve or the graphite block, the fuel compact 10 is mechanically brought into contact with the inner surface of the fuel sleeve or the graphite block, and an impact is applied to the fuel compact 10. Ten cylindrical corners 10b (see FIG. 7) may be missing.

  Thus, when a defect occurs in the fuel compact 10, when the fuel compact 10 becomes high temperature in the high temperature gas furnace and thermally expands, the fragment is sandwiched between the fuel compact 10 and the inner surface of the fuel sleeve or graphite block, A high stress is generated at the location, causing damage to the fuel compact 10, the fuel sleeve, and the graphite block.

  In addition, when the fuel compact 10 is used in a high temperature gas furnace, a temperature difference occurs due to a difference in cooling efficiency between the central portion and the outer peripheral portion, and the central portion has a higher temperature than the outer peripheral portion. However, thermal expansion becomes larger than that of the outer peripheral portion, and as a result, there is a tendency to deform into a drum shape. In the fuel compact 10 thus deformed into a drum shape, the corner portion 10b may be in mechanical contact with the inner surface of the fuel sleeve or the graphite block and cause a crack in the fuel compact 10. .

  Accordingly, it is necessary to prevent the fuel compact 10 from being damaged, but in that case, it is also necessary to consider that the coated fuel particles 12 are not damaged by the stress during pressing.

  One problem to be solved by the present invention is to prevent damage to the fuel compact, fuel sleeve, and graphite block easily and at low cost while preventing damage to the coated fuel particles due to stress during pressing. It is to provide a fuel compact that can be used.

  One problem to be solved by the present invention is that a fuel compact capable of preventing damage to a fuel compact, a fuel sleeve, and a graphite block while preventing damage to coated fuel particles due to stress during pressing is simplified. Another object is to provide a method that can be manufactured at low cost.

  According to the first problem solving means of the present invention, in the fuel compact formed by integrally molding the coated fuel particles, chamfers are formed at the corners, and the chamfers have a planar shape or a curved shape. A fuel compact is provided.

  In the fuel compact according to the first problem-solving means of the present invention, the fuel compact has a cylindrical shape, and the chamfer may be formed at a corner of the cylindrical fuel compact. The fuel compact can be formed at the upper and lower corners.

  In the fuel compact according to the first problem solving means of the present invention, when the chamfer has a planar shape, the planar shape may be two or more planes having different chamfer angles in the axial direction of the cylinder. it can.

  Further, when the chamfer has a planar shape, the thickness of the chamfer is preferably 0.10 mm or more. In this case, the chamfering angle of the chamfer is in the range of 30 ° to 60 °, and the chamfer thickness is The upper limit is preferably a dimension corresponding to the thickness when the chamfer surface is in contact with the outer peripheral surface of the coated fuel particles.

  Further, when the chamfer chamfer angle is other than 45 °, the upper limit value of the chamfer thickness is the larger of the two chamfer thicknesses specified when the chamfer surface is in contact with the outer peripheral surface of the coated fuel particles. The dimension corresponds to the value of.

  In the fuel compact according to the first problem-solving means of the present invention, when the chamfer has a curved surface shape, the upper limit value of the chamfer curved surface is a value until the outer peripheral surface of the coated fuel particle is reached.

  According to the second problem solving means of the present invention, in a fuel compact manufacturing method for manufacturing a fuel compact by integrally molding coated fuel particles with a mold, a taper having a planar shape or a curved shape is formed at a corner of the mold. There is provided a method for manufacturing a fuel compact, characterized in that a planar or curved chamfer is formed at a corner of the fuel compact. The planar taper can be in the form of a single or multi-level plane.

  In the fuel compact manufacturing method according to the second problem solving means of the present invention, it is preferable that a taper is formed at the corner of the mold by mounting a ring-shaped taper member having a tapered surface on the mold.

