JPH09168865A - End plug for tube welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve welding strength by improving plastic flow of an inner side protruded part in welding. SOLUTION: The end plug 15 is welded by resistance welding while a tapered face 18 is pressed to an end edge 2b of a covered tube 2. The end plug 15 is provided with a recessed stepped part 20 having right angle cross section between the tapered face 18 and a tip face 19a to press a substance to be filled of fuel pellet, etc. Thus, a wide space 21 is made between the inner wall of the covered tube and stepped part 20, plastic flow in welding is promoted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an end plug for welding the end of a pipe by a resistance welding method.

[0002]

2. Description of the Related Art A fuel rod used as a fuel for a nuclear reactor has a large number of fuel pellets inserted in a long cylindrical cladding tube, and end caps are fixed to both ends of the cladding tube for sealing. Further, in the cladding tube, a plenum spring is interposed between the end plug on the one end side and the fuel pellet to press and hold the fuel pellet on the end plug on the other end side. A resistance welding method, for example, has been adopted as a method for welding the end plugs of the fuel rod having such a configuration to the cladding tube. In this welding method, first, one end of the cladding tube is inserted and arranged in an airtight chamber, and an end plug is fitted. As shown in FIG. 5, the end plug 3 has a substantially cylindrical shape, and the contact portion with the end surface 2a of the cladding tube 2 is chamfered to form a tapered surface 3a, and the tip surface 3b of the end surface 3b forms a fuel pellet p or a plenum spring. An insert such as the above is pressed and held in the covering tube 2. Electrodes 4 and 5 are attached to the outer peripheral surfaces of the covering tube 2 and the end plug 3 so as to be in contact with each other over substantially the entire circumference.

Then, as shown in FIG. 5, while the tapered surface 3a of the end plug 3 is pressed against the inner end edge 2b of the end surface 2a of the covering tube 2, an electric current is passed between the end plug 3 and the covering tube 2, Resistance contact welding is performed on both contact surfaces. Incidentally, the covering tube 2 and the end plug 3 are usually made of a zirconium alloy (zircaloy). According to this welding method, as shown in FIG. 6, an outer bulge portion (outer burr) 7 is formed on the outer peripheral surface of the welding region 6 between the covering pipe 2 and the end plug 3 due to the pressure applied during welding, while On the inner side of the cladding tube 2 in the welding region 6, an inner bulging portion (inner burr) 8 is similarly formed between the inner wall of the cladding tube 2 and the tapered surface 3a of the end plug 3. Since the outer diameter of the welding region 6 is larger than the outer diameter of the cladding tube 2, the outer bulging portion 7 grinds the outer periphery of the welding region 6 to remove the outer bulging portion 7 as shown in FIG. 7. Post-processing is done.

[0004]

However, the inner bulging portion 8 inside the cladding tube cannot be ground. Moreover, the inner bulging portion 8 flows and grows in a narrow tapered space partitioned by the inner wall of the coating tube 2 and the tapered surface 3a of the end plug 3 located in the coating tube, and sometimes grows as shown in FIG. However, there may be a problem that the end plug 3 protrudes from the front end surface 3b and comes into direct contact with and interferes with an insert such as the fuel pellet p. In order to prevent this, as shown in FIG. 9, the length of the taper surface 3a located in the cladding tube of the end plug 3 is adjusted so that the inner bulging portion 8 and the fuel pellet p do not interfere with each other. It must be set relatively large, and the end plug 3 becomes long. Moreover,
Regardless of the shape of the end plug 3 described above, the space in which the inner bulging portion 8 grows is divided by the inner wall of the coating tube 2 and the tapered surface 3a of the end plug 3 located in the coating tube. Since it is a narrow space 9, the fluidity of the molten portion during welding is poorer than that of the outer bulging portion 7 without obstacles. Therefore, plastic flow does not sufficiently occur during welding, so that impurities adhering to the interface between the cladding tube 2 and the end plug 3 before welding are insufficiently removed from the welding region 6, and clean metal surfaces are not separated from each other. Insufficient pressure welding may lead to a decrease in welding strength.

In view of the above situation, the present invention prevents the inner bulging portion generated at the time of welding from interfering with the insert when welding the pipe and the end plug, and causes sufficient plastic flow. An object of the present invention is to provide an end plug for pipe welding.

[0006]

SUMMARY OF THE INVENTION An end plug for welding a pipe according to the present invention is an end plug welded to an end of a pipe by a resistance welding method, the end plug being a taper pressed against an end edge of the pipe. It is characterized in that it has a surface and that the region following the tapered surface is a recess. Therefore, during resistance welding, the molten metal between the pipe and the end plug flows in the pipe as an inner bulge, but the molten metal in the pipe freely flows in the wide space between the inner wall of the pipe and the recess to cause plastic flow. Then, impurities adhering to the interface between the pipe and the end plug before welding are removed from the welding region by plastic flow, and sufficient welding strength can be obtained by pressure welding of clean metal surfaces. Further, it is possible to suppress the inner bulging portion from growing linearly, and it is possible to prevent interference with the insert of the tube.

The concave portion is characterized in that it is a stepped portion having a concave cross-sectional view formed between the tapered surface of the end plug and the tip surface for pressing the insert or the like of the tube. As a result, a wide space is formed between the end plug and the inner region of the tube, which facilitates plastic flow of the molten metal. The taper surface of the end plug is inclined in the range of 30 to 60 ° with respect to the axis of the end plug, and the boundary between the taper surface and the concave portion is the thickness of the cladding tube on the axis side from the intersection of the pipe edge and the taper surface. It is characterized in that it is located at a distance of 1/2 or less. If the angle of inclination of the tapered surface of the end plug with respect to the axis is less than 30 °, the end plug becomes unnecessarily long and the contact area between the inner wall of the pipe and the tapered surface tends to widen,
Since the electric current during welding is not concentrated, the welding capacity of projection welding is reduced. When the inclination angle of the taper surface of the end plug with respect to the axis exceeds 60 °, the contact area between the pipe end surface and the taper surface is likely to widen, and similarly the welding capacity of projection welding decreases. The reason why the boundary between the tapered surface of the end plug and the recess is a distance of 1/2 or less of the thickness of the cladding tube from the intersection of the end edge of the tube and the tapered surface is that the inner wall of the tube exceeds 1/2. This is because the space between the taper surface and the taper surface is small and the plastic flow during welding is poor. In addition, the end plug has a distal end surface formed so as to have a length such that the inner bulge does not protrude beyond the recess, and presses the inner insert in the tube.

[0008]

FIG. 1 is a block diagram showing an embodiment of the present invention.
4 to FIG. 4, the same reference numerals are used for the same parts or members as those in the above-described related art, and the description is omitted. 1 and 2 show a first embodiment of the present invention. FIG. 1 is a cross-sectional view of essential parts showing respective configurations of a cladding pipe and an end plug which are coaxially positioned before welding, and FIG. 2 is welding. It is a principal part sectional view which shows the connection structure of a coating tube and an end plug after. The end plug 15 welded to the end surface 2a of the cladding tube 2 before the welding of the fuel rod ends shown in FIG. 1 is made of, for example, a zirconium alloy and has an outer peripheral surface having the same diameter as the outer peripheral surface of the cladding tube 2. The main body 16 has a substantially columnar shape, and the end surface on the side opposite to the cladding tube 2 is chamfered 17 over the entire circumference. In the cladding tube side region facing the chamfer 17 side of the main body portion 16, the tapered surface 1 pressed against the inner end edge 2b of the end surface 2a of the cladding tube 2.
8 is formed in a ring shape, the maximum outer diameter of the tapered surface 18 is the same as the outer diameter of the cladding tube 2, and the minimum outer diameter is set to be slightly smaller than the diameter of the inner end edge 2b of the cladding tube 2.

Further, on the end surface 18a which is orthogonal to the axis O of the coating tube 2 and the end plug 15 and has the minimum outer diameter of the tapered surface 18, the outer diameter is smaller than that of the end surface 18a coaxially with the main body portion 16, for example, substantially. A cylindrical pressing portion 19 is formed, and the tip surface 19a thereof presses and holds an insert such as a fuel pellet. Therefore, in the end plug 15, a concave step portion 20 having a cross section of a substantially right angle is formed over the entire circumference between the tapered surface 18 and the tip surface 19a of the pressing portion 19. Further, the axial length of the outer peripheral surface 19b of the pressing portion 19 is such that the inner bulging portion 24 generated during resistance welding has the fuel pellet p.
It should be set to a size that does not interfere with interpolated objects such as.

