JP2008249608A - Method of measuring zirconium carbide layer density - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a density calculation method for a zirconium carbide layer that is the outermost layer of a zirconium carbide layer coated particle. <P>SOLUTION: The zirconium carbide layer is removed after measuring a mass W<SB>a</SB>and a volume V<SB>a</SB>of the zirconium carbide layer coated particle having the exposed zirconium carbide layer, and a mass W<SB>b</SB>and a volume V<SB>b</SB>of an obtained zirconium carbide layer removed particle to calculate a density ρ<SB>ZrC</SB>of the zirconium carbide layer, pursuant to Expression (1) ρ<SB>ZrC</SB>=(W<SB>a</SB>-W<SB>b</SB>)/(V<SB>a</SB>-V<SB>b</SB>), in this method of measuring the zirconium carbide layer density of the present invention. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a zirconium carbide layer density measuring method, and more particularly to a zirconium carbide layer density measuring method that can easily measure the density of zirconium carbide used as the third layer from the surface side of a fuel core.

  In the high temperature gas reactor, the core structure including the fuel is made of graphite having a large heat capacity and good high-temperature soundness. In a high-temperature gas furnace, by using a gas such as helium gas that does not cause a chemical reaction even at a high temperature, the cooling gas can be taken out even when the outlet temperature is high. High-temperature heat enables safe heat utilization in a wide range of fields such as hydrogen production and chemical plants as well as power generation.

The fuel for the HTGR of the HTGR is a total of four layers around a fuel core having a diameter of about 350 μm or more and 650 μm or less obtained by sintering uranium dioxide (hereinafter sometimes abbreviated as “UO ₂ ”) into a ceramic form. Coating.

The first layer is made of low-density pyrolytic carbon having a density of about 1 g / cm ³ , functions as a gas reservoir for gaseous fission products (hereinafter sometimes referred to as “FP”), and fuel nucleus. It functions as a buffer that absorbs swelling. The second layer is made of 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 made of carbon silicon (hereinafter sometimes abbreviated as “SiC”) or zirconium carbide (hereinafter sometimes abbreviated as “ZrC”), has a function of holding a solid FP, and is a coating layer. The main strength material. The fourth layer is made of high-density pyrolytic carbon having a density of about 1.8 g / cm ³ like the second layer, has a function of holding the gaseous FP, and also functions as a protective layer for the third layer. Have.

  The diameter of a general coated particle is about 500 μm or more and 1000 μm or less. The coated particles are dispersed in a graphite matrix and molded into a fixed fuel compact shape. In addition, a certain amount of compact is put in a cylinder made of graphite, and it is shaped like a fuel rod that is plugged up and down. Finally, the fuel rod is inserted into a plurality of insertion ports of the hexagonal column type graphite block, and a plurality of the hexagonal column type blocks are stacked in a honeycomb array to constitute a core.

  The HTGR fuel as described above is generally manufactured through the following steps.

  First, uranium oxide powder is dissolved in nitric acid to obtain a uranyl nitrate stock solution. Next, 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. As the thickener, for example, a polyvinyl alcohol resin, a resin having a property of solidifying under an alkaline condition, polyethylene glycol, Metrose, or the like can be used. The prepared dropping stock solution is cooled to a predetermined temperature to adjust its viscosity, and is dropped into an aqueous ammonia solution using a small-diameter dropping nozzle. The droplets dropped onto the aqueous ammonia solution are sprayed with ammonia gas before reaching the surface of the aqueous ammonia solution. Since the droplet surface is gelled by this ammonia gas, it is possible to prevent the droplet from being deformed when reaching the surface of the aqueous ammonia solution. Uranyl nitrate in the droplets in the aqueous ammonia solution sufficiently reacts with ammonia to become ammonium heavy uranate. Thereby, heavy uranium aqueous solution particles are formed in the aqueous ammonia solution. Heavy uranium ammonium particles are roasted in the atmosphere to form uranium trioxide particles, and then the uranium trioxide particles are reduced and sintered to form high density ceramic uranium dioxide fuel core particles. .

  The fuel core particles are loaded on the fluidized bed, and the coating is performed by thermally decomposing the gas for forming the coating layer. In the case of the first layer of low-density pyrolytic carbon, acetylene is pyrolyzed at about 1400 ° C. In the case of the high density pyrolytic carbon of the second layer and the fourth layer, propylene is pyrolyzed at about 1400 ° C. When the third layer is SiC, methyltrichlorosilane is thermally decomposed at about 1600 ° C., and when the third layer is ZrC, the coating is applied at about 1500 ° C. by the reaction of the formula (X).

