JPS5925196B2 - Support grid for nuclear fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a support grid for nuclear fuel assemblies, and particularly to an improved structure of its corner portions.

Fuel assemblies that do not have a jacket tube inside the reactor (canless assembly), such as fuel assemblies used in pressurized water reactors.
When handling fuel assemblies at the reactor side, fuel assemblies may interfere mechanically with other fuel assemblies, storage racks, handling jigs, etc. Moreover, there is a risk of damage to the supporting grid, especially its corner portions, which have relatively weak structural strength.

That is, FIG. 1 is a perspective view showing a corner part of a conventional support lattice, and shows a plurality of cells constituted by a plurality of strip plates 1 arranged in a lattice structure and a strip outer plate 2 surrounding the four sides of the outer periphery of the lattice structure. 3a, 3b, 3c.

It has 3d...

As is well known, fuel elements are inserted into each cell, and in order to arrange and maintain the fuel elements at appropriate intervals, support parts 4 and 5 protruding from the strip plate 1 and the outer plate 2 are formed in each cell. ing.

In the conventional support grid shown in FIG. 1, the corner cells 3a have the same support structure as other peripheral cells 3b, 3c or internal cells 3d, and usually two adjacent sides of each cell have the same support structure. It is inserted by a total of four supporting parts 4, one pair each on the upper and lower sides, and two supporting parts 5, one in each of the other two adjacent sides. The fuel element is supported from four directions at 90 degree intervals when viewed from above.

As a countermeasure against interference at the corners of a support grid with such a structure, when handling fuel assemblies, the assemblies are lifted up and down in the vertical direction, and the support grid can cause mutual interference due to relative movement in the vertical direction. A chamfered portion 6 is formed at a portion of the corner in order to minimize the outward protrusion of the corner portion of the support grid.

Further, measures are taken for the outer periphery of the support grid, such as providing guide vanes 7 bent inward at the upper and lower edges of the outer plate.

However, with the above-mentioned measures, there is a limit to reducing the protrusion of the corner part due to the constraint of supporting the fuel element in each cell from four directions when viewed two-dimensionally. There is a risk of damage.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved support grid structure that can effectively support fuel elements of corner cells and further reduce the protrusion of the corners of the skin.

Another object of the present invention is to provide a support grid that is further provided with a tapered guiding structure similar to the side portions to prevent interference in the vertical direction at the corner portions.

That is, the nuclear fuel assembly support lattice of the present invention is a support lattice for nuclear fuel assemblies in which strips are assembled into a lattice and the four outer periphery sides of the lattice are surrounded by outer plates of the strips. A supporting part of the outer plate for the fuel element in the corner cell is formed integrally with the flat part of the outer plate, and a separate support part is provided on each of the orthogonal band plates constituting the corner cell. The corner cell has a support structure from three directions when viewed in plan with respect to the fuel element, and in this way, the support part from the outer plate for the fuel element in the corner cell is By providing it only on the corner cell, the flat part can be retracted into the corner cell to a greater extent than in conventional corner cells that are supported in four directions when viewed from above, and the protrusion of the corner part becomes smaller accordingly. .

Furthermore, in the support grid of the present invention, in addition to the above, at least one of the upper and lower edges of the flat portion is bent or curved inward to the corner cell so as to form an obtuse angle with the flat portion, and this inward edge is bent or curved to form an obtuse angle with the flat portion. The outer surface of the curved portion serves as a tapered guide surface to smoothly escape to the side in the event of interference and prevent the corner portion from getting caught.

To explain this invention in detail together with the illustrated embodiment, FIG. 2 is a perspective view showing a corner portion of a support grid according to an embodiment of the invention, similar to FIG. 1, and the same reference numerals as in FIG. The corresponding parts are shown.

In FIG. 2, corner cells 3a are located at the corners of the outer panel 2.
There is nothing in the position facing the support parts 4, 4 of the strip plate 1,
Therefore, since the outer plate 2 is only thick, the outer plate is bent from this opposing position to form a wide flat part 6 in the corner.

