JPS62107895A - Sealing method for high-temperature heat-resistant capsule - Google Patents

Abstract

PURPOSE:To seal a capsule consisting of W, etc., having the m. p. higher than the m. p. of a high melting nuclear fuel material such as nuclear fuel material without exerting a thermal influence upon the nuclear fuel material by forming the sealing part of the capsule and cap into a thin-walled construction and quickly welding the same with the smaller welding energy in the stage of sealing the above-mentioned nuclear fuel material into the above- mentioned capsule. CONSTITUTION:The high melting nuclear fuel material such as nuclear fuel material is put into the capsule body 10 made of W having the m. p. further than the m. p. of the nuclear fuel material and the cap 14 made of W is welded thereto to seal the nuclear fuel material into the capsule in the case of measuring the m. p. of the above-mentioned nuclear fuel mate rial by a heat detaining method of the capsule sealing type. A thin-walled opening edge 18 is provided to the opening at the top end of the above-mentioned cylindrical capsule 10 made of W and a thin-walled riser part 16 provided to the peripheral part of the cap 14 is fitted to the step part 20 thereof. The step part 24 is welded by an electron beam welding method. Since the two members 16, 18 in the fitting part are thin-walled, the quick welding is executed with the smaller welding energy and the nuclear fuel material can be sealed into the capsule with substantially no thermal influence of welding on the nuclear fuel material in the capsule.

Description

DETAILED DESCRIPTION OF THE INVENTION E. Industrial Field of Application The present invention relates to a method for melt-sealing capsules made of high-melting point metal so as not to exert much thermal influence on the enclosed objects, and is not particularly limited. However, the present invention relates to a method for melt-sealing a high-temperature heat-resistant capsule, which is suitable for producing a sample for measuring the melting point of a nuclear fuel material by a thermal retention method, for example.

[Prior Art] One of the methods for measuring the melting point (approximately 2,500 to 2,800° C.) of nuclear fuel materials such as uranium oxide and plutonium oxide is a sealed-capsule thermal retention method. In this method, nuclear fuel material is sealed in a capsule in advance, and the melting point is measured by detecting a decrease in the temperature rise rate of the capsule due to latent heat when the enclosed substance melts during temperature rise.

Therefore, in preparation for measurement, it is necessary to seal the objects to be enclosed in a capsule made of a high melting point metal such as tungsten (melting point: about 3000° C.).

The conventional technology adopts a configuration in which the object to be enclosed is placed in a bottomed cylindrical capsule body, a disk-shaped lid is simply fitted into the upper opening of the capsule body, and the surrounding area is melt-sealed by electron beam welding or the like. It is being

[Problems to be solved by the invention] However, during melt sealing, the temperature of the welded part is higher than the melting point of the capsule constituent material (i.e., about 30°C in the case of tungsten force cells).
00°C or higher), which has a large thermal effect on the substance to be enclosed within the capsule, and there is a problem in that the substances that can be encapsulated are limited.

Therefore, for example, in the case of spent nuclear fuel material in a nuclear reactor, capsule melting is impossible because the welding heat input applied during the melting process releases the gases and volcanic substances contained therein.

For this reason, the materials to be enclosed were limited to unused nuclear fuel material from nuclear reactors that generate little gas.

However, as a practical matter, the melting point of the nuclear fuel material used in a nuclear reactor is one of the most important physical properties in the design process. The melting point of radioactive materials subjected to irradiation may be affected by the possibility of melting point depression due to the formation of multi-component materials between fission products and nuclear fuel materials, changes in the molar ratio of oxygen and metal due to irradiation, and segregation of uranium and plutonium. This is because melting point measurement using spent nuclear fuel material is an extremely important measurement item as it may change.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to make it possible to exert almost no thermal influence on enclosed objects such as spent nuclear fuel materials, which are likely to release gases and volatile substances. The object of the present invention is to provide a method that allows the capsule to be melt-sealed into a capsule made of a high-melting-point metal without any problems.

[Means for Solving the Problems] The present invention, which can achieve the above objects, has a thin wall structure for the joint between the capsule body and the lid made of a high-melting point metal, so that it can be melted quickly with less welding energy. This is a method of sealing.

That is, in the present invention, the lid has a structure in which a thin rising portion is formed around a plate-shaped lid body, and the cylindrical capsule body has a structure in which a thin-walled opening edge is formed at the end. Then, the lid is fitted so that its thin-walled rising portion is surrounded by the thin-walled opening edge of the capsule body, and welded by electron beam welding or the like so that the thin-walled opening edge and the end of the thin-walled rising portion that are in contact with each other are rounded. This is a method of sealing.

Such a method of melt-sealing a high-temperature heat-resistant capsule is particularly suitable for preparing a sample for measuring the melting point of an oxide nuclear fuel material by a thermal retention method, for example. In that case, tungsten or the like is used as the constituent material of the capsule body and lid.

[Operation] Do the capsule body and the lid hold their thin parts together? Because of the 8-contact structure, melting can be carried out quickly with less energy, making it possible to reduce the thermal influence on the objects enclosed in the capsule as much as possible. In addition, since only the part to be welded is thinned, it is difficult for welding heat input to be transmitted to the capsule body side, and heat is difficult to accumulate inside the capsule.

Therefore, even spent nuclear fuel material, which has conventionally been considered impossible to melt into a capsule due to the gases and volatile substances contained therein, can be melt-sealed into a capsule made of a high-melting point metal.

