JP2007101429A - Method and device for overcoating coated fuel particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an overcoating method and an overcoating device which enable the equation and higher precision of particle diameters, the reduction of costs and the improvement in mass productivity in the manufacture of coated fuel particles that are overcoated. <P>SOLUTION: The device is equipped with a stirring step for stirring coated fuel particles A by rotating a coating container 31 accommodating them in a part of its internal space in a state where they pile up and a coating step for supplying a graphite matrix material for overcoating to the coated fuel particles A in the coating container 31 to form an overcoating layer (b) made of the graphite matrix material on the surface of each particle as synchronous steps. At the coating step, the graphite matrix material is supplied from the inside of the pileup layer of the coated fuel particles. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to techniques suitable for overcoating coated fuel particles, and more particularly to an overcoat method and apparatus for rational production of high quality overcoated coated fuel particles.

  As is well known for high-temperature gas reactors, the core structure (including fuel) is composed of graphite with a large heat capacity and good high-temperature soundness, and an inert gas such as He gas that does not cause a chemical reaction even at high temperatures is used as a cooling gas. Used. By doing so, the inherent safety is increased, and the He gas having a high outlet temperature can be taken out. The high heat of about 900 ° C. obtained from this HTGR enables heat utilization in a wide range of fields including power generation, hydrogen production, chemical plants, and others.

  Regarding the fuel of the HTGR, the following can be said with reference to the following Patent Documents 1 and 2, Non-Patent Document 1, and the like. The coated fuel particles having a diameter of 500 to 1000 μm are obtained by coating four layers on the outer peripheral surface of a fuel nucleus (diameter 350 to 650 μm) made of an oxide of nuclear fuel material. A coating layer of coated fuel particles, the first coating layer made of low-density carbon having both a gas reservoir function for accumulating gaseous fission products FP and a buffer function for absorbing fuel nuclear swelling It is. The second coating layer made of high-density carbon has a holding function for gaseous FP, and the third coating layer made of silicon carbide SiC has a holding function for solid FP. The fourth coating layer made of high-density carbon similar to the second coating layer has a function of retaining the solid FP and also has a protective function for the third coating layer. In addition to these, a fuel compact is obtained by mixing coated fuel particles with graphite powder and sintering to a certain shape, and a fuel rod is obtained by sealing a certain number of fuel compacts in a graphite tube. Eventually, a high-temperature gas reactor fuel is obtained by loading a predetermined number of fuel rods into the insertion ports of the graphite block.

  Generally, the fuel for the HTGR is manufactured as follows. In the initial step of creating fuel nuclei, uranyl nitrate stock solution is dropped into an ammonia solution to form ammonium heavy uranate particles, which are dried, then oxidized, reduced, and sintered. When the fuel nuclei are coated with the first coating layer to the fourth coating layer to produce coated fuel particles, the fuel nuclei are introduced into a high-temperature fluidized bed and a CVD method is performed to form each layer. When making a fuel compact, coated fuel particles are coated with a graphite matrix material to form overcoated fuel particles (sometimes simply referred to as coated fuel particles or overcoat particles), and then the overcoated particles are molded and sintered. To do. In the step of making the fuel rod, the fuel compact may be enclosed in a graphite tube. The fuel in the HTGR is completed by loading the thus obtained fuel rods into the insertion ports of the graphite block.

  In the ready-made fuel used in the HTGR, the coated fuel particles have a diameter of 500 to 1000 μm, and in the case of overcoat particles coated with a graphite matrix material, the diameter is 1000 to 2000 μm. Therefore, a graphite matrix material having a thickness of 100 to 500 μm is interposed on the outer peripheral surface of the coated fuel particles. In order to uniformly disperse the overcoat particles in the fuel compact, it is important to finish the diameter (outer diameter) of the overcoat particles with high accuracy. Otherwise, it is caused by uneven dispersion of the particles. The fuel becomes low quality Further, if the coated fuel particles with high overcoat accuracy can be produced at high speed with high yield, the final fuel product will be highly accurate and inexpensive.

As a particle production means taking such technical matters into consideration, there is a rolling granulation technique in which overcoat particles are produced while making the outer diameter uniform. As is well known, this rolling granulation technique is a method in which the surface of particles is coated with a graphite matrix material while rotating a pan containing a coated fuel particle (a dish-shaped coating container). More specifically, after a predetermined amount of coated fuel particles before overcoating are placed in a coating container, the coated fuel particles are rolled by rotating the container while spraying a graphite matrix material (including a binder) through a nozzle. -Rotate to form an overcoat layer of graphite matrix material on the particle surface. In this case, a single nozzle spot-feeds the graphite matrix material to the coated fuel particles in the coating container. In forming the overcoat layer, the surface of the coated fuel particles is also moistened with a particle wetting liquid such as alcohol to improve the adhesion of the graphite matrix material.
Japanese Patent Laid-Open No. 06-265669 JP 07-218674 A Atomica Encyclopedia ATMICA [Search on the Internet on December 7, 2004] <URL: http://www-atm.jst.go.jp/atomica/03030301_1.html>

