JP2007147451A - Device and method for overcoating coated fuel particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a uniformly thick overcoating layer on a coated fuel particle without being affected by work environment such as temperature and humidity. <P>SOLUTION: The coated fuel particles 1 are filled into a closed-type pan 20C with an exhaust vent 20H for vaporizing ingredients. By spraying a graphite matrix 2 from a graphite matrix supply nozzle 40 on a fluidized domain of the coated fuel particles 1 together with a solvent while imparting fluidity to the coated fuel particles 1 through the rotation of the closed-type pan 20C, the coated fuel particles 1 are overcoated with the graphite matrix 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an overcoat apparatus and method for coated fuel particles for producing overcoat particles used to produce a molded fuel such as a fuel compact for a HTGR, and more particularly, to uniformly coat a graphite matrix on the coated fuel particles. The present invention relates to an overcoat apparatus and method for coated fuel particles that can be overcoated.

  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 in the 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 the solid FP and a function as a main reinforcing member of the coating. 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 solution of the uranyl nitrate stock solution dropped 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 dropped into ammonia water using a method of vibrating a small-diameter dropping 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.

  Since the particle size and sphericity of the fuel nucleus greatly influence the production conditions of the coated fuel particle, the fuel nucleus is released to the coating step after performing particle size selection and sphericity selection by a sieve.

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 screening the particle size and sphericity using a sieve. The

  The overcoat particles are released into the compact press process after overcoating the surface with a graphite matrix composed of graphite powder and a binder to form overcoat particles.

  The fuel compact for HTGR uses overcoat particles in a hollow cylindrical or cylindrical mold together with a graphite matrix and warm-presses to form a green compact (compact compact). Pre-baking for the purpose of removing the binder, and finally baking for the purpose of graphitizing the matrix.

  In the manufacturing process of this fuel compact, in order to obtain a fuel compact with good quality, it is required to mix the coated fuel particles and the graphite matrix at a predetermined ratio, and the combustion characteristics of the fuel compact in the reactor are improved. In consideration, in order to avoid local combustion, it is required that the coated fuel particles contained in the fuel compact are uniformly dispersed.

  In general, the weights of each of the coated fuel particles and the graphite matrix are measured in order to mix them in a predetermined ratio. However, measuring the weight every time one fuel compact is manufactured increases the number of processes and increases the productivity. There was a downside. In addition, in order to uniformly disperse the coated fuel particles and the graphite matrix, the coated fuel particles and the graphite matrix are loaded into the mold and then stirred with a stirring jig. In addition to increasing the number of steps, the density difference between the coated fuel particles and the graphite matrix is large, and the mold shape for the fuel compact is complicated, so that uniform stirring is difficult.

  In the prior art, the purpose of overcoating the graphite matrix on the coated fuel particles was to prevent the coated fuel particles from being damaged when the fuel compact was formed. When used to adhere the graphite matrix necessary for molding, it is not necessary to mix the graphite matrix during molding of the fuel compact, or only a little mixing is required, and the uniform dispersibility of the coated fuel particles is improved. It is advantageous. In this case, the filling rate of the coated fuel particles, the amount of uranium, and the graphite matrix density during fuel compact molding are determined according to the ratio of the weight of the coated fuel particles to the weight of the graphite matrix used for the overcoat. .

  Therefore, the ratio between the weight of the coated fuel particles and the weight of the graphite matrix is always constant, the diameter of the overcoat particles obtained by adhering the graphite matrix around the coated fuel particles is made uniform, and this uniform diameter is It is necessary to form a fuel compact using the overcoat particles it has.

  In the overcoat method of the prior art, as shown in FIG. 3, the open pan 20 is rotated by the pan rotation driving means 30 about the oblique rotation axis XI, and the coated fuel particles 1 are formed in the open type. The fuel 20 is placed in the pan 20, the pan 20 is rotated about the rotation axis XI, and the coated fuel particles 1 are allowed to flow below the pan 20, and the graphite matrix 2 is coated with the ethyl alcohol as a solvent from the graphite matrix supply nozzle 40. It was sprayed toward particle 1. Ethyl alcohol is vaporized after jetting to form overcoat particles.

