JPH0782100B2 - Grid spacer support structure - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a support structure for a grid spacer which is a fuel element spacer of a fuel assembly of a reduced speed nuclear reactor and a fast breeder reactor.

[Conventional technology]

In the core of a low-moderator reactor, in order to reduce the volume ratio of moderator water and fuel, the fuel elements are arranged in a dense lattice array, and the average energy of neutrons is increased from the thermal neutron region to the medium / fast neutron region and converted. The objective is to make effective use of nuclear fuel by improving the ratio.

The fuel assembly of the light water moderator reactor has a square lattice fuel arrangement, whereas that of the reduced speed reactor has a triangular lattice arrangement or a dense square lattice arrangement.

Further, the fuel assembly of the fast breeder reactor also has a triangular lattice arrangement in order to arrange the fuel elements as close as possible.

A grid or a wire is used as the fuel element spacer in the triangular lattice arrangement, but when the grid spacer is used, its axial support is required, and a tie rod or the like is generally adopted.

Therefore, in the conventional fuel assembly using the grid spacer and the tie rod, the trumpet tube 1 protects the strength member and fuel element of the assembly itself like the fuel assembly for fast breeder reactor shown in FIG. 13 and FIG. It has a function of securing a flow path and the like, and its cross-sectional shape is a thin hexagonal shape, and the upper part of the trumpet tube 1 is welded and fixed to the handling head 2 and the lower part to the entrance nozzle 3. In general, the wrapper tube is manufactured by forming a round tube or the like, which is a raw material, into a hexagonal shape by repeating hot and cold drawing.

On the other hand, in the conventional axial support of the grid spacer, as shown in FIGS. 13 and 14, the grid spacer 5 is provided by a tie rod 6 and a sleeve 7 which have substantially the same outer shape as the fuel element 4.

[Problems to be solved by the invention]

Therefore, when a grid spacer is used for a fuel assembly, the number of fuel elements is reduced by that amount, and if the assembly becomes large like a fuel assembly of a reduced speed reactor, a large number of grid spacers are required to secure the strength of the grid spacer. I need a tie rod,
Since the number of fuel elements is reduced accordingly, the output power density of the assembly is reduced and the performance of the fuel assembly is deteriorated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a support structure for a grid spacer in which fuel elements in a fuel assembly are not reduced.

[Means for solving problems]

Therefore, the support structure of the grid spacer of the present invention,
In the fuel assembly of the low-moderation reactor and the fast breeder reactor,
On the inner surface of the trumpet tube formed by the plate, concave grooves are formed by bending the plate at predetermined intervals at right angles to the longitudinal direction, the grid spacers are housed in the concave grooves, and the grid spacers are arranged on the fuel element.

[Action]

The peripheral portion of the grid spacer is securely held in the axial direction and the radial direction by the concave groove provided on the inner wall of the trumpet tube, and the holding portion area is remarkably larger than that of the tie rod type, so that the holding function is increased.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a vertical cross-sectional view of a fuel assembly showing an embodiment of a grid spacer support structure according to the present invention, FIG. 2 is a cross-sectional view of a grid spacer of the fuel assembly, FIG. 3 (a), ( b) and (c) are schematic views of a procedure for processing the trumpet tube of the present invention, FIG. 4 is an explanatory view of a method of inserting the grid spacer according to the present invention into the trumpet tube, and FIG. 5 is a diagram illustrating a method of inserting the grid spacer according to the present invention into the trumpet tube. FIG. 6 is a state diagram after insertion, FIG. 6 is an explanatory view of a groove processing for processing a trumpet tube of the present invention, and FIG. 7 is an overall view of a flat plate after processing a groove for processing a trumpet tube of the present invention
FIG. 8 is an explanatory view of a hexagonal bending process of a flat plate used for the trumpet tube of the present invention, and FIG. 9 is a cross-sectional view of the trumpet tube after the hexagonal bending process of the present invention, FIGS. 10 (a), (b), ( FIG. 11C is a procedure explanatory view showing an example of processing of a flat plate provided with a notch for processing the trumpet tube of the present invention, and FIGS.
FIG. 12 (a), (b), and (c) is an explanatory view of a method for inserting the grid spacer into the trumpet tube of the present invention, showing other processes of the flat plate provided with the notch for processing the trumpet tube of the present invention. It is a procedure explanatory view showing an example of.

In FIG. 1, 1 is a trumpet tube, 2 is a handling head, 3 is an entrance nozzle, 4 is a fuel element, 5 is a grid spacer, 9 is a groove, and the grid spacer 5 is shown in FIG. In the figure, the trumpet tube 1 is formed of a plate in a hexagonal shape, and is provided with concave grooves 9 into which an outer peripheral hexagonal grid spacer 5 is fitted at predetermined intervals at an inner surface thereof.

The fuel element 4 is entirely formed in the hole 5a of the grid spacer 5.
Is provided.

A trumpet tube having a hexagonal cross section having a conventional structure is manufactured by an integral drawing method, but it is difficult to attach grid spacers of several stages in the axial direction of the inner surface.

In order to manufacture the trumpet tube of the present invention, before bending a flat plate and bending it into a hexagon, a band-shaped concave groove having the thickness (height) of the grid spacer is processed into a flat plate and then By bending it into a square shape, inserting the grid spacer in the band-shaped groove, butting the longitudinal direction together, and welding the opening at the end, the grid spacer with multi-stage axial direction becomes the first.
It can be easily attached to the side plate without using the tie rod 6 shown in FIG.

