JP2000094169A - Fuel rod end tap welding method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a weld zone the surface of which is smooth and to which a ultrasonic inspection is applicable in end tap welding for a nuclear fuel rod capable of welding at a high speed and having high welding efficiency. SOLUTION: With respect to fuel rod end tap welding equipment which executes end tap welding for a coated tube of a fuel rod 9 within a welding chamber 8 which is kept in an inert gas atmosphere, a laser beam welding window 16 and a TIG welding torch 14 are disposed on the surface orthogonal to the axial line of the fuel rod 9 attached to the welding chamber 8 and including a weld point of the end tap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for welding a fuel rod end plug which is a component of a fuel assembly for nuclear power generation.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 4, a nuclear fuel rod for nuclear power generation is obtained by welding an end plug 2 to one end of a cladding tube 1 and then inserting a predetermined number of nuclear fuel pellets 3 from the opening end side into the cladding tube 1. , A coil spring 5 is charged into a space 4 formed between the nuclear fuel pellet 3 and the open end of the cladding tube 1, and further, the cladding tube 1 is filled with an inert gas 6, and the end is formed at the opening end. It is made by attaching a stopper 7 and sealingly welding.

The cladding tube 1 and the end plugs 2 and 7 are made of a zirconium-based alloy called Zircaloy 2 or Zircaloy 4. Since these are active at a high temperature, they are usually welded in an inert gas atmosphere. FIG. 5 is a view showing a schematic configuration of the welding apparatus for end plugs, wherein an opening end side of a nuclear fuel rod 9 is inserted into a welding chamber 8 having an airtight structure from one side wall. The nuclear fuel rod 9 is held by a holding mechanism 10 and is rotated around an axis by a rotating mechanism 11. On the other hand, a movable shaft 13 having an end plug holder 12 provided at the tip is inserted through the other side wall of the welding chamber 8, the end plug 7 is held in the end plug holder 12, and the end plug 7 is covered with a cladding tube. 1, the joint between the end plug 7 and the cladding tube 1 is welded by the TIG welding torch 14 while rotating the cladding tube 1 and the end plug 7 while rotating the cladding tube 1 and the end plug 7. The inside of the welding chamber is replaced with an inert gas atmosphere by a vacuum exhaust mechanism and an inert gas supply mechanism (not shown).

[0004] TIG welding and laser welding are generally applied to welding of end plugs. As shown in FIG. 5, a TIG welding torch 14 is provided at an upper portion of a welding chamber 8, or as shown in FIG. Thus, a window 16 for guiding a laser beam 15 is attached to the TIG welding torch 14 instead of the welding torch,
Welding is performed by converging and irradiating a laser beam 15 from above the welding chamber.

[0005]

The end plug welds thus welded are all non-destructively inspected for blowholes and other welding defects in order to confirm the soundness of the welds. are doing. As this non-destructive inspection method, a method using X-ray imaging or an ultrasonic method is known. However, for a welded part requiring high reliability such as a welded part of a fuel rod, the detection accuracy of the welded part is high. Inspection by the ultrasonic method is essential from the height.

On the other hand, from the viewpoint of welding work efficiency, laser welding, which is high energy density welding, is advantageous because sufficient penetration can be obtained even when the welding speed is increased. However, due to the high energy density, the surface of the welded portion may be wavy and rough. In the case of laser welding, in particular, in order to smoothly perform the crater treatment at the end of welding, welding with a pulse waveform is often performed, but in this case, fine ripple-like irregularities are generated on the surface.

However, in the inspection using an ultrasonic wave, there is a problem that it is impossible to perform the inspection because the ultrasonic wave is irregularly reflected on the surface in such a surface state.

[0008] TIG welding has a very smooth weld surface and is a welding method suitable for ultrasonic inspection. However, since the heat input energy density is much smaller than that of a laser, sufficient penetration is obtained. However, it is necessary to reduce the welding speed or to repeat welding several times, and there is a problem that welding work efficiency is poor. In other words, if a welding method with a high welding speed and high work efficiency (laser welding) is adopted, ultrasonic inspection cannot be applied, and if an ultrasonic inspection is applied, the work must be performed to smooth the surface. There was a problem that an inefficient welding method (TIG welding) had to be adopted.

The present invention has been made in view of the above points, and in the end plug welding of nuclear fuel rods for nuclear power generation, it is possible to perform welding at high speed with high welding efficiency, and has a smooth welded surface and an ultrasonic inspection. It is an object of the present invention to obtain a welding method and a welding device capable of forming a possible weld.

[0010]

A first aspect of the present invention is a fuel rod end plug welding method for welding an end plug to a fuel rod cladding tube in a welding chamber in an inert gas atmosphere. The end plug is welded by laser welding, and the welded portion is then re-welded by TIG welding.

According to a second aspect of the present invention, there is provided a fuel rod end plug welding apparatus for welding an end plug to a fuel rod cladding tube in a welding chamber in an inert gas atmosphere, wherein an axis of a fuel rod mounted in the welding chamber is provided. And a laser welding window and a TIG welding torch are disposed on a plane orthogonal to.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a view showing a schematic configuration of a welding apparatus according to the present invention. FIG. 2 is a sectional view of the welding apparatus viewed from the side at a welding position. A window 16 for guiding the laser beam 15 is provided so that the laser beam 15 can be obtained.
And a nozzle 19 for guiding the laser beam 15 introduced through the window 16 to the welded portion of the end plug 12 is provided inside the welding chamber 8.

The laser beam generated by the laser processing head 18 is condensed by the condensing lens 17 and
Is introduced into the welding chamber 8, the butt position of the cladding tube 1 and the end plug 7 is irradiated, and the corresponding portion is welded.

The welding chamber 8 further includes a TIG
A welding torch 14 is also provided. The TIG welding torch 14 and the window 16 for introducing a laser beam are disposed on the same plane orthogonal to the axis of the fuel rod 9 mounted in the welding chamber 8. A predetermined angle, for example, 45 ° in the rotation direction of the rod 9 (arrow in FIG. 2)
It is located at the offset position.

By the way, the fuel rod 9 is welded by a part of the cladding tube 1 and the end plug 7 in a welding chamber as in the conventional welding method.
After the gas is replaced with an inert gas atmosphere by vacuum evacuation, the two are fitted together, and welding is performed at the butt position while rotating them around an axis. That is, in order to obtain the necessary penetration size specified in the welding specification, first, as described above, the butting position between the cladding tube 1 and the end plug 7 by the laser beam 15 introduced through the window 16 above the welding chamber 8. Perform welding. In this case, the laser output and the welding speed (rotation speed of the fuel rod) are separately selected depending on the thickness and dimensions of the fuel rod and the required penetration depth.

In this way, laser welding of the fuel rod is started, and when the welded portion rotates 45 ° to a position facing the TIG welding torch 14, the TIG welding torch 14 is operated and rotated 45 ° after the laser welding. From the TIG
Surface treatment welding by welding is performed. In this case, the necessary penetration has already been obtained by laser welding,
In the TIG welding, only the vicinity of the surface is melted, and the part where the surface is roughened by the laser welding is melted to obtain a smooth finish.

FIG. 3 is a view showing the concept of these molten states. In the butt surface 21 between the cladding tube 1 and the end plug 7, the melted portion 22 formed by laser welding has a sufficient penetration depth including the butt surface. Is obtained and the subsequent TI
By G welding, a smooth weld surface is obtained by melting only the vicinity of the surface as indicated by reference numeral 23.

As described above, the TIG welding in the present invention involves only surface melting, and it is not necessary to consider the penetration depth. Therefore, the melting speed (rotation speed of the fuel rod) can be selected relatively freely. One round welding is sufficient. Also, as is known, laser welding has a high energy density and can be welded at high speed, and it is relatively easy to obtain the necessary penetration by one round welding, although it depends on parameters such as laser output. Therefore, in the present invention, basically, the necessary welding is completed by one round welding of the fuel rod.

After welding over the entire circumference by laser welding, it is also possible to switch to TIG welding and perform surface treatment welding. However, as described above, TIG welding is started at a delay of 45 °, ie, 1/8 of a round, and By welding, the welding time can be reduced. Since the laser welding point and the TIG welding point have a shift of 1/8 turn, the TIG welding starts with a delay of 1/8 turn after the laser welding, and (1 + 1/8) turns are required in total. Actually, terminal processing such as crater processing is required.
Welding can be completed in 1.5 turns.

[0021]

As described above, in the present invention, by combining the deep penetration characteristics of laser welding, which is high energy density welding, with the characteristics of TIG welding, in which the penetration is shallow but a smooth surface can be obtained. In addition to performing high-speed and efficient welding equivalent to laser welding, the welding surface can be made smooth, and a welded portion can be inspected by ultrasonic waves with high inspection accuracy. Therefore, there is an effect that the welded portion of the end plug can be made high quality and highly reliable.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing a schematic configuration of a laser welding apparatus according to the present invention.

FIG. 2 is a vertical sectional side view of the laser welding apparatus of the present invention.

FIG. 3 is a view showing a concept of a molten state when welding according to the present invention is performed.

FIG. 4 is a longitudinal sectional view showing an example of a nuclear fuel rod.

FIG. 5 is a diagram showing an example of a conventional welding device using TIG welding.

FIG. 6 is a diagram showing an example of a conventional welding device using laser welding.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Clad tube 2, 7 End plug 3 Nuclear fuel pellet 8 Welding chamber 9 Nuclear fuel rod 11 Rotation mechanism 14 TIG welding torch 15 Laser beam 16 Window 17 Condenser lens 18 Laser processing head

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B23K 28/02 B23K 28/02 37/02 301 37/02 301A G21C 21/02 G21C 21/02 A

Claims (4)

[Claims] 1. A fuel rod end plug welding method for welding an end plug to a fuel rod cladding tube in a welding chamber in an inert gas atmosphere, wherein the fuel rod cladding tube and the end plug are welded by laser welding. After that, the welding portion is re-welded by TIG welding. 2. The fuel rod end plug welding method according to claim 1, wherein after a predetermined amount of laser welding has been performed in the circumferential direction of the fuel rod, TIG welding of the welded portion is started. . 3. A fuel rod end plug welding apparatus for welding an end plug to a fuel rod cladding tube in a welding chamber in an inert gas atmosphere, wherein the fuel rod end plug welding device is orthogonal to an axis of a fuel rod mounted in the welding chamber. A fuel rod end plug welding device, comprising a laser welding window and a TIG welding torch disposed on a surface including a welding point of the end plug. 4. The fuel rod end plug welding according to claim 3, wherein the TIG welding torch is disposed at a position deviated from the laser welding window by a predetermined angle in the direction of rotation of the fuel rod. apparatus.