JPH0315157B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an end plug for a nuclear fuel rod, and more particularly to an end plug for a nuclear fuel rod that prevents the formation of a cavity inside a welded portion.

(Technical background of the invention and its problems) In general, a nuclear fuel rod for a nuclear reactor consists of a cladding tube 2 loaded with nuclear fuel material 1 and a spring 3 disposed inside the cladding tube 2, as shown in FIG. , and end plugs 4, 4 joined to both ends of the cladding tube 2, and the end plugs 4, 4 are fixed to the cladding tube 2 by welding.

Incidentally, TIG welding has conventionally been used to weld the end plug 4, but laser welding has come to be used due to the need to improve welding efficiency and reduce welding thermal distortion. This laser welding method is similar to conventional TIG
Compared to welding methods, the welding energy density is high, deep penetration can be achieved at high speed, and there is little effect of welding heat.
Can perform welding with low distortion.

However, when the conventional end plug 4 is welded to the end of the cladding tube 2 by laser welding, a cavity 6 is generated near the deepest part of the welded tube 5 as shown in FIG. There are problems such as ease of use.

(Object of the Invention) In view of the above points, an object of the present invention is to obtain an end plug for a nuclear fuel rod that can prevent the formation of a cavity inside the weld between the end plug and the cladding tube.

(Summary of the Invention) The present invention provides an end plug for nuclear fuel rods that is welded to the tube end of a cladding tube loaded with nuclear fuel material and seals the inside of the cladding tube, in which the cladding tube and the end plug are fitted into a welded part where the cladding tube and the end plug are welded. The inner end plug of this fitting part is opened on the inner end surface side and extends in the axial direction, and the keyhole of the welded part by the laser beam communicates through it, forming a circumferential groove deeper than the welded part. This is characterized by the fact that during laser welding, the keyhole reaches a deep circumferential groove in the penetration direction, and the gas generated near the deepest part of penetration is released through the circumferential groove, and the inside of the welded part is This is to prevent cavities from forming.

(Embodiment of the Invention) Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

Generally, it is thought that the reason why cavities occur in a welded part by laser welding is as follows. That is, as shown in FIG. 3, the energy density of the irradiated part of the laser beam 7 is extremely high, and when the irradiated part is instantly melted and vaporized, the keyhole-shaped keyhole 8 is filled with the surrounding molten metal 9. In addition, it is thought that gas generated near the deepest part of penetration causes incomplete filling of the molten metal, and a cavity 6 is generated in that part.

Therefore, in order to prevent the formation of the above-mentioned cavities, it is sufficient that the gas generated in the vicinity of the above-mentioned deepest part of penetration is successfully removed.

The present invention makes it possible to effectively remove the gas from a deep circumferential groove provided inside the welded portion where the cladding tube and the end plug fit together. That is, FIG. 1 is a partial cross-sectional view showing a state in which the end plug 4 of the present invention is welded to the cladding tube 2, and the welded portion of the cladding tube 2 and the end plug 4 has a fitting portion 2 with a tapered surface.
a and 4a are provided, and the two are installed straight while maintaining concentricity.

By the way, on the inside of the end plug surface on the side of the cladding tube 2 near the fitting parts 2a and 4a of the cladding tube 2 and the end plug 4, there is a keyhole that is opened on the inner end surface side, extends in the axial direction, and is formed by a laser beam. A circumferential groove 10 is formed which extends in the circumferential direction and is deeper than the welded portion. The diameter of the outer circumferential inner surface of the circumferential groove 10 is the same as the inner diameter of the cladding tube 2.

When the cladding tube 2 and the end plug 4 are rotated and a laser beam 7 is irradiated onto the joint between them, a keyhole 8 formed by the laser beam 7 is formed in the welded portion 5.
penetrates in the welding direction and reaches into the circumferential groove 10. Therefore, when the keyhole 8 is filled with the surrounding molten metal as the end plug 4 moves, the gas generated near the deepest part of penetration is released through the circumferential groove 10, and the welded part No cavities are generated inside the gas chamber 5 due to the gas.

FIG. 2 also shows an end plug 4 in which the joint between the cladding tube 2 and the end plug 4 has a joint surface perpendicular to the joint of the cladding tube 2, and has a conical tapered fitting portion 4b. This is a partial cross-sectional view showing a state in which the end plug 4 is welded to the cladding tube 2, and in this case as well, similarly to the first embodiment shown in FIG. A circumferential groove 10 is formed which extends into the welded portion and is deeper than the welded portion.

In this case as well, as in the first embodiment, the keyhole 8 caused by the laser beam 7 reaches into the circumferential groove 10, and the gas generated near the deepest part of penetration is released through the circumferential groove 10. Therefore, no cavity is generated inside the welded portion 5 due to the above gas.

〔Effect of the invention〕

The present invention provides a fitting part at the joint between the cladding tube and the end plug as described above, and a keyhole formed by a laser beam is opened on the inner surface side of the end plug and communicates through the welded part. Since the deeper circumferential groove is formed, the gas generated near the deep penetration part during welding is discharged into the circumferential groove, and no cavity is created by the gas inside the welded part. Therefore, the quality of the welded portion can be extremely excellent.

[Brief explanation of the drawing]

FIGS. 1 and 2 are partial cross-sectional views showing embodiments of the present invention, FIG. 3 is a cross-sectional view of a nuclear fuel rod,
Figure 4 is a sectional view showing the welded part of a conventional end plug;
The figure is an explanatory diagram of the cavity generation mechanism in the welded part. 2... Cladding tube, 4... End plug, 5... Welded part, 6
... hollow, 8 ... keyhole, 9 ... molten metal,
10...Groove.

Claims (1)

[Claims] 1. In an end plug for a nuclear fuel rod that is welded to the end of a cladding tube loaded with nuclear fuel material and seals the inside of the cladding tube, a fitting part is provided at the welded part where the cladding tube and the end plug are welded, and this fitting part For a nuclear fuel rod, the inner end plug has a circumferential groove that is open on the inner end surface side, extends in the axial direction, communicates through the keyhole of the welded part by laser light, and is deeper than the welded part. End plug.