  According to the first problem-solving means of the present invention, as described above, the chamfer (chamfering) is formed at the corner of the cylindrical fuel compact, so that the fuel compact is the fuel sleeve during handling and thermal expansion. Even when mechanically in contact with the inner surface of the graphite block, the stress applied to the fuel compact is reduced, so that the fuel compact can be prevented from being broken or cracked, and the fuel sleeve or graphite block can be damaged. There is no.

  In particular, it is preferable that the chamfer has a planar shape or a curved surface shape having two or more steps, since the thickness and surface area of the chamfer can be increased, and the loss and cracking of the fuel compact can be more effectively prevented.

  In addition, when the thickness and chamfering angle of the planar chamfer are adjusted appropriately, or when the upper limit value of the curved surface of the curved chamfer reaches the outer peripheral surface of the coated fuel particle, the shape of the coated fuel particle Therefore, even when the chamfer is formed, the coated fuel particles are not unnaturally stressed during pressing, so that the coated fuel particles are not damaged, and the coated fuel is not damaged. The strength against mechanical impact of the fuel compact can be improved while preventing breakage of particles.

  According to the second problem solving means of the present invention, a flat or curved taper is formed at the corner of the mold and a chamfer is formed at the corner of the cylindrical fuel compact. A fuel compact that can be effectively prevented can be easily manufactured.

  In this case, if the taper at the corner of the mold is formed by a ring-shaped taper member having a taper surface, the existing manufacturing equipment can be installed without making a major change by simply mounting the taper member inside the mold. Since it can be utilized, a fuel compact capable of effectively preventing breakage can be easily manufactured at low cost.

  An embodiment for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 shows a fuel compact 10 according to a first embodiment of the present invention. This fuel compact 10 has a mold shown in FIG. A plurality of overcoat particles 12 shown in an enlarged view in FIG. 1B are compressed and integrally molded by heating while being pressed or molded.

  More specifically, the fuel compact 10 is obtained by dispersing a predetermined amount of coated fuel particles 12A in a graphite matrix made of graphite powder, a binder, etc. to form overcoat particles 12, and FIG. As shown, it is manufactured by putting it into a metal die 1 and compressing it in the die 1 with upper and lower metal punches 2A and 2B. In FIG. 1B, reference numeral 14 denotes an overcoat layer.

  When manufacturing the fuel compact 10, the overcoat particles 12 are heated by heating the die 1 and the punch 2, thereby softening the phenol resin contained in the graphite matrix material in the overcoat layer 14 to produce graphite. The matrix material is integrated as a binder between the coated fuel particles 12 and formed into a cylindrical fuel compact 10 shown in FIG. In FIG. 2, reference numeral 3 indicates a core rod for forming a hollow portion in the cylindrical fuel compact 10, and this core rod 3 is not necessary when a solid fuel compact is manufactured. Moreover, these dies 1, punch 2, and core rod 3 can be formed from alloy tool steel, for example.

  As described above, the coated fuel particles 12A are formed by coating the surface thereof with a graphite matrix material made of graphite powder, a binder or the like as shown in FIG. 1B before compression. The overcoat layer 14 is covered. The overcoat layer 14 1) prevents the coated fuel particles 12A from being damaged by pressure during press molding or the like, and 2) serves as an intermediate between the coated fuel particles 12A in the fuel compact 10. Is formed to prevent the coated fuel particles 12A from being thermally and mechanically damaged during molding and heat treatment. For this reason, it is common to make the fuel compact 10 after uniforming the diameters of the overcoat particles 12 so that the coated fuel particles 12A are uniformly dispersed.

  The overcoat layer 14 can be formed by dispersing the coated fuel particles 12A in a graphite matrix material made of graphite powder, a binder or the like. At this time, the thickness of the overcoat layer 14 is By appropriately setting the mesh size of the sieve and adjusting the time for overcoating when sieving the coated fuel particles 12 with the overcoat layer 14 formed in the middle and at the end of the overcoat process , Can be adjusted to an appropriate thickness.

