JP4417867B2 - 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 is generally coated with a total of four layers, centering 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 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 thickener include a polyvinyl alcohol resin, a resin having a property of solidifying under an alkaline condition, 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, a fluidized bed reactor as a production apparatus for coated fuel particles for a HTGR is provided with a fuel core 22 made of uranium dioxide through an upper window (not shown) of the fluidized bed main body, and a fluidized gas inlet. 26, a reaction tube 25 for coating by flowing a coating gas and a flowing gas through a gas introduction nozzle 24 and a gas ejection nozzle 23, and a graphite heater 21 which is disposed on the outer periphery of the reaction tube 25 and heats fuel nuclei. And a heat insulating material 28, which is also made of graphite and disposed on the outer periphery of the heater 21. The coating gas and the flowing gas are discharged out of the furnace through the waste gas discharge rod 27.
JP 2000-284084 A

  In such a fluidized bed reactor, the gas ejection nozzle 23 is moved to remove the coated fuel particles having four layers coated on the fuel core 22 from the raw material and the fluidized gas inlet 26 at the bottom of the fluidized bed. In general, the ejection nozzle 23 and the reaction tube 25 are not mechanically fixed. For this reason, the coating gas and the flowing gas leak from the gap between the gas ejection nozzle 23 and the reaction tube 25 and fill around the heater 21 and the heat insulating material 28.

  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.

An apparatus for producing coated fuel particles for a HTGR according to the invention described in claim 1 includes a gas reservoir 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 fuel nuclear swelling, a second coating layer that consists of high-density pyrolytic carbon, and that holds gaseous fission products, and a solid fission product that consists of silicon carbide A third coating layer having a function of holding an object and a function as a main strength member of the coating layer, a function of holding a gaseous fission product made of high-density pyrolytic carbon, and a function of the third coating layer as a protective layer In a device for producing coated fuel particles for a high temperature gas reactor, comprising a fluidized bed reactor for applying a total of four coating layers with a fourth coating layer having
In order to discharge the coating gas and / or fluid gas leaked from the reaction tube of the fluidized bed reactor to the outside of the fluidized bed reactor, a sweep separate from the coating gas and fluidized gas outside the reaction tube in the fluidized bed. A sweep gas supply pipe for supplying gas toward the reaction pipe of the fluidized bed reactor is provided , and a sweep gas discharge port is provided on the side beyond the reaction pipe .

  An apparatus for producing coated fuel particles for a HTGR according to claim 2 is characterized in that the sweep gas according to claim 1 is an inert gas such as nitrogen gas or argon gas. To do.

  According to a third aspect of the present invention, there is provided an apparatus for producing HTGR coated fuel particles, wherein the sweep gas flowing in the region outside the reaction tube in the fluidized bed according to claim 1 or 2 is contained in the reaction tube. It is characterized by being discharged out of the fluidized bed from the same outlet as the flowing coating gas or flowing gas.

  In the present invention, as described above, the distribution of the coating temperature in the furnace, which greatly affects the characteristics of the coating layer, is constant without change even if it is repeatedly manufactured, and is suitable for continuous production. There is an effect that a particle production apparatus 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,
In order to discharge the coating gas and / or fluid gas leaked from the reaction tube of the fluidized bed reactor to the outside of the fluidized bed reactor, a sweep separate from the coating gas and fluidized gas outside the reaction tube in the fluidized bed. A sweep gas supply pipe for supplying gas 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.

  The present invention allows another gas (sweep gas) to flow in a region outside the reaction tube in the fluidized bed, and discharges the coating gas and fluidized gas leaking from the gap between the gas ejection nozzle and the reaction tube to the outside of the fluidized bed. It is characterized by. Even if hydrogen gas, which is a fluid gas, leaks from the gap between the gas ejection nozzle and the reaction tube when the third layer is coated, it is discharged out of the fluidized bed by another gas flow. It is possible to prevent hydrogen from reacting with graphite and reducing graphite.

  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.

