JPS6337912B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear reactor emergency shutdown device for urgently shutting down a nuclear reactor in a boiling water (BWR) nuclear power plant in the event of an abnormality in the reactor, and particularly to a control rod for shutting down a nuclear reactor. This invention relates to an emergency shutdown system for a nuclear reactor that facilitates emergency operation to improve reliability and prevents release of radioactive materials to the outside.

Generally, the reactor emergency shutdown system of a nuclear reactor in a boiling water nuclear power plant reduces the neutron flux of the reactor by inserting a control rod driven by a hydraulic piston into the reactor in a few seconds. Nuclear reactors are being forced to shut down urgently.

The conventional reactor emergency shutdown system that constitutes such a reactor emergency shutdown system consists of a hydraulic piston connected to a control rod that can be inserted into the reactor, a cylinder that houses this piston, and an upper cylinder of this cylinder. A drainage tank connected to the chamber, a drain valve and a bend valve connected to the reactor vessel of the reactor, and a drain valve and a bend valve installed in this drainage tank that close immediately upon receiving a reactor emergency stop signal from the reactor. The accumulator is connected to the lower cylinder chamber of the cylinder in which the reactor is operated, and operates the hydraulic piston in response to a reactor emergency stop signal from the reactor.

In a nuclear reactor emergency system with such a configuration, when an emergency stop signal for emergency insertion of a control rod is generated and the accumulator is activated, water pressurized by nitrogen gas from the accumulator is sent into the lower cylinder chamber of the cylinder. Water in the reactor vessel is pumped to drive a hydraulic piston, which
Water in the upper cylinder chamber of the cylinder is drained and sent to a drain receiving tank.

In addition, when the accumulator operates, an emergency stop signal is generated, and the drain valve and vent valve, which normally open during standby to empty the drain tank, close immediately, potentially causing radioactive contamination inside the reactor vessel. Some wastewater passes through the cylinder and reaches the wastewater receiving tank, and the wastewater is prevented from flowing further outside the wastewater receiving tank.

However, in this conventional reactor emergency shutdown system, when an emergency stop signal is generated from the reactor control system, the accumulator is activated and the drain valve and vent valve of the drainage tank are immediately closed. The water level in the tank rises in proportion to the drive of the hydraulic piston, compressing the air layer in the waste water receiving tank and increasing the tank internal pressure. This is due to an increase in the back pressure of the hydraulic piston, which acts as a force that impedes the emergency operation of the hydraulic piston.As a result, the emergency operation of the control rods cannot be performed smoothly and has the disadvantage of slow operation. .

In addition, in the conventional nuclear reactor emergency shutdown position, as described above, the capacity of the wastewater receiving tank must be increased in order to reduce the compression of the air layer within the wastewater receiving tank, which has the disadvantage of increasing the size of the tank.

It is an object of the present invention to provide a nuclear reactor emergency shutdown device which eliminates the above-mentioned drawbacks, and the object is to provide a nuclear reactor emergency shutdown device between the upper cylinder chamber and the drainage receiving tank and between the lower cylinder chamber and the accumulator. A scram valve will be installed that is opened by the reactor emergency stop signal from the reactor control system, and a timer will be installed to transmit the reactor emergency stop signal from the reactor control system to the drain valve and vent valve of the waste water receiving tank after a predetermined time. It is achieved by doing so.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a reactor pressure vessel, and a control rod 3 is inserted into a reactor core 2 within this reactor pressure vessel 1 so as to be freely insertable.

For example, if the thermal output of this reactor core 2 is 3000MW _T class, there are approximately 185 control rods 3. However, in FIG. 1, one control rod 3 is shown for illustrative purposes. Further, the hydraulic control device that drives the control rod 3 during normal operation will also be omitted.

A hydraulic piston 4 is connected to the lower end of the control rod 3, and this hydraulic piston 4 moves up and down within a cylinder 5. The upper cylinder chamber 6 of this cylinder 5 is connected to a wastewater receiving tank 8 via a scram valve 7 that opens upon receiving an emergency stop signal from the reactor control system 22. This wastewater receiving tank 8 is provided with a vent valve 9 and a drain valve 10, and the vent valve 9 and drain valve 10 are normally opened during standby to release air and wastewater 11, and the reactor control system It closes when it receives an emergency stop signal from 22. Moreover, in the present invention, this closing is particularly delayed by about 10 seconds for reasons described later.

