JP2006266805A - Manufacturing equipment and manufacturing method for coated fuel particle for high-temperature gas-cooled reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more efficiently and safely form the first coated layer to the fourth coated layer. <P>SOLUTION: In a manufacturing equipment of coated fuel particle for high-temperature gas-cooled reactors, the raw material gas is discharged for supplying from a gas discharge nozzle device into a reaction vessel and fluidizing and heating uranium dioxide fuel kernel with the discharge flow so that kernel surface of the fuel is coated with an molecule evaporation layer of a material molecule by a stuff gas thermal decomposition reaction. For a sampling mechanism for extruding the fuel kernel in the reaction vessel out to the external sample vessel during coating reaction, a sample receiver for receiving fuel kernel passing through the nozzle hole which has an inner diameter allowing passing of the fuel kernel as at least a part of the gas discharge nozzle device when the material gas discharge is stopped, and is penetrated through the bottom of the reaction vessel and falling down, a sample extrusion pipe for extruding the fuel kernel from the sample receiver to outside by natural fall, a sample vessel for containing the fuel kernel falling from the sample extrusion pipe, and an on-off valve provided to the sample extrusion pipe are provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus for producing coated fuel particles constituting, for example, a loaded fuel of a HTGR, and more particularly to a fuel nucleus sampling mechanism in a coating layer forming process.

  High temperature gas reactors have inherent safety by using a gas coolant that does not cause chemical reactions even at high temperatures, such as helium, which is formed of graphite with a large heat capacity and good high temperature integrity. The reactor is capable of extracting helium gas with a high and high outlet temperature, and the resulting 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 for such a high temperature gas reactor is generally composed of a fuel nucleus having a diameter of about 350 to 650 μm, which is obtained by sintering uranium dioxide produced from a solution containing uranium as a starting material into a ceramic form, and the outer surface of the fuel nucleus. Using coated fuel particles formed with a plurality of coating layers.

For example, a low density pyrolytic carbon layer having a density of about 1 g / cm ³ is formed as a first coating layer, and a high density pyrolytic carbon having a density of about 1.8 g / cm ³ is formed as a second coating layer. Forming a layer, and further forming a silicon carbide (SiC) layer with a density of about 3.2 g / cm ³ as a third coating layer and a high-density pyrolytic carbon layer with a density of about 1.8 g / cm ³ as a fourth coating layer. In general, a coating with a total of four layers is applied.

  The first coating layer has both a function as a gas stopper for gaseous fission products and a function as a buffer for absorbing deformation of the fuel nucleus. The second coating layer has a function of holding gaseous fission products, and the third coating layer has a function of holding solid fission products, and is a main strength member of the coating layer. The fourth coating layer has a function as a protective layer of the third coating layer as well as the function of holding the gaseous fission product similar to the second coating layer.

  Typical of such coated fuel particles are about 500-1000 μm in diameter. The coated fuel particles are dispersed in a graphite base material and formed into a compact fuel compact shape. Further, a fixed amount of the compact is put into a graphite tube, and the fuel rod 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.

  The fuel core before coating, which is a general coated fuel particle, is manufactured by the following process, and the external gelation method that obtains gel-like particles by vibration dripping is often used as a method capable of mass formation. Yes. Specifically, first, a powder of uranium oxide is dissolved in nitric acid to obtain a uranyl nitrate stock solution, and pure water and additives are added to the uranyl nitrate stock solution and stirred to obtain a dripping stock solution. The additive is a thickening agent that causes the dripped uranyl nitrate droplet to become spherical due to its surface tension during dropping, and at the same time is added to cause the stock solution to gel by contact with ammonium. Examples thereof include polyvinyl alcohol resins, resins having a property of gelation under alkaline conditions, polyethylene glycol, and metroses.

  The dripping stock solution prepared as described above is cooled to a predetermined temperature, adjusted in viscosity, and then dropped into an aqueous ammonia solution by vibrating a small-diameter dropping nozzle. The undiluted solution that has entered the aqueous ammonia solution as droplets is allowed to react sufficiently with the ammonia uranyl nitrate, and at the same time the additive is gelled to form gel-like particles containing ammonium heavy uranate (ADU). The obtained ADU gel particles are roasted in the air, moisture and additives are removed to form uranium trioxide particles, and further reduced and sintered to form spherical fuel composed of high-density ceramic uranium dioxide. Become the nucleus.

