JP6473601B2 - Core structural material - Google Patents

Description

  The present invention relates to a core structure material for a pebble bed reactor.

  Graphite has a high neutron absorption cross-section and a large neutron moderating ability, so it has a high reduction ratio, high heat resistance, and large materials can be easily obtained. It's being used. In particular, it is an important material as a material for a moderator, a reflector, etc. of a gas cooling furnace such as a Magnox furnace, an improved graphite furnace (AGR furnace), a high temperature gas furnace.

  Patent Document 1 describes a graphite structure with improved strength by using ceramics to compensate for the brittleness of graphite itself without impairing the core properties and thermal properties of graphite as a moderator and reflector. The surface of the nuclear reactor structure such as moderator and reflector made of solid graphite was covered with heat-resistant ceramics such as silicon carbide (SiC) to improve the strength without impairing the core and thermal performance. Graphite structures have been proposed.

Japanese Utility Model Publication No. 61-206897

  The gas-cooled furnace includes a conventional furnace using carbon dioxide gas as a coolant such as a Magnox furnace and an improved graphite furnace, and a new furnace using helium as a coolant such as a high-temperature gas furnace. Since carbon dioxide used in conventional reactors causes a chemical reaction with the graphite of the core structure material, the temperature of the coolant at the outlet of the reactor is limited by the chemical reaction between the graphite and carbon dioxide. However, by using helium gas as a coolant, a chemical reaction between the coolant and graphite does not occur, and the operating temperature of the reactor can be increased.

  High temperature gas furnaces using helium as a coolant include a block type high temperature gas furnace and a pebble bed type high temperature gas furnace depending on the fuel shape. In a block type HTGR, for example, a hexagonal graphite block (fuel column) in which fuel rods are housed, a hexagonal graphite block (movable reflector) in which fuel rods are not housed, and those Consists of fixed reflectors surrounding the outside. The graphite structure of Patent Document 1 is a technique related to a block-type HTGR.

  On the other hand, in the pebble bed type HTGR, fuel balls (pebbles) formed by mixing coated fuel particles with graphite particles into a spherical shape are used, and a large number of these are stacked randomly in a space formed by graphite blocks. Form. The diameter of the fuel ball is about 6 cm. It is characterized in that the fuel balls with a lowered nuclear reaction are taken out from below during operation and are continuously exchanged by supplying new fuel balls from the top. Therefore, it is not necessary to stop the operation and change the fuel as in the case of the block type high temperature gas reactor, and the operation period of the nuclear reactor can be lengthened.

  However, since the pebble bed type HTGR can in principle be operated for a longer time than the block type HTGR, it can be operated for a long time by extending the replacement period of the graphite block used. To. For this reason, further life-up of the graphite block is desired.

  In view of the above problems, an object of the present invention is to provide a core structure material used for a pebble bed reactor capable of long-term operation.

The core structure material and pebble bed type reactor of the present invention for solving the above problems are as follows:
(1) A core structural material for a pebble bed type nuclear reactor, comprising a graphite block comprising a base material made of graphite and a ceramic coating covering the base material, and an inner wall surface facing the pebble storage space of the graphite block And a ceramic tile further covering the core structure material.
(2) The ceramic tile includes a protrusion that is locked to a narrow portion provided in the graphite block.
(3) The ceramic tile is gripped by a fastener inserted into a hole provided in the graphite block.
(4) The graphite block includes a protrusion that is locked to a narrow portion provided in the ceramic tile.
(5) The ceramic tile is composed of a ceramic / ceramic composite material.
(6) The ceramic tile is made of a SiC / SiC composite material.
(7) The ceramic tile is made of SiC.
(8) The ceramic coating is a core structure material made of SiC.
(9) A pebble bed nuclear reactor comprising the core structure material according to any one of (1) to (8).
(10) The ceramic tile is a pebble bed nuclear reactor in which one piece is provided for each graphite block.
It is characterized by that.

  A core structure material obtained by the present invention includes a base material made of graphite, a ceramic coating covering the base material, a graphite block, and a ceramic tile further covering an inner wall surface facing a pebble storage space of the graphite block. Consists of. Since the graphite block has a corrosion-resistant ceramic coating formed on the surface of the graphite, the graphite and the fission product do not come into contact with each other, and deterioration of the graphite block can be suppressed. In addition, since the ceramic tile is on the inner wall facing the pebble storage space, even if the load applied from the pebble is concentrated on one point, the ceramic tile distributes the load and damages the ceramic coating on the surface of the graphite block. Can be prevented. For this reason, the graphite of the core structure material does not come into contact with fission products or the like even when used for a long period of time, and can be prevented from being consumed.

The schematic diagram which shows an example of the pebble bed type | mold reactor in which the core structural material which concerns on this invention is used. The schematic diagram which shows an example of the pebble storage space where the core structure material which concerns on this invention is used. FIG. 5 is a schematic diagram showing the bonding between the graphite block and the ceramic tile of the core structure material according to the present invention, and (a) Example 1, (b) Example 2, and (c) Example 3. The perspective view of the core structure material which concerns on this invention.

