JPH07159576A - Control rod driving mechanism - Google Patents

Abstract

PURPOSE:To mitigate the load applied to a guide ribbon and a roller and improve reliability. CONSTITUTION:This control rod driving mechanism is provided with a stop piston 33 for surrounding a hollow piston 19 in an outer tube 46, a guide ribbon 39 kept in contact with the lower face of the stop piston 33 at its upper end, a spring 43 to follow the stop pin 33 on the guide ribbon 39, and a magnet at the lower section of the guide ribbon 39. The control rod driving mechanism can be smoothly operated while no impact force is applied to the guide ribbon 39 at the time of a scram and no eccentric reaction force is applied to the stop pin 33.

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 (hereinafter referred to as CRD) used in a boiling water reactor (hereinafter referred to as BWR) as a light water reactor.

[0002]

2. Description of the Related Art FIG. 3 shows a schematic structure of a conventional BWR, in which a coolant 2 also serving as a moderator is provided in a reactor pressure vessel 1.
While the core 3 is housed therein, the core 3 is arranged in the lower central part and is surrounded by the core shroud 4. A large number of fuel assemblies (not shown) are loaded in the core 3, and the control rods 5 are housed so as to be freely inserted and removed between a set of four fuel assemblies.

In this BWR, the coolant 2 flows upward in the core 3, while heat generated by the fission chain reaction from the core 3 is transferred to the coolant 2 to heat the coolant 2. The heated coolant 2 becomes a gas-liquid two-phase flow of water and steam, moves above the core 3, and is guided from the core 3 to the steam separator 6.

After the gas-liquid two-layer coolant is separated into water and steam by a steam separator 6, the steam is sent from a main steam pipe to a steam turbine system through a steam dryer (not shown) to drive a steam turbine. Let The steam that has worked in the steam turbine system is condensed in the condenser to be condensed water, and then returns to the reactor pressure vessel 1 again as supply water through the reactor condensate system and the water supply system.

On the other hand, the water separated by the steam-water separator 6 is guided to the lower part of the core in a state where the downcomer section 7 is flown and mixed with the feed water sent through the reactor condensate system and the feed water system. It is guided to the core 3 again.

Further, a control rod 5 is provided in the core 3 of the reactor pressure vessel 1 for controlling the start and stop of the reactor and adjusting the reactor power.
It is taken in and out by. The CRD 8 is an integral structure (assembly) housed in a CRD housing 9 extending downward from the bottom portion 1a of the reactor pressure vessel 1, and is fixed to a lower flange 9a of the CRD housing 9 by bolting.

The CRD 8 is an electric drive type CRD as shown in FIG. 4, and the rotating shaft 11 from the electric motor 10 to which the electric motor 10 is attached at the bottom is connected to a drive shaft 13 of the CRD 8 via a gear coupling mechanism 12. Be connected. The drive shaft 13 is connected to the ball screw shaft 14 so as to rotate integrally therewith.
A ball nut 15 is screwed onto 14.

A pair of rollers 16 is attached to the ball nut 15 in the axial direction.
It is installed so as to sandwich 18. A hollow piston 19 is installed above the ball nut 15, and the piston 19 is a coupling 20 installed at the upper end of the piston tube 19a.
Is connected to the control rod 5 via.

The ball screw shaft 14 is rotated via the rotary shaft 11 and the drive shaft 13 by driving the electric motor 10, and the ball nut 15 is vertically moved by the rotation of the ball screw shaft 14. At that time, the ball nut 15 is attached to the mounting plate 18
The rotation of the ball nut 15 is restricted by the
By the vertical movement of the control rod 5, the control rod 5 moves up and down via the piston 19.

The vertical movement of the control rod 5 adjusts the amount of insertion and withdrawal into and from the core 3 to control the reactor output. Reference numeral 21 is an electromagnetic brake, reference numeral 22 is a synchro position detector, reference numeral 23 is a motor bracket, and reference numeral 24 is a spill piece.

Next, a case where an emergency situation occurs in the BWR and the reactor is scrammed will be described.

At the time of scram of the reactor, the scrum insertion pipe connected to the lower flange 9a of the CRD housing 9
High-pressure drive water is supplied to the lower surface side of the piston 19 from 25 through the water injection port 26. By supplying this high-pressure drive water, the piston 19 installed on the ball nut 15 is pushed upward to insert the control rod 5 into the core 3 at high speed, and the reactor is scrammed.

In such a CRD 8 structure, the insertion position of the control rod 5 inserted into the core 3 is detected from the rotation of the electric motor 10 during normal driving.
By.

