JP2006200935A - Method of marking molded fuel for high temperature gas furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To apply a marking display such as its kind and performance to molded fuel for a high temperature gas furnace such as a fuel compact, without having any influence on quality of a covered fuel particle. <P>SOLUTION: The marking display is printed by using ink just after press-molding the fuel compact for the high temperature gas furnace, and the ink is quickly dried by using the press temperature, and afterwards, an impurity component in the ink is removed in a preliminary baking process and a baking process of the fuel compact, and the component of the ink is carbonized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of marking on a molded fuel for a HTGR (for example, a fuel compact). More specifically, the uranium enrichment of the molded fuel, the coating particle filling rate, the amount of uranium for each molded fuel solid, The present invention relates to an improvement in a method for providing markings for indicating the physical properties and performance of a molded fuel.

  The HTGR consists of graphite that has a large heat capacity and maintains soundness at high temperatures, and uses helium gas that does not cause chemical reactions at high temperatures as a cooling gas. Therefore, inherent safety is high, and helium gas having a high outlet temperature of about 900 ° C. can be recovered, and this high-temperature heat can be used in a wide range of fields such as power generation, hydrogen production, and chemical plants.

The fuel of this HTGR is formed by coating four layers 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 coating of low density pyrolytic carbon with a density of about 1 g / cm ³ , which absorbs the function of the gaseous fission product (FP) as a reservoir and fuel nuclear swelling. It also has a function as a buffer. The second layer is a coating of high density pyrolytic carbon having a density of about 1.8 g / cm ³ , which has a retention function for gaseous FP. The third layer is a coating of silicon carbide (SiC) having a density of about 3.2 g / cm ³ , which has a function of holding solid FP and functioning as a main reinforcing member of the coating. Finally, the fourth layer, like the second layer, is a high-density pyrolytic carbon coating with a density of about 1.8 g / cm ³ , which is a gaseous FP retention function and third layer protection. It functions as a layer.

  Typical coated fuel particles have a diameter of about 500-1000 microns. The coated fuel particles are dispersed in a graphite matrix, and then molded into a fixed fuel compact shape. A fixed amount of the fuel compact is placed in a graphite tube, and the top and bottom are sealed with plugs to form fuel rods. The This fuel rod is inserted into a plurality of insertion ports of the hexagonal column type graphite block and becomes fuel for the high temperature gas furnace. A large number of hexagonal columnar graphite blocks are stacked in multiple stages on a honeycomb array to constitute a core.

  Generally, the fuel for the HTGR is manufactured as follows. First, uranium oxide powder is dissolved in nitric acid to form a uranyl nitrate stock solution, and pure water and a thickener are added to the uranyl nitrate stock solution and stirred to prepare a dropping stock solution. The thickener acts so that the dropped solution of the uranyl nitrate stock solution dropped into a spherical shape with its own surface tension during dropping. As such a thickener, a resin having a property of solidifying under an alkaline condition, for example, a polyvinyl alcohol resin, polyethylene glycol, or metroise can be used. The dripping stock solution prepared in this manner is cooled to a predetermined temperature and the viscosity is adjusted, and then dropped into ammonia water using a method of vibrating a small-diameter dropping nozzle.

  The droplet liquid is prevented from being deformed at the time of landing by spraying ammonia gas in a space until it reaches the surface of the aqueous ammonia solution to gel the surface. Uranyl nitrate is sufficiently reacted with ammonia in ammonia water to form particles of ammonium biuranate. These particles are roasted in the atmosphere to become uranium trioxide particles, and further reduced and sintered to become fuel nuclei of high-density ceramic uranium dioxide.

  Since the particle size and sphericity of the fuel nucleus greatly affect the production conditions of the coated fuel particle, the fuel nucleus is released to the coating step after performing the particle size selection and the sphericity selection.

In the coating process, fuel nuclei are loaded into a fluidized bed, and a reaction gas (coating gas) is supplied in the fluidized bed and thermally decomposed to be coated. The first layer of low density pyrolytic carbon is coated by pyrolyzing acetylene (C ₂ H ₂ ) at about 1400 ° C. The high density pyrolytic carbon of the second and fourth layers is coated by pyrolyzing propylene (C ₃ H ₆ ) at about 1400 ° C. The third layer of SiC is coated by pyrolyzing methyltrichlorosilane (CH ₃ SiCl ₃ ) at about 1600 ° C.

  Since the particle size and sphericity of the coated fuel particles greatly affect the production conditions of the overcoat particles, the coated fuel particles are released to the overcoat process after performing the particle size selection and the sphericity selection.

  The overcoat particles are formed by coating the coated fuel particles with a graphite matrix material composed of graphite powder and a binder. Since the particle size of the overcoat particles greatly affects the production conditions of the fuel compact, the overcoat particles are released to the compact press molding process after the particle size selection.

  The fuel compact is formed by warm-pressing overcoat particles into a hollow cylindrical shape or a cylindrical shape. The fuel compact is fired in order to remove the binder contained in the matrix material of the overcoat particles or to carbonize the matrix material.

  On the other hand, there are multiple types of fuel compacts with different uranium enrichments and coating fuel particle filling rates, and the amount of uranium for each fuel compact solid is important as an indicator of performance. When performing 100% inspection, it is necessary to identify the type and solidity of the fuel compact.

