JPH0453599Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to nuclear fuel assemblies used in nuclear reactors such as pressurized water reactors, and particularly relates to nuclear fuel assemblies that are spaced apart in the longitudinal direction of the nuclear fuel assemblies. It relates to a support grid that holds fuel rods laterally spaced apart.

[Prior Art] As is well known, the support grid of such a nuclear fuel assembly includes a first group of a plurality of mutually parallel grid plates and a second group of plural grid plates that intersect at right angles to the first group of grid plates. The grid plates are parallel to each other, and the first group and the second group are crossed.
It is composed of a peripheral grid plate surrounding a group of grid plates, and a number of square cells are defined by the intersection of the first group and second group of grid plates, and fuel rods are vertically separated into the cells. It is designed to be placed and held in the axial direction. The intersecting portions of the crossed pairs of lattice plates are line-joined by brazing over substantially the entire length in the axial direction, or as disclosed in Japanese Utility Model Publication No. 49-37037 and Japanese Unexamined Patent Publication No. 51-111593. As disclosed in the publication, it is typical that the upper and lower ends of the intersection in the axial direction are locally spot-joined by welding.

On the other hand, especially in recent years, materials with small neutron absorption cross sections such as Zircaloy have been used for support grids from the perspective of improving neutron economy;
Since there is no solder suitable for use inside a nuclear reactor, spot joining by welding has been forced. However, during transport of fuel assemblies or during earthquakes, the support grid receives lateral loads on one or two of its sides, and the strength against such loads is higher than that of line joints made by welding, compared to line joints made by brazing. It is lower in the case of

Therefore, in order to compensate for the decrease in strength, support grids having a welded point joint structure are usually designed to have thicker grid plates or larger plate widths (dimensions in the height direction).

[Problems to be solved by the invention] Therefore, due to the dimensions of the conventional support grid having a welded point joint structure, the manufacturing cost is high and the lifting force at the support grid part due to the coolant is high. The problem was that it became larger and design measures had to be taken to accommodate it. The object of the present invention is to provide a support grid for a nuclear fuel assembly that does not have such problems.

[Means for Solving the Problems] For this purpose, the present invention has a first group of a plurality of mutually parallel lattice plates, and a second group of a plurality of mutually parallel lattice plates that intersect at right angles to the first group of lattice plates. It consists of a grid plate and a peripheral grid plate that surrounds the crossed grid plates of the first group and the second group, and each intersection of the grid plates of the first group and the second group is welded at both ends. In the support grid of a nuclear fuel assembly provided with a projection for use, a notch having a projection is formed in the axially central portion of the intersection portion of each grid plate of the first group,
Furthermore, a notch is formed at the intersection of each of the second group of lattice plates so as to engage with the protrusion in the notch of the first group of lattice plates when the lattice plates intersect with the first group of lattice plates. It is characterized by having a notch.

[Function] At the intersection of the lattice plates, protrusions are provided not only at the upper and lower ends but also between both ends, so by welding the protrusions, the bonding strength between the lattice plates is increased. As a result, deformation at the intersections of the grid plates is suppressed against lateral loads during earthquakes and the like. Therefore, there is no need to increase the thickness or width of the grid plate.

[Embodiments] Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which the same reference numerals indicate the same or corresponding parts.

Although only a part of the support grid 1 according to the present invention is shown in FIG. 1, this support grid 1, like the conventional support grid, includes a first group of a plurality of parallel grid plates 2a, and a first group of parallel grid plates 2a. a second group of a plurality of mutually parallel lattice plates 2b intersecting the lattice plates 2a at right angles;
It is composed of a peripheral lattice plate (not shown) that surrounds the first group and second group of lattice plates 2a and 2b which are intersected. A number of square cells 3 (only one shown) are defined and adapted to hold fuel rods 4 vertically in laterally spaced relation to each other.

a and b in FIG. 2 are such a first group and a second group.
Parts of the grating plates 2a and 2b of the group are shown, respectively. Since the grid plates 2a and 2b have substantially the same shape and there is no need to explain them in detail except for the parts constructed according to the present invention which will be described later, FIG.
Only the grid plate 2a will be explained.

The area or lattice plate portion 5a sandwiched between the two imaginary lines L ₁ and L ₂ defines one side surface of the cell 3 when combined with the second group of lattice plates 2b. In order to allow the grid plates 2a and 2b to intersect, a slit 6a is formed on the above-mentioned virtual line in approximately the lower half of the grid plate 2a, and the slit 6a is similarly formed in approximately the upper half of the grid plate 2b. It is adapted to fit into a corresponding slit 6b formed therein. Each region 5a also includes a fixing protrusion 7, horizontally extending slits 8 provided above and below the fixing protrusion for forming the fixing protrusion, a corrugation 9 that is a bulge for increasing strength, an elastic protrusion 10, and both sides of the fixing protrusion 7. Elastic protrusion forming slits 11 and the like provided in the longitudinal direction are provided in the same manner as in the prior art, and these serve functions such as supporting the fuel rods as well known to those skilled in the art.

