JPS6118154B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for disconnecting a control rod from a control rod drive in a boiling water nuclear reactor.

[Technical background of the invention]

As shown in FIG. 1, the control rod drive device 11 is housed in a control rod housing 20 which is integrated with a reactor pressure vessel (not shown) and projects downward from the reactor pressure vessel. A housing flange 21 is attached to the lower surface of the control rod housing 20. This housing flange 21 has an inner tube 22 that penetrates into the control rod housing 20 and serves as a guide for the index tube 16. An outer tube 2 is connected to the outside of this inner tube 22 via a cylinder tube 23.
4 is placed. This outer tube 24
extends further upward than the inner tube 22, and a guide cap 25 is provided at the upper end thereof, and the index tube 1 is slidably supported by the guide cap 25.

A collector piston 26 is slidably inserted above the cylinder tube 23. This collect piston 26 has a collect finger 27 that engages in a circumferential groove provided on the side surface of the index tube 16 and moves it upward.
is installed.

A stop piston 28 is provided within the index tube 16 to limit upward movement of the index tube 16, and the stop piston 28 is fixed to the upper portion of the piston tube 29. This piston tube 29 is detachably fixed to the housing flange 21 via a ring flange 31. The lower end of the index tube 16 is connected to the control rod 10 by sliding the piston tube 29 and the inner tube 22 in a watertight manner.
The drive piston 30 scrams the piston.

With the control rod drive device 11 configured as described above, the control rods 10 (the speed limiter provided at the bottom of the control rods is shown in the figure) used in boiling water reactors can be moved up and down. It is slid by. The control rod 10 and the control rod drive device 11 are connected by a detachable connector 12 provided on both sides.

The coupling 12 is composed of a coupling socket 13, a coupling spud 14 and a locking plug 15. The coupling socket 13 is a cylindrical body protruding from the center of the lower surface of the control rod 10, and has a groove cut in its inner wall in the circumferential direction. The coupling spud 14 is fixed to the tip of the index tube 16 located in the axial center of the control rod drive device 11, and fits into a groove provided in the circumferential direction of the coupling socket 13. It is a cylindrical body with a convex portion. Several slits are cut into this coupling spud 14 in the axial direction. The lock plug 15 is connected to the coupling socket 1.
After the coupling socket 13 and the coupling spud 14 are connected, it is pushed into the coupling spud 14 and the coupling socket 13 and the coupling spud 14 are connected. This is to ensure the connection of the two.

However, since the control rod 10 has a much shorter lifespan than the lifespan of the reactor itself, it is necessary to replace it with a new control rod. In addition, the control rod drive device 1
1 also requires maintenance and inspection or parts replacement to maintain its functionality. Replacement of the control rod 10 or maintenance and inspection of the control rod drive device 11 is performed by releasing the connector 12. This coupling 12 can be released by pulling up an uncoupling rod (not shown) provided in the index tube 16 or a locking plug 15.

[Problems with background technology]

If a malfunction should occur in the connector 12 having the above configuration, there is a possibility that the connection may not be released. For example, there may be a case where the coupling spud 14 and the lock plug 15 are stuck together, or a case where the coupling socket 13 and the coupling spud 14 are welded together.

When such a situation occurs, it becomes difficult to maintain and inspect the control rods 10 and the control rod drive device 11, and the control characteristics of the reactor deteriorate, making it difficult to maintain an appropriate output of the reactor. Furthermore, even if the restriction of the stop piston 28 is released, the guide cap 25 that slides and supports the index tube 16 will restrict the upward movement of the drive piston 30. Withdrawals are not possible. Furthermore, if the control rod 10 is forcibly pulled out from above, the control rod drive device 11 after being pulled out will become distorted due to the stress caused by the forceful pull out, and the parts inside the control rod drive device 11 that were forcibly pulled out will Since distortion occurred, there was a problem in reusing it.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and when the coupling of the coupling device becomes impossible to release, the present invention minimizes damage to the control rod and the control rod drive device, and quickly connects the control rod. The purpose is to obtain a method that can separate the control rod drive device.

[Summary of the invention]

In the present invention, a housing flange is provided at the lower end of the control rod housing, a piston tube is inserted into the control rod housing through a ring flange, and an index tube surrounds the outer periphery of the piston tube. In this method, the ring flange is removed and the lower part of the piston tube is controlled by the weight of the piston tube. After exposing the control rod to the outside of the housing, a sealing member is attached to the lower surface of the housing flange to seal between the housing flange and the piston tube, and then the lower part of the piston tube exposed to the outside of the control rod housing is cut. Next, the piston tube remaining in the control rod housing is pushed into the index tube with the pole of an electrical discharge tool having a docking member that connects the piston tube, and the electrode provided on the pole of the electrical discharge tool is discharged. The present invention provides a method for disconnecting a control rod from a nuclear reactor control rod drive device, comprising cutting the index tube from its inner surface.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. Note that the same parts as in FIG. 1 are given the same reference numerals, and the explanation of the structure will be omitted. Here, FIG. 2 shows a lower sectional view of the control rod drive device showing a state in which the piston tube is cut. In the figure, the procedure for disconnecting the connection according to the present invention is to first remove the ring flange 31 and pull the piston tube 29 out of the control rod housing 20. As shown in the figure, since the control rod drive device 11 is installed vertically, the piston tube 29 has a stop piston 28 installed at the top of the piston tube 29 and a stop piston 28 installed at the bottom of the index tube 16. It descends due to gravity until it abuts against the drive piston 30 that is located thereon. Since the stop piston 28 is provided to limit the upward movement of the index tube 16, unless the index tube 16 can be removed from inside the control rod housing 20, the stop piston 28 will also move inside the control rod housing 20. It cannot be taken outside.

