JPS6049291A - 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 combustion chamber assembly used in fast breeder reactors and the like.

[Technical foreground of invention]

A large number of fuel assemblies each having a predetermined number of fuel pins arranged in the core of a high-speed JJQ breeder reactor are loaded.

FIG. 1 shows an example of such a conventional fuel assembly. This fuel assembly is equipped with a hexagonal duct 1 in order to collect more nuclear fuel into the cylindrical reactor core. In the lower part of duct I, cooling 1. An entrance nozzle 3 with a (sodium) inlet hole 2 is attached by welding. A handling rod 4 which also serves as an upper shield is attached to the upper part of the duct 1 by welding. Inside duct 1, there are multiple fuel
The pins 5 are supported at their lower ends by a support frame 6 and are arranged at intervals. The fuel pin 5 is as shown in FIG.
It has a structure in which end plugs 9 and 10 are respectively provided at the upper and lower sides 81 of the cladding tube 8 in which a large number of pellets 7 are housed.

By the way, in such a fuel assembly, if the fuel pins 5 come into contact with each other or with the inner wall surface of the duct 1, the contact area of the fuel pins 5 will become abnormally high temperature, and the cladding tube 8 will melt and break. There is a risk of

Therefore, in such a conventional fuel assembly, in order to avoid the above-mentioned contact and to secure a flow path for the coolant, a spacer wire 11 is attached to the fuel pin 5 as shown in FIGS. 1 to 3. The spacer wire 11 consists of a single wire with a circular cross section.

tffiA diameter 1 of material pin 5, diameter D2 of spacer wire 11, spacer wire 11 and F
#The open gear and the contacting fuel pin 5 are 7 each.
mm, 1 mm, 3 mm, and a valence of about 0.1.

By the way, in such a fuel assembly, the temperature reaches its maximum at 2119 minutes, which is located slightly above the core, during operation.
Swelling, creep, etc. occur significantly in this part. However, while the temperature of the fuel pin 5 at this highest temperature point is about 700°C, the temperature of the duct l
The temperature is quite low, around 500℃. For this reason, duct 1
Compared to the degree of elongation and creep deformation of the heat/swelling 1, the degree of heat/swelling 11α and creep deformation of the natural bottle 5 becomes considerably large. As a result, there is no cable between the spacer wire 11 and the adjacent fuel pipe pin 5 at the highest temperature point, and the wire pin 5 is in the duct l':, 7. While strongly pressurized, the fuel pins 5 are connected to each other at 11. There was a problem in that they were pushed together very strongly, which adversely affected the integrity of pin 5.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel assembly that can minimize the 12" contact load generated by the expansion of the fuel pin.

[Structure of the invention]

In the present invention, a spacer wire made by twisting several thin wires is used, and when a part of the fuel pin undergoes thermal expansion, swelling, and creep deformation, this spacer wire is also twisted into pieces. There is a method in which the falsehood is resolved, thereby securing a cap between the spacer wire and the adjacent fuel pin.

〔Example〕

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

FIG. 4 shows the spacer wire diameter::+< of the fuel book assembly 1 in this embodiment, and FIG. 5 shows the 11-no. This spacer wire 21 is made of three thin wires 22 twisted together. Diameter D4 of circumscribed circle 23 of spacer wire 21
is the diameter D2 of the conventional spacer wire 11 mentioned above.
The value is almost equal to . Therefore, the diameter D of the thin wire 22
5 is a slightly smaller value than 1/2·D2. This spacer wire 21 is spirally wound around a fuel pin (not shown) in the same manner as in the prior art.

Therefore, in the fuel assembly of this embodiment, when the fuel pin undergoes heat/swelling expansion and creep deformation, the spacer wire 21 is tensed and receives a load as shown by the arrow in FIG. It will be inserted between the remaining two thin wires 22 as appropriate. The maximum thermal/swelling 1 engraving and creep deformation of the fuel pin occurs at a location slightly above the core. Therefore, the twist of the spacer wire 21 wound around this portion is appropriately untwisted as shown in FIG. 6, and finally, as shown in FIG. 7, the three thin wires 22 are arranged substantially in a line.

In the state shown in FIG. 7, if thermal/swelling expansion, creep deformation, and tensile strain of the thin wire 22 are ignored for convenience (the same applies hereafter), the distance from the point of contact with the fuel pin of the spacer wire 21 to the farthest point is The interval has a value equal to the diameter D5 of the thin wire 22. In the fuel assembly of this embodiment, for example, if 271 fuel pins 26 are housed inside the duct 25 as schematically shown in FIG. There will be 10 columns. Since the diameter Ds of the thin wire 22 is slightly smaller than 1/2 of the diameter of the circumscribed circle 23 of the spacer wire 21, there is a margin of 9.5D4 or more in the largest row.
In the smallest row, there is a margin of 5D or more.

Since such a large margin is created, a sufficient gap is ensured between the spacer wire 21 and the adjacent fuel pin 26 at the highest temperature portion.

In the above embodiment, the spacer wire 21 is made by twisting three thin wires 22 together, but it is of course possible to use a spacer wire made by twisting four or more thin wires together.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to always ensure a sufficient gap between the spacer wire and the adjacent combustion pin. Therefore, the fuel pins do not come into pressure contact with the inner wall surface of the tank or the fuel pins press against each other, and the health of the fuel bottle can be improved. Also, if the diameter of the circumscribed circle of the spacer wire is the same as the diameter of the conventional spacer wire, the cross-sectional area will decrease, so
The flow path area has increased, and the material of the spacer wire (SUS
)'s clearness decreases, and the core ↑! It is possible to improve the r properties.

[Brief explanation of drawings]

Figure 1 schematically shows an example of a conventional fuel assembly.
7r front view, Figure 2 shows the combustion in the same sintered aggregate)::l
FIG. 3 is a cross-sectional plan view taken along line [Ll, -, ill of FIG. 1, and FIG. 4 is a spacer according to an embodiment of the present invention. FIG. 5 is a diagram showing the ``reverse aSS'' of the wire, and FIG.
Figures u6 and 8 are 1 m horizontal plan views schematically showing the fuel cantilever assembly in this embodiment. 21. Spacer wire, 22. Thin wire. Applicant: Japan Atomic Energy Corporation Representative Patent Attorney Ume Yamauchi 11 Figure 1 Figure 2 Figure 3 Figure ○ Figure 4 ■ Shin 5 Figure 22 2 Figure 6 ↓ Figure 7 Closed Figure 8 B

Claims (1)

[Claims] A duct, a plurality of fuel pins housed in the duct at intervals, and a spacer wire made of several fine wires twisted together spirally wound around these fuel pins are used. Characteristic fuel assembly.