被覆層が形成され、被覆燃料粒子を形成した後、高温ガス炉用燃料は、一般的な燃料コンパクトに成型される。この燃料コンパクトは、高温ガス炉用燃料を黒鉛粉末、粘結剤等からなる黒鉛マトリックス材とともに、中空円筒形等又は円筒形にプレス成型又はモールド成型したのち、焼成して得られる。

After the coating layer is formed and the coated fuel particles are formed, the HTGR fuel is formed into a general fuel compact. This fuel compact is obtained by press-molding or molding a high-temperature gas reactor fuel into a hollow cylindrical shape or a cylindrical shape together with a graphite matrix material made of graphite powder, a binder or the like and then firing it.

  Non-Patent Document 1 discloses a method for measuring the density of SiC when SiC is used as the third layer.

The coated fuel particles coated up to the fourth layer are mechanically broken and roasted at about 800 ° C. in an oxidizing atmosphere. As a result, the first layer, the second layer, and the fourth layer are oxidized to carbon monoxide or carbon dioxide and vaporized. The SiC layer of the third layer is kept as it is, and UO ₂ which is a fuel nucleus is oxidized to triuranium octoxide (hereinafter sometimes abbreviated as “U ₃ O ₈ ”). When this SiC and U ₃ O ₈ are boiled with a nitric acid solution, U ₃ O ₈ dissolves and only SiC fragments remain. The SiC debris is taken as the third layer test sample and taken out from the nitric acid solution.

  The density of the inspection sample taken out can be measured by, for example, the floating sedimentation method.

  Specifically, using a heavy liquid such as methylene iodide-benzene and confirming that the test sample floats in the heavy liquid for a certain period of time, the density of the heavy liquid is measured using a specific gravity bottle. This measured value is the density of SiC.

  The above density measurement method can be applied when the third layer of the coated fuel particles is SiC, but is difficult to apply when the third layer of the coated fuel particles is ZrC. The reason why it is difficult to apply is that when the coated fuel particles are roasted in the air, the volume of ZrC changes due to the oxidation of ZrC to zirconium oxide. It will be inaccurate. Moreover, even if it can be extracted in the form of ZrC by some method, it is difficult to find a suitable solvent because ZrC is considerably higher in density than SiC in the suspended sedimentation method used for measuring the density of SiC. The floating sedimentation method is not adopted.

Noriaki Kobayashi, Shusaku Shiozawa, Kimio Hayashi et al., “Fuel Inspection Standard for High Temperature Engineering Test Reactor” JAERI-M 92-079 (1992)

  The problem to be solved by the present invention is to provide a method for measuring the density of a zirconium carbide layer covering the outermost layer of the zirconium carbide layer-coated fuel particles without using the floating sedimentation method.

As a means to solve the above problems,
Claim 1
“First measurement step of measuring mass W _a and volume V _a of zirconium carbide-coated fuel particles having a plurality of coating layers formed on the outer surface of the fuel core and having an exposed zirconium carbide layer,
A removal step of removing the zirconium carbide layer;
A second measuring step of measuring mass W _b and volume V _b of the zirconium carbide layer-removed fuel particles formed by removing the zirconium carbide layer;
(1) a calculation step of calculating the density ρ _{ZrC of the} zirconium carbide layer by the formula,
A method for measuring the density of a zirconium carbide layer, comprising:
ρ _ZrC = (W _a −W _b ) / (V _a −V _b ) (1) ”,
Claim 2
“The removal step is characterized in that a heat treatment at 520 ° C. or more and 620 ° C. or less is performed on the zirconium carbide layer-coated fuel particles, and zirconium oxide generated by oxidation of zirconium carbide is removed by mechanical treatment or chemical treatment. The zirconium carbide layer density measuring method according to claim 1.

  According to the present invention, it is possible to easily measure the density of zirconium carbide, which was difficult with the floating sedimentation method.

  One embodiment of the method for measuring the density of the zirconium carbide layer of the present invention shown in FIG. 1 will be described.

  The zirconium carbide layer density measuring method of the present invention includes a first measuring step, a removing step, a second measuring step, and a calculating step.

  In the first measurement step, the mass and volume of the fuel particles coated with the zirconium carbide layer formed by covering the fuel core with a plurality of coating layers and exposing the zirconium carbide layer are measured.