This flat part 6 is provided with only one support part 5 by stamping in one piece, and this support part 5 faces towards the intersection of the strips 1.1 of the corner cell 3a.

Each support point 4, 4 of the strip plate 1, 1 in the corner cell 3a
are separated by an angle of 90 degrees from each other and are directed towards the center of the corner cell 3a, so that the fuel element inserted into the corner cell 3a is directed towards the center on the outer circumferential surface between the two support points 4, 4 of the strip 1. and the support point 5 on the flat part 6 of the outer panel 2, and are supported from a total of three directions in plan view, and the planar angular interval between the support points in these three directions is the distance between the support points 4 and 4. No.9
13 between 0 degrees and one support point 4 and the support point 5 of the flat part
13 between the support point 4 on the other side and the support point 5 on the flat part
It becomes a balanced five degrees.

Any of the support points 4, 4, and 5 may be a rigid support point, an elastic support point, or a combination thereof, and may be arbitrarily determined according to various design specifications.

Since the support point 5 of the corner cell 3a by the outer plate 2 is provided on the flat part 6, the outer plate forming the corner cell can be moved inward from the position facing the support point of the opposing strip plate. Since the flat portion 6 can be formed by bending the support grid, the protrusion of the outer peripheral angle of the support grid can be greatly reduced, and the chances of interference can be reduced.

Furthermore, in this invention, similarly to the guide vanes 7 on the side portions of the outer panel 2, at least one of the upper and lower carryovers of the flat portion 6 is bent inward to the corner cell so as to form an obtuse angle with the flat portion 6, and this inwardly bent portion 8 serves to prevent the guide vane 7 from getting caught in the event of interference, similar to the guide vane 7.

In other words, by providing this inward bending portion 8, the corner portions do not come into contact at right angles when mutual interference occurs, but instead serve as a guide to escape horizontally by moving upwards relative to the interfering partner; therefore, this inward bending If part 8 is on either the upper or lower side, the supporting grid of either the vertically moving assembly or the interference partner assembly that receives them will guide the other party by the above-mentioned inward bending of the corner part. It is sufficient to provide the inwardly bent portion 8 only on either the upper or lower edge of the flat portion 6 of the flat portion 6.

Of course, it goes without saying that the inwardly bent portions may be provided on both the upper and lower edges of the flat portion 6 of the corner portion.

As described above, according to the present invention, the protrusion of the corner of the support grid is greatly reduced, making it difficult to interfere with it, and
Since the guiding function of the inwardly bent portions can be performed even at the corner portions, the occurrence of damage due to interference is extremely reduced.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a corner portion of an example of a conventional support grid for a nuclear fuel assembly, and FIG. 2 is a perspective view showing a corner portion of an example of a support grid for a nuclear fuel assembly according to the present invention. . DESCRIPTION OF SYMBOLS 1... Lattice-structured band plate, 2... Outer plate of the band plate, 3a... Corner cell, 3b, 3c.
...Outer cell, 3d...Inner cell, 4.
...Supporting part of the band plate, 5... Supporting part of the outer plate, 6... Flat part, 8... Inwardly bent part.

Claims (1)

[Claims] 1. In a support lattice for a nuclear fuel assembly in which strips are assembled into a lattice and the four sides of the outer periphery are surrounded by outer panels of the strips, chamfered flat portions are formed by the outer panels at the corners of the outer periphery, and the corners in the corner cells are A support portion of the outer plate for the fuel element is integrally formed only on this flat portion, and the support portion and another support portion provided on each of the orthogonal band plates constituting the corner cell allow the corner cell to become the fuel element. In contrast, the corner cell has a support point structure in three directions when viewed in plan, and at least one of the upper and lower edges of the flat portion is bent inward so as to form an obtuse angle with respect to the flat portion. A support grid for nuclear fuel assemblies characterized by: