JPH09243771A - Manufacturing method of support grid for nuclear reactor fuel assembly - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To fabricate a support grid for a nuclear reactor fuel assembly, which is easy to work and strong. SOLUTION: When manufacturing a support grid for a nuclear reactor fuel assembly, a narrow widthwise slit is formed in straps 11 and 13, and the slits are used to fit the straps 11 and 13 at right angles to each other so as to cross each other. The welding electrodes 31 and 31 are attached to the straps 11 and 13 adjacent to the intersecting portion 12, a welding current is passed through the intersecting portion 12, and the straps 11 and 13 orthogonal to each other at the intersecting portion 12 are formed.
Are joined by resistance welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a support grid for a nuclear reactor fuel assembly, and more particularly to a method of manufacturing the same.

[0002]

2. Description of the Related Art Reactor fuel loaded in a reactor vessel for nuclear reaction or combustion generally forms a fuel assembly by bundling a number of sealed fuel rods filled with a fuel material containing a fissile material. Used in. As an example, the structure of a fuel assembly widely used in a pressurized water reactor is shown in FIG. In the figure, an upper nozzle 2 and a lower nozzle 3 having a coolant flow hole (not shown) of a fuel assembly 1 are connected by a plurality of control rod guide tubes 4 arranged in parallel with each other. Egg-holding frame-shaped rectangular support grids 5 are fixed to the control rod guide tubes 4 by inserting them, and generally, a large number of fuel rods 6 are inserted side by side and supported by a plurality of support grids 5. Has been done. More specifically, the support grid 5
Is a thin strip of nickel-based alloy or zirconium-based alloy (hereinafter referred to as a strap) 7 as shown in FIG.
A and 7b are combined orthogonally to each other, and a space (hereinafter referred to as a cell) 8 having a quadrangular cross section is defined between them, and the fuel rod 6 is inserted into and supported by the cell 8. Straps 7a, 7b integrally formed with supporting protrusions and springs
Are joined by brazing 9 at the intersection, but instead of brazing, both ends of the straps 7a, 7b may be joined by laser welding.

[0003]

Therefore, the support grid 5
In order to braze the straps 7a, 7b together, the material is manufactured so that the gap between them is narrow and constant.
Steps for heating the entire support grid 5 in a heating furnace with a braze placed on the joint are followed. Therefore, since the manufacturing process is complicated, the manufacturing cost is considerably high. Further, in the method of joining the straps by laser welding as described above, there is a problem that the joining portions are limited to both ends because it is necessary to guide the laser light to the joining portions. As described above, the fuel rod 6 is supported by the spring or the protrusion integrally formed with the strap. Therefore, if the central portion of the strap close to these is not fixed, the fuel rod 6 is bent and it is difficult to obtain a necessary supporting force. is there. Therefore, the problem to be solved by the present invention is to provide a method for manufacturing a support grid for a nuclear reactor fuel assembly that can secure the strength and rigidity required for supporting fuel rods and that is easy to work.

[0004]

In order to solve the above problems, according to the method of the present invention, a support grid for a reactor fuel assembly is assembled by crossing thin metal strips or straps at right angles to each other. The straps are fixedly joined by resistance welding. Specifically, a narrow widthwise slit is formed on the strap, and the slits are used to form the intersecting parts by making the straps orthogonal to each other and fitting together. An electrode is attached, a welding current is passed through the intersection, and both straps are welded by using resistance heat generated between the straps at the intersection. In order to perform stable resistance welding, a metal pressing plate is disposed with diagonally intersecting intersecting parts of orthogonal straps, and the pressing plate and the metal strip plate are sandwiched together by welding electrodes, and the intersecting parts are Weld current should be passed through. As another method for stable resistance welding, a similar intersection is sandwiched diagonally by wire clips, and then spot welding electrodes are pressed against the wire clips,
Spot weld the straps at the intersection with the wire clips.

[0005]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The present invention relates to a method for manufacturing a support grid for a nuclear reactor fuel assembly. In order to facilitate understanding of the method of the present invention, first, the structure of the support grid manufactured by this method will be described in detail. The planar shape of the support grid 10 is shown in FIG. As can be seen from the figure, the support grid 10 is basically configured by fitting a plurality of straps 11 and a plurality of straps 13 so as to intersect each other at a right angle. Although the attachment of the peripheral strap 15 is slightly different, the detailed description thereof is omitted because it is not directly related to the present invention. FIG. 3 shows the blank (material) shape of the straps 11 and 13. The strap 11 has a width direction slit 17 having a length approximately half the width on the lower side (in the figure), and the strap 13 has a width direction slit 19 having the same length on the upper side (in the figure) by punching or the like. Has been formed. The width of the slits 17 and 19 is slightly larger than the thickness of the material of the straps 11 and 13.

