JPH03259795A - Supporting grid for fuel assembly - Google Patents

Abstract

PURPOSE:To simplify an assembly operation for the supporting grid by providing the lower rear parts of corners having a self-aligning characteristic in the inlets of slits to facilitate the positioning and inserting of the slits. CONSTITUTION:The supporting grid 4 for the fuel assembly is formed by combin ing plural sheets of straps 4a perpendicularly with the slits S formed therein. Chamfers C1 of corner working parts which can grip the straps 4a facing each other at a wide inlet width and automatically position the straps 4a around the slits with slight insertion are provided in the inlets of the respective slits S at this time. The force to align the center lines of the respective slits S is, therefore, acted simply by lightly pressing the slits to each other. The delicate positioning in all the slits S of one array is thus automatically completed. The force to align the center lines of the slits to each other is acted at all times by the chamfers C1 at the time of inserting the straps to each other by pressing. The smooth insertion free from the relief deformation and distortions of the straps 4a is assured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a support grid that is used in a power reactor fuel assembly and supports fuel rods in the horizontal direction, particularly regarding its slit shape, and relates to the assembly of the support grid. The purpose is to facilitate.

[Prior Art] Figure 2 shows the structure of a fuel assembly for a pressurized wooden reactor (hereinafter referred to as PWR), which is a common power reactor.
8) is a front view, and (b) is an enlarged sectional view taken along line PP in the figure (a). Although several hundred fuel assemblies are actually arranged to constitute the pwR core, only one is shown here.

In FIGS. 2(a) and 2(b), the fuel rods 1 are spaced apart in the horizontal direction between the upper nozzle 2 and the lower nozzle 3 by 7 to 9 spacers (support grids 4) inserted. keep. The upper and lower nozzles 2.3 and each of the 7 to 9 support grids 4 are
The vertical positional relationship is fixed by the control rod guide tube 5,
The fuel rod 1 is held elastically within a body made up of these members so as not to receive any load other than its own weight.

The upper and lower nozzles 2.3, the control rod guide tubes 5, and each support grid 4 are a skeletal structure, and a large number of individual spaces along the fuel rod 1 held by them exchange heat from the nuclear fuel. A cooling water path (hereinafter referred to as a subchannel) is formed. During PWR operation, cooling water supplied from the bottom of the lower core plate 6 passes through the lower nozzles 3 and ascends all subchannels, removing heat from the surface of the fuel rods 1, that is, exchanging heat, and the cooling water is heated. state and is released to the second part. Therefore, the support grid 4 has a structure that does not excessively narrow the subchannel cross-sectional area, and is made of thin plates (
It is constructed by combining straps 4a) vertically and horizontally in a grid pattern.

FIG. 3 is a perspective view for explaining the assembly work of the support grid 4.

In FIG. 3, the support grid 4 is constructed by engaging the swans +-S in a direction perpendicular to the straps 4a, which are arranged at equal intervals in front and back with the swans 1-S facing ``2''. After inserting the wraps 1 to 4a one by one and assembling (C), each intersection point is spot-melted and fixed to each other.

Fig. 4 is for illustration purposes only, and shows the strap 4a (
(a) is a plan view of the strap 4a, and (b) is an enlarged view of the slit portion A thereof.

In FIGS. 4(a) and 4(b), the slit S of the strap 4a, which is formed by punching out a thin plate, is made so that the width of the slit S is equal to the width of the strap 48 (s) - the width of the wrap 48 so as not to cause any wobbling after assembly. The population of Swan I-S is defined to be approximately equal, and the population of Swan I-S is cut linearly.

[Problem to be solved by the invention] Since the population of the slits S of the conventional strap 4a is forced and twisted in a straight line, when the straps 4a are combined at right angles and the slits S are engaged with each other, the swan 1-s
Is this assembly work non-'+' because they fit into each other or are separated from each other?
＋ 'l D required practice and a lot of time.

