JPH0566557B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a boiling water nuclear power plant (hereinafter referred to as a BWR plant) whose purpose is to control the water level in a nuclear reactor pressure vessel (reactor water level) to a constant level. (abbreviated as ) water supply control device.

[Background of the invention]

Conventionally, in the feed water control system of a BWR plant, the methods for controlling the feed water flow rate include single-element control that uses the reactor water level signal as an input, and inputs measurement signals of the feed water flow rate and main steam flow rate in addition to the reactor water level signal. There is a three-element control system that is used as a control, and the latter is used in normal output operating conditions.

According to this three-element control method, the reactor water level can be sufficiently controlled to the target value when a relatively gradual transient change occurs. However, when reactor pressure, recirculation flow rate, and reactor output suddenly change, such as when an abnormality occurs, it may not always be possible to stably control the reactor water level.

In order to improve this point, there are the following systems that improve the quick response of the water supply control system.
In other words, in addition to the above three elements, the measured value of the recirculation pump flow rate is input (Japanese Patent Application Laid-open No. 55-109998),
One that takes the measured value of the reactor pressure as input (Japanese Patent Application Laid-Open No. 1983-1999)
-109999) etc. According to these prior art techniques, water level control characteristics are improved when reactor pressure and recirculation flow rate suddenly change. However, it is not possible to improve water level control characteristics in the event of erroneous control rod insertion or selective control rod insertion due to plant interlock, which may occur during operation. This is because the recirculation pump flow rate does not change when the control rods are inserted, and the reactor pressure is controlled by the pressure control system, so the effect of control rod insertion does not directly appear on the reactor pressure. by.

Therefore, in these conventional techniques, since the water level fluctuates greatly during rapid control rod insertion, there is a possibility that a scram due to a low water level or a turbine trip or scram due to a high water level may occur. For this reason, a large disturbance is inadvertently applied to the plant, which may adversely affect the health of the equipment and may reduce the plant operating rate due to the occurrence of scram.

[Purpose of the invention]

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and improve the water supply control characteristics during sudden insertion of control rods, thereby preventing the spread of abnormal disturbances occurring in a BWR plant, and The aim is to improve plant operation rates.

[Summary of the invention]

In order to achieve the above object, the present invention provides a water supply control system that controls the reactor water level, which is the water level in the pressure vessel of a boiling water reactor, to a fixed value to a target value, based on the measured value of the reactor water level. A reactor feed water control device that automatically switches between single-element control that controls the flow rate of water feed into the pressure vessel and three-element control that controls based on measured values of the reactor water level, feed water flow rate, and main steam flow rate. , the feed water flow rate exceeds the main steam flow rate, and the reactor water level is below a reference water level,
When the reactor water level is decreasing, the single-element control is performed, and in other cases, the three-element control is performed.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples. FIG. 1 is a block diagram showing the configuration of a water supply control device according to an embodiment. As shown, BWR
In the plant, steam generated in a reactor core 2 within a pressure vessel 1 is guided to a turbine 4 via a main steam pipe 3. The steam passing through the turbine 4 is condensed in a condenser 5, and then sent to a condensate pump 6 and feed water pumps 7 and 8.
The pressure is increased, and water is again injected into the pressure vessel 1 via the water supply pipe 9. The water pump has turbine 1
a turbine-driven water pump 7 driven by 0;
and a motor-driven water supply pump 8 driven by a motor. The flow rate of these water supply pumps is determined by a control valve 12 that increases or decreases the amount of steam guided to the turbine 10 based on a signal from a water supply control device 11, or
It is controlled by adjusting the valve opening degree of the water supply adjustment valve 13 provided on the discharge side of the motor-driven water supply pump 8. The feed water control device 11 of this embodiment includes a flow meter 141 that measures the main steam flow rate _WMS , a feed water flow rate
Signals from the flow meter 142 that measures W _FW and the water level meter 15 that measures the reactor water level are used as inputs.

As shown in the figure, in the device of this example, the water supply flow rate is
The measurement signals of W _FW and main steam flow rate W _MS are sent to adder 1.
61 and their difference is calculated. After the signal is converted into a water level equivalent signal by the calculator 17, it is led to the switch 18. This switch 18 is turned ON/OFF using the mismatch between the feed water flow rate and the main steam flow rate (W _FW - W _MS ) and the water level signal L.
It will be turned off. When the switch is ON, the water level equivalent signal is led to the adder 162, added to the water level signal, and then input to the adder 163. On the other hand, when the switch 18 is OFF, only the water level signal is input to the adder 163.

The adder 163 calculates the difference between this input signal and the water level target value from the water level setter 19, and the difference signal is input to the proportional integrator 20. The proportional integrator 20 outputs the water supply operation amount to the control valve 12 or the water supply adjustment valve 13 .

FIG. 2 is a circuit diagram showing the functions of switch 18. In the figure, 211, 212, and 213 are comparators that output a "1" signal when the input signal is larger than the value set at the reference signal terminal, and output a "0" signal when it is smaller. 221, 22
2,223 is a NOT gate. 24 is an AND gate, 25 is an OR gate, and 23 is a differential circuit.

As described above, the switch 18 receives the feed water/main steam mismatch signal (W _FW - W _MS ) and the water level signal, and turns OFF when the following conditions are met.