  However, the evaporation of ethyl alcohol is greatly influenced by external factors such as temperature and humidity in the work environment. The higher the temperature of the working environment, the faster the vaporization of ethyl alcohol, and the higher the humidity of the working environment, the slower the vaporization of ethyl alcohol. If the vaporization of ethyl alcohol is fast, the graphite matrix will adhere to the walls around the device before it is coated with the coated fuel particles, resulting in a lack of overcoat, and if the vaporization of ethyl alcohol is slow, it will flow in the pan. The graphite matrix and alcohol adhere to the coated fuel particles that are more than necessary, resulting in an excessive amount of overcoat, and in any case, the thickness of the coating layer deposited on the coated fuel particles becomes non-uniform. Therefore, it is necessary to optimally maintain the temperature and humidity of the working environment, but it is difficult to maintain such a working environment constant, and therefore the overcoat cannot be performed uniformly, so the particle size is not uniform. There was a drawback.

  In addition, the prior art overcoat method requires a large number of pans and separate pan rotation driving means for rotationally driving them in order to inject a graphite matrix onto a large amount of coated fuel particles. Therefore, since a large amount of overcoat particles cannot be produced with one apparatus, the working time becomes long and the working efficiency is low.

  One problem to be solved by the present invention is to provide a coated fuel particle overcoat apparatus and method capable of forming an overcoat layer having a uniform thickness on the coated fuel particles without being affected by the working environment. There is.

  Another problem to be solved by the present invention is to provide a method for overcoating coated fuel particles, which can improve the working time and work efficiency by overcoating a large amount of coated fuel particles without increasing the working space. It is to provide.

  The first problem-solving means of the present invention is a pan loaded with coated fuel particles to which a graphite matrix is to be attached, and a pan rotation driving means for driving the pan so that the peripheral surface of the pan rotates around the rotation axis. And a coated fuel particle overcoat apparatus comprising a graphite matrix supply nozzle for injecting a graphite matrix together with a solvent onto the coated fuel particles in the pan, wherein the pan is provided outside the flow region of the mixture of the coated fuel particles and the graphite matrix. Another object of the present invention is to provide a coated fuel particle overcoat apparatus comprising a closed pan having an exhaust port.

  In the first problem-solving means of the present invention, it is preferable that a stirring member is provided in the closed pan to stir the mixture while the mixture is flowing. Also, a plurality of closed pans are arranged in parallel, each closed pan is provided with a graphite matrix supply nozzle, and a pan rotation driving means is connected to each closed pan so as to drive the plurality of closed pans simultaneously. More preferably.

  The second problem-solving means of the present invention is that the pan is rotated and driven so that the peripheral surface of the pan rotates around the rotation axis while injecting the graphite matrix together with the solvent onto the coated fuel particles loaded in the pan. In the method of overcoating the fuel particles with the graphite matrix, the pan is a closed pan having an exhaust port provided outside the flow region of the mixture of the coated fuel particles and the graphite matrix, and one batch stored in the closed pan. The weight P (g) of the surrounding coated fuel particles is P (g) ≦ (W × R) / 2 when the width of the peripheral surface of the pan is W (cm) and the outer diameter is R (cm). It is an object of the present invention to provide a method for overcoating coated fuel particles characterized by setting.

  In the second problem-solving means of the present invention, a plurality of closed pans are arranged in parallel and a graphite matrix supply nozzle is provided in each closed pan, and the plurality of closed pans are rotated from a common pan rotation driving unit. It is preferable to drive.

  Thus, when the pan is made of a closed pan having an exhaust port provided outside the rotation region of the mixture of the coated fuel particles and the graphite matrix, the coating is not affected by the working environment such as temperature and humidity. The fuel particles can be overcoated, so that overcoat particles having a uniform thickness overcoat layer and a predetermined particle size can be obtained.

  In addition, since the exhaust port for discharging the solvent to be vaporized is provided outside the flow region of the mixture of the coated fuel particles and the graphite matrix, the mixture is not discharged from the exhaust port, and the solvent is surely discharged from the pan. be able to.

  Furthermore, when the stirring member is provided in the closed pan, the mixture is automatically stirred by contacting the stirring member by the flow of the mixture, so that the dispersibility of the coated fuel particles is further improved.