Also, during scram, the control rod 5 and piston are
Since 19 is driven separately from above the ball nut 15,
The position of the control rod 5 cannot be detected by the synchro position detector 22 described above. In this case, the position of the control rod 5 is controlled by a magnet 27 attached to the lower end of the piston 19 and a position detector 29 having a reed switch 28 that operates by magnetic force. The position of 5 is detected.

However, the upper part of the CRD 8 is the reactor pressure vessel 1
Since the position detector 29 is installed outside the CRD and the upper end is restricted by the bottom 1a of the reactor pressure vessel 1, the entire stroke of the control rod 5 cannot be detected.

The conventional position detector 29 has 0%, 10%, 40%, and
The position of the control rod 5 of 60% can be detected. Furthermore, the specification value of the insertion time at the time of scrum is determined 100
It is necessary to detect even with%, and this is detected by another mechanism.

That is, as shown in FIG. 5, a coil spring 32 and a stop spin 33 are provided in a cylinder 31 below the disc spring mechanism 30 for braking the control rod 5 and the piston 19 during scram.
The magnet 34 shown in FIG. 4 is attached to the stop spin 33 through a long guide ribbon 39.

With such a mechanism, when the control rod 5 and the piston 19 are fully inserted, the stop piston 33 and the magnet 34 are slightly pushed up by the piston 19, and the position detector
Reed switch 28 built in 29 detects 100% position.

In addition to the above, the CRD 8 is provided with a separation detecting mechanism for detecting that the control rod 5 and the piston 19 are separated from above the ball nut 15 in order to prevent the control rod 5 from falling accidentally.

That is, in the spool piece 24, a magnet holder 36 having a magnet 35 built therein is slidably fitted to the drive shaft 13, and a coil spring 37 is provided below the magnet holder 36. Further, a separation detector 38 having a built-in reed switch is installed outside the CRD 8.

With such a structure, the control rod 5 and the piston 19 are in a hanging state due to frictional resistance between the control rod 5 and the fuel assembly while the control rod 5 is being pulled out.

The control rod 5 and piston 19 are ball nuts 15.
When separated from above, the load of the control rod 5 and the piston 19 acting on the magnet holder 36 is released, so that the coil spring 37 extends and the magnet 35 is pushed up, and the reed switch of the separation detector 38 operates. It operates, and it is detected that the control rod 5 and the piston 19 are separated from the ball nut 15.

[0023]

The above-mentioned conventional CRD 8 is provided with three detectors, that is, the position detector 29, the separation detector 38, and the synchro position detector 22 at the time of scram, in order to operate the detectors. An all insertion position detection mechanism and a separation detection mechanism having a complicated structure are provided inside the CRD 8.

In the full insertion position detecting mechanism, as shown in FIG. 5, the piston 19 is inserted at a high speed at the time of scram and collides with the stop piston 33 mounted in the lower cylinder 31 to cause the stop piston 33 to move. Normally, the coil spring 33 and the disc spring mechanism 30, which are normally pushed down, absorb the shock and then stop. A ribbon 39 is fitted to the stop piston 33 in order to transmit the movement of the stop piston 33 to the lower magnet 34.

The guide ribbon 39 passes through a key groove-shaped space provided on the outer surface of the guide tube 17 and is a magnet located below.
It is a long thin strip-shaped plate joined with 34, and the piston
When 19 collides with stop piston 33 and disc spring mechanism
Impact load acts when 30 starts and stops. It is desirable to increase the plate thickness of the guide ribbon 39 in order to sufficiently withstand this impact load, but it was difficult due to space constraints.

When the piston 19 collides with the stop piston 33, the stop piston 33 moves upward in the lower cylinder 31 by the roller 40 attached to the stop piston, but is inclined by the reaction force of the guide ribbon 39 described above. However, moving in the lower cylinder 31 causes a large load to be applied to some of the rollers 40, which causes a problem of increased wear of the rollers. Reference numeral 41 is a cover 42 and a band.

The present invention has been made to solve the above problems, and eliminates the need for mechanical connection between the stop piston and the guide ribbon for transmitting the movement of the stop piston to the magnet below, thereby eliminating the need for a guide ribbon. Another object of the present invention is to provide a control rod drive mechanism that reduces the load acting on rollers and the like and has improved reliability.

[0028]

In order to solve the above-mentioned problems, a control rod drive mechanism according to the present invention transmits the rotation of an electric motor to a piston elevating mechanism via a drive shaft mechanism to elevate a piston, The lower end surface of the stop piston in the control rod drive mechanism configured to insert and pull out the control rod into the core and to rapidly insert the control rod into the core by injecting high pressure water during scram and pushing up the piston. By installing a full insertion position mechanism that operates following the movement of the stop piston by pressing the upper end of the guide ribbon with a spring, it is not necessary to connect the stop piston and the guide ribbon.

[0029]

With this CRD, the upper end of the guide ribbon is pressed against the lower end face of the stop piston by the force of the spring, and when the hollow piston collides with the stop piston and moves upward during scram, the stop piston first moves the piston. After being pushed up by, the guide ribbon is raised by the spring to the lower end face of the stop piston, and the lower magnet is raised to detect that the guide ribbon is fully inserted. The guide ribbon is not fitted on the stop piston.

Therefore, the impact force when the piston collides with the stop piston is not transmitted to the guide ribbon.
Further, even when stopped, the stop piston is pushed up by the force of the spring after stopping, so that the impact force at the time of stop can be sufficiently reduced by appropriately setting the length and force of the spring in the guide ribbon.

Further, since the guide ribbon and the stop piston are only pressed by the spring force, the piston collides with the stop piston and the guide ribbon and the stop piston are separated during the rapid upward movement. The reaction force of the ribbon is not transmitted, the stop piston does not tilt, and it moves in the lower cylinder, so that the load on the roller becomes uniform.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the control rod drive mechanism according to the present invention will be described with reference to FIGS.

This control rod drive mechanism (CRD) is an electric drive type control rod drive mechanism (FMC) constructed as shown in FIG.
RD). This CRD is a CR that extends downward from the bottom (lower mirror) 1a of the reactor pressure vessel 1.
Since it is fixed to the lower flange 9a of the D housing 9 by bolting or the like, and the entire configuration is substantially the same as that of the CRD shown in FIG. 4, the same reference numerals are given and described.

The electric motor 10 is attached to the lower part of the CRD,
The rotational driving force from the electric motor 10 is transmitted to the piston lifting mechanism via the drive shaft mechanism. The drive shaft mechanism has a rotary shaft 11 of the electric motor 10 and a drive shaft 13 connected to the rotary shaft 11 via a gear coupling mechanism 12, and the drive shaft 13 has a ball screw shaft 14 of a piston lifting mechanism.
Are connected.

The piston lifting mechanism has a ball screw shaft 14 and a ball nut 15 screwed onto the ball screw shaft 14,
The ball nut 15 is prevented from rotating by the roller 16 being sandwiched by a mounting plate 18 axially provided inside a guide tube 17.

A piston 19 is placed on the ball nut 15, and the piston 19 is integrally lifted as the ball nut 15 moves up and down. A piston tube 19a extends integrally upward in the guide tube 17 from the piston 19, and a coupling capable of engaging with a control rod (not shown) is provided at the upper end of the piston tube 19a.

The CRD 40 is constructed as described above, and the ball screw shaft 14 of the piston elevating mechanism is rotated by the rotational drive of the electric motor 10 via the drive shaft mechanism to elevate the ball nut 15.

As the ball nut 15 moves up and down, the piston 19 moves up and down, and the control rod (not shown) moves up and down via the piston tube 19a. By raising and lowering the control rod, the control rod is inserted into or pulled out from the core, and the power of the furnace is adjusted.

The control rod is held at the insertion position by restricting the rotation of the ball screw shaft 14 by the holding torque of the electric motor 10 itself.

When scramming the reactor, CRD
High-pressure drive water is supplied to the lower surface side of the piston 19 via the scrum insertion pipe 25 connected to the lower flange 9a of the housing 9 and the inlet 26. Ball nut by this supply
The piston 19 mounted on 15 is pushed upwards to rapidly insert the control rods into the core and scram the reactor.

When the piston 19 rises to the full insertion position both when driven by the electric motor 10 and when driving the scrum, the hollow piston 19 contacts the stop piston 33,
The coil spring 32 installed above the stop piston 33 is compressed.

The stop piston 33 and the coil spring are concentrically installed in the lower cylinder 31, and a lid-shaped ring having a roller for guiding the piston tube 19a is installed at the upper end of the lower cylinder 31. A plurality of disc spring mechanisms 30 are installed above the disc spring mechanism 30 to reduce the impact during scrum.

