JPS63235890A - Fuel aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel assembly used in a nuclear reactor, and particularly to a structure for fixing a fuel spacer within the fuel assembly.

[Conventional technology]

Conventionally, in fuel assemblies used in nuclear reactors, fuel rods containing nuclear fuel and deceleration rods for decelerating neutrons and flattening the heat generation distribution are arranged in a grid pattern. Further, in order to maintain the spacing between these fuel rods and deceleration rods, fuel spacers are provided at several locations along the axial direction of the fuel assembly. FIG. 4 is a plan view of a fuel spacer in a conventional fuel assembly. The fuel spacer has plates arranged in a grid pattern and holds fuel rods and deceleration rods in unit cells surrounded by the plates.

In boiling water reactors, the deceleration rod is a circular water rod through which cooling water flows.

The fuel spacer is fixed in a fuel assembly using water rods by sandwiching and fixing the spacer between two protrusions attached to the surface of the water rod in the axial direction, as shown in Figure 5. . Therefore, when assembling the fuel assembly, as shown in Figure 6, insert the reduction rod by rotating it so that the protrusion does not hit the spacer, and when the spacer reaches the specified position, rotate the reduction rod. , the spacer is engaged with the protrusion.

Another method of fixing the spacer within the fuel assembly is
There is a method of fixing the spacer by providing a spring on the water rod, as shown in Japanese Unexamined Patent Publication No. 61-217794.

In recent years, the development of fuel assemblies to achieve higher burnup in nuclear reactors has been progressing. In particular, in fuel assemblies used in boiling water reactors, it is necessary to increase the amount of fuel loaded by reducing the diameter of the fuel rods and increasing the number of fuel rods to accommodate higher burnup.

In such a fuel assembly, in order to increase the neutron moderating ability of the central part of the assembly, it is necessary to use a water rond with a large cross-sectional area, and it is desirable to use a water rond with a square cross-sectional shape rather than a cylindrical shape.

[Problems to be Solved by the Invention] In such a fuel assembly, since square water rods are used, the fuel spacer cannot be fixed using conventional methods. That is, since the water rod inserted into the fuel spacer cannot rotate and change its direction, the protrusion attached to the surface of the water rod cannot be engaged with the fuel spacer and cannot be fixed.

On the other hand, another method of fixing the fuel spacer is disclosed in Japanese Patent Application Laid-open No. 61
A method disclosed in Japanese Patent No. 217794 has been considered. In this method, a spring is provided on the surface of the water rod, a fuel spacer is inserted with the spring compressed, and the lower end of the fuel spacer is supported with the spring extended.

However, although this technique can prevent the fuel spacer from falling downward within the fuel assembly, it cannot prevent the fuel spacer from being moved upward by the flow. Also,
When disassembling the fuel assembly, the fuel spacer cannot be easily pulled out.

An object of the present invention is to provide a fuel assembly in which a fuel spacer can be attached and detached and fixed even when a rectangular moderator is used.

[Means for solving problems]

In order to achieve the above object, in the present invention, a recess or hole is provided on the wall surface of the deceleration rod, a temporary spring is provided on the wall surface of the spacer at the position where the deceleration rod is inserted, and this leaf spring is connected to the deceleration rod. The fuel spacer is fixed by fitting into the recess or hole.

In particular, for square water rods, by providing multiple recesses or holes in the water rod wall and attaching multiple leaf springs to the fuel spacer, these leaf springs can be fitted into the recesses or holes in the water rod. This fixes the fuel spacer.

[Effect]

In the fuel assembly of the present invention, when assembling the fuel assembly, the fuel spacer is installed horizontally, and the deceleration rod is inserted into the fuel spacer from above. By lowering the deceleration rod,
The plate spring provided on the spacer is pressed by the deceleration rod and temporarily moves into the adjacent unit cell. When the recess or hole of the deceleration rod reaches the spacer position, the recess of the deceleration rod fits into the hole due to the elastic force of the leaf spring, and the spacer and water rond are fixed.

The fuel spacer is not moved by gravity or by the lift force that builds up in the flow, but the leaf spring is deflected by a force greater than these forces, and the leaf spring is pushed out again to the adjacent unit cell, and the spacer decelerates. You can move up and down the bar. The fuel spacer is thus fixed in place within the fuel assembly.

It is clear that this procedure is reversed when separating the fuel spacer and water rod during disassembly of the fuel assembly.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a plan view of a fuel spacer used in the fuel assembly of the present invention. The fuel spacer 3 is composed of a large number of round cells 5. The round cell 5 is composed of a cylindrical plate that surrounds the fuel rod 2. A part of the plate is extruded inward to form a rigid support part 7, and the other part of the plate has an elastic support part. A spring 8 is provided for this purpose. The fuel rods 2 are supported in the round cells 5 by these supports.

A hole 20 is provided in the center of the fuel spacer into which a water rod 11, which is a deceleration rod, is inserted. A plate spring 22 for coupling with the water rod is provided on the wall surface of the round cell 21 constituting this hole, and when the water rod 11 is inserted, a recess (not shown) provided in the water rod 11 is provided. is fitted to.

The water rod 11 in this embodiment is cross-shaped and can have a larger cross-sectional area than a round water rod, and can increase the neutron moderating ability, so it is possible to achieve a high burnup of the fuel. can improve the economic efficiency of

FIG. 2 is a partial sectional view of a fuel spacer and water rond used in the fuel assembly of the present invention. A leaf spring 22 is welded to the fuel spacer 3 facing the water rod 11 at a point 23 . When the water rod 11 is inserted into the hole 20 at the position where the water rod 11 is inserted, the leaf spring 22 is pressed toward the round cell 5 side and deforms.

When the recess 25 provided in the water rod reaches the fuel spacer position, the protrusion 24 of the leaf spring 22 moves into the recess 2 of the water rod 1.
5, and the fuel spacer 3 and water rod 11 are fixed. When the fuel spacer 3 is pushed in the axial direction of the water rod 11 with a sufficiently large force, the leaf spring 22 is elastically deformed and the fuel spacer 3 can be moved.

FIG. 3 is a partial sectional view of a fuel spacer and a water rod in another embodiment of the fuel assembly of the present invention. water rod 1
1 is provided with a hole 26 that penetrates the wall surface, and the projection 24 of the leaf spring 22 of the fuel spacer 3 is structured to fit into the hole 26 of the water rod 11. If there are holes 26 in the wall of the water rod 11, cooling water may flow into the water rod 11 from outside, but if the holes 26 in the water rod 11 are small, this flow rate will be small and the fuel cooling performance will be reduced. There is almost no decline.

FIG. 7 is a plan view of a fuel spacer in another embodiment of the fuel assembly according to the present invention. The spacer 3 is composed of a grid-like plate, and the central part has a square water rod 11.
can be inserted. Water rod 1 to be inserted
A plurality of recesses or holes (not shown) are provided in the wall surface of the fuel spacer 3, while a plurality of leaf springs 22 are provided in the wall surface of the plate constituting the fuel spacer 3. When the water rod 11 is inserted into the center, the leaf spring 22 is deformed by the pressure of the water rod 3 and moves into the adjacent unit cell 30. When the recess or hole provided in the water rod 11 reaches the fuel spacer position, the protrusion of the leaf spring 22 fits into the recess or hole of the water rod, and the fuel spacer 3 and the water rod 11 are fixed. In this embodiment, a total of eight recesses or holes are provided on the wall surface of the water rod 11 at the height position where the fuel spacer 3 is fixed, and the fuel spacer is fixedly supported by eight leaf springs 22 provided on the fuel spacer. be done.

FIG. 8 shows another embodiment of the invention. In the figure, 3
4 is a fuel rod, 37 is a spring, 38 is a vertical leaf spring, 39 is a round independent cell, 40 is a cross-shaped water rod (ie, a spacer support rod), and 41 is a cross-shaped cell. fuel rod 34
is inserted into the round independent cell 39, and the protrusion 37. It is supported by a vertical leaf spring 38. Further, the spacer support rod 40 is inserted into the cross-shaped cell 41 and supports the spacer in the following manner.

FIG. 9 shows a perspective view of the cross-shaped cell 41 for spacer support rods. Further, FIG. 10 shows a perspective view of the round independent cell 39. The vertical leaf spring 38 connects the spacer support rod cross-shaped cell 41 and the adjacent round independent cell through an opening 44 provided in the wall surface thereof. When the spacer support rod 4o is inserted into the cruciform cell 41 for spacer support rods, and then the fuel rod 4 is inserted into the adjacent cell, the spring force of the vertical plate spring 38 causes the spacer support rod 40 to
and the fuel rods 34 are fixed horizontally.

Furthermore, the shape of the vertical plate spring 38 is set to a shape (convex) that protrudes toward the spacer support rod side as shown in FIG. Transform it into a concave shape as shown in the figure. In this way, the spacer support rod 41, fuel rod 34, and spacer can be fixed in the axial direction.

In this example, a spacer and its supporting structure necessary for constructing a fuel assembly having a cross-shaped water rond in a nine-by-nine-column lattice are shown.

Such a fuel has excellent nuclear properties as a high burnup fuel, which has been in increasing demand in recent years, and can be easily put into practical use by applying this embodiment.

In the above embodiments, the case where the water rod, that is, the spacer support rod is cross-shaped has been described, but the present invention is also effective for other shapes.

Examples are shown below.

FIG. 13 shows a case where the water rod 40 has a rectangular shape, and in this case as well, the spacer is held by fixing the water rod 4o and the fuel rod 34 via a vertical plate spring. .

FIG. 14 shows a case where the water rod 40 is intermediate between a cross shape and a square shape, and in this case also, the spacer support structure is the same as above.

Other shapes of the water rod include an oval shape, a polygonal shape, and the like.

Incidentally, this shape of the water rod can be similarly applied to the cases shown in FIGS. 15 to 19 shown below.

The embodiment shown in FIGS. 15 and 16 is a case where engaging protrusions 36 are provided on two sides of a cross-shaped water rod.

In this case, in order to pass the water rod 40 into the cross-shaped spacer support cell 41, it is necessary to shift the water rod 40 toward the side where the engaging protrusion 36 is not attached, as shown in FIG. Once the water rod 40 is inside the spacer, a fuel rod is then inserted into the adjacent cell 45. As a result,
The spring force of the vertical leaf spring 38 pushes the water rod 10 in the direction of the surface on which the engagement protrusion 36 is attached, so that the engagement protrusion 36 and the spacer support rod cell cross-shaped cell 41 can engage with each other.

In the embodiment shown in FIG. 17, after passing the water rod through the spacer, the engaging protrusion 36 is welded to the water rod to hold the spacer.

In this case, in order to facilitate welding work, we adopted a structure in which only the spacer supporting iron cells were made longer than the other round cells.

In this embodiment, the spacer is divided into two parts as shown in FIG. 18, and the respective divided pieces of the water rod 40 and the spacer 33 are engaged with the engaging projections 36, and then the spacer 33 is integrated by welding. . FIG. 19 shows an engaging protrusion provided on the water rod 40.

As a deceleration aid, instead of water rondo, hydrogen density is high,
Even when a solid moderator encapsulated with a solid moderator having a small neutron absorption cross section is used, the fuel spacer can be supported by the method according to the present invention, and the same effect can be obtained.

〔Effect of the invention〕

According to the present invention, the fuel spacer can be fixed within the fuel assembly simply by placing the fuel spacer at a predetermined position of the deceleration rod.

In addition, it is possible to use a square water rod as a moderator.
This water rod achieves high burnup of the fuel assembly,
Fuel economy can be improved.

[Brief explanation of drawings]

FIG. 1 is a plan view of a fuel spacer used in a fuel assembly according to an embodiment of the present invention, FIG. 2 is a partial sectional view of a fuel spacer and water rod used in a fuel assembly of the present invention, and FIG. A partial sectional view of a fuel spacer and a water rond in a second embodiment of the fuel assembly of the invention, FIG. 4 is a plan view of a fuel spacer of a conventional fuel assembly, and FIG. 5 is a fuel spacer of a conventional fuel assembly. and a partial sectional view of a water rod, FIG. 6 is a conceptual diagram showing a conventional method of fixing a fuel spacer, FIG. 7 is a plan view of a fuel spacer in another conventional embodiment, and FIG. 8 is a third embodiment of the present invention. FIG. 9 is a spacer plan view of the third embodiment of the present invention, and FIG.
The figure is a perspective view of a round cell according to a third embodiment of the present invention, FIG. 11 is a sectional view of a vertical leaf spring according to a third embodiment of the present invention, and FIG. 12 is a water rod according to a third embodiment of the present invention. Perspective view, FIG. 13. FIG. 14 is a plan view of a spacer according to a fourth embodiment of the present invention, and FIG. 15 is a plan view of a spacer according to a fifth embodiment of the present invention.
Figure 6 is a perspective view of the water rod of the fifth embodiment of the present invention;
FIG. 17 is a spacer and water rod according to a sixth embodiment of the present invention, FIG. 18 is a plan view of a spacer according to a seventh embodiment of the present invention, and FIG. 19 is a water rod according to a seventh embodiment of the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Reduction rod, 2... Fuel rod, 3... Fuel spacer, 5... Round cell, 7... Rigid support part, 8... Spring, 10... Protrusion, 11...・・Water rod, 20
... Hole for water rod, 22 ... Leaf spring, 23 ... Welding point, 24 ... Projection. Figure q /4 1st /,! S mouth (e)

Claims (1)

[Scope of Claims] 1. In a fuel assembly configured by bundling fuel rods containing nuclear fuel material, moderation rods containing neutron moderator, and spacers that maintain the spacing between the fuel rods and the moderation rods. , a fuel assembly characterized in that the spacer is fixed by providing a plurality of recesses on the wall surface of the speed reduction rod, providing a leaf spring on the wall surface of the spacer, and fitting the leaf spring into the recess of the speed reduction rod. body. 2. A patent characterized in that the spacer is fixed by providing a plurality of holes in the wall surface of the deceleration rod, and fitting the leaf spring provided in the wall surface of the spacer into the hole of the deceleration rod. A fuel assembly according to claim 1.