JPH09150272A - Welding electrode holder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the temperature rise of an electrode when a nuclear fuel rod is welded with pressure, and prevent deterioration of the welding quality by providing a cooling means in which a cooling material is circulated to cool a collet on an outer circumferential part of the collet to hold the electrode. SOLUTION: A cooling material chamber 26 is integrated with an outer circumferential wall of an electrode collet 25, and the cooling material such as water passes therein through a conduit tube 27. When a cover tube of a nuclear fuel rod is welded to an end plug, the heat is deprived by the cooling material to be circulated in the cooling material chamber 26 even when the current density of an electrode 24 is increased by the pinch effect under the pressurization in a welding chamber and the temperature rises, and the melting and deformation of the electrode 24 can be suppressed. Deviation of the arc is thus suppressed, and as a result, fluctuation in the penetration area is suppressed, and generation of incomplete penetration area, etc., is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding electrode holder for butt welding end plugs to a cladding tube of a nuclear fuel rod.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 3, a nuclear fuel rod used in a nuclear reactor for power generation has a predetermined number of pellets 2 such as uranium dioxide UO ₂ in a cladding tube 1 made of a zirconium alloy or stainless steel. The pellet 2 is filled with a pushing spring 3 which is inserted from one end, and the end plug 4 made of the same material as that of the cladding tube 1 is welded to the opposite end in advance. The end plug 5 made of the same material as that of the end plug 4 is welded to the end portion subjected to.

By the way, FIG. 4 is a view showing a welding device for welding the end plug 5 to the end portion of the coating pipe 1, and a welding chamber 6 which is a high pressure tight chamber is provided with the coating from one side wall thereof. The opening side end of the pipe 1 is inserted,
An end plug holder 7 for holding the end plug 5 is provided on the opposing wall. Further, a welding torch 9 having an electrode 8 protruding from the lower end thereof is attached to the top wall portion of the welding chamber 6 by insertion.
Further, the welding chamber 6 is connected with a pressure adjusting device having first and second pressure control valves 10 and 11.

Therefore, when welding the end plug 5, the opening end of the cladding tube 1 of the fuel rod is inserted into the welding chamber 6, and the end plug 5 is held by the end plug holder 7, and the welding chamber 6 is welded. After the inside is evacuated to a predetermined degree of vacuum, the inside of the welding chamber 6 is pressurized by filling the interior of the welding chamber 6 with an inert gas through the welding torch 9, and the above-mentioned pressurization is performed by the first control valve 10. Held in a state. Then, in this state, the end plug 5 is press-fitted into the open end of the covering pipe 1 to seal the covering pipe 1, and subsequently, an arc is generated between the electrode 8 and the end plug 5, so that the covering pipe 1 and the end plug are sealed. The butt surfaces of No. 5 are welded in the circumferential direction.

However, in this case, since the cladding tube 1 is hermetically sealed, the internal pressure of the cladding tube 1 suddenly rises due to the heat effect at the time of welding, and sealed welding becomes impossible. The valve 11 is switched to, and welding is performed by applying a pressure equal to the internal pressure increase ΔP of the cladding tube 1 as shown in FIG.

[0006]

However, since the welding is generally performed under 1 atmospheric pressure, that is, atmospheric pressure, the arc is stable. However, under the above-mentioned pressure, the pinch effect acts on the arc and the electrode 8 The current density of the electric field will increase remarkably. According to the literature, the current density at 1 atm in N ₂ gas atmosphere is about 6 A / cm ² , but it is about 1 A at 5 atm.
2 A / cm ² , about 20 A / cm ² and 2 at 10 atmospheric pressure
It is known to triple. Therefore, when arc welding is performed under such a situation, as described above, the electrode 8
Current density increases, and the temperature rise of the electrode 8 causes the tip to remarkably melt and deform. As a result, the directivity of the arc 12 deteriorates, the arc 12 fluctuates, and the melt becomes non-uniform, resulting in a partially melted incomplete region 13 as shown in FIG. 6 (a), or the tip of the end plug. Depending on the shape, due to the pressure applied during welding, the weld metal 14 is pushed into the gap between the end plug 5 and the inner wall of the cladding tube, takes in air bubbles 15 at the end plug, generates porosity 16, and deteriorates welding quality. I have a problem.

