JP4409460B2 - Production equipment for coated fuel particles for HTGR - Google Patents

Description

  TECHNICAL FIELD The present invention relates to an apparatus for producing a fuel for a high temperature gas reactor, and relates to a coating for a high temperature gas reactor provided with a fluidized bed reactor in which multiple coating layers are formed on a fuel core made of a uranium compound such as uranium dioxide to form coated fuel particles. In the fuel particle manufacturing apparatus, the distribution in the furnace of the coating temperature, which greatly affects the characteristics of the coating layer, remains constant even when repeatedly manufactured, and is suitable for continuous production.

  The HTGR is composed of graphite, which has a large heat capacity and good high-temperature soundness, and uses a gas such as helium gas that does not cause a chemical reaction even at high temperatures as a cooling gas. Helium gas with high safety and high outlet temperature can be taken out, and the high temperature heat of about 900 ° C enables heat utilization in a wide range of fields such as hydrogen production and chemical plants as well as power generation. is there.

The fuel in the HTGR has a total of four coatings 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 with a density of about 1 g / cm ³ , which has both a function as a gas reservoir for gaseous fission products (FP) and a function as a buffer for absorbing fuel swelling. is there. The second layer is a high-density pyrolytic carbon having a density of about 1.8 g / cm ³ and has a function of holding a gaseous FP. The third layer is silicon carbide (hereinafter referred to as SiC) having a density of about 3.2 g / cm ³ and has a function of holding a solid FP, and is a main strength member of the coating layer. The fourth layer is a high-density pyrolytic carbon having a density of about 1.8 g / cm ³ , which is the same as that of the second layer, and has a function of holding the gaseous FP as well as a protective layer of the third layer.

  Typical coated fuel particles have a diameter of about 500-1000 μm. The coated fuel particles are dispersed in a graphite matrix and molded into a compact fuel compact shape, and a certain amount of compact is put into a cylinder made of graphite and is shaped into a fuel rod that is plugged up and down. Finally, the fuel rod is inserted into a plurality of insertion holes of the hexagonal column type graphite block, and a large number of the hexagonal column type graphite blocks are stacked in a honeycomb array to constitute a core.

  Such a HTGR fuel is generally manufactured through the following steps. First, uranium oxide powder is dissolved in nitric acid to obtain a uranyl nitrate stock solution. Pure water and a thickener are added to this uranyl nitrate stock solution and stirred to obtain a dripping stock solution. The thickener is added so that the dropped uranyl nitrate droplet becomes a true sphere due to its surface tension during dropping. Examples of the thickening agent include polyvinyl alcohol resin, resin having a property of solidifying under alkaline conditions, polyethylene glycol, and metroise.

  The dropping stock solution adjusted as described above is cooled to a predetermined temperature to adjust the viscosity, and then dropped into ammonia water by vibrating a small-diameter dropping nozzle. The droplets are prevented from being deformed at the time of landing by applying ammonia gas in a space until landing on the surface of the aqueous ammonia solution to gel the surface. Uranyl nitrate reacts sufficiently with ammonia in ammonia water to form particles of ammonium heavy uranate.

  The ammonium heavy uranate particles are roasted in the atmosphere to become uranium trioxide particles, and further reduced and sintered to become fuel nuclei made of high-density ceramic uranium dioxide.

The fuel nuclei are loaded onto a fluidized bed, and coating is performed by thermally decomposing the coating gas. In the case of the low density carbon of the first layer, acetylene (C ₂ H ₂ ) is thermally decomposed at about 1400 ° C. In the case of the second and fourth layers of high-density pyrolytic carbon, propylene (C ₃ H ₆ ) is pyrolyzed at about 1400 ° C. In the case of SiC of the third layer, methyltrichlorosilane (CH ₃ SiCl ₃ ) is thermally decomposed at about 1600 ° C.

  When each coating layer is formed using the aforementioned coating gas, the particles are sufficiently flowed in the reaction tube using another gas in order to uniformly apply the coating layer to each particle. This is why the coated fuel particle production apparatus is called a fluidized bed. As a gas for flowing particles, argon gas which is one of inert gases when coating the first, second and fourth layers, and hydrogen gas or hydrogen gas when coating the third layer + Argon gas, which is one of inert gases, is generally used.

