JPS6241355B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a support grid for a nuclear reactor fuel assembly, and more particularly to an improvement in the overlapping joints of the skins thereof.

In a fuel assembly loaded into a nuclear reactor, a plurality of fuel rods, etc. are inserted through a support grid to maintain a constant gap between them. In particular, the corner portions of the support grid protrude outwards to a large extent, so that the corner portions of the support grid may be exposed to other parts or objects during handling such as loading the fuel assembly into the reactor. There was a high risk of interference with the support grid of the fuel assembly, causing it to become caught and damage to the support grid. FIG. 1 is a perspective view showing the appearance of such a support lattice with respect to a corner part.
and an outer plate 2 surrounding the four outer peripheries of this lattice assembly, and the squares of each lattice constitute cells for insertion and support of fuel rods and the like. The outer panel 2 has both end edges 2a,
2b are overlapped to form a chamfered portion at the corner of the corner cell 3, and are connected by spot welding by pressing welding electrodes from the inside and outside. By the way, normally in such an overlapping part, both end edges 2
There is a small gap between the flat plates a and 2b, and they are completely in contact with each other at the spot welds, so as shown in Figs. Openings 4, 4 occur at the upper and lower edges of the edge portions 2a, 2b. As a result, if the upper and lower edges of the outer plate edge 2a are bent outwards from the support grid due to the above-mentioned opening 4, they will interfere with the support grids of other fuel assemblies when handling the fuel assembly, and the thin The outer panel may get caught in the gap between the openings 4, resulting in serious damage such as curling of the outer panel.

This invention was made to solve the above problems, and by bending the upper and lower edges of the outer panel in advance when forming the outer panel, it eliminates the occurrence of openings due to interference. The aim is to obtain a support grid that is less prone to damage.

That is, in this invention, as shown in FIGS. 4a and 4b, inwardly bent portions 6 are formed in advance on the upper and lower edges of the edge portion 2a that becomes the outer side at the overlapping connection portion of both edge portions of the outer panel. Then, after stacking this on the inner edge part 2b, it is joined by pressure welding and spot welding part 5 at several places so as to eliminate the gap 7 at the flat part between the upper and lower bent parts 6, 6. This is what happens. In this case, as shown in FIG. 4a, a gap is formed between the upper and lower bent parts 6, 6 in the overlapping state,
By pressing the welding electrodes from both sides and spot welding so as to eliminate this gap, the bent portion 6 presses the upper and lower edges of the inner edge portion 2b inwardly of the support grid, and therefore overlaps. At the upper and lower edges of the connection part, the inner and outer edges 2a and 2b are connected as shown in FIG.
A seamless seam 8 is formed where the upper and lower edges of the
Even if this is done as it is, the above-mentioned opening 4 will not occur, and if this joint is seam welded by TIG welding or the like, a more favorable result can be obtained. Although Fig. 4 shows the case where the vertical dimensions of both end edges 2a and 2b are equal, the vertical dimension of the outer edge 2a is set to be larger than the vertical dimension of the inner edge 2b as shown in Fig. 5. It may be made larger, and in this case, the bent portion 6 may be largely bent inward so that its outer slope serves more as a guide surface to prevent catching in the event of interference.

The problem with support grid interference is that the upper and lower edges of the outer skin get caught when the fuel assembly moves up and down in the axial direction, that is, when the outer skin 2 moves vertically in the height direction (Figures 4 and 5). Yes, therefore, the edge 2 of the edge portion 2a
a' can be left as is as shown in Figure 6a, but
Preferably, as shown in FIG. 6B, the edge 2a' is also provided with an inwardly bent portion 6' in advance, so that the edge 2a' is bent inwardly.
a' is made to contact the outer surface of the inner outer plate edge portion 2b without any gap, and furthermore, the tangential seam 9 is seam welded by TIG welding or the like across the upper and lower edges.

Incidentally, it is preferable that the seam welds of the seams 8 and 9 are ground and finished into a smooth shape. Furthermore, in each of the above-mentioned embodiments, the outer panel edge portions are overlapped and connected at the corner portions, but the present invention also applies to a case where both outer panel edge portions are overlapped and connected at the flat side of the outer periphery. It goes without saying that the structure of can be applied.

As described above, according to the present invention, the upper and lower edges do not open at the overlapping connection between both ends of the outer panels of the outer periphery of the support grid, and the existence of the bent portions of the upper and lower edges prevents the overlapping connection. The strength of the bent part is also improved, and since the outward slope of this bent part serves as a guide surface, it effectively prevents the fuel assembly from getting caught when it interferes with the support grid of another fuel assembly, and prevents damage such as peeling of the outer panel. This results in very few support grids.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the corner portion of a conventional support grid, Fig. 2 is an enlarged plan view of the overlapping connection portion of the corner portion, Fig. 3 is a sectional view taken along the line A-A in Fig. 4a is a cross-sectional view showing the overlapping joint part in the middle of assembly according to the embodiment of the present invention in the same direction as in FIG. 3, FIG. 4b is a cross-sectional view showing the state after welding of the previous figure, and FIG. Figures a and b show another embodiment of this invention.
6a and 6b are cross-sectional views taken along the line B--B in FIG. 4b, and particularly, FIG. It is a diagram. 1: band plate, 2: outer plate, 2a, 2b: outer plate edge,
2a': edge, 5: welded part, 6,6': bent part,
7: Gap, 8, 9... Seam.

Claims (1)

[Scope of Claims] 1. In a support lattice for a nuclear fuel assembly formed by lattice-forming a plurality of strips and surrounding the four outer periphery sides with strip outer plates, the edge portions of the outer plates overlap each other. Both the upper and lower edges of the outer skin edge at the mating joint are bent inward in advance, and the flat part between these bent parts is overlapped and spot welded to the inner skin edge. A support grid for a nuclear reactor fuel assembly, characterized in that: 2. The support grid for a reactor fuel assembly according to claim 1, which is formed by seam welding the upper and lower overlap joints of both the inner and outer outer plate edge portions at the overlap connection portion. 3. For a nuclear reactor fuel assembly according to claim 1, which is formed by seam welding the overlapping joint between the outer edge of the outer outer plate edge and the outer surface of the inner outer outer plate edge. Support grid. 4. The support grid for a reactor fuel assembly according to claim 1, wherein the outer edge of the outer skin plate is bent inward.