That is, for every fraction of the slits S of the sluff 4a group that have been aligned and temporarily positioned in the direction after eruption as the work progresses, all the slits S of one strap 4a that can be assembled in the perpendicular direction are At the same time, it is necessary to engage vertically,
Moreover, the width of each slit S does not have enough margin for the thickness of the strap 4a, and furthermore, if some warpage remains in the punched strap 4a, the above-mentioned positioning can be performed by resisting this warpage. When carried out, while positioning one set of slits, the other set of swans failed. In addition, even after spending a great deal of time, there were cases in which assembly was impossible due to trial and error. Also,! No matter how many minutes of swan 1 to S positioning is successfully completed, if the strap 4a is strained or loose when inserted vertically, the insertion may be rough or difficult.
If this is done with excessive force, the support grid after assembly may be bent, or the strap 4a may be partially deformed or destroyed, and the strap 4a may be determined to be defective without waiting for the welding process. I had something to do.

The present invention facilitates positioning and insertion of the slit S,
1] The purpose is to simplify the assembly work of the support grid 4.

[Means for Solving the Problems] The fuel assembly support grid of the present invention is a fuel assembly support grid formed in a grid shape by combining a plurality of straps at right angles through slits formed in the straps. A corner processing portion with self-alignment property is provided in the slit population.

[Function] The support grid for fuel assemblies of the present invention is made by assembling a large number of straps at right angles and connecting the slits to each other as in the conventional case! i
They are then assembled by attaching them to each other.

Here, each swan has a corner processing part (for example, a chamfer) that can grip an opposing strap with a substantially wide width and automatically positions the strap in the center of the slit by slight insertion. is provided. Therefore, by roughly assembling the slits and lightly pushing them together, a force is applied to keep the center lines of both slits coincident, and the fine positioning of all the slits in the row is automatically completed. In addition, even when pushing further and inserting each other, the corner processing section always applies a J force to align the center lines of the mutual slits.
Smooth insertion work is possible without leaving wrap deformation or distortion.

[Embodiments of the invention] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is for explaining the structure of a strap used in a support grid for a fuel assembly according to an embodiment of the present invention.
a) , (b) , (c) Enlarged plan views of the population area.

In FIG. 1(a), since the slit S has a small chamfered CI as the first corner of the alignment, it is easy to position the slits S when the straps 4a are assembled at right angles. ′, Swat [~
Fewer pieces are needed when inserting Ss into each other.

FIGS. 1(b) and 1(c) show another example of the shape of this alignment course, which provides the same effect. In FIG. 1(b), the chamfer C2 is further formed deeper than the double chamfer C3, which further reduces the force required to insert the slits S into each other. Also,
In FIG. 1(C), the slits S are made into parallel wide portions C3 to increase the gripping force between the straps 4a.

[Effects of the Invention] In the support grid for a fuel assembly of the present invention, sufficient positioning is completed by pushing the swaps of the straps combined at right angles to each other roughly < 1F11, and then pushing from there. Since it is possible to perform smooth insertion work without leaving slippage deformation or distortion of the strap or wrap, the work is simplified compared to conventional assembly work, and the actual work time and worker training are reduced. Significant time savings are achieved. Moreover, this also makes it possible to mechanize the assembly-C work. Furthermore, since operational errors and strain on the straps are reduced, there will be no residual strain on the assembled support grid, variations among the plurality of support grids will be reduced, and surface scratches caused by repeated slit positioning and insertion will be eliminated.

[Brief explanation of drawings]

FIGS. 1(a), 1(b), and 1(c) are partially enlarged cross-sectional views of a strap used in a support grid for a fuel assembly according to an embodiment of the present invention. Figure 2 is for explaining the structure of a conventional general nuclear fuel assembly for PWR. FIG. FIG. 3 is a perspective view illustrating the assembly work of a conventional fuel assembly support grid. Figure 4 shows straps 4 of a conventional fuel assembly support grid.
(a) is a top view of slap I to wrap 4, and (1) is an enlarged plan view of part A in the figure (a). [Explanation of symbols of main parts] 4...Support grid 1a...Struff S...
・Slit C1, C2... Chamfer C3...
Wide part

Claims (1)

[Claims] In a fuel assembly support lattice formed by combining a plurality of straps at right angles through slits formed in the straps to form a lattice, the slit entrances are provided with corner processing portions having self-alignment properties. A support grid for a fuel assembly, characterized in that it is provided with a support grid for a fuel assembly.