JPH0141236B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for assembling and disassembling a nuclear fuel assembly, and in particular to a method for reliably preventing damage to the surface of fuel rods during assembly or disassembly. This invention relates to methods for assembling and disassembling nuclear fuel assemblies.

[Technical background of the invention and its problems]

Generally, in a fuel assembly for a nuclear reactor, fuel rod spacers are provided at a plurality of locations in the longitudinal direction of the fuel assembly to maintain the spacing between the plurality of fuel rods.

That is, FIG. 1 is a longitudinal cross-sectional view of the fuel assembly for the above-mentioned nuclear reactor, and in the fuel channel 1, there are
A plurality of fuel rods 4 and water rods 5 are installed in an array, with their upper and lower ends supported by an upper tie plate 2 and a lower tie plate 3, respectively. A plurality of spacers 6 are provided in the axial direction of the fuel rods 4 for restraining vibration and ensuring a coolant flow path.

The spacer 6 has a square outer frame 7, as shown in FIGS. 2 and 3, and is comprised of bars 8, 9 and dividers 10, 11 arranged in a grid pattern within the outer frame 7. Multiple small partitions 12
is formed. Further, at each intersection of the bars 8 and 9, a leaf spring portion 1 protruding outward on each side is provided.
A lantern spring 13 having a diameter 3a is attached, and the fuel rod 4 inserted into each of the small partitions 12 is guided from the corner of the small partition 12 to the S vents 10a, 11a formed in the dividers 10, 11.
It is made to come into elastic pressure contact with.

Therefore, when assembling the above-mentioned nuclear fuel assembly, the lower plate 3 and the spacer 6 are fixed in a predetermined position, and the fuel rods 4 and water rods 5 are respectively pushed into the small partitions 12 of the spacer 6.
The lower end is attached to the lower tie plate 3, and the upper tie plate 2 is attached and fixed to the upper end.

However, in assembling the fuel assembly as described above, when each fuel rod 4 is inserted into the small partition 12, the fuel rod is inserted into the leaf spring portion 13a of the lantern spring 13 of the spacer 6 and the S vents 10a, 11a. The surface of the fuel rod may be scratched because it comes into sliding contact with the surface of the fuel rod.

Therefore, conventionally, in order to prevent the surface of the fuel rod from being damaged, the plate spring portion 13a of the lantern spring 13 of the spacer 6 and the S vent 10
a and 11a with a string to hold down the protruding part of the spring to enlarge the space into which the fuel rod is inserted, or to store the fuel rod at sub-zero temperatures to form a film of ice or frost on its surface. Alternatively, methods such as cooling a mixture of water, alcohol, or other substances and using the mixture as a lubricant have been taken.

However, the method of tying the spring part with string is very complicated and time-consuming, and if a film of ice or other material is to be formed on the surface of the fuel rod, it is necessary to keep the fuel rod at sub-zero temperature beforehand. When using lubricants, there is a risk that impurities may adhere to the fuel rods, reducing their performance, and a cleaning process must be added, which increases the number of work steps and makes assembly more troublesome. There is a problem.

[Purpose of the invention]

In view of the above, an object of the present invention is to provide a method for assembling and disassembling a nuclear fuel assembly that can reliably prevent the occurrence of scratches on the surface of fuel rods using a relatively simple method. .

[Summary of the invention]

In the present invention, the fuel rods are each inserted into a small partition formed by bars and day binders arranged in a lattice shape, each having at least one elastic member for pressing the fuel rods, thereby preserving the spacing of the nuclear fuel rods. In the method for assembling and disassembling a nuclear fuel assembly, the above-mentioned The present invention is characterized in that the fuel rods are inserted into or withdrawn from the small partition after covering at least the portion of the inner surface of the small partition that is in contact with the fuel rod or the portion that is in contact with the fuel rod.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 4 to 12.

In FIG. 4, reference numeral 20 is a jig used in the present invention, and the jig 20 is made of a material having elasticity and self-lubricating properties, such as polyethylene or polystyrene, and has an arm 21 protruding from one end side. A notch 23 is formed in the cylinder 22 and extends over the entire length in the axial direction.

Therefore, when assembling a fuel assembly, first, the cylinder 22 of the jig 20 is coaxially inserted into the small partition 12 of the spacer into which the predetermined fuel rod 4 is to be inserted, and the cylinder 22 of the jig 20 is inserted into the cylinder 22. Insert the rod 4 from one end (FIG. 5). After the fuel rods 4 are inserted in this way, the jig 20 is moved in the axial direction of the fuel rods 4, and the small partition 1 of the spacer 6 is moved.
2, and then move the jig 20 in a direction perpendicular to the axis of the fuel rod 4 to cut out the notch 23.
At this point, the jig 20 is removed from the fuel rod 4.

