JPH0511877B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a support grid for a fuel assembly for a nuclear reactor.

[Prior Art] A fuel assembly loaded into a nuclear reactor consists of a large number of long cylindrical fuel rods in which a large number of short cylindrical pellets are sealed and arranged parallel to each other at regular intervals. It is formed by In this case, as a means to hold the fuel rods in such a positional relationship,
A support grid is used.

As shown in FIG. 9, this support grid is made up of a large number of straps 1 made of rectangular thin plates arranged vertically and horizontally in a grid pattern.

Of the inner surfaces of each cell 2 of such a support grid,
As shown in FIGS. 10 and 11, a spring 3 having elasticity is formed toward the center of the cell 2 on two adjacent surfaces closer to the lattice center, and the protrusion of this spring 3 A dimple 4 is formed toward the center of the cell 2 on the surface opposite to the surface facing the cell 2.

When a fuel rod is inserted into each cell 2 of such a support grid, the fuel rod is pressed against the dimple 4 by the elastic force of the spring 3 and is supported at a predetermined position regulated by the dimple 4, in this case at the center of the cell 2. be done.

Therefore, by installing support grids at several locations in the longitudinal direction of the fuel rods, it is possible to construct a fuel assembly in which a large number of fuel rods are supported in parallel at regular intervals.

[Problems to be solved by the invention] By the way, in the above-mentioned support grid,
Since it is necessary to press the fuel rod against the dimple 4 with spring 3, in order to do so, press spring 3
The fuel rod insertion space formed by the dimples 4 and 4 is set to be narrower than the outer diameter of the fuel rod. For this reason, when inserting a fuel rod into each cell 2, the fuel rod must be inserted in sliding contact with the tops of the springs 3 and dimples 4. , so-called scratches may be formed, and these scratches impair the appearance of the fuel rods, so after inserting the fuel rods into the support grid, it was necessary to remove the scratched portions to clean the appearance. Since this is done manually, it is troublesome, and there is also the problem of additional work such as the need to dispose of polishing debris.

[Means for Solving the Problems] The present invention has been made to solve the above problems. Oa, Oc
Fuel rod holding protrusions protruding toward the cell center are formed on two adjacent wall surfaces, and the middle lattice B
is equally divided into four square lattice structures by two mutually orthogonal line segments passing through the lattice center Ob,
These lattice structures are movable along the diagonal lines of the lattice B, and the lattice center is
It is characterized by forming fuel rod holding protrusions protruding toward the cell center on two wall surfaces in the direction opposite to Ob.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

In FIGS. 1 to 5, reference numeral 10 indicates upper and lower gratings (grids A, C), and 11 indicates an intermediate grating (grid B).
0 and the intermediate grid 11 constitute a support grid. Note that P is a fuel rod.

The upper and lower lattices 10 have a large number of rectangular straps 12 made of Zircaloy thin plates incorporated in a lattice pattern vertically and horizontally.
A rectangular strap 13 made of a thin Zircaloy plate is also attached.

A large number of lattice spaces, ie, cells 14, are formed in the upper and lower lattice 10 by these straps 12 and 13.

On the inner surface of each cell 14, on two adjacent surfaces on the side of the center point A in the plane of the lattice body shown in FIG. 5, as shown in FIGS. A dimple 15 is provided to protrude and support the structure.

As shown in FIG. 5, one intermediate lattice 11 has four lattice structures 11a to 11d formed by two mutually orthogonal line segments l passing through the lattice center Ob.
It is divided equally into.

In these lattice structures 11a to 11d, straps 16 formed in a rectangular shape made of a spring material such as Inconel (trade name) are incorporated vertically and horizontally in a lattice shape. An outer strap 17 shaped like the shape is attached.

By means of these straps 16 and 17, cells 18 having the same size as the cells 14 of the upper and lower grids 10 are formed inside each of the grid structures 11a to 11d.

Of the four wall surfaces that define each cell 18 of such lattice structures 11a to 11d, two wall surfaces located in the opposite direction to Ob at the center of the lattice have walls protruding toward the cell center as shown in FIG. A spring 19 is formed.

The above upper and lower lattices 10 and each lattice structure 11
a to 11d are assembled, and fuel rods P are inserted into each cell 14 and each cell 18 to form a support grid. How to assemble it will be explained below.

(1) First, as shown in FIG. 1, the upper and lower grids 10 are arranged in parallel with a slight interval so that the cells 14 at the same location are coaxial.

(2) Each grid structure 11a to 11d is connected to the grid body 1
0, and as shown in FIG. 5, the centers Oa and Oc of the upper and lower gratings 10 are arranged slightly outwardly along the diagonal _l1 in the plane of the grating structure 10. As shown in FIG.
11d and the top of the spring 19 (indicated by a dashed line r) is set so that the fuel rod P can be inserted therein.

(3) The fuel rods P are connected to each cell 14 of the upper and lower lattice 10 and each cell 18 of each lattice structure 11a to 11d.
Insert into. At this time, the dimples 15 of the upper and lower gratings 10 and each of the grating structures 11a to 11d
The circumferential surface of the fuel rod P should not touch the top of the spring 19 as much as possible.

