JP2010112822A - Method of manufacturing fuel compact for high-temperature gas-cooled reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a good-quality fuel compact wherein coated fuel particles are uniformly distributed without necessity of overcoating work requiring experienced skills and troublesome work of checking the thickness of an overcoating layer. <P>SOLUTION: A graphite matrix is temporarily molded in a specified shape at a low pressure in advance, and the coated fuel particles 12 are injected into a graphite matrix temporary molding 10 through an injection nozzle 22 via a particle supply pipe 20 to uniformly distribute the coated fuel particles 12 in the graphite matrix temporary molding 10, and thereby a mixture is formed. Then, the mixture is molded by a press to make the fuel compact. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a fuel compact for a HTGR, and more particularly, to a method for producing a fuel compact that can be produced while easily performing uniform distribution of coated fuel particles in a graphite matrix.

  The HTGR consists of graphite that has a large heat capacity and maintains soundness at high temperatures, and uses helium gas that does not cause chemical reactions at high temperatures as a cooling gas. Therefore, inherent safety is high, and helium gas having a high outlet temperature of about 900 ° C. can be recovered, and this high-temperature heat can be used in a wide range of fields such as power generation, hydrogen production, and chemical plants.

The fuel of this HTGR is formed by coating four layers around a fuel core having a diameter of about 350 to 650 microns obtained by sintering uranium dioxide into a ceramic form. The first layer is a low density pyrolytic carbon coating with a density of about 1 g / cm ³ , which absorbs the function of the gaseous fission product (FP) as a reservoir and fuel nuclei swelling. It also has a function as a buffer. The second layer is a coating of high density pyrolytic carbon having a density of about 1.8 g / cm ³ , which has a retention function for gaseous FP. The third layer is a coating of silicon carbide (SiC) having a density of about 3.2 g / cm ³ , which has a function of holding solid FP and a function as a main reinforcing member of the coated fuel particles. . Finally, the fourth layer, like the second layer, is a high-density pyrolytic carbon coating with a density of about 1.8 g / cm ³ , which is a gaseous FP retention function and third layer protection. It functions as a layer.

  Typical coated fuel particles have a diameter of about 500 to 1000 microns. The coated fuel particles are dispersed in a graphite matrix, and then molded into a fixed fuel compact shape. A fixed amount of the fuel compact is placed in a graphite tube, and the top and bottom are closed with plugs to form fuel rods. . This fuel rod is inserted into a plurality of insertion ports of the hexagonal column type graphite block and becomes fuel for the high temperature gas furnace. A large number of hexagonal columnar graphite blocks are stacked in multiple stages on a honeycomb array to constitute a core.

  Generally, the fuel for the HTGR is manufactured as follows. First, uranium oxide powder is dissolved in nitric acid to form a uranyl nitrate stock solution, and pure water and a thickener are added to the uranyl nitrate stock solution and stirred to prepare a dropping stock solution. The thickener acts so that the dropped uranyl nitrate stock solution drops into a spherical shape with its own surface tension during dropping. As such a thickener, a resin having a property of solidifying under an alkaline condition, for example, a polyvinyl alcohol resin, polyethylene glycol, or metroise can be used. The dripping stock solution prepared in this manner is cooled to a predetermined temperature and the viscosity is adjusted, and then dripped into ammonia water using a method of vibrating a small-diameter dripping nozzle.

  The droplet liquid is prevented from being deformed at the time of landing by spraying ammonia gas in a space until it reaches the surface of the aqueous ammonia solution to gel the surface. Uranyl nitrate is sufficiently reacted with ammonia in ammonia water to form particles of ammonium biuranate. These particles are roasted in the atmosphere to become uranium trioxide particles, and further reduced and sintered to become fuel nuclei of high-density ceramic uranium dioxide.

The fuel nuclei are loaded on the fluidized bed, and the reaction gas (coating gas) supplied into the fluidized bed is thermally decomposed to coat the fuel nuclei. The first layer of low density pyrolytic carbon is coated by pyrolyzing acetylene (C ₂ H ₂ ) at about 1400 ° C. The high density pyrolytic carbon of the second and fourth layers is coated by pyrolyzing propylene (C ₃ H ₆ ) at about 1400 ° C. The third layer of SiC is coated by pyrolyzing methyltrichlorosilane (CH ₃ SiCl ₃ ) at about 1600 ° C. In this way, four layers of coating are applied to obtain coated fuel particles.

