JP4357437B2 - 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 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 is coated with a total of four layers centered on a fuel core having a diameter of about 350 to 650 μm 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 ports of a hexagonal column type graphite block, and a large number of these 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 thickener include polyvinyl alcohol resin, a resin having a property of solidifying under alkaline conditions, polyethylene glycol, and metroses.

  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. 2 is an explanatory view showing a configuration of a conventional apparatus for producing coated fuel particles for a HTGR. As shown in FIG. 2, the apparatus for producing coated fuel particles for a high temperature gas reactor introduces a fuel core 22 made of uranium dioxide from an upper window (not shown) of a fluidized bed reaction tube 25 and introduces gas from a fluidized gas inlet 26. A fluidized bed reaction tube 25 for coating by flowing a coating gas and a flowing gas through the nozzle 24 and the gas ejection nozzle 23; a graphite heater 21 disposed on the outer periphery of the reaction tube 25 for heating the fuel core; It is also made of graphite and is provided with a heat insulating material 28 disposed on the outer periphery of the heater 21. The coated gas and fluidized gas are discharged out of the furnace through the waste gas discharge port 27, and the coated coated fuel particles are removed from the fluidized gas inlet 26.
JP 2000-284084 A

  In such a fluidized bed reaction apparatus, by moving the gas ejection nozzle 23, in order to take out the coated fuel particles coated on the fuel core 22 from the fluidized gas inlet 26 at the lower part of the fluidized bed, The reaction tube 25 is generally not mechanically fixed. For this reason, the coating gas or the flowing gas leaks from the gap between the gas jet nozzle 23 and the reaction tube 25 and fills around the heater 21 and the heat insulating material 28 inside the housing 29 constituting the outer shell of the main body.

  There is no problem when the first, second, and fourth layers are coated, but when the third layer is coated, if hydrogen gas, which 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 that is the material of the heater 21 and the heat insulating material 28 is reduced. Therefore, in the case of the heater 21, the resistance value changes, and as a result, the amount of generated heat changes.

  In the case of the heat insulating material 28, 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.

  The present invention provides an apparatus for producing coated fuel particles for high-temperature gas furnaces suitable for continuous production, in which the distribution in the furnace of the coating temperature, which greatly affects the properties of the coating layer, remains constant even after repeated production. The purpose is to obtain.

The apparatus for producing coated fuel particles for a HTGR according to the invention described in claim 1 has a plurality of layers on the surface of a fuel core obtained by sintering a uranium dioxide by flowing a coating gas and / or a flowing gas in a heating environment. A fluidized bed reaction tube for forming a coating layer, a graphite heater for heating the fluidized bed reaction tube, a heat insulating material surrounding an outer periphery of the fluidized bed reaction tube and the graphite heater, the fluidized bed reaction tube and the graphite heater, In the manufacturing apparatus for coated fuel particles for a HTGR provided with a cylindrical housing containing therein a heat insulating material,
A suction pump means for discharging the coating gas and / or fluid gas leaking from the fluidized bed reaction tube to the outside of the housing is provided.

  The apparatus for producing coated fuel particles for a HTGR according to claim 2 is characterized in that the suction pump means according to claim 1 is explosion-proof.

  An apparatus for producing coated fuel particles for a HTGR according to a third aspect of the invention is characterized in that the suction pump means according to the first or second aspect includes a low vacuum pump.

  The present invention provides an apparatus for producing coated fuel particles for a HTGR suitable for continuous production, in which the distribution in the furnace of the coating temperature, which greatly affects the properties of the coating layer, remains constant even when it is repeatedly manufactured. There is an effect that can be obtained.

