JPH057593Y2 - - Google Patents

Description

[Detailed description of the invention] <<Industrial application>> The present invention relates to a fuel cladding tube into which uranium dioxide pellets, etc., which are the fuel in nuclear fuel rods, and a spring for restraint are inserted. This invention relates to an improvement in an end plug that is secured by fitting welding means to close the end of a tube.

<<Prior Art>> As is known, the end plugs of nuclear fuel rods are classified into upper end plugs and lower end plugs depending on the position where they are fixed to the fuel cladding tube. , threaded end plugs (tie rod end plugs) for attaching to the lower tie plate, and those with various shapes to enable identification of the type of fuel contained in the fuel cladding tube. Exists.

However, the conventional lower end plug, for example, has a fuel cladding tube A as shown in Fig. 3, and has a fitting part b with a flange a fitted into the tube end B, and a fitting part b connected to this. The fitting part b is tapered from the flange a and is formed into a solid truncated cone shape.

Therefore, in order to assemble a nuclear fuel rod using the lower end plug as described above, the fuel cladding tube A and the lower end plug must be loaded into a welding chamber with an inert gas atmosphere of argon, helium, etc. , and an end plug holding device is installed in the welding chamber, and is operated so that the lower end plug moves by a predetermined stroke on the axis of the fuel cladding tube, and the end plug of the fuel cladding tube A is connected to the tube end B of the fuel cladding tube A. Inside, the fitting part b
, thereby pressing the flange a against the pipe end rim B' of the pipe end B, and while maintaining this state.
A welded portion d is formed between the flange a and the tube end edge B' by TIG welding.

Then, after loading the required number of fuel such as uranium dioxide pellets from the still open upper end of the fuel cladding tube A, a restraining spring is installed to prevent the fuel from moving in the axial direction. The upper end plug closes the upper end port by the same means as the lower end plug.

In this way, with conventional means, not only the fuel cladding tube A and the end plug must be loaded into the welding chamber in an inert gas atmosphere, but also the
The above-mentioned end plug retaining device must also be installed, which not only requires the provision of a welding chamber with a considerably large floor area, but also the ability to fit the end plug into the fuel cladding. However, since this state must be maintained during welding, it is difficult to automate the entire process.

[Problems to be solved by the invention] In view of the above-mentioned problems when attempting to manufacture nuclear fuel rods using the conventional end plugs, the present invention creates a hollow cylindrical fitting portion of the end plug instead of simply making it solid. By forming a portion and cutting an open end slit, the fitting portion is given elastic force against diameter reduction, and
By appropriately setting the thickness of the hollow cylindrical part, just by fitting it onto the end of the fuel cladding tube, the fitting part comes into elastic contact with the inner wall surface of the end of the pipe. This prevents the end plug in the fitted state from inadvertently shifting and becoming abnormal, or even falling off due to loosening of the fitting. This makes it possible to fit a fuel rod into a fuel cladding tube in advance in the atmosphere, load it into a welding chamber, and perform only welding in the chamber, thus reducing capital investment in assembling nuclear fuel rods. The purpose is to make it possible to significantly reduce costs, facilitate full automation, and improve production efficiency.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a method in which a flange fitted into the tube end of a fuel cladding tube in a nuclear fuel rod and abutting against the tube end lip is fixed by welding. The fitting part has a fitting part and an extension part for attachment connected to the fitting part, and the fitting part has a hollow cylindrical part with an open end cavity opened on the inner end side, and a hollow cylindrical part is formed in the hollow cylindrical part. A predetermined number of end-opening slits are cut in the longitudinal direction, and the outer diameter of the elastic fitting outer peripheral surface of the hollow cylindrical portion formed at the cut location of the end-opening slit is set to be larger than the inner diameter of the fuel cladding tube. When the hollow cylindrical portion is fitted to the tube end of the fuel cladding tube, the diameter of the hollow cylindrical portion is large enough to apply a desired elastic contact force to the inner wall surface of the tube end by reducing the diameter of the elastic fitting outer circumferential surface. The aim is to provide end plugs for nuclear fuel rods made of

<<Operation>> By mechanical means such as supplying the fuel cladding to an end plug supply device installed in the atmosphere,
When the end plug of the present invention is fitted to the end of a fuel cladding tube from its fitting part, the elastic fitting outer circumferential surface, which has a larger diameter than the inner diameter of the tube end, However, at this time, the hollow cylindrical part with the open end slit is able to be elastically deformed in the radial direction, so the diameter is reduced, and as a result, the elastic fitting outer circumferential surface becomes inner. It will come into contact with the wall.

Moreover, due to the above-mentioned fitting, the flange abuts against the tube end edge of the tube end, and the axes of the end plug and the fuel cladding tube coincide, and this state is ensured by the above-mentioned elastic contact. Therefore, even during the process of transferring the end plug into the welding chamber or welding it, if the end plug moves to an incorrect position or falls off, there will be no problem.

《Example》 The present invention will be described in detail with reference to the illustrated example.
As shown in FIGS. 2 and 2, the flange 1a is fitted into the tube end B of the fuel cladding tube A, as in the conventional example, and comes into contact with the tube end edge B' of the tube end B.
and a fitting part 1 formed by an inner fitting protrusion 1b protruding toward the inner end side, and a mounting extension part 2 extending from the fitting part 1 toward the outer end side. However, in the present invention, the configuration of the fitting portion 1 is different from the conventional example as described below.

