JP2006266806A - Manufacturing device of coated fuel particle for high-temperature gas-cooled reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing device of coated fuel particles for a high-temperature gas-cooled reactor to stabilize temperature distribution in the reactor even in performing continuous production, thereby stabilizing the quality of coating layers having an important role in a fissile material containment function of a high-temperature gas-cooled reactor fuel. <P>SOLUTION: This manufacturing device is equipped with a fluidized-bed reaction tube for forming a plurality of coating layers on a surface of a fuel core obtained by sintering uranium dioxide while causing a coating gas and/or a flowing gas to flow in a heating environment and a graphite heater for heating the reaction tube. This device is further equipped with an inert gas introduction tube for introducing inert gas into an outside region of the reaction tube and a control means for controlling the pressure of the inert gas in the outside region of the reaction tube so as to be equal to or higher than the inner pressure of the reaction tube. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 with a high heat capacity and good high-temperature soundness, and helium gas (He gas) that does not cause a chemical reaction even at high temperatures. It is possible to extract He gas with high outlet temperature and high outlet temperature, and 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.

The fuel of the HTGR is a fuel core having a diameter of 350 to 650 μm obtained by sintering uranium dioxide into a ceramic form and coating four layers. Of the four layers of coatings, the first layer is low density pyrolytic carbon with a density of about 1 g / cm ³ and functions as a reservoir for gaseous fission products (FP) and a buffer that absorbs fuel nuclear swelling. It also has the function as. 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 500 to 1000 μm. The coated fuel particles are dispersed in a graphite matrix and then molded into a fuel compact having a fixed shape. Furthermore, a certain amount of fuel compact is put into a cylinder made of graphite and plugged up and down to become a fuel rod. Finally, the fuel rod is inserted into a plurality of insertion ports of the hexagonal columnar graphite block, and becomes a fuel for the HTGR. Further, a large number of hexagonal columnar graphite blocks are stacked in a plurality of stages on the honeycomb array to constitute the core of the high temperature gas reactor.

  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, 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 spraying ammonia gas in a space until landing on the surface of the aqueous ammonia solution to gel the surface. In ammonia water, uranyl nitrate reacts sufficiently with ammonia 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-like 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 above-described 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 order to remove the coated fuel particles from the lower side of the fluidized bed by moving the gas ejection nozzle 23, the gas ejection nozzle 23 and the reaction tube 25 are generally not mechanically fixed. For this reason, the coating gas or the flowing gas leaks from the gap between the gas ejection nozzle 23 and the reaction tube 25 and fills the heater 21 and the heat insulating material 28 inside the apparatus main body 29.

  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 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 makes it possible to stabilize the temperature distribution in the furnace even in continuous production, and to stabilize the quality of the coating layer that plays an important role in the fissile material confinement action of the HTGR fuel. An object of the present invention is to obtain an apparatus for producing coated fuel particles for a HTGR.

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 or / and a flowing gas in a heating environment. In an apparatus for producing coated fuel particles for a high temperature gas furnace, comprising a fluidized bed reaction tube for forming a coating layer of the above and a graphite heater for heating the fluidized bed reaction tube,
An inert gas introduction tube for introducing an inert gas into the outer region of the fluidized bed reaction tube;
And a control means for controlling the inert gas pressure in the outer region of the fluidized bed reaction tube to be equal to or higher than the internal pressure of the fluidized bed reaction tube.

  According to a second aspect of the present invention, there is provided an apparatus for producing coated fuel particles for a high temperature gas reactor, wherein the inert gas introduced into the outer region of the fluidized bed reaction tube according to the first aspect is inert, typically argon. It is characterized by being a gas.

  The apparatus for producing coated fuel particles for a HTGR according to claim 3 is characterized in that the inert gas introduced into the outer region of the fluidized bed reaction tube according to claim 1 is nitrogen gas. It is what.