  The fuel compact is coated with a graphite matrix material consisting of graphite powder, binder, etc. on the surface of the coated fuel particles, and is pressed or molded into a hollow cylindrical shape or cylindrical shape, and then included as a binder in the green compact. In order to carbonize the phenol resin obtained, heat treatment is carried out, and further, heat treatment aimed at removing gas components contained in the compact is carried out (for example, see Patent Document 1).

FIG. 3 is an explanatory view showing a configuration of a conventional apparatus for producing coated fuel particles for a HTGR. As shown in FIG. 3, a fluidized bed reactor as an apparatus for producing coated fuel particles for a high-temperature gas reactor includes a fuel core 32 made of uranium dioxide through an upper window (not shown) of the fluidized bed main body, and a fluidized gas inlet. A reaction tube 35 for coating by flowing a coating gas and a flowing gas from 36 through a gas introduction nozzle 34 and a gas ejection nozzle 33, and a graphite heater 31 disposed on the outer periphery of the reaction tube 35 to heat fuel nuclei. And a heat insulating material 38, which is also made of graphite and disposed on the outer periphery of the heater 31.
JP 2000-284084 A

  In such a fluidized bed reactor, by moving the gas ejection nozzle 33, the coated fuel particles obtained by forming the coating layer on the fuel core 32 are taken out from the coating gas and the fluidized gas inlet 36 at the lower part of the fluidized bed. Therefore, the gas ejection nozzle 33 and the reaction tube 35 are generally not mechanically fixed. For this reason, the coating gas and the flowing gas leak from the gap between the gas ejection nozzle 33 and the reaction tube 35 and fill around the heater 31 and the heat insulating material 38.

  There is no problem when the first, second, and fourth layers are coated, but when the third layer is coated, if hydrogen gas that is a flowing gas leaks, it is heated to about 1600 ° C. Certain graphite and hydrogen react to generate hydrocarbons. The generation of hydrocarbons means that the graphite, which is the material of the heater 31 and the heat insulating material 38, decreases. In the case of the heater 31, the resistance value changes, and as a result, the amount of generated heat changes.

  In the case of the heat insulating material 38, heat easily escapes from the portion where the graphite is reduced, and the heat insulating performance is lowered. As a result, the distribution of the coating temperature in the furnace, which greatly affects the properties of the coating layer, changes. Therefore, in the case of continuous production, the production conditions will change from batch to batch, so the quality of the coating layer, which is very important for the confinement action of the fissile material in the HTGR fuel, becomes unstable. A serious problem arises.

  Even in the case of continuous production, the temperature distribution in the furnace, which greatly affects the properties of the coating layer, can be stabilized without change, and the coated fuel particles for HTGR suitable for continuous production can be obtained. It aims at obtaining a manufacturing apparatus.

The fuel particle manufacturing apparatus for a high temperature gas reactor according to the invention described in claim 1 includes a gas reservoir and a fuel nucleus of a gaseous fission product made of low density pyrolytic carbon on the surface of a fuel nucleus obtained by sintering uranium dioxide. A first coating layer that functions as a buffer that absorbs the swelling of the carbon, a second coating layer that is composed of high-density pyrolytic carbon and has a function of retaining gaseous fission products, and a solid fission product composed of silicon carbide. A third coating layer having a holding function and a function as a main strength member of the coating layer; a holding function for gaseous fission products made of high-density pyrolytic carbon; and a function as a protective layer for the third coating layer In the apparatus for producing coated fuel particles for a HTGR equipped with a fluidized bed reactor for applying a total of four coating layers with the fourth coating layer,
A space fluidized bed reactor gas introducing means for flowing through the gas introducing nozzle coating gas and / or liquid gas in the main body into the reaction tube in the fluidized bed is present, the heater and the heat insulating material in a fluidized bed reactor main body The existing spaces are separated from each other by a cylindrical leak-proof cylindrical member provided on the outer peripheral side of the gas introduction nozzle .

