JPH09297192A - Nuclear fuel rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a cavity in a weld part at the time of welding an end plug to a covering pipe. SOLUTION: The outer periphery of a tip small diameter part of an end plug 31 fitted into a covering pipe is provided with a circumferential groove 34 penetrating a keyhole formed in a weld part 35 at the time of welding the covering pipe 30 and the end plug 31, and gas generated near a deepest part of the weld part 35 is released to the peripheral groove 34 to prevent the generation of a cavity in the weld part 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear fuel rod, and more particularly to a nuclear fuel rod in which a cavity is not formed in a welded portion when the end plug is welded to a cladding tube.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 3, a nuclear fuel rod 10 for a nuclear reactor has a cladding tube 13 loaded with a nuclear fuel material 11 and springs 12, and both ends of the cladding tube 13. It is constituted by the end plug 14 to be joined.

Conventionally, the TIG welding method has been used to weld the end plug 14 to the covering tube 13.

However, in place of the TIG welding method, a laser welding method has recently been adopted for reasons such as improvement of welding efficiency and reduction of welding heat distortion.

Compared with the TIG welding method, this laser welding method has a higher welding energy density and a deeper penetration can be obtained at a high speed, and the influence of welding heat and strain can be reduced.

However, as shown in FIGS. 4 and 5, when the conventional cladding tube 13 and the end plug 14 are laser-welded as they are, the energy density is extremely high at the laser beam irradiation portion,
A part of the irradiated portion is instantly melted and vaporized to form a keyhole-shaped keyhole 16 in the welded portion 15.
When the molten metal of the cladding tube 13 and the end plug 14 is filled in 6, molten gas is generated in the vicinity of the deepest portion and the molten metal may be incompletely filled to form a cavity H.

The generation of the cavity H is caused by the covering tube 13 and the end plug 14.
In order to reduce the welding strength between and, various measures have conventionally been taken to prevent this. For example, as shown in FIG. 6, a concentric small-diameter protruding portion 20 having a diameter smaller than the inner diameter of the covering tube 13 is provided at the tip of the end plug 14, and when the protruding portion 20 is inserted into the covering tube 13, It is formed when the cladding tube 13 and the end plug 14 are welded by the laser light L so that the annular space 21 is formed between the welded portion 15 of the end cap 14 and the welded portion 13 of the end plug 14. The keyhole is passed through the space 21 to prevent the generation of a cavity when the molten metal is filled.

However, according to this structure, the cavity H of the welded portion 15 is prevented, but the joint surface of the end plug 14 and the covering tube 13 are prevented.
It is necessary to improve the processing accuracy with respect to the joint surface, and if this processing accuracy is lowered even a little, the center axis between the end plug 14 and the covering tube 13 is deviated, and proper welding cannot be performed, which is not suitable for practical use. there were.

Further, as shown in FIG. 7, a circumferential groove 25 is formed on the outer peripheral portion of the tip of the end plug 14 of the same diameter which is fitted inside the covering pipe 13.
By this, the keyhole formed in the welded portion 15 between the joint surface of the end plug 14 and the joint surface of the covering pipe 13 during welding is communicated with the circumferential groove 25 so that the molten metal is filled in the keyhole. It was sometimes proposed to prevent the formation of voids.

However, even with this structure, the cavity H of the welded portion 15 can be prevented, but it is difficult and costly to form the circumferential groove 25 at the outer peripheral portion of the end of the end plug 14 with high accuracy. There is.

In order to solve these problems, the present invention provides a nuclear fuel rod in which a cavity is not formed in the welded portion between the end plug and the cladding tube when laser light is emitted to the welded portion. It is intended.

[0012]

SUMMARY OF THE INVENTION In order to solve these problems, the present invention relates to a nuclear fuel rod in which end plugs are welded to both ends of a cladding pipe loaded with a nuclear fuel material, and the nuclear fuel rod is fitted into the cladding pipe at the end plug. A circumferential groove through which a keyhole formed when the end plug is welded penetrates is formed on the outer periphery of the small tip small diameter portion to be joined.

Further, the length between the circumferential groove of the present invention and the surface including the joint surface where the end surface of the cladding tube contacts the end plug is 0.2 to 1 times the wall thickness of the cladding tube. It is characterized in that an end plug base portion which is fitted to the covering pipe is formed.

Furthermore, the circumferential groove of the present invention is characterized in that it has a rectangular cross section or a triangular cross section.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a nuclear fuel rod of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, a tip small diameter portion 32 having the same diameter D0 as the inner diameter of the cladding tube 30 of the end plug 31 is fitted into the end portion of the cladding tube 30 of the nuclear fuel rod of the present invention.

