JPS6312272B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel assembly for a pressurized water nuclear reactor.

Generally, the concentration of nuclear material required for nuclear reactor operation is achieved through an array of fuel rods.

These fuel rods are loaded into the reactor core as a fuel assembly formed by bundling a plurality of fuel rods together with a control rod guide tube that connects an upper nozzle and a lower nozzle on a support grid at a predetermined pitch.

As shown in FIG. 1, the above-mentioned conventional fuel assembly A has an upper nozzle a and a lower nozzle b connected by a control rod guide tube c, and a plurality of fuel rods d...
. . . had a structure in which they were simply bundled together with the control rod guide tube c between the upper nozzle a and the lower nozzle b by a support grid e.

Therefore, since the fuel rods d and the support grids e are in an exposed state, when handling the fuel assembly A by lifting it with a crane or the like and loading it into the reactor core, the fuel rods d and the support grids e are exposed, so that when handling the fuel assembly A by lifting it with a crane or the like and loading it into the reactor core, If the fuel assemblies A to be used interfere with each other, the support grid e of the direct fuel rod d is likely to be damaged, and in the worst case, it may be damaged.

In addition, since the structure is such that the upper nozzle a and the lower nozzle b are simply connected by the control rod guide tube c, there is a problem with the rigidity, and in the event of a strong earthquake, the control rod guide tube c may be damaged during core loading or pooling. As a result, the control rods may be significantly deformed, making it difficult to insert the control rods and making it impossible to shut down the reactor when it becomes necessary to do so.In addition, if the fuel assemblies A collide with each other, , directly applying an impact load to the fuel rod d and the support grid e, the fuel rod d,
There was also a risk of damaging the support grid e.

Therefore, in order to eliminate the above-mentioned conventional defects, the present invention has a small gap between fuel assemblies when loading fuel assemblies into the reactor core, so that the fuel being loaded is larger than the already loaded fuel assemblies. After considering the circumstances in which the assembly would interfere with each other if it was tilted by approximately 100 mm, and the position where mutual interference is most likely to occur during handling other than loading, we decided to install a control rod guide tube in which multiple fuel rods connect the upper and lower nozzles. With,
In a fuel assembly structure formed by bundling at a predetermined pitch on a support grid, axial reinforcing members are erected on the outer surface of each of its four corners to support both the upper and lower nozzles. The gist is that support pins are provided inside each axial reinforcement at the same height, and the corners of the support grid are attached to these support pins in such a way that lateral movement is restricted but vertical movement is possible. The purpose of this is to prevent damage to the fuel rods and support grids due to mutual interference between the fuel assemblies during loading and handling of the fuel assemblies, and to prevent damage to the fuel rods and support grids during earthquakes. The support grid must be rigid enough to prevent bending of the fuel rods, etc., and at the same time be able to move up and down even if the fuel rods are deformed due to thermal expansion during use. Therefore, the support grid moves together with the fuel rods, and the aim is to increase the strength so as not to cause damage due to friction between the two.

The present invention will be described in detail below based on drawings showing embodiments. In FIG. 2, a fuel assembly structure 1 is
A plurality of fuel rods 2 each made of a long metal cladding tube containing a uranium compound in the form of pellets are connected together with a plurality of control rod guide tubes 5 connecting an upper nozzle 3 and a lower nozzle 4. This is similar to the conventional fuel assembly in that it is formed by bundling in a predetermined pitch arrangement around a support lattice 6 formed by framing strips in a lattice shape.

In the present invention, rod-shaped axial reinforcing members 7 are further provided vertically on the outer surface of the four corners of the fuel assembly structure 1, supporting the upper and lower ends of the upper nozzle 3 and the lower nozzle 4, respectively. A support pin 8 is attached to the inside of each of the axial reinforcing members 7 at a high position corresponding to the attachment position of the support grid 6, and the support grid 6 is attached to each support pin 8.
Each corner is fitted so that horizontal movement is restricted but vertical movement is possible.

Here, the bolts 9 and positioning pins 10 are attached from both upper and lower ends of each of the above-mentioned reinforcing members 7 as shown in FIG.
As shown in FIG. 4, the bolts 9 and positioning pins 10 are formed to extend parallel to each other in the axial direction.
The nuts 13 are fitted into the bolt insertion holes 11 and the positioning holes 12 which are arranged in parallel to the upper nozzle 3 and the lower nozzle 4, respectively, and the nuts 13 are screwed to position the upper and lower nozzles 3 and 4 in the axial direction. It is fixed in a removable manner.

