JPS632074B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control rod drive mechanism (hereinafter referred to as CRD) that controls nuclear reactions in a nuclear reactor. This prevents the activated argon gas and sodium vapor inside the reactor from leaking into the upper part of the reactor, and allows the reactor to operate even when the bellows is damaged.Furthermore, during maintenance, the boundary between the inside and outside of the reactor is not destroyed. This invention relates to a CRD that allows the removal of the upper drive section and the replacement of the bellows backup seal device.

Shaft seals for sliding parts of CRD in fast reactors require low pressure in the reactor (~10Kg/cm ² G or less) and extremely strict allowable leakage rate (~1×10 ⁷ Acc/sec).
Below) The temperature of the shaft seal part is high (~550℃)
°C), the sliding distance and speed are relatively long (distance approximately 1000 mm, maximum extension speed ~5 m/sec), and methods such as lubrication are difficult (reaction with the inside of the furnace, radiation exposure, etc.). A welded bellows, which is made by welding a structural material (such as SUS316L or Inconel 718) with pole groove thickness (t = 0.1 to 0.4 mm) into a bellows shape (accordion shape), is used as the shaft seal.

Next, let us describe the configuration of the shaft seal of a conventional CRD.
As shown in Fig. 1, the CRD shaft seal is roughly divided into a guide tube 2a fixed to the reactor vessel 6a side, an extension tube 3a which is a movable part, and a bellows 4 which is a shaft seal.
It is composed of a. The extension tube 3a moves up and down to control the nuclear reaction and expands and contracts the bellows 4a. On the other hand, the gas pressure inside the bellows 4a is made higher than the pressure outside for the purpose of detecting leaks when the bellows 4a breaks, so the bellows 4a meandered and buckled due to the expansion and contraction movement (up and down movement of the control rod). The part is
They will come into contact with the inner surface of the extension tube 3a or the inner surface of the guide tube 2a, and will damage each other.

In particular, during the scram operation of the CRD, the sliding speed of the extension tube 3a increases to a maximum of about 5 m/s, so the wear and tear of the thin-walled bellows 4a and the welded parts of the same material increases significantly. Become.

Furthermore, not only is the material worn away due to meandering, but when "galling" or the like occurs due to surrounding environmental conditions, the extension tube 3a, which is a movable part, falls rapidly, but the extension of the bellows 4a cannot follow it. As a result, the bellows 4a, which is a thin-walled shaft seal, will undergo large local deformations, and there is a strong possibility that it will be damaged.
If the reactor is operated with the bellows 4a damaged in this way, the activated argon gas 7a, sodium 8a, and sodium vapor inside the reactor will be removed by the breathing action caused by the vertical movement of the CRD extension tube 3a. A large amount will be sucked into the upper drive unit. For this reason, a large amount of activated sodium adheres to the electrical components and sliding parts in the drive unit, causing deterioration and sticking.
The integrity of the CRD would be compromised and the reactor would have to be shut down. Furthermore, during maintenance of the upper drive section and the lower mechanism, the radiation level is high, which poses a problem of radiation exposure for workers, and work efficiency becomes extremely poor.

The present invention has been made in view of the above points, and the first object is to provide a second sealing device (bellows back-up) in addition to the bellows that forms the boundary between the inside and outside of the BRD reactor. The aim is to enable continued operation of the reactor without compromising the integrity of the CRD even if the CRD is damaged, and furthermore to reduce radiation exposure during maintenance and improve the safety of the reactor. A second object is to provide a CRD that can be safely maintained without destroying the boundaries inside and outside the reactor when replacing the sealing part and sliding part of the bellows backup seal device.

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the control rod drive mechanism according to the present invention will be described in detail with reference to the drawings.

The control rod drive mechanism has an upper drive part 1 and a lower mechanism 2 as shown in FIG. The book has been planted. Upper drive part 1
has an elongated cylindrical housing 4 that is housed in an elongated cylindrical drive guide tube 34 that extends from the upper cover 3 to the upper part of the core upper mechanism upper shell 30 and extends to a disc spring 35 provided at the upper end of the lower mechanism 2. The disc spring 35 may be of any type as long as it is elastic enough to uniformly transmit a static load from one end to the other end, and that can cushion the dynamic load and is highly reliable. A ring-shaped fixing ring 32 is attached to the core upper mechanism upper body 30 through bolts 33 in the outer top concave portion of the housing 4, and the outer top convex portion of the housing 4 and the inner top portion of the drive guide tube 34 are connected to each other. The recessed portion has a gap corresponding to the amount of displacement generated in the disc spring 35 via the housing 4 before and after tightening the bolt 33 to the core upper mechanism upper shell 30, and comes into contact with the bolt 33 after tightening.