In the present invention, a fluidized bed reaction tube for forming a plurality of coating layers on the surface of a fuel core obtained by flowing a coating gas and / or a fluidized gas in a heated environment to sinter uranium dioxide, and the fluidized bed reaction tube A high temperature heater comprising: a graphite heater that heats; a heat insulating material surrounding an outer periphery of the fluidized bed reaction tube and the graphite heater; and a cylindrical housing that accommodates the fluidized bed reaction tube, the graphite heater, and the heat insulating material therein. In an apparatus for producing coated fuel particles for a gas furnace,
Suction pump means for discharging the coating gas and / or fluid gas leaking from the fluidized bed reaction tube to the outside of the housing is provided. As a result, the coating temperature distribution in the furnace, which greatly affects the characteristics of the coating layer, is constant without changing even if it is repeatedly manufactured. Obtainable.

  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 a high-density pyrolytic carbon layer as a fourth layer.

  In the present invention, the outside region of the fluidized bed reaction tube is decompressed by a suction pump means, and the coating gas and fluidized gas leaking from the gap between the gas ejection nozzle and the reaction tube are discharged out of the housing holding the heater and the heat insulating material. To do. As a result, even if hydrogen gas, which is a flowing gas, leaks from the gap between the gas jet nozzle and the reaction tube when the third layer is coated, it is discharged out of the housing by the vacuum pump. It is possible to prevent hydrogen from reacting with graphite 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 plays an extremely important role in confining fissionable materials in HTGR fuel. It becomes possible to stabilize the quality of the coating layer having the.

  The suction pump means of the present invention may be any means as long as it discharges the coating gas and / or fluid gas leaking from the fluidized bed reaction tube to the outside of the housing, and a more preferable aspect is a rotary pump or a mechanical booster pump. As long as a low vacuum pump is included. Further, in the first, second, and fourth layer coatings, a flammable coating gas is used, and therefore the suction pump means is preferably an explosion-proof type.

  Another specific configuration of the suction pump means of the present invention includes at least a suction pipe communicating with the inside of the housing and the suction pump. The suction pipe may be any pipe that penetrates the outer wall of the housing and sucks the internal gas. More preferably, the suction pipe is near or above the gap between the gas ejection nozzle and the reaction pipe where the coating gas or the flowing gas easily leaks. With a suction tube opening. Thereby, the leaked gas can be favorably guided to the opening.

  The suction pump may be driven during the entire process of forming the first to fourth coating layers. However, since the hydrogen gas at the time of forming the third coating layer reacts with graphite, a problem occurs. It is better to drive only.

  Further, the inside of the housing is lowered from the outside air pressure, the gas ejection nozzle and the reaction tube by driving the suction pump. If it is too low, the coating gas and the flowing gas will leak significantly from the gap between the gas ejection nozzle and the reaction tube. Therefore, it is preferable that the inert gas from the inert gas cylinder is purged to the vicinity of the suction pipe. More preferably, the supply port for the inert gas is provided at a position opposite to the opening of the suction pipe with the gap between the gas jet nozzle and the reaction pipe in between. Thereby, the leaked gas is easily sucked by the inert gas.

  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 HTGR is provided with a fuel core 12 made of uranium dioxide through an upper window (not shown) of a fluidized bed reaction tube 15. A reaction tube 15 that coats by flowing a coating gas and a flowing gas through the introduction nozzle 14 and the gas ejection nozzle 13, a graphite heater 11 that is disposed on the outer periphery of the reaction tube 15 and heats fuel nuclei, And a heat insulating material 18 made of graphite and disposed on the outer periphery of the heater 11.

  That is, the apparatus itself is configured from the outside in the order of the housing 19, the heat insulating material 18, the heater 11, and the reaction tube 15. More specifically, the size of the housing 19 of the fluidized bed reactor is approximately 700 mm × H approximately 2200 mm, and the size of the reaction tube 15 is approximately 200 mm × H approximately 1000 mm. As for the heater 11, the cylindrical heater 11 is used in this embodiment, but a plurality of rod-shaped heaters may be used. In that case, it arrange | positions equally on the outer periphery of the reaction tube 15. FIG.

