JPS61201193A - 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 the Invention] The present invention relates to a fuel assembly used in a boiling water nuclear reactor.

[Technical Background of the Invention] Conventional examples of fuel assemblies for boiling water nuclear reactors will be described with reference to FIGS. 4 to 6. FIG. 4 is a longitudinal cross-sectional view showing a fuel assembly. This fuel assembly 1 is made up of a large number of elongated cylindrical fuel rods 2. The upper part of the bundle is connected by an upper tie plate 3, and the lower part is connected by a lower tie plate 4. has been done. In this bundle, the fuel rods 2 are maintained at equal intervals by spacers 5. In addition to the fuel rods 2, a water rod 6 is incorporated into the bundle. The outer periphery of this bundle is surrounded by a channel box 7, whose upper part is joined to the upper tie plate 3 and its lower part is joined to the lower tie plate 4.

The fuel rod 2 has a cladding tube loaded with a large number of cylindrical U○2 fuel pellets (not shown), and the F lower end of this R-tube is sealed with a single end plug 8 and a lower end plug 9. ing. The upper end plug 8 is provided with an extension that can be inserted into a support cavity in the upper tie plate 3. The lower end plug 9 has a fitting that fits into a support cavity in the lower tie plate 4.

FIG. 5 shows a perspective view of the water rod, and as shown in the figure, the water rod 6 has a hollow tube 10 made of Zircaloy with both ends connected to an upper end plug 11 and a lower end plug 12 made of Zircaloy. The lower end plug 12 is constructed by welding and has a prismatic shape to prevent the water rod 6 from rotating. A total of 14 tabs 13 are welded to the hollow tube 10 to ensure the spacing between the spacers 5. A plurality of cooling water inlet holes 14 are provided near the lower end of the hollow tube 10, and a plurality of cooling water outlet holes 15 are provided near the upper end.
During operation of the nuclear reactor, cooling water flows inside the hollow tube 1o from the bottom to the top.

In recent years, in the conventional example described above, an improvement example shown in FIG. 6 has been attempted in order to effectively utilize the channel box and improve the nuclear and thermal hydraulic characteristics. Here, FIG. 6 shows a side view of a fuel assembly showing an improved conventional example.

In FIG. 6, the same parts as those in FIG. 4 are designated by the same reference numerals, and the explanation of the structure will be omitted. In addition, in order to make effective use of the channel box, an example is shown in which the side surface of the lower tie plate and the lower support part of the fuel rod (hereinafter referred to as the lower support plate) are separated, and the side surface of the lower tie plate and the channel box are combined. , the figure shows a state with the channel box removed. In FIG. 6, a fuel assembly 20 has a large number of fuel rods 2 and water rods 21 bound together, and is connected at the upper part by an upper tie plate 3 and at the lower part by a lower support plate 22.

The water rod 21 has a shorter length than the fuel rod 2.

[Problems in the Background Art] In the above configuration, the upper end of the A-talorado in the conventional improved example is free, so in the conventional fixing method,
If the water rod floats upward in the axial direction, the lower end may come off the lower support plate, and in some cases, the water rod may rotate, making it difficult to maintain support for the spacer. For this reason, a method of screwing the lower end of the water rod was taken, but since the main purpose was to prevent floating, there was no risk of rotation due to loosening of the screw due to hydraulic vibration during reactor operation. I couldn't remove it.

[Object of the Invention] An object of the present invention is to provide a fuel assembly 19 that has good nuclear and thermo-hydraulic properties and can prevent rotation and floating of water rods.

[Summary of the Invention] The present invention provides a fuel assembly in which a large number of fuel rods and water rods are arranged in a square array, the fuel rods are fixed in the vertical direction by upper and lower support plates, and the middle part is supported by a spacer. The lower end plug of the water rod has a notch that fits into the lower support plate and prevents rotation, and the lower support plate and the lower end plug of the water rod are screwed together by a nut. , this nut is in the fuel assembly 971@, which is prevented from rotating by a washer.

[Embodiments of the Invention] A first embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Note that the same parts as in the conventional example are given the same reference numerals, and the explanation of the structure will be omitted. The water rod of the fuel assembly according to the present invention has a structure as shown in FIG. FIG. 2 shows a side view of the water rod according to the present invention. In FIG. 2, the water rod 30 includes a lower end plug 32 fixed to the lower end of a hollow tube 31 made of Zircaloy. The shaft portion 33 of the lower end plug 32 is formed to have a square cross section in order to prevent rotation of the water rod 30, and a threaded portion 34 is provided at the lower portion thereof. The hollow tube 31
A plurality of cooling water holes 3]5 are bored near the lower end of the cooling water pump, and the upper end thereof is open.

