JPH0110633Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a configuration of a nuclear reactor fuel element that improves the fitting diameter of a blind plug that is butt-welded to the end of a cladding tube and reduces processing costs.

As shown in FIG. 1, the reactor fuel element includes a spring 3 that fills a cladding tube 1 with nuclear fuel material 2 and applies a compressive load to the cladding tube 1, and a blind plug 4 that seals both ends.
The abutting portion of the blind plug 4 and the end of the cladding tube 1 is welded 5 by TIG welding or the like to seal the tube. For example, taking a fuel element incorporated into a boiling water fuel assembly as an example, the fuel cladding tube 1 constituting the fuel element is made of Zircaloy-2 material, and the nuclear fuel material 2 filled therein is carbon dioxide. It's uranium pellets. And the spring 3 that gives compression to this is Inconel-X
Alternatively, the blind plug 4 made of stainless steel material and used for sealing both ends is made of Zircaloy-2 material, and the cladding tube 1 and the blind plug 4 are butted together,
That part is welded using TIG welding method.

However, although the soundness of the butt weld between the cladding tube 1 and the blind plug 4 is evaluated by an X-ray transmission test or an ultrasonic flaw detection test, the structure and dimensions of the fitting portion between the blind plug and the cladding tube It is known that this causes welding defects such as pores to occur.

That is, in the same fitting part, the insertion part of the blind plug,
If the fit with the cladding tube is loose, problems such as welding pores are likely to occur, the bead shape of the weld part is defective, and centering is difficult, etc., while if the fit is tight, it is difficult to tap the blind plug. If the parts are welded together, the problem arises that they are likely to be defective.

In general, the butt structure between the blind plug and the cladding tube can be roughly divided into two types, as shown in FIG. One is the case where the extension from the abutting part of the cladding tube 1 and the blind plug 4 to the blind plug is short, as shown in Fig. 2A, and the entire extension is welded during welding. One is the case where the extension from the abutting part of the cladding tube 1 and the blind plug 4 to the blind plug is long, as shown in FIG.

In any case, in order to increase the welding yield of the butt weld between the blind plug and the cladding tube, the diameter (D) of the fitting part inserted into the cladding tube of the blind plug is
must match the inner diameter of the cladding tube.

Conventionally, the method for this purpose was to divide the blind plug into several groups, taking into account the variation in the inner diameter of the cladding tube, and to perform actual matching for each corresponding group to control the dimensions of the diameter of the fitting part. At the same time, the dimensions of the blind plug are made larger by about 0.01 mm, and the inner diameter of the cladding tube is reduced while ensuring the minimum designed wall thickness. In other words, dimensional control of the diameter of the fitting part between the cladding tube and the blind plug has a large effect on the welding yield, and is closely related to the quality of the fuel element, so it is important to obtain a blind plug that matches the inner diameter of the cladding tube. Therefore, several types of blind plugs are made to match the inner diameter, and the one that fits is selected and welded.

However, in the above-mentioned method, high precision is required for the fitting part between the cladding tube and the blind plug, which reduces the processing yield of the blind plug, which increases the processing cost and increases the overall price. However, since several types of blind plugs must be prepared, their identification and management becomes complicated.

This invention was devised to deal with the actual situation and overcome these problems, and in terms of welding design,
By dividing the parts into important parts and non-important parts, the problem-prone fitting part has a simple structure, and the cost is reduced by using less materials.

In other words, the feature of the present invention is that a conical ring is manufactured separately, and the ring that matches the inner diameter of the cladding tube is fitted into the cladding tube insertion portion of the blind plug that has been manufactured in advance, allowing for butt welding. It is in.

To explain this in more detail, the cladding tube of the fuel element,
At the butt welding part with the blind plug, a separate insertion part made of a material that can weld the insertion part of the blind plug into the cladding tube to the cladding tube, the outer diameter of which has a maximum diameter that matches the inner diameter of the cladding tube. The insertion part on the maximum diameter side of the conical ring is inserted into the recess formed on the inner periphery of the butt weld on the side facing the inside of the cladding tube of the blind plug, and its tip position is is fitted so that it slightly enters the blind plug side from the welded part of the cladding pipe and the blind plug,
The nuclear reactor fuel element is constructed by integrating a blind plug, a conical ring, and a cladding tube with a very small gap between the butt weld and the ring.

Hereinafter, the present invention will be explained in detail with further reference to the accompanying drawings.

Figures 3A and 3B show various aspects of the butt welded part according to the present invention, and the fact that the blind plug 4 is butt welded 5 at the end of the cladding tube 1 is no different from the conventional method, but the present invention In the invention, a conical ring 6 having an insertion part on the maximum diameter side a of the conical shape inside the tube end of the cladding tube 1 is inserted into the end of the blind plug 4 on the side facing the inside of the cladding tube. It is fitted and inserted into a recess c formed on the inner periphery of the butt weld portion 5 at surface b.