  Hereinafter, a preferred embodiment of a core structure material according to the present invention will be described in detail with reference to FIGS.

  FIG. 1 is a schematic diagram showing an example of a pebble bed reactor. In the pebble bed type reactor 1, a reactor core 3 is housed in a reactor vessel 2, and a plurality of pebbles 4 that are fuel balls are loaded in the reactor core 3. In the core 3, a pebble storage space 40 is formed in which the upper part, the lower part, and the periphery are constituted by a plurality of core structural members 10. In addition, the core 3 is configured by stacking a plurality of core structural materials 10 to minimize the amount of neutron leakage to the outside. A coolant pipe 5 is connected to the lower part of the reactor vessel 2 and is connected to a power converter 6 having a generator at the upper part, a gas turbine or compressor at the center, and a cooler at the lower part.

  FIG. 2 is a schematic diagram illustrating an example of a pebble storage space 40 configured with the core structure material 10 of the present embodiment.

  The pebble 4 loaded in the pebble storage space 40 has a spherical shape with a diameter of about 6 cm. For example, the pebble 4 is composed of a large number of coated fuel particles containing uranium oxide as a nuclear fuel material and a graphite matrix containing the particles. The region is surrounded by a graphite shell. Then, the pebble 4 is mixed with the graphite powder and filled into a spherical mold in order to contain the coated fuel particles in the graphite material as the neutron moderator. The primary sphere is secondarily pressed together with the graphite powder to form spherical particles with a shell, and the surface is ground to make it into a true sphere, and then completed through preliminary firing and firing steps.

  The core structure material 10 constituting the pebble storage space 40 includes a graphite block 20 and a ceramic tile 30 that covers the surface of the graphite block 20. The graphite block 20 of the present embodiment has an inner wall surface 20a on the side facing the pebble storage space 40, has a substantially quadrangular prism shape including a cylindrical surface having upper and lower surfaces 20b and left and right side surfaces 20c, and is a base made of graphite. It consists of a material 21 and a ceramic coating 22 that covers the substrate 21. The cylindrical surface does not need to be a complete cylindrical surface. For example, the inner wall 13 facing the pebble storage space of the graphite block 20 is configured as a flat surface, so that the pebble storage space 40 is formed into a polygonal column. You may comprise by the wall surface.

  Further, the ceramic tile 30 covers the inner wall surface 20 a facing the pebble storage space 40 of the graphite block 20. The combination of the graphite block 20 and the ceramic tile 30 is achieved by, for example, gripping the narrowed portion 25 formed on the upper and lower surfaces 20b of the graphite block 20 or gripping the narrowed portion formed on the upper and lower surfaces of the ceramic tile 30. Either is possible.

  Although it has been described that the narrowed portion 25 is formed on the upper and lower surfaces 20b, the left and right side surfaces 20c may be formed, or may be formed on the entire circumference of the graphite block 20.

  In a nuclear reactor, various gaseous fission products are generated with fission. A component that reacts with graphite may be generated in the gaseous fission product. The pebble 4 used in the pebble bed nuclear reactor 1 contains a large amount of high-density elements such as uranium and moves while rolling on the surface of the core structural material 10 composed of the graphite block 20. At the contact point of the structural member 10, high pressure is concentrated at one point. For this reason, when the ceramic coating 22 is broken, the graphite and the fission product react to deteriorate the graphite block 20.

  In this embodiment, the core structure material 10 further includes a graphite block 20 composed of a base material 21 made of graphite and a ceramic coating 22 covering the base material 21, and an inner wall surface 20 a facing the pebble storage space 40 of the graphite block 20. The ceramic tile 30 is covered.

  Since the graphite block 20 has the corrosion-resistant ceramic coating 22 formed on the graphite surface, the graphite and the fission product do not come into contact with each other, and deterioration of the graphite block 20 can be suppressed.

  Further, since the ceramic tile 30 is provided on the inner wall surface 20 a facing the pebble storage space 40, even if the load applied from the pebble 4 is concentrated on one point, the ceramic tile 30 disperses the load and the surface of the graphite block 20. It is possible to prevent the ceramic coating 22 from being damaged. For this reason, the graphite of the core structure material 10 does not come into contact with fission products and the like even when used for a long period of time, and wear can be prevented.

  The ceramic coating 22 is preferably SiC. Since the pebble 4 is formed by solidifying particles obtained by coating nuclear fuel with pyrolytic carbon, SiC, etc., the pebble 4 is hard and has a high ability to wear the core structure material 10. Therefore, by covering the core structure material 10 with the same material as the hardest SiC contained in the pebble 4, the core structure material 10 can be made difficult to be damaged even when pressure is applied from the pebble 4. SiC has little influence on the fission chain reaction because it absorbs less neutrons. Further, since it has strength and high heat-resistant temperature, it can be suitably used as the graphite block 20 of the core structure material 10.

  Moreover, the ceramic coating 22 may cover the entire surface of the base material 21 of the graphite block 20 as shown in the present embodiment, or may be applied only to the inner wall surface 20a facing the pebble storage space 40. good.

