JPS6015917B2 - Nuclear reactor water supply control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water supply control system for a reactor in a boiling water nuclear power plant, and particularly relates to improvements in response measures when abnormally high water levels occur due to transient changes in the plant, etc. .

Generally, in boiling water nuclear power plants, water supply to the reactor is controlled by a water supply control system equipped with complex interlocks.

This feed water control system normally receives three signals as input signals: the reactor water level signal, the main steam flow rate signal, and the feed water flow rate signal, and based on the calculation results of these three signals, the reactor output is adjusted to 25%.
If the water level is too high, the rotation speed of the turbine-driven water pump is controlled, and when the reactor output is below 25%, the outlet flow rate of the motor-driven water pump is controlled to maintain a constant water level in the reactor. It has become something to do. However, when a transient change occurs in the plant such as a scram due to a turbine trip, the reactor water level rapidly decreases due to the pressure increase in the reactor.・This will cause a mismatch between the set water level and the actual water level, so the water supply control system will issue a water supply increase command to each water supply pump. Therefore, the reactor water level rose rapidly after that, and finally reached an abnormally high water level (hereinafter referred to as water level L-8).
leading to. By bringing the reactor to a water level of L-8, sufficient coolant is secured and the integrity of the fuel is ensured. However, if the reactor water level rises further than this, water will overflow into the main steam pipes, so in order to prevent this, a pump trip signal is sent out when the water level reaches L-8 and all water pumps are automatically turned off. It is a tripping experience. Note that such an operation occurs not only when a transient change occurs in the plant, but also due to a failure of the water supply control system itself. Water pump is at water level L
When all the units trip due to the trip signal at -8,
All water supply will be temporarily lost. Therefore, after that
The water level in the reactor begins to fall due to steam escaping from decay heat. If this situation is left as it is, the water level in the reactor will continue to fall, eventually leading to the activation of the emergency core cooling system. Therefore, operators continuously monitor the reactor water level, and when the reactor water level drops below L-8, they usually manually start the motor-driven water supply pump and begin injecting cooling water into the reactor. It is necessary to maintain a constant reactor water level.

Moreover, the above startup operation needs to be performed accurately within a short time after a transient change or the like occurs in the reactor. However, since the starting operation is dependent on manual operation by an operator, it lacks promptness and accuracy. Furthermore, even if the startup operation is performed properly, if the subsequent operation is incorrect, there is a risk that the reactor water level will reach L-8 again and the automatic trip of the water pump will occur again. Unnecessarily starting and stopping the pump drive motor, which is a large-capacity motor, due to operational clumsiness as described above is not desirable in terms of equipment protection. The present invention was made to eliminate such problems in the conventional water supply control system and water supply system, and its purpose is to eliminate the problem when the reactor water level L-8 signal is sent due to the occurrence of transient changes in the plant, etc. It is possible to prevent water from overflowing into the main steam pipe (unless at least some of the water supply pumps are stopped), and the subsequent reactor water level can be automatically stabilized at a predetermined level without manual operation by operators; To provide a water supply control device for a nuclear reactor that can avoid unnecessary stopping and starting of the water supply pump itself even if a situation in which the reactor water level reaches the upper limit level again occurs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration, effects, etc. of the present invention will be explained in detail below with reference to embodiments shown in the drawings.

The drawing shows the water supply control system of a boiling water nuclear power plant.
1 is the main water level controller. During plant operation, this main water level controller 1 compares and calculates three signals, the reactor water level signal SI, the main steam flow rate signal S2, and the feed water flow rate signal S3, which arrive at input terminals T1, T2, and T3, and A water level control signal is sent to control the water level to the set water level. The water level control signal is input to the automatic side signal input terminals of manual/automatic switching devices (hereinafter referred to as M/A switching devices) 2A, 2B and 3A, 3B. M/A switch 2A, 2B and 3A, 3
When B is switched to the automatic side, it sends out the signal from the main water level controller 1 as an output signal, and when it is switched to the manual side, it sends out specific signals given to terminals 4A, 4B and 5A, 5B as an output signal. . The signals sent from the M/A switchers 2A and 2B are input to the valve opening degree fixing device 14, which will be described later, on the one hand, and are sent to the pump outlet via the normally closed contacts 150 and 15b2 of the relay 15, which will be described later, on the other hand. It is applied to the flow rate regulating valves 6A and 6B.

The flow rate regulating valves 6A, 68 are for adjusting the outlet flow rate of the motor-driven water supply pumps 8A, 88 driven by the motors 7A, 7B. M/A switch 3A, 3
The signal sent from B is the turbine steam amount control valve 9A,
Given to 9B. The control valves 9A, 98 are the turbine 1
This is for controlling the rotational speed of the turbine-driven water supply pumps 11A and 11B by adjusting the amount of steam supplied to 0A and 1OB. The turbine-driven water pumps 11A and 11B operate when the reactor output is 25% or more, and the motor-driven water pumps 8A and 8B operate when the reactor output is 25% or less. When the turbine-driven water pumps 11A, 11B are stopped, the motor-driven water pumps 8A, 8B are automatically started by a system not shown. By the way, the reactor water level signal SI arriving at the input terminal TI is also input to a pair of alarm setting devices 12 and 13. These alarm setting devices 12 and 13 operate when the reactor water level signal SI exhibits a value indicating the water level L-8, that is, when the reactor water level exceeds the limit level, and send out an alarm signal as a contact output. . That is, the alarm setting device 12 closes a pair of normally open contacts 12a, 12a2 when activated, and the alarm setting device 13 closes a pair of normally open contacts 13a, 13a when activated.
2 is closed. On the other hand, the valve opening degree fixing device 14
The water level control signal obtained via the A switch 2A, 2B is
This is to fix the valve opening degrees of the pump outlet flow rate regulating valves 6A and 6B to maintain the current status when even one abnormality occurs due to a power loss or the like, and at the same time, the normally open contact 1
4a.

A relay 15 connects the alarm setting device 1 between the control power bus lines V and W.
The normally open contacts 12a2 and 13a2 are connected in series, and the normally open contacts 15b, 15b are connected in series during operation.
2 is opened, and normally open contacts 15a, 15a2 are closed.

The above normally closed contacts 15q and 15Q are M/A as mentioned above.
The normally open contacts 15a, 15a2 are interposed between the switching devices 2A, 2B and the regulating valves 6A, 6B, respectively, and the normally open contacts 15a, 15a2 are interposed between the fully closed signal generator 16 consisting of a constant current source and the regulating valves 6A, 6B. They are intervening. That is, the relay 15 is an input signal switching element that switches the input of the regulating valves 6A, 6B from the M/A switch 2A, 2B side to the fully closed signal generator 16 side during operation. trip coil 17
is connected in parallel with the relay 15, and the contact 12
When a2 and 13a2 are closed, they are energized and trip the turbine-driven water supply pumps 11A and 1IB.

The trip coil 18 is connected to the pair of alarm setting devices 12 and 1.
3 and the normally open contact 14a of the valve opening degree fixing device 14 are connected between the control power bus lines V and W, and when energized, the motor Trip the driven water supply pumps 8A and 8B.

Next, the operation of the apparatus configured as described above will be explained.

First, the case where the reactor output is 25% or more will be explained.
In this case, the turbine-driven water pumps 11A and 11B are in operation. Therefore, in steady state, M/A
The rotational speeds of the pumps 11A, 11B are controlled according to water level control signals given to the regulating valves 9A, 9B via the switching devices 3A, 3B, thereby controlling water supply. When the reactor water level reaches water level L-8, the saddle point 1 of the alarm setting devices 12 and 13
2a2 and 13a2 are closed, and relay 15 and trip coil 17 are energized. Therefore, on the one hand, the turbine-driven water supply pumps 11A and 11B are stopped, and on the other hand, by closing the relay contacts 15a and 15a2, a fully closed signal from the fully closed signal generator 16 is given to the regulating valves 6A and 6B. . For this reason, the regulating valve 6A. 68 is in a fully closed state. Therefore, motor-driven water pump 8A,
Even if 8B is automatically started in response to the tripping of turbine-driven water supply pumps 11A and 11B, water is not supplied to the reactor. When the reactor water level falls below L-8, alarm setting device 1
Since the contacts 12a2 and 13a2 of 2 and 13 are opened, the relay 15 returns to its original state. Therefore, the relay contacts are switched back to their original states, and the water level control signal is applied to the regulating valves 6A, 6B via the normally closed contacts 150, 15Q. Therefore, after that, steady water level control according to the water level control signal through the M/A switch 2A, 2B is performed by the motor-driven water supply pumps 8A, 8B.
The reactor water level is stabilized at the set water level.
Next, a case where the reactor output is 25% or less will be explained.

In this case, the motor-driven water supply pumps 8A and 8B are in operation. Therefore, in steady state, M/A
The water level control signals passed through the switches 2A and 28 are applied to the regulating valves 6A and 6B via the normally closed contacts 150 and 15Q of the relay 15, respectively. For this reason, each outlet flow rate of the water supply pumps 8A, 8B is controlled according to the value of the water level control signal. now,
When the reactor water level reaches water level L-8, the alarm setting device 12,1
3 is activated, contacts 12a, 12a2, 13a, 13
Close a2.

