JP2728753B2 - Control rod drive mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a control rod drive mechanism (hereinafter, referred to as CRD) of a boiling water reactor (hereinafter, referred to as BWR).

A conventional example will be described with reference to FIGS. Fifth
FIG. 1 is a sectional view showing a schematic configuration of a BWR. In the figure, reference numeral 1 denotes a reactor pressure vessel, in which a coolant 2 is housed and a reactor core 3 is housed. . The reactor core 3 is supported by a shroud 4 installed in the reactor pressure vessel 1 and includes a plurality of fuel assemblies (not shown) and control rods 5 (only two are shown in the figure). The coolant 2 flows upward through the core 3, and at this time, the temperature rises due to the nuclear reaction heat of the core 3. The heated coolant 2 becomes a two-phase flow of water and steam, and is introduced into the steam separator 6 installed above the reactor core 3. The coolant 2 introduced into the steam separator 6 is separated into water and steam. The separated steam is introduced into a steam dryer (not shown) to be dried to be dried steam, transferred to a turbine system via a main steam pipe (not shown) connected to the reactor pressure vessel 1, and used for power generation. The steam that has worked in the turbine system is introduced into the condenser and condensed and liquefied to become condensed water. After being purified by the purification system, the steam is returned to the reactor pressure vessel 1 as feedwater. On the other hand, the inner water separated in the reactor pressure vessel 1 flows down to the downcomer section, and is mixed with the above-mentioned water supply.
Is transported below. Hereinafter, the same cycle is repeated.

The control rod 5 is adjusted in the amount of insertion and withdrawal into the core 3 by the CRD 11, whereby the output of the core 3 is controlled. The CRD 11 is inserted and fixed in a CRD housing 12 fixed to the bottom 1a of the reactor pressure vessel 1.

Next, the configuration of the CRD 11 will be described with reference to FIG. CRD11
Is an electric motor, that is, reference numeral 13 in FIG. 6 is an electric motor. The rotary shaft 14 of the electric motor 13 is connected to a drive shaft 16 of the CRD 11 via a gear type coupling (not shown) and a coupling case 15. The drive shaft 16 is connected to a ball screw shaft 19 via a key and a spline. A ball nut 20 is screwed onto the ball screw shaft 19. A roller 21 is provided on the ball nut 20, and the roller 21 is provided so as to sandwich a plate 23 attached to the inner peripheral surface of the guide tube 22 in the axial direction. Above the ball nut 20, a hollow piston 24 is provided.
This piston 24 has a coupling 25 installed at its upper end.
Is connected to the control rod 5. That is, the electric motor
The ball screw shaft 19 is rotated via the rotation shaft 14 and the drive shaft 17 by the driving of 13. The rotation of the ball screw shaft 19 causes the ball nut 20 to move up and down. In addition, this ball nut
The rotation of 20 is regulated by the rollers 21 holding the plate 23. Piston by vertical movement of ball nut 20
The control rod 5 moves up and down via 24. Thereby, the amount of insertion and withdrawal of the control rod 5 into and from the reactor core 3 is adjusted. In addition,
In the figure, reference numeral 26 denotes a bracket, and 27 denotes a labyrinth seal.

Next, a case in which an emergency situation occurs in the nuclear reactor and the nuclear reactor is shut down (hereinafter referred to as a scrum) will be described. When an emergency occurs, high-pressure driving water is supplied to the lower surface side of the piston 24 via the insertion pipe 17 and the injection port 18.
By the supply of the high-pressure driving water, the piston 24 simply placed on the ball nut 10 is pushed upward, and as a result, the control rod 5 is inserted into the core 3 at a high speed, and the reactor is shut down immediately.

Further, in the above configuration, the insertion position of the control rod 5 is held by the ball screw shaft by the holding torque of the electric motor 1 itself.
This is done by regulating the rotation of the nineteen. At the same time, in order to prevent the control rod
28 are provided. That is, if the pressure-resistant portion of the insertion pipe 17 or the CRD 11 breaks, the internal pressure of the CRD 11 decreases, and as a result, the pressure in the reactor pressure vessel 1 acts as a force for pushing down the piston 24. . This pressing force acts on the ball screw shaft 19 as a large pulling torque in the direction in which the control rod 5 is pulled out. At that time, it is not possible to resist the pulling torque only by the holding torque of the electric motor 13 described above, and it is expected that the control rod 5 is pulled out due to the rotation of the ball screw shaft 19 in the pulling direction. Also, CRD11
When the pressure difference between the internal pressure of the reactor and the pressure in the reactor pressure vessel 1 is large, the control rod 5 is withdrawn at a high speed, and the withdrawal speed exceeds the allowable value for maintaining safety in the reactor core 3 and suddenly It is also expected that the reactor core 3 will be damaged by an accelerated reaction. For this reason, a braking device 28 having a sufficient holding torque is provided below the electric motor 13 in addition to the holding torque of the electric motor 13 itself. As shown in FIG. 7, the braking device 28 has a coil 29 provided in the field 30. When the coil 29 is energized, an electromagnetic force is generated. A disk-shaped armature 31 formed of a magnetic material and provided opposite to the field 30 is attached to the field 30 by a pin 32 so that it can move in the axial direction but cannot rotate.

Field 30 is the frame or bracket 26 of motor 13
It is fixed to.

On the other hand, the inner driver 33 is fitted to the rotating shaft 14 of the electric motor 13 and fixed by a nut 34. Key 35 is rotary shaft 14
And the inner driver 33 transmits torque. A disk 36 is fitted around the outer periphery of the inner driver 33 by a spline so as to be movable in the axial direction, and friction plates 37 are fixed to both surfaces of the disk 36. In the braking device 28 having the above structure, when the coil 29 is not energized, the plurality of springs 38 press the armature 31 upward. Therefore, the disc 36 is strongly sandwiched between the side plate 46 and the armature 42, and the rotating shaft 14 of the electric motor 13 is restrained by the frictional force between the side plate 39 and the friction plate 37 and between the friction plate 37 and the armature 31. . Also coil
When the power is supplied to the power supply 29, the electromagnetic force generated in the field 30 causes the armature 31 to overcome the spring 38 and be attracted to the field 30, so that the disk 36 is released and the braking force is lost. When the control rod 5 is inserted or withdrawn in the CRD11, a braking device that normally has no braking power and has no braking force
After energizing 28 and releasing the braking force, the motor 13 is rotated to drive the control rod 5.

After the driving, the motor 13 is stopped, and then the power supply to the braking device 28 is cut off to bring the braking state.

(Problems to be Solved by the Invention) However, the conventional CRD11 having the above-described braking device
In the case of the power failure in the braking device 28 or the braking device 28
If the disk itself becomes inoperable due to the disconnection of the coil 29 or the like, the disk 36 is strongly sandwiched between the side plate 39 and the armature 31 and the braking force is maintained. Therefore, there is a problem that the rotation of the electric motor 13 is prevented and the control rod 5 cannot be inserted or pulled out. The fact that the control rod 5 cannot be inserted into the reactor core 3 is not preferable in terms of safety of the nuclear reactor.

The present invention has been made to solve the above-mentioned problem. Even if the above-described control rod withdrawing force is generated due to damage to the insertion pipe 17 or the like, the control rod is reliably prevented from being pulled out and braking is performed during normal operation. It is an object of the present invention to provide a control rod drive mechanism capable of inserting a control rod by an electric motor even when the device cannot be released.

[Constitution of the Invention] (Means for Solving the Problems) The present invention transmits the rotation of an electric motor to a ball screw shaft via a rotation shaft and a drive shaft of the electric motor. The screwed ball nut moves up and down, and the ball nut moves up and down, so that the piston mounted on the ball nut moves up and down, thereby moving the control rod connected to the piston into the core. In the control rod drive mechanism for inserting / removing, the control device provided in the electric motor includes an electromagnetic induction coil, a field containing the electromagnetic induction coil, and a rotation restricted on this field so as to be movable in the axial direction. An armature made of attached magnetic metal, a plurality of springs installed to press the armature, and a rod mounted facing the armature The rotor, the rotor and the armature are each provided with a braking device having a structure in which teeth that can mesh with each other are provided in a circumferential shape, the rotor teeth are fitted to the rotation shaft or the drive shaft, and the field is fixed. It is characterized by being installed.

Further, a stepping motor that rotates at a constant angle for each pulse is used as an electric motor, and the tooth pitch of the braking device is adjusted to the pulse angle of the stepping motor, and the tooth shape of the braking device is formed in a sawtooth shape. .

(Operation) The braking device of the present invention operates when the power is turned off and is released when the power is turned on. If the withstand pressure portion of the control rod driving mechanism is damaged and a pulling force is generated on the control rod, the braking device can operate properly. Tooth engagement is maintained. This prevents the control rod from being pulled out and allows the electric motor to drive the control rod even if the braking device cannot be released due to disconnection or the like during normal operation. That is, the tooth profile provided on the armature and the rotor is formed in a sawtooth shape, and the control rod is set so that the withdrawal side is locked with the sawtooth and the insertion side with the sawtooth is slippery. This allows the control rod to be inserted into the core even if the control device breaks down due to a coil disconnection or the like. Further, the teeth are meshed with each other by adjusting the number of teeth to the step angle of the step motor.

(Embodiment) An embodiment of a control rod driving mechanism according to the present invention will be described with reference to FIGS. The same parts as in FIG. 7 of the conventional example are denoted by the same reference numerals, and the description of the overlapping parts will be omitted. Reference numeral 28a in FIG. 1 is a braking device showing a main part of the present invention.

As shown in FIG. 1, the braking device 28a has a coil 29 mounted in a field 30 which is a main body.
When an electric current is supplied to the, an electromagnetic force is generated. The field 30 is made of a magnetic material, and moves to attract the armature 31 by strengthening the magnetic force.

The armature 31 is a disk made of a magnetic material and can be moved in the axial direction by a screw 40 and a sleeve 41, but is attached to the feed 30 so as not to rotate. At the same time, the armature 31 is pressed upward by a plurality of springs 38. The field 30 is fixed to the frame of the electric motor 13 or the bracket 26.

On the other hand, the rotor 42 is fitted to the rotating shaft 14 of the electric motor 13,
It is fixed with a nut 34. The key 35 transmits torque 7 between the rotating shaft 14 and the rotor 42. The rotor 42 and the armature 31 are provided with saw-toothed teeth 43 and 44 on the opposing surfaces as shown in FIG. 2 and FIG.
The directions of the saw teeth 43 and 44 lock the rotation of the rotor 42 in the control rod withdrawal direction, and the rotation of the rotor 42 in the control rod insertion direction is slid.

In the above structure, when the coil 29 is not energized, the armature 31 is pressed by the spring 38 while being engaged with the rotor 42 (see FIG. 4). When the coil 29 is energized, the armature 31 overcomes the spring 38 and Sucked on, armature 31 and rotor
The engagement of 42 is released (see FIG. 3).

The operation will be described based on the above configuration. First, the normal operation will be described. When the control rod 5 is inserted and withdrawn during normal operation, the control device 28a is energized, and the armature 31 is sucked over the spring 38,
The engagement between 42 and the armature 31 is released. After that, the electric motor 13 is driven. The rotation of the electric motor 13 is transmitted to the drive shaft 16 via the rotation shaft 14 and the braking device 28a, and further transmitted to the ball screw shaft 19. The rotation of the ball screw shaft 19 causes the ball nut 20 to move up and down.
The control rod 5 is inserted into or pulled out of the reactor core 3 via.

After the motor 13 is stopped, when the power to the braking device 28a is turned off, the armature 31 of the braking device 28a is pressed against the rotor 42 by the force of the spring 38. At this time, since the number of teeth of the braking device 28a is adjusted to the step angle of the electric motor 13, the phases of the teeth 43 and 44 of the armature 31 and the rotor 42 are always matched at the stop position of the electric motor 13 to ensure a sufficient meshing.

Next, a case where the pressure-resistant portion of the insertion pipe 31 or the CRD 11 is broken for some reason will be described. In this case, as described above, the internal pressure of the CRD 11 decreases, and the pressure in the reactor pressure vessel 1 acts as a force for pushing down the piston 24. Then, an attempt is made to rotate the ball screw 19 in the pulling-out direction. In this case, the armature 31 of the braking device 28a and the teeth 43, 44 of the rotor 42 are engaged, and the saw teeth 43, 44 lock the rotation of the rotor 42,
The ball screw shaft 19 does not rotate, and the position of the control rod 5 is maintained.

Also, during normal operation, if the braking device 28a cannot be released due to disconnection of the coil 29, failure of the power supply, or the like, the armature 31
The rotor and the rotor 42 remain engaged with each other, but the pulling out of the control rod is locked, but the insertion of the control rod can be driven by the power of the electric motor 13 because the saw teeth 43 and 44 slide in the sliding direction.

 According to the present embodiment, the following effects are obtained.

(1) First, even if an accident such as breakage of the insertion pipe 31 or the pressure-resistant part of the CRD 11 occurs and a phenomenon in which the control rod 5 is unnecessarily attempted to be pulled out occurs, the braking device 28 a It is possible to reliably prevent the adverse effects on the CRD 11 and to maintain the soundness and safety of the CRD 11 as well as the core 3 and the plant.

(2) Since the number of teeth provided on the armature and the rotor of the control device is adjusted to the step angle of the electromagnetic machine 13, the engagement of the teeth is guaranteed, and the reliability of the braking device is high.

(3) By forming the meshing teeth in a saw-tooth shape, the control rod can be inserted and driven even if the braking device fails, thereby improving the safety of the plant.

[Effects of the Invention] According to the present invention, the pressure-resistant part of the control rod drive mechanism should be used.
In the event of a rupture accident that causes the control rods to be unnecessarily pulled out, the control rods can be held without adversely affecting the reactor core, and the control rods can be retained even if the control device fails. Can be inserted.

Therefore, the soundness and safety of the control rod drive mechanism, the core, and the plant can be greatly improved.

[Brief description of the drawings]

1 to 4 illustrate an embodiment of a control rod driving mechanism according to the present invention. FIG. 1 is a longitudinal sectional view showing a braking device, and FIG. 2 is a relationship between an armature and teeth. FIG. 3 is a side view showing a state in which the rotor teeth and the armature teeth are floating, FIG. 4 is a side view showing a state in which the teeth in FIG. 3 are meshed, and FIG. FIG. 7 is for explaining a conventional example, FIG. 5 is a longitudinal sectional view schematically showing the inside of a reactor pressure vessel, FIG. 6 is a longitudinal sectional view showing a control rod driving structure, and FIG. FIG. 7 is a longitudinal sectional view showing the braking device in FIG. 6. 1 ... reactor pressure vessel 2 ... coolant 3 ... core 4 ... shroud 5 ... control rod 6 ... steam-water separator 11 ... CRD 12 ... CRD housing 13 ... electric motor 14 ... rotating shaft 15 Coupling case 16 Drive shaft 17 Insert piping 18 Injection port 19 Ball screw shaft 20 Ball nut 21 Roller 22 Guide tube 23 Plate 24 Piston 25 … Coupling 26… Bracket 27… Labyrinth seal 28, 28a… Braking device 29… Coil 30… Field 31… Armature 32… Pin 33… Inner driver 34… Nut 35… Key 36 … Disc 37… Friction plate 38… Spring 39… Side plate 40… Screw 41… Sleeve 42… Rotor 43, 44… Sawtooth

Claims (1)

(57) [Claims] The rotation of a motor is transmitted to a ball screw shaft via a rotation shaft and a drive shaft of the motor, and the rotation of the ball screw shaft causes a ball nut screwed on the ball screw shaft to move up and down. A piston mounted on the ball nut moves up and down as the ball nut moves up and down, whereby a control rod connected to the piston is inserted into and pulled out of the core. The control device is provided with an electromagnetic induction coil, a field containing the electromagnetic induction coil, and an armature made of a magnetic metal that is mounted on the field so that rotation is restricted and axially movable. A plurality of springs installed to press the armature; a rotor mounted facing the armature; and a rotor and the armature. The mature is composed of teeth provided circumferentially so as to be able to mesh with each other, the rotor is fitted to the rotating shaft or the drive shaft, and the field is installed on a fixed side, Control rod drive mechanism.