  As shown in FIG. 1, the fuel compact 10 of the present invention has a planar chamfer 16 (chamfered) formed at a corner 10 a of a cylindrical fuel compact 10. As shown in FIG. 1A, the chamfer 16 is preferably formed over the entire circumference of the upper and lower corners 10a of the cylindrical fuel compact 10.

  The chamfer 16 reduces the stress by dispersing the mechanical impact applied to the corner 10a as compared to the case where a load is applied to one corner 10b as in the conventional fuel compact 10 shown in FIG. Further, it is possible to prevent breakage of a fuel sleeve (not shown) and a graphite block due to the fuel compact 10 and, in turn, fragments thereof.

  The chamfer 16 is basically formed by mechanically cutting the upper and lower corners of the fuel compact 10 formed as shown in FIG. In this case, it is necessary not to damage the coating layer of the coated fuel particles 12A. For this reason, the thickness range of the chamfer 16 described later is extremely important. Instead of this mechanical processing, as shown in FIG. 2, taper 2a is formed at the corners of the upper and lower punches 2A, 2B, etc., and chamfer 16 is formed by compression molding overcoat particles 12. It may be formed. In this case, as shown in FIG. 2, the taper 2a can be formed by attaching a ring-shaped taper member 4 having a planar taper surface to the upper and lower punches 2A and 2B.

  When the manufacturing method shown in FIG. 2 is used, the manufacturing method of the present invention is carried out only by attaching the taper member 4 to the general punches 2A and 2B used conventionally shown in FIG. can do. Thus, since the existing manufacturing equipment can be used effectively, the fuel compact 10 of the present invention having the chamfer 16 can be manufactured easily and at low cost. The taper member 4 can be attached to the corners of the upper and lower punches 2A and 2B by setting the diameter thereof equal to the diameters of the upper and lower punches 2A and 2B.

  The thickness t, t ′ (see FIG. 1B) of the chamfer 16 is preferably at least 0.10 mm. This is because when the thickness t, t ′ of the chamfer 16 is larger, the chamfer surface area of the chamfer 16 can be made larger, and the mechanical shock applied to the fuel compact 10 is dispersed to sufficiently reduce the stress. This is because the loss of the fuel compact 10 can be sufficiently prevented. In the present invention, the thicknesses t and t ′ of the chamfer 16 are chamfers formed across the orthogonal upper surface (or lower surface) 10A and side surface 10B of the fuel compact 10, as shown in FIG. 16, the distance from the position of one end surface (upper surface (or lower surface) 10A or side surface 10B) to the position where the chamfer 16 intersects the other end surface (side surface 10B or upper surface (or lower surface) 10A).

  As described above, the chamfer 16 is desirably set to have the thicknesses t and t ′ as large as possible in order to prevent the fuel compact 10 from being damaged. On the other hand, the chamfers 16 have a thickness t and t ′ that is too large. When the chamfer 16 is formed by mechanical processing, the coating layer of the coated fuel particles 12A is shaved to affect the irradiation behavior, and when the chamfer 16 is formed by the method of FIG. Since the strength of the fuel particles 12A is affected, it is preferable to set the thickness within a range not affected by such influence. Further, in order to increase the thickness t, t ′ of the chamfer 16, the chamfering angles θ, θ ′ of the chamfer 16 (see FIG. 1B): the inclination angle of the chamfer 16 from the end surface of the fuel compact 10: θ + θ ′ = If the angle 90 ° is set larger than necessary (the other chamfer angle is reduced), the stress reducing function as the chamfer 16 is deteriorated.

  For this reason, the chamfer angles θ and θ ′ (see FIG. 1B) of the chamfer 16 are set within a range of 30 ° to 60 °, and the thickness t and t ′ of the chamfer 16 (see FIG. 1B). It is desirable that the upper limit value of (see)) be a dimension corresponding to the thickness when the chamfer surface is formed deeply until it contacts the outer peripheral surface of the coated fuel particle 12A (see FIG. 1C).