(4) When the insertion of the fuel rods P is completed, each grid structure 11a to 11d is aligned with the diagonal l ₁ of the upper and lower grids 10.
, to the upper and lower grating centers Oa and Oc, forming a three-layered grating consisting of the upper and lower gratings 10 and the middle grating 11, as shown in FIGS. 3 and 4. Then, in this state, each joint on the outer periphery of each of the lattice structures 11a to 11d is fixed by welding means, and the intermediate lattice 11 is integrally connected.

As described above, a support grid is constructed by assembling the upper and lower grids 10 and the intermediate grid structures 11a to 11d, and at the same time, the fuel rods P are supported by this support grid.

According to this support grid, the elastic force of the spring 19 formed in each cell 18 of the middle grid 11 allows the fuel rods P to move into each cell 14 of the upper and lower grids 10.
It is pressed against the dimple 15 formed in the area and is supported in a fixed state at that position.

Therefore, by installing these support grids at several locations in the longitudinal direction of the fuel rods P, it is possible to construct a fuel assembly in which a large number of fuel rods are supported in parallel at regular intervals.

As described above, according to this embodiment, by shifting each of the lattice structures 11a to 11d when inserting the fuel rod P, the circumferential surface of the fuel rod P can be adjusted to the dimple 15.
And it can be made so that it does not come into sliding contact with the top of the spring 19. Therefore, it is possible to insert the fuel rod P into the support grid without substantially scratching the circumferential surface of the fuel rod P.

In addition, in this embodiment, the upper and lower grids 10 are made of Zircaloy, which absorbs very little neutrons generated from the fuel rods during the operation of the nuclear reactor, which has the advantage of improving neutron economy. be.

Note that in this embodiment, each of the lattice structures 11a to 11
Although the connection d is performed by welding means, for example, a clamp 20 as shown in FIG. 6 may also be used. This clamp 20 has a T-shape in plan view and has a fitting part 21 inside.
By fitting into the T-shaped joints on the outer circumferential side of each of the lattice structures 11a to 11d, each lattice structure 1
It connects 1a to 11d. Since the clamp 20 is removable, it is effective when reassembling or disassembling the fuel assembly.

Further, as shown in FIG. 7, each lattice structure 11
A pair of metal bands 22 surrounding the lattice structures 11a to 11d are used, and these are fitted around the outer peripheries of the grid structures 11a to 11d, and their ends are fixed by welding, or the ends are fixed as shown in FIG. The lattice structures 11a to 11d may be connected by caulking.

[Effects of the Invention] As explained above, according to the support grid of the fuel assembly for a nuclear reactor of the present invention, when the fuel rods are inserted into the cells of the support grid, the peripheral surfaces of the fuel rods are in contact with the inner surfaces of the cells. This allows the fuel rods to be inserted into the support grid with little scratching. Therefore, it is possible to omit the scratch removal work that was conventionally performed.

Furthermore, by appropriately selecting the material of the lattice, it is possible to improve the neutron economy.

[Brief explanation of the drawing]

1 to 5 are views showing one embodiment of the present invention, in which FIG. 1 is a partial side view of the support grid before assembly, FIG. 2 is a plan view thereof, and FIG. 3 is after assembly. Fig. 4 is a plan view of the supporting grid, Fig. 5 is a partial side view of the support grid.
The figure is a schematic plan view, FIG. 6 is a perspective view of another connecting means of the lattice structure and a part of the lattice structure, and FIGS. 7 and 8 are perspective views showing other connecting means.
9 is a perspective view of a conventional support grid, and FIG. 10 is a perspective view of a conventional support grid.
The figure is a partial plan view, and FIG. 11 is a perspective view thereof. 10... Lattice A, C, 11... Lattice, 11a~
11d... Lattice structure, 12, 13, 16, 17
...Strap (partition), 14, 18...Cell,
15... dimple (fuel rod holding protrusion), 19...
...Spring (fuel rod holding protrusion), P...Fuel rod,
l... line segment, l ₁ ... diagonal line.

Claims (1)

[Claims] 1 Three lattices A, B, and C are formed by arranging partitions vertically and horizontally within a square frame to form a large number of square cells of the same size. The fuel rods are arranged in layers, and the fuel rods penetrate the cells of these three grids A, B, and C.
The support lattice of a nuclear reactor fuel assembly has a layered structure, and the upper and lower lattices A and C are attached to two adjacent wall surfaces closer to each lattice center Oa and Oc among the four wall surfaces that define each cell. is formed with a fuel rod holding convex part that protrudes toward the center of the cell, and the middle lattice B is
It is equally divided into four square lattice structures by two mutually orthogonal line segments passing through the lattice center Ob, and each of these lattice structures is movable along the diagonal of the lattice B. Among the four wall surfaces defining each cell in the lattice structure, two wall surfaces in the opposite direction from the lattice center Ob are formed with fuel rod holding protrusions that protrude toward the cell center. supporting grid.