JPH0161198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control rod drive mechanism that controls the output of a nuclear reactor, and particularly to a control rod drive mechanism that can accurately position control rods and prevent them from falling.

In a boiling water reactor (BWR), reactions are controlled by multiple control rods placed within the reactor core. The control rods are inserted into and withdrawn from the reactor core by a control rod drive mechanism connected to their lower ends.

In general, high-speed emergency insertion (scram operation) of control rods is performed by opening the scram valve of the hydraulic control unit, which is connected via piping to the inlet and outlet of the control rod drive mechanism. Slow insertion and slow withdrawal (shim operation)
By opening the shim selection valve of the control rod drive mechanism, high pressure water flowing in from the outlet or inlet acts on the pressure receiving surface of the index tube, driving the control rods connected to the upper end of the index tube. It's summery.

By the way, if a control rod falls unexpectedly, it will cause a sudden increase in nuclear reactivity, and the operation of the reactor will become unstable.

However, in the conventional control rod drive mechanism,
If the shim selection valve connected to the outlet of the control rod drive mechanism fails while it remains open during slow withdrawal of the control rod, water pressure is applied to the collect finger to maintain the unlocked state. At the same time, water pressure continues to act on the index tube in the direction of pulling it out, making it difficult to prevent the control rod from falling. However, in reality, the control rod does not fall due to the activation of other safety devices.

Furthermore, in the conventional control rod drive mechanism, the collection finger (latch) is removed by hydraulic drive, and therefore a water supply pipe, a control valve, a device, etc. for removing the collect finger are required. For this reason, the number of parts for operating the collect finger increased and complicated water supply piping was required. This is undesirable from the viewpoint of reliability, cost, etc. of the control rod drive mechanism.

The present invention was made with the aim of eliminating the above-mentioned drawbacks of the conventional ones, and provides a control rod drive mechanism with a simple structure and high reliability by reducing the number of parts of the drive mechanism. be. The control rod drive mechanism according to the present invention has an opening at the upper end,
A hollow control rod drive mechanism body is provided with a high-pressure water inlet in the lower part, and the control rod drive mechanism body is arranged to be movable in the axial direction within the control rod drive mechanism body, and a control rod connecting member is attached to the upper end, and a hollow piston having a concave groove formed therein; and a hollow piston disposed slidably in the axial direction between the control rod drive mechanism main body and the hollow piston;
A hollow cover tube in which a window hole penetrating the peripheral wall is formed, and the window is arranged such that the proximal end is fixed to the control rod drive mechanism main body and the distal end is pressed against the outer periphery of the cover tube. a collect finger that is inserted through the hole and engaged with the concave groove of the hollow piston;
a driving screw shaft whose rear end is connected to a rotating means;
It is screwed onto the driving screw shaft, has a claw part on the upper end that comes into contact with the lower end of the cover tube, and has a side wall part that also serves as a rotation stopper for sliding in the axial direction along the control rod drive mechanism body. A driving body is provided with a sliding member, and has a through passage for injecting high-pressure water that communicates between the threaded shaft and the bottom of the hollow piston. and a spring member that urges the cover tube downward, which is connected to the upper end of the cover tube.

The present invention will be explained below with reference to embodiments shown in the drawings.

FIG. 1 schematically shows the inside of a reactor vessel of a boiling water reactor. Fuel assemblies 4 are arranged in a line inside a core shroud 3 in a reactor vessel 2 supported by a reactor vessel support skirt 1. ing. A control rod guide tube 5 is disposed below this fuel assembly 4, and a control rod drive mechanism housing 6 that penetrates the lower part of the reactor vessel 2 is further disposed below this control rod guide tube 5. has been done. And this housing 6
A control rod drive mechanism (not shown) inserted into the control rod guide tube 5 from below moves the control rod (not shown) housed in the control rod guide tube 5 up and down to control the reactivity of the reactor. ing.