According to a second aspect of the present invention, there is provided an apparatus for producing coated fuel particles for a HTGR as a gas introduction means according to the first aspect, provided as a cylindrical leak-proof cylinder provided on the outer peripheral side of the gas introduction nozzle. With
The lower part of the leak-proof cylinder is fixed to the corresponding reactor main body,
The upper part of the leak-proof cylinder is threaded so as to be screwed together with the lower part of the corresponding reaction tube.

  An apparatus for producing coated fuel particles for a HTGR according to a third aspect of the invention is characterized in that the outer peripheral side of the leak-proof tubular member according to the second aspect is further covered with a heat insulating material made of graphite. To do.

An apparatus for producing coated fuel particles for a HTGR according to a fourth aspect of the present invention is a cylindrical leak-proof cylinder provided on the outer peripheral side of the gas introduction nozzle as the gas introduction means according to the first aspect. With
The leakage prevention cylinder is extended from the lower part of the reaction tube so as to cover the outer periphery of the gas introduction nozzle,
The lower part of the leak-proof cylinder is threaded so as to be screwed into the lower wall of the corresponding fluidized bed reactor.

  As described above, the present invention can stabilize the temperature distribution in the furnace, which has a great influence on the properties of the coating layer, even when continuously produced, and can be stabilized without change. There is an effect that an apparatus for producing coated fuel particles can be obtained.

In the present invention, on the surface of a fuel nucleus sintered with uranium dioxide, a first coating made of low-density pyrolytic carbon and serving as a buffer for absorbing gas fission product gas reservoirs and fuel nucleus swelling. A layer, a second coating layer made of high-density pyrolytic carbon and having a function of holding a gaseous fission product, a function of holding a solid fission product made of silicon carbide, and a function as a main strength member of the coating layer. A total of four coating layers are applied, including a third coating layer having a fourth coating layer made of high-density pyrolytic carbon and having a function of retaining a gaseous fission product and a function as a protective layer of the third coating layer In an apparatus for producing coated fuel particles for a HTGR equipped with a fluidized bed reactor,
A space in which there is a gas introduction means for the coating gas and / or fluid gas in the fluidized bed in the fluidized bed reactor main body, and a space in the fluidized bed reactor main body in which the heater and the heat insulating material are present. Are isolated from each other. This makes it possible to stabilize the temperature distribution in the furnace, which has a great influence on the characteristics of the coating layer, even when continuously produced, and to stabilize the fuel distribution for high-temperature gas reactors suitable for continuous production. A device can be obtained.

  More specifically, the present invention is an apparatus for producing coated fuel particles contained in a HTGR fuel. A fuel core made of a compound of uranium such as uranium dioxide is used as a fuel nucleus from a first low-density carbon layer. The present invention relates to a device for a fluidized bed reactor that covers up to the fourth high-density pyrolytic carbon layer.

  The present invention includes a space in which gas is introduced into a reaction tube in a fluidized bed and / or a coating gas in the fluidized bed reactor main body, a heater and a heat insulating material in the fluidized bed reactor main body. Isolate existing spaces from each other. This prevents the coating gas or fluid gas leaking from the gap between the gas jetting means and the reaction tube from flowing toward the heater or heat insulating material, so that graphite, which is the material of the heater or heat insulating material, reacts with hydrogen. It is possible to prevent the graphite from being reduced.

  Since there is no decrease in heaters and insulation, the temperature distribution in the furnace is stable without change even in continuous production, which is very constrained by the fissile material confinement action of the HTGR fuel. It becomes possible to stabilize the quality of the coating layer having an important role.

  In the present invention, the two spaces are separated from the gas from the space where the gas introduction means to the reaction tube in the fluidized bed exists into the space where the heater and the heat insulating material exist in the fluidized bed reactor main body. Anything that inhibits migration may be used. As a more preferred embodiment, the gas introduction means includes a cylindrical leak-proof cylinder provided on the outer peripheral side of the gas introduction nozzle, and the lower part of the leak-proof cylinder is fixed to the corresponding reactor main body, The upper part of the leak-proof cylindrical material is one that is threaded so as to be screwed together with the lower part of the corresponding reaction tube.

