JPS5914798Y2 - Grid for nuclear fuel assembly - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a grid for a nuclear fuel assembly, particularly a grid for a nuclear fuel assembly for a light water reactor.

A fuel assembly for a nuclear reactor, particularly a light water reactor, comprises a plurality of long fuel rods arranged in parallel, and the lateral spacing of the fuel rods is determined by a plurality of grids arranged at intervals in the longitudinal direction of the assembly. Adjusted and supported.

A large number of reactor fuel assemblies configured in this way are loaded into the reactor core 3 inside the reactor vessel 2 using the fuel exchanger 1 as shown in FIG. The side surface of the fuel assembly 4 that has already been loaded may come into contact with the side surface of the fuel assembly 5 that is to be newly loaded.

In particular, in the case of a so-called canless type fuel assembly that does not have a housing on the outside, the outermost outer frame of the grid is exposed, so if the sides of the fuel assembly touch each other as described above, loading will occur. If the side surface of the fuel assembly 5 in the middle is slanted, the corner part 7 of the grid 6 of this fuel assembly will overlap the loaded fuel assembly 4, as shown in part A of FIG. 1 and FIG.
The corners of the grids 6 may interlock with each other at the corners 7' of the grids 6.

If the fuel assemblies 4 and 5 move vertically relative to each other in this engaged state, the lattice will be deformed or damaged, so even if the side of the fuel assembly is slanted, the corners of the lattice will not engage with each other. It has traditionally been desired to do so.

In the conventional lattice, as shown in FIGS. 2 and 3, the strip-shaped outer frame 8 located at the outermost side has vanes 9 and tabs 10 above and below, and vanes 9 adjacent to the vanes 9 and adjacent vanes 9. The vanes 9 and tabs 10 are each provided with hypotenuses 11, 11' between the tabs 10 and 10, and the vanes 9 and tabs 10 are bent inward to change the direction of coolant flow through the fuel assembly and to improve cooling. In addition to having the effect of mixing materials,
It has the function of preventing the grids 6 from interlocking with each other,
Furthermore, although the oblique side portions 11 and 11' similarly have the function of preventing meshing of the gratings with each other, these functions alone are insufficient to prevent meshing of the corner portions of the gratings.

For this reason, the present applicant has proposed a nuclear fuel assembly that does not develop into interlocking at the corners of the lattice even when the sides of the fuel assembly come into contact with each other, and that has a simple structure and can function well. (Patent application No. 53-151047)
(see issue).

In order to reliably prevent accidental mutual engagement with adjacent fuel assembly grids during loading or unloading of fuel, the fuel assembly grid of the above-mentioned application has an upper edge near the corner of the grid of the fuel assembly grid outer frame. and/or an internally curved portion is formed at the lower edge, but as a result of various subsequent tests, it was found that the gap between the internally curved portion and the fuel rod facing it is minute at the edge of the circularly curved portion. It turns out that there is some problem with coolant flow resistance for other purposes, such as cooling the fuel rods.

This invention was made in view of the above circumstances, and can prevent mutual engagement between adjacent fuel assembly grids.
Another object of the present invention is to provide a lattice for a nuclear fuel assembly having sufficient coolant flow path gaps.

In response to this purpose, the nuclear fuel assembly lattice of this invention has a plurality of lattice plates and a band-shaped outer frame that partitions the outside to form a plurality of cells into which fuel rods are inserted. A lattice for a nuclear fuel assembly comprising an internally curved portion formed by bending an upper edge and/or a lower edge near a corner inward, the lattice comprising a notch at an edge of the internally curved portion. It is characterized by

The details of this invention will be explained below with reference to the drawings showing one embodiment.

In FIGS. 4 and 5, 14 is a fuel assembly;
The fuel assembly 14 includes a plurality of long fuel rods 15 arranged in parallel.

The fuel rods 15 are laterally spaced by grids 16 spaced longitudinally of the fuel assembly 14 .

The lattice 16 has a plurality of lattice plates 12 .
It is provided with a strip-shaped outer frame 18 that partitions the outside of 6.