  According to a fourth aspect of the present invention, there is provided a manufacturing apparatus for coated fuel particles for a high temperature gas reactor, wherein the control means according to any one of the first to third aspects is not introduced into an outer region in a fluidized bed reaction tube. The pressure value of the active gas is controlled according to the coating layer.

  The present invention makes it possible to stabilize the temperature distribution in the furnace even in continuous production, and to stabilize the quality of the coating layer that plays an important role in the fissile material confinement action of the HTGR fuel. There is an effect that an apparatus for producing coated fuel particles for a high temperature gas reactor can be obtained.

In the present invention, a fluidized bed reaction tube that forms a plurality of coating layers on the surface of a fuel core obtained by flowing a coating gas or / and a fluidized gas in a heated environment to sinter uranium dioxide, and the fluidized bed reaction tube. In an apparatus for producing coated fuel particles for a high-temperature gas reactor equipped with a graphite heater for heating
An inert gas introduction tube for introducing an inert gas into the outer region of the fluidized bed reaction tube;
And a control means for controlling the inert gas pressure in the outer region of the fluidized bed reaction tube to be equal to or greater than the internal pressure of the fluidized bed reaction tube. As a result, even in the case of continuous production, it is possible to stabilize the temperature distribution in the furnace and to stabilize the quality of the coating layer that plays an important role in the fissile material confinement action of the HTGR fuel.

  That is, the present invention provides a gap between the gas ejection nozzle and the reaction tube by pressurizing the outer region of the fluidized bed reaction tube with an inert gas such as argon gas or nitrogen gas so as to be higher than the pressure inside the reaction tube. Therefore, it is possible to prevent leakage of the coating gas and the flowing gas, and it is possible to prevent graphite and hydrogen, which are materials of the heater and the heat insulating material, from reacting and reducing graphite.

  Furthermore, since there is no decrease in heaters and heat insulation, the temperature distribution in the furnace is stable without change even in continuous production, so the fissile material confinement action of the HTGR fuel, It becomes possible to stabilize the quality of the coating layer having a very important role.

  As the inert gas introduced into the outer region of the fluidized bed reaction tube in the present invention, a gas that does not easily react with other elements such as a rare gas such as argon, neon, and helium, or a nitrogen gas is used. More preferably, argon gas used as a flowing gas is suitable.

  If the inert gas pressure is controlled to be higher than the internal pressure of the fluidized bed reaction tube, the control means in the present invention makes it difficult for the gas in the reaction tube to leak out of the tube, but it is introduced into the outer region of the fluidized bed reaction tube. If the pressure of the inert gas is higher than the pressure in the tube, the inert gas may enter the reaction tube and change the ratio between the coating gas and the flowing gas (including inert gas). There is. Therefore, more preferably, the inert gas pressure is controlled to be equal to or slightly higher than the internal pressure of the fluidized bed reaction tube.

  In addition, in order to form each coating layer for a plurality of coating layers of fuel nuclei, the flow rate of the coating gas and the flowing gas differs depending on each coating layer. It depends on. Therefore, as a preferred embodiment, the control means controls the pressure value of the inert gas introduced into the outer region in the fluidized bed reaction tube according to the coating layer.

  FIG. 1 is an explanatory view showing a configuration of a production apparatus for coated fuel particles for a HTGR according to an embodiment of the present invention. As shown in FIG. 1, the apparatus for producing coated fuel particles for a high temperature gas reactor introduces a fuel core 12 made of uranium dioxide from an upper window (not shown) of a fluidized bed reaction tube 15 and introduces gas from a fluidized gas inlet 16. A fluidized bed reaction tube 15 for coating by flowing a coating gas and a flowing gas through the nozzle 14 and the gas ejection nozzle 13; a graphite heater 11 disposed on the outer periphery of the reaction tube 15 for heating the fuel core; It is also made of graphite, and further includes a heat insulating material 18 disposed on the outer periphery of the heater 11. The coated gas and fluidized gas are discharged out of the furnace through the waste gas discharge port 17, and the coated coated fuel particles are removed from the fluidized gas inlet 16.

