JPS6150073B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a tube end welding method for welding an end plug to the end of a cladding tube of a fuel rod used, for example, in a nuclear reactor. Conventionally, nuclear reactors are loaded with fuel assemblies, and fuel rods are incorporated into the fuel assemblies. To manufacture this fuel rod, as shown in FIG.
A spring 3 is fitted to prevent the fuel beret 2 from moving or being damaged, and then end plugs 4 and 6 are fitted into both ends of the cladding tube 1, and the joints between the end plugs 4 and 6 and the cladding tube 1 are fitted. Weld the cladding tube 1
After filling the interior with an inert gas (for example, helium gas) 5 through an end plug having one through hole, this through hole is melt-sealed. However, in the conventional method of welding the end of the cladding tube 1, the cladding tube is hermetically welded in an inert gas atmosphere of 1 atmosphere, so the fuel is affected by the heat during welding. In some cases, the gas inside the rod expanded and a bulge 8 was formed in the welded portion 7, as shown in FIG. When a bulge 8 occurs in the welded part 7, the wall thickness of the cladding tube 1 near the welded part 7 becomes thinner, which not only weakens the strength, but also increases the outer diameter of the welded part, which becomes an obstacle to the fuel rod. The drawback was that it could not be incorporated into a fuel assembly. In addition, pinholes 9 and undercuts 10 were formed in the welded portion 7 as shown in FIG. 3 due to gas expansion in the welded portion, and these had the risk of weakening the strength of the fuel rod. This invention was made in view of the above circumstances,
At least one end plug having a small through hole is fitted to both ends of the pipe, a negative pressure source is communicated with the small through hole to reduce the pressure inside the pipe, and the pipe and the end plug are welded. An object of the present invention is to provide a method for welding a tube end portion, which can prevent defects such as bulges, pinholes, and undercuts from occurring in the welded portion. Hereinafter, one embodiment of the present invention will be described based on FIG. 4. In this embodiment, the same parts as in the conventional example are given the same reference numerals, and the explanation thereof will be omitted. Reference numeral 11 in FIG. 4 is a welding machine main body, and a welding chamber 12 is formed in this welding machine main body 11. A through hole 14 is provided in the wall 13 on one side of the welding machine main body 11.
However, through holes 16 are formed in the wall 15 on the other side of the welding machine main body 11, respectively. A rotation holding mechanism 17 connected to the welding machine main body 11 via a connecting member (not shown) is provided on the right side of the welding machine main body 11 in FIG. This rotation holding mechanism 17
is adapted to hold and rotate the fuel rod 18 inserted therein. End plugs 19 are fitted to both ends of the fuel rod 18 . A small through hole 20 is formed in the center of at least one end plug 19 of the both end plugs. Further, a conical surface 21 is formed on the outer periphery of the tip portion of the end plug 19. In addition, at a predetermined location on the upper part of the welding machine main body 11,
A welding electrode 22 is provided with its tip protruding into the welding chamber 12 so as to be vertically adjustable. A shaft portion 24 of a stopper 23 is rotatably fitted into the through hole 14 via a linear motion bearing 25. The stopper 23 has a flange 27 , and a thrust bearing 26 is interposed between the flange 27 and the linear motion bearing 25 . A recess 28 is formed in the end surface of the flange 27 and is tightly fitted to the end of the end plug 19 . A communication hole (through hole) 29 that communicates the inside and outside of the welding chamber 12 is formed in the center of the stopper 23 . A vacuum pump (negative pressure source) 30 is connected to the stopper 23, and this negative pressure source 30 and the communication hole 29 are communicated with each other. Note that 31 is a stopper assembly presser attached to the wall 13. Therefore, in order to weld the end plug 19 to the cladding tube 1, the vacuum pump 3 is attached to the shaft portion 24 of the stopper 23 in advance.
Connect 0. Next, end plugs 1 are attached to both ends of the cladding tube 1.
9, insert the cladding tube 1 into the rotation holding mechanism 17, and then insert it into the welding chamber 12 through the through hole 16. The end plug 19 is brought into contact with the stopper 23 and the end plug 19 is inserted into the recess 28. Fit the tips tightly. The cladding tube 1 is then held by a rotation holding mechanism 17. As a result, the small through hole 20 of the end plug 19 and the communication hole 29 of the stopper 23 communicate with each other, and the vacuum pump 3
0 and the inside of the cladding tube 1 are communicated through a communication hole 29 and a small through hole 20. Next, when the vacuum pump 30 is operated, the pressure inside the cladding tube 1 is reduced. Next, move the welding electrode 22 and adjust the end plug 19.
and the cladding tube 1 at an appropriate position. Next, the rotation holding mechanism 17 is operated to rotate the cladding tube 1.
Rotate. At this time, the stopper 23 also rotates in accordance with the rotation of the cladding tube 1. Next, inert gas is blown out from the welding electrode 22 to fill the welding chamber 12 with this inert gas, and then a current is passed through the welding electrode 22. As a result, the joint between the end plug 19 and the cladding tube 1 is welded. During this welding, the pressure inside the cladding tube 1 is lower than that inside the welding chamber 12 on the outside, so a force that pulls the molten metal at the welded area toward the inside of the cladding tube causes bulges in the welded area, pinholes, undercuts, etc. will not occur. After this, inert gas is pressurized and filled into the cladding tube 1 through the small through hole 20.
Melt seal the parts. By the way, when helium gas is flowing in the welding chamber 12 at approximately 30/min, the cladding tube 1
Table 1 and FIG. 5 show the results of welding tests conducted while varying the pressure difference between the inside and the inside of the welding chamber 12. Table 1 shows the bulge of the welded portion and the occurrence of undercuts in response to the differential pressure, and FIG. 5 shows the bead width and bead diameter after welding. The welding current in this welding test was about 30A. In addition, Table 1,
The differential pressure in FIG. 5 indicates the differential pressure between the inside of the cladding tube 1 and the inside of the welding chamber 12, which is the same as when this differential pressure was conventionally zero. Looking at the test results, there was no difference in the bead width between the conditions, but the number of undercuts, the number of tubes with bulging defects, and the bead diameter became smaller as the differential pressure between the inside of the cladding tube 1 and the inside of the welding chamber 12 increased. A tendency was observed, and the change in bead diameter was observed in Experiment 1.
In Experiment 5, it was -0 mm, and in Experiment 5 it was -0.014 mm. It can be clearly seen that increasing the degree of vacuum in the cladding tube 1 to increase the differential pressure helps to eliminate the defects of the weld.