  Since the particle size and sphericity of the coated fuel particles greatly affect the production conditions of the overcoat particles, the coated fuel particles are released to the overcoat process after selecting the particle size and sphericity using a sieve. Is done.

  These coated fuel particles are coated with graphite matrix consisting of graphite powder, binder, etc. on the surface to form overcoat particles, and these overcoat particles are hot-pressed into a hollow cylindrical shape or a cylindrical shape. It becomes a fuel compact. This fuel compact is pre-fired to remove the binder contained in the graphite matrix, and further fired to degas from the graphite matrix.

  In order to produce a high-temperature gas reactor fuel compact with good quality, in the production process, graphite matrix (graphite powder) that forms the fuel compact is mixed with the coated fuel particles at a predetermined ratio, and then molded. In addition, when considering the combustion characteristics in the high-temperature gas reactor of the fuel compact, it is also necessary that the coated fuel particles contained in the fuel compact be uniformly dispersed in order to prevent local combustion .

  In the prior art, in order to uniformly coat and mix the coated fuel particles in the graphite matrix, an overcoat process is employed in the high-temperature gas reactor fuel compact manufacturing. This step is a step of coating the outer surface of the coated fuel particles with a graphite matrix powder containing a phenol resin or the like uniformly inside.

  However, in the overcoat process currently performed, in order to obtain overcoat particles having an overcoat layer having a uniform thickness, a highly skilled worker is required and a predetermined level of overcoat thickness is required. There is a drawback that the work for confirming that it is obtained is troublesome and requires a great deal of cost.

  The problem to be solved by the present invention is a fuel capable of obtaining a high-quality fuel compact while uniformly distributing the coated fuel particles without requiring skilled work and without requiring troublesome confirmation work. The object is to provide a compact manufacturing method.

    The problem-solving means of the present invention is a method for producing a fuel compact by press molding a mixture obtained by dispersing coated fuel particles in a graphite matrix, and preliminarily molding the graphite matrix into a predetermined shape at a low pressure, A high temperature gas furnace characterized in that a coated fuel particle is injected into a graphite matrix preform so that the coated fuel particles are uniformly distributed in the graphite matrix preform and a mixture is formed, and then the mixture is press-molded. Another object of the present invention is to provide a method for manufacturing a fuel compact for a vehicle.

  In the problem-solving means of the present invention, the coated fuel particles are driven into the graphite matrix preform from at least one ejection nozzle provided at the tip of the particle supply pipe. It is preferable to displace so as to move sequentially along the surface of the temporary molded body.

  In the problem-solving means of the present invention, it is preferable to apply the supply pressure when the coated fuel particles are injected.

  In the fuel compact according to the present invention, the mixture of the coated fuel particles and the graphite matrix is obtained by implanting the coated fuel particles into the preformed graphite matrix molding so as to be uniformly distributed. Therefore, high-quality fuel compacts can be easily and economically distributed evenly, without requiring the high level of skill required for overcoat operations and the need for complicated confirmation work. Can get to.

  An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a method for producing a fuel compact according to the present invention in the order of steps. A graphite matrix temporary molded body in which the particles are uniformly dispersed is formed, and then the graphite matrix temporary molded body in which the coated fuel particles are dispersed is formed in step 3 to form a fuel compact molded body, This compact fuel compact is pre-fired in steps 4 and 5, respectively, and fired to complete the fuel compact.

  In step 1, a graphite matrix temporary molded body 10 having a predetermined shape is formed from the graphite matrix. In this temporary molding step, the slurry-like graphite matrix is temporarily formed at a low pressure so that the coated fuel particles are easily driven in the next step 2. Mold. In the form of FIG. 2, the hollow cylinder is divided into two parts according to the shape of the desired fuel compact. Of course, the shape of the temporary molded body 10 does not need to be matched to the shape of the final fuel compact, and has a shape other than a hollow cylindrical shape, for example, a plate shape or the like, which can be easily driven later. can do.