  In other words, the zirconium carbide layer-coated fuel particles have a fuel nucleus and a plurality of coating layers covering the surface thereof, and the zirconium carbide layer is exposed. The fuel nucleus may be formed of a nuclear material such as uranium dioxide or plutonium oxide. The outermost layer of the coating layer may be formed of zirconium carbide, and the coating layers other than the outermost layer may be formed of carbon. Such zirconium carbide layer-coated fuel particles, for example, in the process of producing fuel particles for high-temperature gas reactors, after coating up to zirconium carbide, the flowing gas is stopped instantaneously, and a part of the coated particles being jetted Can be obtained by taking out

  The HTGR fuel particles can be produced by a conventionally known method. For example, high-density uranium dioxide fuel core particles in a ceramic form are supplied to a fluidized bed, and about 1300 to 300 in the fluidized bed. Carbon formed, for example, by decomposing acetylene at 1400 ° C. is deposited on the surface of the uranium dioxide fuel core particles to form a first layer of low-density pyrolytic carbon, and then, for example, propylene is decomposed at about 1400 ° C. Depositing the carbon formed on the surface of the first layer to form a second layer of high-density pyrolytic carbon and then reacting, for example, bromine and zirconium at about 600 ° C. with zirconium bromide and methane Is heated to about 1500 ° C. to form a third layer made of zirconium carbide, and finally, the surface of this third layer is formed with about 1 Propylene at 00 ° C. to deposit carbon is formed by pyrolysis, by forming a fourth layer of high density pyrolytic carbon is produced.

  In the present invention, the fuel particles obtained by forming a third layer of zirconium carbide obtained in the process of producing the fuel particles for a high temperature gas reactor are used as the zirconium carbide layer-coated fuel particles in the present invention. it can.

The mass of the zirconium carbide layer-coated fuel particles can be measured using an ordinary mass measuring device. The mass measuring device is appropriately selected according to the accuracy of measuring the density of the zirconium carbide layer, and examples thereof include an electromagnetic balance type electronic balance. The measured mass of the zirconium carbide layer-covered fuel particles is defined as W _{a in the} equation (1).

The volume of the zirconium carbide layer-coated fuel particles can be measured using a normal volume measuring method. The volume measurement method is appropriately selected according to the properties of the zirconium carbide layer-coated fuel particles, and examples thereof include an immersion replacement method and a gas replacement method. In the immersion replacement method, for example, a sufficient amount of immersion liquid to cover the zirconium carbide layer-coated fuel particles is weighed in a Chapman flask, and the precisely measured zirconium carbide layer-coated fuel particles are added to the immersion liquid and shaken. The volume of the immersion liquid replaced with the zirconium carbide layer-coated fuel particles can be measured by measuring the volume of the immersion liquid and the zirconium carbide layer-coated fuel particles after the air is expelled by means of, for example. The immersion liquid is appropriately selected according to the properties of the zirconium carbide layer-coated fuel particles, and for example, water or alcohol can be used. Further, in the gas replacement method, for example, two containers having a known volume and a constant volume that can be pressurized are connected via a valve, and when both containers are in an equilibrium state at atmospheric pressure, the valve is closed and After the zirconium carbide layer-coated fuel particles are charged into the container, the container into which the zirconium carbide layer-coated fuel particles are charged is pressurized and the valve is opened. The volume of the container charged with the zirconium layer-coated fuel particles, the volume of the container not charged with the zirconium carbide-coated fuel particles, the pressure when the container charged with the zirconium carbide-coated fuel particles was pressurized, and after pressurization The volume of the zirconium carbide-coated fuel particles can be measured from the equation of state using the pressure of the container after the valve is opened. The volume of the measured the zirconium carbide layer coated fuel particles and V _a is a (1) wherein.

  The removal step is a step of removing the zirconium carbide layer of the zirconium carbide layer-coated fuel particles.

In the removing step, for example, the zirconium carbide layer fuel particles whose mass W _a and volume V _a are measured are put into a heat treatment apparatus, and the zirconium carbide layer-coated fuel particles are converted into the zirconium carbide layer-coated fuel particles in an air atmosphere of 520 ° C. or more and 620 ° C. or less. Heat treatment is performed. If the heat treatment temperature is less than 520 ° C., zirconium carbide may not be oxidized. On the other hand, if it exceeds 620 ° C., the inner pyrolytic carbon layer may be oxidized, which is not preferable. As long as the object of the present invention is achieved and the zirconium carbide layer of the zirconium carbide layer-coated fuel particles is oxidized, the selection of the heat treatment apparatus and the heat treatment time are not limited. As the heat treatment apparatus, for example, a muffle furnace or a crucible furnace can be used. The heat treatment time is preferably, for example, 15 minutes or more and 5 hours or less. This is because when the heat treatment is performed for less than 15 minutes, the zirconium carbide layer-coated fuel particles may not be sufficiently oxidized, and when the heat treatment is performed for more than 5 hours, the oxidation of zirconium carbide is completed. This is because it is not economical because it may heat up. This heat treatment time is preferably determined appropriately according to the particle shape. Further, the environment in which the heat treatment of the zirconium carbide layer-coated fuel particles is performed may be in the air atmosphere because it is a suitable environment in which the heat treatment is economically performed, and there is a need to further shorten the heat treatment time. In some cases, heat treatment may be performed in an oxygen atmosphere by appropriately injecting oxygen.

