JPH0622235Y2 - Taper end plug for sealing nuclear fuel pin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an end plug for sealing a nuclear fuel pin cladding tube of a nuclear reactor.

[Conventional technology]

A nuclear fuel pin is a fuel body used in a nuclear reactor, and is composed of fuel pellets that are shaped and sintered into cylindrical pellets and a cladding tube that protects the fuel pellets. The cladding tube is filled with fuel pellets and then sealed at both ends with end plugs.

In the fast breeder reactor, a stainless steel tube is generally used as a cladding tube, and has an elongated shape with an outer diameter of several mm and a length of 2 m or more, and both ends are welded with end plugs of a stainless steel round bar for sealing. .

FIG. 3 is a diagram for explaining a conventional end plug, and FIG. 4 is a diagram showing a partial cross-section whole circumference welded portion of the conventional end plug, in which 20 is an end plug, 21 is an end plug main body, 22 Is a brim, 23 is an R curved surface, 24
Is a cylindrical portion, 25 is a tapered portion, 26 is a butt portion, 27 is a bead, and 28 is a cladding tube.

In the figure, an end plug 20 includes an end plug main body 21, a collar 22 provided at one end thereof, a cylindrical portion 24, and a taper portion 25.
The outer diameter of the brim 22 is larger than the inner diameter of the cladding tube 28 and slightly smaller than the outer diameter. Cylindrical part 24
The outer diameter of the plug is large enough to fit into the coating pipe 28, and the taper portion 25 has a tapered shape so that the end plug 20 can be easily fitted into the coating pipe 28. Further, one surface of the brim 22 is in contact with the end plug body 21 with an R curved surface, and the other surface is a surface perpendicular to the central axis of the end plug 20 up to the cylindrical portion 24, which is a butt portion with the cladding tube 28. .

Generally, the welding of the joint between the end plug 20 and the covering pipe 28 is performed by TIG.
Welding method is used. The end plug 20 is fitted by inserting the taper portion 25 and the cylindrical portion 24 into the covering tube 28 until the abutting portion 26 comes into contact with the covering tube end surface.
Grab it with a bag chuck and hold it in an inert gas atmosphere for T
An arc is generated between the tungsten electrode of the IG torch and the weld, and the heat is used to melt the coating tube 28 and the end plug 20 while rotating the weld about 3 times, and as shown in FIG. Are welding.

[Issues to be solved by the device]

In such a conventional end plug, R is provided between the brim and the end plug body.
A curved surface is provided to control the dispersion of heat by the TIG torch into the end plug body. However, with a narrow R curved surface, the heat distribution from the welded portion to the end plug body tends to be too large or too small.
The welding conditions such as the position of the IG torch, the arc gap and the welding current are narrow, and this welding condition must be changed frequently during welding. If the welding conditions are narrow, welding defects caused by the electrode of the TIG torch accidentally contacting the weld or the welding rod, or undercutting due to evaporation of the weld pool at the weld caused when the welding current is too large, If the torch current is too small and the molten pool gathers near the electrodes and becomes too large and overlaps, the bead outer diameter becomes too large, or welding defects such as bead shoulders cause a problem in that the strength of the welded part decreases. Further, the above-mentioned problems may occur even when the welding conditions are changed due to the difference in the chemical composition of the material of the cladding tube and the end plug.

The present invention is intended to solve the above-mentioned problems, and by constructing one end of the end plug to be welded to the cladding tube to have a proper heat dispersion effect, a wide range of welding conditions can be set and welding defects can be prevented. It is an object of the present invention to provide a tapered end plug for sealing a nuclear fuel pin, which can reduce the occurrence of

[Means for Solving the Problems]

To this end, the present invention provides an end plug in which the tip is fitted to the cladding tube and the abutting portion is brought into contact with and welded to the cladding tube end surface to seal the nuclear fuel pin cladding tube end portion. It is characterized in that a taper portion having a maximum outer diameter on a surface in contact with the cladding tube end surface is provided, and a groove is provided in a part of the taper portion in the circumferential direction.

[Action]

The taper-shaped end plug for sealing the nuclear fuel pin of the present invention has a structure in which one end of the end plug to be welded to the end of the cladding tube is formed into a taper shape with a groove in the circumferential direction, so that heat input from the weld to the end plug body can be achieved. By adjusting, the welding condition setting range can be widened and the occurrence of welding defects can be reduced.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a view showing an embodiment of a tapered end plug for sealing a nuclear fuel pin according to the present invention, and FIG. 2 is a view showing a partial cross-section full circumference welding of the end plug according to the present invention. The same numbers as indicate the same contents. 1 is an end plug, 2 is an end plug main body, 3 is a tapered portion, 4 is a first tapered portion, 5 is a second tapered portion, 6 is a groove, 7
Is a butt portion, and 8 is a bead.

