JPH067185B2 - Support grid - Google Patents

Description

TECHNICAL FIELD The present invention relates to a support grid for a nuclear fuel assembly loaded in a nuclear reactor such as a pressurized water reactor.

"Prior Art" As is well known, in a nuclear fuel assembly, as shown in FIG. 3, a plurality of control rods are provided between an upper nozzle 1 and a lower nozzle 2 which are vertically opposed to each other. The guide pipes 3 are passed over and fixed, and a plurality of support grids 5 for supporting a large number of fuel rods 4 are attached to the control rod guide pipes 3 so as to be spaced apart from each other in the vertical direction.

The support grid 5, as shown in FIGS. 4 and 5,
The inner straps 6 in the form of thin strips having side tabs 6a, 6a formed at both ends in the longitudinal direction are orthogonal to each other to form a lattice main body 7 in the form of a square lattice. After inserting the side tabs 6a, 6a into the slits 8a, 8a formed in the above, bending part of the side tabs 6a, 6a protruding from the slits 8a, 8a to temporarily secure the outer strap 8, and then brazing these Then, the protruding side tabs 6a, 6a are assembled by grinding and removing.

Further, vanes 8b inclined toward the inner strap 6 are formed at both edges of the outer strap 8 in the width direction at predetermined intervals in the longitudinal direction of the outer strap 8. This vane
8b promotes the agitation of cooling water in the reactor, and the edge of the outer strap 8 of the support lattice 5 interferes with the adjacent nuclear fuel assemblies when a large number of nuclear fuel assemblies are taken in and out of the reactor. Thus, the nuclear fuel assemblies are prevented from being caught in each other or damaged.

[Problems to be Solved by the Invention] By the way, in the reactor, the cooling water is vigorously circulated from the lower side to the upper side during its operation, and the cooling water violently collides with the vanes 8b. Since the edge of this vane 8b is a free end, its mechanical strength cannot withstand the pressure of the cooling water, and the vane 8b may be torn from its bent portion, etc., and may be mixed as foreign matter in the cooling water. is there. Thus, if foreign matter is mixed into the cooling water, problems such as damage to the nuclear fuel assembly occur.

Further, in the support grid 5, since the mechanical strength of the outer peripheral portion thereof is lower than that of the inner portion thereof, the outer peripheral portion is apt to buckle.

It is an object of the present invention to solve the above problems.

"Means for Solving the Problem" The support grid of the present invention has a collar portion formed on both edges of the outer strap in the width direction along the longitudinal direction of the outer strap and having a drainage hole. The collar portion is formed on both edges of the outer strap and is inclined toward the inner strap side, and the longitudinal edge portion of the inclined plate is formed toward the inner strap, and the inner edge portion is formed. The reinforcing plate is joined to the widthwise edge of the strap.

"Operation" In the support grid of the present invention, the reinforcing plate is formed on the edge portion of the inclined plate formed on both edge portions in the width direction of the outer strap,
Since the edge portion of the reinforcing plate is joined to the inner strap, the mechanical strength of the collar portion composed of the inclined plate and the reinforcing plate is remarkably improved as compared with the conventional vane, so that the collar portion is prevented from being damaged. You can

In addition, the collar improves the mechanical strength of the outer strap (in particular, the buckling strength), and since the edge of the reinforcing plate forming the collar is joined to the inner strap, the mechanical strength of the entire support grid ( In particular, the buckling strength) is improved.

Furthermore, since a part of the cooling water that collides with the collar passes through the drain hole, the pressure of the cooling water that acts on the collar is reduced, and in this respect as well, damage to the collar can be prevented.

"Embodiment" An embodiment of the support grid of the present invention will be described below with reference to Figs.
It will be described with reference to the drawings.

In these figures, reference numeral 10 indicates a lattice main body.

The lattice main body 10 includes a plurality of thin strip-shaped inner straps 1
1 are orthogonal to each other and assembled in a square lattice shape,
Side tabs 11a are formed along the width direction of the straps 11 at the central portions of both ends of each inner strap 11 in the longitudinal direction.

A thin strip belt-shaped outer strap 12 is attached to the four circumferences of the lattice body 10 by inserting the side tabs 11a into slits 12a formed in the surface thereof and seam welding the side tabs 11a protruding from the slits 12a. ing.

Collars 15 are provided on both edges of the outer strap 12 in the width direction.
Are formed along the longitudinal direction of the outer strap 12. The collar 15 has a substantially V-shaped cross section, is formed integrally with the edge of the outer strap 12, and is inclined toward the inner strap 11 side.
And a reinforcing plate 17 that is integrally formed with the edge portion of the inner strap 11 and extends from the edge portion toward the edge portion in the width direction of the inner strap 11. The intersection between the edge of the reinforcing plate 17 and the edge of the inner strap 11 is spot-welded. Further, a rectangular water drain hole 18 is formed in the inclined plate 16 so as to be located between the adjacent slits 12a in the longitudinal direction of the inclined plate 16.

According to the support grid having the above-described configuration, the vane 8a plays a role of a conventional vane 8a that promotes stirring of cooling water and prevents interference between the nuclear fuel assemblies when a large number of nuclear fuel assemblies are taken in and out of the reactor. Attach the collar 15 to the outer strap 12
Since the slanting plate 16 is integrally formed on the edge portion of the and the reinforcing plate 17 integrally formed on the slanting plate 16 and the edge portion is spot-welded to the inner strap 11, Mechanical strength is significantly improved compared to the conventional vane 8a. Therefore, it is possible to prevent the collar portion 15 from being damaged by the pressure of the cooling water in the reactor.
It is possible to solve the problem caused by the fragments of the collar 15 being mixed in the cooling water.

Further, the collar portion 15 improves the mechanical strength (in particular, buckling strength) of the outer strap 12, and the edge portion of the reinforcing plate 17 that constitutes the collar portion 15 is welded to the inner strap 11. Since the strap 11 and the outer strap 12 are joined by welding the side tabs 11a protruding from the slits 12a, the mechanical strength (in particular, buckling strength) of the entire support grid is significantly improved as compared with the conventional one, and as a result, Seismic resistance and buckling strength of nuclear fuel assemblies are improved.

Further, since the drain hole 18 is formed in the inclined plate 17 that constitutes the collar portion 15, a part of the cooling water that collides with the collar portion 15 circulates through the drain hole 18 in the nuclear reactor. Therefore, the pressure of the cooling water acting on the collar portion 15 is reduced, and in this respect also, the collar portion 15 can be prevented from being damaged.

[Advantages of the Invention] As described above, according to the present invention, the agitation of cooling water is promoted, and the interference between nuclear fuel assemblies is prevented when a large number of nuclear fuel assemblies are taken in and out of a nuclear reactor. Since the collar portion for this is composed of the inclined plate formed on both edges of the outer strap in the width direction and the reinforcing plate formed on the inclined plate and the edge portion of which is joined to the inner strap, Mechanical strength is significantly improved over conventional vanes. Therefore, it is possible to prevent the collar portion from being damaged by the pressure of the cooling water in the nuclear reactor, so that it is possible to solve the problem caused by the inclusion of the broken pieces of the collar portion in the cooling water.

In addition, the collar improves the mechanical strength of the outer strap (in particular, the buckling strength), and since the edge of the reinforcing plate forming the collar is joined to the inner strap, the mechanical strength of the entire support grid ( (Buckling strength in particular) is significantly improved compared to the conventional one,
As a result, the seismic resistance and buckling strength of the nuclear fuel assembly are improved.

Further, since the drainage hole is formed in the collar portion, some cooling water that collides with the collar portion circulates through the drainage hole in the nuclear reactor. Therefore, the pressure of the cooling water acting on the collar portion is reduced, and in this respect as well, damage to the collar portion can be prevented.

[Brief description of drawings]

1 and 2 show one embodiment of the support grid of the present invention. FIG. 1 is a schematic perspective view showing the main part of the support grid, and FIG. 2 is a sectional view of the main part of the support grid. FIG. 3 is a front view of a nuclear fuel assembly, FIGS. 4 and 5 show an example of a conventional support grid, FIG. 4 is a perspective view of the support grid, and FIG. It is a perspective view of the principal part of a lattice. 10 ... Lattice body, 11 ... Inner strap, 12 ... Outer strap, 15 ... Collar, 16 ... Inclined plate, 17 ... Reinforcement plate, 18 ... Drainage hole.

Claims (2)

[Claims] 1. A support lattice in which a periphery of a lattice main body formed by intersecting a plurality of thin-plate strip-shaped inner straps with each other is surrounded by a thin-plate strip-shaped outer strap, wherein the outer straps have the same outer edges. Forming a collar along the longitudinal direction of the strap, the collar being formed on both edges of the outer strap and inclined toward the inner strap side; and the longitudinal direction of the inclined plate A support grid, which is formed at an edge of the inner strap toward the inner strap, and the edge is formed by a reinforcing plate joined to the widthwise edge of the inner strap. 2. The support grid according to claim 1, wherein a drainage hole is formed in the collar portion.