Therefore, the piston tube 29 that has come out of the control rod housing 20 is cut along the line AA. The piston tube 29 may be cut by either a mechanical method or an electrical method. Note that when the piston tube 29 is cut, the control rod 10
The index tube 1 leaks from the joint with the index tube 1.
Since the reactor water accumulated between the piston tube 6 and the piston tube 29 will spout out, it is desirable to seal it with the seal member 35. This sealing member 35 may be formed by dividing a donut-shaped disk into two parts.

An embodiment of the present invention after the piston tube 29 has been cut will be described with reference to FIG. As shown in the figure, the remaining piston tube 29 is pushed up by the electrical discharge tool 37, and then the index tube 16 is cut. This electric discharge machining tool 37 includes a drive unit main body 38 configured to be attachable to the flange 21, a pole 39 vertically installed in the center of the drive unit main body 38, and a pole 39 provided above the pole 39. The electrode 40 rotates in the horizontal direction. Further, a docking member 41 connected to the piston tube 29 is provided at the upper end of the pole 39. A pole 39 supporting the electrode 40
is preferably a cylinder having the same outer diameter as the piston tube 29. Since the surface of the index tube 16 becomes a sliding part, it is hardened and requires a large cutting force when mechanically cutting. However, index tube 16
has a small inner diameter of about 9 cm, and furthermore, the distance between the cutting part and the flange surface on which the electric discharge machining tool 37 is attached is large, so it is difficult to provide a device with a large cutting force. In addition, installing a device with a small cutting force requires time to work inside the reactor, and there are also problems in reducing radiation exposure of workers. Therefore, as a cutting tool, it is desirable to have a simple mechanism that requires no cutting load and only operates the electrode, and to use electrical discharge machining that can use water from the reactor pressure vessel as machining fluid.

The docking member 41 of the electric discharge machining tool 37 configured as described above is installed at the cut end of the cut piston tube 29. Thereafter, the electric discharge machining tool 37 is pushed up to push the piston tube 29 into the index tube 16. Then, the electrical discharge tool 37 is fixed to the housing flange 21. At this time, the pole 39 of the electric discharge tool 37 needs to be long enough to pass through the drive piston 30 of the index tube 16 so that the electrode 40 directly faces the index tube 16. While the setting of the electric discharge machining tool 37 is completed, the index tube 16 is damaged by reactor water leaking from the joint with the control rod 10.
The inside is filled with water. Therefore, cutting work within the index tube 16 is an underwater work. When the setting of the electric discharge machining tool 37 is completed, a voltage is applied to the electrode 40 to cut the index tube 16 by electric discharge. Note that the index tube 16 has a notch for holding the control rod 10 in a fixed position, and if the cutting operation is performed at the position of this notch, the index tube 16 can be easily removed because the tube thickness is thinner by this notch. can be cut.

Once the index tube 16 is cut off, the control rod 10 and control rod drive device 11 can be completely separated. Thereafter, the control rods 10 are taken out from above the reactor pressure vessel, and the control rod drive device 11 is taken out from below for maintenance inspection and parts replacement.

As explained above, according to the method of the present invention, the connection with the control rod drive device can be quickly and reliably released. In addition, since the cutting waste is small, it is easier to discharge the cutting waste at the same time as the reactor water is discharged than with the mechanical cutting method. It is economical because only one part is damaged and the other parts can be used again. Furthermore, by using electric discharge machining tools, remote control becomes possible, reducing radiation exposure for workers. Automatic cutting is also possible.

〔Effect of the invention〕

According to the present invention, when the connection between the control rod and the control rod driving device cannot be released by a regular method, after cutting the piston tube, the index tube is cut from its inner surface using an electrical discharge tool, and the control rod and the control rod are separated. Since the connection with the drive device is released, damage to the control rod and the control rod drive device can be minimized, and furthermore, the control rod and the control rod drive device can be separated in a short time.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical sectional view showing the connection between a conventional control rod drive device and the lower part of the control rod, FIG. 2 is a bottom sectional view of the control rod drive device showing a state in which the piston tube is cut in the present invention, and FIG. 3 FIG. 2 is a bottom sectional view of the control rod drive device showing a state in which an index tube is cut in the present invention. 10... Control rod, 11... Control rod drive device, 16...
Index tube, 20... Control rod housing, 21... Housing flange, 29... Piston tube, 31... Ring flange, 35... Seal member, 37... Electric discharge tool, 39... Pole, 40...
Electrode, 41...Docking member.

Claims (1)

[Claims] 1. A housing flange is provided at the lower end of the control rod housing, a piston tube is inserted into the control rod housing through a ring flange, and an index tube is provided surrounding the outer periphery of the piston tube,
In this method of releasing a control rod and a control rod drive device in which a control rod is connected to an index tube via a coupling device, the ring flange is removed and the lower part of the piston tube is moved out of the control rod housing by the weight of the piston tube. After being exposed to
A seal member is attached to the lower surface of the housing flange to seal between the housing flange and the piston tube, and then the lower part of the piston tube exposed outside the control rod housing is cut off, and then the lower part of the piston tube that remains inside the control rod housing is cut off. The piston tube is pushed into the index tube by a pole of an electrical discharge tool having a docking member that connects the piston tube, and the electrode provided on the pole of the electrical discharge tool is discharged to cut the index tube from its inner surface. A method for disconnecting a nuclear reactor control rod drive device and a control rod, the method comprising: