JPH0363040B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION This invention relates to a method for cutting a spent nuclear fuel channel in a boiling water nuclear reactor to reduce its volume.

[Technical background of the invention]

Conventionally, spent nuclear fuel channels have been cut to reduce their volume using cutting methods such as saws, chips, electrical discharge machining, and plasma arcs.

[Problems with background technology]

The conventional method for cutting spent nuclear fuel channels has a problem in that highly radioactive chips are generated during cutting, making safe disposal of the chips difficult.

[Purpose of the invention]

The present invention was made to solve the problems of the conventional method for cutting a spent nuclear fuel channel, and an object of the present invention is to provide a method for cutting a spent nuclear fuel channel that does not generate chips during cutting.

[Summary of the invention]

The method for cutting a spent nuclear fuel channel (hereinafter simply referred to as a nuclear fuel channel) according to the present invention is as follows:
A prismatic jig whose outer cross section is almost similar to the square through hole extending over the entire length of the nuclear fuel channel, and which is slightly smaller than the square through hole and has concave cut grooves extending toward the center at the four corners along the entire length, and is longer than the nuclear fuel channel. Then, a nuclear fuel channel is inserted and supported through the square through hole, and a shearing tool having a pointed V-shaped tip cross section is pressed against a corner wall of the nuclear fuel channel, and this corner wall is cut by the tool. By pushing the nuclear fuel channel into the groove and deforming and breaking it, and moving the nuclear fuel channel and jig relative to the tool in the length direction of the nuclear fuel channel, the nuclear fuel channel was cut without generating chips to achieve the above purpose. It is something.

[Embodiment of the Invention] An embodiment of the invention will be described with reference to FIGS. 1 and 2.

1 and 2 are a plan view and a partially sectional front view of an example of a cutting device used to carry out the method of the present invention.

The jig 1 is made of a vertical through hole whose outer cross section is approximately similar to the through hole extending over the entire length of the nuclear fuel channel 2, which is a long rectangular tube with an approximately square shape with slightly rounded corners at the four corners. It has a prismatic shape and has cut grooves 3 at its four corners with a V-shaped cross section toward the center over the entire length, and the length is slightly longer than the nuclear fuel channel 2. The lower end of the jig 1 forms a flange portion 4 whose outer cross section is substantially the same as that of the nuclear fuel channel 2, and the nuclear fuel channel 2 can be vertically supported on the flange portion 4 at its lower end. A female screw 5 is fixed to the lower end of the jig 1 with a common vertical center axis. A long upright screw shaft 7 having a worm foil 6 fixed to its lower part is screwed into the female thread 5. The upper part of the screw shaft 7 extends upward through the center hole of the jig 1. The screw shaft 7 is a worm wheel 6
At the same time, it is supported via a bearing on a base plate 8 having an approximately square outer cross section that is the same as that of the nuclear fuel channel 2, so as to be rotatable about a vertical axis and restrained from moving up and down. The worm wheel 6 is engaged with a worm of a worm shaft 9 which is horizontally supported in a base plate 8 via a bearing so as to be rotatable and restrained from moving in the axial direction. The worm shaft 9 is reversibly rotated by an electric motor 10 connected to its shaft end and fastened to the side surface of the base plate 8. On the four sides of the base plate 8,
The lower ends of guide plate columns 11 each having a reinforcing rib and extending vertically upward are fixed at their lower ends. The nuclear fuel channel 2 is fitted between the jig 1 and the guide plate pillar 11 along the jig 1 from above.
is placed on the flange portion 4 of.

When the worm shaft 9 is driven by the electric motor 10, the jig 1 whose rotation is prevented by the guide plate column 11, together with the nuclear fuel channel 2 fitted therein, drives the worm wheel 6, screw shaft 7, and female screw 5. is moved vertically through the When the lower end surface of the jig 1 contacts the upper end surface of the base plate 8, the jig 1 occupies the lower limit position of its movement.