The support structure of the grid spacer by the trumpet tube and the grid spacer of the present invention is shown in FIGS. 3 (a), (b) and (c).
As shown in Fig. 7, a recessed groove 9 in which the thickness (height) of the grid spacer 5 is inserted in the direction perpendicular to the longitudinal direction of a rectangular flat plate 8 of a size in which a hexagonal tube is expanded in advance is formed by pressing a required number of times in the direction perpendicular to the longitudinal direction. Then, bend this into a hexagonal shape, and use the circumferential elasticity of a hexagonal tube in which a part of the hexagon is open in the longitudinal direction as shown in FIG. 5 is stored, and the opening 10 is finally butted and welded as shown in FIG.

As shown in FIG. 6, the method for manufacturing the trumpet tube 1 used in the present invention is a rectangular flat plate 8 having a width obtained by expanding a hexagonal tube.
The groove width in which the thickness (height) of the grid spacer 5 fits at a predetermined position in the direction perpendicular to the longitudinal direction by the upper mold 11 and the lower mold 12 is sequentially performed in the longitudinal direction to form the groove 9 perpendicular to the longitudinal direction.
To provide. FIG. 7 shows an overall state diagram after this processing is completed.

Next, as shown in FIG. 8, it is bent into a hexagonal shape by the upper mold 13 and the lower mold 14 for long hexagonal bending, based on the longitudinal bending position and the processing order ,.
A hexagonal tube as shown in FIG. 9 is used.

Then, as described above, as shown in FIG. 4, the opening 10 is slightly expanded by utilizing the circumferential elasticity of the hexagonal tube in which a part of the hexagon is open in the longitudinal direction, and the grid is formed in the groove 9. The spacer 5 is inserted, rotated, and accommodated, and as shown in FIG. 5, the opening 10 is finally butted and the portion is welded by TIG welding which is inert gas arc welding.

10 (a), (b), (c) and FIG. 11 (a),
In order to facilitate the bending of the flat plate in the longitudinal direction, (b) can be manufactured in the same manner as described above in the manufacturing order of the groove 9 part of which is notched.

Further, FIGS. 12 (a), (b), and (c) show the order in the case of producing a hexagonal tube from two flat plates in the same manner, which facilitates the storage of the grid spacer 5. is there.

[Effects of the Invention] According to the grid spacer support structure of the present invention described in detail above, the following effects are achieved.

Since tie rods and the like are unnecessary and fuel elements can be loaded accordingly, the performance as a fuel assembly is improved.

It is possible to increase the thickness of the "frame plate" that is the strength member in the outermost peripheral component of the grid spacer, and to improve the strength of the grid spacer itself in the radial direction, bending, etc.

Since the structure of the grid spacer that allows the fuel elements at the outermost periphery of the fuel element bundle to be located as close as possible to the inner surface of the trumpet tube is established, the peripheral flow effect can be reduced, and the temperature gradient in the radial direction can be flattened. An excellent fuel assembly can be obtained.

Since a multi-stage strip-shaped projection is formed on the outer surface side of the side plate (trumpet tube), it can be expected to function as a spacer pad provided as a spacer for the adjacent assembly tube.

In connection with the above, a large number of protrusions, which are superior to the spacer pad function, are present on the outer surface of the fuel assembly in the axial direction of the assembly, so that an assembly advantageous in seismic resistance can be obtained.

The recessed groove provided in the trumpet tube acts as a beam and can suppress the deformation of the hexagonal flat surface, reducing the ballooning of the trumpet tube due to the internal pressure of the coolant, which is a problem in fuel assemblies of fast breeder reactors. The effect of reducing (radial bulging of the hexagonal side) can be expected.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a fuel assembly showing an embodiment of a grid spacer support structure according to the present invention, FIG. 2 is a cross-sectional view of a grid spacer of the fuel assembly, FIG. 3 (a), ( b) and (c) are schematic views of a procedure for processing the trumpet tube of the present invention, FIG. 4 is an explanatory view of a method of inserting the grid spacer according to the present invention into the trumpet tube, and FIG. 5 is a diagram illustrating a method of inserting the grid spacer according to the present invention into the trumpet tube. FIG. 6 is a state diagram after insertion, FIG. 6 is an explanatory view of a groove processing for processing a trumpet tube of the present invention, and FIG. 7 is an overall view of a flat plate after processing a groove for processing a trumpet tube of the present invention
FIG. 8 is an explanatory view of hexagonal bending of a flat plate used for the trumpet tube of the present invention, FIG. 9 is a cross-sectional view of the trumpet tube after hexagonal bending of the present invention, FIGS. 10 (a), (b), ( c) is a procedure explanatory view showing an example of processing of a flat plate provided with a notch, which is processed into the trumpet tube of the present invention, and FIGS.
FIG. 10 is an explanatory view of a method for inserting a grid spacer into the trumpet tube of the present invention, and FIGS. 12 (a), (b) and (c) are processing of a flat plate having a notch for processing the trumpet tube of the present invention. FIG. 13 is a longitudinal sectional view of a conventional fuel assembly for a fast breeder reactor, and FIG. 14 is a sectional view taken along the line AA of FIG. 1 ... Trumpet pipe, 2 ... Handling head, 3 ... Entrance nozzle, 4 ... Fuel element, 5 ... Grid spacer,
5a ... hole, 6 ... tie rod, 7 ... sleeve, 8 ... flat plate, 9
… Concave groove, 10… Opening, 11,13… Upper mold, 12,14… Lower mold

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G21C 3/32 GDF F

Claims (1)

[Claims] 1. A fuel assembly for a reduced-speed nuclear reactor and a fast breeder reactor, wherein a groove formed by bending a plate at a predetermined interval at a right angle to the longitudinal direction is provided on the inner surface of a trumpet tube formed by the plate, and the groove is formed in the groove. A support structure for a grid spacer, characterized in that the grid spacer is housed and a fuel element is arranged in the grid spacer.