JPS646425B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to nuclear fuel insert structures and, more particularly, to improvements in attachment devices for nuclear fuel inserts such as burnable poison rods and simple plugs.

Used as nuclear fuel inserts in nuclear reactors, such as burnable poison rods that control the reactivity of nuclear fuel and simple plugs that adjust the pressure loss of cooling water flowing through nuclear fuel assemblies. There is. The general configuration of these nuclear fuel inserts is that they are attached to the superstructure of the nuclear fuel insert structure in clusters and hanging down, and they are inserted into the control rod guide thimble of the nuclear fuel assembly and held. It is used by being pressed and fixed to the upper core plate via a down spring. To explain this in detail according to the drawings, as shown in Fig. 1, an upper part has a hold-down bar 1, an end plate 2, a sleeve 3 connecting these, and a hold-down spring 4 interposed on the outer periphery of this sleeve 3. A large number of burnable poison rods 6 and simple plugs 7 are attached to the end plate 2 of the structure 5.
The upper ends of each are welded and fixed. To fix it, as shown in Fig. 2, a small diameter part 9 is formed on the upper end plug 8 formed at the upper end of the burnable poison rod or simple plug, and a two-piece screw 10 is carved into the tip of the small diameter part 9. Then, this upper end plug 8 is fitted into a round hole 14 bored in the end plate 2 of the upper structure 5, and a nut 1 is inserted into the screw 10 protruding from the upper part.
1 are screwed together, a pin 13 is inserted into the crack groove 12 of the screw 10, and the nut 11 is welded to this.

By the way, burnable poison rods are used to maintain a constant reactivity in a nuclear reactor, that is, to absorb excess neutrons generated in nuclear reactions, so burnable poison rods are Poison sticks are radioactive and post-treatment is extremely difficult. Therefore,
Conventionally, used burnable poison rods have been stored as radioactive waste, for example, in the area of a nuclear power plant for a long period of time.

However, since the used burnable poison rod is welded to the upper structure 5 as described above, it is stored together with the upper structure 5 as a nuclear fuel insert structure. On the other hand, in order to store the spent nuclear fuel insert structures that are generated one after another for a long period of time, a vast storage space is required, and the current situation is that there is a limit to the storage.

In addition, although the upper structure 5 and the simple plug 7 can be reused, they are disposed of as waste because they are integrated as described above.

The present invention has been made to solve the above-mentioned problems, and aims to reduce the volume of the nuclear fuel insert structure so that the burnable poison rod, which is radioactive waste, can be stored alone for a long time. It is an object of the present invention to provide an improved nuclear fuel insert structure in which the structure, simple plug, etc. can be reused.

The present invention, which is suitable for the above purpose, is characterized in that a square hole is formed in the end plate of the upper structure of the nuclear fuel insert structure, and a square hole is formed in the upper end plug body of the nuclear fuel insert. A screw having a partially notched portion is formed to form a square portion that fits into the square hole, and a nut having a crimping cylinder portion integrally formed at the tip of the upper end plug is screwed into the nut. This is because they are screwed together and caulked.

Hereinafter, the present invention will be explained in more detail based on examples thereof.

FIG. 3 is an overall cross-sectional view of the burnable poison rod 6, showing a cladding tube 2 containing B ₄ C-filled alumina sintered pellets 21 and a plenum coil spring 22 that presses the pellets in the axial direction of the burnable poison rod 6.
3, a lower end plug 24 fixed to the lower end of the cladding tube 23, and an upper end plug 8 fixed to the other end of the cladding tube 23.

Of the above-mentioned parts, the present invention particularly relates to the improvement of the upper end plug 8 part, in which a screw 26 having a notch 25 in the axial direction is carved in a part of the outer periphery of the tip part. A corner portion 27 is formed with a stepped surface 28 at the root portion of the plug 26, that is, the body portion of the upper end stopper. On the other hand, the end plate 2 of the upper structure 5 is provided with a square hole 29 into which the corner portion 27 of the upper end plug 8 is fitted.

Moreover, in correspondence with the screw 26 having the notch 25 in a part of the outer periphery, the present invention provides a nut 3 integrally molded with a caulking cylinder part 30 as shown in FIG.
1 is used, and after this nut 31 is screwed onto the screw 26, its cylindrical portion 30 is caulked at a location corresponding to the notch 25 of the screw.

The present invention is constructed as described above, and as shown in FIG.
The rotation of the burnable poison rod 6 is prevented, and the stepped surface 28 comes into contact with the lower surface of the end plate 2.