  By this heat treatment, zirconium carbide in the zirconium carbide layer-coated fuel particles is oxidized to zirconium oxide.

  Zirconium oxide generated by the heat treatment of zirconium carbide often adheres to an inner layer adjacent to the zirconium oxide layer, and thus it is necessary to remove the zirconium oxide. There, the zirconium oxide is removed by mechanical or chemical treatment. Thereby, zirconium carbide layer-removed fuel particles obtained by removing the zirconium carbide layer from the zirconium carbide layer-coated fuel particles can be obtained.

  The zirconium carbide layer-removed fuel particles have a fuel nucleus and a plurality of coating layers covering the surface thereof, and are formed by removing the zirconium carbide layer constituting the outermost layer of the zirconium carbide layer-coated fuel particles. .

  Examples of the mechanical treatment include a treatment in which particles are put into a volatile organic solvent and zirconium oxide is removed by ultrasonic cleaning or the like. As the volatile organic solvent, it is preferable to select a solvent that does not affect the inner layer of the zirconium carbide layer. Examples of the volatile organic solvent include lower alcohols such as methanol, ethanol, and propanol, and lower ketones such as acetone.

  Examples of the chemical treatment include a treatment of removing zirconium oxide with a mixed solution of concentrated sulfuric acid, nitric acid, and hydrofluoric acid. As long as zirconium oxide can be removed, the treatment conditions of the mixed solution can be changed as appropriate. For example, the mixed solution may be heated to 100 ° C. or higher and 200 ° C. or lower in order to increase the efficiency of removing zirconium oxide.

  In the second measurement step, the mass and volume of the zirconium carbide layer-removed fuel particles obtained by removing the zirconium carbide layer constituting the outermost layer of the zirconium carbide layer-coated fuel particles are measured.

The second measuring step, after washing the zirconium carbide layer removing the fuel particles, dried, the mass of the zirconium carbide layer removing the fuel particles (the W _b in which the (1) formula.) And volume (this Is _{Vb in the} equation (1)). The apparatus and / or measurement method for measuring the mass and volume of the zirconium carbide layer-removed fuel particles and the apparatus and / or measurement method for measuring the mass and volume of the zirconium carbide layer-coated fuel particles may be the same. Well, and not necessarily the same. An apparatus and / or measurement method for measuring the mass and volume of the zirconium carbide layer-removed fuel particles is appropriately selected according to the properties of the zirconium carbide layer-removed fuel particles and the accuracy of measuring the density of the zirconium carbide layer. be able to.

In the calculation step, the density ρ _{ZrC of} zirconium carbide is calculated by the equation (1) using the measured mass W _a and mass W _b , volume V _a and volume V _b .
_ρZrC = (W _a −W _b ) / (V _a −V _b ) (1)
The calculated density of the zirconium carbide layer can be used as a management item for fuel particles including the zirconium carbide layer, and can be used for quality control of the fuel particles including the zirconium carbide layer.

FIG. 1 is a schematic view showing a processing procedure of zirconium carbide layer-coated fuel particles performed for density measurement of a zirconium carbide layer.

Explanation of symbols

1 Fuel particles (zirconium carbide coated fuel particles)
2 Fuel Core 3 Low Density Pyrolytic Carbon 4 High Density Pyrolytic Carbon 5 Zirconium Carbide 6 Zirconium Oxide 7 Fuel Particles (Zirconium Carbide Layer Removal Fuel Particles)

Claims (2)

A first measurement step of measuring _a mass W _a and a volume V _a of zirconium carbide-coated fuel particles having a plurality of coating layers formed on the outer surface of the fuel core and having an exposed zirconium carbide layer;
A removal step of removing the zirconium carbide layer;
A second measuring step of measuring mass W _b and volume V _b of the zirconium carbide layer-removed fuel particles formed by removing the zirconium carbide layer;
(1) a calculation step of calculating the density ρ _{ZrC of the} zirconium carbide layer by the formula,
A method for measuring the density of a zirconium carbide layer, comprising:
_ρZrC = (W _a −W _b ) / (V _a −V _b ) (1)   The removing step is characterized in that a heat treatment at 520 ° C. or more and 620 ° C. or less is performed on the zirconium carbide layer-coated fuel particles, and zirconium oxide generated by oxidation of zirconium carbide is removed by mechanical treatment or chemical treatment. The zirconium carbide layer density measuring method according to claim 1.

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