  Preferably, in the case where the outer peripheral side of the leak-proof cylindrical material is further covered with a heat insulating material made of graphite, the two spaces are more reliably separated. Furthermore, melting of the metal gas introduction nozzle can be prevented.

  In the present invention, a cylindrical tube is further provided outside the gas introduction nozzle to extend the cylinder, and the lower side of the cylinder is fixed to the fluidized bed body so that no gas flows out to the outside. As another gas introduction means, a cylindrical leakage prevention cylinder provided on the outer peripheral side of the gas introduction nozzle is provided, and the leakage prevention cylinder extends from the lower part of the reaction tube so as to cover the outer circumference of the gas introduction nozzle. The lower part of the leakage prevention cylinder is threaded so as to be screwed into the lower wall of the corresponding fluidized bed reactor, so that the coating gas and fluidized gas leaking from the gap between the gas ejection nozzle and the reaction tube can be removed. It may be prevented from flowing toward the heater or the heat insulating material.

  By adopting such a configuration, even when hydrogen gas, which is a flowing gas, leaks from the gap between the gas ejection nozzle and the reaction tube when the third layer is coated, it is in the space surrounded by the cylinder and the reaction tube, and to the outside side. Therefore, it is possible to prevent graphite and hydrogen, which are materials of the heater and the heat insulating material, from reacting with each other and reducing graphite. Since there is no reduction in heaters and insulation, the temperature distribution in the furnace remains stable even when continuously produced, so it is very important for the containment of fissile material in HTGR fuel. It becomes possible to stabilize the quality of the coating layer having a role.

  FIG. 1 is an explanatory view showing the configuration of an embodiment of the production apparatus for coated fuel particles for a HTGR according to the present invention. As shown in FIG. 1, a fluidized bed reactor as a production apparatus for coated fuel particles for a high temperature gas reactor has a fuel core 12 made of uranium dioxide inserted through a window (not shown) provided in the upper part of the fluidized bed main body. A reaction tube 15 for coating by flowing a coating gas and a flowing gas from the flowing gas inlet 16 through the gas introduction nozzle 14 and the gas jet nozzle 13 and graphite for heating the fuel core disposed on the outer periphery of the reaction tube 15 A heater 11 made of graphite, and a heat insulating material 18 that is also made of graphite and disposed on the outer periphery of the heater 11.

  In this embodiment, a carbon cylinder 10 is provided on the lower side of the reaction tube 15, and a threaded portion is applied to the receiving portion in which the upper portion of the cylinder 10 and the lower portion of the reaction tube 15 facing the cylinder 10 are formed in a cylindrical shape. , Each other is screwed. A graphite heat insulating material 20 was attached to the outside of the carbon cylinder 10. This is because generally the purpose is to prevent the metal gas introduction nozzle 14 from melting at a high temperature in the furnace. The size of the fluidized bed reactor main body 19 was approximately 700 mm × H approximately 2200 mm, and the size of the reaction tube was approximately 200 mm × H approximately 1000 mm.

With such an apparatus for producing coated fuel particles for a HTGR, the coated fuel particles are produced by placing about 3.8 kg of uranium dioxide fuel nuclei having an average diameter of 0.6 mm in a fluidized bed at about 1400 ° C. after C 2 _{H 2)} covering the low-density carbon of the first layer by flowing a gas, covering the high-density pyrolytic carbon of the second layer flows into the propylene (C 3 _{H 6)} at about 1400 ° C., Next, methyltrichlorosilane (CH ₃ SiCl ₃ ) is introduced at about 1600 ° C. to cover the third SiC layer, and finally, propylene (C ₃ H ₆ ) is introduced at about 1400 ° C. The layer was coated with high density pyrolytic carbon.

  When this coating operation was repeated, no deterioration was observed due to the generation of hydrocarbons by reaction with hydrogen in the heater 11 and the heat insulating material 18, and the average diameter of the obtained coated fuel particles was 0.93 mm. The thickness of each layer was 0.06 mm for the first layer, 0.03 mm for the second layer, 0.03 mm for the third layer, and 0.045 mm for the fourth layer.