A fuel rod 15 is inserted into each cell 17 . A plurality of vanes 19 are formed to protrude from the upper edge of the outer frame 18, and an oblique side portion 20a is formed between adjacent vanes 19.

20b is formed.

The vanes 19 are bent obliquely toward the inside of the lattice 16.

Further, a plurality of tabs 21 are formed to protrude from the lower edge of the outer frame 18, and between the adjacent tabs 21 there are oblique sides 20'a,
20'b is formed.

The tabs 21 are bent toward the inside of the grid 16.

Particularly noteworthy is the configuration near the corner portion 22 of the outer frame 18.

That is, at the upper edge of the outer frame 18 of the lattice 16, the outer part is formed between the corner part 22 and the vane 19 adjacent thereto, or over the cell 17 closest to the corner part 22 or the cell 17' adjacent thereto. The protrusion integral with the frame 18 is connected to the grid 1
6 is provided with an internally bent portion 23 formed by bending it inward.

Also, at the lower edge of the outer frame 18, between the corner portion 22 and the adjacent tab 21, or over the cell closest to the corner portion 22 or the cell 17' adjacent thereto,
An internally bent portion 24 is provided by bending a protruding portion integral with the outer frame 18 to the inside of the lattice 16.

Further, a notch 25 is provided at the end edge of the inner curved portions 23 and 24 at a position facing the fuel rod 25 so as to maintain a sufficient gap between the coolant flow and the periphery of the fuel rod.

In the fuel assembly having the lattice constructed in this way, the vane 19, the tab 21, and the hypotenuse portions 20a, 2
0b, 20'a, and 20'b, the inner bent portions 23 and 24 perform the guiding function, and when loading the fuel assembly into the reactor core, its side surface is It is possible to prevent the corners of the grid from developing into an interlocking state even if they come into contact with the sides of a finished fuel assembly.

Moreover, the structure of the lattice is not particularly complicated.

Additionally, as a result of experiments, by providing the notches 25 when forming the inner bent portions 23 and 24, the restriction on the amount of bending was relaxed and processing became easier.

Note that the shape of the notch is not limited to the arc shape shown in the above embodiment, as long as it can maintain a sufficient coolant flow path between the opposing fuel rods.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the state in which fuel assemblies are loaded into the reactor core, Figure 2 is a plan explanatory diagram showing the interference state of the grid in a conventional fuel assembly, and Figure 3 is an illustration of the outer frame of the conventional grid. FIG. 4 is a partial front view showing a fuel assembly lattice according to an embodiment of this invention, and FIG. 5 is a partial front view showing an outer frame of a lattice according to an embodiment of this invention. be. 14...Fuel assembly, 15...Curved fuel rod, 16
... Curved lattice, 18... Outer frame, 19... Vane, 21... Curved tab, 20a. 20 b, 20' a, 20' b ---
・Hypotenuse part, 22・Curve/corner part, 23° 23', 24・
...Curved part, 25.25'...Curved notch.

Claims (3)

[Scope of utility model registration request] (1) A lattice for a nuclear fuel assembly that forms a plurality of cells into which fuel rods are inserted, with a plurality of lattice plates and a band-shaped outer frame that partitions the outside, the outer frame being located near a corner. A nuclear fuel assembly comprising a circular portion formed by bending an upper edge and/or a lower edge inward, the nuclear fuel assembly having a notch at the end edge of the circular portion at a position facing the fuel rods. lattice. (2) The outer frame includes a plurality of vanes on the upper edge, and the curved portion is located between the corner and the vane adjacent to the corner, or between the cell or the vane closest to the corner. A lattice for a nuclear fuel assembly according to claim 1, characterized in that the lattice is formed over adjacent cells. (3) The outer frame has a plurality of tabs on the lower edge, and the curved portion is located between the corner and the tab adjacent to the corner, or between the cell closest to the corner or A lattice for a nuclear fuel assembly according to claim 1 or 2, characterized in that the lattice is formed over adjacent cells.