  When a large number of closed pans are arranged in parallel and are driven to rotate by a common pan rotation driving means, a large amount of coated fuel particles can be simultaneously applied in a small work space compared to a case where a large number of independent devices are arranged in multiple stages. An overcoat can be applied, and work can be efficiently performed in a short work time.

  When the width of the peripheral surface of the closed pan is W (cm) and the outer diameter is R (cm), the weight P (g) of the coated fuel particles per batch stored in the closed pan is expressed as P (g ) ≦ (W × R) / 2, the processing amount per batch supplied to the pan is reduced as compared with the conventional one. However, a large number of closed pans arranged in parallel are rotated from a common pan rotation driving means. By driving, it is possible to obtain overcoat particles having an overcoat layer having a uniform thickness while maintaining high working efficiency.

  An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an overcoat apparatus 10 for coated fuel particles according to the present invention, and this overcoat apparatus 10 deposits a graphite matrix. A pan 20 loaded with the coated fuel particles 1 to be loaded, a pan rotation driving means 30 for driving the pan 20 so that a peripheral surface 20P of the pan 20 rotates about the rotation axis X, and a coated fuel particle in the pan 20 1 is provided with a graphite matrix supply nozzle 40 for injecting the graphite matrix 2 together with a solvent such as ethyl alcohol.

  The pan 20 used in the present invention includes a closed pan 20C having left and right side walls 20SW and a peripheral wall 20PW. As will be described later, the closed pan 20C rotates about the horizontal rotation axis X, so that the mixture of the coated fuel particles 1 and the graphite matrix 2 always changes to the lower part of the peripheral wall 20PW (although it changes sequentially with rotation, The portion is located in a region surrounded by 20PWL and the left and right side walls 20SW and the lower portion 20SWL corresponding to the peripheral wall lower portion 20PWL. This region is hereinafter referred to as a flow region of the mixture. The closed pan 20C has a loading port 20E for the coated fuel particles 1 in a part of the peripheral wall 20PW, and this loading port 20E is closed by a lid 20EC during the overcoat process. Reference numeral 20ECP denotes a lid opening prevention means.

  The closed pan 20C is provided with an exhaust port 20H that discharges a vaporized component of the solvent generated in the pan 20C during the overcoat operation, and this exhaust port 20H is a flow of the mixture of the coated fuel particles 1 and the graphite matrix 2. It is provided outside the area. That is, if the flow region of the mixture is a dimension Ph in the rotation axis direction with respect to the outer periphery of the peripheral wall 20PW, the exhaust port 20H is provided corresponding to the position of the dimension Hh further from the rotation axis X than this dimension Ph. The exhaust port 20H is preferably provided on both the left and right side walls 20SW as in the illustrated embodiment, but may be provided only on one side wall 20SW. In the illustrated embodiment, each of the side walls 20SW is provided with two exhaust ports 20H, but the number thereof can be arbitrarily set according to the amount of the vaporized component. The diameter r of the exhaust port 20H is preferably smaller than the outer diameter of the coated fuel particle 1, but may be larger than the outer diameter of the coated fuel particle 1 if the coated fuel particle 1 does not scatter. The exhaust port 20H may be porous instead of a single hole.

  The pan rotation drive means 30 includes a rotation drive source 30D supported by a base (not shown) and a rotation shaft 30S detachably connected to a rotation shaft connection member 20F provided on the pan 20. The drive source 30D can be a combination of an electric motor and a speed reducer.

  The graphite matrix supply nozzle 40 is arranged so as to inject the graphite matrix and ethyl alcohol toward the mixture flow region in the closed pan 20, and this supply nozzle 40 is connected to the graphite matrix feeder 42 via a pipe 44. Has been. The pipe 44 is introduced into the pan 20 along the rotation axis X of the pan 20 so that the rotation of the pan 20 is not hindered.

  In the illustrated embodiment, the overcoat apparatus 10 includes a stirring member 50 that is provided in the closed pan 20 and stirs the mixture while the mixture is flowing. In the illustrated example, stirring members 50P and 50S are provided on the inner surface of the peripheral wall 20PW of the pan 20 and the inner surfaces of the left and right side walls 20SW, respectively, and these stirring members 50P and 50S It functions to penetrate and contact the mixture and to stir the mixture by this contact. In the illustrated example, the stirring member 50P has a shape of a conical protrusion, and the stirring member 50S has a shape of a plate extending in the outer diameter direction toward the inside, but may be any other shape. it can.