Therefore, the relay 15 is activated and the normally closed contacts 150, 15b
2 opens, and the normally open contacts 15a, 15a2 close. Therefore, a fully closed signal from the fully closed signal generator 16 is applied to the regulating valves 6A, 6B, and the regulating valves 6A, 6B are brought into a fully closed state. Therefore, water supply to the reactor will be stopped. When the reactor water level decreases by the amount of steam flowing out due to decay heat and becomes less than L-8, the alarm setting devices 12 and 13 return to contact 12a, .
Open 12a2, 13a, 13a2. When this happens, the relay 15 is reset and the contacts return to their original states as described above, so a water level control signal is applied to the regulating valves 6A, 6B via the M/A switchers 2A, 2B. Therefore, after that, steady water level control according to the above signal is performed by the motor-driven water supply pumps 8A, 8.
B is performed, and the reactor water level stabilizes at the set water level. In addition, if for some reason the reactor water level reaches L-8 again after switching to water supply control using the motor-driven water supply pumps 8A, 88, the relay 15 will be activated again and the regulating valves 6A, 6B will be activated. When the reactor water level becomes fully closed and the reactor water level falls below L-8, the relay 15 is reset and water supply control is performed using the water level control signal from the above-mentioned aircraft.

In other words, unnecessary stoppage of the pump motor, which is a large-capacity electric motor,
You can avoid line reversals at startup. By the way, if the water level control signal is lost due to power loss or other reasons, valve control level fixing device 1
4 works to lock the relationship between the regulating valves 6A and 6B to the current state.

Therefore, at this time, as mentioned above, the reactor water level is at water level L-8.
Even if such a situation occurs and the relay 15 operates and a fully close signal is given to the regulating valves 6A, 6B, the regulating valves 6A, 6B do not become fully closed. However, in this device, when the above situation occurs, the normally open contacts 12a, 13a of the alarm setting devices 12, 13, and the normally open contact 14a of the valve relationship fixing device 14 are all closed. The trip coil 18 is energized to stop the motor-driven water supply pumps 8A and 8B. Therefore, water supply to the reactor will be stopped. In addition, the evening bottle drive type water supply pump 11A,
118 is unconditionally stopped when the water level reaches L-8, so the above operation is not performed. Note that the present invention is not limited to the above-mentioned embodiment.

For example, in the above embodiment, two motor-driven water pumps and two turbine-driven water pumps are installed, but the number of these pumps can be determined arbitrarily depending on the required water supply amount and the capacity of each pump. do it. In addition, in the above embodiment, the alarm signal of the alarm setting device was output by the opening/closing operation of the contact, but when the semiconductor switch is turned on,
, it may be output by an OFF operation. Similarly, although a relay is shown as an input signal switching element to the regulating valve, a semiconductor switch may be used instead of this relay. Of course, various other modifications can be made without departing from the gist of the present invention. As explained above, according to the present invention, when the water level in the reactor exceeds the limit level (water level L-8), the signal switching means is activated by the alarm signal from the alarm setting device, and a fully closed signal is given to the flow rate regulating valve. When the water level in the reactor falls below the limit level and the alarm signal disappears, the signal switching means returns and a water level control signal is given to the flow rate adjustment valve to return to normal water supply control operation, so the water supply pump It is possible to prevent water from overflowing into the main steam pipe without shutting down the reactor itself, and the subsequent water level in the reactor can be automatically stabilized at a predetermined level without relying on manual operations by operators. Since the feed water pump is stopped only when the reactor water level reaches the limit level or higher in an abnormal state, even if the reactor water level reaches the upper limit level again, the signal switching means will not be able to make any adjustments. It is possible to provide a water supply control device for a nuclear reactor, which eliminates the need for unnecessary stopping and starting of a large-capacity electric motor, etc. when the water supply pump itself is operated, by only changing the opening and closing operations of the valves.

[Brief explanation of the drawing]

The figure is a diagram showing a circuit configuration of an embodiment of the present invention. 1... Main water level controller, 6A, 6B...
Flow rate adjustment valve, 8A, 8B...Motor-driven water supply pump, 9A, 9B...Steam amount adjustment valve, 11A, 1
1B...Turbine-driven water pump, 14...
...Valve function fixing device, 15... Relay, 17, 18...
...Trip coil.

Claims (1)

[Scope of Claims] 1. A water supply pump that supplies water to the nuclear reactor, a flow rate adjustment valve that adjusts the flow rate of water supplied by this water supply pump, and a means for controlling the valve opening by applying a water level control signal to this flow rate adjustment valve. an alarm setting device that issues an alarm signal when the water level in the reactor is above a limit level, and a fully closed signal sent to the regulating valve in place of the water level control signal during the period when the alarm signal is being sent from the alarm setting device. a signal switching means for changing the valve opening degree to a fully closed state;
a valve opening degree fixing device that fixes the valve opening degree of the regulating valve when the water level control signal exhibits an abnormality, and a state in which the valve opening degree of the regulating valve is fixed by the valve opening degree fixing device; A water supply control device for a nuclear reactor, comprising means for stopping the water supply pump when an alarm signal is sent from the alarm setting device. 2. The water supply control device for a nuclear reactor according to claim 1, wherein the water supply pump is a motor-driven water supply pump that operates at low output of the nuclear reactor. 3. The water supply control device for a nuclear reactor according to claim 1, wherein the signal switching means has a switching element that is a relay that responds to an alarm signal.