Next, a nut 31 with a cylindrical portion 30 as shown in FIG. 5 is screwed into the screw 26 projecting above the end plate 2. At this time, since the rotation of the burnable poison rod 6 is prevented by the square hole 29 of the end plate 2, the nut 31 can be easily rotated without accompanying rotation of the burnable poison rod 6. The rod can be firmly fixed to the end plate 2 of the superstructure 5.

Thus, after the nut 31 is screwed, the cylindrical portion 30 of the nut 31 is caulked at a location corresponding to the notch 25 of the screw 26, thereby preventing the nut 31 from loosening. By setting this caulking amount in advance, when removing a used burnable poison rod, applying a torque to the nut 31 that destroys the caulking will release the loosening, making it possible to easily remove the nut 31. can.

As a result, the burnable poison rod can be easily extracted from the end plate 2 and stored alone, making it possible to reduce the volume of the spent nuclear fuel insert structure with an extremely simple operation. Become.

In this removal work of the burnable poison rod 6, for example, unlike when cutting the upper end plug 8, there is no generation of chips or damage to the end plate 2, and therefore the upper structure 5 and Simple plugs can be disassembled in a state where they can be reused.

Incidentally, as shown in FIG.
If a corner part 32 is further formed below the corner part 27 of the burnable poison bar 6, the direction of the burnable poison bar 6 is ordered by an alignment means (not shown) when inserting the burnable poison bar into the end plate 2. This is convenient because the crimping position of the nut 31 with the cylindrical portion 30 can be adjusted in a fixed direction.

The present invention is applicable not only to the burnable poison assembly consisting of the above-mentioned burnable poison rod, simple plug, and upper structure, but also to a simple plug assembly consisting of a simple plug and an upper structure, and a burnable poison rod and seam. Needless to say, the present invention can also be applied to various nuclear fuel insert structures such as a neutron source assembly consisting of a pull plug, a neutron source, and a superstructure.

As described above, the present invention provides a structure in which a square hole is formed in the end plate of the upper structure of a nuclear fuel insert structure, and a square hole is formed in the upper end plug body of the nuclear fuel insert to fit into the square hole. A burnable poison rod that cannot be reused is made because a screw with a partial notch is carved into the tip of the upper end plug to screw into a nut with a crimping tube integrally formed at the tip of the upper end plug. It can be removed from the superstructure without scattering chips, etc., and not only can the spent fuel storage pool be kept clean, but burnable poison rods can be stored separately from the superstructure as part of the vehicle body. Therefore, the space required for long-term storage of spent nuclear fuel insert structures can be greatly reduced. In addition, since the new burnable poison rod can be easily attached to the superstructure after use, the used superstructure and simple plug can be reused, which is highly effective in terms of resource conservation.

In addition, in the present invention, the fitting between the square hole and the corner portion prevents the nuclear fuel insert from rotating when it is attached to the upper structure, and furthermore, when the nut is screwed together, the nut is rotated along with the rotation. The nuclear fuel insert can be easily rotated without any problems, the nuclear fuel insert can be firmly attached to the upper structure, and a notch is formed in the thread, and the nut cylinder portion is moved to a position corresponding to the notch. The crimping also has the effect of preventing the nut from loosening, and there are great expectations for its practical use in the future.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing a conventional example of a nuclear fuel insert structure in which a burnable poison rod or the like is attached to a superstructure, Fig. 2 is a partial perspective view showing the welded and fixed state, and Fig. 3 is a An overall cross-sectional view of the burnable poison rod, FIG. 4 is a perspective view of the main part showing the fixed state of the burnable poison rod according to the present invention, and FIG. 5 is a partial cross-section of a nut with a cylindrical portion that fixes the burnable poison rod. It is a diagram. 1...Hold down bar, 2...End plate, 5...
...Superstructure, 6...Burnable poison rod, 7
...Simple plug, 8...Top end plug, 25...
Notch, 26...Screw, 27...Corner part, 29...
...Square hole, 30...Cylinder part, 31...Nut, 32...
...angular part.

Claims (1)

[Claims] 1 A large number of nuclear fuels are inserted into holes provided in the end plate of a superstructure having a hold town bar, an end plate, a sleeve connecting these, and a hold town spring interposed on the outer periphery of the sleeve. In the nuclear fuel insert structure formed by fitting and mounting the upper end plug of the nuclear fuel insert, the hole in the end plate is formed into a square hole, while the upper end plug body of the nuclear fuel insert is formed with a square hole. A screw having a stepped surface to form a square portion that fits into the square hole, and a screw having a partial notch on the tip of the upper end plug into which a nut having an integrally molded caulking cylinder portion is screwed is provided. A nuclear fuel insert structure, characterized in that the nut is screwed into the threaded part, and the cylindrical part is caulked at a location corresponding to the notch of the thread.