  As a manufacturing process of the coated fuel particles using the fuel core, the fuel core is introduced into the reaction vessel of the fluidized bed, and the raw material gas of the coating layer that also functions as a flowing gas for flowing the fuel core is introduced into the gas. There is a method in which coating is carried out by feeding to the bottom of the reaction vessel through a tube, ejecting from the gas ejection nozzle opening in the bottom to the inside of the reaction vessel, and thermally decomposing here (see, for example, Patent Document 1). .

For example, in the case of the low-density carbon layer of the first coating layer, acetylene (C ₂ H ₂ ) is thermally decomposed at about 1400 ° C., and the high-density pyrolytic carbon layer of the second and fourth coating layers. Is carried out by thermally decomposing propylene (C ₃ H ₆ ) at about 1400 ° C. In the case of the SiC layer of the third coating layer, methyltrichlorosilane (CH ₃ SiCl ₃ ) is thermally decomposed and coated at about 1600 ° C.

  A general fuel compact is obtained by press-molding or molding coated fuel particles into a hollow cylindrical shape or a cylindrical shape together with a graphite matrix material made of graphite powder, a binder, and the like, and then firing.

JP-A-5-273374

  In the production process of the coated fuel particles as described above, the formation from the first coating layer to the fourth coating layer is the same as a continuous series of steps by changing the heating temperature by switching to the corresponding source gas. It can be carried out in a fluidized bed reaction vessel.

  However, in order to inspect the performance such as the appearance, thickness and density of each coating layer, it is necessary to sample fuel nuclei at the end of the formation of each coating layer. A stainless steel rod with a sampling rod-like sampling container was inserted into the container through the window for use, and the fuel nucleus in the flowing state was inserted into the sampling container to remove the fuel nucleus.

  For this reason, when opening the sampling window, there is a risk that the operator will be exposed to very high temperature hot air, and in order to prevent this, the process is interrupted for each sampling, and the reaction vessel is cooled. Measures were necessary, and the formation steps from the first to the fourth coating layers could not be carried out continuously.

  In addition, since sampling is performed with the fuel nucleus flowing due to the inflow of argon gas, soot generated by the coating or dust containing uranium ground from the fuel core rises up at the same time. There was also a risk of being released outside the device.

  In view of the above problems, an object of the present invention is to provide a manufacturing apparatus and a manufacturing method for coated fuel particles for a high-temperature gas reactor capable of forming the first coating layer to the fourth coating layer more efficiently and safely than in the past. It is to provide.

  In order to achieve the above object, in the coated fuel particle manufacturing apparatus for a HTGR according to the first aspect of the present invention, a coating material gas is jetted and supplied from a gas jet nozzle device into a reaction vessel containing a uranium dioxide fuel nucleus. In the coated fuel particle manufacturing apparatus for high temperature gas reactors, in which the surface of the fuel nucleus is coated with the vapor deposition layer of the coating raw material molecule by the thermal decomposition reaction of the raw material gas by heating the fuel nucleus while flowing in the jet, A sampling mechanism for deriving fuel nuclei in the reaction vessel to an external sample vessel, and a nozzle hole penetrating in the bottom of the reaction vessel with an inner diameter allowing passage of fuel nuclei as at least part of the gas ejection nozzle device The sampling mechanism includes a sample receiver that receives fuel nuclei falling through the nozzle hole in a state where the injection of the raw material gas is stopped, and the sample receiver A sample derivation pipe for deriving fuel nuclei from the fuel receptacle to the outside by natural fall, a sample container for containing fuel nuclei falling from the sample derivation pipe, and an on-off valve device provided in the sample derivation pipe; It is equipped with.

  Moreover, in the coated fuel particle manufacturing apparatus for a high temperature gas reactor according to the invention described in claim 2, in the coated fuel particle manufacturing apparatus for a high temperature gas reactor according to claim 1, the sample container has an end of the sample outlet pipe. It is detachably attached to the part.

  According to a third aspect of the present invention, there is provided a method for producing a coated fuel particle for a HTGR, wherein a coating material gas is jetted and supplied into a reaction vessel containing a uranium dioxide fuel nucleus, and the fuel nucleus is heated while flowing through the jet stream. In the method for producing coated fuel particles for a high-temperature gas reactor in which the surface of the fuel nucleus is coated with a vapor deposition layer of coating raw material molecules by a pyrolysis reaction of the raw material gas, the fuel nucleus in the reaction vessel is transferred to an external sample container during the coating reaction. A sampling step for deriving, wherein the sampling step stops the supply of the raw material gas to settling the fuel nuclei flowing in the reaction vessel, and the settling fuel nuclei pass through the fuel nuclei at the bottom of the reaction vessel And dropping into the sample container through a nozzle hole penetrating in a possible manner.

