JPS601114B2 - How to assemble nuclear fuel rods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for assembling a nuclear fuel rod in which the joint surface between a cladding tube and an end plug is improved.

For example, the nuclear fuel rods of light water reactors and fast breeder reactors have the structure shown in FIG.

That is, one end of the longest cladding tube 1 is closed with an end plug 2, a number of nuclear fuel pellets 3 are loaded, and the pellets 3 are closed with a spring 4.
is fixed, the plenum chamber 5 is filled with helium gas, and the other end of the cladding tube 1 is closed at the end 6. The method for assembling this nuclear fuel rod is to insert an end plug 2 made of the same material into a cladding tube 1, weld the seam between the two, and then insert a nuclear fuel pellet 3 and a spring 4 into the cladding tube 1 to inactivate the rod. An end plug 6 is fitted with iron at the end of the cladding tube 1 in an atmosphere of gas, such as helium gas, and is sealed by welding. Here, the nuclear fuel pellet 3 is formed into a cylindrical shape by compacting and sintering mixed oxide powder of uranium and plutonium. By the way, when the nuclear fuel pellets 3 are loaded into the cladding tube 1, if the fine powder of the nuclear fuel pellets 3 is attached to the end surface of the cladding tube 1, the cypress 2 and the cladding tube will be separated as shown in FIG. These powders 9 are entangled in the welded part 8 of the joint surface 7 with the welded part 8, causing welding defects and not only defective welded products, but also radiation contamination of the surface of the nuclear fuel rod cladding tube 1. In order to remove this, troublesome beam removal work must be carried out in the subsequent process. To prevent this, conventionally, as shown in FIG. 3, a pipe opening mask 12 having a thin tubular sleeve portion 11 is attached in advance so as to be in contact with the inner surface 10 of the cladding tube 1, and then the nuclear fuel pellet 3 is inserted into the cladding tube. A method is known in which the end plug 2 is welded and sealed after the mask 8 is removed after the end plug 1 is loaded. However, in this method, the assembly work is naturally performed in the glove box, but the pipe opening mask 12
Because it becomes contaminated, all of it has to be taken out of the glove box as radioactive waste, which has the disadvantage of exposing workers to radioactive radiation and increasing the amount of waste. The present invention has been made to eliminate the above-mentioned drawbacks, and is capable of preventing welding defects occurring from the ends of cladding tubes, eliminating the need for tube masks, eliminating waste, and reducing radiation exposure to workers. An object of the present invention is to provide a method for assembling nuclear fuel rods that can reduce the amount of fuel used. That is, the present invention provides a method for assembling a nuclear fuel rod in which a nuclear fuel pellet is loaded into a cladding tube, both ends of the cladding tube are completely closed, and the joint surfaces are welded. A thin-walled cylindrical portion is formed by cutting the surface, and a protruding portion is provided at the end of the end plug to contact the pellet loaded into the cladding tube, and a cut is made from the protruding end so that the thin-walled cylindrical portion fits together. The assembly of a nuclear fuel rod is characterized in that a cylindrical recessed groove is provided, and after the thin cylindrical portion and the recessed groove are inserted and joined together, the joint surfaces of the outer peripheral surfaces of the cladding tube and the end plug are welded. It's a method.

Hereinafter, with reference to FIGS. 4 to 6, 1 of the method of the present invention will be explained.
An example will be explained. In the figure, the same parts as in FIGS. 1 and 2 are indicated by the same reference numerals, and the explanation of the overlapping parts will be omitted. In FIG. 4, a thin-walled cylindrical portion 13 is formed at the end of the cladding tube la by cutting from the outer circumferential surface, and a step portion 15 is formed on the inner surface of the cladding tube la to support the thin-walled cylindrical portion 13. Insert it into the guide tube 14 for loading LET 3.

Then, the plurality of pellets 3 are slid from the inner surface 16 of the guide tube 14, passed through the thin-walled cylindrical portion 13, and loaded into the cladding tube la. Note that the guide tube 14 is placed on rollers 17 to provide left and right flexibility. On the other hand, as shown in FIG. 5, the end plug 2a has a protrusion 18 formed at the end of the cladding tube la that contacts the pellet 3. A concave groove 19 having a diameter substantially the same as the diameter is cut. This end plug 2a is inserted through the thin cylindrical portion 13 of the cladding tube la, and the joint surfaces 7 thereof are welded to assemble a nuclear fuel rod. Thus, the thin cylindrical portion 13 formed in the cladding tube 1 serves as a loading guide for the pellets 3, and a large number of pellets 13 are arranged in the axial direction, and the center of the koji of the cladding tube la is connected to the guide tube 14. can be placed on the same axis.

Therefore, the radioactive powder scattered from the pellet 13 does not adhere to the welded mating end surface 13a of the cladding tube la. On the other hand, when the end plug 2a is inserted into the cladding tube la and sealed by welding as shown in FIG. The protruding portion 18 serves as a guide, and the end surface stepped portion 20 of the end plug 2a and the end surface 13 of the cladding tube la can be easily joined by welding without involving radioactive powder. That is, in the present invention, as shown in Fig. 5, the shape of the cladding tube and the overall shape of the end that is fitted with it are such that the tip of the cladding tube, where radioactive materials are more likely to adhere when loading the pellet, is smaller than the welded portion. They are sufficiently far apart, and since the concave groove covers this by inserting the end plug, it is possible to prevent the radioactive powder from scattering to the outside.

As explained above, according to the present invention, in the method of assembling the cladding tube and the terminal of a nuclear fuel rod, the cladding tube is used as a means for preventing contamination from the end of the cladding tube from nuclear fuel pellets and for solving welding defects caused by this. By changing the shape of the end and the shape of the cypress that is fitted to it, there is no need to use auxiliary parts such as traditional pipe masks, reducing manufacturing costs and reducing weld defects and contamination. It has the effect of preventing

Furthermore, in the welding and assembly process of nuclear fuel rods, there is no need for a mechanism to feed the pipe mask into the glove box or to take it out of the glove box after use, which has the advantage of greatly simplifying and streamlining the processing process. .

It should be noted that the present invention is not limited to the above embodiments, but is not particularly limited to any shape that can be joined, such as a tubular sleeve at the end of a cladding tube or a groove in an end plug.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view showing one example of a nuclear fuel rod, and Figure 2 is a vertical cross-sectional view showing an example of a nuclear fuel rod.
FIG. 3 is a longitudinal cross-sectional view showing an enlarged view of the joint between the cladding tube and the end plug in FIG.
The figure is a sectional view for explaining the method of assembling a nuclear fuel rod according to the present invention, and FIG. 5 is a perspective view showing a partial cross section of an example of an end plug for closing the end of the cladding tube shown in FIG. 4. FIG. 6 is a longitudinal sectional view showing an example in which the end plug shown in FIG. 5 is joined to a cladding tube. 1...Claying tube, 2...End plug, 3...
・Nuclear fuel beret, 4... Spring, 5...
Plenum chamber, 6... end plug, 7... joint surface, 8... welding part, 9... nuclear fuel powder,
DESCRIPTION OF SYMBOLS 10... Inner surface of cladding tube, 11... Tubular sleeve part, 12... Tube mask, 13... Thin cylindrical part, 14... Guide tube, 15 ...Stepped portion, 16...Inner surface, 17...Coroto 18...Protrusion,
19... Concave groove, 20... End step. Younger brother's figure 2 Grandson 3 Younger brother 4 Grandfather's figure 6

Claims (1)

[Claims] 1. In a method for assembling a nuclear fuel rod by loading nuclear fuel pellets into a cladding tube, closing both ends of the cladding tube with end plugs, and welding the joint surfaces, the outer peripheral surface of at least one end of the cladding tube is cut to form a thin wall. forming a cylindrical part, and providing at the end of the end plug a protruding part that comes into contact with the pellets loaded into the cladding tube, and also providing a cylindrical groove cut into the protruding part and into which the thin cylindrical part fits; A method for assembling a nuclear fuel rod, comprising: inserting and fitting the thin-walled cylindrical portion and the groove, and then welding the joint surfaces of the cladding tube and the end plug at their outer peripheral surfaces.