The overcoat method described above has the following drawbacks.
(1) The graphite matrix material is simply spot-supplied from the upper space to a large amount of coated fuel particles that spread in the coating container, so that it does not sufficiently cover the coated fuel particles at various locations in the container, and the coating The overcoat layer thickness tends to be non-uniform between the fuel particles. More specifically, the graphite matrix material tends to be present in the upper layer region of the coated fuel particle deposition layer, and does not reach the middle layer region or the lower layer region of the coated fuel particle deposition layer. Therefore, it is not possible to obtain overcoat-coated fuel particles having a uniform particle outer diameter with a high yield.
(2) The coated fuel particles have a higher specific gravity than the graphite matrix material. Therefore, the specific gravity of the coated fuel particles in the overcoat decreases as the adhesion amount of the graphite matrix material increases and the coating film thickness increases. From another point of view, the coated fuel particle deposition layer in the coating container has a classification phenomenon due to the difference in specific gravity, and “high coating thickness (low specific gravity)” is on the upper layer side, and “small coating thickness ( The ratio of “significant)” tends to be the lower side. Under such circumstances, the graphite matrix material adheres concentrated on the coated fuel particles in the upper layer region of the coated fuel particle deposition layer. Therefore, also in this respect, the outer diameter of the overcoat-coated fuel particles tends to be uneven.
(3) Even if the supply amount per unit time of the graphite matrix material is increased in order to solve the above-mentioned problem, it is not necessary to supply the graphite matrix material from the upper space in the coating container with a spot supply nozzle that does not diffuse the material. The uneven distribution or local excess or deficiency of the graphite matrix material in each part is further promoted. Therefore, a measure simply by increasing the supply amount and supply speed of the graphite matrix material cannot eliminate the unevenness and non-uniformity of the overcoat layer.
(4) The particle wetting liquid for wetting the surface of the coated fuel particles cannot be evenly supplied to each coated fuel particle for the same reason as that of the graphite matrix material. It becomes difficult to improve the adhesiveness.
(5) Supply rate and supply rate of graphite matrix material / particle wetting liquid etc. are not suitable for a large amount of coated fuel particles, and the coating growth rate is also slow, so coated fuel particles overcoated with a predetermined thickness Spend a lot of time to get. Since it becomes a bottleneck in mass production, high productivity cannot be expected for the overcoat coated fuel particles.
(6) Since the yield of non-defective products is low and productivity is low, these cost push factors increase the cost of overcoated fuel particles. Since the impact also affects the final fuel product, it is difficult to reduce the cost of HTGR fuel.

  In view of such technical problems, the present invention aims to achieve uniform particle size, high particle size accuracy, high coating speed, low cost, mass productivity, etc. when producing overcoat-coated fuel particles. It is an object of the present invention to provide an overcoat method and an overcoat apparatus that can be applied.

  The overcoat method for coated fuel particles according to claim 1 of the present invention is characterized by the following means for solving the problems in order to achieve the intended purpose. That is, the overcoat method according to claim 1 includes a stirring step for rotating the coating container containing the coated fuel particles in a deposited state in a part of the internal space to stir the coated fuel particles, And a coating step for supplying an overcoat layer of the graphite matrix material on the surface of each particle by supplying the graphite matrix material for coating to the coated fuel particles in the coating container. It supplies from the inside of a covering fuel particle deposition layer, It is characterized by the above-mentioned.

  The overcoat method for coated fuel particles according to claim 2 of the present invention is characterized in that, in the method described in claim 1, the graphite matrix material is supplied from a plurality of locations in the coated fuel particle deposition layer.

  A method for overcoating coated fuel particles according to a third aspect of the present invention is characterized in that, in the method according to the first or second aspect, the graphite matrix material is also supplied from the upper part of the deposited fuel particle deposition layer.

  The overcoat method for coated fuel particles according to claim 4 of the present invention is characterized by the following problem solving means in order to achieve the intended purpose. That is, the overcoat method according to claim 4 includes a stirring step for rotating the coating container containing the coated fuel particles in a deposited state in a part of the internal space to stir the coated fuel particles, and a particle wetting. A wetting step for supplying the liquid to the coated fuel particles in the coating container to wet the surface of each particle with the wetting liquid, and supplying a graphite matrix material for overcoat to the coated fuel particles in the coating container. And a coating step for forming an overcoat layer with a graphite matrix material on the particle surface of the particle as a synchronization step, and supplying the particle wetting liquid from the inside of the coated fuel particle deposition layer in the wetting step and the graphite matrix material in the coating step It supplies from the inside of a covering fuel particle deposition layer, It is characterized by the above-mentioned.