  In the HTGR coated fuel particle manufacturing apparatus of the present invention, the fuel nucleus in the reaction vessel can be taken out by the sampling mechanism without opening the upper cover window of the reaction vessel. It is not necessary to interrupt the coating reaction by cooling the inside of the reaction vessel for each formation up to the coating layer, and each coating layer forming process can be proceeded almost continuously, so that the efficiency of the manufacturing process of the coated fuel particles is totally improved. In addition to the improvement, there is also an effect that it is possible to ensure higher safety because the danger of the operator being exposed to high-temperature hot air or the release of soot and dust containing uranium to the outside is avoided.

  In the coated fuel particle manufacturing apparatus for a HTGR according to the present invention, as a sampling mechanism for deriving the fuel core in the reaction vessel to an external sample vessel, at least one of the gas ejection nozzle devices for ejecting the coating raw material gas into the reaction vessel. The nozzle hole of the part is used.

  That is, in the sampling mechanism of the present invention, the nozzle hole used for sampling is formed in the bottom of the reaction vessel with an inner diameter that allows the passage of fuel nuclei, so that the reaction can be performed in a state where the injection of the raw material gas is stopped. The fuel core in the container passes through the nozzle hole and drops to the sample receiver, and the fuel core received in the sample receiver naturally falls in the sample outlet pipe from the sample receiver to the external sample container. It is to be accommodated.

  Therefore, in the present invention, when each coating layer forming step is completed, or when switching to the source gas for forming the next coating layer, the fuel nucleus only receives the sample from the nozzle hole due to its own weight. Since the sample container can be automatically taken out to the sample container, there is no need to interrupt the cooling of the container and the process can be immediately shifted to the next condition setting for coating layer formation. In addition, the formation process from the first to the fourth coating layer can be continuously advanced, and the efficiency of the production process of the coated fuel particles is improved.

  As described above, in the sampling mechanism of the present invention, sampling can be performed by dropping fuel nuclei from the nozzle holes when gas ejection is stopped. Therefore, the sampling amount is the number and size of nozzle holes that can pass through the fuel nuclei. The sampling amount can be easily controlled by adjusting the gas ejection stop time.

  The fuel nucleus as a sample contained in the sample container may be directly taken out from the sample container and used for analysis. However, if the sample container is detachably attached to the end of the sample outlet pipe. The sample fuel core can be moved together with the sample container, and the handling becomes simple. As a mechanism for attaching the sample container to the end portion of the sample outlet pipe, any mechanism that can be easily attached and detached, such as a clamp mechanism, can be used widely and is not particularly limited.

  Since the sample outlet pipe is provided with an on-off valve device, when the sample container is to be attached to and detached from the sample outlet pipe as described above, the fuel core sampling is usually performed by closing the valve. There is no problem if you forget to attach the sample container.

  The sample outlet pipe may be of any length that leads to the outside of the apparatus, but the fuel core immediately after being received in the sample receiver from within the reaction vessel at 1400 ° C. or higher also has high heat. The length of the fuel core may be set long enough to be cooled before reaching the sample container, or the fuel core may be naturally cooled in the sample container.

  In addition to the sample receiver that accepts fuel nuclei with high heat, the sample outlet pipe and the sample container are preferably made of a heat-resistant material such as stainless steel.

  In addition, the gas injection nozzle including the nozzle hole for dropping the fuel core communicates with the piping for supplying the raw material gas, so the sample receiver and the sample outlet piping are arranged so as not to interfere with the raw material gas supply piping. It shall be.

  The sample receptacle and sample container shall have a volume corresponding to the predetermined amount of fuel nuclei to be sampled, and the sample outlet piping shall have a diameter sufficient to allow the naturally falling fuel nuclei to pass through without stagnation. For example, the detailed design of the sampling mechanism may be appropriately selected based on the actual sampling plan.

  Further, in the method for producing fuel particles for a HTGR according to the present invention, as a sampling step for deriving the fuel nuclei in the reaction vessel to the external sample vessel during the coating reaction, The fuel nuclei are allowed to settle and fall into the sample vessel through a nozzle hole penetrating through the bottom of the reaction vessel so that the fuel nuclei can pass through. Opening of the reaction container such as the top cover window, which may cause the operator to be directly exposed to hot air inside the container, or dust and soot containing uranium to be discharged to the outside, as in the sampling method of scooping up fuel nuclei. Work safety is also improved.

