JPS6247634B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an airtight welding device using laser light, which welds objects to be welded, such as nuclear fuel rods or spacers for fuel assemblies, using laser light. Regarding.

[Technical background of the invention and its problems]

In general, nuclear fuel rods used in power reactors, etc. are manufactured by welding an end plug 2 to one end of a zirconium alloy or stainless steel cladding tube 1, and then inserting the end plug into the cladding tube 1, as shown in Fig. 1. A pellet 3 made of nuclear fuel material such as uranium dioxide UO ₂ is loaded, a coil spring 5 is inserted into the space 4 formed between the pellet 3 and the open end of the cladding tube 1, and a large It is manufactured by filling an inert gas with a pressure higher than atmospheric pressure, fitting an end plug 6 into the open end, and sealingly welding the end plug 6 into a welding chamber under a high pressure atmosphere. .

On the other hand, in a fuel assembly constructed by assembling a large number of nuclear fuel rods manufactured as described above, spacers for maintaining the spacing between each nuclear fuel rod are as shown in FIGS. 2 and 3. , bar 7, divider 8, spring 9, band 1
0 etc., bar 7 and divider 8
The intersection between the bar 7 and the band 10, or the intersection between the bar 7 and the band 10, etc., are welded. By the way, when performing these welds, in order to prevent oxidation and nitridation of the weld zone, part or all of the work to be welded is inserted into an airtight welding chamber, and the inside of the welding chamber is filled with inert gas. Welding of the above-mentioned parts to be welded is performed in an atmosphere.

FIG. 4 is a partially sectional side view schematically showing a welding apparatus for welding nuclear fuel rods or spacers as described above, in which a laser beam introduction window 12 is provided on one side wall of a sealed welding chamber 11. An exhaust pipe 13 for performing evacuation and a conduit 14 for supplying inert gas at a pressure higher than atmospheric pressure into the welding chamber 11 are connected to appropriate locations in the welding chamber 11.

On the other hand, on the outside of the welding chamber 11,
A laser beam generator 1 that irradiates a welding part of a workpiece 15 with a laser beam through the laser beam introduction window 12
6 is provided, and its laser light generating device 16
The laser beam irradiated from the welding part is focused on the welding part through the condensing lens 17 to weld the part.

Therefore, when welding the part 15 to be welded, the part 15 to be welded is placed in the welding chamber 11.
The air in the welding chamber 11 is evacuated through the exhaust pipe 13, and then an inert gas is introduced through the conduit 14 to create a pressure atmosphere higher than atmospheric pressure. Then, the laser beam from the laser beam generator 16 is focused through the condensing lens 17 and the laser beam introducing window 12 onto the welding part of the object to be welded, thereby welding the welded part.

However, in such a device, the thickness of the window material needs to be increased for structural strength because the laser light introduction window is required to withstand vacuum pressure and pressurize inert gas. Therefore, a thick transparent material is interposed between the condensing lens and the workpiece, which deteriorates the focusing ability of the laser beam and reduces the energy density, resulting in the deep penetration characteristic of laser welding. There are problems such as not being able to obtain In addition, since welding is performed with inert gas sealed inside the welding chamber,
There are also problems such as plasma generated by the metal vapor, which absorbs the energy of the laser beam and impairs weld penetration.

[Purpose of the invention]

In view of these points, it is an object of the present invention to provide an airtight welding device using a laser beam that allows good weld penetration.

[Summary of the invention]

The present invention is an airtight welding device using a laser beam, which inserts a part or all of a workpiece into an airtight welding chamber and welds the workpiece in a high-pressure inert gas atmosphere inside the welding chamber. The welding chamber is characterized in that a condensing optical system is provided in the welding chamber to focus the laser beam incident on the welding chamber at or near the surface of the welded part.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

Figure 5 shows a welding device for welding nuclear fuel rods,
An opening 20 is provided in one side wall of the welding chamber 11 into which the end of the cladding tube 1 of the nuclear fuel rod can be inserted, and at a position opposite to the opening 20,
An end plug press-fitting mechanism 21 is provided which holds the end plug 6 and allows it to be press-fitted to the end of the cladding tube.

On the other hand, a laser beam introducing window 12 is provided on a side wall perpendicular to the side wall in which the opening 20 is provided, and furthermore, a laser beam introducing window 12 is provided on the outer side of the welding chamber 11 through the laser beam introducing window 12. A laser beam generator 16 is provided that irradiates the welded portion with a laser beam. In addition, a guide tube 22 is provided in the welding chamber 11 concentrically with the laser beam introduction window 12.
is provided in a protruding manner, and a condensing optical system 23 is mounted within the guide tube 22 so as to be slidable and adjustable in the axial direction.

That is, inside the guide tube 22, a shield cap 24 having a truncated conical tube portion at the tip is provided so as to be slidable in the axial direction of the guide tube 22. A condensing lens 25 is provided at. Further, the shield cap 24 is connected to an optical system drive device 26, and is moved along a guide rod 27 protruding into the welding chamber 11 by the operation of the optical system drive device 26. The condenser lens 25 moves forward and backward relative to the welded portion.

Further, a vacuum exhaust pipe 30 having a solenoid valve 28 and a relief valve 29 is provided at an appropriate location in the welding chamber 11, and an inert gas having a pressure higher than atmospheric pressure is supplied to the welding chamber 11 through the solenoid valve 31.
An inert gas supply pipe 32 is connected to each of the inert gas supply pipes 32 to feed the inside. The inert gas supply pipe 32 is connected to the inside of the shield cap 24 via a pipe 33 and to a gas nozzle 34 that opens near the welding point.

Therefore, when welding the end plug 6 to the open end of the cladding tube 1, the open end of the cladding tube 1 is welded to the opening 20.
into the welding chamber 11 through the solenoid valve 2.
8 to exhaust the air inside the welding chamber 11 through the vacuum exhaust pipe 30, and then open the solenoid valve 31 to send inert gas into the welding chamber 11 through the relief valve 29. to create a pressure atmosphere higher than atmospheric pressure.
Therefore, the end plug 6 is press-fitted into the open end of the cladding tube 1 by the end plug press-fitting mechanism 21, and the condensing lens 25 is retracted together with the shield cap 24 by the optical system drive device 26, so that the focus of the laser beam is The laser beam generator 16 is moved to a desired position on or near the surface of the welding part, and while continuing to supply inert gas into the shield cap 24 and blowing the inert gas from the gas nozzle 34 onto the surface of the welding part. Laser light introduction window 1
2 and condenser lens 25 to the welded portion between the end plug and the cladding tube, and the welded portion is welded by rotating the cladding tube 1. In this way, welding is carried out by concentrating the laser beam into an arbitrary minute diameter and setting the energy density to a state suitable for weldability, and at the same time, the metal vapor generated during welding is removed by the inert gas, and plasma is generated during welding. is prevented from occurring.

In addition, when welding the spacers, each welding part can be positioned by moving and rotating the spacers. Further, the condensing optical system is not limited to a condensing lens, and for example, a concave mirror may be used.

〔Effect of the invention〕

As explained above, in the present invention, a condensing optical system is provided in the welding chamber to focus the laser beam incident on the welding chamber at or near the surface of the welded part. There is no thick transparent material between the condensing optical system and the part to be welded, which prevents deterioration of light convergence and energy density, and enables deep penetration, which is unique to laser welding, to be achieved in a healthy manner. Welding quality can be obtained. Furthermore, if the condensing optical system is made to move forward and backward relative to the part to be welded, it is possible to more reliably condense the laser beam into a sufficiently small spot diameter, ensure sufficient energy density, and further improve the ability to cover the welded part with inert gas. When welding is performed while spraying onto the surface of the welding part, the metal vapor is prevented from turning into plasma in the laser beam path, and deterioration of weld penetration due to plasma can be further prevented.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view showing an example of a nuclear fuel rod for a nuclear reactor, Figure 2 is a plan view of a spacer, Figure 3 is a side view of a spacer, and Figure 4 is a part of a laser beam welding device that has already been proposed. FIG. 5 is a partially sectional side view of the welding apparatus of the present invention. 1... Cladding tube, 2, 6... End plug, 11... Welding chamber, 12... Laser light introduction window, 16...
Laser light generator, 23... Condensing optical system, 24...
...Shield cap, 25...Condensing lens, 30
...Evacuation pipe, 32...Inert gas supply pipe, 3
4...Gas nozzle.

Claims (1)

[Claims] 1. In an airtight welding device using laser light that inserts part or all of the workpiece into an airtight welding chamber and welds the workpiece in a high-pressure inert gas atmosphere inside the welding chamber, the above-mentioned A condensing optical system capable of changing a laser beam focal point position for focusing the laser beam incident into the welding chamber on or near the surface of the welded part is provided in the welding chamber, and An airtight welding device using a laser beam, characterized in that an inert gas is supplied into a welding chamber from a gas nozzle that opens near a welded part.