JPS6158903A - Turbine controller for nuclear reactor - Google Patents

Abstract

PURPOSE:To prevent scram of nuclear reactor due to occurrence of a failure in a power transmission system by detecting the opening of a regulating valve and furthermore controlling the opening of a bypass valve on the basis of the opening of the regulating valve. CONSTITUTION:In the controller of a boiling water reactor turbine, a signal from the opening detector 49 of a regulating valve 4 is applied to the opening controller 50 of a turbine bypass valve 6. The bypass valve 6 is controlled in accordance with the opening of the regulating valve 4. Thereby, fluctuation in the pressure of a nuclear reactor can be prevented if the operating characteristic between the regulating valve and the bypass valve may become unbalanced because of occurrence of disturbance in a power transmission system.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a nuclear reactor turbine control device, and particularly to a turbine control device suitable for application to a boiling water nuclear reactor.

[Background of the invention]

In order to suppress pressure fluctuations in a boiling water basin nuclear reactor during load following operation, a turbine control system for a nuclear reactor is used to control the turbine control valve and the turbine bypass valve. -V] of the turbine control system of this nuclear reactor is disclosed in Japanese Patent Application Laid-Open No. 57-84395.
It is shown in the publication No. The turbine control device inputs the main steam pressure to the steam pressure regulator and controls the turbine bypass valve based on the output of the pressure fA regulator, and inputs the rotational speed of the turbine to the turbine speed controller to control the turbine. The turbine control valve is controlled based on the lower output signal of the output signals of the speed controller and the steam pressure regulator. A turbine control valve is installed in a main steam pipe that guides steam generated in a reactor pressure vessel of a boiling water reactor to a turbine. The turbine bypass valve is provided in turbine bypass piping that connects the main steam pipe and the condenser.

[Purpose of the invention]

An object of the present invention is to provide a turbine control device for a nuclear reactor that can prevent a scram in a nuclear reactor due to a failure in a power transmission system.

[Summary of the invention]

A feature of the present invention is that the opening degree of the control valve is detected and the opening degree of the bypass valve is adjusted based on the detected opening degree.

The present invention was made by studying the characteristics of conventional boiling water reactor turbine control devices.

If the amount of load loss in the power system is large, it will be necessary to quickly close the turbine control valve, so this loss amount was
As shown in FIG. 1 of the specification of Japanese Patent No. 60439, it is considered that the power load unbalance relay is used to detect the problem, and the turbine control valve is rapidly closed, and the turbine bypass valve is also rapidly closed.

However, if there is a sudden change in the power transmission system, even a small-scale disturbance that does not cause the power load unbalance relay to operate, the difference in the opening and closing characteristics of the turbine control valve and the turbine bypass valve may cause fluctuations in the reactor pressure. , which may lead to high neutron flux scrams.

Here, in a boiling water reactor, the reactor output is adjusted by the amount of voids (steam bubbles) in the reactor core, so the neutron flux responds sensitively to changes in reactor pressure. Therefore, during normal operation of the nuclear reactor, the turbine control valve is preferentially controlled by the total main steam flow rate signal based on the detected reactor pressure.

However, the load setting value is set to about 10% above the total main steam flow rate signal so that the control valve will not operate due to relatively small fluctuations in turbine speed.

Therefore, the speed request signal must be within 10% (generally, the speed adjustment rate is 100% control signal, 15% speed change, and 50H
z corresponds to 0.7.5 Hz), the turbine booster rK valve does not respond and preferentially performs pressure control.

On the other hand, for a turbine speed increase where the speed/load control signal decreases by more than 10% (that is, a frequency increase of 0.25 Hz or more), the speed/load control signal is lower than the total main steam signal and the turbine A throttling operation of the control valve is performed.

At this time, the surplus steam due to the throttling operation of the turbine control valve is transferred to the turbine bypass valve using a signal obtained by subtracting the control valve flow rate request signal and the bias value from the total steam flow rate signal, that is, the bypass valve flow rate request signal. is opened and discharged to the condenser through the bypass pipe. In this way, the turbine control valve and the turbine bypass valve work together, and the reactor pressure continues to operate stably with almost no change. The above-mentioned disturbance may occur, for example, due to an accident such as a lightning strike in the power transmission system. In such a case, the circuit breaker in the power transmission system operates and the load is dropped, causing the system frequency to rise.

Thereafter, the fault in the power transmission system is removed by the operation of the protection circuit of the power transmission system, and the frequency of the power system immediately returns to its normal value. The reason why the reactor scrams in such a case is explained below.

As shown in Figure 7, a failure occurred in the power transmission system to the extent that the power load unbalance relay did not operate, resulting in a relatively large increase in turbine speed (0,25)IZ or more), and then the system became stable again. Explain the response of #Tengshuimen nuclear power plant in the case.

As mentioned above, when an accident such as a lightning strike occurs in a power transmission system, the power transmission system breaker operates and the load is lost, causing the system frequency to rise. Thereafter, the fault is removed by the operation of the power transmission system protection circuit, and the frequency is set to a steady value.

At this time, the speed control signal becomes a negative value due to the increase in turbine speed, and the speed/load control signal also decreases from its normal value.

When the turbine speed increases by approximately 0.25 Hz, the speed/
When the level of the load control signal falls below the level of the total main steam flow signal, the low value priority circuit selects and outputs the speed/load control signal. Therefore, the opening of the turbine regulator valve is decreased based on the decrease in the speed/load control signal, and the turbine speed is decreased.

As a result, the value obtained by subtracting the regulator valve flow rate request signal from the main steam flow rate signal becomes a positive value, which exceeds the chattering prevention bias. The turbine bypass valve is then opened in response to the turbine bypass valve flow rate request signal, and the reactor pressure is controlled by the turbine bypass valve. The amount of steam a passing through the turbine control valve is referred to as the control valve flow rate, and the steam flow rate passing through the turbine bypass valve is referred to as the bypass valve steam flow rate.

After that, in the process of returning the turbine rotational speed (turbine speed) to a steady state due to fault removal on the power transmission system side, the turbine control valve opens as the speed/load control signal increases, and the turbine bypass valve closes accordingly. Tonanashi returns to normal plant operation.

In the above transient changes, if the operating characteristics of the turbine control valve and the turbine bypass valve are the same, the reactor pressure control will smoothly transition from "turbine control valve → turbine bypass valve → turbine control valve" and no pressure fluctuations will occur. do not have. but,
In reality, mechanical constraints on the turbine control valve and the turbine bypass valve cause differences in characteristics and pressure fluctuations. That is, the turbine control valve has the characteristic that the opening operation side is hydraulically controlled by a hydraulic servo mechanism, and the closing operation side is operated by spring pressure, and the opening operation is much slower than the closing operation.

On the other hand, the turbine bypass valve uses a hydraulic servo system for both opening and closing operations, and its opening and closing characteristics are almost the same. Further, the turbine bypass valve is a /G type and has better responsiveness than the turbine regulator valve.

Therefore, in the event shown in Figure 7, Figure 7 (A)
Although the regulator valve #C and the quantity control signal decrease in response to the increase in turbine speed (Fig. 7 (B)), the actual closing operation of the turbine regulator valve is slightly delayed, as seen in the delay in the decrease in the regulator valve flow rate. On the other hand, the opening operation of the turbine bypass valve follows the increase in the bypass valve flow rate request signal due to the decrease in the control valve flow rate and the request signal without a delay of about tX. This is clear from the rapid increase in the bypass valve flow rate in FIG. 7(B). For this reason, as shown in Figure 7 (C), the reactor pressure once drops slightly, but even after the opening operation of the turbine bypass valve is completed, the throttling operation of the turbine cutter valve continues and the slight pressure drop is corrected. As the turbine bypass valve is slightly throttled, the reactor pressure increases and returns to its initial value. Further, in the process of returning the turbine speed to the normal value, the turbine control valve opens, but as described above, the control valve opening operation characteristics are further delayed compared to the closing operation. At this time, the turbine bypass valve is also closed, but the bypass valve flow rate request signal does not depend on the actual response of the turbine control valve, but only follows the change in the control valve flow rate request signal.

