JPS59231475A - Aggregate of nuclear fuel - 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 the Invention] A plurality of nuclear fuel rods 1 containing nuclear fuel material are bundled at equal intervals by spacers 2, as shown in FIG. The upper tie plate 4 and the lower tie plate 5 are connected by eight coupled fuel rods 3 with screws 3a.
is held between.

The bundle of nuclear fuel rods 1 is inserted into the channel box 6 as shown in FIGS. 2 and 3, and the upper tie plate 4
Spring 8a and guard 8 are inserted into the hole provided in the boss 7 of
A channel fastener 8 consisting of b is fixed to the channel box 6 by screwing it together with a screw 9 through a channel clip 10.

A leaf spring (not shown) is placed between each side of the lower tie plate 5 and the channel box 6 for the purpose of suppressing the leakage of cooling water to the outside of the channel box 6. It receives a large interference force from the spring and is severely restricted from moving in the axial direction.

The nuclear fuel rods 1 of the conventional nuclear fuel assembly as described above have a nearly fixed structure at both upper and lower ends.

During nuclear reactor operation, nuclear fuel rods normally expand in the axial direction by the amount of thermal expansion and irradiation growth of the nuclear fuel rod cladding. Generally, the channel box 6 is made of Zircaloy like the cladding tube, and since the channel box 6 also exhibits the same degree of axial expansion, even if both ends of the nuclear fuel rod 1 are fixed, a particularly large compressive force is applied to the nuclear fuel rod. It will never change to 1.

It is a generally well-known fact that the coefficient of thermal expansion of the nuclear fuel material (1) is larger than that of the cladding.
There is a gap between the cladding tube and the nuclear fuel material.
It is absorbed by a spring (not shown) placed at the top inside the nuclear fuel rod 1. Therefore, in nuclear fuel rods that generate a large amount of power, the nuclear fuel material expands greatly in the radial direction and comes into contact with the inner surface of the cladding tube, causing a large interference force that may cause the nuclear fuel material and the cladding tube to stick together. be. In this case, the axial expansion of the high power fuel rod is dominated by the nuclear fuel material, and the nuclear fuel rod expands axially to a greater extent than other nuclear fuel rods or channel boxes. As a result, a large compressive stress is applied to the nuclear fuel rod, causing the nuclear fuel rod to bend, and eventually causing fuel damage such as insufficient cooling due to insufficient spacing between adjacent nuclear fuel rods and burnout of the cladding. There is a risk of it happening.

[Purpose of the invention]

An object of the present invention is to provide a nuclear fuel assembly that does not impose an undesirable load on nuclear fuel rods.

[Overview of the invention]

A bundle of nuclear fuel rods whose upper ends are supported by a lower tie plate, a channel box in which the main parts of the bundle of nuclear fuel rods are stored, and an outer part of the upper end of the channel box. A nuclear fuel assembly comprising: a channel fastener provided in contact with a corner of the top tie plate, coupled to a boss embedded in an upper tie plate, and provided without being coupled to a channel box.

[Embodiments of the invention]

The present invention will be described in detail below with reference to the drawings.

FIG. 4(a) shows a state in which the boss 7, channel fastener 8 and channel box 6 of the upper tie plate are engaged.

In the present invention, the channel fastener 8 (consisting of 8a and 8b) is connected to the boss I.7 of the upper tie plate in 1-contact contact without using the channel chrysalis 10.

In addition, the channel clip 10 is provided at a part of the upper end corner of the channel box, which was not previously attached, and the boss 7 of the upper tie plate is also newly provided at a corresponding position, and the channel clip 10 is simply placed on the bonnet 7.
It is also possible to add a structure that allows

〔Effect of the invention〕

In the nuclear fuel assembly according to the present invention, the bundle of nuclear fuel rods 1 and the channel box 6 are not fixed in the axial direction. Then,
According to the present invention, the nuclear fuel rods are not restrained in any way in the axial direction by the channel box.During reactor operation, the nuclear fuel rods 1 undergo thermal expansion,
4 (b) expands due to irradiation growth or interaction between the nuclear fuel material and the cladding tube and forms a gap between the channel box 6 and the cladding tube.
Even if a large expansion and insertion occurs as shown in ), the nuclear fuel rod 1
Since the upper part is not fixed in any way, the upper tie plate 4
That is, the post 7 can be pushed up and freely expanded in the axial direction. Thus, no compressive stress is generated in the cladding tube that could lead to fuel failure, and the present invention significantly reduces the occurrence of fuel failure.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view showing a conventional nuclear fuel assembly, Fig. 2 is a plan view showing a conventional nuclear fuel assembly, Fig. 8 is a longitudinal sectional view showing the main parts of the conventional nuclear fuel assembly, and Fig. 4 is a longitudinal sectional view showing the conventional nuclear fuel assembly. FIG. 3 is a vertical cross-sectional view showing main parts. 1... Nuclear fuel rod 2... Spacer 3... Combined fuel rod 4... Upper tie plate 5... Lower tie plate 6... Channel box 7... Bost 8... Channel fastener 9 ···screw
10...Channel Clip Agent Patent Attorney
Kensuke Chika (and 1 other person) Figure 1 Figure 2 Figure Otsu' Figure 3 Figure 4 (0,) (b)

Claims (2)

[Claims] (1) A bundle of nuclear fuel rods whose upper and lower ends of the bundle ix are supported by a lower tie plate with the lower ends of the bundle ix using spacers, a channel box in which the main parts of this bundle of nuclear fuel are stored, and the upper end of this channel box. A nuclear fuel assembly comprising a channel fastener provided in contact with a corner of an outer part, coupled to a post planted in an upper Quig Grate, and provided without being coupled to a channel box. (2) Does not include the mounting position of the Changi Lufastener)
The nuclear fuel assembly according to item 1, wherein channel clips are provided at two diagonal corners of the upper end of the channel box.