The coated fuel particles are produced by placing about 3 kg of uranium dioxide fuel nuclei having an average diameter of 0.6 mm in a fluidized bed and flowing acetylene (C ₂ H ₂ ) gas at about 1400 ° C. to form the first layer of low density carbon. Then, propylene (C ₃ H ₆ ) was introduced at about 1400 ° C. to coat the second layer of high-density pyrolytic carbon, and then methyltrichlorosilane (CH ₃ SiCl ₃ ) was added at about 1600 ° C. Inflow to coat the third layer SiC layer and finally inject propylene (C ₃ H ₆ ) at about 1400 ° C. to cover the fourth layer high density pyrolytic carbon.

  When performing coating from the first layer to the fourth layer, a vacuum pump 10 for low vacuum such as a rotary pump or a mechanical booster pump is provided in a region where the heater 11 and the heat insulating material 18 exist between the housing 19 and the reaction tube 15. Pull on. The vacuum pump 10 communicates with the bottom of the housing 19 by the suction pipe 9. As a result, even when the coating operation is repeatedly performed, deterioration due to the occurrence of hydrocarbons in the heater 11 and the heat insulating material 18 is not observed, and stable coated fuel particles can be obtained.

  In the first, second, and fourth layer coatings, a flammable coating gas is used, so an explosion-proof vacuum pump is preferable.

  That is, in the present invention, the region outside the fluidized bed reaction tube is decompressed by the suction pump means, and the coating gas and fluidized gas leaking from the gap between the gas ejection nozzle 13 and the reaction tube 15 are retained by the heater and the heat insulating material. It is discharged out of the housing. As a result, even if hydrogen gas, which is a flowing gas, leaks from the gap between the gas jet nozzle 13 and the reaction tube 15 when the third layer is coated, it is discharged out of the housing 19 by the vacuum pump 10. It is possible to prevent graphite and hydrogen, which are the materials of the above, from reacting and reducing graphite.

  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 it is very important for confinement of fissile material in HTGR fuel. It becomes possible to stabilize the quality of the coating layer having a different role.

  As described above, even when hydrogen gas, which is a flowing gas, leaks from the gap between the gas jet nozzle 13 and the reaction tube 15 when the third layer is coated, the vacuum pump 10 discharges it outside the fluidized bed. 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 do not decrease, the temperature distribution in the furnace is stable without change even in continuous production. It becomes possible to stabilize the quality of the coating layer having an important role in the process.

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 the manufacturing apparatus of the conventional coating | coated fuel particle | grain for high temperature gas reactors.

Explanation of symbols

9 ... suction tube,
10: suction pump means,
11 ... Heater,
12. Fuel kernel,
13: Gas ejection nozzle,
14 ... Gas supply nozzle,
15 ... reaction tube,
16 ... Fluid gas inlet,
17 ... Waste gas discharge tank,
18 ... heat insulation,
19 ... Housing,

Claims (3)

A fluidized bed reaction tube for forming a plurality of coating layers on the surface of a fuel core obtained by flowing a coating gas and / or a flowing gas in a heating environment to sinter uranium dioxide, and a graphite heater for heating the fluidized bed reaction tube And a heat insulating material surrounding an outer periphery of the fluidized bed reaction tube and the graphite heater, and a tubular housing containing the fluidized bed reaction tube, the graphite heater and the heat insulating material therein, and a coated fuel for a HTGR In the particle production equipment,
An apparatus for producing coated fuel particles for a high temperature gas furnace, comprising suction pump means for discharging the coating gas and / or the flowing gas leaked from the fluidized bed reaction tube to the outside of the housing.   The said suction pump means is explosion-proof specification, The manufacturing apparatus of the coated fuel particle for high temperature gas reactors of Claim 1 characterized by the above-mentioned. The apparatus for producing coated fuel particles for a HTGR according to claim 1 or 2, wherein the suction pump means includes a low vacuum pump.

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