The jig 1 is shaped like a disk whose center axis is approximately on a horizontal plane including the upper edge of the nuclear fuel channel 2 which is fitted into the jig 1 at the lower limit position and placed on the flange portion 4 of the jig 1, and whose outer circumferential cross section is the jig 1. The shearing tool 2 has a V-shape with a slightly sharp point beyond the cutting groove 3.
The four shearing devices 21, each equipped with a shearing device 0, are each fastened on a stationary support 22. The shearing device 21 includes a tool 20, a tool stand 23 that supports the tool 20 horizontally and rotatably on a central axis that does not intersect with the central axis of the jig 1 but is perpendicular thereto;
A bed 24 supports the tool stand 23 horizontally so as to be movable in the diagonal direction of the nuclear fuel channel 2, and is supported by the bed 24 horizontally so as to be rotatable and restrained from moving in the axial direction, through a female thread fixed to the tool stand 23. A screw shaft 25 for moving the tool stand 23 along the bed 24 is provided. A handle 26 at the end of the screw shaft 25 is configured to be operable from a distance using an operating tool (not shown).

A method for cutting the nuclear fuel channel 2 will be described below.

The tool 20 is moved to the outer extreme position away from the jig 1 by operating the handle 26 and placed there. To the jig 1 whose lower end surface is in contact with the upper end surface of the base plate 8 and is at the lower limit position,
The nuclear fuel channel 2 is inserted and placed on the flange portion 4 of the jig 1. By sequentially operating the handles 26 of the four shearing devices 21 and pushing the tool 20 against the corner wall of the nuclear fuel channel 2, the corner wall of the nuclear fuel channel 2 is cut into the cut groove 3 of the jig 1 by the tool 20. The part is deformed and fractured. Next, when the electric motor 10 is operated, the jig 1
, while supporting the nuclear fuel channel 2, attach the worm shaft 9, the worm wheel 6, the screw shaft 7, and the female screw 5.
The nuclear fuel channel 2 is deformed and sheared from above to below by the tool 20 at the four corners facing the cut groove 3 of the jig 1, and is finally cut into four plate shapes. The volume is reduced. At this time, the tool 20 rotates due to the frictional force between it, the nuclear fuel channel 2, and the jig 1, and changes the shearing area, thereby prolonging its durability.

After the nuclear fuel channel 2 is separated into four parts, operate the handle 26 to move the tool 20 away from the jig 1, operate the electric motor 10 in the opposite direction to lower the jig 1 to the lower limit position, Return to original position.

〔Effect of the invention〕

As described in detail above in the embodiment, the method for cutting a nuclear fuel channel of the present invention is to cut a through hole over the entire length of the nuclear fuel channel and an outer cross section that are substantially similar to each other, so that the through hole is slightly smaller than the through hole and is centered at the four corners. The nuclear fuel channel is inserted and supported in a prismatic jig that is longer than the nuclear fuel channel and has a concave cut groove along its entire length, and a shearing tool with a V-shaped cross section with a pointed tip is inserted into the nuclear fuel channel. The corner wall is pushed into the cut groove with a tool to deform and break, and the nuclear fuel channel is moved along with the jig relative to the tool in its length direction, so that the corner wall part is moved over the entire length. Since cutting is performed by deformation shearing, there are no chips generated during cutting unlike in the case of the conventional method.
This has the effect of resolving the difficulty of disposing of highly radioactive chips.

[Brief explanation of drawings]

1 and 2 are a plan view and a partially sectional front view, respectively, of a cutting device used to carry out the method of the present invention. 1...Jig, 2...Spent nuclear fuel channel, 3...
Cutting groove, 20... shearing tool.

Claims (1)

[Claims] 1. Penetrating the spent nuclear fuel channel, whose outer cross section is a long rectangular cylinder with a slightly rounded corner and a substantially square shape, through a square through hole that spans its entire length, with the square through hole and the outer cross section being approximately similar. It is inserted and supported in a prismatic jig that is slightly smaller than a square hole and has concave cut grooves extending toward the center at the four corners over the entire length, and is longer than the nuclear fuel channel, so that the tip has a V-shaped cross-sectional shape with a pointed tip. A shearing tool having a shearing tool is pressed against a corner wall of the nuclear fuel channel, and the corner wall is pushed into the cut groove with the tool to deform and break, and the nuclear fuel channel and jig are set against the tool to cut the length of the nuclear fuel channel. A method for cutting a spent nuclear fuel channel, which cuts the nuclear fuel channel by relatively moving in a direction.