A circumferential groove 34 having a rectangular cross section is provided on the outer peripheral portion of the tip small diameter portion 32. An end plug base portion 33 having a width T0 of 0.2 to 1 times the wall thickness T1 of the covering pipe is provided between the circumferential groove 34 and the plane including the joint surface where the end face of the covering pipe 30 contacts the end plug 31. Is provided. The circumferential groove 34 has a laser beam L oblique to the welded portion 35 of the joining surface between the cladding tube 30 and the end plug 31, for example, an angle θ of 5 degrees to 30 degrees with respect to the joining surface, and the cladding tube 30 has The keyhole formed in the welded portion 35 is formed so as to communicate therethrough when irradiated toward the central axis.

The tip small diameter portion 32 of the end plug 31 is fitted inward from the end of the covering pipe 30 so that the joint surface of the end plug 31 faces the joint surface of the covering pipe 30. The contact surface, that is, the welded portion 35 is irradiated with the laser light L from an obliquely upper portion toward the circumferential groove 34. During the irradiation of the laser light L, the coating tube 30 and the end plug 31 are integrally rotated by an electric motor (not shown).

The joint surface between the coating tube 30 and the end plug 31 is melted by the irradiation of the laser beam L, and the keyhole generated at this time is communicated with the circumferential groove 35. Therefore, this penetration communication prevents the gas generated in the vicinity of the deepest portion of the welded portion 35 from being discharged to the circumferential groove 34 to form a cavity in the welded portion 35.

FIG. 2 shows another modification of FIG. 1 in which the circumferential groove 34 having a rectangular cross section is replaced with a circumferential groove 44 having an inclined cross section. Even in this case, it is possible to prevent the formation of a cavity in the welded portion when laser welding the cladding tube and the end plug in the nuclear fuel rod of the present invention.

[0021]

INDUSTRIAL APPLICABILITY The present invention relates to a nuclear fuel rod in which end plugs are welded to both ends of a cladding tube loaded with a nuclear fuel material.
Since a circumferential groove through which a keyhole formed during welding of the end plug communicates is formed on the outer periphery of the small tip portion of the end plug fitted into the covering pipe, the keyhole generated during welding is a circumferential groove. The gas generated in the vicinity of the deepest part of the weld is discharged into the circumferential groove to prevent a cavity from being generated in the weld.

The length between the circumferential groove of the present invention and the surface including the joint surface where the end surface of the cladding tube contacts the end plug has a length of 0.2 to 1 times the wall thickness of the cladding tube. By forming the end plug base portion fitted in the cladding tube, the keyhole formed in the weld portion by the obliquely radiated laser beam L is surely communicated with the circumferential groove to form the cavity of the weld portion. Can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of welding an end plug and a cladding tube of a nuclear fuel rod of the present invention.

FIG. 2 is a cross-sectional view showing a welding example of another end plug and a cladding tube of the nuclear fuel rod of the present invention.

FIG. 3 is a cross-sectional view of a commonly used nuclear fuel rod.

FIG. 4 is an explanatory view showing a welding example of a conventional end plug and a covering pipe.

FIG. 5 is a sectional view showing an example of welding of a conventional end plug and a covering pipe.

FIG. 6 is a sectional view showing an example of welding of another conventional end plug and a covering pipe.

FIG. 7 is a cross-sectional view showing a welding example of still another conventional end plug and a covering tube.

[Explanation of symbols]

 10 Nuclear Fuel Rods for Nuclear Reactors 11 Nuclear Fuel Materials 12, 30 Cladding Pipes 13 Springs 14, 31 End Plugs 15 Welds 16 Keyholes 20 Projections 21 Spaces 25 Circumferential Grooves 32 Tip Small Diameter Part 33 End Plug Bases 34, 44 Circumference Directional groove 35 Weld

Claims (3)

[Claims] 1. A nuclear fuel rod in which end plugs are joined by welding to both ends of a cladding tube loaded with a nuclear fuel material, wherein the end plug is welded to the outer periphery of a small tip portion fitted in the cladding tube of the end plug. A nuclear fuel rod characterized in that a circumferential groove through which the formed keyhole communicates is formed. 2. The wall thickness of the cladding tube is 0.2 to 0.2 between the circumferential groove and the surface including the joint surface where the end surface of the cladding tube contacts the end plug.
The nuclear fuel rod according to claim 1, wherein an end plug base portion having a length of one time and fitted into the cladding tube is formed. 3. The nuclear fuel rod according to claim 1, wherein the circumferential groove has a rectangular cross section or a triangular cross section.