  When the thickness t, t ′ of the value of the chamfer 16 exceeds the above upper limit value, the chamfer 16 is formed so as to cut out a part of the coating layer of the coated fuel particles 12A. When the coated fuel particles 12A are compressed, an excessive load is applied to the coated fuel particles 12, and the coated fuel particles 12A may be damaged, which may cause an unfavorable state in terms of holding fission products. In particular, when the thickness of the chamfer 16 exceeds the above upper limit value and is formed by mechanical processing, the coating layer of the coated fuel particles is cut to an undesirable state in which a problem occurs in the fission product holding function. . Accordingly, the thickness t, t ′ of the chamfer 16 is set to an upper limit value when the chamfer surface is set at a position where at least the chamfer surface overlaps the outer periphery of the coated fuel particle 12A (see FIG. 1C), and is not set any more. It will be necessary. Thereby, the intensity | strength with respect to the mechanical impact of the manufactured fuel compact 10 can be improved, preventing damage to the covering fuel particle | grains 12A.

  When the chamfer angle of the chamfer 16 is set to 45 ° as in the illustrated embodiment, the chamfer angles θ and θ ′ are both 45 °, and the thickness of the chamfer 16 is also the same as that of the fuel compact 10. The thickness t from the upper surface (or lower surface) 10A is equal to the thickness t ′ from the side surface 10B. However, as shown in FIGS. 3A and 3B, when setting the chamfer angle to other than 45 °, There are chamfer angles θ and θ ′ of different values in the chamfer 16 (for example, 30 ° and 60 ° and vice versa). As a result, the thickness of the chamfer 16 in the above sense is also shown in FIG. As shown in (B), different values of thickness are specified.

  That is, in the embodiment shown in FIG. 3A, the thickness X1 from the upper surface 10A is different from the thickness X2 from the side surface 10B, and in the embodiment shown in FIG. The thickness Y1 is different from the thickness Y2 from the side surface 10B. In this case, the thickness of the chamfer 16 is set with the larger value of the chamfer thickness X1 or X2 (Y1 or Y2) when the chamfer surface is in contact with the outer peripheral surface of the coated fuel particle 12A as the upper limit value. Then, the thickness of the chamfer 16 is set so as not to exceed the value.

  More specifically, in the embodiment shown in FIG. 3A, the value of the thickness X1, which is the distance from the upper surface (lower surface) 10A, is the side surface in the embodiment shown in FIG. By setting the value of the thickness Y2 that is the distance from 10B as the upper limit value of the thickness of the chamfer 16 so that the thickness of the chamfer 16 does not exceed the upper limit value, the other thickness (X2, Y1) The thickness is always smaller than the upper limit thickness (X1, Y2), the chamfer 16 does not affect the coated fuel particles 12A, and the coated fuel particles 12A can be prevented from being damaged.

  A modification of the first embodiment of the present invention is shown in FIG. 4, in which the chamfer 16 has a two-step planar shape with different chamfer angles in the axial direction of the cylindrical fuel compact 10. In the illustrated example, the chamfering angle θu of the first-stage (upper) planar chamfer portion 16U is smaller than the chamfering angle θd of the second-stage (lower) planar chamfer portion 16D. In this modification, as shown in FIG. 4B, the overcoat layer 14 may be cut so that the chamfer 16 is in contact with the coating layer of the coated fuel particles 12A, as in FIG. 1C. Good.

  According to this modification, the thickness and surface area of the chamfer can be made larger than that of the single planar chamfer 16 shown in FIGS. 1 and 3, so that loss and cracking of the fuel compact can be more effectively prevented. preferable.

  FIG. 5 shows a fuel compact 10 according to a second embodiment of the present invention. In this embodiment, the chamfer 16 has a curved surface shape as shown in FIG. . Thus, when the chamfer 16 has a curved shape, the thickness t (see FIG. 5B) and the surface area of the chamfer 16 can be set larger than those of the planar chamfer 16 of FIG.

  In the example shown in FIG. 5B, the curved chamfer 16 has a curved surface radius R1 that is in contact with the outer surface of the overcoat layer 14 on the coated fuel particles 12A (the curved surface radius in this case is that of the overcoated particles 12). Is the same as the radius). However, as shown in FIG. 5C, the curved chamfer 16 may be formed in a state in which the overcoat layer 14 is scraped to increase the radius of the curved surface. As shown in FIG. 5 (C), the upper limit value R2 of the curved surface radius is set so that the curved surface of the chamfer 16 is on the outer peripheral surface of the coated fuel particle 12A (the outer peripheral surface of the coating layer) so as not to be cut or damaged. The radius of the curved surface in contact. If the radius of the curved surface is made larger than this, the coating layer is damaged and must be avoided.

  In this way, when the chamfer 16 is curved and the thickness t is increased, the area of the chamfer surface of the chamfer 16 can be increased, so that the fuel compact 10 is not handled at the time of handling or thermal expansion. The mechanical impact applied to the fuel compact 10 can be dispersed even when mechanically contacted with the fuel compact 10 and the stress can be sufficiently reduced, so that the mechanical strength against defects and cracks is improved in the fuel compact 10, and therefore the fuel sleeve And the graphite block can be sufficiently prevented from being damaged.

  Further, since the chamfer 16 has a curved surface shape that follows the shape of the coated fuel particle 12A even if the curved surface thickness is increased to the upper limit value, stress is not unnaturally applied to the coated fuel particle 12A during pressing. The coated fuel particles 12A are not damaged, and the strength of the fuel compact 10 against mechanical impact can be improved while preventing the coated fuel particles 12A from being damaged.

  In addition, when the thickness of the curved surface of the chamfer 16 does not reach the upper limit value, a graphite matrix material is interposed between the chamfer surface and the coated fuel particles 12A, and the graphite matrix material is compressed during pressing. As a result, pressure is unnaturally applied to the coated fuel particles 12A, and there is no possibility that the coated fuel particles 12A are damaged.

  As described above, when the upper limit value of the thickness of the curved surface of the chamfer 16 is set so as not to scrape or damage the coating layer of the coated fuel particles 12A, the stress applied to the coated fuel particles 12A is sufficiently reduced and the coated fuel particles are reduced. Since the thickness t of the chamfer 16 can be set to a sufficiently large value close to the radius of the coated fuel particle 12 while preventing the breakage of the particles 12A, the mechanical strength of the fuel compact can be improved, Damage to the fuel sleeve and graphite block can be sufficiently prevented.

  As in the embodiment of FIG. 1, the curved chamfer 16 is also formed by mechanical cutting. Instead, as shown in FIG. 6, the corners of the upper and lower punches 2A, 2B, etc. In this case, the curved surface portion 2a is formed, and the coated fuel particles 12A having the overcoat layer 14 (that is, the overcoat particles 12) are compressed. In this case, in order to be able to use the existing manufacturing equipment effectively, the curved surface portion 2a has a tapered ring-shaped taper member 4 having a curved surface shape as shown in FIG. It can be formed by attaching to 2A and 2B.

  According to the present invention, the chamfer (chamfering) provided at the corner of the cylindrical fuel compact allows the fuel compact to mechanically contact the inner surface of the fuel sleeve or graphite block during handling or thermal expansion. Since the stress applied to the fuel compact is reduced, it is possible to prevent the fuel compact from being broken or cracked, to provide a high-quality fuel compact, and to improve industrial utility.

The fuel compact by the 1st Embodiment of this invention is shown, The figure (A) is the perspective view, The figure (B) is the partially expanded sectional view, The figure (C) is FIG. FIG. 2 is an enlarged cross-sectional view of a chamfer having a form different from that of FIG. It is a schematic sectional drawing which shows the state which implements the manufacturing method of the fuel compact by this invention. The fuel compact which deform | transformed the 1st Embodiment of this invention is shown, The figure (A) is the perspective view, The figure (B) is the partially expanded sectional view, The figure (C) is a figure (B) ) Is an enlarged cross-sectional view of a chamfer having a form different from that of FIG. The fuel compact which further deform | transformed the 1st Embodiment of this invention is shown, The same figure (A) is the partially expanded sectional view, The same figure (B) is sectional drawing of the same part as the same figure (A). FIG. 5 is an enlarged cross-sectional view of a chamfer having a form different from that of FIG. The fuel compact by the 2nd Embodiment of this invention is shown, The figure (A) is the perspective view, The figure (B) is the partially expanded sectional view, The figure (C) is FIG. FIG. 6 is an enlarged cross-sectional view of a chamfer having a form different from that of FIG. It is a schematic sectional drawing which shows the state which implements the manufacturing method of the fuel compact of FIG. The fuel compact of a prior art is shown, The figure (A) is the perspective view, The figure (B) is the partially expanded sectional view. It is a schematic sectional drawing which shows the state which manufactures the fuel compact of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Die 2 Punch 2A Upper punch 2B Lower punch 2a Taper or curved surface part 3 Core rod 4 Tapered member 10 Fuel compact 10A Upper surface (lower surface) of fuel compact
10B Side of fuel compact 10a Corner of fuel compact 10b Corner of fuel compact 12 Overcoat particles 12A Coated fuel particles 14 Overcoat layer 16 Chamfer 16U Chamfer part of the first stage (upper stage) 16D Chamfer of the second stage (lower stage) Part t, t ′, X1, X2, Y1, Y2 Chamfer thickness θ, θ ′, θu, θd Chamfer angle of chamfer

Claims (11)

A fuel compact formed by integrally molding coated fuel particles, wherein a chamfer is formed at a corner, and the chamfer has a planar shape or a curved shape. 2. The fuel compact according to claim 1, wherein the fuel compact has a cylindrical shape, and the chamfer is formed at a corner of the cylindrical fuel compact. 3. The fuel compact according to claim 1, wherein the chamfer has two or more flat surfaces having different chamfer angles. 3. The fuel compact according to claim 1, wherein the chamfer is formed at corners of an upper end and a lower end of the fuel compact. 4. 2. The fuel compact according to claim 1, wherein the chamfer has a planar shape, and the chamfer has a thickness of 0.10 mm or more. 6. The fuel compact according to claim 5, wherein a chamfer angle of the chamfer is in a range of 30 ° to 60 °, and an upper limit value of the thickness of the chamfer is that the chamfer surface is an outer peripheral surface of the coated fuel particles. A fuel compact characterized in that it has a dimension corresponding to the thickness when contacting the fuel. 2. The fuel compact according to claim 1, wherein the chamfer has a planar shape, a chamfer angle of the chamfer is in a range of 30 ° to 60 °, and an upper limit value of the chamfer thickness is chamfer A fuel compact having a dimension corresponding to a thickness when a surface is in contact with an outer peripheral surface of the coated fuel particle. 8. The fuel compact according to claim 6, wherein when the chamfering angle of the chamfer is other than 45 °, an upper limit value of the thickness of the chamfer is such that the chamfer surface is an outer peripheral surface of the coated fuel particle. A fuel compact characterized by having a dimension corresponding to a value on the larger side of the thicknesses of the two chamfers specified when contacting with the fuel. 2. The fuel compact according to claim 1, wherein the chamfer has a curved surface shape, and an upper limit value of a thickness of the curved surface of the chamfer is a value until the outer peripheral surface of the coated fuel particle is reached. And fuel compact. In a fuel compact manufacturing method of manufacturing a fuel compact by integrally molding coated fuel particles with a mold, a flat or curved taper is formed at a corner of the mold, and a flat surface is formed at the corner of the fuel compact. A method for manufacturing a fuel compact, characterized by forming a chamfer having a shape or a curved surface. 11. The fuel compact manufacturing method according to claim 10, wherein a taper is formed at a corner of the mold by mounting a ring-shaped taper member having a taper surface on the mold. Fuel compact manufacturing method.

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