W _FW −W _MS ＞0 ……(1) LL _Set ……(2) dL/dt0 ……(3) Here, L _Set is the reference water level determined in advance by analysis using the reactor transient analysis program, etc. . From (1), (2), and (3), this switch means that the mismatch between the feed water and main steam flow rates is positive, the reactor water level is below the reference water level, and the time differential value of the reactor water level is zero. It can be seen that it is turned off only in the following cases. On the other hand, if any one of conditions (1), (2), and (3) does not hold, the switch is turned ON.

FIG. 3 is a diagram showing the effects of the device according to this embodiment, and shows the plant response during rapid insertion of control rods when using the conventional three-element control device and the device according to this embodiment. . When the control rods are inserted, the main steam flow rate W _MS sharply decreases because the reactor power decreases. Therefore, the mismatch between the feed water and main steam flow rates (W _FW - W _MS ) becomes a positive value. For this reason, 3
In the element control device, the water level equivalent signal due to this mismatch becomes positive (this acts in the direction of decreasing the water supply flow rate), and despite the decrease in the reactor water level,
A water supply flow rate reduction request signal is temporarily output. As a result, the reactor water level drops significantly as shown in the figure.

On the other hand, in the device of this example, the feed water/main steam mismatch (W _FW - W _MS ) becomes positive and the reactor water level falls below the reference water level L _Set , so while the water level is falling, (That is, while the time differential value of the water level is less than or equal to zero), single-element control is performed using only the reactor water level signal as the control input. Therefore, since the feed water/main steam flow rate mismatch (W _FW −W _MS ) is positive, a positive water level equivalent signal (acting in the direction of decreasing the feed water flow rate) is no longer input to the proportional integrator. As a result, a request to increase the water supply flow rate is output when the reactor water level decreases, and the width of the decrease in the reactor water level becomes smaller as shown in the figure. Therefore, there is an increased possibility of avoiding scrams caused by low water levels.

Note that the apparatus according to this embodiment can also be easily realized by a computer control method using a process computer.

FIG. 4 is a circuit diagram showing the functions of a switch for switching between three-element control and single-element control used in the device according to the second embodiment. Here, the configuration of this device is exactly the same as that of the device according to the first embodiment.

In the figure, 214 and 215 are comparators, 22
4,225 is NOT gate, 241,242 is
AND gate, 251 is OR gate. As shown in the figure, in this switch, the feed water/main steam flow rate mismatch (W _FW - W _MS ) is positive, the water level L is below the value L' _Set determined in advance by analysis, and the control rod The signal related to rapid insertion (scram signal or selective control rod insertion signal) is “1”
The switch is turned “OFF” only when
state. According to this device, when a control rod is rapidly inserted, a positive water level equivalent signal (which acts in the direction of reducing the feedwater flow rate) that is generated due to a mismatch between the feedwater and main steam flow rates is input to the proportional integrator. It becomes possible not to do so. As a result, the same effect as the device of the first embodiment can be obtained at the time of scram or selective control rod insertion.

〔Effect of the invention〕

As described above, according to the present invention, water level control characteristics are improved when rapid insertion of control rods occurs in a BWR plant. As a result, it is possible to improve the plant operation rate by preventing an adverse effect on the health of the plant's component equipment and avoiding scrams caused by water level fluctuations. Therefore, the use of such a water supply control device has a significant effect on improving safety and economy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a device that is an embodiment of the present invention, Fig. 2 is a circuit diagram showing the functions of a switch included in the device that is an embodiment, and Fig. 3 is an effect of the device that is an embodiment of the invention. FIG. 4 is a circuit diagram showing the functions of the switch used in the device according to the second embodiment. DESCRIPTION OF SYMBOLS 1...Pressure vessel, 2...Reactor core, 3...Main steam pipe, 4...Turbine, 5...Condenser, 6...Condensate pump, 7...Turbine-driven water supply pump, 8...
Motor-driven water supply pump, 9... Water supply pipe, 10...
Turbine, 11... Water supply control device, 12... Adjustment valve, 13... Water supply adjustment valve, 141, 142... Flow meter, 15... Water level gauge, 161, 162, 163
... Adder, 17 ... Arithmetic unit, 18 ... Switch, 19 ... Water level setter, 20 ... Proportional integrator,
211, 212, 213, 214, 215... Comparator, 221, 222, 223, 224, 225
...NOT gate, 23... Differential circuit, 24,2
41,242...AND gate, 25,251...
...OR gate.

Claims (1)

[Claims] 1. A water supply control system that controls the reactor water level, which is the water level in the pressure vessel of a boiling water reactor, to a target value at a fixed value,
A single-element control that controls the flow rate of water supply into the pressure vessel based on the measured value of the reactor water level, and a three-element control that controls the flow rate of the water supply into the pressure vessel based on the measured values of the reactor water level, the feed water flow rate, and the main steam flow rate. In a reactor feed water control device that automatically switches the flow rate, if the feed water flow rate exceeds the main steam flow rate, the reactor water level is below a reference water level, and the reactor water level is decreasing, the single element control is performed. ,
In other cases, the reactor water supply control device is characterized by the three-element control.