For this reason, the turbine bypass valve is throttled even though the actual adjustment valve opening operation is not sufficient, resulting in an increase in reactor pressure as shown in FIG. 7(C).

In boiling water reactors, the reactivity is controlled by the amount of voids in the core as described above, and the behavior of neutron flux is extremely sensitive to changes in reactor pressure.

Therefore, the neutron flux fluctuates due to the reactor pressure fluctuation as described above, and there is a high possibility that the neutron flux will reach the high scram setting value as shown in FIG. 7(D).

As a scram prevention measure against such phenomena, it is possible to adjust the opening/closing characteristics of the turbine control valve or the turbine bypass valve. High-speed operating characteristics are required, and turbine control valves have limitations in terms of valve hardware, making it difficult to improve the valve body.

In the present invention, there is an imbalance in the operating characteristics of the regulator valve and bypass valve, which open and close due to turbine speed fluctuations, when a disturbance occurs in the power transmission system. Focusing on the fact that pressure fluctuations occur, this system controls the opening of the bypass valve to prevent reactor pressure fluctuations by feeding back the actual opening and closing operations of the control valve.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A turbine control device which is a preferred embodiment of the present invention applied to a boiling water nuclear reactor will be described with reference to FIG. 1, FIG. 2, and FIG.

The cooling water in the reactor pressure vessel 1 is pressurized by the recirculation pump 27 and guided to the reactor core 2 through the recirculation piping 28 and the jet pump 29, where it absorbs the heat of the fuel rods and becomes steam. The rotation speed of the recirculation pump 27 is determined by the recirculation flow rate control fic
is controlled by the position 26.

The steam is separated into saturated water and steam in a steam/water separator 25,
The saturated water returns to the reactor pressure vessel 1. Steam reaches the turbine 8 through a main steam pipe 3 in which a turbine control valve 4 is provided. The amount of steam supplied to the turbine 8 is adjusted by controlling the opening of the turbine control valve 4 . Steam discharged from the turbine 8 is condensed in a condenser 11 and returned to water, and is supplied to the reactor pressure vessel 1 again. Tarpi/8
The rotational force is transmitted to the generator 9 and converted into electrical output. Electricity generated by the generator 9 is sent to the power grid 10 1
Led.

In order to control the reactor output, the rotational speed of the recirculation pump 27 is changed to increase or decrease the flow rate of cooling water flowing through the reactor core 2.

Next, the steam flow rate supplied to the turbine 8 is determined by adjusting the opening degree of the turbine steam control valve 40 to the turbine inlet pressure (pressure detector 13
(measured at ) is controlled so that it remains constant. The main steam pressure is controlled by a steam pressure regulator 15. The steam pressure regulator 15 receives the output signal of the pressure detector 13 attached to the main steam pipe 3, the output signal of the pressure setting device 14, and the output signal of the set pressure adjustment circuit 20. Setting pressure adjustment circuit 2
0 inputs the load request signal 53. For example, when the steam pressure increases (decreases) by more than the set value as a result of increasing (decreasing) the reactor output by controlling the recirculation flow rate, the steam pressure regulator 15 outputs an output signal Ps in response to the increase (decrease) in the reactor output. do. This output signal P+ adjusts the opening degree of the regulating valve 4 so as to keep the steam pressure constant. That is, the low value selection circuit 16 selects the signal P1 as the regulating valve flow rate request signal C1. This output signal P1 is input to a function generator 48 and converted into a signal Ft. The function generator 48 also compensates for the nonlinearity of the turbine control valve 4. A deviation signal D4 between this signal F1 and the output signal of the opening detector 49 of the turbine adjustment J, 4 is transmitted to the adjustment valve servo 5. The control valve servo 5 adjusts the opening degree of the turbine control valve 4 based on the deviation signal D4. If the steam pressure further increases and the increase in steam pressure cannot be suppressed even if the turbine control valve 4 is opened, the steam pressure controller 15 opens the turbine bypass valve 6 by the function of the degree tracking controller 50. The steam flowing through the main steam pipe 3 is dumped directly into the condenser 11 via the turbine bypass pipe 12. This controls the rise in steam pressure.

