JPS6312549B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear fuel assembly used in a nuclear reactor, and more particularly to a support grid corner of a nuclear fuel assembly equipped with a support grid consisting of a plurality of orthogonal grid plates and outer plates on the four sides thereof. This invention relates to an improved structure for preventing interference between parts.

In conventionally known nuclear fuel assemblies, the support lattice has a structure in which four outer plates of strips surrounding the four sides of the outer periphery are attached to a plurality of thin strip plates as the middle plate arranged in an orthogonal lattice. It's getting old,
The outer panels are connected and fixed to each other by spot welding the overlapped ends at the corners of the outer periphery of the lattice structure. That is, Fig. 1 shows the corner part of this conventional example, where 1 is a strip plate with a lattice structure as the middle plate, and 2 and 2' are welded at the overlapping part 3 at one corner part. These are two adjacent outer panels attached to the outer periphery of the lattice structure.

In the conventional support grid, as shown in FIG. Resistance spot welding and subsequent brazing or TIG to join the outer panels
This is done firmly by welding, and the corner portions are usually chamfered at the overlapping portions 3 to prevent them from catching on the support grids of other adjacent fuel assemblies in the furnace. However, when handling fuel assemblies such as replacing them in the middle of their service life, the fuel assemblies may overlap with the support grids of other fuel assemblies due to bending, etc., and the fuel assemblies may be pulled out or inserted in that state. If the loading work is carried out by doing so, there is a high risk that damage will occur due to interference between the support grids. That is, in a nuclear fuel assembly equipped with a support grid as described above, as shown in FIG.
The strip outer plates 2 and 2' protrude from the outer surface of the rod-like element 7, such as a nuclear fuel rod, which is inserted into the corner cell 4 and supported, and in particular, the overlapping portion 3 at the corner corner of the outer plate of the corner cell is Overhang dimension at the side L ₁
In addition, as shown in Fig. ₁ , guide vanes 8 that are inclined inward are provided on the upper and lower edges of the outer panel to prevent them from getting caught due to interference. However, there is not enough dimensional space to install such guide vanes at the corners, so if the nuclear fuel assembly bends during use, the upper and lower edges of the outer skin at the corners, which protrude greatly, may be exposed to other objects during loading. It gets caught on the outer plate of the support grid of the nuclear fuel assembly, causing damage.

This invention was made in order to solve the above-mentioned problems, and its purpose is to minimize the protrusion of the support grid at the corners, and to prevent damage caused by catching during loading work. There is.

If this invention is explained along with the drawings of the embodiment, the third
In the figure, another rod-shaped element 7a having the same outer diameter as the rod-shaped element 7, such as a nuclear fuel rod, inserted into the inner region and side cells of the support grid 10 is inserted into the corner cell. , a nuclear fuel rod having a connection structure of a nuclear fuel element part 71 other than the support grid corresponding part and a segment 72 of the support grid corresponding part,
The segment 72 itself is composed of an alloy of non-fissile material such as a zirconium alloy.

FIG. 4 is a perspective view showing a corner portion of the support grid 10 used in the nuclear fuel assembly of the present invention, and FIG. 5 shows a cross section when combined with the rod-like elements 7, 7a. That is, the support grid 10 is bent so that the outer plate of the corner cell 4 is in contact with the outer surface of the segment 71 of the internal rod-shaped element 7a to form a large chamfered part 11, and the elastic support part 12 such as the cell 6 on the side part is bent. Instead, this chamfered portion 11 functions as a corner cell elastic support portion that presses the segment 72 portion against the rigid support portion 9 of the lattice strip 1 by its own elasticity.

Although the chamfered portion 11 forms a curved surface in the illustrated example, it may also form a flat surface, and in any case, the corner portion of the outer panel 2 has a large escape inward from the support grid. This will smoothly connect the adjacent outer edges. Furthermore, the segments 72 and the chamfered portions of the outer panel may be welded together, and in this case, the rigid support portions 9 in the corner cells are not required.

As mentioned above, since the nuclear fuel rods in the corner cells of the support grid are made of segments made of non-fissile material, these segments do not generate heat and therefore can be brought into direct contact over a large area with the support grid outer plate. As a result, the outer plate of the corner of the support grid can be moved inward by a large width, eliminating the overhang of the corner of the support grid of the nuclear fuel assembly, and preventing it from getting caught due to interference during loading work. be.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a corner portion of a support grid of a conventional nuclear fuel assembly, FIG. 2 is a cross-sectional view showing an arrangement of rod-like elements at the corner portion, and FIG. 3 is a perspective view showing an arrangement of rod-like elements at the corner portion. FIG. 4 is a partial front view showing a rod-like element at a corner of a nuclear fuel assembly; FIG. 4 is a perspective view of a corner portion showing an embodiment of a support grid used in the nuclear fuel assembly of the present invention; FIG. 5 is a cross-sectional view showing the corner arrangement when the element is combined with the support grid of FIG. 4; 1: Strip plate, 2, 2': Strip plate outer plate, 4: Corner cell, 5: Inner region cell, 6: Side cell, 7,
7a: Rod-shaped element, 71: Nuclear fuel element portion, 72: Segment, 8: Guide vane, 10: Support grid, 1
1: Chamfered part.

Claims (1)

[Claims] 1. In a nuclear fuel assembly having a support lattice in which a plurality of strips are arranged in a lattice, the four sides of the outer periphery of the lattice are surrounded by strip outer plates, and the lattice cells are cells for insertion and support of rod-shaped elements such as nuclear fuel rods, the above-mentioned A connecting structure in which a rod-like element inserted into a corner cell of a support grid axially connects the nuclear fuel element part other than the support grid corresponding part and the non-fissile material alloy segment part of the support grid corresponding part is formed. 1. A nuclear fuel assembly comprising nuclear fuel rods having a support lattice, wherein the strip outer plates of the corner cells of the support lattice are smoothly bent so as to be in contact with the outer surface of the segment portion, and adjacent outer edges of the outer periphery of the support lattice are connected. body.