Furthermore, the reinforcing member 7 has a support pin 8, as shown in FIG.
As shown in FIG. 6, one end 8a is removably attached using a pin 14, and the two ends are arranged side by side with an interval l that allows insertion of the strip plate 6' of the support grid 6, and the other end 8b is provided with an axial reinforcing member. 7, which facilitates the assembly work with the support grid 6, and even if the member expands or contracts in the axial direction due to thermal expansion, the support grid 6 follows the expansion and contraction. It is designed so that it can be moved up and down.

Further, in the illustrated example, a notch 7a is provided inside the axial reinforcing member 7, and the support pin 8 is fitted into the notch 7a, thereby making the entire structure compact.

Furthermore, in the illustrated example, the fuel assembly structure 1
No fuel rods are inserted into each corner of the support grid 6, and the support pins 8 are inserted therein.

Further, each of the axial reinforcing members 7 is connected to each supporting grid 6 by tightening bolts 16 of a lateral reinforcing member 15 disposed at an outer position corresponding to each support grid 6, thereby increasing the rigidity. At the same time, the support grid 6 is covered and protected to prevent damage to the support grid 6 due to interference between fuel assemblies.

Incidentally, the axial reinforcement 7 is incorporated when the fuel assembly structure 1 is assembled, while the lateral reinforcement 1
After the fuel assembly structure 1 is assembled, bolts 16 are tightened and spot welded to prevent them from loosening.

As explained above, according to the pressurized water type fuel assembly according to the present invention, the axial reinforcing member 7 is provided on the outer surface of each corner of the fuel assembly structure 1 where the fuel assemblies tend to interfere with each other.
is supported by both the upper and lower nozzles 3 and 4 and arranged in the axial direction, thereby preventing damage to the fuel rod 2 support grid 6 due to mutual interference of fuel assemblies during handling such as loading into the core. It is possible,
This makes it easier to handle, reduces periodic inspection time, and improves the reactor operating rate.The increased rigidity also reduces the bending of the fuel assembly, making it easier to insert control rods in the event of an earthquake. The fuel rods can now be easily handled after combustion, and the fuel rods are supported by the support grid 6, which is prevented from moving laterally by support pins 8 attached to the axial reinforcements 7. , the overall rigidity is improved, and since the support grid 6 is not restricted in its vertical movement by the support pins 8, it can absorb thermal expansion and bending when the fuel rod is used, and is not forced to do so. There are no problems caused by stress.

[Brief explanation of the drawing]

Fig. 1 is a front view showing a conventional pressurized water fuel assembly, Fig. 2 is a partially cutaway front view showing a pressurized water fuel assembly according to the present invention, and Figs. 3 and 4 are the same fuel assembly. Each enlarged vertical side view showing an example of connection between the axial reinforcement and the upper nozzle or the lower nozzle in the body, FIG. 5 is an enlarged vertical side view of section B in FIG. 2, and FIG. 6 is an enlarged section of B in the same figure. FIG. 1...Fuel assembly structure, 2...Fuel rod, 3...
Upper nozzle, 4... Lower nozzle, 5... Control rod guide tube, 6... Support grid, 7... Axial reinforcement, 8
... Support pin, 9 ... Bolt, 10 ... Positioning pin, 14 ... Pin, 15 ... Lateral reinforcing member.

Claims (1)

[Claims] 1. In a fuel assembly structure in which a plurality of fuel rods are arranged at a predetermined pitch on a support grid and bundled together with a control rod guide tube connecting an upper nozzle and a lower nozzle, On the outside of each corner,
Axial reinforcing members are supported and erected on both the upper and lower nozzles, and support pins are provided inside each of the axial reinforcing members at the same height, and the corner portions of the support grid are attached to the support pins. , a pressurized water type fuel assembly characterized in that it is installed so that lateral movement is restricted but vertical movement is possible. 2. The pressurized water type fuel assembly according to claim 1, wherein the axial reinforcing member is formed by a bottle that can be detachably attached to the upper nozzle and the lower nozzle and can be positioned and fixed, and a positioning pin protruding from the end. body. 3. The pressurized water type fuel assembly according to claim 1, wherein one end of the support pin is pinned to the axial reinforcing member, and the other end is attached free. 4. A pressurized water fuel assembly according to claim 1, wherein the axial reinforcements are connected by lateral reinforcements at corresponding outer positions of the support grid.