JPH08262172A - Control rod driving mechanism and shaft seal changing device - Google Patents

Abstract

PURPOSE: To provide a shaft seal changing device for control rod driving mechanism which can easily change gland packings by substituting for the driving section of the control rod driving mechanism and a control rod driving mechanism provided with a sliding type feeding mechanism. CONSTITUTION: A shaft seal changing device for control rod driving mechanism is composed of a long outer pipe 25 which substitutes for the driving section of a control rod driving mechanism provided to the end plate 5 at the top of an atomic reactor and has an changing port 32 in its upper section, long fixed shaft 28 which has the same diameter as the extension pipe 9 of the control rod driving mechanism has at its central part and is provided with a connecting section which is connected with and disconnected from the upper end of the extension pipe 9, and the rack rail 30, pinion 39, and elevating/ lowering motor 40 of an elevating/lowering mechanism equipped with a seal changing mechanism which is used for changing the gland packing housing 18 of the control rod driving mechanism under the guidance of the fixed shaft 28 and composed of a bolt tightening motor 33 and control shaft 35.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control rod drive mechanism and a shaft seal exchanging device for easily exchanging a shaft seal of a control rod operating shaft in a control rod drive mechanism for a fast reactor.

[0002]

2. Description of the Related Art Conventionally, in fast breeder reactors that use liquid sodium as a coolant, the output of nuclear fuel in the core is controlled, and when an abnormal situation occurs in the reactor, it absorbs neutrons in the reactor. It is well known that the operation of stopping the nuclear reaction is performed by using the control rod made of a neutron absorber for these operations.

This control rod has a shape in which the upper and lower ends of a plurality of absorption pins implanted in the trumpet tube are supported by a lattice plate, and a gripping portion is formed on the upper part of the trumpet tube as a gripping mechanism. The nuclear reaction in the nuclear reactor is controlled by changing the absorption amount of neutrons by inserting or extracting the control rod into the core region.

When an abnormal situation occurs in the core, a control rod drive mechanism which is connected to the control rod to operate, or a gravity drop causes the control rod to be rapidly inserted into the core to stop the operation of the reactor. Let In addition, when refueling the reactor, it is necessary to separate the control rod drive mechanism from the control rod with the control rod completely inserted in the core region, and move the upper core mechanism in which this control rod drive mechanism is installed. There is.

In a conventional fast reactor, a rotating plug that closes the upper part of the core is provided with important equipment for reactor operation, such as a fuel exchanger and a control rod drive mechanism. In order to change the position of the refueling machine, the rotary plug has a double rotation structure. Further, in order to prevent heat in the nuclear reactor from being transferred to the main equipment installed above the rotary plug, a complicated heat insulating mechanism is attached to the core side of the rotary plug.

As described above, since the structure of the rotary plug is complicated, the physical quantity becomes large and the construction cost of the fast breeder reactor becomes high. I lost it, and made the upper part of the reactor a mirror plate,
It was devised to directly install the control rod drive mechanism and the refueling machine on this end plate.

As shown in the longitudinal sectional view of FIG. 8, this control rod drive mechanism comprises a control rod drive mechanism 1 and a concrete shield 2.
The long tubular upper guide tube 4 is inserted into the outer cylinder 3 provided in the through hole 2a of the above, and the upper portion of the upper guide tube 4 is joined to the end plate 5. In addition, a cylindrical housing 6 is connected to the upper part, and a motor 7 of a driving part is mounted on the top part.
On the other hand, the lower end of the upper guide tube 4 is immersed in the coolant in the reactor vessel, that is, liquid sodium 8.

An extension tube 9 which is a drive shaft is inserted in the center of the upper guide tube 4, and the extension tube 9 is connected to the upper portion of the extension tube 9 to connect and disconnect the drive section. A mechanism 10 is installed, and a nut 11 is fixed on the connecting mechanism 10, and the nut 11 is screwed into a screw shaft 12 which is rotated by the rotation of the motor 7. Also,
A gripping mechanism 13 is provided at the lower end of the extension pipe 9,
It is mechanically connected to a handling head 17 installed above the control rod 16 in a lower guide tube 15 planted in 14.