  However, unlike the light water reactor fuel pellet, the high temperature gas reactor fuel compact contains coated fuel particles that have the function of confining gaseous fission products (FP), so it can be stamped with a marking needle or a vibratory stamp. Such a mechanical marking method should be used to mark the fuel compact because it is likely to adversely affect the quality of the fuel compact. I can't.

  In addition, there is a known method for marking by using the uneven surface of a press mold that has been used conventionally in fuel pellets for light water reactors (see Patent Document 1). Since it is difficult to change and the amount of information is limited, it is difficult to use in a fuel compact that requires many different markings.

JP-A-10-090458

  The problem to be solved by the present invention is to provide a method for marking a molded fuel for a high-temperature gas reactor that can appropriately mark the molded fuel without affecting the quality of the coated fuel particles. It is in.

  The problem-solving means of the present invention is characterized in that immediately after press molding of a molded fuel for a high temperature gas furnace, printing is performed on the surface of the molded fuel using ink, and the ink is rapidly dried using the press temperature to give a marking display. An object of the present invention is to provide a marking method for a molded fuel for a HTGR.

  In the problem-solving means of the present invention, it is preferable that the impurity component in the ink is volatilized in the preliminary firing step of the molded fuel, and the ink component is carbonized by firing the molded fuel.

  According to the present invention, since the marking display is performed by printing using ink, there is no mechanical influence on the coated fuel particles, and information that cannot be identified by the uneven surface of the press die. Appropriate markings can be displayed on the molded fuel without causing an insufficient amount.

  Ink is also dried after press molding of the fuel compact and is rapidly dried using the press temperature, so that the marking display on the fuel compact is clear without causing rubbing when the product is handled or contact marking. Can be applied.

  Furthermore, the impurities contained in the ink are removed using the pre-firing process and the calcining process of the fuel compact, and the ink is carbonized, which may cause unexpected activation products when used in a nuclear reactor. Absent.

  An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 systematically shows a marking method of a fuel compact for a HTGR according to the present invention. Overcoat particles are put into a press mold and warm-pressed to produce a fuel compact (see step S1 in FIG. 1).

  Immediately after the fuel compact is press-molded in this way and taken out from the mold, as shown in FIG. 2, ink is used on the end face of the fuel compact 12 using a non-contact printer 16 such as an ink jet printer. The marking display 14 is printed (see step 2 in FIG. 1). Since the marking display 14 is printed immediately after being taken out of the press mold and before being cooled, the ink of the marking display 14 is rapidly dried using the press temperature.

  After the printed fuel compact 12 is cooled, the fuel compact 12 is sent to the preliminary firing step (see step 3 in FIG. 1). As described above, this pre-baking step removes the binder contained in the matrix material of the overcoat particles, and with this treatment, the carbon component is converted into an impurity component such as a dye in the ink of the marking display 14. Remove and evaporate.

  Finally, the fuel compact 12 is sent to a calcination process (see step 4 in FIG. 1). This calcination process carbonizes the matrix material in the overcoat particles as described above. The 14 ink components are also carbonized. Therefore, since only the carbon component remains in the marking display 14, when the fuel compact 12 is used as a fuel in the high temperature gas furnace, no activation product is generated from the ink component.

  The ink used in the marking method of the present invention is required to be free of components that are inconvenient for use as a fuel compact. Therefore, impurity analysis and activation analysis are performed in advance, and typical examples are boron and lead. Therefore, it is required to select and use an ink that does not contain an element having a neutron inhibiting ability or a halogen element.

  In the above embodiment, the case where the marking display is printed on the fuel compact has been described. However, as long as the process after press molding is the same, the fuel compact is not limited to the cylindrical or hollow cylindrical fuel compact. The present invention can also be applied to spherical fuel and other molded fuels for gas furnaces.

  In an embodiment of the present invention, the fuel compact 12 molded by a press mold has an outer diameter of about 26 mm and a height of about 39 mm, and the depth of one end face of the fuel compact 12 within the mold is about 5 mm. Four or more characters, for example, 5-6 alphanumeric characters, were printed on an area having a width of about 20 mm by an ink jet method, and were subjected to a pre-baking and baking process, and a marking display was made with ink that was carbonized without impurities. Even if various inspections and other processes for confirming the quality of this fuel compact were performed, the marking display did not disappear during that time, and the individual could be identified reliably.

  According to the present invention, since the marking display is performed by printing using ink, the coated fuel particles are not mechanically affected and the amount of information is not insufficient. Proper marking can be applied, and the ink is carbonized with impurities removed, so there is no unexpected activation product when used in a nuclear reactor, and industrial applicability. Will improve.

It is a schematic system diagram which shows the marking method of the shaping | molding fuel for high temperature gas reactors (fuel compact) based on this invention in order of a process. It is a perspective view in the state where the marking display is printed on the fuel compact.

Explanation of symbols

12 Fuel Compact 14 Marking Display 16 Contactless Printing Machine

Claims (3)

Immediately after press molding of a molded fuel for a high temperature gas furnace, printing is performed using ink on the surface of the molded fuel, and the ink is rapidly dried using the press temperature to display a marking. Marking method for molded fuel. 2. The marking method for a molded fuel for a HTGR according to claim 1, wherein the impurity component in the ink is volatilized in the preliminary firing step of the molded fuel. . 3. A marking method for a molded fuel for a HTGR according to claim 1 or 2, wherein the ink component is carbonized in a firing step of the molded fuel. .

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