  According to a fifth aspect of the present invention, there is provided an overcoat apparatus for coated fuel particles according to the fourth aspect of the present invention, wherein one or more of a particle wetting liquid and a graphite matrix material are provided in the coated fuel particle deposition layer. It is characterized by supplying from a location.

  A coated fuel particle overcoat apparatus according to claim 6 of the present invention is the method according to claim 4 or 5, wherein at least one of the particle wetting liquid and the graphite matrix material is applied to the coated fuel particle deposition layer. It is also characterized by being supplied from the top.

  The overcoat apparatus for coated fuel particles according to claim 7 of the present invention is characterized by the following problem solving means for achieving the intended purpose. That is, the overcoat apparatus according to claim 7 includes a coating container having a particle deposition space for accommodating the coated fuel particles therein, a driving means for rotating the coating container, and a particle deposition space of the coating container. And a nozzle for injecting a graphite matrix material disposed therein.

  The overcoat apparatus for coated fuel particles according to claim 8 of the present invention is characterized by the following problem solving means in order to achieve the intended purpose. That is, the overcoat apparatus according to claim 8 includes a coating container having a particle deposition space for accommodating the coated fuel particles therein, a driving means for rotating the coating container, and a particle deposition space of the coating container. And a nozzle for injecting the particle wetting liquid disposed therein, and a nozzle for injecting the graphite matrix material disposed in the particle deposition space of the coating container.

The coated fuel particle overcoat method according to the present invention has the following effects.
(1) The graphite matrix material supplied from the inside of the coated fuel particle deposition layer in the coating container coats these while adhering to the coated fuel particles in the middle layer region and the lower layer region of the coated fuel particle deposition layer. As a result, the specific gravity of the coated fuel particles for growing the overcoat film decreases as the film growth increases, and the specific gravity becomes smaller than that of the uncoated or insufficiently coated fuel particles. When the coated fuel particles are stirred and coated in this way, the coated fuel particles are switched up and down due to the difference in specific gravity due to the amount of coating growth. In other words, particles with relatively low specific gravity (particles with a large coating growth amount) move from the middle or lower layer of the coated fuel particle deposition layer to the upper layer region, and particles with relatively high specific gravity (uncoated or coating growth amount). (Particles with a small amount of particles) move from the upper layer region to the middle layer region or the lower layer region of the coated fuel particle deposition layer. Moreover, during the two synchronized steps (stirring step and coating step), such particle behavior occurs constantly, so that each coated fuel particle grows almost uniformly while constantly changing up and down. Thus, each coated fuel particle is almost uniformly overcoated in the coating vessel. As a result, the overcoat layer of each coated fuel particle is finished uniformly and with high accuracy, and overcoat coated fuel particles having a uniform particle outer diameter can be obtained with a high yield.
(2) When the graphite matrix material is supplied from within the coated fuel particle deposition layer, the above-mentioned coated fuel particles are switched up and down, so the overcoated coated fuel particles can be increased even if the supply amount per unit time of the graphite matrix material is increased. The particle size variation is difficult to occur. Therefore, when the supply amount of the graphite matrix material is increased, there is no problem in high-speed material supply for realizing high-speed coating.
(3) Since the coating growth rate can be increased by high-speed internal supply of the graphite matrix material, coated fuel particles having an overcoat layer having a predetermined thickness can be obtained in a short time. Therefore, high productivity can be obtained by mass-producing the overcoat-coated fuel particles by increasing the coating speed.
(4) When the particle wetting liquid is supplied from the inside of the coated fuel particle deposition layer in the coating container, each coated fuel particle is wetted almost uniformly by the particle wetting liquid as described above. This even wetting ensures a more uniform overcoat on the coated fuel particles.
(5) By taking these measures, such as supplying graphite matrix material and particle wetting liquid from multiple locations in the coated fuel particle deposition layer or from the top of the coated fuel particle deposition layer, excellent quality is achieved. High production of overcoat coated fuel particles.
(6) Since the yield of non-defective products is high and the productivity is high, the cost of overcoat coated fuel particles can be reduced based on this.

The coated fuel particle overcoat apparatus according to the present invention has the following effects.
(7) Since it is an improved device mainly composed of nozzles for graphite matrix material injection and particle wetting liquid injection, the burden on facilities and operation is almost the same as existing devices. On the other hand, when the method of the present invention is carried out using the apparatus, the effects described above can be obtained. Thus, it is a useful and useful device as a means for overcoating the coated fuel particles.

  As for the overcoat apparatus according to the present invention, the first embodiment of FIG. 1 will be described first, then the second embodiment of FIG. 2 will be described, and then the third embodiment of FIG. 3 will be described.