  The sweep gas of the present invention is one that discharges the coating gas and / or fluid gas leaked from the reaction tube of the fluidized bed reactor to the outside of the fluidized bed reactor, and does not react with metals or graphite members at high temperatures. It is necessary to be. For example, an inert gas such as nitrogen gas or argon can be used.

Further, the supply pipe for supplying the sweep gas of the present invention discharges the coating gas and / or fluid gas leaking from the reaction pipe of the fluidized bed reactor to the outside of the fluidized bed reactor. It supplies toward the reaction tube, and a sweep gas discharge port is provided on the side beyond the reaction tube.

  Further, the discharge of the sweep gas supplied from the sweep gas supply pipe of the present invention may be discharged to the outside through a discharge port dedicated to the sweep gas, but the sweep gas does not react with a metal or a graphite member at a high temperature. Therefore, there is no problem even if mixed with a coating gas or a flowing gas. Therefore, preferably, the sweep gas flowing in the region outside the reaction tube in the fluidized bed is discharged from the fluidized bed through the same outlet as the coating gas and fluidized gas flowing in the reaction tube. It is not necessary to produce a simple exhaust port or exhaust gas treatment device.

  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. More specifically, the size of the fluidized bed reactor was about 700 mm × H about 2200 mm, and the size of the reaction tube was about 200 mm × H about 1000 mm.

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 and flowing acetylene (C ₂ H ₂ ) gas at about 1400 ° C. After coating the density carbon, propylene (C ₂ H ₆ ) was introduced at about 1400 ° C. to coat the second layer of high-density pyrolytic carbon, and then at about 1600 ° C. methyltrichlorosilane (CH ₂ SiCl _2). ) Was applied to coat the third layer of SiC, and finally, propylene (C ₂ H ₆ ) was introduced at about 1400 ° C. to coat the fourth layer of high-density pyrolytic carbon.

  When performing coating from the first layer to the fourth layer, nitrogen as a sweep gas was passed through the sweep gas supply port 10 in a region where the heater 11 and the heat insulating material 18 between the main body 19 and the reaction tube 15 existed. . The flow rate was 50 liters / minute. Nitrogen of the sweep gas and the coating gas and fluid gas leaking from the gap between the gas jet nozzle 13 and the reaction tube 15 are discharged from the waste gas discharge rod 17 to the outside of the furnace.

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

  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 is discharged out of the fluidized bed by another gas flow. In addition, it is possible to prevent the graphite, which is the material of the heat insulating material 17, from reacting with hydrogen and reducing the graphite.

  In addition, since the heater 11 and the heat insulating material 17 are not reduced, 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

10 ... Sweep gas supply port,
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 ... body,

Claims (3)

A first coating layer composed of low density pyrolytic carbon and having a function as a buffer for absorbing gas fission product gas reservoirs and fuel nucleus swelling, on the surface of a fuel nucleus sintered with uranium dioxide; A second coating layer made of pyrolytic carbon and having a function of holding a gaseous fission product, and a third coating layer made of silicon carbide and having a function of holding a solid fission product and a function as a main strength member of the coating layer And a fluidized bed reactor comprising a total of four coating layers comprising a high-density pyrolytic carbon and a fourth coating layer having a function of retaining gaseous fission products and a function as a protective layer of the third coating layer In the provided high temperature gas reactor coated fuel particle manufacturing apparatus,
In order to discharge the coating gas and / or fluid gas leaked from the reaction tube of the fluidized bed reactor to the outside of the fluidized bed reactor, a sweep separate from the coating gas and fluidized gas outside the reaction tube in the fluidized bed. Production of coated fuel particles for high-temperature gas reactors, comprising a sweep gas supply pipe for supplying gas toward the reaction pipe of a fluidized bed reactor, and a sweep gas outlet on the side beyond the reaction pipe apparatus.   The said sweep gas is inert gas including nitrogen gas and argon gas, The manufacturing apparatus of the coated fuel particle for high temperature gas reactors of Claim 1 characterized by the above-mentioned.   The sweep gas flowing in the region outside the reaction tube in the fluidized bed is discharged out of the fluidized bed from the same outlet as the coating gas or fluidized gas flowing in the reaction tube. Manufacturing equipment for coated fuel particles for HTGR.

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