The opening follow-up controller 50 will be explained based on FIG. 2. The opening follow-up controller 50 detects the signal P, the output signal of the bias 21, the deviation signal of the regulating valve flow rate request signal CL (i.e., the bypass valve flow rate request signal) Dl, and the opening detector 49 of the turbine regulating valve 4. The output signal RI and the signal P1 are input. The output signal of the opening detector 49 is transmitted to the opening follow-up controller 5.
0 is input to a function generator 52 and converted into a signal F2.

Opening degree detector 49 provided in each of the four main steam pipes 3
A signal F2 obtained by converting the output signal of each function generator 52 is added to obtain a total control valve flow rate signal D2. The signal P+, the signal of the bias 53, and the adjustment valve follow-up bypass valve flow rate request signal D3, which is a deviation signal of the adjustment valve flow rate total signal D2, are input to the high value selection circuit 51. The high value selection circuit 51 outputs a signal with a higher level among the bypass valve flow rate request signal D1 and the control valve follow-up bypass valve flow rate request signal D3 as a corrected bypass flow rate request signal H. This signal H is an output signal of the opening follow-up controller 50 and is input to the bypass valve servo 7. 4
A is the Yasugi signal CI which controls the opening degrees of the other three turbine regulator valves 4.

Here, the bias 53 is installed for the same purpose as the bias 21 for preventing chattering of the turbine bypass valve 6. However, the bias signal of the bias 53 has a high value when the change in the regulator valve flow rate request signal CI is gradual and the opening degree control of the turbine regulator valve 4 can sufficiently follow it. The bias signal of the bias 21 is also set to be slightly larger so that it is selected by the selection circuit 51.

The operation of the turbine bypass valve 6 will be explained in detail based on FIG.

Generally, there are a plurality of turbine bypass valves 6 (6a).

6b,...6n), and in normal operation, the turbine bypass valves 6a, 6b,...
Bypass valve opening bias setting device 36 so as to open in the order of 6n.
The values of a, 36b, . . . 36n are set in stages. If there are two turbine bypass valves 6,
If the total capacity is 25%, the gain/gain of the amplifier 44 is set to 200÷25=8 so that a signal of 2 valves x 100=200% is output at an input of 25%.

(When setting the bypass valve open bias setting device 36a to 0%,
200% to f-path valve open bias setting device 36b 〒2=10
Apply a 0% bias. The correction bypass valve opening request signal H1, which is the output of the opening follow-up controller 50, is 0 to 25%.
When the output of the amplifier 44 gradually changes from 0 to 200
%. As a result, first, the turbine bypass valve 6a is turned on 100% at one time. Next, the turbine bypass valve 6b starts to open and reaches 100% at the 200% signal.
(200%-100%) opening degree.

1 when the correction bypass valve opening request signal H+ changes slowly.
The input signal to the servo amplifier 37 is such that the correction ``bypass valve opening request signal H+'' and the bypass valve position signal deviation signal which is the output of the displacement detector 42 do not become large (within 5%). In this case, the deviation detector 40 does not operate and the servo amplifier 37
only works.

This causes the length valve 38 to operate and the hydraulic cylinder 39 to
operate the piston. This movement of the piston opens the turbine bypass valve 6a.

When the speed of increase in the correction bypass valve opening request signal H1 is rapid, the deviation detector 40 is activated to close the electromagnetic quick opening valve, and as in the case of the turbine control valve 4, the oil in the hydraulic cylinder 39 is suddenly removed. It becomes possible to remove it. As a result, the turbine bypass valve 6b is suddenly closed.