On the other hand, a drive motor 5 is mounted at the top inside the housing 4.
is stored. The output shaft of the drive motor 5 is connected to a lead screw 7 supported by a ball bearing 6.
extends vertically downward, and its lower end is inserted into the finger support cylinder 8.

On the other hand, a screw nut 9 is screwed into the lead screw 7, and an electromagnet 21 is integrally attached to the screw nut 9. The electromagnet 21 is moved up and down by the rotation of the drive motor 5, and the up and down movement of the electromagnet 21 is caused by the engagement of the guide protrusion of the screw nut 9 with the guide groove on the inner circumferential wall of the housing 4. Guided without rotation.

The armature 22 is mounted on the upper end of the finger support cylinder 8, while the lower end of the finger support cylinder 8 is connected to the outer extension tube 12 via a latch mechanism 10.
and grips the inner extension tube 13.

A cylindrical latch cylinder 25 is provided on the outer periphery of the latch mechanism 10, and a transmitter 26 and a receiver 27 of a photoelectric limit switch are attached to the lower part of the latch cylinder 25 facing the housing 4. The photoelectric signal transmitted from the transmitter 26 passes through the coaxial hole 24 provided in the outer extension tube 12 and the inner extension tube 13 and is received by the receiver 27, thereby detecting the latched or unlatched position with the control rod 15. .

The lower mechanism 2 also has a guide tube 11 that is inserted into the upper cover 3 of the reactor vessel and hangs down from the upper cover into the reactor vessel, and includes an outer extension tube 12 and an inner extension tube 1.
3 is incorporated so as to be slidable in the vertical direction. A pair of grippers 14 are provided at the lower end of the outer extension tube 12.
is swingably supported, and the gripper 14
is adapted to fixedly support the control rod 15 inserted into the reactor core. Note that bellows 16 and 17 are interposed between the guide tube 11 and the outer extension tube 12 and between the extension tubes 12 and 13, respectively, to prevent radioactive gas or steam from leaking into the housing 4. are doing.

On the other hand, a bellows is fixedly inserted into the lower part of the disc spring 35 to maintain a sealing state with the inner surface of the guide tube 11, and is slidably inserted with the outer surface of the outer extension tube 12 to maintain a sealing state. The back up seal device 40 is pushed downward by the spring force of the disc spring 35. 3 to 5 show the detailed structure of the bellows backup seal device 40, and FIGS. 6 to 10 show a method for replacing the backup seal device 40, and replacement jigs A60 and B70. show.

The back up seal device 40 includes a seal box 41 that maintains a sealed state with the outer surface of the outer extension tube 12 and the inner surface of the guide tube 11, and an inner extension tube that maintains a sealed state with the inner surface of the outer extension tube 12 and the outer surface of the inner extension tube 13. There is a handling head 50, both of which are installed in a replaceable manner. first,
Inside the seal box 41 is an outer extension tube 1.
2 A seal cover 4 into which a sliding seal 42 that maintains a sliding seal with the outer surface is inserted and screwed.
It is fixed by 3. Further, a fixed seal 44 that maintains a sealed state with the inner surface of the guide tube 11 is incorporated on the outside of the seal box 41. A rotation prevention pin 45 is fixedly driven into the base of the upper flange of the seal box 41, and during operation, it is pressed by the spring force of the disc spring 35 and meshes with the structure at the bottom of the guide tube handling head 11a to prevent vibrations, etc. It prevents rotation due to Additionally, stepped keys 46 and 47 are integrally attached at intervals on the outside of the seal box 41 and on the inside of the guide tube 11 in the circumferential direction.
It serves as a guide when installing or removing it. Further, a second disc spring 48 is incorporated in the lower part of the seal box 41, and in the operating state when the upper drive unit 4 is attached, the upper disc spring 3
5 and is compressed by seal box 41. On the other hand, in the maintenance state in which the upper drive section 4 is removed, the spring force of the upper disc spring 35 is resolved as shown in FIGS. 6 and 8, so that the second
The disc spring 48 is adapted to push up the seal box 41.

Next, the inner surface of the outer extension tube 12 and the inner extension tube 13
The inner extension tube handling head 50, which maintains a sealing state with the outer surface, is attached to the upper part of the inner extension tube 13 and is removably screwed to the inner extension tube 13. A sliding seal 51 for sealing between the inner extension tube handling head 50 and the inner extension tube 13 and a fixed seal 52 for sealing the connection between the inner extension tube handling head 50 and the inner extension tube 13 are replaceably incorporated. A handling head 50 is removably screwed onto the top of the inner extension tube 13, and a lock bar 53 with a square cross section that is biased upward by a spring 54 is attached to the top of the inner extension tube.
is provided to be movable up and down, and is non-rotatably fitted into a hole formed in the lower part of the handling head 50. Therefore, when the push rod above the lock bar 53 is used to push down the lock bar 53 and the handling head is screwed onto the top of the inner extension tube, when the push rod is released, the tip of the lock bar is inserted into the handling head, causing vibration. The threaded part will not loosen due to

Next, the bellows backup seal device 40
The structure when replacing is explained. 6 to 8 show a replacement jig A60 for the seal box 41 of the bellows backup seal device 40. The replacement jig A60 is attached from the upper part of the drive section guide tube 34, and the tip end is cylindrical and has fingers 61 that further protrude inward. Further, the finger 61 engages with a groove on the upper part of the seal box 41 to transmit rotation and pulling force. Additionally, a handle 6 is provided at the top of the replacement jig A60.
2 is attached and has a structure that can be rotated and pulled out manually.