[Table] In the above embodiment, the case where the end plug 19 having a small through hole 20 is welded to the pipe 1 is described, but the present invention is not limited to this, and the end plug 19 without a small through hole at the other end can be welded to the pipe 1. When welding the cladding tube to the cladding tube, as shown in FIG. The end plug 19 without a through hole can be welded to the cladding tube 1 by bringing the stopper 23, which is rotatably held and connected to the negative pressure source 30, into contact with the cladding tube 1 to reduce the pressure inside the cladding tube 1. can. Furthermore, in the above embodiments, the present invention has been explained with reference to an example in which the end plug 19 is welded to the cladding tube 1 of a fuel rod, but the present invention is not limited to this, and can be applied to the case where the end plug 19 is welded to a general metal pipe. can also be applied. As explained above, according to the present invention, in the method of welding end plugs to both ends of a pipe, an end plug having a small through hole is fitted to one end of the pipe, and a negative pressure source is applied to the small through hole. communicating to bring the inside of the pipe into a reduced pressure state,
Since it is a method of welding the pipe and the end plug,
Since the inside of the pipe can be welded under reduced pressure during welding, it is possible to prevent the occurrence of bulges, pinholes, undercuts, etc. in the welded part, and prevent a decrease in the strength of the pipe and problems when assembling the pipe. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing an example of a conventional fuel rod for a nuclear reactor, Figs. 2 and 3 are views showing defects occurring in the welded portion, respectively, and Fig. 4 is a longitudinal cross-sectional view showing an example of a conventional fuel rod for a nuclear reactor. FIG. 5 is a diagram showing the experimental results, and FIG. 6 is a partially cutaway longitudinal sectional view showing another embodiment of the present invention. 1... Cladding tube, 11... Welding machine main body, 12...
Welding chamber, 17, 17a... Rotation holding mechanism, 18...
... Fuel rod, 19 ... End plug, 20 ... Small through hole, 2
2...Welding electrode, 23...Stopper, 29...
Communication hole (through hole), 30...vacuum pump (negative pressure source).

Claims (1)

[Claims] 1. In a method of welding end plugs to both ends of a pipe, an end plug having a small through hole is fitted to one end of the pipe,
A method for welding an end of a tube, comprising communicating a negative pressure source to the small through hole to reduce the pressure inside the tube, and welding the joint between the tube and the end plug.