JPH07159567A - Fuel assembly - Google Patents

Abstract

(57) [Summary] [Object] To provide a fuel assembly in which the integrity of the fuel cladding can be maintained by bending the coolant flow holes 1 in the lower tie plate of the fuel assembly to prevent foreign matter from entering. To do. A fuel assembly according to a first aspect of the invention is a fuel assembly in which the upper and lower ends of a plurality of fuel rods 3 are supported by an upper tie plate 5 and a lower tie plate 14, and the periphery is surrounded by a fuel channel 2. In the body, the lower tie plate
It is characterized in that the circulation hole 15 through which the coolant 12 passes in the network portion 14 has a spiral shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly loaded in a nuclear reactor, and more particularly to a fuel assembly employing a lower tie plate for preventing damage to a fuel cladding tube.

[0002]

2. Description of the Related Art As shown in the longitudinal sectional view of FIG. 4, a fuel assembly loaded in a nuclear reactor has a fuel channel 1 having a rectangular tubular fuel channel 2. A plurality of fuel rods 3 and at least one water rod 4 are housed in.

An upper tie plate 5 and a lower tie plate 6 are mounted on the upper and lower portions of this fuel assembly, respectively.
In the upper tie plate 5 and the lower tie plate 6,
Both ends of the fuel rod 3 and the water rod 4 are provided with upper end plugs 7.
And is fixed by the lower end plug 8. A plurality of spacers 9 are attached to the water rod 4 at predetermined intervals in the axial direction, and the spacers 9 support the fuel rods 3 in an aligned manner and suppress the bending of the fuel rods 3.

The plan view of FIG. 5 shows the network portion 10 of the lower tie plate 6, which is
The hole 10 into which the lower end plug 8 for supporting the fuel rod 3 and the water rod 4 is inserted, and the flow hole 13 into which the coolant 12 shown in FIG. 4 flows from the lower tie plate 6 are formed. .

The enlarged cross-sectional view of the main part of FIG. 6 shows a vertical cross section of the conventional lower tie plate 14, in which the coolant 12 flows in from the lower portion of the fuel assembly 1 and the flow hole 13 of the lower tie plate 6 is introduced. The fuel rod 3 flows through the upper part of the fuel assembly 1 while removing the heat generated by the fuel rod 3.

[0006]

During the periodic inspection of the reactor, the fuel assembly 1 is replaced by opening the lid of the reactor pressure vessel (not shown). During this periodic inspection, metal pieces such as wire used for the work may fall into the reactor pressure vessel.

Further, there is a possibility that the reactor structure is partially peeled off due to oxidation or other reasons, and the peeled pieces fall into the reactor pressure vessel. Since foreign matters such as metal pieces and exfoliated pieces are usually small in weight, they are guided to the core along the flow of the coolant 12 during the operation of the reactor, and a part of them passes through the flow holes 13 of the lower tie plate 6 to make fuel. There is a possibility that the fuel may flow into the assembly 1 and be caught by the fuel assembly 1.

If foreign matter is caught in the fuel assembly 1 and comes into contact with the fuel clad tube of the fuel rod 3 due to a change in the flow velocity of the coolant 12, the fretting phenomenon may damage the fuel clad tube.

An object of the present invention is to bend the flow passage 1 for the coolant in the lower tie plate of the fuel assembly to prevent foreign matter from entering, thereby maintaining the integrity of the fuel cladding tube. To provide the body.

[0010]

In order to achieve the above object, a fuel assembly according to the invention of claim 1 supports the upper and lower ends of a plurality of fuel rods at upper and lower tie plates and surrounds them. In the fuel assembly surrounded by the fuel channels, the circulation hole through which the coolant passes in the network portion of the lower tie plate has a spiral shape.

A fuel assembly according to a second aspect of the invention is
In a fuel assembly in which the upper and lower ends of a plurality of fuel rods are supported by upper and lower tie plates and the periphery is surrounded by fuel channels, the cross section of the flow hole through which the coolant passes in the network portion of the lower tie plate is cut. It is characterized by having a letter shape.

A fuel assembly according to a third aspect of the invention is
In a fuel assembly in which the upper and lower ends of a plurality of fuel rods are supported by upper and lower tie plates and the periphery is surrounded by fuel channels, a cross section of a flow hole through which a coolant passes in a network portion of the lower tie plate is keyed. It is characterized by

[0013]

According to the first aspect of the present invention, foreign matter that has flowed into the lower tie plate together with the coolant is prevented from entering the spiral shaped flow holes of the network portion and does not flow into the fuel assembly, so the fuel cladding tube is not damaged. . It should be noted that the coolant passes through without any problem.

According to the second aspect of the present invention, foreign matter that has flowed into the lower tie plate together with the coolant is prevented from entering the V-shaped flow holes of the network portion and does not flow into the fuel assembly, so the fuel cladding tube is Do not damage. It should be noted that the coolant passes through without any problem.