On the other hand, a replacement jig B70 for the inner extension tube handling head 50 of the bellows backup seal 40 has a structure shown in FIGS. 9 and 10, and is attached from the top of the drive section guide tube 34. The replacement jig B70 has a double structure, and a lock bar push rod 71 penetrates from the top to the top surface of the lock bar 53 at the lower end on the inside.
3 can be pushed into the lower part against the upward force of the spring 54. In addition, the replacement jig B
The tip of 70 is the inner extension tube handling head 50
Since its cross section is square, rotational force can be transmitted. Furthermore, a ball latch mechanism 72 is provided at the tip of the replacement jig B70.
is incorporated and engages with the groove at the tip of the inner extension tube handling head 50, so that it can also transmit upward pulling force. Incidentally, these transmission forces can be applied manually using the handle 73 and lever 74 attached to the upper end of the replacement jig B70.

Next, the operation of the control rod drive mechanism will be described.

During normal operation, the electromagnet 21 is maintained in an energized state during a shim operation to compensate for a decrease in reactor reactivity. As shown in FIG.
The vertical movement of the electromagnet 21 is converted into the vertical movement of the armature 22,
The signal is transmitted to the control rod 15 via the finger support cylinder 8, the latch finger 10, and the outer extension tube 12, and causes the control rod 15 to move up and down. The shim operation is performed in this manner.

Further, during scram, the electromagnet 21 is demagnetized. By demagnetizing the electromagnet 21, the armature 22 is separated from the electromagnet 21, whereby the finger support cylinder 8, the latch finger 10, both extension tubes 12, 13, and the control rod 15 are dropped together, and are dropped by the shock absorber at the lower end. The scram movement is performed while absorbing the impact force of the time.

On the other hand, during normal operation, the bellows 16 and 17, which are used to prevent radioactive argon gas and sodium inside the reactor from leaking into the upper part of the reactor, expand and contract in the axial direction by shim movement and scram movement. Repeat. While repeating this expansion and contraction movement,
In the event that the bellows 16 and 17 are damaged, activated argon gas and sodium in the furnace will pass between the two extension tubes 12 and 13 or inside the bellows due to the breathing action of the bellows 16 and 17. , will rise. However, the seal box 41 of the bellows back-up seal device 40 seals fixedly to the inner surface of the guide tube 11 and slidably seals to the outer surface of the outer extension tube 12, and the inner extension tube handling head 50 seals the outer extension tube 12 in a slidable manner. Since the inner surface of the pipe 12 is slidably sealed and the connection part with the inner extension pipe 13 is fixedly sealed, the atmosphere inside the bellows 16 and 17 and the atmosphere inside the upper drive section 1 are sealed. will be completely separated. Therefore, inside the bellows 16, 17 and both extension pipes 12, 1
Activated argon gas and sodium in the furnace that have risen between 3 do not rise above the bellows back up seal device 40, and the parts inside the upper drive section 1 deteriorate due to activation and the sodium It is possible to prevent the product from sticking due to this problem, and furthermore, it is possible to continue normal operation as it is. Next, during maintenance, as shown in Figure 6, the bellows 16, 17
Even if the back-up seal device 4 is damaged,
0, it is possible to easily remove only the upper drive section 1, which also reduces radiation exposure.
Furthermore, if the sliding seals 42, 51 of the back-up seal device 40 themselves need to be replaced due to wear or the like, the upper drive section 1 is first removed as shown in FIG. By removing the upper drive unit 1, the seal box 41 of the backup seal device 40 releases the pressing force of the upper disc spring 35, and at the same time, the compressed lower disc spring 48 expands. pushed upwards. In this state, as shown in FIG. 8, the key 46 outside the seal box 41 and the key 4 inside the guide tube 11 are connected.
Since the pin 45 at the base of the upper flange of the seal box 41 comes out of the groove of the guide tube handling head 11a at the same time that the stepped portion 7 comes into contact, the seal box 41 can only rotate in one direction. Next, attach the replacement jig A60 from the top of the drive section guide tube 34, and align the two claws 61 attached to the tip of the replacement jig A60 with the grooves provided on the top of the seal box 41 to form a key shape. lower it to the groove. When the replacement jig A60 is rotated in this state, the seal box 41 also rotates at the same time, and the key 46 on the outside of the seal box stops at the position where it hits the key on the inside of the guide tube. (This is shown by the imaginary line in Figure 8.)
Next, by pulling up the replacement jig A60, the claw 61 will catch on the upper part of the key-shaped groove, and the seal box 41 will also be pulled up. Therefore, the key 46 of the seal box 41 passes between the keys of the guide tube 11 without interference, and the seal box 41
can be easily removed from the guide tube 11.