Further, the lower cylinder chamber 12 of the cylinder 5 is connected to a scram accumulator 14 via a scram valve 13 that opens upon receiving an emergency stop signal from the reactor control system 22. A nitrogen gas cylinder 15 is connected to the scram accumulator 14, and water 16 pressurized by the nitrogen gas in the cylinder 15 is supplied to the scram accumulator 14.
enclosed within. Furthermore, the lower cylinder chamber 12
is connected to the reactor pressure vessel 1 via a ball check valve 17, and the reactor water 18 in the reactor pressure vessel 1 is supplied with water pressure by the scram accumulator 14 to the lower cylinder chamber 12 from the water pressure of the reactor water 18. When the temperature is low, the ball check valve 17 opens and the water flows into the lower cylinder chamber 12.

Further, the vent valve 9 and drain valve 10 of the wastewater receiving tank 8 are provided with a timer 19 that transmits a reactor emergency stop signal from the reactor control system 22 after 10 seconds. This timer 19 is located between the reactor core 2, the bend valve 9, and the drain valve 10 in FIG. 2, which shows the control system in the nuclear reactor emergency shutdown system of this embodiment. The reactor emergency stop signal from the reactor control system 22 is sent to a reactor emergency stop signal generator (not shown) that detects abnormally high neutron flux, abnormally high pressure in the reactor pressure vessel 1, abnormally low water level, etc. figure)
Occurs due to

The reactor emergency shutdown system having such a configuration opens the scram valves 7 and 13 in response to generation of a reactor emergency shutdown signal from the reactor control system 22 due to a reactor accident, and is activated by nitrogen gas in the nitrogen gas cylinder 15. The pressurized water 16 in the scram accumulator 14 flows into the lower cylinder chamber 12 of the cylinder 5 and pushes up the hydraulic piston 4. This upward movement of the hydraulic piston 4 causes the upper cylinder chamber 6 to
The water flows into the wastewater receiving tank 8 through the scram valve 7, and the wastewater 1 stored in the wastewater receiving tank 8 is
1 is discharged to the outside through the drain valve 10. When the amount of water flowing from the upper cylinder chamber 6 into the drainage tank 8 is greater than the amount of water flowing out through the drain valve 10, the water level in the drainage tank 8 rises and gas is discharged from the vent valve 9. Therefore, the pressure in the drain tank 8 immediately after the reactor emergency stop signal is generated is still below the vent valve 9.
Since the drain valve 10 is open, the pressure is the same as the external pressure outside the tank 8, and the pressure does not become high as in the conventional case. Therefore, no back pressure acts on the hydraulic piston 4, and the hydraulic piston 4 rises smoothly.

By the way, when the reactor emergency signal is generated, the scram valves 7 and 13 are opened, and the waste water 11 flows into the waste water receiving tank 8 as described above. There is a gap between them, through which the lower cylinder chamber 1
Also included is reactor water 18 that has entered the upper cylinder chamber 6 from 2. Since this reactor water 18 may be contaminated with radioactivity, it must be prevented from being released to the outside. There, the drainage tank 8
The drain valve 1 is discharged 10 seconds after the reactor emergency stop signal is generated by the timer 20.
0 and the vent valve 9 is closed and stopped.

The time from when the reactor emergency stop signal is generated to when the drain valve 10 and vent valve 9 close is set to 10 seconds.The reason for this is that the period from when the reactor emergency stop signal is generated to when the drain valve 10 and vent valve 9 close is set to 10 seconds. This is because, in the worst case, it will take several tens of seconds at the earliest after 13 is opened, that is, after the reactor emergency stop signal is generated.

Further, when the water pressure in the scram accumulator 14 decreases as the piston 4 rises, the reactor water 18 in the reactor pressure vessel 1 is pumped through the ball check valve 1.
7 and flows into the lower cylinder chamber 12,
The hydraulic piston 4 is further pushed up.

In this way, the control rod 3 is inserted into the reactor core 2 by the rise of the hydraulic piston 4, but the control rod 3
The insertion time required is a few seconds.

FIG. 3 shows a modified embodiment of the nuclear reactor emergency shutdown system of the present invention. The same components as in the previous embodiment are given the same reference numerals as in the previous embodiment, and the explanation thereof will be omitted, and only the differences will be explained.

In this embodiment, a radiation monitor 20 is provided in the waste water receiving tank 8. This radiation monitor 20
monitors the radiation level in the waste water 11 in the waste water receiving tank 8, and when the reactor emergency stop signal is generated and detects the required count of radiation dose from the waste water 11, it issues a valve closing signal, and the fourth As shown in the figure, the drain valve 10 and vent valve 9 are closed only when the reactor emergency stop signal from the timer 19 and the valve closing signal from the radiation monitor 20 are sent to the AND circuit 21.

