JPS61201165A - Quantitatively determining method for free carbon in sintered graphite material - Google Patents

Abstract

PURPOSE:To permit the easy quantitative determination of the free carbon in a fuel compact by electrolyzing a sintered graphite material immersed into an oxidative acid soln. and determining quantitatively the weight loss of the solid matter generated when the solid residue after the decomposition is heated. CONSTITUTION:A coiled platinum anode 4 is inserted and disposed into a through-hole 5 of the fuel compact 2 and a cylindrical platinum cathode 3 is disposed to the outside circumference of the fuel compact 2. The sintered graphite material, for example, the fuel compact 2 is immersed into the oxidative acid soln. 1 and a voltage is impressed to both electrodes to electrolyze the compact. The solid residue of the compact 2 is filtered after the electrolysis and the resulted solid residue is heated to evaporated the free carbon of the higher order. The weight of the compact 2 prior to the electrolysis and the weight of the solid matter obrd. after the heating are measured and the free carbon in the compact 2 is calculated from the difference therebetween, by which the free carbon is easily quantitatively determined.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for quantifying free [e] elements in sintered graphite materials such as fuel compacts, and more specifically, to a method for obtaining highly reliable quantitative values in a short time. This is a method for quantifying free carbon in sintered graphite materials that can be obtained, and in terms of fuel compacts, it can be used safely without destroying coated fuel particles.
The present invention relates to a method for quantifying M release carbon that can quantify Ti release carbon.

[Prior art and its problems] Quantifying the amount of free a-carbon in a fuel compact is to determine the percentage of pitch or phenol resin added for forming the fuel compact that is carbonized and remains when the fuel compact is fired. By knowing this value, the density of the fuel compact can be known, which is important for quality control of the fuel compact.

Conventionally, in general, the method for quantifying free carbon in sintered pure graphite materials involves grinding a sample to 50 meshes or less, preferably 100 meshes or less by a physical grinding method, and boiling it in concentrated nitric acid for a long time to obtain a lower-order carbon. The free carbon is oxidized and volatilized as carbon dioxide gas, and the mixture after boiling is then filtered and the resulting residue is dried and heated to about 600°C to volatilize all the higher free carbons. The free carbon is determined from the difference between the weight and the solid content of the tunchu after heating.

However, since the method for quantifying free carbon uses instruments such as a mortar, a crusher, and a blender mill, when the method for quantifying free carbon is applied to the determination of mflll carbon in a fuel compact, the amount of coated fuel in the fuel compact is determined by the quantitative operation. Particles are destroyed, creating a risk of contaminating the surrounding area with radioactive nuclear fuel material. In addition, the boiling time with concentrated nitric acid is so long that low-order free carbon cannot be sufficiently oxidized even after boiling for more than a week, and quantitative analysis takes time. Furthermore, since a highly concentrated acid is used, there are drawbacks such as limited filtering media.

This invention has been made based on the above circumstances. That is, an object of the present invention is to provide a simple method for quantifying free carbon in which the coated fuel particles are not destroyed by the analytical operation and the analysis does not require a long time.

[Means for solving the above problems]

As a result of intensive research to solve the above problems, the inventor found that the above objective could be achieved by adopting an electrochemical crushing method, unlike the physical crushing method used in conventional quantitative methods. We have arrived at the invention of a lever.

That is, the outline of this invention is to electrolyze a sintered graphite material immersed in an oxidizing acid solution between a cathode and an anode, and to reduce the weight loss of solid content caused by heating the solid residue after electrolysis. This is a method for quantifying free carbon in a fuel compact.

Sintered graphite materials to be analyzed by the method of the present invention include those known per se, such as fuel compacts. A fuel compact is a compact made by mixing coated fuel particles and graphite powder and bonding them with a binder to form a compact, which is used as a fuel for a high-temperature gas reactor. As the binder, for example, phenol resin, pitch, etc. are used. In the present invention, there is no limitation as to whether the fuel compact is manufactured by an overpress coating method, an injection molding method, or the like.

In addition, there are various shapes of fuel compacts such as fuller/ ), dish, and chachufa, but regardless of the shape, if the fuel compact can be placed between the cathode and anode and electrolysis can be carried out, then There is no limit, however, in order to efficiently perform electrochemical crushing, as shown in FIG. A fuel compact 2 having a cylindrical shape is preferred.

The oxidizing acid solution l is not particularly limited as long as it is an acid that can generate an oxidizing substance capable of oxidizing free carbon in the fuel compact by electrolysis, and a nitric acid aqueous solution is particularly preferably used. Can be done. When using a nitric acid aqueous solution, the nitric acid concentration is usually 4 to 14N, preferably 6 to 11N. If the nitric acid concentration is lower than 4N, there may be disadvantages such as the current density decreases as the electrolysis progresses, and the electrolysis time becomes longer because fewer nitrogen oxides are generated. If the concentration is higher than the specified value, problems may occur, such as particle breakage due to the high liquid temperature, large amount of gas generated, and corrosion of equipment, etc.

As the electrodes used for electrolysis, for example, a platinum cathode and a platinum anode can be used. What are cathodes and anodes?
For example, when using the cylindrical fuel compact,
As shown in FIG. 1, it is preferable to insert a platinum anode 4 formed into a coil shape into a through hole 5 of the fuel compact, and to arrange a cylindrical platinum cathode 3 around the outer periphery of the fuel compact 2. be. In this invention, since it is sufficient to perform electrolysis with the fuel compact interposed between the cathode and the anode, there is no particular limitation on the shape and position of the cathode and anode, and as shown in FIG. In addition to the cathode and anode of the shape and arrangement shown, for example as shown in FIG.
The structure may be such that the electrolysis tank 6 is used as a cathode, and the plate-shaped or rod-shaped anode 4 is immersed in the oxidizing acid solution 1 filled in the electrolysis tank 6.However, it is possible to crush the fuel compact by electrolysis. Regarding this, the combination of electrodes having the shape and arrangement shown in FIG. 1 will be more effective than the one shown in FIG. 2.

The current density during electrolysis is usually 100m2 at the cathode.
The applied voltage is usually 2 to 18 V, preferably 5 to 15 V.

In the method of the present invention, as described above, a sintered graphite material such as the fuel compact 2 is immersed in an oxidizing acid solution l such as a nitric acid aqueous solution, and the fuel compact 2 is sandwiched between the fuel compacts 2 and the cathode as shown in FIG. For example, when a platinum cathode 3 and an anode such as a platinum anode 4 are arranged and nitric acid is electrolyzed by applying direct current to both electrodes, nitrogen oxides such as nitrogen monoxide, nitrogen dioxide, nitrogen trioxide, etc. are generated on the platinum cathode side. However, due to these nitrogen oxides, fuel compact 2
The free carbon inside is oxidized and becomes carbon dioxide gas, which is volatilized into the atmosphere, and unoxidized free carbon is eluted into the nitric acid solution.

At this time, the crushing of the fuel compact 2 and the oxidation of free carbon proceed simultaneously and within a short period of time.

After electrolysis, the solid residue of the fuel compact is filtered off, and the resulting solid residue is heated to volatilize higher free carbon.

For separating the solid residue by filtration, since the concentration of the oxidizing acid solution is not large, ordinary filtration means such as filter paper can be used, and the filtration means is not limited.

In addition, the heating of the obtained solid residue is usually 450 to 650
℃, preferably 550 to 600℃.

In this invention, lower-order free carbon in a sintered graphite material, such as a fuel compact, is oxidized by electrolysis and volatilized as carbon dioxide gas, and higher-order free carbon in the fuel compact is decomposed and volatilized by heating after electrolysis. Therefore, by weighing the weight of the fuel compact before electrolysis and the weight of the solid content obtained after heating, the free carbon in the fuel compact can be calculated and quantified from the difference.

[Effects of the Invention] According to the method of the present invention, when the sintered graphite material is a fuel compact, the fuel compact is crushed by electrolysis, so that the coated fuel particles in the fuel compact are not destroyed in any way, and the nuclear fuel material is Free carbon can be determined extremely safely with no risk of contaminating the surrounding area. Further, since the method of the present invention employs an electrochemical crushing method and a simple heating operation, free carbon can be accurately quantified in a short time and with a simple operation. Furthermore, since a highly concentrated oxidizing acid solution is not used during electrolysis, there is no restriction on the filter material in the filtration operation of the solid residue, and general-purpose filter paper can be easily used.

[Examples] Next, the present invention will be described in more detail by showing examples of the present invention.

(Example 1-13) Graphite powder in the amount shown in Table 1, coated fuel particles (coated with silicon carbide) in the amount shown in Table 1, and phenol resin were mixed and injection molded. Fuel compacts with the weights shown in the table were obtained.

As shown in FIG. 1, the fuel compact equipped with a coiled platinum anode and a cylindrical platinum cathode was immersed in a 9N nitric acid aqueous solution. Electrolysis of the nitric acid aqueous solution was carried out at a voltage of 15V for 8 hours. The nitric acid concentration of the nitric acid aqueous solution after electrolysis was about 6N.Next, the nitric acid aqueous solution after electrolysis was concentrated to take out the solid residue, and this was
Heated to 0°C. Heating time is 2 hours.

The weight of the solid content after heating was weighed, and Table 1 shows the weighing results and the weight of free carbon obtained from the weighing results.

(Hereinafter, blank space) Table 1 If the weights of A and B in Table 1 do not change during the production of the fuel compact and the analysis of free carbon, the total weight of A and B should be the value of D. be. As the data in Table 1 shows, the ratio of the total weight of A and B to the weight of D is 98.8 to 100°2%, so the value of D can be calculated as an analytical quantitative value using this method. It is fully reliable.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing one aspect of electrolysis in the method of the present invention, and FIG. 2 is a longitudinal sectional view showing another aspect of electrolysis in the invention. 1...Oxidizing acid solution, 2...Fuel compact, 3.
・φ cathode, 4... anode. Patent applicant Nuclear Fuel Industry Co., Ltd. Figure 1 Figure 2

Claims (2)

[Claims] (1) A sintered graphite material immersed in an oxidizing acid solution is electrolyzed between a cathode and an anode, and the solid residue after electrolysis is heated to quantify the weight loss of the solid content. A method for quantifying free carbon in sintered graphite materials. (2) The method for quantifying free carbon in a sintered graphite material according to claim 1, wherein the sintered graphite material is fuel compact.