  In order to obtain a good stirring state, the stirring member 50P may be provided over the entire circumference of the peripheral wall 20PW, and the stirring member 50S is provided over the entire circumferential direction of the side wall 20SW. May be. As described above, when the stirring members 50P and 50S are respectively provided on the entire circumference of the peripheral wall 20PW and the entire circumferential direction of the side wall 20SW, the stirring member always enters the flow region and stirs the mixture, so that the stirring efficiency is improved. . Note that a plurality of stirring members 50P and 50S may be provided intermittently rather than continuously in the circumferential direction of the inner periphery and the side wall 20SW of the peripheral wall 20PW.

  In FIG. 1, reference numeral 30 </ b> B denotes a rotating shaft support base, and reference numeral 40 </ b> B denotes a support base for the graphite matrix pipe 44.

  Next, a method for applying the overcoat of the graphite matrix 2 to the coated fuel particles 1 using the overcoat apparatus 10 will be described. The coated fuel particle loading port 20E is opened and a predetermined amount of the coated fuel particles 1 is loaded. . After the coated fuel particle loading port 20E is closed with the lid 20EC, a predetermined amount of graphite matrix 2 is supplied from the graphite matrix supply nozzle 40 while the pan rotation driving means 30 is driven to flow the coated fuel particles 1 in the closed pan 20. Are sprayed onto the coated fuel particles 1 together with ethyl alcohol as a solvent.

  Since the pan 20 is a closed pan 20C that is closed except for the exhaust port 20H, the temperature and humidity inside the pan are maintained at predetermined values as compared with the case of using a conventional open pan, and the coated fuel particles External factors that affect the weight ratio of 1 to the graphite matrix 2 can be eliminated.

  The weight P (g) of the coated fuel particles 1 per batch loaded into the closed pan 20C is as follows. When the width of the peripheral wall 20P of the pan 20 is W (cm) and the outer diameter is R (cm), P (g) ≦ (W × R) / 2 is set. This makes it easier for the graphite matrix 2 to reach the entire coated fuel particles 1 and to contact the coated fuel particles 1 evenly, with a weight less than about 5 kg loaded in the prior art. That is, the graphite matrix 2 is not supplied to the entire coated fuel particles 1 in the pan 20, but is first supplied to the coated fuel particles 1 located on the surface of the flow region, and the coated fuel by the rotation of the pan 20. The coated fuel particles 1 reach the entire coated fuel particles 1 as the particles 1 flow. However, when the loaded weight P (g) of the coated fuel particles 1 is set as described above, the entire coated fuel particles 1 per batch are not biased to the entire graphite matrix 2. Can be evenly contacted and an overcoat layer having a uniform thickness can be obtained. Here, since the weight of the coated fuel particles loaded on the pan 20 is premised on the amount that the uranium does not reach the critical state, it is loaded on the pan in order to avoid human error in the overcoat process. It is preferable that the above loading condition is satisfied after the weight of uranium of the coated fuel particles is set to 1/2 or 1/3 of the weight that reaches criticality.

  The ethyl alcohol supplied together with the graphite matrix 2 is vaporized to adhere the graphite matrix 2 to the coated fuel particles 1, and this vaporized component is exhausted from the exhaust port 20H.

  After a predetermined amount of the graphite matrix 2 is supplied to the coated fuel particles 1 per batch, the driving of the pan rotation driving means 30 is stopped, and the loading port 20E is on the lower side so that the lid of the loading port 20E is covered. 20EC is opened, overcoat particles are discharged, and work per batch is completed.

  The above operation is repeated to overcoat a predetermined batch of coated fuel particles 1 with a graphite matrix 2 to produce a predetermined amount of overcoat particles, and a fuel compact is formed using the overcoat particles.

  An overcoat apparatus 10 for coated fuel particles according to another embodiment of the present invention is shown in FIG. The overcoat apparatus 10 includes a plurality of, in the illustrated example, three closed-type pans 201 to 203 arranged in parallel, and each of the closed-type pans 201 to 203 is provided with a graphite matrix supply nozzle 401 to 403 to drive pan rotation. The means 30 is the same as that of the embodiment of FIG. 1 except that the means 30 are connected in series to each of the closed pans 201 to 203 so as to drive a plurality of closed pans 201 to 203 simultaneously. In addition, the same code | symbol is attached | subjected to the same part as FIG.

  The leftmost closed pan 201 is directly connected to the rotary shaft 30S of the pan rotation driving means 30, and the other closed pans 202 and 203 are connected to the adjacent closed pan via the connecting rotary shafts 30S2 and 30S3, respectively. 201 and 202, respectively.

  The overcoat apparatus 10 of FIG. 2 is also used in the same manner as the apparatus of FIG. 1. However, even if the loading weight of the coated fuel particles 1 per batch is small, the overcoat apparatus 10 is arranged in multiple stages in this way and shared pan rotation is performed. Since it is connected in series to the drive means 30, it is possible to overcoat a large amount of coated fuel particles simultaneously in a small work space, compared to the case where a large number of independent devices are arranged in multiple stages, and the work can be performed in a short work time. It can be done efficiently.

  According to the present invention, the coated fuel particles can be coated with a uniform thickness on the coated fuel particles without being affected by external factors such as temperature and humidity in the working environment, and thus a molding having high dispersibility. The fuel can be obtained, and can be beneficially used for producing a fuel for a HTGR.

It is a schematic explanatory drawing of the overcoat apparatus of the covering fuel particle | grains by one embodiment of this invention. It is a schematic explanatory drawing of the overcoat apparatus of the covering fuel particle | grains by other embodiment of this invention. It is a schematic explanatory drawing of the overcoat apparatus of the covering fuel particle | grains by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coated fuel particle 2 Graphite matrix 10 Coated fuel particle overcoat apparatus 20 Pan 20C, 201, 202, 203 Closed type pan 20P Peripheral surface 20PW Peripheral wall 20PWL Lower part 20SW Side wall 20SWL Lower part 20H Exhaust port 20E Coated fuel particle loading port 20EC Lid 20ECP Lid opening prevention means 20F Rotating shaft support 30 Pan rotation driving means 30D Rotation driving source 30S, 30S2, 30S3 Rotating shaft 40, 401, 402, 403 Graphite matrix supply nozzle 42 Graphite matrix feeder 44 Piping 50, 50S, 50P Stirring Element

Claims (5)

A pan loaded with coated fuel particles to which the graphite matrix is to be attached; a pan rotation driving means for driving the pan so that a peripheral surface of the pan rotates about a rotation axis; and the coated fuel particles in the pan In a coated fuel particle overcoat device comprising a graphite matrix supply nozzle for injecting the graphite matrix toward the pan, the pan is closed having an exhaust port provided outside the flow region of the mixture of the coated fuel particles and the graphite matrix An overcoat apparatus for coated fuel particles, comprising a mold pan. The overcoat apparatus for coated fuel particles according to claim 1, further comprising a stirring member that is provided in the closed pan and stirs the mixture while the mixture is flowing. An overcoat device for coated fuel particles. The overcoated apparatus for coated fuel particles according to claim 1 or 2, wherein a plurality of closed pans are arranged in parallel, and each of the closed pans is provided with the graphite matrix supply nozzle. An overcoat apparatus for coated fuel particles, wherein the plurality of closed pans are connected to each closed pan so as to be driven simultaneously. A method of overcoating the coated fuel particles with the graphite matrix by rotating the pan so that the peripheral surface of the pan rotates around the rotation axis while injecting the graphite matrix onto the coated fuel particles loaded in the pan The pan is a closed pan having an exhaust port provided outside the flow region of the mixture of the coated fuel particles and the graphite matrix, and the weight P of the coated fuel particles per batch stored in the closed pan. (G) is a coating characterized by setting P (g) ≦ (W × R) / 2 when the width of the peripheral surface of the bread is W (cm) and the outer diameter is R (cm) Fuel particle overcoat method. 5. The method of overcoating coated fuel particles according to claim 4, wherein a plurality of closed pans are arranged in parallel, the graphite matrix supply nozzle is provided in each closed pan, and the plurality of closed pans are shared. A method for overcoating coated fuel particles, wherein the method is rotationally driven from a pan rotation driving means.

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