  In the overcoat apparatus illustrated in FIG. 1, 11 is a base, 21 is a driving means, 31 is a coating container, 41 is a material supply system, and 51 is a wetting liquid supply system.

  On the base 11 in FIG. 1, drive means 21 is provided via a support stand 12. In this case, the base 11 and the support stand 12 are made of any material having excellent mechanical characteristics among metal, synthetic resin, and composite materials thereof. The drive means 21 includes an electric motor (motor) or an electric motor and a rotation transmission mechanism, and includes an output shaft 22 that receives the rotation of the electric motor. In FIG. 1, the output shaft 22 of the driving means 21 supported by the support stand 12 is inclined at an inclination angle of 20 to 50 °, more specifically at an inclination angle of about 35 °.

  The coating container 31 illustrated in FIG. 1 has a dish shape called a pan. This is formed by the bottom wall 32 and the peripheral wall 33, and the upper surface is open. The coating container 31 is also provided with a shaft 34 protruding from the center of the outer surface of the bottom wall 32. The coating container 31 is also made of any material having excellent mechanical properties among metals, synthetic resins, and composite materials thereof. As a typical example, each part of the coating container 31 is made of metal. In the coating container 31 of FIG. 1, a shaft 34 on the bottom wall 32 is connected to the output shaft 22 by a known coupling 23. Therefore, the coating container 31 is inclined as shown. In the coating container 31 in this inclined posture, the lower side in the container becomes the particle deposition space 35.

  The material supply system 41 illustrated in FIG. 1 is mainly composed of a supply pipe 42 having a nozzle 43 at the tip and members and equipment related thereto. In this case, the supply pipe 42 and the nozzle 43 are also made of any material having excellent mechanical characteristics among metal, synthetic resin, and composite materials thereof. A part of the supply pipe 42 may be flexible. In FIG. 1, the nozzle 43 is attached to the tip of the supply pipe 42. The nozzle 43 employed in this case includes a single-hole type having only one injection hole and a multi-hole type (including a shower-type porous type) having two or more injection holes. May be. Incidentally, in the embodiment of FIG. 1, a single-hole type nozzle 43 is employed. The nozzle 43 attached to the tip of the supply pipe 42 can be taken in and out of the coating container 31 by an operation mechanism (not shown) or an operation of a worker. As an example when the nozzle 43 is set at a predetermined position in the coating container 31 through an operation mechanism or the like, the nozzle 43 is disposed in the coating container 31, more specifically in the middle layer region or the lower layer in the particle deposition space 35. Placed in the area. On the other hand, the base end portion of the supply pipe 42 is connected to a material supply machine 44 having a material supply function.

  The wetting liquid supply system 51 illustrated in FIG. 1 is also configured mainly with a supply pipe 52 having a nozzle 53 at the tip and members and equipment related thereto. In this wetting liquid supply system 51, the constituent material of the supply pipe 52 and the nozzle 53 is made of the above-mentioned arbitrary material, the part of the supply pipe 52 is flexible, and the nozzle 53 is a single hole type. Or the point which consists of a double hole type | mold etc. is not substantially different from the case of the material supply system 41. FIG. Incidentally, in the embodiment of FIG. 1, a shower type porous type (multi-hole type) is adopted as the nozzle 53. The nozzle 53 attached to the tip of the supply pipe 52 can also be taken in and out of the coating container 31 by an operation mechanism (not shown) or an operator's operation. As a specific example when the nozzle 53 is set at a predetermined position in the coating container 31 via an operation mechanism or the like, the nozzle 53 is disposed above the particle deposition space 35 in the coating container 31. On the other hand, the base end portion of the supply pipe 52 is connected to a wetting liquid supply machine 54 having a liquid supply function.

  In the overcoat apparatus of FIG. 1, the wetting liquid supply system 51 may be omitted.

  The example illustrated in FIG. 2 is obtained by adding a part of the material supply system 41 and a part of the wetting liquid supply system 51 in the overcoat apparatus of FIG. More specifically, in the case of the material supply system 41, two systems of the supply pipe 42 a with the nozzle 43 a and the supply pipe 42 b with the nozzle 43 b are connected to the material supply machine 44, and in the case of the wetting liquid supply system 51, the nozzle The two systems of the supply pipe 52 a with 53 a and the supply pipe 52 b with the nozzle 53 b are connected to the material supply machine 54. In the material supply system 41 in the illustrated example, the nozzle 43 a of the supply pipe 42 a is disposed in the middle layer region or the lower layer region in the particle deposition space 35, and the nozzle 43 b of the supply pipe 42 b is disposed above the particle deposition space 35. Has been. Further, in the case of the wetting liquid supply system 51, the nozzle 53 a of the supply pipe 52 a is disposed above the particle deposition space 35 and the nozzle 53 b of the supply pipe 52 b is disposed in the middle layer region or lower layer region in the particle deposition space 35. ing. 2 are substantially the same as or similar to those of the previous example.

  In the overcoat apparatus of FIG. 2, the material supply system 41 may have three or more supply pipes with nozzles, or the wetting liquid supply system 51 may have three or more supply pipes with nozzles. is there. In such a case, the nozzle of at least one supply pipe in the material supply system 41 is disposed in the middle layer region or the lower layer region in the particle deposition space 35. For other supply pipes in the material supply system 41 and the wetting liquid supply system 51, some or all of the nozzles may be disposed in the particle deposition space 35, or some or all of the nozzles may be arranged. It may be disposed above the particle deposition space 35. In FIG. 2, only the supply pipe 42b with the nozzle 43b is omitted, only the supply pipe 52a with the nozzle 53a is omitted, only the supply pipe 52b with the nozzle 53b is omitted, and the supply pipe 42b with the nozzle 43b is omitted. And the supply pipe 52a with the nozzle 53a may be omitted, or the supply pipe 52a with the nozzle 53a and the supply pipe 52b with the nozzle 53b may be omitted. The supply pipes 42a and 42b made of independent pipes in FIG. 2 may be changed to branch type pipes in which these base end portions are combined into one. The same applies to the supply pipes 52a and 52b made of the other independent pipe.

  The overcoat apparatus illustrated in FIG. 3 is different from that of FIG. One of the differences is that each supply pipe 42a, 42b, 52a, 52b has a branch pipe structure at the tip side, and nozzles 43a, 43b, 53a, 53b are attached to the tips of the respective branch pipe parts. That is. Another difference is that each nozzle 43a of the material supply pipe 42a disposed in the middle layer region or the lower layer region in the particle deposition space 35 and the middle layer region or the lower layer region in the particle deposition space 35 are disposed. That is, the nozzles 53a of the wetting liquid supply pipe 52a have different depths (positions in the vertical direction) in stages such as a middle stage, a slightly lower stage, and a considerably lower stage. 3 are substantially the same as or similar to those of the previous example.

  In the case of the overcoat apparatus illustrated in FIG. 3, one or more of the supply pipes 42b, 52a, and 52b may be omitted, the nozzles 43a of the material supply pipe 42a, and the wetting liquid supply pipe 52a. The nozzles 53a may be set to the same depth. Also, one of the same-system supply pipes 42a and 42b, the other same-system supply pipes 52a and 52b, and the like may be changed to a branched pipe that is integrated into one on the base end side. In addition, some or all of the supply pipes 42a, 42b, 52a, and 52b are independent, and a nozzle may be attached to the tip of the independent supply pipe.

  Examples of embodiments not shown include the following specific examples. That is, the independent material supply pipe (42, 42a, 42b) described in FIGS. 1 and 2 is S1, and the independent wet liquid supply pipe (52, 52a, 52b) described in FIGS. ) Is T1, the branch type material supply pipe (42a, 42b) described in FIG. 3 is S2, and the branch type wet liquid supply pipe (52a, 52b) described in FIG. 3 is T2. , Two or more kinds of material supply pipes selected from S1 to S2 are used in combination, or one or more kinds of material supply pipes selected from S1 to S2 and T1 to T2 are selected. One or more types of wetting liquid supply pipes may be used in combination. In these embodiments, at least one material supply pipe is disposed in the particle deposition space 35 inside the coating container 31.

  The coated fuel particle A illustrated in FIG. 4 is used in the present invention. As is apparent with reference to FIG. 4, the coated fuel particle A has a fuel core a in the core portion, and the first coating layer a1, the second coating layer a2, the third coating layer a3, and the fourth coating are provided on the outer peripheral surface thereof. It has the layer a4. The coated fuel particles A as shown in FIG. 4 are produced by carrying out the following processes.

  In the formation of the fuel core a, first, uranium oxide powder is dissolved in nitric acid to form a uranyl nitrate stock solution, and then pure water and a thickener are added to the uranyl nitrate stock solution and stirred to form a dripping stock solution. The thickener in this case is added so that the uranyl nitrate stock solution dropped and dropped becomes a true sphere by its surface tension. Examples of the thickener include polyvinyl alcohol resin, resin capable of coagulating under alkaline conditions, polyethylene glycol, and metroses. The dripping stock solution prepared as described above is dropped into ammonia water from here after the viscosity is adjusted by cooling at a predetermined temperature while vibrating a small-diameter dropping nozzle. The droplets at this time are gelled by spraying ammonia gas between the lower end of the nozzle and landing on the aqueous ammonia solution, so that deformation during landing is prevented. In such a case, uranyl nitrate becomes particles of ammonium deuterated uranate in an aqueous ammonia solution. The ammonium deuterated uranate particles are roasted in the atmosphere to form uranium trioxide particles, which are further reduced and sintered to obtain fuel nuclei a composed of high-density ceramic uranium dioxide. As an example, the diameter of the fuel core a is 350 to 650 μm.