Hereinafter, in the same manner, each small partition 12 of the spacer 6
The fuel rods 4 are sequentially inserted therein to assemble a nuclear fuel assembly. The movement of the jig 20 in each direction can be controlled using a ball screw, a pulse motor, or the like.

Since the jig 20 is used to insert the fuel rod into the spacer, the lantern spring 1
3 is covered by the cylinder of the jig 20, the outer surface of the fuel rod 4 does not come into sliding contact with the lantern spring 13, etc., and the outer surface of the fuel rod 4 is not damaged. There isn't. On the other hand, although the fuel rods slide along the inner surface of the cylinder 22 of the jig 20, since the jig has self-lubricating properties, there are almost no scratches caused by the sliding.

That is, since the friction between the fuel rod 4 and the jig 20 is smaller than the friction between the fuel rod 4 and the lantern spring 13 and S bends 10a, 11a of the spacer, the fuel rod 4 can be easily inserted into the small partition 12 of the spacer 6.
Moreover, since the jig 20 is elastic and has an axial notch 23 on the cylindrical side surface, it can be easily removed from the fuel rod 4.

In the above embodiment, the notch 23 of the jig 20 has a narrow opening, but the sixth
As shown in the figure, the cylindrical part may be formed in a spiral shape with the opening inside the cylinder, and the shape of the jig 20 may be such that the arm 21 is on one side of the center of the cylindrical part as shown in FIG. Further, as shown in FIG. 8, a cylindrical portion 24 having a square cross section
It may also have the following. The cylindrical part of the jig 20 is widened at the rear, as shown in FIG. 9, in order to facilitate insertion of the fuel rod, and the front part is tapered to facilitate insertion into the spacer 6. It may have a split end 25, or it may be formed by two semicircular members in cross section as shown in FIG.

Furthermore, the cylindrical portion may be a thin metal cylinder with a plastic layer layered on the inner surface.

On the other hand, even if the spacer 6 does not use a lantern spring as shown in FIG. 2, if the fuel assembly is equipped with a lattice-shaped spacer having an elastic element for press-supporting the fuel rods, The present invention can be applied to anything.

When dismantling a fuel assembly, the cylindrical portion 22 of the jig 20 is attached so as to wrap around the fuel rod to be extracted using the notch 23 in the axial direction. The tool 20 is slid in the axial direction, the thin-walled cylinder 22 is inserted between the lantern spring 13 of the spacer, the vents 10a, 11a, etc., and the fuel rod 4, and then the fuel rod 4 is pulled out in the axial direction. Therefore, the fuel rod 4 can be removed from the spacer without slidingly contacting the lantern spring 13 or the like. By performing such operations on each fuel rod, the fuel assembly can be disassembled.

〔Effect of the invention〕

As explained above, the present invention involves inserting a jig into the small partition of the spacer and inserting and removing the fuel rod into the jig prior to inserting or withdrawing the fuel rod into the spacer. Therefore, it is possible to reliably prevent damage to the outer surface of the fuel rod due to the lantern spring, etc., and the process is extremely simple, and there is no need to add complicated equipment or processes.

[Brief explanation of drawings]

Figure 1 is a longitudinal side view of the nuclear fuel assembly, Figure 2 is an enlarged plan view of the spacer, and Figure 3 is the same as in Figure 2.
4 is a perspective view of the jig, FIG. 5 is a plan sectional view showing the state in which the fuel rod is inserted into the spacer using the jig, and FIGS. 6 to 10 are FIG. 7 is a diagram showing other examples of the jigs. 2... Upper tie plate, 3... Lower tie plate, 4... Fuel rod, 6... Spacer, 10a,
11a...S bend, 12...Small partition, 13...
...Lantern spring, 20...Jig, 21...
Arm, 22...Cylinder, 23...Notch.

Claims (1)

[Claims] 1. The fuel rods are each inserted into a small partition formed by bars, day binders, etc. arranged in a lattice pattern and each having at least one elastic member for pressing the fuel rods, and the spacing of the nuclear fuel rods is maintained. In the method for assembling and disassembling a nuclear fuel assembly, the small partitions are assembled using a thin-walled cylindrical jig having elasticity and self-lubricating properties and having at least one notch extending along the entire length in the axial direction. A nuclear fuel assembly characterized in that the fuel rods are inserted into or withdrawn from the small partition after covering at least the portion of the inner surface that is in contact with the fuel rods or the portion that is in contact with the fuel rods. Assembly and disassembly methods.