JPS6224187A - 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] <Industrial application field> The present invention relates to a fuel assembly for a nuclear reactor.

<Prior art> As a conventional fuel assembly, there is a wire spacer type fuel assembly shown in JP-A-59-13979 (Figs. 4 and 5).
, a grid spacer type fuel assembly (FIG. 6) and a finned fuel assembly (not shown) shown in Japanese Patent Publication No. 52-24199.

As shown in FIGS. 4 and 5, the wire spacer type fuel assembly has a plurality of fuel elements 2 arranged in a triangular lattice in a wrapper tube 1.

A wrapping wire 4 is attached to the outer periphery of the cladding tube 3 of this fuel element 2.
is wound in a spiral.

Further, as shown in FIG. 6, in the grid spacer type fuel assembly, a large number of hexagonal elements 5 are incorporated in the wrapper tube 1. This element 5 has three inward protrusions (
The fuel element 2 is restrained by the protrusion 6.

<Problems to be Solved by the Invention> Fuel elements of fuel assemblies, especially fast neutron nuclear fuel elements (fuel elements of fast breeder reactors), expand due to irradiation, and the amount of expansion increases as the fuel time increases. The above conventional wire installed to secure the coolant flow path,
Mechanical interference with spacers such as grids or fins may occur. The cause I! (1) Regarding wire spacers and fin spacers, the spacer is installed continuously in the axial direction with respect to the fuel element. (2) Regarding the grid spacer, since the fuel elements are spaced in all directions by the spacer, the fuel element bundles do not need to be rearranged.

FIG. 7 shows a partial vertical sectional view of a wire spacer type fuel assembly as an example. 1 is a wrapper tube, 2 is a fuel element, and 7 is a wire spacer. As the combustion time increases from the state shown in Figure 7 a), the coolant flow path narrows or the load from the wire spacer 7 causes the As shown in FIG. 7(b), the fuel element 2 eventually breaks. Because of this, the fuel assembly is subject to a burnup limitation, v! 4 Nuclear reactors must be operated with fuel replaced frequently, which is a factor that increases power generation costs.

The present invention has been made in view of the above-mentioned circumstances, and solves the problem in the first stage of (1) above by spacing the fuel element bundles at discontinuous positions in the axial direction. By spacing only the partial orientation at the spacing position of , the rigidity of the spacer is softened, the rearrangement of the fuel element bundle is made possible, and the problems of the latter stages of (1) and (2) are avoided. By solving this problem, it is possible to provide a long-life fuel assembly in which the above-mentioned restrictions are largely relaxed.

Means for Solving the Problems> Therefore, the fuel assembly of the present invention has a structure in which a plurality of holes are arranged in one direction in a frame plate that fits on the inner surface of the wrapper tube to maintain the gap between the fuel elements. Spacers whose height is shorter than the axial length of the fuel elements in which corrugated plates are arranged in parallel are arranged and fixed in the wrapper tube at predetermined intervals, and the corrugated direction of each spacer is set to the axial position of the fuel element bundle. The difference was made according to the following.

Effect> The eastern part of the fuel element of the fuel assembly of the present invention is spaced by a spacer that is short in the axial direction and has anisotropy in the direction of holding the fuel elements in the cross section.

Therefore, when the fuel element is expanded by irradiation or the like, the fuel element bundle is rearranged in the direction of the gap, so that the permissible amount of expansion of the fuel element is greatly increased. Although rearrangement of fuel elements occurs to some extent in wire spacer type fuels, the effect of rearrangement is small because of the presence of continuous Cζ spacers in the axial direction.

<Example> Hereinafter, the present invention will be described in detail based on the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. This fuel assembly is
The fuel element gap is maintained by the spacer 8 whose height l is shorter than the fuel element axial length. The spacer 8 is made up of a plurality of corrugated plates 8b arranged in the B direction and a hexagonal frame plate 8a installed on the inner surface of the trumpet tube 1. It is also possible to omit the frame plate 8a and directly connect the corrugated plate 8b to the trumpet tube 1. The corrugated plate 8b may be provided with a fuel element 2 as required.
It is also effective to provide a dimple (not shown) at a position where it makes contact with the surface. The displacement of the fuel element 2 in the A direction is suppressed by the corrugated plate 8b. fuel element 2
expands under the influence of irradiation, fuel element 2 in direction B
The spacer 8 and the fuel element 2 can easily slide together without rearrangement resulting in a strong interaction between the spacer 8 and the fuel element 2.

