JPS63204196A - Control-rod drive mechanism - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a control rod drive mechanism suitable for a boiling water nuclear reactor (hereinafter referred to as BWR), and in particular, when operating a shim, the motor This invention relates to a control rod drive mechanism that inserts and withdraws control rods from below the core of a nuclear reactor.

(Prior Art) Generally, a BWR is constructed as shown in FIG. 7, and a reactor core 2 is housed in a reactor J-force vessel 1 immersed in reactor water.

A plurality of fuel assemblies (not shown) are loaded in the reactor core 2, and a plurality of control rods 3, each having a cross-shaped cross section, are placed below the reactor core 2 in required gaps between these fuel assemblies. inserted or removed.

Each control rod 3 has a control rod drive mechanism (hereinafter referred to as CRD).
4 are respectively driven to insert and withdraw from the reactor core 2, and by appropriately adjusting the degree of insertion, the nuclear reactor is discharged.

Conventionally, this type of CRD 4 has a control rod drive mechanism housing (hereinafter referred to as CRD housing) 5 vertically penetrating through the bottom 1a of the reactor pressure vessel 1, and installed vertically in the CRD housing 5. is reactor pressure vessel 1
It is filled with reactor water from

As shown in FIG.
The -C control rod 3 and the hollow piston 6 are integrally connected by a connecting member provided at the top of the -C control rod 3 and the hollow piston 6.

CR04 is a relatively slow insertion/extraction movement fl (shim operation) of the control rod 3 that is performed to adjust and maintain the reactor output at a predetermined state during normal times, and a control rod 3 that is performed to make an emergency shutdown of the reactor in an emergency. It has the function of performing rapid insertion (scrum operation). --3 Generally, the shim operation is performed by motor drive, and the scram operation is performed by hydraulic drive.

That is, during shim operation, the motor 7 is driven and its rotational motion is transmitted to the hollow ball screw shaft 9 via the drive shaft 8, and the ball screw nut screwed onto the ball screw shaft 9 so as to be movable in the axial direction. 10 and the hollow piston 6 placed on the ball screw put 10 are moved up and down. As a result, the control rod 3 supported and connected to the hollow piston 6 is inserted into or withdrawn from the reactor core 2.

On the other hand, during scram operation, high-pressure scram water flows from the water pressure control unit (not shown) to () to (CU) via the insertion pipe 11, and through the insertion flow path roughly formed in the outer peripheral flange 12 to the CRD housing. High pressure water is injected into the reactor core 5, and the high pressure water pressurizes the hollow piston 6 and pushes it upward, thereby inserting the control rod 3 into the reactor core 2 at high speed.

When the control rod 3 is shimmed, the lower ends of the left and right pair of latch fingers 13a and 13b provided at the lower end of the hollow piston 6 are connected to the left and right pawl storage portions 1, as shown in FIG.
4a and 14b.

These pair of latch fingers 13a, 13b are always urged outward by springs 15a, 15b as shown in FIG. 10, and their tips are shown in FIG. It is closed by being sandwiched between the pair of claw storage parts 14a and 14b.

Therefore, the lower ends of the hollow screws 1 to 6 are simply placed on the ball screw nut 10 in the center hole 16a of the ring-shaped latch guide 16, so that the control rod 3
During the shim operation, the ball screw shaft 9 rotates around the shaft due to the rotational drive of the motor 7, and when the ball screw nut 10 and the latch guide 16 rise, the hollow piston 6 is pushed up by the ball screw nut 10, and the control rod 3
is inserted into the reactor core 2.

On the other hand, ball screw neck h 10 Onibi latch guide 16
When the control rod 3 descends, the hollow piston 6 descends due to its own weight with the pair of latch fingers 13a and 13b fitted into the pair of pawl housings 14a and 14b, and the control rod 3
is pulled out from the reactor core 2.

During the scram operation of the control rod 3, the hollow piston 6 to which high-pressure water is applied rapidly oscillates.However, the ball screw nut 10 and the latch guide 16 remain stationary, so that they rise rapidly. The latch finger 13a of the hollow piston 6.

13b is pulled upward from the claw storage parts 14a, 14b of the latch guide 16 and released, and the pair of latch fingers 1
The tips of 3a and 13b expand outward.

For this purpose, as shown in FIG.
The hollow screw 1 is inserted into the pair of notches 17a and 17b.
The position of the upper part of the ring 6 is maintained.

Therefore, the insertion position of the control rod 3 connected to the hollow screw 1 hem 6 into the reactor core 2 is maintained, and the reactor scram is maintained.

Further, as shown in FIG. 11, on the outer circumference of the latch guide 16, a plurality of rollers 18a, 18b, 18G, and 13d that rotate while contacting the inner circumference of the guide cove 17 are arranged at a required pitch in the circumferential direction. , these rollers 18a-18
d guides the latch guide 16 and the hollow piston 6 to move up and down.

Among these rollers 18a to 18d, an arcuate plate-shaped guide rail 19 is interposed between the adjacent required rollers 18a to 18d in the circumferential direction, and the convex curved surface of this guide rail 19 extends to the inner periphery of the guide cove 17. fixed to the surface. For this purpose, the adjacent rollers 18a and 18d are
While the downward movement is guided by one guide rail, the circumferential rotation of the latch guide 16 is guided by the guide rail 19.
It is regulated by both aspects of

In this way, the rotation of the latch guide 16 is restricted, and the rotation of the ball screw nut 10 that fixes the latch guide 16 is restricted, and the rotational movement of the ball screw shaft 9 is restricted to the ball screw nut. 10 vertical movements.

In FIG. 8, reference numeral 20 is a shaft sealing portion, which seals the drive shaft 8 which is detachably connected in the axial direction to the output shaft of the L-tough. Further, at the lower end of the back sheet 21 which is fixed to the lower end of the ball screw shaft 9, a boss 22 having a key groove carved in the inner periphery is fixed coaxially to the ball screw shaft 9.

Fitted into the boss 22 is a spline shaft portion formed as a spline shaft, which is the upper end portion of a drive shaft 8 detachably connected to the output shaft of the motor 7 . For this purpose, the drive shaft 8 can be removed both from the output shaft of the motor 7 and from the boss 22.

Further, the upper end portion of the divided sheet 23 having a sheet portion that is in watertight contact with the lower surface of the back sheet 21 is connected to the outer peripheral flange 1.
2, and the back sheet 21 is seated on the seat portions of the divided seas 1 to 23, thereby preventing leakage of reactor water in the CRD housing 5 downward from this portion. The upper inner circumferential surface of the shaft seal 20 is in close contact with the outer circumferential surface of the divided sheet 23 in a watertight manner.

(Problem to be Solved by the Invention) However, when pulling out the control rod 3 using such a conventional control rod drive mechanism, the motor 7 is rotated in a predetermined direction to rotate the ball screw shaft 9 around the shaft. Rotate it to
The ball screw nut 10 is lowered, and the hollow piston 6 to which the control rod 3 is connected is caused to follow the ball screw nut 10 by its own weight and fall next to it.

Therefore, although the weight of the control rod 3 is large and is sufficient for pulling out, there is a possibility that the control rod 3 cannot be pulled out under its own weight due to friction between the control rod 3 and the fuel assembly. Taking this into consideration, measures are required to forcibly pull out the control rods 3 from the reactor core 2 even in such a case.

Therefore, an object of the present invention is to remove the control rod from the core for 1.s. if the control rod is not pulled out from the core due to its own weight.
The object of the present invention is to provide a control rod drive mechanism that can be forcibly pulled from the +.

[Structure of the invention]

(Means for solving the problem) The present invention provides a latch guide with a trigram 1 part that is latched to a latch finger of a hollow piston connecting a control rod,
If for some reason the control rods cannot be pulled out of the core, hook the latch part of the latch guide onto the latch finger.
The control rod is connected to the ball screw nut 1 through the latch guide and the hollow piston, and the control rod is forcibly pulled out of the reactor core by retracting the ball screw nut. The first invention is configured as follows.

A ball screw nut is screwed onto a ball screw shaft that is rotated around the shaft by a motor and descends in the axial direction, and an end portion that is connected to a control rod and is placed on the ball screw node 1 above. a hollow piston provided with a latch finger that can be freely expanded; and a latch guide fixed to the ball screw nut to regulate rotation of the ball screw nut and provided with a latching portion that is latched to the latch finger. The control rod drive fJ] is housed in a control rod housing which is passed through and fixed to the bottom of the reactor pressure vessel and accommodates reactor water.

Further, the second invention of the present invention is to prevent reactor water from leaking from the control rod drive mechanism housing when implementing the first invention.
) -U- This is an invention of an apparatus used exclusively for

A ball screw nut 1~ which is screwed onto a ball screw shaft rotated around the shaft by a motor and moves up and down in the axial direction, and an end connected to a control rod and placed on the ball screw nut 1~-[ a hollow screw 1 which is provided with a latch fin force that can be expanded freely; and a latching portion that is fixed to the ball screw nut 1 to regulate rotation of the ball screw nut and that is latched to the latch finger. A latch guide is installed in the control rod drive mechanism housing that passes through the bottom of the reactor pressure vessel and is fixed to the bottom of the reactor pressure vessel to accommodate reactor water. A bag is fixed to one end of the ball screw shaft inside the sealed casing that is detachably and watertightly installed in place of the sealing part and accommodates the reactor water in the control rod drive mechanism housing. a divided sheet handling device that supports and detaches the divided sheet that is seated on the seat, seals water, and is screwed to the outer periphery flange; and an operating shaft that is detachably connected to the boss of the back seat. and a ball screw handling device for rotating the ball screw shaft to a latching position where the latching portion of the latch guide is engaged with and latched to the latch finger, and the ball screw handling device and the above-mentioned The present invention is characterized in that each operating end of the divided sheet handling device extends watertightly to the outside of the casing.

(Function) If the control rod is not pulled out of the reactor core for some reason, engage the latch finger of the latch guide with the latch finger of the hollow piston to which this control rod is connected, and then remove the latch guide. The control rods are forcibly pulled out of the reactor core by descending downward.

However, since such work requires safely removing the shaft seal of the control rod drive mechanism housing, first, drive the motor to rotate the ball screw U-shaft, and then remove the lower end of the ball screw shaft. Bring the back sheet into close contact with the divided sheet, and remove the shaft seal after applying the sun protection and IJ method to prevent reactor water from leaking.

Next, the sealed casing is watertightly attached to the position where the shaft seal was removed, and then the operating end of the divided sheet handling device is operated from outside the sealed casing to move the divided sheet to the outer circumference 7.
Remove it from the lunge and catch the water inside the control rod drive mechanism housing with a sealed casing.

Thereafter, the operating end of the ball screw handling device is operated from outside the closed casing to rotate the ball screw shaft to a position where the latching portion of the latch guide is latched to the latch finger of the hollow piston.

Further, the ball screw handling device pushes the ball screw shaft upward to hold the ball screw nut in a state where its rotation is restricted.

Next, the motor is rotated to rotate the ball screw shaft, and the ball screw nut and latch guide are raised.
The hook part of the latch guide is hooked to the latch finger.

Thereby, the control rod is connected to the ball screw nut via the hollow piston and the latch guide.

Therefore, next time, the control rod can be forcibly pulled out by driving the motor in reverse rotation to lower the ball screw nut downward.

(Example) Hereinafter, one example of the present invention will be described based on FIGS. 1 to 5. In FIGS. 1 to 5, parts common to those in FIGS. 7 to 11 are designated by the same reference numerals.

FIG. 3 is a longitudinal sectional view of a main part of an embodiment of the first invention of the present invention. In FIG. 3, a hollow ball screw shaft 9 is housed coaxially within a cylindrical guide tube 17. As shown in FIG.

A ball screw nut 10 is screwed into the ball screw shaft 9 so as to be movable in the axial direction, and a ring-shaped latch guide 16 is coaxially fixed onto the ball screw nut 10.

As shown in FIG. 1, in the latch guide 16, for example, four rollers 18a to 18d are arranged at appropriate pitches in the circumferential direction, and the outer circumferential surface of each roller 18a to 18d is aligned with the inner circumferential surface of the guide duplex 17. The latch guide 16 is inscribed in the latch guide 16 and rotates in the downward direction to guide the latch guide 16 in its upward and downward movements.

Also, adjacent required rollers, for example 18a.

An arcuate plate-shaped guide rail 19 is fixed to the inner circumferential surface of the guide tube 17 partitioned by the guide tube 18 d over almost the entire length of the guide tube 17 , and rollers 18 a are provided on both left and right sides of the guide rail 19 .

Both sides of 18d are in contact.

Therefore, the guide rail 19 guides the vertical movement of the rollers 18a, 18d in the axial direction, while restricting the rotation of the rollers 18a, 18d in the circumferential direction of the guide rail 17.

Thereby, the rotation of the latch guide 16 and the ball screw nut 10 is restricted, and the rotational movement of the ball screw shaft 9 is converted into the vertical movement of the ball screw nut 10.

The latch guide 16 has a pair of diametrically opposed pawl storage parts 14a and 14b standing on its outer circumference, and a pair of left and right latch fingers 13a and 13b are stored in these pawl storage parts 14a and 14b. The lower end of the hollow piston 6 is placed on this latch guide 16.

The latch fingers 13a, 13b are biased by springs 15a, 15b (see FIG. 10) so that their lower ends are expanded, and the claw housing portion 14a.

14b and is held in a closed state, the lower end of the hollow piston 6 simply passes through the center hole 16a of the latch guide 16 and rests on the ball screw nut 10. .

Therefore, the hollow piston 6 and this hollow piston 6
The control rod 3 connected to the ball screw nut 10 is pushed up by the upward movement of the ball screw nut 10.
As the hollow piston 6 descends, the hollow piston 6 follows due to its own weight and descends.

As shown in FIG. 1, on the latch guide 16,
A pair of hooks 30a, 30b are erected to face each other in a direction substantially perpendicular to the direction in which the pair of claw storage parts 14a, 14b face each other.

The upper ends of these hooks 30a, 30b are bent inward at a substantially right angle as shown in FIG. 2, and -16=a pair of latch fingers 13a as shown in FIG.

It is formed in a hook portion that engages and is hooked to 13b.

Further, a taper is formed on the inner side of the upper end of each hook 30a, 30b to gradually expand upward, and each hook 30a, 30b is opened from below the pair of latch fingers 13a, 13b.
By making contact with the upper limit of 0b, the expanding lower end portions of each latch finger 13a, 13b are connected to each hook 30a,
Each hook 30a, 30b is guided by the taper of 30b.
It is introduced inside and then interlocked.

Therefore, the latch guide 16 and the ball screw nut 10 are rotated by a required angle, for example, 90 degrees, and each hook 30 is
a, 30b to the latching position of each latch finger 13a, 13b, each latch finger 13a,
Each knock 30a, 3Qb can be stopped at 13b.

However, the rotation of the latch guide 16 is limited to the required rotation of the roller 18a.
, 18a, the latch guide 1G cannot be rotated by 90° in this state.

Therefore, it is necessary to retreat the latch guide 16 below the lower end of the guide rail 19 and rotate the latch guide 16 by, for example, 90 degrees at a position where it is released from the restriction of the guide rail 19.

However, in order to retract the latch guide 16 to below the lower end of the guide rail 19, there is not enough space under the CRD housing 5 and the bottom must be opened. If this is done, water in the CRD housing 5 will leak to the outside, which is inconvenient from the standpoint of reducing radiation exposure to workers.

Therefore, in order to proceed with the work while preventing leakage of reactor water inside the CRD housing 5 in such a case, the device of the second invention of the present invention is required, and one embodiment thereof is as shown in FIG. It is configured.

That is, as shown in FIG. 5, after removing the shaft seal 20 shown in FIG. 8, the right-bottom cylindrical, transparent sealed casing 40 is attached to the outer periphery 7 flange 12 at the removal position.
The shaft sealing portion 20 is replaced with the shaft sealing portion 20, and is detachably fixed by a pole l-408.

The axial length of the sealed casing 40 is as shown in FIG.
Even if the lower end of the boss 22 is rearwardly lowered, the boss 22 can be accommodated.
A divided section sheet handling device 41, a ball screw handling device 42, etc. are attached to the bottom of the sealed casing 40, depending on the length to be obtained.

The main shaft portion 41a of the divided sheet punching device 41 vertically penetrates the bottom of the sealed casing 40 in a watertight and freely rotatable manner, and the V end accommodated in the sealed casing 40 has at least two shafts extending in the direction perpendicular to the axis. A pair of arms 41b
, 11c are fixed.

Each of the arms 41b and 41C has a pin 41 fitted into a recess formed in the bottom of the divided seam 1-23.
cj and 41e are respectively planted.

A handle 41f extending in a direction perpendicular to the axis is fixed at the upper end of the main shaft part 418 of the divided sheet handling device 41, and by rotating the handle 41f, the arms 41b and 41G are rotated. 41d, 41e
By rotating the divided sheet 23 fitted into the recess in an appropriate direction, the divided sheets 1 to 23 can be removed from or attached to the outer flange 12.

The main shaft portion 41a of the divided sheet handling device 41 is coaxially rotatable with the main shaft portion 42a of the ball screw handling device 42,
The main shaft portion 42a has a spline shaft 4 which is removably fitted into the boss 22 at the end thereof.
2b, the lower end of which is formed into a handle 42C, and the ball screw shaft 9 and latch guide 16 are rotated in an appropriate direction by rotating the handle 42C.

Next, the operation of each of the above embodiments will be explained.

In the unlikely event that the control rods 3 inserted into the reactor core 2 shown in Figure 7 cannot be pulled out for some reason, first stop the reactor operation and then proceed as shown in Figure 6. Attach each hook 30a, 30b of the latch guide 16 with the hollow screw 1.
It is necessary to engage and engage each latch finger 13a, 13b of the hem 6.

For this purpose, 1-ra 18a, 18 of the latch guide 16
d and the guide rail 19, and the latch guide 16 and the ball screw nut 10 need to be rotated, for example, 90'.

However, as mentioned in 11 above, it is necessary to perform this operation without leaking reactor water to the outside of the CRD housing 5, and for this purpose, the division seal 1 handling neck 41, ball screw handling device 42, etc. Requires use.

Therefore, after first stopping the reactor operation, the motor 7
is rotated in a desired direction to rotate the ball U shaft 9 around the shaft, and the ball screw nut 10 is attached to the lowest end of the ball screw shaft 9, and the back seat 21 is moved as shown in FIG.
The lower surface of the split sheet 23 is watertightly separated from the bottom surface of the split sheet 23 to prevent leakage of reactor water.

In this state, remove the drive shaft 7 from the bottom of the CRD housing 5, and then remove the drive shaft 8 connected to the output shaft of the motor 7.
The shaft seal 20 shown in FIG. 8 is removed from the outer flange 12 by pulling out the boss 22J.

Next, as shown in FIG. 5, the transparent hermetic casing 40 is watertightly fixed at the position where the shaft seal 20 of the outer peripheral flange 12 is removed, and the operator looks through the inside of the hermetic casing 40 from the outside while looking at the divided part. Each arm 4 of the sheet handling device 41
Each pin 41d, 41e of 1b, 41c is connected to the divided sheet 2.
3 and rotate the handle 41f to remove the divided sheet 23 from the outer peripheral flange 12 and move it to the bottom inside the sealed casing 40.

Reactor water leaking from the removed position of the divided seam 1-23 is received by the sealed casing 40, and leakage to the outside is prevented.

Thereafter, the ball screw handling device 42 is operated to fit the spline shaft portion 42b of the main shaft portion 42a into the boss 21, and the handle 42C is rotated in the desired direction to move the latch guide 16 as shown in FIG. The rollers 18a to 18d are lowered to below the lower end of the guide rail 19, and the ball screw nut 10 is lowered -q to a position where the engagement between them is released.

Next, the handle 42c is rotated, for example, by 90 degrees in a desired direction, and the hooks 3Qa and 30b of the latch guide 16 are rotated to the engagement position where they engage with the latch fingers 13a and 13b of the hollow piston 6, and at this position, Handle 42G
Push up the required two rollers 18C and 18d.
The latch guide 16 is raised to a position where the guide rail 19 is interposed therebetween, and the rotation of the latch guide 16 is held in a state where the guide rail 19 restricts the rotation.

At this point, the lower end of the hollow screw 1 6 connected to the control rod 3 that has not been pulled out from the core 2 is suspended in the upper part of the guide tube 17, and the pair of latch fingers 13a and 13b are directed downward. It has been expanded.

After that, the divided part sheet 23 is attached to the outer peripheral flange 12 again by appropriate operations of the divided part seam 1 to the handling device 41, and is brought into close contact with the back sheet 21, and the CRD housing 5 is
The sealed casing 40 is removed after preventing leakage of reactor water inside.

Next, the drive shaft 8, the morph, and the shaft seal 20 are attached to each attachment position.

Thereafter, the motor 7 is driven to rotate to move the ball screw nut 10 and the latch guide 16 upward, and the pair of latch fingers 13a and 13b expand downward.
A pair of hooks 30a of the latch guide 16,
The latch fingers 13a and 13b are brought into contact with the taper of the upper end to guide the introduction direction, and the lower ends of the latch fingers 13a and 13b are connected to the hook 3.
0a.

30b, and each hook 30a, 30b is engaged with each latch finger 13a, 13b to be engaged, as shown in FIG.

Next, the motor 7 is reversely rotated to rotate the ball screw nut 10.
When lowered, each hook 30a of the latch guide 16,
The hollow piston 6 having the latch fingers 13a, 13b hooked on the hollow piston 30b and the control rod 3 connected to the hollow piston 6 are gradually lowered, and the control rod 3 is forcibly withdrawn from the core 2.

Therefore, according to this embodiment, even if a case arises in which the control rods 3 cannot be pulled out from the reactor core 2, the control rods 3 can be forcibly pulled out from the reactor core 2.

Furthermore, the control rod 3 can be forcibly withdrawn safely and reliably.

[Effect beam of invention]

As explained above, in the first invention of the present case, the latch guide is provided with a latch portion that is hooked on the latch finger of the hollow screws 1 to 1 that connect the control rods. By latching and lowering the latch guide, the control rod can be forcibly pulled out of the reactor core.

In addition, the second invention of the present invention provides the following:
It is possible to prevent leakage of the reactor core from the control rod drive mechanism housing, and the first invention can be carried out safely and reliably.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of essential parts of an embodiment of the control rod drive mechanism according to the first invention of the present invention, FIG. 2 is a cross-sectional view taken along line B-B in FIG. 1, and FIG. Fig. 4 is a vertical sectional view of the main part showing the state in which the latch finger is fitted into the pawl housing part of the latch guide in the embodiment (not shown), and the shaft seal part is removed in the embodiment shown in Fig. 1. A longitudinal sectional view of the main part showing the condition, Figure 5 is the main part! FIG. 6 is a vertical cross-sectional view of a main part of an embodiment of the control rod drive mechanism according to the second invention of 1. In the embodiment shown in FIG. FIG. 7 is a schematic vertical sectional view showing the configuration around the core of a general WR, and FIG. 8 is a schematic vertical sectional view showing the overall configuration of a conventional control rod drive mechanism. Longitudinal cross-sectional view partially cut away, FIGS. 9 and 1
0 is a partially enlarged vertical cross-sectional view for explaining the operation of the conventional example not shown in FIG. 8, and FIG. 11 is a cross-sectional view of a part of the conventional example shown in FIG. 8. 3... Control rod, 4... Control rod drive mechanism, 5... c
RD housing, 6...Hollow piston, 7...Motor, 8...Drive shaft, 9...Ball screw shaft, 10...
- To ball screw nut 1, 13a, 13b...Latch finger, 14a, 14. b...Claw storage section, 16 river latch guide, 17...Guide tube, 18a to 18d
. . . Roller, 19 .
Hook (hanging part), 40... Sealed casing, 41.
... Divided section sheet handling device, 42... Ball screw handling device. Applicant's agent Hisashi Hatano Figure 1 Figure 2 Figure 4 Figure 5 Figure 7 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] 1. A ball screw nut that is screwed onto a ball screw shaft rotated around the shaft by a motor and moves up and down in the axial direction, and a ball screw nut that is connected to a control rod and placed on the ball screw nut. a hollow piston that is provided with a latch finger at its end that can be freely expanded; and a latch that is fixed to the ball screw nut to regulate rotation of the ball screw nut and that is provided with a latching portion that is latched to the latch finger. 1. A control rod drive mechanism characterized in that a guide is built into a control rod drive mechanism housing that penetrates and is fixed to the bottom of a reactor pressure vessel and accommodates reactor water. 2. A ball screw nut that is screwed onto a ball screw shaft that is rotated around the axis by a motor and moves up and down in the axial direction, and a latch finger at the end that is connected to a control rod and placed on the ball screw nut. a hollow piston that is provided with a hollow piston that can be freely expanded; and a latch guide that is fixed to the ball screw nut to regulate rotation of the ball screw nut and that is provided with a latching portion that is latched to the latch finger. It is fixed to the bottom of the pressure vessel and is built into the control rod drive mechanism housing that accommodates reactor water, and is also detachable by being replaced at the mounting position of the shaft seal of the outer periphery flange of the control rod drive mechanism housing. Inside the sealed casing, which is watertightly installed and accommodates reactor water in the control rod drive mechanism housing, is seated on a back seat fixed to one end of the ball screw shaft to seal the reactor water and the outer peripheral flange. a divided sheet handling device that supports and attaches/detaches the divided sheet screwed to the back sheet; and an operating shaft removably connected to the boss of the back sheet, so that the hooking portion of the latch guide is connected to the latch finger. A built-in ball screw handling device rotates the ball screw shaft to a locking position where it engages and locks, and each operating end of the ball screw handling device and the divided sheet handling device is connected to the sealed casing. A control rod drive mechanism characterized by extending watertightly to the outside of the control rod.