The conical ring 6 is usually prepared in several types according to the dimensions of the cladding tube, and has an insertion part at a fixed position that is fitted into the recess of the blind plug 4.
The above-mentioned types are selected and used as appropriate by keeping the fitting position fixed to the cladding tube 1, with the outer diameter matching the cladding tube inner diameter, and the outer diameter of the maximum diameter part is at least 1.
It is large enough to be inserted into the inside of the cladding tube 1, and is approximately the same as the inner diameter of the cladding tube 1.
For example, if the cladding tube 1 is Zircaloy-2, the ring 6 is made of Zircaloy-2 or Zircaloy-4, while if the cladding tube 1 is stainless steel, the ring 6 is made of the same material or of a material that can be welded to each other. The ring 6 is made of stainless steel, Ni-based alloy, or the like.

When fitting this conical ring 6 into the blind plug, as can be seen from Figure 3 A and B, the tip of the insertion part should be positioned closer to the butt weld between the cladding tube 1 and the blind plug 4. The design has been devised so that it enters the blind plug side a little, so that it does not coincide with the butt part, and there is a very small gap e between the butt weld part and the ring part. This is because a ring 6 is placed on the film during an X-ray transmission test to evaluate the integrity of the weld.
This is because the butting position of the blind stopper 4 and the blind stopper 4 is photographed as a long line on the X-ray film, making it difficult to distinguish it from a welding defect above and below the film.

In addition, as a countermeasure against such pseudo defects, electron beam welding may be used, but it is also possible to eliminate the butt weld by making the weld deeper than usual.

The thickness of the conical ring 6 and the degree of fitting into the blind stopper 4 may be determined empirically as long as they are sufficient for sealing.

On the other hand, as mentioned above, the blind plug main body 4 that is combined with the conical ring 6 is constructed of the conical ring 6 in important parts where dimensional control is required, so it requires greater precision than necessary. Production will be streamlined accordingly.

In this way, the insertion part of the conical ring 6 is adapted to the recess of the blind plug, several types of common outer diameters and dimensions are prepared, the blind plug is finished to a certain size, and a ring that matches the cladding pipe is fitted into it. By abutting the cladding tube as a blind plug and welding that portion, both ends of the fuel element can be reliably sealed.

As described above, the present invention is formed by separately fitting a conical ring having an insertion part into the cladding tube insertion part of the conventional blind plug. By appropriately selecting the diameter and dimensions to suit the cladding tube, it is possible to obtain a fit that is equivalent to or better than that of the conventional case, and a good welding yield can be expected, as well as the conical ring's simple shape. Therefore, it is not only possible to automate manufacturing, but also to reduce costs through mass production, which is also advantageous in terms of stock.In particular, it is difficult to manufacture a conventional ring with an integral insertion part inside the cladding tube, but the ring of the present invention eliminates machining errors. Even if you do, the loss will be small,
It is sufficient to simply replace the ring, and together with the small amount of material used, this significantly contributes to reducing processing costs.

In addition, in the present invention, the tip of the insertion part on the maximum diameter side of the ring is placed a little closer to the blind plug side than the butt welding part of the cladding tube and the blind plug, so that they do not coincide, and the position of the butt weld part and the ring part Since a very small gap is ensured between the welds, unlike when they are in close contact with each other on the entire surface, it is easy to distinguish welding defects from welding defects during X-ray inspection, and reliable welding can be achieved.

Moreover, unlike conventional blind plugs, the present invention has no problems in size or structure, and can be easily manufactured using an automatic control panel, and is also highly effective in terms of manufacturing.

[Brief explanation of the drawing]

Figure 1 is an overview of the entire fuel element with some parts omitted;
Figures A and B are detailed views of the vicinity of the conventional butt weld, and Figures A and B are detailed views of the vicinity of the butt weld between the blind plug and the cladding tube according to the present invention. 1...Fuel cladding tube, 2...Nuclear fuel material, 3...
Spring, 4... Blind plug, 5... Welded part, 6...
conical ring.

Claims (1)

[Scope of utility model registration request] At the butt welding part 5 between the cladding tube 1 of the fuel element and the blind plug 4, the insertion portion of the blind plug into the cladding tube is welded to the cladding tube, the outer diameter of which is the largest diameter part matching the inner diameter of the cladding tube. It is formed by a conical ring 6 having a separate insertion part made of a suitable material, and the insertion part on the maximum diameter side a of the conical ring is brought into contact with the above-mentioned butt at the surface b of the side facing the inside of the cladding tube of the blind plug. The welded portion 5 and the ring portion 6 are fitted into the recessed portion c formed on the inner periphery of the welded portion 5 so that the tip thereof is slightly closer to the blind plug than the butted position d of the welded portion of the cladding tube and the blind plug. A nuclear reactor fuel element characterized in that a blind plug 4, a conical ring 6, and a cladding tube 1 are integrated with a very small gap e between them.