  The first coating layer a1, the second coating layer a2, and the fourth coating layer a4 each deposit a thermal decomposition reaction product (fine CVD reaction product) of a hydrocarbon-based vapor phase raw material to a predetermined thickness. Can be formed. In the case of the 3rd coating layer a3, hydrogen or argon is made into carrier gas, a silane compound is supplied to a CVD reaction area | region, and it forms by depositing the thermal decomposition reaction product of the silane compound to predetermined thickness. About this kind of coating layer, although each layer may be formed one by one, each layer is usually formed continuously. A typical example of the apparatus used at that time is a heated fluidized bed having an electric furnace structure. Of course, the source gas is the hydrocarbon system described above, and the carrier gas is an inert gas such as argon. In addition, when each coating layer is continuously formed in the same fluidized bed, the inside of the fluidized bed may be purged with a purge gas every time one coating layer is formed.

The first coating layer a1 made of low-density carbon is first formed on the outer peripheral surface of the fuel core a introduced into the fluidized bed. The raw material gas at this time is made of acetylene (C ₂ H ₂ ) as an example, and carbon fine particles obtained by thermally decomposing this at a temperature of 1400 ° C. are deposited on the outer peripheral surface of the fuel core a to form a first coating layer having a predetermined thickness. a1 is formed. Next, a second coating layer a2 made of high-density carbon is formed. The raw material gas at this time is made of propylene (C ₃ H ₆ ) as an example, and carbon fine particles obtained by pyrolyzing this at a temperature of 1400 ° C. are deposited on the outer peripheral surface of the first coating layer a 1 to form a second film having a predetermined thickness. A coating layer a2 is formed. Next, a third coating layer a3 made of silicon carbide (SiC) is formed. The raw material gas at this time is made of, for example, methyltrichlorosilane (CH ₃ SiCl ₃ ), and silicon carbide fine particles obtained by thermally decomposing it at a temperature of 1600 ° C. are deposited on the outer peripheral surface of the second coating layer a 2 to have a predetermined thickness. The third coating layer a3 is formed. After this, a fourth coating layer a4 made of high-density carbon is formed. In the case of the 4th coating layer a4, it forms in predetermined thickness in the same way as the 2nd coating layer a2.

The specifications of each coating layer of the coated fuel particles A thus obtained are as follows. The first coating layer a1 made of low-density carbon (low-density pyrolytic carbon) has a thickness of 30 to 150 μm and a density of 0.8 to 1.2 g / cm ^{3. In} one example, the thickness is 60 μm and the density is 1.0 / cm ^3. belongs to. The first coating layer a1 has a gas storage function for storing gaseous fission products (FP) and a buffer function for absorbing fuel nuclear swelling. The second coating layer a2 made of high density carbon (high density pyrolytic carbon) thickness 20 to 50 m, a density 1.6~2.0g / cm ^3, a thickness of 30μm in one example, density 1.8 g / cm ³ It is. The second coating layer a2 has a function of holding the gaseous FP. The third coating layer a3 thickness 20~50μm consisting silicon carbide (SiC), a density 3.0-3.2 / cm ^3, a thickness of 25μm in one example, the density 3.2 / cm ^3. The third coating layer a3 is a main strength assurance layer and also has a holding function for the solid FP. The fourth coating layer a4 made of high-density carbon (high-density pyrolytic carbon) similar to the second coating layer a2 has a thickness of 20 to 80 μm and a density of 1.6 to 2.0 g / cm ^3. It is 45 μm and the density is about 1.8 g / cm ³ . The fourth coating layer a4 has a function of holding the solid FP and also has a protection function for the third coating layer a3. The coated fuel particles A in which the first coating layer a1 to the fourth coating layer a4 are formed on the outer peripheral surface of the fuel core a have a diameter (outer diameter) of 500 to 1500 μm, and in one example, a diameter of 1000 μm.

  The overcoat-coated fuel particles B shown in FIG. 5 are those produced by an embodiment of the method of the present invention described later, that is, on the outer peripheral surface of the coated fuel particles A (the outer peripheral surface of the fourth coating layer a4). An overcoat layer b is formed. The overcoat layer b is made of a graphite matrix material. As a specific example, the graphite matrix material is obtained by uniformly kneading a graphite powder with a binder. The thickness of the overcoat layer b is in the range of 20 to 400 μm, and in a typical example, the thickness is 50 μm. Since the overcoat coated fuel particles B are such, their diameter (outer diameter) is in the range of 540 to 2300 μm. As a specific example, the overcoat-coated fuel particle B has a diameter of 1300 μm. When the overcoat layer b is formed, the outer peripheral surface of the coated fuel particles A is wetted with the wetting liquid in order to improve the adhesion of the graphite matrix material. As the wetting liquid, in addition to alcohol, known or well-known ones are used. Typical examples are alcohol alone or alcohol as a main component.

