JPS5942838B2 - Nuclear reactor control rod drive mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control rod drive mechanism for a nuclear reactor that enables high-speed scram and fine adjustment of control rods that adjust and control the output of a boiling water reactor.

In a nuclear reactor, the reactivity of the reactor is controlled by control rods placed within the reactor core.

The control rod performs a vertical positioning operation using a hydraulically driven locking piston type control rod drive mechanism, and also performs a scram operation with priority over other signals.

That is, as shown in Fig. 1, to insert a control rod, the insertion selection valve a is opened, pressure from the drive header is applied to the lower surface of the drive piston b, and the upper surface passes through the inner core of the index tube C and is ejected as a scram. A control rod d connected to the water header and connected to the upper end of the index tube C is inserted.

The position of this control rod is detected by a series of sealed glass-sealed switches spaced 75 mm apart in the tube inside the fixed piston tube e and by a permanent magnet built into the drive piston b.

This control rod drive mechanism has the following problems because the driving force for both the positioning operation and the scram operation is provided by the hydraulic header.

First, positioning operations require complicated control using a hydraulic system, and it takes time to complete a series of operations.

In addition, the positioning adjustment accuracy is rough, making it impossible to finely adjust the reactor output using a single control rod, which greatly affects the economic efficiency of nuclear fuel.

Next, regarding scram operation, a reactor pressure header introduction pipe and drain piping are required for scram using reactor pressure, and measures against exposure to radiation during maintenance due to reactor water reciprocating within the control rod drive mechanism are required. This is a serious problem.

In addition, the scram speed is not sufficient for control rod movement alone; in the event of a turbine trip accident, it may be necessary to close the main steam valve and open the pressure reducing valve at the same time as the control rod drive mechanism scrams.

High-speed scrum is desired.

Furthermore, in order to arrange the necessary number of control rod position indicating detectors in the longitudinal direction of the control rod drive mechanism, they are inserted all at once into the pipe and inserted into the center of the control rod drive mechanism from the bottom.

This method has disadvantages in that it takes up space, that even if one detector is damaged, the entire pipe must be pulled out and replaced, and that the position M of each individual detector cannot be adjusted.

The present invention addresses the above-mentioned problems and provides a control rod drive mechanism that is capable of fine adjustment and high-speed scram in a limited space, and that is equipped with a position detection device that can particularly track the performance of the scram.

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 shows the relative positional relationship of the pressure vessel 1, fuel 2, control rod guide tube 3, and control rod drive mechanism housing 4, which are the main parts of a boiling water reactor plant.

The control rod drive mechanism is inserted into the housing 4 from below and connected to a control rod housed in a control rod guide tube 3 located outside the reactor atmosphere.

FIG. 3 shows the main parts of the control rod drive mechanism of the present invention.

A piston tube 5 is arranged along the inner wall of the housing 4,
A cylinder tube 7 is provided with a gap 6 therein.

The cylinder tube 7 accommodates an index tube 9 having a drive piston 8 at its lower end.

The lower end of the cylinder tube 7 is closed, and the drive piston 8
A drive header pressure water introduction hole 10 opens in the lower cylinder tube γ.

The back of the drive piston 8 communicates with the gap 6 and the scram discharge water header (communication hole 11).

A ball screw 12 is inserted into the index tube 9.

This ball screw 12 is supported by a bearing 13, passes through the lower end of the cylinder tube 1, and is connected to an electric motor or the like to provide reversible rotation.

14 indicates a seal at the penetration portion.

Further, a nut 15 that engages with the ball screw 12 is set below the drive piston 8.

The nut 15 is non-rotatably guided on the inner wall of the cylinder tube 1 by a guide key or the like.

An uncoupling operating rod 16 for uncoupling the upper end of the index tube 9 from the control rod passes through the inner center of the ball screw 12.

A magneto 1-17.17 is embedded in the outer periphery of the drive piston 8 and the nut 15.

On the other hand, an indicator pipe 18 fixed to the cylinder tube 7 is provided in the gap 6 to indicate the position (see FIG. 4).

The contents of the indicator pipe 18 are shown in FIG.

A thin wire 19 such as a piano wire runs inside the pipe, and a reed switch 21 as a detector is fixed to this wire with a stopper grip 20.

22° 22 is the electrical wiring of the reed switch 21.

The inside of the indicator pipe 18 is gas-sealed with the same gas as the gas filling the reed switch 21, and a plurality of the indicator pipes 18 are arranged around the outer periphery of the cylinder tube 7.

The present invention is constructed as described above, and its operation will be described next.

The control rod drive mechanism performs two main movements: positioning operation and scram operation.

In the positioning operation, the rotational movement of the drive unit is transmitted to the ball screw 12, thereby moving the nut 15 up and down.

The drive piston 8 and index tube 9 on the upper surface of the nut 15 move up and down together with the nut 15, thereby driving the control rod.

Fine adjustment is possible because the displacement is performed in the axial direction using a screw.

In the scram operation, a valve is opened by a signal, and when the valve is opened, water pressure pushes up the drive screw, rapidly inserting the control rod.

At this time, while the drive piston leaves the nut 15,
During this time, the nut 15 is gradually raised by the drive of the ball screw 12 and stopped at a predetermined position.

In both of the above two operations, the drive piston 8 and the nut 15
The magnets 17, 1γ attached to the rod actuate the reed switch 21 in the indicator pipe 18, allowing the position and movement status of the control rod to be known.

The installation and removal of the reed switch 21 from the indicator pipe is carried out using a thin wire 19.

Adjustment of the installation position is also performed using this thin line 19.

The control rod drive mechanism of the nuclear reactor in this example uses a drive system using a ball screw nut, which enables fine adjustment of positioning, and by making the position indicating device more compact, By cleverly arranging the piston tube in the housing, it is possible to perform high-speed scram using water pressure in a limited space without changing the size of the conventional housing.

The safety of the nuclear reactor is sufficiently maintained, and the reactor output can be finely adjusted, greatly improving the economic efficiency of nuclear fuel.

In addition, the indicator pipe used for the position indicating device is a thin tube, which contributes to the above-mentioned space saving, and it can be set individually, allowing the reed switch to be replaced as a single unit, and the piano wire supports the detector. It is possible to set an accurate detection position and is effective in vibration resistance.

Additionally, by filling the interior with gas, the reed switch can still operate even if the glass seal is damaged.

This is a highly reliable control rod drive mechanism, which is a unique feature that can be expected to improve the operating rate of the entire reactor.

As explained above, the present invention accommodates a hydraulically driven drive piston and an index tube connected above the piston and connected to the lower end of a control rod in a cylinder tube provided in a housing, and also accommodates a hydraulically driven drive piston and an index tube connected to the lower end of a control rod in the cylinder tube. A ball screw is inserted through the drive piston and the lower end of the cylinder tube, connected to a drive source such as an electric motor, and is reversibly rotated by the drive source, and is engaged with the ball screw to guide the cylinder tube in a non-rotatable manner. A nut is placed in contact with the lower surface of the drive piston, a magnet is embedded in the outer periphery of the drive piston and the nut, and multiple indicator pipes are placed in the gap between the cylinder tube and the piston tube installed on the outer periphery of the cylinder tube. ,
The indicator pipes above are filled with gas, and reed switches are placed inside each indicator pipe, making it possible to fine-tune the positioning of the control rods, and even perform high-speed scrams using water pressure in limited spaces. Become.

Therefore, there are advantages in that the reliability of the entire nuclear reactor is improved and its operating rate is also improved.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing a conventional control rod drive mechanism, Fig. 2 is a layout diagram inside a nuclear reactor showing the installation position of the control rod drive mechanism,
FIG. 3 is a longitudinal cross-sectional view showing the main parts of the mechanism of the present invention, FIG. 4 is an enlarged cross-sectional view showing the arrangement position of the indicator pipe, and FIG. 5 is a vertical cross-sectional view of the same. 1... Reactor pressure vessel, 2... Fuel,
Meter: control rod guide tube, 4: control drive mechanism housing, 5: piston tube, 6:
...Gap, 7...Cylinder tube, 8
... Drive piston, 9 ... Index tube, 12 ... Ball screw, 15 ...
...Natsuto, 17,17...Magnet, 1
8... Indicator pipe, 21...
·Reed switch.

Claims (1)

[Claims] 1 A cylinder tube provided in the housing accommodates a hydraulically driven drive piston and an index tube connected above the piston and connected to the lower end of the control rod,
A ball screw is inserted into the index tube, passes through the drive piston and the lower end of the cylinder tube, and is connected to a drive source such as an electric motor, and is reversibly rotated by the drive source. A non-rotatably guided nut is provided in contact with the lower surface of the drive piston, a magnet is embedded in the outer periphery of the drive piston and the nut, and a plurality of indicators are installed in the gap between the cylinder tube and the piston tube installed on the outer periphery of the nut. A control rod drive mechanism for a nuclear reactor, characterized in that pipes are arranged, gas is sealed in the indicator pipes, and reed switches are arranged inside each indicator pipe.