However, if sliding in the B direction is allowed without limit, there is a risk that the fuel elements 2 will come into contact with each other in the B direction, but in order to prevent this, the arrangement direction of the corrugated plates 8b must be aligned in the axial direction of the fuel element bundle. Different depending on location. This makes it possible to maintain the gap between the fuel elements 2 stably even when combustion progresses from the initial stage of combustion and the diameter of the fuel elements expands.

FIG. 2 shows another embodiment in which spacing positions are provided.

In this fuel assembly, the gap between the fuel elements 2 is maintained by a spacer 9 having the same function as the example shown in FIG. B of the corrugated plate 9b that connects the spacer 9 to the spacing wire in the radial direction (direction B in FIG. 2).
It consists of a plurality of bodies lined up in the direction and a hexagonal frame plate 9a that is fitted and fixed to the inner surface of the trumpet tube 1. This embodiment is the same as the previous embodiment except that the direction in which the corrugated plates 9b are arranged is different depending on the axial position of the fuel element bundle. It is also possible to omit the frame plate 9a and directly connect the corrugated plate 9b to the trumpet tube 1. In this embodiment, the corrugated plate 9b is a spacing wire 9
By simply bonding C, there is no need for it to serve as a strength member, and the thickness of the corrugated sheet can be made as thin as possible.

FIG. 3 shows yet another embodiment. In this fuel assembly, gaps between fuel elements are maintained by spacers 10.

The spacer 10 includes a space pipe 10c located in the center of a coolant flow path having a triangular flow path cross section, and a connecting plate io that connects the space pipe 10c.
lined up in the B direction consisting of b and t! It consists of a plurality of bodies and a surrounding hexagonal frame plate 10a. In this embodiment as well, the hexagonal frame plate 10a is omitted, and the connecting plate 10b and the space pipe 1
It is also possible to directly connect the corrugated plate-like member that is the connecting body of 0c to the trumpet tube 1. With this configuration, the connecting plate can be made as thin as possible. The space tube 10c can also be made hollow while maintaining the thickness (diameter) necessary for spacing, and in this case, the hollow portion can be used as a path for the coolant. As in this embodiment, if connecting plates are arranged every other row in the B direction, the fuel elements 2
Even if the expansion occurs not only in the direction of B but also in the direction of 1. It can also be displaced in the A direction, making it possible to extremely increase the margin of error against expansion. In order to stably hold the fuel elements 2 in the entire axial direction, the direction of the connecting plate 10b (direction B in this example) is changed depending on the axial position of the fuel element bundle.
It is advantageous to arrange the spacers 10 in the axial direction of the fuel assembly at angles of between 90 degrees and the same applies to the spacers 8 and 9.

<Effects of the Invention> By using the fuel assembly of the present invention as described in detail above, it becomes possible to burn fuel in a furnace with a fuel burn-up of 150,000 to 200,000 MWd/l, Helps significantly reduce power generation costs. Further, if the fuel assembly of the present invention is used, the coolant pressure loss in the reactor core can be kept low, which greatly contributes to reducing the construction cost of a nuclear reactor plant.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of a fuel assembly showing one embodiment of the present invention, FIG. 1(b) is a cross-sectional view taken along the line CC in FIG.
@ Cross-sectional view, Figure 2 (a) is a cross-sectional view of a fuel assembly showing another embodiment of the present invention, Figure 2 (b) is D of Figure 2 (a)
-D line sectional view, FIG. 2(c) is a partial perspective view of the corrugated plate of the fuel assembly, and FIG. 3(a) is a cross-sectional view of the fuel assembly showing still another embodiment of the present invention. , Figure 3(b) is Figure 3(a)
FIG. 4 is a cross-sectional view of a conventional wire spacer type fuel assembly, FIG. 5 is a front view of the fuel element of the wire spacer type fuel assembly of FIG. 4, and FIG. Partial cross-sectional view of a conventional grid spacer type fuel assembly, FIG.
) and (b) are partial longitudinal sectional views of a conventional wire spacer type fuel assembly. 1...Trumpet tube, 2...Fuel element, 3...Claying tube, 4
...Wrapping wire, 5...Element, 6...Protrusion, 7...Wire spacer, 8,9.10...Spacer, 8a, 9a, 10a...Frame plate, 8
b, 9b... corrugated plate, 10b... connecting plate, 9 c...
Spacing wire, 10c...Space tube 7〒3Fig.

Claims (1)

[Claims] A spacer whose height is shorter than the axial length of the fuel element, in which multiple corrugated plates are arranged in parallel to maintain the gap between the fuel elements in one direction within the frame plate that fits on the inner surface of the wrapper tube, is placed at a predetermined interval. A fuel assembly characterized in that the spacers are arranged and fixed in a wrapper tube, and the directions of the corrugated plates of each of the spacers are made different depending on the axial position of the fuel element bundle.