JPS60152983A - Nuclear 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] [Technical field of invention] The present invention relates to a nuclear fuel assembly used in a nuclear reactor.

[Technical background of the invention and its problems] Nuclear fuel assemblies are constructed in consideration of improvements in operating characteristics, fuel efficiency, and safety of nuclear reactors. In other words, Figure 1 (
2. As shown in FIG. 2, dozens of fuel rods 1 containing water and one water rod 2 are arranged in a square array, their upper and lower ends are bundled by upper and lower tie plates 3 and 4, and the middle is held by a spacer 5. , the entire structure is covered with a fuel channel 6.

Among these many fuel rods 1, for example, eight fuel rods 1 located around the convergence shown in FIG. ing. As shown in FIG. The upper tie plate 4 is screwed into the screw hole 11 of the plate 4, the upper end plug 7 is passed through the support hole 12 of the upper tie plate 3, and the hexagonal nut 13 is tightened to the threaded part 9 at the tip of the plate 4 through the non-turning washer 14. A tie plate 3 and a lower tie plate 4 are connected.

On the other hand, the lower end plug 8 of the standard fuel rod 1 and water rod 2
The connection relationship between the and lower tie plate 4 is as follows:
However, as shown in FIG. 4B, the upper end plug 7 only passes through the support hole 12 of the upper tie plate 3 and is not tightened with a hexagonal nut. In addition, standard fuel hanging rod 1. In the combined fuel rod 1a and the water rod 2, a compression spring 16 is provided between the lower surface of the upper tie plate 3 of the upper end plug 7 and the flange portion 15, as shown in FIGS. 3 and 4A. ing. This compression spring 16 serves to press the fuel rods 1, 1a and the lower end plug 8 of the water rod 20 against the lower tie plate 4 and hold them in place. Note that the upper tie plate 3 is provided with a handle 17 that is used when loading a nuclear fuel assembly.

However, in a nuclear fuel assembly configured in this way, when it is installed in a nuclear reactor and burned, the fuel rods 1.18 inside the assembly undergo thermal expansion, interaction between pellets and cladding, irradiation growth, etc. A phenomenon of stretching in the axial direction occurs.

At this time, the fuel rods 1.1a are restrained from extending downward by the lower L'B tie plate 4, so they extend upward.

On the other hand, since the upper tie plate 3 and the lower tie plate 4 are connected via the combined fuel rods 1a, the fuel rods 1, which have a larger axial elongation than the combined fuel rods 1a as shown in FIG. 16 is compressed by the difference in elongation from the combined fuel rod 1a (2, this difference in elongation is greater than the difference between the tight contact length b and the assembled length a of the fuel rod 16, as shown in Fig. 5). Then, there is a risk that the upper tie plate 3 and the fuel rods 1 will interfere and be damaged.In particular, in the nuclear fuel assembly,
It is required to burn to a high burnup. Along with this, as the burnup increases, the difference in axial elongation between the fuel rods 1 in the fuel assembly tends to increase, and the upper tie plate 3 and the fuel rods 1 interfere more often. Become.

[Objective of the Invention] The object of the present invention is to prevent the fuel rods and the upper tie plate from interfering with each other due to axial elongation even at high burnup, and to prevent the fuel rods from interfering with each other during transportation and operation. The present invention provides a nuclear fuel assembly configured to prevent movement.

[Summary of the Invention] The nuclear fuel rod assembly according to the present invention has a conventional coupling structure between the upper and lower tie plates of the coupled fuel rods, and a compression coil spring between the standard fuel rods and water rods and the upper tie plate. In other words, the lower tie plate refers to the lower end plug (which is characterized by being configured with a cotter pin structure having longitudinal grooves opening in two axial directions for connection with a cotter pin).

[Embodiment of the Invention] The present invention will be described below with reference to an embodiment shown in FIGS. 6 and 7. In FIGS. 6 and 7, the same reference numerals as in FIGS. 1 to 3 indicate the same parts, and the explanation thereof will be omitted. In Figure 6, combined fuel rod 1
The connection structure of a to the upper tie plate 3 and lower tie plate 4 is the same as the conventional structure shown in FIG. 3, and a compression spring 16 is provided between the upper end plug 7 and the upper tie plate 3. . On the contrary, no conventional compression spring 16 is provided between the upper end plug 7 and the upper tie plate 3 of the standard fuel rods 1 and water rods 2 other than the combined fuel rod 1a.

Therefore, even if the lower end plug 8 of the standard fuel rod 1 and the water rod 2 and the lower tie plate 4 are connected by threaded connection as in the past, the upper end plug 7 and the upper tie plate 3 Since the compression spring 16 is not inserted into the upper tie plate 3 and the tip of the upper end plug 7 just passes through the support hole 12 of the upper tie plate 3, irradiation prevents axial elongation between the combined fuel rod 1 and the Even if the difference becomes large, the upper tie plate 3 and the fuel rods 1 will never interfere with each other.

It is also known that at this time, the difference in axial elongation with the combined fuel rod 1a poses almost no problem.

Furthermore, in the present invention, the connection structure between the lower end plug 8 of the standard fuel rod 1 and the lower tie plate 4 has been improved.

That is, as shown in FIGS. 7 and 8, the lower end plug 8
A vertical groove 20 opening in the direction of the solid axis is provided, and the diameter dl of the shank portion 21 of the lower end plug 8 is machined. The support hole 22 of the lower tie plate 4 into which the shank portion 21 of the lower end plug 8 is inserted is processed to have a hole diameter ds. The relationship between the diameter dl and the hole diameter portion is dl>dB.

Therefore, if the shank portion 21 of the lower end plug 8 is firmly fitted into the support hole 22 of the lower tie plate 4, the groove 20 will be compressed due to the relationship dl>dB, and the shank portion 21 will be inserted into the support hole 22.
Thereafter, a restoring force is generated that causes the groove 20 to expand, and the shank portion 21 and the lower tie plate 4 are strongly coupled. This is a so-called split pin connection.

This coupling method does not require any rotation prevention compared to the conventional screw coupling method, and the coupling can be performed extremely easily. Furthermore, there is no need to worry about the fuel rods moving during fuel transportation or floating during operation.

Although not shown, the lower end plug of the water rod 2 and the lower tie plate 4 also employ this split pin coupling method. Further, the cross-sectional shape of the shank portion 21 of the lower end plug 8 does not necessarily have to be circular, and may be polygonal depending on the case.

Next, in another embodiment shown in FIG.
and the shank portion 21 of the lower end plug 8 of the water rod 2
This is an improved version of . A vertical groove 20 is provided in the shank portion 21, and a small diameter portion 21m and a large diameter portion 21b are formed at the tip thereof. Then, as shown in FIG. 9, FIG. 1O, and FIG. 11, the diameter dl of the small diameter portion 21m of the shank portion 21 is set,
This is the diameter portion of the large diameter portion 21b, and is machined to have the diameter d8 of the groove 20. Also, the diameter of the support hole 22 of the lower tie plate 4 that receives the shank portion 21 of the lower end plug 8 is set to d4.
Therefore, the relationship between the can diameter 'l+dB+odor of the shank portion 21 and the diameter d4 of the support hole 22 is d0≧'4+'II
>'4 m '8 = '! The setting is made so that l-'4 is satisfied, and appropriate tightening margins are provided at the mutual fitting locations.

Therefore, when the standard fuel rod 1 and water rod 2 having the shank portion 21 of the lower end plug according to this embodiment are connected to the lower tie plate 4, the diameter of the large diameter portion 21b at the tip of the shank portion 21 is the same as that of the support hole 22. Since it is slightly larger than the diameter and has a vertical groove 20 in the direction of the solid shaft of the shank,
When the large diameter portion 21b of the shank portion 21 first passes through the hole 22, it passes through the hole 820 while being compressed. As soon as the large diameter portion 21b passes through the hole 22, as shown in FIG. 12, due to the restoring force of the groove 20, the large diameter portion 21b enters a connected state occupying the diameter d11.

In the coupled state shown in FIG.
Since the large diameter portion 21b at the tip is larger than the support hole 22 of the lower tie plate 4, the lower tie plate 4 will not separate from the lower end plug 8. Since the compression spring 16 is not interposed between the flange of the upper end plug 7 of the rod 1 and the upper tie plate 3, even if the difference in axial elongation with the combined fuel rod 1a becomes large due to irradiation, the upper tie plate 3 and fuel rod 1 would interfere at all. Furthermore, it is known that the difference in axial elongation between coupled fuel rods poses almost no problem.

[Effects of the Invention] As described above, in the present invention, since compression springs are not interposed in the upper end plugs of the standard fuel rods and water rods other than the combined fuel rods in the nuclear fuel assembly, the shaft remains stable even at high burnup. There is no interference between the fuel rods and the upper tie plate due to directional elongation. In addition, a vertical groove that opens in the axial direction is provided in the shank part of the lower tie plate of the lower end plug of all fuel rods and water rods, which is inserted into the support hole of the lower tie plate, and a vertical groove is provided between the diameter of the shank part and the diameter of the support hole. By providing an appropriate tightening margin, the lower end plug and the lower tie plate form a so-called cotter pin connection, which makes it extremely easy to connect the two and to facilitate movement and operation of fuel rods and water rods during fuel transportation. It is possible to prevent floating accidents in

[Brief Description of the Drawings] Figure 1 is a longitudinal sectional view showing a conventional nuclear fuel assembly, Figure 2 is a plan view of Figure 1 seen from above, and Figure 3 is the upper and lower parts of a conventional combined fuel rod. Figure 4 is an enlarged view showing how the combined fuel rods and standard fuel rods are connected to the upper tie plate. FIG. 6 is a longitudinal sectional view showing an embodiment of the nuclear fuel assembly according to the present invention, and FIG. 7 is a view showing the lower end of the fuel rod according to the present invention. Fig. 8 is a state diagram showing an embodiment of the coupling method of the stopper and the lower tie plate.
FIG. 9 is a state diagram showing another embodiment of the coupling method of the lower end plug of the fuel rod and the lower tie plate in the present invention, and FIG. 10 and FIG. A sectional view taken along the line XX and IXIX in the figure, and FIG. 12 is a state diagram showing the state of connection between the lower end plug and the lower tie plate in FIG. 9. - Combined fuel rod 2...Water rod 3...Upper tie plate 4...Lower tie plate 5...Spacer 6...Fuel channel 7...Upper end plug 8...Lower end plug 16 -...Compression spring 20...Vertical groove 21-...Shank portion 21a.
...Small diameter part 21b -...Large diameter part 22...Support hole, embedded Patent attorney Yoshiaki Inomata (and one other person) No. 2
Figure 4 (/1) (β) Figure 5 (fl) (13) Figure 9. Figure 12

Claims (1)

[Scope of Claims] (1) A large number of fuel rods and one or more water rods are arranged in a lattice pattern (; in a square arrangement, and the upper and lower end plugs of each fuel rod and water rod are arranged in the upper The upper and lower end plugs of a plurality of fuel rods supported by a tie plate and a lower tie plate and arranged around the plurality of fuel rods are respectively connected to the upper and lower tie plates to form a combined fuel rod; In a nuclear fuel assembly whose outside is connected by a fuel channel, a compression coil spring that presses the combined fuel rod downward is interposed between the flange of the upper end plug of the combined fuel rod and the upper tie plate, and the combined fuel Nuclear fuel assembly characterized by having a structure in which the upper end plugs of fuel rods and water rods other than the rods are compressed; no coil springs are interposed (2) Support of the lower tie plate of the lower end plugs of fuel rods and water rods The nuclear fuel assembly according to claim 1, characterized in that a vertical groove opening in the axial direction is provided in the shank portion inserted into the hole, and the diameter of the second shank portion is configured to be slightly larger than the diameter of the support hole. The shank portion of the lower end plug of the nuclear fuel assembly (4) according to claim 2, wherein the lower end plug of the combined fuel rod of the fuel rod (8) and the lower tie plate are screwed together. When inserting into the small diameter part and the support hole, the diameter of which is equal to or slightly larger than the diameter of the lower tie plate, the vertical groove is compressed to a diameter that allows insertion, and after insertion, the diameter becomes larger than the diameter of the support hole. The diameter dl of the small diameter part in the shank part of the lower end plug of the nuclear fuel assembly (5) according to claim 2, characterized in that it has a two-stage structure with a large diameter part. Assuming the diameter d8 and the diameter d4 of the support hole of the lower tie plate, 'l = '4 r '8 >
The nuclear fuel assembly according to claim 4, characterized in that it is configured to satisfy the following relationship: '4 + '8 == d, -d4.