That is, a hollow cylindrical portion 1d is formed in the internal fitting protrusion 1b by opening an open end cavity 1c on the inner end side, and further, a hollow cylindrical portion 1d is formed from the end opening periphery 1e toward the rear end side. 1g in the figure indicates the rear end edge of the end open slit 1f, and as shown in the example, the end open slit 1f is bored in the longitudinal direction.
When drilling a plurality of threads f, it is preferable to arrange them so that they are spaced apart from each other by the same distance on the circumference.

Next, the hollow cylindrical portion 1d at the location where the end open slit 1f is cut has an elastic fitting outer peripheral surface 1h.
However, in the illustrated embodiment, the top of the arcuate circumferential surface 1i that is tapered toward the end periphery 1e of the hollow cylindrical portion 1d is the elastic fitting outer circumferential surface 1h. In the embodiment, the outer circumferential surface 1h is formed closer to the end opening periphery 1e than the terminal rear edge 1g of the open end slit 1f.

Therefore, when assembling a nuclear fuel rod using the above-mentioned end plugs, it is practical to cut and finish the tube end rim B' of the fuel cladding tube A in advance, so that when fitting the end plugs described later, The fitting accuracy, that is, the degree of normality of the attachment angle of the end plug to the fuel cladding tube A is improved.

Next, in order to clean the inner and outer surfaces of the fuel cladding tube A, wipe them with gauze moistened with acetone or alcohol.

On the other hand, by preparing the end plug of the present invention that has gone through the processes of processing, inspection, and cleaning, and supplying it to the end plug supply device installed in the atmosphere, the fitting part 1 of the end plug is automatically connected to the flange. The fuel cladding tube 1a is inserted and fitted until it comes into contact with the tube end edge B' of the fuel cladding tube A.

Here, in the present invention, the elastic fitting outer peripheral surface 1h
The outer diameter of the fuel cladding tube A is set to be larger than the inner diameter determined by the inner wall surface of the fuel cladding tube A, and in practice it is 0.005~
It is preferable to make the outer diameter larger than the inner diameter by about 0.015 mm.

As a result, due to the above-mentioned fitting, the elastic fitting outer peripheral surface 1
h is pressed in the radial direction by the inner wall surface of the tube end B,
As a result, the hollow cylindrical portion 1d, which is freely deformable in the radial direction due to the cut of the end-opening slit 1f, is reduced in diameter, and the resilient force based on the reduction in diameter causes the elastically fitting outer peripheral surface 1h to be moved to the tube end B. It is brought into close contact with the inner wall surface of the housing with a desired elastic contact force.

Fuel cladding tube A with the end plug fitted in this way
is transferred to a welding chamber or the like, where the flange 1a of the end plug is welded using the TIG welding method as described above.
It is sufficient to weld to the tube end rim B' of the fuel cladding tube A in an inert gas atmosphere to form a welded part d, and the subsequent assembly process is the same as that of the conventional example described above.

<<Effects of the invention>> Since the present invention is constructed as described above, the fitted end plug is brought into contact with the inner wall surface of the fuel cladding tube by the spring force in the radial direction. As a result, even during handling before being fixed by welding, the fitted state could become loose, causing unwanted fluctuations in the end plug, or even falling off from the pipe end. Therefore, there is no need to perform the fitting of the end plug in the welding chamber, and there is no problem even if it is carried out in the atmosphere, so it can be carried out in the atmosphere where it is easy to carry out the fitting process. This makes it easy to automate the process, making it possible to downsize the welding chamber, significantly reducing equipment investment, and making it possible to manufacture highly accurate nuclear fuel rods without much effort.

[Brief explanation of drawings]

Figure 1 is a partially cutaway front view showing the main parts of a nuclear fuel rod using an end plug according to the present invention, and Figure 2 is a partially cutaway front view of a nuclear fuel rod using an end plug according to the present invention.
FIG. 3 is a partially cutaway front view of a nuclear fuel rod using a conventional end plug. 1... Fitting part, 1a... Flange, 1c... End open cavity, 1d... Hollow cylindrical part, 1e... End opening periphery, 1f... End opening slit, 1g... End rear edge,
1h... Resilient fitting outer circumferential surface, 1i... Arc-shaped circumferential surface, 2
...Extension for installation, A...Fuel cladding tube, B...Tube end, B'...Tube end rim.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A fitting part in which a flange that is fitted into the tube end of a fuel cladding tube in a nuclear fuel rod and comes into contact with the tube end lip is fixed by welding, and a fitting part connected thereto. A hollow cylindrical portion is formed in the fitting portion by opening an end-opening cavity on the inner end side, and a required end-opening slit is formed in the hollow cylindrical portion in the longitudinal direction. At the same time, the outer diameter of the elastic fitting outer circumferential surface of the hollow cylindrical portion formed at the cut location of the end-open slit is set so that the outer diameter of the elastic fitting outer circumferential surface of the hollow cylindrical portion is smaller than the inner diameter of the fuel cladding tube. An end plug for a nuclear fuel rod formed to have a diameter large enough to apply a desired elastic contact force to the inner wall surface of the tube end by reducing the diameter of the elastically fitting outer circumferential surface when the end plug is fitted to the end of the tube. (2) The elastic fitting outer circumferential surface is formed by the top of an arcuate circumferential surface that tapers toward the end periphery of the hollow cylindrical part, and the top is closer to the end periphery than the terminal rear edge of the end-open slit. The end plug of a nuclear fuel rod according to claim 1 of the utility model registration, which is provided at the position of the claim 1.