JPS6020710B2 - Support grid for nuclear fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a support grid for a nuclear fuel assembly, and more particularly to an improvement in the joining structure of outer plates surrounding four circumferences of a plurality of strips arranged in an orthogonal grid.

Conventionally known support grids for nuclear fuel assemblies have a structure in which a plurality of thin strip plates are assembled into an orthogonal lattice as a middle plate, and four strip outer plates surrounding the four sides of the outer circumference are attached. The outer panels are connected and fixed to each other by spot welding the overlapping ends of each other at the corner cells on the outer periphery of the lattice structure.

That is, FIG. 1 shows the corner cell part of this conventional example, where 1 is a lattice-structured strip plate serving as an intermediate plate;
' are two adjacent outer plates attached to the outer periphery of the lattice assembly with their ends welded together at the overlapping part 3' in one corner cell C, C portion. In such a support grid, sufficient assembly precision is required for the original purpose of maintaining proper spacing between the fuel elements that are arranged and held inside. Bonding is not preferable in terms of assembly accuracy, and since the outer plate itself is thin, it is difficult to restrain it after positioning with a jig, and it is difficult to restrain it after positioning with a jig. It is difficult to determine the dimensions, and it is easy to cause distortion due to heating during assembly.

Furthermore, when handling nuclear fuel assemblies at a reactor site, the corner cells of the support grid, which protrude most outwardly and have a relatively weak strength, are damaged due to mutual interference with other nuclear fuel assemblies, etc. There are many things. Furthermore, if the outer panels are joined at the corner cell portions, the joint strength cannot be increased to the strength of the material, increasing the possibility of damage to the corner cell portions. In order to avoid this damage, some kind of interference impact mitigation structure should be attached to the corner cell part, or
Alternatively, it is possible to increase the strength of the corner cell portion to increase resistance to damage. This invention has been made in view of the above-mentioned circumstances, and is an improvement to the support grid that makes it possible to assemble the support grid easily and with high precision, and in particular improves the accuracy of the outer dimensions of the corner parts and increases the strength of the corner cell parts. Furthermore, it is intended to provide an improved structure in which it is easy to attach a shock-reducing reinforcing structure to the corner cell portion so that it hits the other party on the inclined surface in the event of interference. That is, in the support lattice of the present invention, the strip outer plates surrounding the four outer periphery sides of the orthogonal lattice set of a plurality of strips are joined end to end at the side cell parts instead of at the corner cell parts at the four corners of the lattice set. Therefore, a plurality of outer panels having L-shaped or U-shaped corners are used. As a result, in the support grid of the present invention, the outer periphery of the corner cell portion is integrally formed with a single outer plate, and its strength is as high as the material strength of the outer plate. Since it is a plate, it is possible to integrally form inclined guide surfaces on the upper and lower corners of the corners to reduce interference impact by press forming before assembly, and chamfers can also be formed in arbitrary dimensions. Of course, the above shape and dimensions of the corner part are made with high precision by press processing before assembly, and the corner cell part is not heated for joining during assembly, so there is no deformation or misalignment, and the positioning restraint by the jig can be used during assembly. It is possible to easily assemble a support grid of a predetermined shape and size without getting in the way. The present invention will be explained in detail with reference to the drawings as follows.

Now, when a support grid having the same shape as the conventional example shown in FIG. 1 is assembled according to the present invention, it will be assembled as shown in FIG. 2. In FIG. 2, parts corresponding to those in FIG. ,
One outer panel 2 and the other outer panel 2' are corner cells C,
The chamfered part 3 of the C part is integrally formed with one of the outer plates 2, and is joined at the joint part 4 with the strip plate 1 as the middle plate at the outer periphery of the side cell CH part outside the corner cell part. There is. In this case, since the corner cell portion is integrally formed with the outer panel 2, there is no decrease in its strength, and the dimensions and squareness of the corner curvature due to the outer panel 2, including the dimensions of the double-sided portion 3, are determined before assembly. It is determined with high precision by press forming, and there is also the advantage that even if the corner cell portion is restrained with a jig, the jig does not interfere with the welding or brazing work of joining at the side part. An example of the planar shape of the outer panels formed before assembly is the L-shaped outer panels 2a, 2b, 2c, and 2d shown in FIG.
When using two sheets, or when using U-shaped outer panels 2A and 2B shown in FIG.
There are various possibilities other than those shown in the drawings, such as a case where two sheets of the support grid are used. In this case, it is desirable to reduce the number of joints of the outer panels as much as possible for the entire support grid.

Furthermore, the joints 4 between the ends of the outer panels can also adopt various forms, as shown in Figs. 5 to 8, in addition to those shown in Figs. 3 and 8. That is, in FIG. 5, the ends of both outer plates 2 and 2' are bent and abutted against both ends of the strip plate 1, and the reinforcing pongee plate 5 is ironed into the recess formed by the bent parts. Joined together by attaching or welding.

In FIG. 6, the ends of both outer plates 2 and 2' are formed into a concave-convex mating shape as shown, and each middle plate mating slit 6 is formed at the end of the strip plate 1. After the protrusions 7 are welded together and competed with each other, the protrusions 7 peeking out from the gap between the concave and convex bran mating and the slit 6 are brazed or welded.

In Fig. 7, the weave of one of the outer panels 2 is bent by the wall thickness to form a recess, and the end of the other outer panel 2' is overlaid on this recess and brazed or welded. Board 1 and outer board 2
, 2' are joined by, for example, slits and protrusions as shown in FIG. Furthermore, in FIG. 8, the end of one of the outer panels 2 is aligned with the end surface of the band plate 1, and the end of the other outer panel 2' is bent inward to meet the end surface of the one outer panel 2 and the band plate. These are brazed or welded after being aligned on the 0 side of No. 1.

In the support grid of the present invention, as described above, the outer panels that integrally include the corner cell portions are connected at the outer periphery other than the corner cell sections, and therefore the outer panels of the corner cell sections are originally integral, so the corner cells It is easy to extend the upper and lower edges of the part and integrally mold the inclined guide part for reducing interference impact.

That is, FIG. 9 shows a corner cell portion having such an inclined guide portion, and the outer panel 2 has a portion bent inwardly at the upper and lower edges of the chamfered portion 3 of the corner 0 cell portion. It extends over part of the sides on both sides, and this bent portion 8
The slanted guide portion serves to prevent the corner cell portion from getting caught in the event of interference and to increase strength.

5. As described above, according to the present invention, the shape of the corner cell portion can be precisely determined by press processing during the manufacture of the outer panel, and there is no need to join the corner cell portion during assembly, so dimensions due to deformation etc. during assembly can be determined precisely. It is possible to easily complete the shape and dimensions as accurately positioned using the assembly jig without causing any deviation, and since the corner cell part is formed from an integral outer panel, it is strong. There is no decrease in the strength, and furthermore, design improvements can be made freely, such as extending the top and bottom of the corner cell part to strengthen it.
On the other hand, when joining near the center of the side, there is relatively little mutual mechanical interference between the assemblies, and when joining the outer panels on a flat part, it is possible to explore free joint structure including overlapping, and it is also possible to Reinforcing materials can be added without difficulty, and the design can be varied over a wide range to accommodate various specifications.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a corner cell portion of a conventional support grid, FIG. 2 is a perspective view showing a corner cell portion of a support grid according to an embodiment of the present invention, and FIGS. 3 and 4 are views of the present invention. FIG. 5 is a partial plan view showing an example of the joint between the skins of the present invention, and FIG. 6 similarly shows another example of the joint. A perspective view, FIGS. 7 and 8 are partial plan views showing further examples of joints, and FIG. 9 is a corner cell of the support grid of the present invention when an inclined guide part for impact reduction is attached. It is a perspective view which shows a part. 1... Lattice-like strip plate, 2, 2', 2a,
2b, 2c, 2d, 2A, 2B... Band plate outer plate,
3... Chamfered part, 4... Joint part, 8...
・Inclination guide part. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1. In a support lattice for a nuclear fuel assembly in which a plurality of strips are assembled into a lattice and the four sides of the outer periphery are surrounded by outer plates of the strips, the ends of the outer plates are arranged so that the ends of the outer plates are located within the cells on the outer periphery of the lattice. A support grid for a nuclear fuel assembly, characterized in that the support grid is joined at an outer peripheral part other than a corner cell part.