  The coated fuel particles 12 are driven uniformly over the entire surface of the graphite matrix temporary shaped body 10 having a predetermined shape. This driving operation can be performed by a carrier such as compressed gas or compressed liquid. Any gas or liquid as a carrier can be used as long as it does not affect the quality of the fuel compact.

  In the form of FIG. 2, the coated fuel particles 12 are supplied by being pumped through the particle supply pipe 20 extending through the center of the hollow cylindrical graphite matrix preform 10, provided at the tip of the particle supply pipe 20, and horizontally radiating. Are ejected from the four ejection nozzles 22 spreading toward the surface of the temporary shaping body 10 and driven into the temporary shaping body 10. In addition, although the number of the ejection nozzles 22 may be one, in order to make driving efficiency high, a plurality are more preferable.

  The particle supply pipe 20 and the plurality of ejection nozzles 22 at the tip thereof are rotated at a predetermined speed around the central axis of the hollow cylindrical graphite matrix preform 10, that is, around the central axis of the supply pipe 20 at a predetermined speed. Thus, the coated fuel particles 12 are uniformly driven into the temporary molded body 10 by vertically moving from the lowermost end to the uppermost end. Accordingly, the coated fuel particles 12 can enter the temporary shaped body 10 with a uniform distribution, whereby a mixture in which the coated fuel particles 12 are uniformly dispersed in the graphite matrix can be obtained.

  When the pressure of the coated fuel particles 12 injected from the injection nozzle 22 is constant, the driving depth is constant. Therefore, when the coated fuel particles 12 are driven deep into the temporary molded body 10, the pressure is increased. When driving into a shallow position, it is necessary to reduce the pressure. Therefore, the driving pressure is changed sinusoidally with time in accordance with the movement of the injection nozzle 22 in the depth direction of the temporary molded body 10. Make sure you are evenly driven.

  In the fuel compact, specifications such as the amount of uranium per one and the covering fuel particle filling rate are determined, and the covering fuel particles are injected into the graphite matrix in an amount that satisfies this specification.

  In this way, the graphite matrix molded body (mixture) 10 in which the coated fuel particles 12 are implanted and uniformly dispersed is weighed in predetermined amounts, loaded into a mold having a predetermined shape, pressed, and pressed into a fuel compact. A molded body is formed (see step 3).

  The preliminary firing in step 4 is performed to remove the binder and the like contained in the graphite matrix, and the final firing in step 5 is performed to degas the graphite matrix.

  According to the present invention, since the mixture of the coated fuel particles and the graphite matrix is obtained by implanting the coated fuel particles so as to be uniformly distributed in the graphite matrix preform, a process of overcoating the coated fuel particles with the graphite matrix is required. Therefore, it is possible to easily and economically obtain a high-quality fuel compact while uniformly distributing the coated fuel particles, without requiring a high degree of skill required for overcoat operations and troublesome confirmation work. And industrial use is improved.

It is process drawing of the manufacturing method of the fuel compact of this invention. It is a perspective view which shows an example of the implantation process of the covering fuel particle | grains which is the principal part of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Graphite matrix temporary molding 12 Coated fuel particle 20 Supply pipe 22 Injection nozzle

Claims (4)

In a method for producing a fuel compact by press molding a mixture obtained by dispersing coated fuel particles in a graphite matrix, the graphite matrix is previously molded into a predetermined shape at a low pressure, and the coating is formed in the graphite matrix molded body. A method for producing a fuel compact for a high temperature gas reactor, comprising forming the mixture by implanting the coated fuel particles into the graphite matrix molded body so that the fuel particles are uniformly distributed, and then pressing the mixture. . The method for producing a fuel compact for a HTGR according to claim 1, wherein the coated fuel particles are driven into the graphite matrix preform from at least one ejection nozzle provided at a tip of a particle supply pipe. A method of manufacturing a fuel compact for a HTGR characterized by the above. 3. The method for manufacturing a fuel compact for a high temperature gas reactor according to claim 2, wherein the particle supply pipe is displaced so that a pre-injection nozzle sequentially moves along the surface of the graphite matrix preform. The manufacturing method of the fuel compact for HTGR. A method for producing a fuel compact for a HTGR according to any one of claims 1 to 3, wherein a supply pressure is applied when the coated fuel particles are injected. Production method.

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