  FIG. 2 is an explanatory diagram showing the configuration of another embodiment. As shown in FIG. 2, instead of the carbon cylinder 10 shown in FIG. 1, a cylinder 30 is formed by extending the lower side of the reaction tube 15 into a cylindrical shape. The floor portion of the main body 19 is the same as that shown in FIG. 1 except that it has a structure in which screw processing is performed and each other is screwed.

  As described above, even when hydrogen gas, which is a flowing gas, leaks from the gap between the gas ejection nozzle 14 and the reaction tube 15 when the third layer is coated, it does not flow into the space where the heater 11 and the heat insulating material 18 are located. It is possible to prevent the graphite, which is the material of the material 18, from reacting with hydrogen and reducing the graphite.

  In addition, since the heater 11 and the heat insulating material 18 are not reduced, the temperature distribution in the furnace is stable without change even in continuous production, so that the fissile material in the HTGR fuel is confined. It becomes possible to stabilize the quality of the coating layer having a very important role.

It is explanatory drawing which shows the structure of one Example of the manufacturing apparatus of the covering fuel particle | grain for high temperature gas reactors of this invention. It is explanatory drawing which shows the structure of another Example of the manufacturing apparatus of the coating | coated fuel particle | grain for high temperature gas reactors of this invention. It is explanatory drawing which shows the structure of the manufacturing apparatus of the conventional coating | coated fuel particle | grain for high temperature gas reactors.

Explanation of symbols

10 ... carbon cylinder,
11 ... Heater,
12. Fuel kernel,
13: Gas ejection nozzle,
14 ... Gas introduction nozzle,
15 ... reaction tube,
16 ... Fluid gas inlet,
17 ... Waste gas outlet,
18 ... heat insulation,
19 ... body,
20 ... heat insulating material,
30 ... Cylinder,

Claims (4)

A first coating layer comprising a low-density pyrolytic carbon surface on the surface of a fuel nucleus sintered with uranium dioxide and serving as a buffer for absorbing gas fission product gas reservoirs and fuel nucleus swelling; A second coating layer made of pyrolytic carbon and having a function of holding a gaseous fission product, and a third coating layer having a function of holding a solid fission product made of silicon carbide and a function as a main strength member of the coating layer And a fluidized bed reactor for applying a total of four coating layers comprising a high density pyrolytic carbon and a fourth coating layer having a function of retaining a gaseous fission product and having a function as a protective layer of the third coating layer. In an apparatus for producing coated fuel particles for high temperature gas reactors,
A space fluidized bed reactor gas introducing means for flowing through the gas introducing nozzle coating gas and / or liquid gas in the main body into the reaction tube in the fluidized bed is present, the heater and the heat insulating material in a fluidized bed reactor main body An apparatus for producing coated fuel particles for a high-temperature gas reactor, wherein the existing space is separated from each other by a cylindrical leak-proof cylinder provided on the outer peripheral side of the gas introduction nozzle . As the gas introduction means, provided with a cylindrical leak-proof cylinder provided on the outer peripheral side of the gas introduction nozzle,
The lower part of the leak-proof cylinder is fixed to the corresponding reactor main body,
2. The apparatus for producing coated fuel particles for a high temperature gas reactor according to claim 1, wherein the upper part of the leak-proof cylindrical member is threaded so as to be screwed together with the lower part of the corresponding reaction tube.   The apparatus for producing coated fuel particles for a HTGR according to claim 2, wherein the outer peripheral side of the leak-proof cylinder is further covered with a heat insulating material made of graphite. As the gas introduction means, provided with a cylindrical leak-proof cylinder provided on the outer peripheral side of the gas introduction nozzle,
The leakage prevention cylinder is extended from the lower part of the reaction tube so as to cover the outer periphery of the gas introduction nozzle,
2. The apparatus for producing coated fuel particles for a high temperature gas reactor according to claim 1, wherein the lower part of the leak-proof cylinder is threaded so as to be screwed into a lower wall of a corresponding fluidized bed reactor. .

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