  FIG. 3 is a schematic diagram showing the bonding between the graphite block 20 and the ceramic tile 30 of the core structure material 10, (a) is Example 1, (b) is Example 2 (c), and Example 3; FIG. 4 is a perspective view of the core structure material 10. In FIG. 4, the description of the ceramic coating on the side surface is omitted, and the substrate is exposed.

  As described above, the first embodiment has a structure in which the ceramic tile 30 holds and holds the narrowed portion 25 formed on the side surface 20c of the graphite block 20.

  In the pebble bed reactor 1, when it is used at one end, a substance having a long half-life is formed, and the internal maintenance cannot be easily performed. For this reason, high reliability is required for fixing the graphite block 20 and the ceramic tile 30. Since the core structure material 10 of the present embodiment has a structure in which the ceramic tile 30 grips the constricted portion 25 of the graphite block 20, it does not require frictional force and adhesive force, and therefore, between the graphite block 20 and the ceramic tile 30. This can make it difficult to generate stress.

  Furthermore, it is desirable to have a clearance between the narrowed portion 25 of the graphite block 20 and the ceramic tile 30. If the ceramic tile 30 has a structure in which the narrowed portion 25 of the graphite block 20 is gripped, it does not come off even if there is a clearance, and stress due to thermal strain and reaction strain does not occur between the two structural members.

  In the second embodiment, the ceramic tile 30 is gripped by the fasteners 27 inserted into the holes 26 provided in the graphite block 20. Further, the ceramic tile 30 may be held or locked by the fastener 27 with respect to the graphite block 20.

  As the fastener 27, a screw to be screwed into a graphite block, a pin to be inserted, or the like can be used. It is preferable that at least the surface of any fastener 27 is ceramic. For example, as for the fastener 27, the whole is ceramic, the thing which coat | covered ceramics, such as graphite, etc. are mentioned. Moreover, it is preferable that the fastener 27 is locked so as to have a clearance with the ceramic tile 30. This is because the generation of stress between the ceramic tile 30 and the graphite block 20 can be suppressed.

  As described above, the third embodiment has a structure in which the narrowed portion 25 formed on the side surface of the ceramic tile 30 is locked when the graphite block 20 grips it.

  The ceramic tile 30 is preferably made of a ceramic / ceramic composite material. Since the ceramic / ceramic composite material has strength and has ceramic fibers inside, the ceramic / ceramic composite material can retain its shape even if cracks occur, and can be suitably used as the core structure material 10.

  The ceramic tile 30 is preferably a SiC / SiC composite material.

  The pebble 4 is formed by solidifying particles in which nuclear fuel is coated with pyrolytic carbon, SiC or the like. For this reason, the pebble 4 is hard and has a high ability to wear the graphite block 20. However, since the ceramic tile 30 is formed of the same material as the hardest SiC contained in the pebble 4, it is damaged even if pressure is applied from the pebble 4. Can be difficult. Moreover, since SiC absorbs little neutrons, it has little effect on the fission chain reaction.

  The ceramic tile 30 is preferably a SiC sintered body. SiC has little influence on the fission chain reaction because it absorbs less neutrons. Moreover, since it has intensity | strength and heat-resistant temperature is high, it can utilize suitably as the ceramic tile 30 of the core structure material 10. FIG.

  Furthermore, it is desirable to have one ceramic tile 30 for each graphite block 20.

  When the ceramic tile 30 of the core structure material 10 of the present embodiment is provided one for each graphite block 20, the joint of the ceramic tile 30 can be prevented from coming into contact with the ceramic coating 22. Can prevent the ceramic coating 22 from being damaged.

  Although the core structure material 10 having a substantially quadrangular prism shape including a cylindrical surface has been described, it may be a hexagonal column shape, and is not limited to a shape as long as a strong and stable core 3 is formed.

  In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

  The core structure material according to the present invention can be applied to the use of a nuclear reactor using a pebble.

1: Pebble-bed type reactor 2: Reactor vessel 3: Core 4: Pebble 10: Core structure material 20: Graphite block 20a: Inner wall surface 20b; 26: Hole 27: Fastener 30: Ceramic tile 40: Pebble storage space

Claims (4)

A core structural material for a pebble bed reactor,
A graphite block comprising a base material made of graphite and a ceramic coating for covering the base material;
Bei example a ceramic tile made of SiC / SiC composites to cover the inner wall surface facing the pebble receiving space of the graphite block,
In at least two opposing outer edges in the inner wall surface of the graphite block, a constriction is provided that is a depression formed in the thickness direction of the graphite block from the inner wall surface,
The ceramic tile is a core structure material including a protrusion locked to the at least two narrowed portions . The core structure material according to claim 1,
The ceramic coating is a core structure material made of SiC. Pebble bed reactor comprising a reactor core structural member according to claim 1 or 2. The pebble bed nuclear reactor according to claim 3 ,
The ceramic tile is a pebble bed type reactor in which one piece is provided for each graphite block.

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