  The size of the apparatus for producing coated fuel particles for a HTGR was about 700 mm × H about 2200 mm, and the size of the fluidized bed reaction tube was about 200 mm × H about 1000 mm.

In the production of the coated fuel particles, uranium dioxide fuel nuclei 12 having an average diameter of 0.6 mm are placed in about 3 kg fluidized bed reaction tube 15 and acetylene (C ₂ H ₂ ) gas is introduced at about 1400 ° C. Low density carbon was coated. Thereafter, propylene (C ₃ H ₆ ) was introduced at about 1400 ° C. to coat the second layer of high-density pyrolytic carbon. Next, methyltrichlorosilane (CH ₃ SiCl ₃ ) was introduced at about 1600 ° C. to cover the third SiC layer. Finally, propylene (C ₃ H ₆ ) was introduced at about 1400 ° C. to coat the fourth layer of high-density pyrolytic carbon.

  When coating from the first layer to the fourth layer, the region where the heater 11 and the heat insulating material 18 exist between the apparatus main body 19 and the reaction tube 15 is pressurized with argon gas using the inert gas introduction tube 10. . As a result, even when the coating operation was repeatedly performed, deterioration due to the generation of hydrocarbons in the heater 11 and the heat insulating material 18 was not observed, and stable quality coated fuel particles could be obtained. The inert gas introduction pipe 10 is provided with a conducting pipe 8 that conducts with the argon gas cylinder 9, and a control device 7 that controls the pressure inside the apparatus main body 19 to a predetermined value in the middle of the conducting pipe 8. The control device 7 controls the pressure values set in advance from the first layer to the fourth layer.

  Since the pressure in the reaction tube during coating was the highest during the third coating, the pressure outside the reaction tube was set to 0.2 MPa (gauge pressure) slightly higher than the pressure in the reaction tube during the third coating. Although this numerical value is the coating condition of the third layer, it depends on the flow rate and temperature, and the pressure on the outside of the reaction tube should be equal to or higher than the pressure on the inside depending on the coating condition. . In this embodiment, the pressure outside the reaction tube during coating is constant at 0.2 MPa (gauge pressure), but may be changed for each coating layer.

  As described above, the hydrogen gas, which is a flowing gas, can be prevented from leaking from the gap between the gas ejection nozzle 13 and the reaction tube 15 when the third coating layer is formed. 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 when continuously produced. 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 the manufacturing apparatus of the coating | coated fuel particle | grain for high temperature gas reactors of one Example 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

7 ... Control device,
8 ... conducting tube,
9 ... Argon gas cylinder,
10 ... inert gas introduction pipe,
11 ... Heater,
12. Fuel kernel,
13: Gas ejection nozzle,
14 ... Gas introduction nozzle,
15 ... Fluidized bed reaction tube,
16 ... Fluid gas inlet,
17 ... Waste gas outlet,
18 ... heat insulation,
19 ... the device body,

Claims (4)

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 or / and a flowing gas in a heating environment to sinter uranium dioxide, and a graphite heater for heating the fluidized bed reaction tube In the apparatus for producing coated fuel particles for a HTGR comprising:
A tube for introducing an inert gas into the outer region of the fluidized bed reaction tube;
An apparatus for producing coated fuel particles for a HTGR, comprising a control means for controlling an inert gas pressure in an outer region of the fluidized bed reaction tube to be equal to or greater than an internal pressure of the fluidized bed reaction tube.   2. The apparatus for producing coated fuel particles for a high temperature gas reactor according to claim 1, wherein the inert gas introduced into the outer region in the fluidized bed reaction tube is an inert gas typified by argon.   2. The apparatus for producing coated fuel particles for a high temperature gas reactor according to claim 1, wherein the inert gas introduced into the outer region in the fluidized bed reaction tube is nitrogen gas. The said control means controls the pressure value of the inert gas introduce | transduced into the outer area | region in a fluidized-bed reaction tube according to a coating layer, The any one of Claims 1-3 characterized by the above-mentioned. Manufacturing equipment for coated fuel particles for HTGR.

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