As explained above, the nuclear reactor emergency shutdown system of the present invention includes a hydraulic piston connected to a control rod that can be freely inserted into a nuclear reactor, a cylinder housing this hydraulic piston, and a cylinder connected to an upper cylinder chamber of this cylinder. a drain valve and a vent valve, which are connected to the lower cylinder chamber of the cylinder, and which are connected to the lower cylinder chamber of the cylinder; In a nuclear reactor emergency shutdown system comprising an accumulator that operates a hydraulic piston in response to a reactor emergency shutdown signal from a reactor control system, there is a space between the upper cylinder chamber of the cylinder and the drainage receiving tank, and between the lower cylinder chamber and the accumulator. A scram valve that is opened by a reactor emergency stop signal from the reactor control system is provided between each of them, and a reactor emergency stop signal from the reactor control system is applied to the drain valve and vent valve of the waste water receiving tank. Since we have a timer that transmits the signal after the specified time, the reactor emergency stop signal is generated, the two scram valves open, the hydraulic piston is driven by the accumulator, and when the control rods are inserted into the reactor, the water is drained. The drain valve and vent valve of the receiving tank are closed by a timer when the reactor emergency stop signal is transmitted after a predetermined time, so the internal pressure of the drain tank is kept low for a predetermined period of time after the reactor emergency stop signal is generated, and the water pressure is reduced. The back pressure of the piston can be reduced, the control rods can be smoothly inserted into the reactor, and the reliability of the emergency shutdown system of the reactor can be improved.

In addition, since the reactor emergency shutdown device of the present invention closes the drain valve and vent valve of the waste water receiving tank after an appropriate predetermined period of time after the reactor emergency shutdown signal is generated, there is a possibility that this will occur during an emergency shutdown of the reactor. It is possible to accurately confine reactor water or the like that is contaminated with radioactivity in the drainage receiving tank, and has the effect of preventing the release of radioactive substances such as water to the outside.

Furthermore, in the nuclear reactor emergency shutdown system of the present invention, the drain is operated to keep the internal pressure of the drainage tank low while the control rods are inserted into the reactor immediately after the reactor emergency shutdown signal is issued from the reactor control system. Since the valve and vent valve are open, the capacity of the drainage tank can be reduced.

In addition, the reactor emergency stop signal and the valve closing signal from the radiation monitor can be routed to an AND circuit to close the drain valve and vent valve only when radiation levels are high. The hydraulic piston can be inserted quickly by maintaining a state in which no back pressure is applied to the hydraulic piston for a long time.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the outline of the emergency reactor shutdown device of the present invention, FIG. 2 is a block diagram showing the control system of the emergency reactor shutdown device, and FIG. 3 is a diagram showing the control system of the emergency reactor shutdown device of the present invention. FIG. 4 is a diagram showing the outline of the reactor emergency shutdown device, and FIG. 4 is a block diagram showing the control system of the reactor emergency shutdown device. 1...Reactor vessel, 2...Reactor core, 3...Control rod, 4...Hydraulic piston, 5...Cylinder, 6...
... Upper cylinder chamber, 7 ... Scram valve, 8 ... Drainage tank, 9 ... Vent valve, 10 ... Drain valve, 12 ... Lower cylinder chamber, 14 ... Scram accumulator, 19 ... Timer, 20... Radiation monitor, 22... Nuclear reactor control system.

Claims (1)

[Claims] 1 A hydraulic piston connected to a control rod that can be freely inserted into the reactor, a cylinder housing this hydraulic piston, a drainage tank connected to the upper cylinder chamber of this cylinder, and a drainage tank installed in this drainage tank. A drain valve and a vent valve that are connected to the lower cylinder chamber of the cylinder and that close in response to a reactor emergency stop signal from the reactor control system, and which are closed in response to a reactor emergency stop signal from the reactor control system. In a reactor emergency shutdown system consisting of an accumulator that operates a hydraulic piston, a reactor emergency shutdown signal is sent from the reactor control system between the upper cylinder chamber and the drainage tank of the cylinder and between the lower cylinder chamber and the accumulator, respectively. A scram valve that is opened by the reactor emergency stop signal is provided, and a time delay is provided from the time the reactor emergency stop signal is output until the time when the cooling water in the upper cylinder room flows into the wastewater receiving tank. A nuclear reactor emergency shutdown system characterized in that a timer is provided that transmits information to a drain valve and a vent valve of the waste water receiving tank.