The stop piston 33 is a hollow piston.
When the inside of the lower cylinder 31 is lifted up integrally while contacting with 19, the guide ribbon 39 pressed against the lower end of the stop piston 33 by the spring 43 moves upward following the movement of the stop piston 33 to reach the lower end of the guide ribbon 39. It is detected that the control rod 5 is fully inserted by moving the attached magnet 34 and operating the full insertion detection reed switch 45 in the position detector 29.

At the time of withdrawal, the stop piston 33 moves integrally with the hollow piston 19 in the lower cylinder 31 by the restoring force of the coil spring 32 in the state where the hollow piston 19 is pulled out downward by the electric motor 10 and is in contact with the hollow piston 19, so that the stop piston 33 follows it. Then, the guide ribbon 39 pressed against the lower end surface of the stop piston 33 by the spring 43 also moves downward, and it is detected that the magnet 34 attached to the lower end of the guide ribbon 39 has moved and the fully inserted state has been released. To be done.

In the conventional example, since it was a strip-shaped plate, it was called a guide ribbon. In the present invention, the rod shape is more rational in space and it is more appropriate to call it a guide rod, but in order to avoid confusion of terms, the guide ribbon is unified. There is no problem even if a strip-shaped plate is used.

In the above embodiment, the spring for pressing the guide ribbon against the stop piston was installed near the upper end of the guide ribbon. However, it may be installed near the magnet on the lower end.

[0047]

According to the present invention, the guide ribbon is pressed against the lower end surface of the stop piston using a spring without mechanically fastening the stop piston and the guide ribbon of the full insertion position detecting mechanism. By transmitting the vertical movement of the stop piston to the magnet at the lower end of the guide ribbon via the guide ribbon, it is possible to detect whether or not the stop piston is at the full insertion position.

As a result, it is possible to prevent the impact load when the piston collides with the stop piston during the scrum from acting on the guide ribbon, and at the same time to prevent the stop piston from moving in the lower cylinder in a tilted state. It is possible to obtain a control rod drive mechanism having a structural strength and improved reliability.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a control rod drive mechanism according to the present invention.

FIG. 2 is a vertical cross-sectional view showing an enlarged part B in FIG.

FIG. 3 is a vertical sectional view showing a general outline of a boiling water reactor.

4 is a longitudinal sectional view showing a conventional control rod drive mechanism in FIG.

5 is a vertical cross-sectional view showing an enlarged part A in FIG.

[Explanation of Codes] 1 ... Reactor pressure vessel, 1a ... Bottom part, 2 ... Coolant, 3 ... Core, 4 ... Core shroud, 5 ... Control rod, 6 ... Steam separator, 7 ... Downcomer section, 8 ... CRD , 9 ... CRD housing, 9a ... lower flange, 10 ... electric motor, 11 ... rotating shaft,
12 ... Gear coupling mechanism, 13 ... Drive shaft, 14 ... Ball screw shaft, 15 ... Ball nut, 16 ... Roller, 17 ... Guide tube, 18 ... Mounting plate, 19 ... Piston, 19a ... Piston tube, 20 ... Coupling , 21 ... Electromagnetic brake, 22 ... Synchro position detector, 23 ... Motor bracket, 24 ... Spool piece, 25 ... Scrum insertion pipe, 26 ... Inlet port, 27 ... Magnet, 28 ... Reed switch, 29 ... Position detector, 30 …
Disc spring mechanism, 31 ... Cylinder, 32 ... Coil spring, 33 ... Stop piston, 34 ... Magnet, 35 ... Magnet, 36
… Magnet holder, 37… Coil spring, 38… Separation detector, 39… Guide ribbon, 40… Roller, 41… Cover, 42… Band, 43… Spring, 44… Stopper, 45… Full insertion detection reed switch, 46… Outer tube.

Claims (3)

[Claims] 1. The rotation of an electric motor is transmitted to a piston elevating mechanism via a drive shaft mechanism to elevate and lower a hollow piston so that a control rod is inserted into and withdrawn from a core, and at the time of scram, high pressure water is injected to move the piston. In a control rod drive mechanism configured to rapidly insert the control rod into the core by pushing it up, a stop piston is provided so as to surround the hollow piston, and the lower end of the stop piston comes into contact with the upper end of the guide ribbon. The control rod drive mechanism is characterized in that a spring is provided on the guide ribbon so as to follow the stop piston, and a magnet is provided under the spring. 2. The control rod drive mechanism according to claim 1, wherein the spring for pressing the guide ribbon against the stop piston is provided on the lower magnet side. 3. The control rod drive mechanism according to claim 1, wherein the position of the magnet is detected by an all-insertion detection reed switch provided in the position detector.