FIG. 2 shows the control rod drive mechanism according to the present invention, and the control rod drive mechanism main body 10 has an upper opening 1.
1, and a hollow piston 13 disposed within the cavity 12 protrudes and retracts from the upper opening 11 to raise and lower a control rod (not shown). . The hollow piston 13
is equipped with a control rod connecting member 14 at its upper end, has a center hole 15 opening downward, and a sliding member 16 of a detent mechanism protruding from the outer periphery of its lower end is inserted into the empty space of the main body 10. It fits into a guide 17 of the same anti-rotation mechanism, which is provided vertically protruding inside 12, so that it can be raised and lowered without rotating. A plurality of grooves 18, 18, . Together, the hollow piston 13
Designed to prevent falls. The collect finger 19 is made of an elastic member and is biased toward the center, but is expanded and released from the groove 18 by passage of a cover tube 20, which will be described later.

The cover tube 20 is arranged so as to be able to slide on the outer periphery of the hollow piston 13,
It is biased downward by a coil spring 21 interposed between the hollow piston 13 and the upper end thereof. This cover tube 20 is formed with window holes 22, 22, . , and a position covering the groove 18.
This cover tube 20 has a protrusion 23 provided at its lower end so as to protrude outward.
Since it fits into the slit 24 formed in the sliding member 16 of the hollow piston 13, it can move relative to the hollow piston 13 by the length of the slit 24, and the cover tube 20 When is located at its lowest position, the window hole 2
2 matches the groove 18 of the hollow piston 13, and the cover tube 20 covers the groove 18 when the cover tube 20 is in its uppermost position.

A buffer member 2 is provided inside the intermediate position of the main body 10.
5 is vertically disposed via a spring 26, and this buffer member 25 comes into contact with the sliding member 16 of the hollow piston 13 that has risen, thereby stopping the movement of the hollow piston 13.

A drive shaft 27 passes through the lower end of the main body 10 via a shaft seal 28 , and a screw 29 is cut into the upper part of the drive shaft 27 . It is inserted with a gap inside. A drive body 30 is rotatably screwed into the screw 29 of the drive shaft 27.
Since the sliding member 31 protruding from this driving body 30 is fitted into the guide 17, this driving body 30
can be raised and lowered as the rotating shaft 27 rotates. When this driving body 30 is raised, the hollow piston 13 and the cover tube 20
It is designed to push these up by coming into contact with the
At this time, the claw 32 of the driving body 30 first contacts the cover tube 20 and pushes the cover tube 20 up against the hollow piston 13, closes the groove 18 of the hollow piston 13, and then pushes both up together. ing.

A conduit 33 is attached to the main body 10 that guides high-pressure water, which serves as a driving source when a control rod is inserted into the main body 10 in a high-speed emergency manner, into the main body 10. passage 34 formed in
The hollow piston 13 is guided into the center hole 15 of the hollow piston 13 by pressing the bottom surface 35 of the center hole 15, which is a pressure receiving surface, to raise the hollow piston 13. A portion of the high-pressure water introduced into the main body 10 from the pipe line 33 leaks into the reactor core through the upper opening 11 of the main body 10.

The shape of the groove 18 of the hollow piston 13 is such that when the collect finger 19 is fitted into the groove 18, the collect finger 19 will not come off even if the hollow piston 13 is lowered;
When the collector finger 19 is raised, the collect finger 19 comes out of the groove 18.

Next, the operation of the above-described embodiment will be explained.

First, slow insertion and withdrawal (shim operation)
The hollow piston 13 is moved up and down via a drive body 30 that moves up and down as the drive shaft 27 rotates. At this time, the claw 32 of the drive body 30 comes into contact with the cover tube 20, so the cover tube 20 rises relative to the hollow piston 13 and closes the groove 18 of the hollow piston 13.
8 is not fitted with the collect finger 19, so that the hollow piston 13 can freely move up and down. This situation is shown in FIG.

Further, high-speed emergency insertion (scram operation) is performed by injecting high-pressure water into the main body 10 from the conduit 33.
Most of this high pressure water is in the passage 3 of the driving body 30.
4, the pressure receiving surface 35 of the hollow piston 13 is pressurized into the center hole 15 of the hollow piston 13, and the hollow piston 13 is rapidly pushed up. As a result, the hollow piston 13 and the cover tube 20 are separated from the driving body 30, and the cover tube 20 is moved away from the spring 2.
1, the hollow piston 13 is lowered relative to the hollow piston 13, and the groove 18 of the hollow piston 13 is opened. Therefore, as the hollow piston 13 rises, the collect finger 19 fits into the groove 18 of the hollow piston 13.
Since the hollow piston 13 is removed from the groove 18, there is no problem in raising the hollow piston 13. When the sliding member 16 of the hollow piston 13 comes into pressure contact with the buffer member 25 and the hollow piston 13 stops rising, the collect finger 19 fits into the groove 18 of the hollow piston 13, as shown in FIG. The hollow piston 13 is prevented from falling.