[Example] Fig. 1 is a longitudinal cross-sectional view showing an example of a high temperature heat-resistant capsule used to carry out the method of the present invention, and Figs. 2 and 3 are enlarged explanatory views of the welded portion thereof.

The high-temperature heat-resistant capsule includes a bottom cylindrical capsule body 10 made of a high-melting point metal such as tungsten, and a capsule body 10 made of a high-melting point metal such as tungsten that covers the top opening.
It consists of 12. The lid 12 has a structure including a disc-shaped lid main body 14 and a thin raised portion 16 formed around the lid main body 14. On the other hand, the capsule main body 10 has a thin opening edge 18 at the upper end, and has an IEI on the inner peripheral surface side slightly below the opening edge 18.
This is a structure in which a stepped portion 20 is formed to receive the outer periphery of the lower surface of 2. The tube body 22 of the back cover, which stands upright from the center of the bottom surface of the push cell main body 10, is for temperature measurement by the heat retention method.

The temperature rise of the enclosed object (sample) in the high-temperature heat-resistant capsule can be continuously measured using a two-color thermometer through the temperature measurement hole 23.

In the present invention, as clearly illustrated in FIG.
2 is fitted onto the stepped portion 20 so that its thin rising portion 16 is surrounded by the thin opening edge 18 of the capsule body 10. After filling the capsule body 10 with the substance to be enclosed and covering it with the lid 12, the upper ends of the thin opening edge 18 and the thin rising portion 16 that are in contact with each other are welded by electron beam welding or the like so as to be rounded. The welded portion is designated by the reference numeral 24 (see FIG. 3).

Next, we will discuss the results of actual prototype experiments.

A high-temperature, heat-resistant capsule whose capsule body 10 and lid 12 are made of tungsten is filled with approximately Log of spent plutonium oxide nuclear fuel containing a large amount of gas and volatile substances, and then melt-sealed by electron beam welding. , it was possible to completely melt-seal without releasing gas or volatile substances from inside. In order to measure the melting point of the spent nuclear fuel material using this fused capsule, the temperature was raised to approximately 2900℃, but there was no leakage from the capsule, and the capsule remained sound during the melting point measurement and clear melting point data was obtained. It was done.

FIGS. 4 and 5 are enlarged explanatory views showing other examples of the joint portion between the capsule body and the lid used in the present invention, respectively. 4 shows a case where the thickness t of the joint part is equal to the thickness T of the capsule body 12, and FIG. 5 shows a case where the thickness t of the joint part is thicker than the thickness T of the capsule body 12. If the thickness T of the capsule body 12 is quite thick, a step 26 may be provided on the outside as in the embodiment shown in FIG. A step 20 is formed only on the inner surface of the opening edge 18, and the lid 12 is formed thereon.
It is also possible to have a structure that holds the .

Although the preferred embodiments of the present invention have been described in detail above, the shapes of the capsule body and lid can be modified in various ways within the scope of the present invention, and their constituent materials are not necessarily limited to tungsten. . It goes without saying that the application of the capsule is not limited to the melt-sealed capsule used in the heat retention method, but can be applied to a wide range of fields including the melt-sealed portion of capsules made of high-melting point metals.

[Effects of the Invention] As described above, the present invention has a configuration in which the joint between the capsule body and the lid has a thin wall structure, and the ends of the thin joint are melt-sealed in a rounded manner, so that less energy is required for welding. (In addition, the heat applied during welding is concentrated in the thin-walled joint, making it difficult to accumulate in the capsule, which has the excellent effect of reducing the thermal influence on the enclosed object.)

For this reason, for example, when manufacturing sealed capsules used to measure the melting point of nuclear fuel materials using the thermal retention method, spent nuclear fuel materials that could not be sealed with conventional technology because the gases and volatile substances contained therein would be released. However, the method of the present invention has an excellent effect in that it can be completely sealed in a capsule and good thermal measurement data can be obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a longitudinal cross-sectional view showing an example of a high melting point metal capsule used in the present invention, Fig. 2 is a cross-sectional view of essential parts showing the fitted state of the joint, and Fig. 3 is a longitudinal cross-sectional view showing an example of a high melting point metal capsule used in the present invention. FIGS. 4 and 5 are cross-sectional views of the main parts showing the state after the solvent has been dissolved, and FIGS. 4 and 5 are respectively cross-sectional views of the main parts showing other examples of the capsule joint used in the present invention. DESCRIPTION OF SYMBOLS 10... Capsule body, 12... Lid, 16... Thin rising part, 18... Thin opening edge, 24... Melting part. Patent applicant: Power Reactor and Nuclear Fuel Development Corporation

Claims (1)

[Claims] 1. In a method in which the opening of a cylindrical capsule body made of a high-melting point metal is covered with a lid made of a high-melting point metal and the surrounding area is melt-sealed, the lid has a thin-walled rising portion around the periphery, and the capsule body has a thin-walled edge at the end. The cap has a structure in which an opening edge is formed, and the lid is fitted so that its thin-walled rising portion is surrounded by the thin-walled opening edge of the capsule body, and the ends of the thin-walled opening edge and the thin-walled rising portion that abut each other are rounded. A method for melt-sealing a high-temperature heat-resistant capsule, which is characterized by welding.