  FIG. 1 shows a sampling mechanism of a coated fuel particle manufacturing apparatus for a HTGR according to an embodiment of the present invention. FIG. 1 is a schematic configuration diagram showing a lower region of the apparatus main body. The apparatus main body 1 has a double structure, and includes a reaction vessel 2 serving as a fluidized bed inside. A heating means (not shown) such as an electric heater is installed on the periphery of the reaction vessel 2 so that a coating raw material gas is supplied as a gas. A plurality of gas jet nozzles 3 formed so as to pass through the bottom of the main body and open to the bottom of the container through a pipe (not shown) are continuously supplied and injected into the reaction container 2. It is exhausted from the waste gas outlet.

  Therefore, the fuel nucleus charged into the reaction vessel 2 is flowed by the jet of gas supplied from the gas jet nozzle 3, and the raw material gas is thermally decomposed in this flow state, so that the raw material molecules are formed on the surface of the fuel core. The coating layer is formed by vapor deposition.

  In the sampling mechanism in this embodiment, at least one of the gas ejection nozzles 3 is a sampling combined nozzle hole having an inner diameter that allows passage of fuel nuclei, a sample receiver 4 installed below the nozzle hole, It is mainly composed of a sample outlet pipe 5 disposed from the lower side of the sample receiver 4 to the outside of the apparatus 1 and a sample container 6 installed at an end portion of the sample outlet pipe 5.

  The sample container 6 is detachably attached to the end of the sample outlet pipe 5 by a clamp 7. Further, the sample outlet pipe 5 was provided with an on-off valve device 8 near the end. Normally, by closing the sample outlet pipe 5 by the on-off valve device 8, even if the sample container 6 is forgotten to be installed and the sampling operation is started, the fuel nucleus that naturally falls from the sample receiver 4 is There is no risk of stopping at this closed part and being released outside.

  In the sampling mechanism configured as described above, the inner diameter of the sampling nozzle hole is about 4 mm, the size of the sample receiver 4 is about 25 mm × about 15 mm, the inner diameter of the sample outlet pipe 5 is about 15 mm, and the length is about 800 mm. In the coating reaction process from the first coating layer to the fourth coating layer in the coated fuel particle manufacturing apparatus in which the size of the container 6 is about 50 × 100 mm, after the formation of the first coating layer and after the formation of the second coating layer The cases where sampling was performed are shown below.

First, after attaching the sample container 6 to the end of the sample outlet pipe 5 with the clamp 7 and confirming that the on-off valve device 8 was closed, uranium dioxide was sintered in the reaction container 2 into a ceramic form. About 3.8 kg of fuel nuclei having an average diameter of about 0.6 mm are introduced, and the fuel nuclei are made into a fluid state by jetting and supplying acetylene (C ₂ H ₂ ) gas as the first coating material gas, and the inside of the reaction vessel 2 is about 1400 ° C. By adjusting under the heating conditions, a process for forming a first coating layer made of low density carbon by thermal decomposition of the coating raw material gas was started.

  When the formation of the first coating layer after maintaining the conditions of this formation process for a predetermined time is completed, the on-off valve device 8 is opened, the spraying of the coating material gas is stopped for 8 seconds, and then the on-off valve device 8 After closing, a flowing gas is introduced until the temperature reaches the second coating layer forming temperature, and the coated particles are caused to flow. At this time, a portion of the fuel core in which the first coating layer has been formed falls from the nozzle hole 3 and is received by the sample receiver 4 after being settled to the bottom of the container in 8 seconds when the gas ejection is stopped. Was naturally dropped and stored in the sample container 6.

  The taken-out first coating layer-formed fuel core sample is cooled in the sample container 6 for 5 minutes, and then moved to the observation step together with the sample container 6 removed from the pipe 5. In the sampling step at this time, about 60 g of the first coating layer formed fuel nucleus was taken out.

On the other hand, propellant (C ₃ H ₆ ), which is the second coating raw material gas, is jetted after the remaining first coating layer formed fuel nuclei are in a fluidized state and the reaction vessel 2 is heated to about 1450 ° C. Thereby, the formation process of the 2nd coating layer by a high-density pyrolytic carbon is performed. A new empty sampling container 6 is attached to the end of the sample outlet pipe 5 until the second coating layer forming step is completed.