As mentioned above, the turbine control valve 4 is connected to the steam pressure regulator 15 which is selected by the low value selection circuit 16 during normal operation.
The opening degree is controlled based on the output signal P1. However, due to load reduction, etc., the number of revolutions of the turbine 8 (tachometer 43
(detected by) exceeds the set value output from the speed/load setting device 18, the output signal S of the turbine speed controller 17
1 is smaller than the output signal Ps of the steam pressure regulator 15, the output signal S1 is selected by the low value selection circuit 16 and becomes the regulating valve flow rate request signal CI. This signal Sl is transmitted to the control valve servo °5 via the function generator 48. The control valve servo 5 controls the opening degree of the turbine control valve 4 based on the output signal S+. In order to prevent the turbine control valve 4 from being controlled based on the output signal S1 of the turbine speed controller 17 during normal operation, the setting value of the speed wave/load setting device 18 is set when the turbine 8 is rotating at the rated speed. is set to a value corresponding to 100.5% of the turbine rotation speed. This prevents the output signal 81 of the turbine speed controller 17 from passing through the low value selection circuit 16 during normal operation, and only the output signal P1 of the steam pressure regulator 15 passes through it. When the load decreases as described above, the value of the signal S1 becomes smaller than the value of the signal P1.

During normal operation of a boiling water reactor, low value selection circuit 1
The signal c1 outputted from the displacement detector 6 is compared with the feedback signal f1 also outputted from the displacement detector 35, as shown in FIG. A deviation signal between the signal c1 and the signal f is amplified by the servo amplifier 31 and transmitted to the servo valve 32. The servo valve 32 controls the hydraulic cylinder 3 based on the deviation signal.
Activate piston 3. The turbine control valve 4 connected to the piston of the hydraulic cylinder 33 is opened and closed as the piston moves.

If the amount of load loss in the power transmission system 10 is extremely large, it is necessary to quickly close the turbine control valve 4, so the power load imbalance relay 24 detects the amount of O loss. This power load unbalance relay 24 is connected to the turbine 8
The mechanical input to the turbine is detected by the pressure detector 22 after the first stage of the turbine, and the generator load is determined by the power generation a! Current signal 23 (full wave rectification)
Detection is made by comparing the two, and the operation is performed based on the operation logic as shown in FIG. In other words, Bawa-
Load unbalance relay 24 has a large load reduction (4%
) and the load range speed is high (40%/10m5).

When the amount of load loss is extremely large and satisfies the logic shown in FIG. 4, the power load unbalance relay 24 is activated, and the electromagnetic quick-closing valve 34 provided in the line that supplies oil into the cylinder 33 is activated.

After the electromagnetic quick-closing valve 34 is closed, the oil in the hydraulic cylinder 33 is rapidly drained to quickly close the turbine control valve 4. At the same time, the no-load setting device 30 is turned on to make the signal S+ zero. Therefore, when the output signal CI of the low value selection circuit 16 becomes zero, the four turbine control valves 4 close simultaneously.

The operation of the opening follow-up controller 50 of this embodiment in the case where a disturbance occurs in the power transmission system 10, which is a small-scale disturbance that does not cause the power load unbalance relay 24 to operate and causes the rotation speed of the turbine 8 to suddenly increase. The operation will be explained based on FIG.

The turbine rotational speed detected by the tachometer 43 based on the occurrence of the above-mentioned disturbance is shown in FIG. 5(A) (FIG. 6(A)).
(period X). Therefore, as shown in FIG. 5(B), the level of the output signal S+ of the turbine speed controller 17 decreases and becomes lower than the level of the output signal Pl. At this point, the opening degree of the turbine control valve 4 is determined by the low value selection circuit 16.
It is narrowed down based on the signal SI selected in . The bypass valve flow rate request signal D+ and the bypass valve flow rate request signal D3 following the adjustment valve opening change as shown in FIG. 5(C).

The actual opening degree of the turbine control valve 4 is throttled slightly later than the control valve flow rate demand compensation signal Cs depending on the characteristics of the valve itself. Select. Therefore, the opening follow-up controller 50 is
During the period X, the signal D1 is output, and the opening degree of the turbine bypass valve 6 is controlled by the signal D+. This is exactly the same operation as a conventional control device.