In view of the above points, the present invention has an object to obtain a welding electrode holder capable of reducing the temperature rise of the electrode during pressure circumferential welding of a nuclear fuel rod and preventing the deterioration of welding quality. And

[0008]

SUMMARY OF THE INVENTION The present invention provides a welding electrode holder for butt-welding end plugs to a cladding tube of a nuclear fuel rod by circulating a coolant around the outer periphery of a collet holding the electrode. A cooling means such as a cooling material chamber or a cooling pipe for cooling the collet is provided to reduce the temperature rise of the electrode during welding and to prevent melting deformation of the electrode tip.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

In FIG. 1, reference numeral 20 is an insulating outer cylinder of the electrode holder, and a cylindrical conduit 2 is provided in the insulating outer cylinder 20.
1 is inserted and mounted, and the base end of the copper nozzle 22 is mounted on the tip of the cylindrical conduit 21. The copper nozzle 22
Is projected from the tip of the insulating outer cylinder 20, and a ceramic nozzle 23 is concentrically attached to the outer periphery of the copper nozzle 22 so as to cover the outer periphery of the copper nozzle 22.

In the copper nozzle 22, an electrode collet 25 having an electrode 24 attached to its tip is concentrically attached to the copper nozzle 22, and the tip of the electrode 24 is projected from the ceramic nozzle 23. ing. A coolant chamber 26 is integrally formed on the outer peripheral wall of the electrode collet 25, and the coolant flows through the duct 27 in the coolant chamber 26. Reference numeral 28 in the drawing is an airtight seal.

However, when welding the covering pipe and the end plug with the welding device having such an electrode holder, a coolant such as water is constantly circulated in the coolant chamber 26. Therefore, when welding the cladding tube and the end plug, even if the current density of the electrode 24 increases due to the pinch effect under pressure in the welding chamber and the temperature rises, the coolant circulating in the coolant chamber 26 is As a result, the above-mentioned rising heat is taken away, and melting deformation of the electrode 24 is reduced. Therefore, the fluctuation of the arc is suppressed, and as a result, the variation of the melted region is suppressed and the generation of the incomplete melted region and the like is prevented.

FIG. 2 is a view showing another embodiment of the present invention. A cooling pipe 29 is wound around the outer circumference of the electrode collet 25. Therefore, the electrode collet 25 is cooled by the coolant flowing through the cooling pipe 29, and the same effect as that shown in FIG. 1 is obtained.

Although water is used as the coolant in the above embodiment, a liquid such as a liquid metal or an inert gas may be used as the coolant.

[0015]

As described above, according to the present invention, in the welding electrode holder for butt welding the end plugs to the cladding tube of the nuclear fuel rod, the coolant is circulated around the outer periphery of the electrode collet holding the electrodes. Since the cooling means for cooling the electrode collet is provided, the temperature rise of the electrode at the time of welding can be reduced, melting deformation of the electrode can be prevented, the arc can be stabilized, and the penetration can be made uniform. Therefore, the molten metal is not pushed into the gap between the inner wall of the cladding and the end plug portion, and the occurrence of welding defects such as porosity can be prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a welding electrode holder of the present invention.

FIG. 2 is a view showing another example of the welding electrode holder of the present invention.

FIG. 3 is a partial cross-sectional side view showing the structure of a nuclear fuel rod.

FIG. 4 is a view showing a welding device for welding a cladding tube and an end plug.

FIG. 5 is a diagram showing a relationship between an increase in internal pressure of the cladding tube and pressurization.

6A and 6B are views showing an example of occurrence of welding defects due to arc wobble.

[Explanation of symbols]

 1 cladding tube 2 pellets 4,5 end plug 6 welding chamber 8 electrode 9 welding torch 12 arc 13 incomplete melted area 14 molten metal 15 bubbles 20 insulating outer tube 21 cylindrical conduit 22 copper nozzle 23 ceramic nozzle 24 electrode 25 electrode collet 26 cooling Material room 29 Cooling pipe

Claims (4)

[Claims] 1. A welding electrode holder for butt-welding an end plug to a cladding tube of a nuclear fuel rod, wherein a cooling means for cooling the collet by circulating a coolant is provided around the outer periphery of the collet holding the electrode. Welding electrode holder characterized in that 2. The welding electrode holder according to claim 1, wherein the cooling means is a coolant chamber formed integrally with the outer peripheral portion of the collet. 3. The welding electrode holder according to claim 1, wherein the cooling means is a cooling pipe wound around the outer peripheral portion of the collet. 4. The welding electrode holder according to claim 1, wherein the coolant is water, a liquid such as a liquid metal, or a gas such as an inert gas.