To release the hollow piston 13 from being held by the aforementioned collect finger 19, the drive shaft 27 is rotated to raise the drive body 30.
contacts the hollow piston 13 and cover tube 20. Then, the cover tube 20 is raised by the claw 32 of the driver 30, and the collect finger 19 is expanded to close the groove 18 of the hollow piston 13. Therefore, when the drive shaft 27 is rotated to lower the drive body 30, the collect finger 19 can no longer fit into the groove 18 of the hollow piston 13, so the hollow piston 13 follows the drive body 30. descend.

As described above, the control rod drive mechanism according to the present invention includes a cover tube that is slidably disposed around a hollow piston that moves up and down as the drive body moves up and down, and a drive body that comes into contact with the cover tube. Since the collect finger opens and closes the groove of the hollow piston into which it fits, the collect finger fits into the groove, allowing accurate positioning of the control rod, and has the excellent effect of reliably preventing the control rod from falling. play. Furthermore, since a hydraulic drive mechanism is not used as the operating mechanism for the collect finger (latch) as in the past, the number of parts of the drive mechanism can be reduced and a highly reliable control rod drive mechanism can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the outline of the inside of a reactor vessel of a boiling water reactor, FIG. 2 is a vertical sectional view showing an embodiment of the control rod drive mechanism according to the present invention, and FIGS. 3 and 4 are respectively FIG. 3 is a partially omitted vertical cross-sectional view showing the operating state of the control rod drive mechanism of FIG. 2; 2... Reactor vessel, 4... Fuel assembly, 5... Control rod guide tube, 6... Control rod drive mechanism housing, 1
0... control rod drive mechanism body, 12... internal space,
13...Hollow piston, 18...Groove, 19...Collection finger, 20...Cover tube, 22
... window hole, 27 ... drive shaft, 30 ... drive body.

Claims (1)

[Scope of Claims] 1. A hollow control rod drive mechanism body having an opening at the upper end and a high-pressure water inlet at the lower part, and a control rod drive mechanism body disposed so as to be movable in the axial direction within the control rod drive mechanism body. A control rod connecting member is attached to the upper end, and a concave groove is formed in the outer circumferential wall, the upper wall being perpendicular to the axial direction, and the lower inclined wall being formed diagonally downward. A hollow piston with a closed upper end is arranged to be slidable in the axial direction between the control rod drive mechanism main body and the hollow piston, and a window hole that can match the groove of the hollow piston passes through the peripheral wall. A hollow cover tube is formed, and the proximal end is fixed to the control rod drive mechanism body, and the distal end is pressed against the outer periphery of the cover tube, and is inserted through the window hole. a collect finger that can be engaged with the groove of the hollow piston; a drive screw shaft whose tip end is inserted into the hollow piston with a space between the ends thereof and whose rear end is connected to a rotating means; and a drive screw. The cover tube is screwed onto the shaft and is mounted on the upper end so that the cover tube is offset with respect to the hollow piston so that the concave groove of the hollow piston that normally abuts the upper end does not coincide with the window hole of the cover tube. The cover tube has a claw portion that comes into contact with the lower end of the cover tube, and the side wall portion is provided with a sliding member that also serves as a stopper for sliding in the axial direction along the control rod drive mechanism main body, and the screw A drive body is formed with a through passage for high-pressure water injection that communicates between the shaft and the bottom of the hollow piston, and a cover tube whose upper end is connected to the hollow piston and whose lower end is connected to the upper end of the cover tube is attached below. a spring member that presses the hollow piston and the lower end of the cover tube away from the drive body by high pressure water injected from the high pressure water inlet during emergency insertion, and the spring member is moved relative to the hollow piston so that the window hole and the groove match, and when the hollow piston reaches an emergency insertion end position, the tip of the collect finger engages with the groove. Features a control rod drive mechanism.