After replacing the sliding seal 42, the seal box 41 can be assembled by performing the above-mentioned operation in reverse.

On the other hand, the inner extension tube handling head 50
When it becomes necessary to replace the sliding seal 51, the upper drive section 1 is first removed in the same way as the seal box 41 removal method described above. Next, as shown in FIG. 9, attach the replacement jig B70 to the top of the drive section guide tube
Install. When the replacement jig B70 is inserted from above, the box portion with a square cross section at the tip is coupled to the top of the inner extension tube handling head 50, and at the same time, the ball latch mechanism 72 incorporated in the tip of the replacement jig B70 is inserted. It engages with a groove on the top of the inner extension tube handling head 50. Next, when the lock bar push rod 71 incorporated in the replacement jig B70 is pushed downward, the tip of the lock bar push rod 71 reaches the top of the lock bar 53. Furthermore, the lock bar push rod 71
When pushed in, the lock bar 53 is lowered against the lower spring 54, and is removed from the connection between the inner extension tube handling head 50 and the inner extension tube 13, releasing the screw from rotating. When the handle 73 on the top of the replacement jig B70 is rotated in this state, the rotation is transmitted from the tip of the replacement jig B70 to the inner extension tube handling head 50, and the inner extension tube handling head 50 and the inner extension tube 13 are rotated. The screw connection part of will come off. Further, by pulling up the replacement jig B70, the inner extension tube handling head 50 is completely separated from the inside of the outer extension tube 12.

Incidentally, to assemble the sliding seal 51 of the inner extension tube handling head 50 after replacement, it is sufficient to perform the above-mentioned operation in reverse.

As explained above, according to the present invention, the outer extension tube is slidably sealed at the upper part of the lower mechanism, and the shim operation and scram operation during reactor operation can be performed reliably, and furthermore, it is possible to easily perform the shim operation and scram operation. By providing a replaceable bellows backup seal device,
Even in the unlikely event that the bellows is damaged, this prevents the internal parts of the upper drive section from deteriorating or sticking due to the rise of radioactive argo gas and sodium in the reactor, increasing the integrity of the control rod drive mechanism and allowing the reactor to continue operating. do. Furthermore, even if the bellows is damaged during maintenance, the upper drive section can be easily removed without damaging the boundaries inside and outside the reactor.
When replacing the bellows backup seal device itself, there is no need to pull out the lower mechanism, and by using a replacement jig, it can be easily replaced by simply removing the upper drive section.

Therefore, it is possible to reduce the working time during maintenance work, reduce radiation exposure, and improve the safety and operation rate of the nuclear power plant.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a conventional control rod drive mechanism, FIG. 2 is a longitudinal sectional view showing an embodiment of the control rod drive mechanism according to the present invention, and FIG. 3 is a longitudinal sectional view showing main parts of the present invention. 4 is a sectional view taken in the direction of the arrow in FIG. 3, and FIG. 5 is a sectional view taken in the circumferential direction of FIG.
FIG. 6 is a sectional view showing another example of the present invention, FIG. 7 is a sectional view taken in the direction of the - arrow in FIG. 6, FIG. 8 is a sectional view showing an example of the operation of FIG. FIG. 10 is a cross-sectional view taken along the - arrow in FIG. 9. DESCRIPTION OF SYMBOLS 1... Upper drive part, 2... Lower mechanism, 40... Bellows backup seal device, 41... Seal box, 50... Inner extension pipe handling head, 60
...Replacement jig A, 70...Replacement jig B.

Claims (1)

[Claims] 1. A drive unit that moves the control rods up and down, an extension tube connected to the control rods, a guide tube installed on the outer periphery of the extension tube, and a bellows that forms a boundary between the reactor atmosphere and the upper part of the reactor. In the control rod drive mechanism, the extension tube is composed of an outer extension tube having a gripper at its tip, and an inner extension tube inserted through the outer extension tube so as to be vertically movable, and the guide tube and the outer extension tube are connected to each other. A seal box that slidably seals these tubes and can be removed from above is provided between the tubes, and a seal box that slides between the inner and outer extension tubes is provided above the inner extension tube. A control rod drive mechanism characterized in that a handling head that seals freely is provided in a manner that can be freely engaged and detached.