  After a predetermined time, when the formation of the second coating layer is completed, after opening the on-off valve device 8, the spraying of the coating material gas is stopped for 4 seconds, and then the on-off valve device 8 is closed, Flowing gas is introduced until the third coating layer formation temperature is reached, and the coated particles are caused to flow. At this time, a part of the fuel core in which the second coating layer is formed falls from the nozzle hole 3 after being settled to the bottom of the container in a state where the gas ejection is stopped for 4 seconds, and is received by the sample receiver 4, and further the sample outlet pipe 5 The inside dropped naturally and was accommodated in the sample container 6.

  The taken-out fuel core sample with the second coating layer formed is cooled in the sample container 6 for 5 minutes, and then moved to the observation step together with the sample container 6 removed from the pipe 5. In the sampling process at this time, about 10 g of the second coating layer formed fuel nucleus was taken out.

Further, after the remaining second coating layer formed fuel nuclei are in a fluidized state and the inside of the reaction vessel 2 is heated to about 1650 ° C., methyltrichlorosilane (CH ₃ SiCl ₃ ), which is the third coating material, is jetted. Thereby, the formation process of the 3rd coating layer which consists of SiC is performed. After a predetermined time, when the formation of the third coating layer is completed, the injection of the raw material is stopped, the flow is switched to the inflow state of only the flowing gas, and the fourth coating layer forming temperature is adjusted to the heating condition of about 1400 ° C. Formation of the fourth coating layer made of high-density pyrolytic carbon is completed by spraying and supplying propylene, which is a raw material gas for the fourth coating layer, and maintaining the environment for a predetermined time.

  In addition, when the first coating layer formed fuel nucleus and the second coating layer formed fuel nucleus taken out by the above two samplings were observed, they were all good without any cracks or chips.

  As described above, in the coated fuel particle manufacturing apparatus for a HTGR according to the present embodiment, each coating layer can be formed safely without opening the container window, which involves not only hot air but also the risk of external discharge of dust and soot containing uranium. While sampling the fuel nuclei immediately thereafter, the formation process from the first coating layer to the fourth coating layer could be performed continuously without interruption such as cooling in the container.

It is a schematic block diagram of the apparatus lower area | region explaining the sampling mechanism with which the high temperature gas reactor fuel particle manufacturing apparatus by one Example of this invention was equipped.

Explanation of symbols

1: Device main body 2: Reaction vessel 3: Nozzle hole 4: Sample receptacle 5: Sample outlet piping 6: Sample vessel 7: Clamp 8: On-off valve device

Claims (3)

Covering the surface of the fuel core by the pyrolysis reaction of the raw material gas by supplying the coating raw material gas from the gas jet nozzle device into the reaction vessel containing the uranium dioxide fuel core and heating it while flowing the fuel core in the jet. In the coated fuel particle manufacturing apparatus for high temperature gas reactors coated with a vapor deposition layer of raw material molecules,
A sampling mechanism for deriving fuel nuclei in the reaction vessel to an external sample vessel during the coating reaction, and an inner diameter allowing passage of the fuel nuclei as at least a part of the gas ejection nozzle device penetrated at the bottom of the reaction vessel With nozzle holes,
The sampling mechanism is configured to receive a fuel nucleus falling through the nozzle hole in a state where the injection of the raw material gas is stopped, and to lead the fuel nucleus from the sample receiver to the outside by natural fall. A coating fuel for a high temperature gas reactor, comprising: a sample outlet pipe; a sample container for storing fuel nuclei falling from the sample outlet pipe; and an on-off valve device provided in the sample outlet pipe Particle production equipment.   2. The coated fuel particle manufacturing apparatus for a HTGR according to claim 1, wherein the sample container is detachably attached to an end portion of the sample outlet pipe. A coating material gas is sprayed and supplied into a reaction vessel containing uranium dioxide fuel nuclei, and the fuel nuclei are heated while fluidizing the fuel nuclei by the jet flow. In the method for producing coated fuel particles for a HTGR coated with
A sampling step for deriving fuel nuclei in the reaction vessel to an external sample vessel during the coating reaction;
The sampling step includes a step of stopping the supply of the raw material gas to settling fuel nuclei flowing in the reaction vessel, and a nozzle that penetrates the settling fuel nuclei at the bottom of the reaction vessel so that the fuel nuclei can pass therethrough. A method of producing coated fuel particles for a high-temperature gas reactor, comprising the step of dropping into the sample container through a hole and storing the sample container.

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