The end plug 15 according to the present embodiment has the above-mentioned structure. Next, the welding method by resistance welding will be described. First, similarly to the above-mentioned conventional technique, the pressing portion 19 of the end plug 15 is attached to the end portion of the coating tube 2 in the chamber.
Is inserted, the tapered surface 18 is pressed against the inner end edge 2b of the end surface 2a of the covering tube 2, and the covering tube 2 and the end plug 15 are coaxially fitted as shown in FIG. In this state, a space 21 having a substantially quadrangular cross section is formed over the entire circumference between the inner wall of the covering tube 2 and the step portion 20 of the end plug 15. Then, in the same manner as in the prior art, while the covering tube 2 and the end plug 15 are pressed into contact with each other, a current is passed between the end plug 15 and the covering tube 2 via the electrodes 4 and 5, and the contact surfaces of both are resistance-welded. To do.

Then, as shown in FIG. 2, in the welding region 22 where the inner end edge 2b of the cladding tube 2 and the tapered surface 18 of the end plug 15 abut, the outer peripheral surface thereof bulges outward due to the pressure applied during welding. The part 23 (outer burr) projects. On the other hand, the inner bulging portion 24 (inner burr) also projects into the space 21 on the inner wall side of the cladding tube 1. At this time, the end plug 15 has a covering tube end surface 2
Since the step portion 20 is formed in the inner region near a,
The generated inner bulging portion 24 can freely flow and grow in the space 21 having a substantially square cross section in a molten state. Therefore, the plastic flow is promoted, and the cladding tube 2 and the end plug 1 are
From the interface between the cladding tube 2 and the end plug 15 in the welding region 22 of 5, impurities are swept away as the inner bulging portion 24 and eliminated,
We will be able to weld by pressing the clean metal surfaces together. Moreover, since the space 21 is a wide space having a substantially quadrangular cross section, the inner bulging portion 24 is linearly shaped to form the fuel pellet p.
It is also possible to suppress the flow in the direction of the equi-interpolated object and suppress the interference with the fuel pellets p and the like.

As described above, according to this embodiment, the concave step portion 20 is formed in the vicinity of the inner side of the tapered surface 18 of the end plug 15 where the inner end edge 2b of the covering tube 2 is pressed. Therefore, the plastic flow of the inner bulging portion 24 in the molten state can be promoted, impurities on the interface can be eliminated, and clean metal surfaces can be pressed against each other, so that the welding strength is high and the reliability of the welding portion is increased. Moreover, it is possible to prevent the inner bulging portion 24 from coming into contact with an insert such as the fuel pellet p.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a partial cross-sectional view showing a fitted state of the cladding tube and the end plug before welding. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In the figure, a stepped portion 27 having a substantially acute angle in cross section is formed over the entire circumference between the tapered surface 18 of the end plug 26 abutting against the inner end edge 2b of the covering tube 2 and the tip end surface 19a of the pressing portion 19. ing. In the case of the present embodiment, the inner wall of the cladding tube 2 and the step portion 2 of the end plug 26
Since the space 28 between the inner bulge portion 7 and the space 7 is larger than the space 21 in the first embodiment, the plastic flow of the inner bulging portion during welding is further increased, and the welding strength is further increased. Moreover, it is possible to more surely prevent the interference between the inner bulging portion and the insert such as the fuel pellet p.

FIG. 4 shows another embodiment of the present invention, in which the space between the tapered surface 18 of the end plug 29 and the tip surface 19a of the pressing portion 19 abutting against the inner end edge 2b of the covering tube 2 is shown. A concave step portion 30 having a substantially obtuse cross section is formed over the entire circumference, and a space 31 is provided between the step portion 30 and the inner wall of the cladding tube. As shown in each of the above-described embodiments, the concave step portion 2 between the tapered surface 18 and the tip surface 19a of the end plug with which the coating tube 2 abuts.
0, 27, and 30 may be right angles, acute angles, or obtuse angles, and therefore, the intersection angle θ between the tapered surface 18 and the end surface 18a.
Is less than 180 °. Preferably space 2
In order to widen 1, 28, 31 etc., the angle is set to 160 ° or less.