The support grid 1 of the present invention is of a type having projections 12a at the upper and lower ends of each intersection of the grid plates 2a and 2b, and the projections 12a are of course aligned on the above-mentioned imaginary line. A pair of adjacent lattice plates 2a and a pair of adjacent lattice plates 2b are cut into slits 6a, 6.
When they are crossed by fitting b, a cell 3 is formed as shown in FIG.

According to the present invention, each grid plate 2a, 2b is provided with a substantially rectangular cutout 13 that is continuous with the inner end of the slit 6a, 6b on the above-mentioned virtual line, Protrusions 13a and 13b extending downward and upward are provided on the top and bottom sides, respectively.
is provided. Therefore, the grid plates 2a and 2b
When these are combined, as shown in FIG. 1, a space 14 is created approximately in the longitudinal center of the intersection, and the above-mentioned protrusion 13a projects slightly into the space 14.

The space 14 at the center of the intersection is designed to have dimensions necessary to easily weld the protrusion 13a.
If the protrusions 12a and 13a are joined by welding as in the conventional case, the state shown in FIG. 3 will be obtained.

In the embodiments of FIGS. 1 to 3, the notch 1
3 was provided separately from the slits 11 for forming the elastic protrusions 10, but as shown in FIG.
extend to slits for forming elastic protrusions at both ends thereof, and the notches 13 and slits 11 of the previous embodiment are integrated. Further, the shape of each protrusion 12a, 13a is not rectangular as shown in FIG. 2, but may be concave in the center as shown in FIG. 4 as long as it can be welded.

Further, as shown in FIG. 5, which shows a part of another lattice plate 2a, slits 6a are formed up to the center of the lattice plate 2a in the height direction, and a rectangular notch 16 is provided in the middle of the slit 6a. A notch 17 having the same shape may be provided in the notch 16 symmetrically with respect to the lateral center line of the lattice plate 2a. In this case, the top side of the notch 16 is provided with a protrusion 18b extending downward, and the bottom side of the notch 17 is provided with a protrusion 18a extending upward. The other lattice plate 2b to be combined with this lattice plate 2s may be considered to have the same shape as in the embodiment described above, except that the positions of the crossing slits are different. Therefore, the grid plates 2a and 2b
When crossed, a protrusion 18 is formed along the crossing part.
A space portion having projections 18a, 18b is formed, and projections 18a, 18b are formed.
18b can be easily welded in the same way as in the previous embodiment. Note that the protrusions 18a and 18b may be provided on the top side of the notch 17 and the bottom side of the notch 16.

[Effects of the invention] As described above, according to the invention, the intersecting parts of the lattice plates are provided with protrusions not only at the upper and lower ends but also at the central and intermediate parts, so that the thickness of the lattice plates can be reduced. The strength of the supporting grid can be easily increased without taking undesirable measures such as increasing the width, the moment of inertia, etc., and the deformation at the intersections of the grid plates is reduced under lateral loads such as those caused by earthquakes. suppressed.

[Brief explanation of the drawing]

FIG. 1 is a partial perspective view showing the assembled support grid of a nuclear fuel assembly according to the present invention, and FIG. 2 a and b are partial side views of two types of grid plates constituting the support grid of FIG. 1. , FIG. 3 is a partial perspective view showing a state in which the protrusions of the support grid shown in FIG. It is a partial side view which shows the modification of . 1... Support grid, 2a... First group grid plate, 2
b...Second group grid plate, 3...Cell, 12a...
Projections at both ends of the intersection, 13, 15, 16,
17... Notch, 13a, 13b, 15a, 15
b, 18a, 18b...Protrusions in the notches.

Claims (1)

[Scope of utility model registration request] A first group of parallel lattice plates, a second group of parallel lattice plates that intersect the first group of lattice plates at right angles, and a first group of intersecting lattice plates and a second group of lattice plates. In the supporting grid of the nuclear fuel assembly, the supporting grid of the nuclear fuel assembly is composed of a peripheral grid plate surrounding the first group and a peripheral grid plate surrounding the first group, and each intersection of the first group and the second group of grid plates is provided with welding protrusions at both ends. A cutout having a protrusion is formed in the axial center of the intersection of each grid plate in the first group, and a notch with a protrusion is formed in the intersection of each grid plate in the second group. A support grid for a nuclear fuel assembly, characterized in that a notch is provided with a protrusion formed to engage with the protrusion in the notch of the first group of grid plates when crossed.