JPS6259788B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear fuel assembly for use in a pressurized water nuclear reactor. Nuclear fuel assemblies of this kind used to be of the so-called can-type type, but later changed to the so-called can-less type, which does not have a can.
As shown in FIG. 1, the canless fuel assembly includes a support lattice 12 in which openings are formed in a lattice shape by vertical strips 13, lateral strips 14, and peripheral strips 15, and are arranged at intervals in the axial direction. a plurality of long hollow support tubes 10 attached to the support grid 12 at the openings of the plurality of support grids 12;
The fuel rods 8 (second
), the hollow support tube 10 is fixed to the upper and lower end structures 6, 7, the support tube 10 and the support grid 12, and the fuel rods 8 inserted into the other openings of the support grid 12 are auxiliary. It attempts to maintain the rigidity of the entire fuel assembly by adding a supporting effect.
Compared to the type with a can that covers the periphery of the assembly with side plates and fixes the side plates to the upper and lower end structures,
The low degree of rigidity is an unavoidable drawback.

For this reason, canless nuclear fuel assemblies are prone to bending, and when considering safety in the event of an earthquake or other accident, it becomes necessary to take measures such as enlarging the support tube, which is the center of the frame. The purpose of efforts to reduce absorption and eliminate blockages in the coolant flow path is lost.

The present invention makes use of the advantage of canless fuel assemblies in that there is no can, while increasing the rigidity of the fuel assembly, increasing its resistance to bending, making it easier to handle, and providing sufficient margin for safety in the event of an accident. This is a system in which extensions extending in the axial direction are formed in some of the strips constituting the support lattice, that is, some of the vertical strips and some of the horizontal strips or some of the peripheral strips, and The invention is characterized in that the strip plate extensions of each support grid are connected to each other.

Embodiments of the present invention will be described below with reference to the drawings.
The embodiment shown in FIG.
In each corner portion, the strip plate is extended in the vertical direction to form extension portions 5a and 5b.
The axially spaced adjacent support grids 2, 2... are extensions 5 of the respective peripheral strips 2.
They are connected by sequentially connecting a and 5b.

The upper and lower extensions 5a and 5b may extend to equal lengths in the vertical direction, one may be longer and the other shorter, or they may extend only in one direction. The extensions are preferably connected to each other by means such as butt welding to avoid creating differences in the joints and disrupting the flow of coolant. Further, from the viewpoint of output peaking, it is desirable not to insert a fuel rod into the opening in contact with this corner.

In the embodiment shown in FIGS. 3 and 4, extensions 3a, 3b, and 4a are provided on the central longitudinal and horizontal strips of the vertical strips 3 and horizontal strips 4 constituting each support grid 2, respectively.
4b is shown. The adjacent support grids 2, 2, which are arranged at intervals in the axial direction, are
Extensions 3 of each central longitudinal strip 3 and horizontal strip 4
They are connected by sequentially connecting a, 3b and 4a, 4b.

The above-mentioned upper and lower extensions may be both of equal length, one of them may be long, or only one of them may be the same length, as in the example shown in Fig. 2, and the connection shall be such that the connection does not cause disturbance to the coolant. The same is true. In some cases, the central vertical and horizontal strips are not inserted into the support grid in advance, and when assembling the aggregate, a long plate extending from the lower end structure to the upper end structure is inserted into the central vertical and horizontal strips. It is also possible to connect the plates and the support lattice by inserting them into the sections and connect the plates and the support grid in the same manner as in the case where the upper and lower extension parts are connected.

As described above, the present invention forms extensions extending in the axial direction in some of the strips of the support grid in a canless fuel assembly, and connects the strip extensions of adjacent support grids to each other. Because of this configuration, the neutron economy, which is an advantage of canless operation, is good.
Coolant can be mixed between fuel assemblies, the surface can be directly viewed during fuel inspection, there is less waste in the reactor, so the spacing between fuel assemblies can be reduced. Therefore, it is possible to significantly increase the stiffness in the lateral and longitudinal directions compared to conventional canless fuel assemblies without diminishing the various advantages such as being able to equalize the fuel rod spacing and flatten the output. .

Therefore, there is less risk of deformation of the fuel rods during transportation and handling of the fuel assembly, and a sufficient margin of safety can be provided in the event of an earthquake or a coolant loss accident. In the case of the embodiment in which extensions are formed at the corners of the peripheral strip, there is also the effect that it is less likely to get caught when loading fuel.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a conventional canless fuel assembly (fuel rods are not shown), Fig. 2 is a perspective view showing main parts of an embodiment of the present invention, and Fig. 3 is a perspective view of another embodiment of the present invention. FIG. 4 is an overall perspective view of the embodiment (support tubes and fuel rods are not shown), and FIG. 4 is a perspective view of the main parts of the same. 1, 11... Fuel assembly, 2, 12... Support grid, 3, 13... Vertical band plate, 4, 14... Horizontal band plate,
5, 15...peripheral band plate, 6...upper end structure, 7...
...Lower end structure, 8...Fuel rod, 3a, 3b...Vertical band plate extension, 4a, 4b...Horizontal band plate extension, 5
a, 5b...peripheral band extension part.

Claims (1)

[Claims] 1. A support grid in which openings are formed in the form of a grid of vertical and horizontal strips, and a plurality of long hollow support tubes attached to the support grid at the openings of the support grid arranged at intervals in the axial direction. , consisting of an upper end structure and a lower end structure attached to the upper and lower ends of the support tube and fuel rods inserted into other openings of the support grid, and axially attached to some strips of the support grid. 1. A nuclear fuel assembly characterized in that an extending portion is formed and the strip extending portions of adjacent support grids are connected to each other.