The length of the tapered surface 18 is
Contact point r1 between the inner end edge 2b of the cladding tube 2 and the tapered surface 18
To the intersection r2 between the tapered surface 18 and the concave step portions 20, 27, 30 is 1 / th of the thickness (t) of the cladding tube 2.
It is preferably 2 or less (see FIG. 4). r1 and r2
The distance s is set to t / 2 or less because if it exceeds 1/2, the space between the inner wall of the pipe and the tapered surface 18 becomes small and the plastic flow during welding deteriorates. The inclination angle α of the tapered surface 18 of the end plug with respect to the axis O is usually in the range of 30 to 60 °, preferably 45 °. Tapered surface 1
If the inclination angle α of the axis 8 with respect to the axis O becomes larger than 60 °, the space between the inner wall of the cladding tube 2 and the tapered surface 18 of the end plug will be small even if the concave step portions 20, 27, 30 are not formed. Can be increased and promote plastic flow during welding, while
Since the contact area between the end surface 2a of the cladding tube 2 and the tapered surface 18 becomes large and the electric current does not concentrate at the time of welding, the welding ability is reduced and the advantage of projection welding is impaired.
On the contrary, if the inclination angle of the tapered surface 18 with respect to the axis O is less than 30 °, there are disadvantages that the contact area between the tapered surface 18 and the inner wall of the cladding tube increases and the end plug becomes long.

Although the end plugs welded to the cladding tube of the nuclear fuel rod have been described in the above embodiments, the present invention is not limited to this, and the end plugs resistance welded to various tubular members will be described. It goes without saying that the invention can be adopted. Further, the method of resistance welding is not limited to the above-mentioned one, and any appropriate method can be adopted. In addition, the concave step portions 20, 28, 30 form a concave portion.

[0017]

As described above, according to the end plug for welding a pipe according to the present invention, the end plug has a tapered surface which is pressed against the end edge of the pipe, and the region following the tapered surface. Since it is a recess, the molten metal between the pipe and the end plug flows inside the pipe as an inner bulge during resistance welding, but the molten metal in the pipe freely flows in the wide space between the inner wall of the pipe and the recess. As a result, plastic flow occurs, impurities adhering to the interface between the pipe and the end plug before welding are removed from the welding region by plastic flow, and sufficient welding strength is obtained by pressure welding of clean metal surfaces. In addition, since the concave portion is a step portion having a concave shape in cross section formed between the tapered surface of the end plug and the tip end surface, a wide space is formed in the inner region of the tube in the end plug. Therefore, plastic flow of the molten metal easily occurs.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part showing an end plug according to a first embodiment of the present invention, showing a configuration of a cladding tube and an end plug before welding.

FIG. 2 is a cross-sectional view of essential parts showing a fitting structure of a cladding tube and an end plug after welding.

FIG. 3 is a cross-sectional view of essential parts showing a configuration before welding of a cladding tube and an end plug according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of essential parts showing a configuration before welding of a cladding tube and an end plug according to a third embodiment of the present invention.

FIG. 5 is a cross-sectional view of essential parts showing a fitting structure of a cladding tube and an end plug before welding of an end portion of a conventional fuel rod.

FIG. 6 is a cross-sectional view of an essential part showing a joint structure of a cladding tube and an end plug after welding of an end portion of a conventional fuel rod.

FIG. 7 is a diagram showing a state after the outer bulging portion of the end portion of the fuel rod of FIG. 6 is ground.

FIG. 8 is a partially enlarged view of the fuel rod end portion similar to that of FIG. 6, in which fuel pellets are mounted, showing a state where the inner bulging portion and the fuel pellets interfere with each other.

FIG. 9 is a view showing a fuel rod end portion similar to that of FIG. 7, in which end plugs are formed in a long shape so that the inner bulging portion and the fuel pellet do not interfere with each other.

[Explanation of symbols]

2 ... cladding tube, 2a ... end face, 2b ... end edge, 15, 26, 2
9 ... End plug, 18 ... Tapered surface, 20, 27, 30 ... Step portion,
21, 28, 31 ... Space, p ... Fuel pellet.

Claims (2)

[Claims] 1. An end plug welded to an end of a pipe by a resistance welding method, wherein the end plug has a tapered surface pressed against an end edge of the pipe, and a region following the tapered surface. End plug for pipe welding, characterized in that it is a recess. 2. The end plug for pipe welding according to claim 1, wherein the recess is a stepped portion formed between the tapered surface and the front end surface of the end plug and having a concave shape in cross section. .