The straps 11 and 13 having the above-mentioned shape
When the other side is received in the slits 17 and 19 of its own and is fitted so as to intersect with each other at a right angle, it becomes as shown in FIG. 2, but when it is partially enlarged and shown, it becomes as shown in FIG. FIG. 5 is a vertical sectional view of FIG. 4, and FIG. 6 is a perspective view thereof. However, in FIG. 6, the fuel rod 6 to be supported is also shown, but this will be described later with reference to the supporting grid 1.
It is inserted and attached after the production of 0 is completed. Incidentally, the fuel rod 6 is a strap 11,
It is elastically supported by a spring 21 and a protrusion (also referred to as a dimple) 23 that are integrally formed on the member 13.

Next, the welding method of the present invention after assembling the blank-shaped straps 11 and 13 shown in FIG. 3 so as to be orthogonal to each other as shown in FIGS. 4 to 6 will be described.
Two welding electrodes 31 adjacent to the intersection 12 as shown in FIG.
Are closely placed and held on the straps 11, 13.
After that, when a predetermined current is applied between the welding electrodes 31, a narrow space is formed between the slits 17 and 19 and the opposite straps 11 and 13, so that resistance heat is generated there and melting causes welding. To be done. This welding is carried out sequentially on a number of intersections of the support grid 10. In order to stably perform welding and obtain more reliable welding, as shown in FIG. 7, the crossing portion 12 is sandwiched between the straps 11 and 13 by a pressing plate 33 having the same L-shaped cross section as that of the straps 11 and 13, and further. Holding plate 3
3 and the straps 11 to 13 may be sandwiched and held together by the welding electrode 35 and welded. Further, as shown in FIG. 8, the wire clip 37 having the shape shown in FIG. 9 is applied to the intersection 12 of the straps 11 and 13. And intersection 1
2, the spot welding electrode 39 is pressed against the wire clip 37 and the welding current is passed. This spot welding is performed in the required number at predetermined intervals in the width direction of the straps 11 and 13 or the length direction of the wire clip 37. Note that the wire clip 37
Are made of the same material as the straps 11 and 13. The straps 11 and 13 assembled orthogonally to each other as described above are firmly joined to each other at the intersection 12 by the electrodes 31 and 35 to the spot welding electrode 39.

[0008]

As described above, according to the present invention, a plurality of straps are fitted orthogonally to each other to form an intersecting portion, and the straps are joined by resistance welding at this intersecting portion. Since a strong joint can be obtained everywhere at the same time, the welding work does not require a complicated process such as brazing, so that the joining work can be facilitated and shortened.

[Brief description of drawings]

FIG. 1 is an explanatory view of a work state according to an embodiment of the present invention.

FIG. 2 is an overall plan view of a support grid manufactured according to the above embodiment.

FIG. 3 is an explanatory view showing a blank shape of a member joined by the embodiment.

FIG. 4 is a partially enlarged plan view of FIG.

FIG. 5 is a vertical sectional view taken along line VV of FIG. 4;

FIG. 6 is a partial perspective view corresponding to FIG.

FIG. 7 is an explanatory diagram showing a work state according to the modification method of the embodiment.

FIG. 8 is an explanatory diagram showing a work state according to the modification method of the embodiment.

9 is an elevation view showing the shape of a member used for the work shown in FIG. 8. FIG.

FIG. 10 is a partially cutaway perspective view showing an example of a nuclear reactor fuel assembly in which a support grid manufactured by the method of the present invention is used.

FIG. 11 is a partial perspective view showing a state of a support grid manufactured by a conventional method.

[Explanation of symbols]

 10 Support Grid 11 Strap 12 Intersection 13 Strap 17 Slit 19 Slit 31 Welding Electrode 33 Holding Plate 35 Welding Electrode 37 Wire Clip 39 Spot Welding Electrode

Claims (3)

[Claims] 1. A narrow widthwise slit is formed in a thin metal strip, and the slits are used to form a crossing portion by fitting the metal strips at right angles to each other and adjoining the crossing portion. A welding grid is attached to a metal strip, a welding current is passed through the intersection, and the metal strips orthogonal to each other at the intersection are resistance-welded to produce a support grid for a reactor fuel assembly. Method. 2. A narrow widthwise slit is formed on a thin metal strip, and the slits are used to form an intersecting portion by fitting the metal strips at right angles to each other, and the intersecting portion is formed diagonally. A metal pressing plate is arranged to sandwich it, and then the pressing plate and the metal strip plate are sandwiched by welding electrodes, a welding current is passed through the intersection, and the metal strips orthogonal to each other at the intersection are resistance-welded. A method for manufacturing a support grid for a nuclear reactor fuel assembly, comprising: 3. A narrow widthwise slit is formed in a thin metal strip, and the slits are used to make the metal strips orthogonal to each other and fitted together to form an intersecting portion, and the intersecting portion is paired with a wire clip. It is sandwiched in the angular direction, and then a spot welding electrode is pressed against the wire clip to sandwich it, and a welding current is passed to the intersection through the wire clip,
A method for manufacturing a support grid for a nuclear reactor fuel assembly, characterized in that the metal strips orthogonal to each other at the intersection are resistance-welded.