Therefore, when the motor 7 of the drive unit arranged at the top is rotated, the screw shaft 12 moves up and down together with the nut 11, the extension pipe 9 and the control rod 16. Further, when the reactor is to be stopped urgently, the control rod 16 is cut off by the gripping mechanism 13 to drop the control rod 16 into the core 14 by its own weight and stop the nuclear reaction in the nuclear reactor.

Further, as shown in the enlarged cross-sectional view of the gland packing mounting portion of FIG. 9, the extension tube 9 is compressed in the gland packing housing 18 which is a shaft seal mechanism provided around the extension tube 9 with a stopper plate 18a and a tightening screw 18b. The provided gland packing 19 separates the reactor sodium atmosphere from the upper mechanism of the control rod drive mechanism 1. When the gland packing 19 is replaced, the maintenance seal 20 arranged in advance under the gland packing 19 isolates it from the reactor sodium atmosphere under the gland packing housing 18.

The maintenance seal 20 has a structure that can be expanded and contracted freely, and high-pressure argon gas is injected into the maintenance seal 20 from the argon gas supply source 22 through the stop valve 21 only when the gland packing 19 is replaced, and the maintenance seal 20 is maintained. 20 is expanded and pressure-bonded to the extension tube 9 to isolate it from the sodium atmosphere. Further, a scraper 23 is attached to the lower part of the maintenance seal 20 so that sodium vapor or the like attached to the extension pipe 9 does not move to the gland packing housing 18, and removes the sodium attached to the periphery of the extension pipe 9. ing.

[0012]

Considering the simplification of the structure of the fast reactor by removing the rotary plug (not shown) at the upper part of the nuclear reactor and mounting the control rod drive mechanism 1 and the like on the end plate 5 as described above. Then, the radiation shielding mechanism of the heat insulating structure which is conventionally installed in the rotary plug causes the concrete shielding 2 on the upper part of the driving part to bear the load, so that the motor 7 etc. of the driving part of the control rod driving mechanism 1 becomes a high temperature atmosphere. Will be exposed.

Further, the gland packing 19 which is the shaft seal of the extension tube 9 is also installed under a high temperature and high radiation environment, and the surrounding space is narrow on it, so that the worker cannot enter. When mounting the gland packing 19, it is necessary to adjust the frictional resistance corresponding to the sealing effect between the sealing material and the extension tube 9,
Therefore, replacement of the gland packing 19 requires a great deal of skill, and there is a problem in that the operator is heavily burdened.

Further, at the tip of the control rod drive mechanism 1, the control rod 16 is detachably held by the gripping mechanism 13. The gripping mechanism 13 supplies power or a signal for attaching and detaching the control rod 16. A power supply line for the control rod drive mechanism 1 is passed through. However, this power line is
A spiral electric wire is laid so that it can be freely expanded and contracted without hindering insertion and withdrawal of the control rod drive mechanism because it is placed in a high temperature and high radiation environment like the gland packing 19. We perform regular maintenance to obtain high reliability.

The object of the present invention is to provide a shaft seal exchanging device for a control rod drive mechanism, which can replace the drive portion of the control rod drive mechanism to easily replace the gland packing, and a sliding type power feeding mechanism. To provide a control rod drive mechanism.

[0016]

In order to solve the above-mentioned object, a shaft seal exchanging device for a control rod drive mechanism according to claim 1,
A control rod installed on the end plate of the upper part of the reactor and held by the end of the extension pipe connected to the drive part is used to pull out and insert the core into the core during the reactor operation, and to insert it into the core during scram. In a shaft seal exchanging device for a control rod drive mechanism using a gland packing as a seal, an outer cylinder provided with an exchange port at an upper portion to be replaceable with the control rod drive mechanism, and the extension pipe provided at the center thereof. A fixed shaft having a long diameter having the same diameter as the upper end of the extension pipe and a connecting portion which can be easily separated from the upper end of the extension pipe, and the mounting and removal of the shaft seal mechanism of the control rod drive mechanism guided by the fixed shaft. And a lifting / lowering mechanism having a seal exchanging mechanism.

According to a second aspect of the present invention, there is provided a shaft seal exchanging device for a control rod drive mechanism, wherein the elevating mechanism is provided with a shaft seal mounting mechanism for attaching and detaching the shaft seal mechanism of the control rod drive mechanism. The shaft seal exchanging device for a control rod drive mechanism according to a third aspect of the present invention is characterized in that the lifting mechanism is provided with a holding mechanism for the shaft seal mechanism of the control rod drive mechanism.

According to a fourth aspect of the present invention, there is provided a shaft seal exchanging device for a control rod drive mechanism, wherein the elevating mechanism is provided with a load detecting mechanism for measuring a friction resistance in a shaft seal of the control rod drive mechanism. The shaft seal exchanging device for a control rod drive mechanism according to claim 5, wherein a power supply rail and a power supply mechanism for collecting current are provided for the lifting mechanism, the gripping mechanism and the shaft seal mounting mechanism installed therein. To do.

A control rod drive mechanism according to a sixth aspect of the present invention includes an extension pipe having an upper end coupled to a drive unit for driving up and down and a lower end provided with a gripping mechanism for connecting and holding the control rod. It is a control rod drive mechanism that pulls up and down the control rod to insert and remove the control rod in the core, and inserts the control rod into the core during scrum. It is characterized by

[0020]

According to the invention described in claim 1, the drive portion of the control rod drive mechanism is removed, and a shaft seal exchanging device is attached instead,
The shaft exchange mechanism of the control rod drive mechanism is taken out by the seal exchange mechanism provided in the lifting mechanism. The shaft seal mechanism in which the gland packing has been exchanged is installed in the control rod drive mechanism again by the elevating mechanism, and then the shaft seal exchange device and the drive unit of the control rod drive mechanism are exchanged to complete the seal exchange.

According to a second aspect of the present invention, the control rod is driven by driving the shaft seal mounting mechanism in a state where the elevating mechanism of the shaft seal exchanging device is lowered into the control rod drive mechanism and is in contact with the shaft seal mechanism. The shaft seal mechanism can be attached and detached from the mechanism.
According to a third aspect of the present invention, the shaft seal mechanism of the control rod drive mechanism that is attached and detached by the shaft seal mounting mechanism of the elevating mechanism is held or released by the elevating mechanism by the holding mechanism.

According to a fourth aspect of the present invention, the shaft seal mechanism in which the gland packing is replaced is fitted on the fixed shaft of the shaft seal exchanging device and then moved up and down by the elevating mechanism, and the friction resistance at this time is set in the load detection mechanism. By appropriately detecting the friction resistance and adjusting the friction resistance appropriately, a proper sealing effect in the control rod drive mechanism can be obtained.

According to the fifth aspect of the present invention, since the power supply and the signal are supplied to the lifting mechanism of the shaft seal exchanging device by the sliding type power feeding mechanism, there is no entanglement or disconnection of the electric wire, and the maintenance is easy. . In the invention according to claim 6, since the power supply and the signal are supplied to the control rod gripping mechanism of the control rod drive mechanism and the like by the sliding type power feeding mechanism, there is no entanglement or disconnection of the electric wire, maintenance is easy and reliability is high. high.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those of the above-described conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in the longitudinal sectional view of FIG. 1, the shaft seal exchanging device 24 is inserted by replacing the drive unit of the control rod drive mechanism 1 extracted from the outer cylinder 3 provided in the through hole 2a of the concrete shield 2 of the nuclear reactor. A support shaft 27 is installed on a long cylinder 25 and a lid 26 on the upper end.

Further, a long fixed shaft 28 having the same diameter as the extension pipe 9 which is a drive shaft for operating the control rod coupled with the support shaft 27, and a gland which is the shaft seal mechanism on the fixed shaft 28. Seal replacement mechanism 29 for replacing the packing housing 18
In addition, a rack rail 30 and a power supply rail 31 are laid on the inner surface of the elongated cylinder 25, and an exchange port 32 is opened at the upper part.

The seal exchange mechanism 29, as shown in the enlarged cross-sectional view of the main part of FIG. 2, holds a bolt tightening motor 33, a gear 34, an operating shaft 35, which is a shaft seal mounting mechanism, and a gland packing housing 18. A load cell 38, which is a load detection mechanism that measures the frictional resistance between the electromagnet 36, which is the mechanism, the armature 37, and the gland packing 19, and the fixed shaft 28.
Is provided with a coupling portion.

An elevating mechanism composed of a pinion 39 and an elevating motor 40 meshing with a rack rail 30 provided on the inner surface of the elongated cylinder 25, and a current collector contacting the power feeding rail 31.
It is composed of a sliding type power feeding mechanism consisting of 41. In addition,
As for the current collector 41, as shown in the cross-sectional view of FIG. 3, a plurality of contacts 41a that come into contact with the respective conductive wires 31a of the power supply rail 31 provided on the inner surface of the elongated cylinder 25 and are electrically connected to each other. It is composed of a spring 41b and a terminal 41c which are electrically connected to each other.

Further, a current collector 41 of this sliding type power feeding mechanism is provided.
Is also applied to the control rod drive mechanism 1, and as shown in the longitudinal sectional view of FIG. 7, the nut 11 that contacts the power supply rail 31 laid on the inner surface of the upper guide tube 4 and is screwed into the screw shaft 12 It is configured to move up and down with the movement of the electric power source to supply electric power to the gripping mechanism 13 and to transmit signals. The support shaft 27, the fixed shaft 28, and the extension tube 9 provided on the lid 26 on the top of the elongated cylinder 25 are easily connected to each other as shown in the enlarged vertical sectional view of FIG.

Next, the operation of the above configuration will be described. In exchanging the gland packing 19 attached to the extension pipe 9 of the control rod drive mechanism 1, first, as shown in the vertical cross-sectional view of FIG. 5, after removing the drive portion above the control rod drive mechanism 1, The stop valve 21 is opened on the maintenance seal 20, and high-pressure argon gas is sent from the argon gas supply source 22. As a result, the maintenance seal 20 expands and comes into close contact with the extension pipe 9 to seal between the gland packing housing 18 and the extension pipe 9.

Next, as shown in FIG. 1, a shaft seal exchanging device
Install 24. The installation part of this shaft seal changing device 24 is
The same size as the drive portion of the control rod drive mechanism 1 is formed, and the long length of the shaft seal exchanging device 24 is attached to the outer cylinder 3 provided in the through hole 2a of the concrete shield 2 as in the case of installing the control rod drive mechanism 1. Insert the cylinder 25. Further, as shown in FIG. 4, the fixed shaft 28 has its lower end fitted to the upper end of the extension tube 9, and then the lower end of the support shaft 27 having the seal exchange mechanism 29 mounted on the upper end of the fixed shaft 28 to fix the lid 26. .

Next, the lifting / lowering motor 40 of the lifting / lowering mechanism in the seal exchanging mechanism 29 shown in FIG. 2 is operated in the descending direction to lower the seal exchanging mechanism 29 along the rack rail 30 so as to contact the gland packing housing 18. Let After that, when the electromagnet 36 is excited and the gland packing housing 18 is adsorbed and held through the armature 37, the state shown in FIG. 1 is obtained.

At this time, the operation shaft 35 of the shaft seal mounting mechanism is
Hounding fixing screw for gland packing housing 18
Since it is fitted to 42, when the bolt tightening motor 33 is rotated in the loosening direction, the honing fixing screw 42 is loosened by the operating shaft 35 via the gear 34, and it is pulled out from the screw hole 43 and the gland packing housing 18 is separated. . After that, by driving the lifting motor 40 of the lifting mechanism in the rising direction,
The gland packing housing 18 is guided by the fixed shaft 28 together with the seal exchange mechanism 29, and the pinion 39 and the rack rail are
Raises upon engagement with 30.

The gland packing housing 18 to which the gland packing 19 is attached is pulled up to the exchange port 32, the electromagnet 36 of the seal exchanging mechanism 29 is released, and after separating from the seal exchanging mechanism 29, the lid 26 is removed. Support shaft 27 fixed shaft
By removing it from 28, the state shown in the vertical sectional view of FIG. 6 is obtained. This makes the gland packing housing
18 can be taken out from the exchange port 32, so gland packing
The replacement of 19 is easily performed by loosening the tightening screw 18b and removing the stopper plate 18a.

In each drawing, the rack rail 30 is arranged on the left inside of the elongated cylinder 25 for convenience of description.
Replace the gland packing housing 18
It is installed inside the front of 25 or inside the right. About gland packing housing 18 New gland packing
The reattachment of the gland packing housing 18 to the extension tube 9 after the replacement with the 19 is performed by a procedure reverse to the above-described removal from the extension tube 9.

The sealing effect of the gland packing 19 with respect to the extension pipe 9 must be adjusted appropriately by adjusting the tightening force applied to the gland packing 19, but this adjustment is performed with the tightening screw 18b and the clasp 18a. This is done by compressing 19. At this time, the friction resistance generated between the gland packing housing 18 and the extension tube 9 is measured by the load cell 38 of the load detection mechanism, and the gland packing housing 18 is moved up and down by the elevating motor 40 to be adjusted easily. A proper sealing effect can be obtained.

The gland packing housing 18 is installed in the reverse order of the above-mentioned removal. That is, after the gland packing housing 18 is fitted to the fixed shaft 28 and is connected to the seal exchanging mechanism 29 to be in the state of FIG. 6, the support shaft 27 together with the lid 26 is fitted to the upper end of the fixed shaft 28. The elevating motor 40 of the seal exchanging mechanism 29 is operated in the descending direction to bring the seal exchanging mechanism 29 into the state shown in FIG.

Further, in order to reattach the gland packing housing 18 to the extension pipe 9, after fitting the operation shaft 35 of the shaft seal mounting mechanism to the honing fixing screw 42 of the gland packing housing 18, the bolt tightening motor 33 is attached. The gland packing housing 18 is fixed by rotating in the tightening direction and tightening the honing fixing screw 42 in the screw hole 43 by the operating shaft 35 via the gear 34.

After this, the electromagnet 36 is released, the seal exchanging mechanism 29 and the gland packing housing 18 are separated, and then the elevating motor 40 of the elevating mechanism is driven in the ascending direction to move the seal exchanging mechanism 29 along the rack rail 30. And pull it up above the long cylinder 25. Further, the shaft seal exchanging device 24 is pulled out from the outer cylinder 3 provided in the through hole 2a of the concrete shield 2 into the state shown in FIG.
The control rod drive mechanism 1 shown in FIG. 8 is assembled by mounting the upper drive unit.

The power supply and signal supply to the lifting motor 40, the bolt tightening motor 33, the electromagnet 36 and the load cell 38 of the shaft seal exchanging device 24 is performed by the power supply mechanism shown in FIG.
Further, the gripping mechanism 13 for the control rod 16 in the control rod drive mechanism 1
The power supply and signals for the same are also configured by a power supply mechanism as shown in FIG.

The contactor 41a of the current collector 41 of this power feeding mechanism is
Each of the power supply rails is always laid on the inner surface of the long cylinder 25.
Can move freely while touching 31. Further, the contact 41a is provided with a spring 41b that absorbs impact to prevent wear, and the spring 41b is connected to the terminal 41c.
Ceramics, which is an insulating material with excellent heat resistance, is used as the surrounding insulating material.

Regarding the power supply mechanism of the control rod drive mechanism 1, as shown in FIG. 7, when the control rod drive mechanism 1 is operated, power is supplied to the gripping mechanism 13 provided at the tip of the screw shaft 12 and the like. Transmission is performed via a movable collector 41 while contacting along a long power supply rail 31 laid on the inner surface of the tube 4.

Therefore, even in the case of the control rod drive mechanism 1 and also in the shaft seal exchanging device 24, the spring 41b is always in contact with a constant pressure for a long distance, so that the power feeding is highly reliable. Furthermore, since no electric wire is used, problems such as slack in the electric wire, disconnection, and entanglement with the screw shaft 12 do not occur. The maintenance is performed only by inspecting the contact state and wear of the current collector 41 and replacing the contact 41a, which does not require the conventional inspection and entire replacement of the electric wire, so that the maintenance is easy.

[0043]

As described above, according to the present invention, it is possible to easily replace the gland packing of the control rod drive mechanism which is arranged in a narrow space with a high temperature and high radiation atmosphere, and at the same time, to move the gland packing. By supplying power to the parts by the sliding type power supply mechanism, the structure is simplified and reliability and maintainability are improved.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a control rod drive mechanism equipped with a shaft seal exchanging device according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a main part of a seal replacement mechanism according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a sliding type power feeding mechanism according to an embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view showing the connection of a fixed shaft according to an embodiment of the present invention.

FIG. 5 is a vertical cross-sectional view of a control rod drive mechanism with a drive unit removed according to an embodiment of the present invention.

FIG. 6 is a vertical cross-sectional view of a control rod drive mechanism during seal replacement according to an embodiment of the present invention.

FIG. 7 is a vertical cross-sectional view of a control rod drive mechanism showing a power supply mechanism of an embodiment according to the present invention.

FIG. 8 is a vertical sectional view of a control rod drive mechanism installed on an end plate.

FIG. 9 is an enlarged vertical sectional view of a gland packing installation portion.

[Explanation of symbols]

1 ... Control rod drive mechanism, 2 ... Concrete shield, 2a ...
Through holes, 3 ... Outer cylinder, 4 ... Upper guide tube, 5 ... End plate, 6 ... Housing, 7 ... Motor, 8 ... Liquid sodium, 9 ... Extension tube, 10 ... Connection mechanism, 11 ... Nut, 12 ... Screw shaft, 13
... gripping mechanism, 14 ... core, 15 ... lower guide tube, 16 ... control rod,
17 ... Handling head, 18 ... Gland packing hounding, 18a ... Clasp, 18b ... Tightening screw, 19 ... Gland packing, 20 ... Maintenance seal, 21 ... Stop valve, 22
... Argon gas supply source, 24 ... Shaft seal exchange device, 25 ... Long cylinder, 26 ... Lid, 27 ... Support shaft, 28 ... Fixed shaft, 29 ... Seal exchange mechanism, 30 ... Rack rail, 31 ... Feed rail, 31a …
Conductive wire, 32 ... Exchange opening, 33 ... Bolt tightening motor, 34 ... Gear, 35 ... Operating shaft, 36 ... Electromagnet, 37 ... Armchair, 38 ...
Load cell, 39 ... Pinion, 40 ... Lifting motor, 41 ... Current collector, 41a ... Contact, 41b ... Spring, 41c ... Terminal, 42 ... Hounsing fixing screw, 43 ... Screw hole.

Claims (6)

[Claims] 1. A control rod, which is installed on an end plate of an upper part of a nuclear reactor and gripped by a tip of an extension pipe connected to a drive unit, is pulled out and inserted into a core during operation of the reactor and is inserted into the core during scram. In a shaft seal exchanging device for a control rod drive mechanism, which uses a gland packing for the shaft seal of the extension pipe, an outer cylinder provided with an exchange port at the top to be replaceable with the control rod drive mechanism, and arranged in the center thereof. And a fixed shaft having a long diameter having the same diameter as that of the extension pipe and a lower end having a connecting portion which is easily coupled and separated from the upper end of the extension pipe, and a shaft seal of the control rod drive mechanism guided by the fixed shaft. A shaft seal exchanging device for a control rod drive mechanism, comprising an elevating mechanism having a seal exchanging mechanism for mounting and removing the mechanism. 2. The shaft seal exchanging device for a control rod drive mechanism according to claim 1, wherein the elevating mechanism is provided with a shaft seal mounting mechanism for attaching and detaching the shaft seal mechanism of the control rod drive mechanism. 3. The lifting mechanism is provided with a holding mechanism for a shaft seal mechanism of a control rod drive mechanism.
A shaft seal exchanging device for the control rod drive mechanism described. 4. The shaft seal exchanging device for a control rod drive mechanism according to claim 1, wherein the elevating mechanism is provided with a load detection mechanism for measuring a friction resistance in a shaft seal of the control rod drive mechanism. 5. The control rod drive mechanism according to claim 1, further comprising a power feed mechanism including a power feed rail and a contact for the lifting mechanism, the gripping mechanism and the shaft seal mounting mechanism installed therein. Shaft seal replacement device. 6. The inside of the reactor core is controlled by moving the extension pipe up and down during the operation of the reactor by having an extension pipe at the upper end which is connected to a drive unit for driving up and down and at the lower end is provided a gripping mechanism for connecting and holding control rods. A control rod drive mechanism for pulling out and inserting the rod and inserting the control rod into the core at the time of scram. The control rod drive mechanism is characterized in that a power feed rail and a power feed mechanism by current collector are provided for the gripping mechanism and the like. .