According to the third aspect of the present invention, the foreign matter that has flowed into the lower tie plate together with the coolant is prevented from entering the hook-shaped flow holes of the network portion and does not flow into the fuel assembly. It should be noted that the coolant passes through without any problem.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those in the above-described conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. In the first embodiment, as shown in the enlarged cross-sectional view of the main part of FIG. 1, in the network portion of the lower tie plate 14 installed in the lower portion of the fuel assembly, the flow hole 15 into which the coolant 12 flows is formed in a spiral shape. ing.

As a function of this structure, even if a foreign matter is mixed in the coolant 12 and flows into the lower tie plate 14, the coolant 12 in the flow hole 15 changes its direction in a spiral shape. Although passing through the flow hole 15, foreign matter is blocked near the inlet of the flow hole 15. Therefore, the foreign matter cannot pass through the flow hole 15, and therefore, the foreign matter does not enter the fuel assembly and come into contact with the fuel cladding tube of the fuel rod 3 to damage the fuel cladding tube.

In the second embodiment, as shown in the enlarged sectional view of the main part of FIG. 2, a lower tie plate installed at the lower part of the fuel assembly.
In the network portion of 16, the flow hole 17 into which the coolant 12 flows has a dogleg-shaped cross section.

As a function of the above structure, even if foreign matter is mixed in the coolant 12 and flows into the lower tie plate 16, the coolant 12 is bent and passes through the flow holes 17, but
Foreign matter is prevented from entering the bent portion of the flow hole 15. Therefore, foreign matter does not enter the inside of the fuel assembly and damage the fuel cladding tube of the fuel rod 3.

In the third embodiment, as shown in the enlarged cross-sectional view of the main part of FIG. 3, the lower tie plate installed at the lower portion of the fuel assembly.
In the network portion of 18, the flow hole 19 into which the coolant 12 flows is formed in a hook shape in cross section.

According to the above-mentioned structure, even if a foreign matter is mixed in the coolant 12 and flows into the lower tie plate 16, the flow passage hole is formed.
At 12, the coolant 12 is refracted and passes, but foreign matter is prevented from entering at the bent portion of the flow hole 19. Therefore, foreign matter does not enter the inside of the fuel assembly and damage the fuel cladding tube of the fuel rod 3.

The above-mentioned lower tie plates 14, 16,
With regard to 18, by considering the flow passage areas of the respective flow holes 15, 17, 19 and making the pressure loss of the passing coolant 12 the same as that of the conventional lower tie plate 6, the coolant 12 in the core is The pressure loss can be made the same as the conventional one, and the core characteristics can be made the same.

[0023]

As described above, according to the present invention, even if a foreign substance flows into the lower tie plate together with the coolant, the foreign substance is prevented from passing through the coolant circulation holes in the network section.
Since it does not enter the fuel assembly, there is an effect that the soundness of the fuel cladding tube can be maintained.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a lower tie plate main part of a fuel assembly according to a first embodiment of the present invention.

FIG. 2 is a vertical sectional view of a lower tie plate main part of a fuel assembly according to a second embodiment of the present invention.

FIG. 3 is a vertical sectional view of a lower tie plate main part of a fuel assembly according to a third embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view of a fuel assembly.

FIG. 5 is a plan view of the network portion of the lower tie plate.

FIG. 6 is a vertical cross-sectional view of a main part of a lower tie plate of a conventional fuel assembly.

[Explanation of symbols]

1 ... Fuel assembly, 2 ... Fuel channel, 3 ... Fuel rod, 4
… Water rod, 5… Upper tie plate, 6, 14, 1
6, 18 ... Lower tie plate, 7 ... Upper end plug, 8 ... Lower end plug, 9 ... Spacer, 10 ... Network part, 11 ... Hole for receiving lower end plug, 12 ... Coolant, 13, 15, 17, 19 ... Coolant flow holes.

Claims (3)

[Claims] 1. A fuel assembly in which the upper and lower ends of a plurality of fuel rods are supported by upper and lower tie plates and the periphery is surrounded by fuel channels, and a through hole through which a coolant passes through a network portion of the lower tie plate. A fuel assembly having a spiral shape. 2. A fuel assembly in which the upper and lower ends of a plurality of fuel rods are supported by upper and lower tie plates and the periphery of which is surrounded by fuel channels, and a through hole through which a coolant passes through a network portion of the lower tie plate. A fuel assembly having a dogleg-shaped cross section. 3. A fuel assembly in which the upper and lower ends of a plurality of fuel rods are supported by upper and lower tie plates and the periphery is surrounded by fuel channels, and a through hole through which a coolant passes through a network portion of the lower tie plate. A fuel assembly having a cross section of a hook shape.