  Next, an embodiment of the overcoat method for coated fuel particles according to the present invention will be described with reference to the accompanying drawings.

  When the overcoat layer b is formed on the outer peripheral surface of the coated fuel particle A using the overcoat apparatus illustrated in FIG. 1, a predetermined amount of particles is placed in the particle deposition space 35 of the coating container 31 via a particle carrying means (not shown). After the coated fuel particles A are charged and the coating container 31 is rotated by the driving means 21, the wetting liquid is injected into the coated fuel particles A in the coating container 31 through the wetting liquid supply system 51 and at the same time a material supply system. The fuel is injected into the graphite matrix-coated fuel particles A through 41. That is, the wet liquid is sprayed onto the coated fuel particles A through the path of the wetting liquid supply unit 54 → the supply pipe 52 → the nozzle 53, and at the same time, the graphite matrix material is coated with the fuel particles through the path of the material supply unit 44 → the supply pipe 42 → the nozzle 43. Inject to A.

  During the above operation, the coated fuel particles A in the particle accumulation space 35 of the coating container 31 rise in the rotation direction of the container, and collapse to the predetermined height by the action of gravity. This rise and fall occur repeatedly during the rotation of the coating container 31, and this becomes the stirring action of the coated fuel particles A. In synchronization with this stirring, the surface of the coated fuel particles A in the particle deposition space 35 is wetted by the wetting liquid from the wetting liquid supply system 51, or the graphite matrix material is injected through the material supply system 41. The coated fuel particles A that receive the injection of the graphite matrix material from the inside of the particle deposition layer while being stirred in this way are uniformly attached to the wet surface of the coated fuel particles A, and are uniformly deposited and grown to a predetermined thickness. It becomes the overcoat layer b. That is, each coated fuel particle A that grows a coating for an overcoat by adhering a graphite matrix material in the middle layer region or the lower layer region of the coated fuel particle deposition layer has an upper and lower position between the particles depending on the amount of coating growth. Each film is made to grow substantially uniformly by repeating the replacement and moving uniformly toward and away from the injection point of the graphite matrix material. Therefore, each coated fuel particle A is overcoated almost uniformly in the coating container 31. As a result, the overcoat layer b of each coated fuel particle is finished uniformly and with high accuracy, and as the overcoat coated fuel particle B described with reference to FIG. 5, particles having a uniform particle outer diameter can be obtained with a high yield. Become.

  The same applies to the case where the overcoat layer b is formed on the outer peripheral surface of the coated fuel particle A using the overcoat apparatus illustrated in FIG. That is, after a predetermined amount of the coated fuel particles A is introduced into the particle accumulation space 35 of the coating container 31 or the coating container 31 is rotated by the same means as described above, the wetting liquid is supplied via the wetting liquid supply system 51. Is injected into the coated fuel particles A in the coating container 31 and simultaneously, the graphite matrix material is injected into the coated fuel particles A in the coating container 31 through the material supply system 41. In the case of FIG. 2, the wetting liquid supply system 51 has a two-system configuration of the wetting liquid supply machine 54 → the supply pipe 52a → the nozzle 53a and the wetting liquid supply machine 54 → the supply pipe 52b → the nozzle 53b. There are two systems: material supply machine 44 → supply pipe 42a → nozzle 43a and material supply machine 44 → supply pipe 42b → nozzle 43b. In addition to this, since the two nozzles 43a and 53a are inside the coated fuel particle deposition layer and the other two nozzles 43b and 53b are above the coated fuel particle deposition layer, the multipoint nozzle injection is performed equally. The film forming ability is further improved. Therefore, in the case of FIG. 2, the above-described overcoat-coated fuel particles B having a uniform particle outer diameter can be obtained at a higher speed and a higher yield.

  The same applies to the case where the overcoat layer b is formed on the outer peripheral surface of the coated fuel particle A using the overcoat apparatus illustrated in FIG. That is, after a predetermined amount of the coated fuel particles A is introduced into the particle accumulation space 35 of the coating container 31 or the coating container 31 is rotated by the same means as described above, the wetting liquid is supplied via the wetting liquid supply system 51. Is injected into the coated fuel particles A in the coating container 31 and simultaneously, the graphite matrix material is injected into the coated fuel particles A in the coating container 31 through the material supply system 41. In the case of FIG. 3, the material supply system 41 and the wetting liquid supply system 51 have a multi-branch type two-system configuration, and a large number of nozzles 43a, 43b, 53a, and 53b are provided inside the coated fuel particle deposition layer and the layers. Since it is scattered on the upper side, the above-mentioned uniform film forming ability is remarkably improved. Therefore, in the case of FIG. 3, as the overcoat-coated fuel particles B described above, particles having a uniform particle outer diameter can be obtained at a higher speed and a higher yield than the previous example.