The short water rod 30 configured as described above is the first
It is fixed as shown in the figure. Here, FIG. 1 shows the first embodiment of the present invention.
FIG. 2 is an enlarged perspective view of a main part showing a coupled state of a water rod and a lower support plate of a fuel assembly according to an embodiment. In FIG. 1, a washer 37 is inserted into the lower support plate 36, the water rod 30 is inserted into the lower support plate 36 through the washer 37, and a nut 38 is screwed into the threaded portion 34 of the water rod 30. The water rod 30
is fixed. The washer 37 is provided to prevent the nut 38 from rotating, and includes three rectangular cylindrical parts that fit into the shaft part 33 of the water rod 30, which also serves to prevent the washer from rotating. Claw part 4
It is composed of 0. Square tube part 3 of this washi v37
9 is fitted into a square hole 41 provided in the lower support plate 36 to prevent the washer 37 from rotating.

With the above configuration, the water rod 30 is fixed to the lower support plate 36 by the nut 38 and washer 37.

Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 3 is an enlarged perspective view of a main part showing a state in which a water rod and a lower support plate are connected to each other in a fuel assembly according to a second embodiment of the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals, and the explanation of the structure will be omitted. In FIG. 3, a shaft portion 45 formed on the lower end plug 32 of the water rod 30 is shown.
is formed with a circular cross section and a partially cut-out shape. Along with this shaft portion 45, a locking portion 46 of the washer 37 that fits into this shaft portion 45 is also formed in the same shape as the shaft portion 45, and the lower support plate 36 that fits with this washer 37
The hole portion 47 is also formed in the same shape as the shaft portion 45.

With the above configuration, first, the locking part 46 of the washer t37 provided for rotation prevention +h is fitted into the circular hole 47 provided in the lower support plate 36 and having a partially cut-out shape. Thereafter, the locking portion 46 of the washer 37 is fitted into a circular, partially cut-out shaft portion 45 provided on the lower end plug 32 of the water rod 30. By the above, water rod 3
9 and washer 37 are prevented from rotating. After the water rod 30, lower support plate 36, and washer 37 are assembled, the water rod 30 is firmly attached to the lower support plate 36 by coupling the nut 38 with the threaded portion 34 of the lower end plug 32 of the water rod 30. be combined.

In the second embodiment, an example in which the shaft portion 45 of the lower end plug 32 is cylindrical is used, but even if this shaft portion is tapered, the present example can have the same effect by providing a notch. effect can be obtained.

[Effects of the Invention] According to the present invention, a notch for preventing rotation is provided in the lower end plug of the water rod, and a rotation preventing mechanism is provided in the support portion of the water rod, so that rotation and floating of the water rod are prevented. It is possible to obtain a fuel assembly that can prevent damage.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of essential parts of a fuel assembly according to a first embodiment of the present invention, FIG. 2 is a side view of the water rod shown in FIG. 1, and FIG. 3 is a perspective view of a fuel assembly according to a second embodiment of the present invention. A perspective view of a main part of such a fuel assembly, FIG. 4 is a longitudinal sectional view of a fuel assembly showing a conventional example,
Figure 5 is a perspective view of the water rod shown in Figure 4;
The figure is a side view of a conventional improved fuel assembly with the channel box removed. 30...Water rod, 31...Hollow tube, 32.
...Lower end plug, 33.45...Shaft portion, 36...Lower support plate, 37...Washer, 38...Natto agent, patent attorney Kensuke Norichika (and one other person) Figure 1 Figure 2 Figure 3 Figure 4 Figure 6

Claims (1)

[Claims] (1) A large number of fuel rods and water rods are arranged in a square arrangement,
In a fuel assembly in which the fuel rods are fixed in the vertical direction by upper and lower support plates, and the middle part is supported by a spacer, the lower end plug of the water rod fits into the lower support plate and is prevented from rotating. 1. A fuel assembly having a notch, wherein the lower support plate and the lower end plug of the water rod are screwed together by a nut, and the nut is prevented from rotating by a washer.