Next, when the power transmission system 10 is restored and the turbine rotation speed starts to decrease as after period X in FIG.
As shown in Figure (B), as the signal S1 rises, the regulator valve flow rate request signal C1 also rises, and the opening degree of the turbine regulator valve 4 increases.

At this time, the actual opening operation of the turbine regulator valve 4 is slightly delayed compared to the rise in the regulator valve flow rate request signal C1, and as shown in FIG. 5(C), the regulator valve opening tracking bypass valve (jrC, jj
j', 5i) The request signal D3 has a higher value than the bypass non-optical fit request signal D1. The high value selection circuit 51 selects the former signal D3 and outputs it to the bypass valve servo 7.

Therefore, the rate of decrease in the opening of the turbine bypass valve 6 is equal to the rate of increase in the opening of the turbine control valve 4. In this embodiment, after the period .

FIG. 6 shows the plant response of the boiling water reactor in this example.

As shown in Fig. 61 (B), the control valve flow rate and the bypass valve flow rate change during the opening operation of the turbine control valve 4 and the closing operation of the turbine bypass valve 6.
As shown in C), almost no pressure fluctuation occurs in the reactor. Therefore, fluctuations in neutron flux are suppressed to below the neutron flux high scram setting value as shown in FIG. 6(D), and the boiling water reactor can continue operating without scram.

If no disturbance occurs in the power transmission system 10 as described above, the high value selection circuit 51 outputs the signal D1. In addition, when the power load unbalance relay 24 operates,
The phenomenon of period X in FIG. 5 occurs in an extremely short period of time, and the turbine control valve 4 is suddenly closed and the turbine bypass valve 6 is suddenly opened.

〔Effect of the invention〕

According to the present invention, even if a disturbance occurs in the power transmission system and the protection circuit of the power transmission system is activated, it is possible to prevent a nuclear reactor from scramming.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a turbine control device that is a preferred embodiment of the present invention applied to a boiling water reactor, Fig. 2 is a block diagram of the opening tracking controller shown in Fig. 1, and Fig. 3! -1: Detailed configuration diagram of the control valve servo and bypass valve servo in Figure 1, Figure 4 is an explanatory diagram of the operation logic of the power rotor unbalance relay shown in Figure 1, Figures 5 (A) to (D) is an explanatory diagram showing the operating state of the opening tracking controller in Fig. 2, and (A) in Fig. 6 is an explanatory diagram showing the operating state of the opening tracking controller in Fig. 2.
-(D) are characteristic diagrams showing changes in each state quantity of the reactor in the embodiment of FIG. It is a characteristic diagram showing 1... Reactor pressure vessel, 3... Main steam pipe, 4...
Turbine control valve, 5... Control valve servo, 6... Turbine bypass square, 7... Bypass valve servo, 8...
Turbine, 9... Generator, 11... Condenser, 12.
... Bypass pipe, 13... Pressure detector, 15... Steam pressure regulator, 16... Low value selection circuit, 17... Turbine speed controller, 24... Power load imbalance relay, 43... Tachometer, 48.52... Function generator, 50... Opening follow-up controller, 51... High value selection circuit.

Claims (1)

[Claims] 1. A control valve that adjusts the flow rate of steam generated in the nuclear reactor and guided to the turbine; and a bypass valve that adjusts the flow rate of steam that reaches the condenser on the downstream side of the turbine without passing through the turbine. , a pressure detector that detects the pressure of the steam, a rotation speed detector that detects the rotation speed of the turbine, a steam pressure controller that inputs an output signal of the pressure detector, and an output signal of the rotation speed detector. A turbine control device for a nuclear reactor, comprising: a turbine speed regulator that inputs the output signals of the steam pressure controller and the turbine speed regulator; It has a means for detecting the opening degree of the adjustment valve, and the opening control means further inputs an output signal of the opening detection means to control the opening degree of the adjustment valve and the bypass valve. A turbine control device for a nuclear reactor.