In the figure, an end plug 1 is made of stainless steel composed of an end plug main body 2, a tapered portion 3 provided at one end of the end plug main body 2, a cylindrical portion 24 provided at the tip thereof, and a tapered taper portion 25. It is made of steel round bar. Further, the taper portion 3 is divided into a first taper portion 4 contacting the cylindrical portion 24 and a second taper portion 5 contacting the end plug body 2 by a groove formed in the circumferential direction of the taper. The maximum outer diameter of the first tapered portion 4 is the cladding tube 2
The outer diameter of the end plug 1 is almost the same as that of the outer end 8 of the end plug 1 and is perpendicular to the central axis of the end plug 1.

In such a configuration, in order to weld the joint between the end plug 1 and the covering pipe 28 by the TIG welding method, first, the taper portion 25 and the cylindrical portion 24 are inserted into the covering pipe 28 and fitted to each other to form the butt portion 7. Abut the cladding end face. In this way, the covering tube is sealed by the fitting of the cylindrical portion 24 and the inner surface of the covering tube and the contact of the abutting portion 7 with the end surface of the covering tube. In this state, the electrodes (not shown) are brought close to each other, and the cladding tube 28 and the end plug 1 are melted and welded by arc heat. At this time, the heat distribution from the welded portion to the end plug body 2 is properly maintained in the groove 6, and the heat can be stably concentrated in the first tapered portion 4, and as shown in FIG. It can be performed.

In addition, the butt portion 7 is also used in the laser welding method in which the output is too large and the deposited metal is scattered during welding, which easily causes undercut.
It is possible to apply it by making the outer diameter of the tube larger than that of the cladding tube 28.

[Effect of device]

As described above, according to the present invention, a tapered portion having a groove is provided at one end of the end plug to properly maintain heat input from the welded portion to the end plug body and to stably concentrate the weld heat at the welded portion. By doing so, the setting range of welding conditions can be expanded, and along with this, the contact of the electrode of the TIG torch with the weld, the shoulder of the cladding, the undercut of the weld, welding defects such as weld pool overlap, etc. Can be remarkably reduced, and a decrease in weld strength can be prevented.

Further, by appropriately setting the magnitude relationship between the diameter of the covering pipe and the outer diameter of the mating portion with end plugs, it is possible to easily cope with the TIG welding method and the laser welding method in terms of design, and the chemistry of the welding portion and the end plugs. Welding conditions due to the difference in composition can also be stabilized. In addition, about 200 nuclear fuel pins are contained in the fuel assembly, and several hundred nuclear fuel pins are contained in the fast breeder reactor as a unit, so it is economical to reduce the processing time and welding defects of the nuclear fuel pins. It has a great effect.

[Brief description of drawings]

FIG. 1 is a view showing an embodiment of a tapered end plug for sealing a nuclear fuel pin according to the present invention, FIG. 2 is a view showing partial cross-section welding of the end plug according to the present invention, and FIG. 3 is a conventional end. Diagram showing the stopper,
FIG. 4 is a view showing a partial cross-section full circumference welding of a conventional end plug. 1 ... End plug, 2 ... End plug body, 3 ... Tapered portion, 4 ...
First taper portion, 5 ... Second taper portion, 6 ... Groove, 7 ...
Butt, 8 ... bead.

Claims (4)

[Scope of utility model registration request] Claim: What is claimed is: 1. An end plug in which the tip is fitted to the cladding tube, and the abutting portion is brought into contact with the cladding tube end surface and welded to seal the nuclear fuel pin cladding tube end portion. A tapered end plug for sealing a nuclear fuel pin, characterized in that a tapered portion having a maximum outer diameter on a surface in contact with the cladding tube end surface is provided, and a groove is provided in a part of the tapered portion in a circumferential direction. 2. The taper width from the butting portion to the groove is several mm.
The end plug according to claim 1. 3. The end plug according to claim 1, wherein the maximum outer diameter of the tapered portion is substantially the same as the outer diameter of the cladding tube. 4. The end plug according to claim 1, wherein the tip end portion that fits into the covering tube is composed of a cylindrical portion and a tapered taper portion.