  The overcoat-coated fuel particles B obtained by the overcoat method as described above are press-molded or molded into a hollow cylindrical shape, and the compact is sintered to form a fuel compact (not shown). Further, a fuel rod (not shown) is formed by putting a certain amount of fuel compact in a graphite tube and sealing the top and bottom with end plugs. As a final product, a fuel (not shown) for the high temperature gas furnace is obtained by loading a predetermined number of fuel rods into the insertion ports of the hexagonal columnar graphite block.

  Speaking of other HTGR fuels, spherical fuel (pebble bed type fuel) is also mainly composed of overcoat coated fuel particles similar to the above, and multiple coating layers are formed on the outer peripheral surface of the spherical fuel core. Has been. The overcoat method and overcoat apparatus according to the present invention can also be applied to overcoat means for producing such a spherical fuel.

  The overcoat method and overcoat apparatus according to the present invention achieve uniform particle size, high particle size accuracy, high coating speed, low cost, mass productivity, etc. when producing overcoat-coated fuel particles. In addition, it can be achieved by an improvement centered on the arrangement of the nozzles, so that the industrial applicability is high.

1 is a cutaway front view schematically showing a first embodiment of an overcoat method and an overcoat apparatus according to the present invention. FIG. 6 is a cutaway front view schematically showing a second embodiment of the overcoat method and overcoat apparatus according to the present invention. FIG. 6 is a cutaway front view schematically showing a third embodiment of the overcoat method and overcoat apparatus according to the present invention. It is the notch front view which showed an example of the covering fuel particle | grains used in this invention. 1 is a cutaway front view showing an example of overcoat-coated fuel particles produced by an overcoat method according to the present invention.

Explanation of symbols

A Coated fuel particle B Overcoat coated fuel particle b Overcoat layer 21 Driving means 22 Output shaft 31 Coating vessel 34 Rotating shaft 35 Particle deposition space 41 Material supply system 42 Supply pipe 42a Supply pipe 42b Supply pipe 43 Nozzle 43a Nozzle 43b Nozzle 44 Wetting liquid supply machine 51 Particle supply system 52 Supply pipe 52a Supply pipe 52b Supply pipe 53 Nozzle 53a Nozzle 53b Nozzle 54 Wetting liquid supply machine

Claims (8)

  An agitation step for agitating the coated fuel particles by rotating the coating container containing the coated fuel particles deposited in a part of the internal space, and a graphite matrix material for overcoating on the coated fuel particles in the coating container And a coating step for forming an overcoat layer of graphite matrix material on each particle surface as a synchronization step, wherein the graphite matrix material is supplied from the inside of the coated fuel particle deposition layer in the coating step. A method for overcoating coated fuel particles.   The method for overcoating coated fuel particles according to claim 1, wherein the graphite matrix material is supplied from a plurality of locations in the coated fuel particle deposition layer.   The method for overcoating coated fuel particles according to claim 1 or 2, wherein the graphite matrix material is also supplied from above the deposited fuel particle deposition layer.   An agitation step for agitating the coated fuel particles by rotating the coating container containing the coated fuel particles deposited in a part of the internal space, and supplying a particle wetting liquid to the coated fuel particles in the coating container, respectively. A wetting step for wetting the particle surface with the wetting liquid, and supplying an overcoat graphite matrix material to the coated fuel particles in the coating container to form an overcoat layer of the graphite matrix material on each particle surface And a coating step for supplying a particle wetting liquid from the inside of the coated fuel particle deposition layer in the wetting step, and supplying a graphite matrix material from the inside of the coating fuel particle deposition layer in the coating step. A method for overcoating coated fuel particles.   The method for overcoating coated fuel particles according to claim 4, wherein one or more of the particle wetting liquid and the graphite matrix material are supplied from a plurality of locations in the coated fuel particle deposition layer.   6. The method of overcoating coated fuel particles according to claim 4, wherein at least one of the particle wetting liquid and the graphite matrix material is supplied also from the upper part of the coated fuel particle deposition layer.   A coating container having a particle deposition space for containing coated fuel particles therein, a driving means for rotating the coating container, and a nozzle for injecting a graphite matrix material disposed in the particle deposition space of the coating container An overcoat apparatus for coated fuel particles, comprising:   A coating container having therein a particle deposition space for containing the coated fuel particles, a driving means for rotating the coating container, a nozzle for injecting a particle wetting liquid disposed in the particle deposition space of the coating container, An overcoat apparatus for coated fuel particles, comprising: a nozzle for injecting a graphite matrix material disposed in a particle deposition space of a coating container.

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