JPS61159198A - Load follow-up controller for boiling water type nuclear power plant - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a load following control device for a boiling water nuclear power plant, and in particular to an Im! This invention relates to a load following control device for a water type nuclear power plant.

[Technical background of the invention and its problems]

In recent years, as the proportion of nuclear power plants in the electric power system has increased, there has been an increasing need to switch the operation of nuclear power plants from conventional rated base load operation to load following operation.

In general, electricity demand has large fluctuations depending on the season, daytime, night, etc., as well as small fluctuations at all times. On the supply side, power plants control their electrical output using the so-called grid automatic frequency control system.
l(AFC) is being performed.

Therefore, if nuclear power plants are to increase their supply share in the power system in the future, in addition to daily output adjustment operation that corresponds to each daytime and nighttime power demand, automatic frequency control operation of the power system at night will be necessary. It becomes necessary. This is because thermal power plants, which have traditionally been responsible for automatic frequency control of the power system, stop operating in response to the drop in power demand at night, and the output that participates in automatic frequency υ control of the power system is reduced. This is because the number of adjustment teeth decreases.

FIG. 6 shows an example of allocating output control on the power plant side with respect to such load fluctuations in the power system.

In other words, the vertical axis shows the magnitude of the load fluctuation, and the horizontal axis shows the period of the load fluctuation. For load fluctuations that have a longer period than fluctuation period B (for example, about 15 minutes) and a larger fluctuation range, Appropriate daily output adjustments are made at each power generation plant that receives a base load signal (DPC signal) from a central power dispatch center (not shown) of the power system. This is described in detail in ``Load Following Automation Device for Nuclear Power Plant'' (Japanese Patent Laid-Open No. 55-20404), for which the applicant of this patent has already filed a patent application. In addition, regarding load fluctuations from fluctuation period A (for example, about 20 seconds) to the same day,
Normally, at the central power dispatch center of an electric power system, the required output adjustment valve is calculated by automatic control@location, and this is distributed to the required power plants that share the frequency l1IIIl in the grid in a uniform ratio, and automatic frequency control is performed. signal (hereinafter referred to as AF
C signal). Each power plant that receives this AFC signal adjusts the furnace output based on the load command value of this signal. Regarding this automatic frequency control (AFC) device for boiling water type nuclear power generation plants, for example, the present patent applicant has filed a patent application [Output control device for boiling water type nuclear power generation plants (published in Japanese Patent Application Laid-Open No. 59-54997). ).

As for the high frequency components below the variable layer jllA,
Each power plant operates by so-called governor-free operation, which controls the opening of the turbine artificial governor valve (main steam control valve). This governor-free operation compares the turbine generator rotation speed with a set value, feeds back the deviation to the turbine, and controls the turbine artificial governor valve (
This is to control the opening of the main steam control valve, but conventional nuclear power plants did not perform such governor-free operation. However, due to the above-mentioned circumstances, governor-free operation is now required even in nuclear power plants. Furthermore, when performing this governor-free operation, it is desirable that cooperation with automatic frequency control (AFC) operation be sufficiently considered.

By the way, the characteristics of governor-free operation are that it targets load fluctuations with a relatively short fluctuation cycle as shown in Fig. 6, and at the same time, the fluctuation range is relatively small, and the required output adjustment valve is small. Therefore, in boiling water nuclear power plants, when performing governor-free operation by utilizing the inertia of the reactor system, such as the mass of fluid in the reactor pressure vessel and main steam pipe, and the inertia of internal energy, it is not always necessary to adjust the reactor output. do not need.

Figures 7 and 8 show cases in which the main steam flow rate to the turbine increases or decreases for a short time without adjusting the output by controlling the recirculation flow IN or control rods in a boiling water nuclear power plant. reactor pressure (phantom/ci)
It is a graph showing the response of and thermal output (% rating), respectively. Main steam flow rate (%) to the turbine as shown in Figure 7
If the reactor pressure is increased by a small amount and for a short period of time, the reactor pressure will increase by 2.
Next, ttb decreases linearly. However, the thermal power in the core remains largely unchanged initially. This indicates that the reduction in reactor pressure has little effect on thermal output. Furthermore, on the contrary, as shown in Figure 8, even when the main steam flow (m<%) to the turbine is reduced by a small amount and for a short time, the reactor pressure increases in a quadratic curve. However, the thermal output hardly changes at the initial stage, indicating that a decrease in reactor pressure has little effect on the thermal output.

Therefore, from the above, the fluctuation period of load fluctuation is relatively short, for example, about 20 seconds or less, and
If the range of variation is small, governor-free operation can be performed using the inertia of the reactor system without causing large fluctuations in the thermal output of the reactor. That is,
In general, in boiling water nuclear power plants, turbine steam 2
1! If the amount, or load, is increased, the reactor pressure will decrease and steam bubbles (voids) in the reactor core will increase, and the negative reactivity effect of these steam bubbles will cause a reverse response in which the reactor output will decrease. It was confirmed that such reverse responses do not need to be taken into account if the load fluctuations are limited to short-term load fluctuations.

However, as shown in FIG.
) When it is around the boundary A with the operating region, an inverse response of the neutron flux is observed. Although this inverse response does not indicate an inverse response of the reactor's thermal output (because the heat flux transferred from the fuel rods to the core coolant is delayed by a time constant of about 6 seconds, for example, compared to the neutron flux), In the case of operation near the rated output, when combined with noise specific to neutron flux, it can cause false alarms due to high neutron flux, for example. In addition, in automatic frequency tit (AFC) operation,
Before controlling the steam flow rate, the reactor output was controlled by AFC.
Since control is often performed by signals, the occurrence of a reverse response of the neutron flux in the governor-free operating region complicates the response in the transition region to the automatic frequency control operating region. Therefore, in such cases, it is desirable to keep the neutron flux constant during governor free operation.

By the way, when a power generation plant is operated to follow the load based on the load command value of the OPC signal or AFC signal transmitted from the central dispatch center, the load setting device must be manually operated according to this load command value, or the load setting device must be operated in accordance with the load command value. Simply replacing the output with the load command value requires constant monitoring of the load command value and the value of the generator output, and the burden on the plant operator will not be reduced.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and the load of the turbine generator II output is automatically controlled by the load command value of the automatic frequency control signal (AFC signal) and base load signal (DPC signal) from the central power dispatch center. Load tracking for a boiling water nuclear power plant where the turbine generator output can automatically and stably follow fluctuations in the load command value.
The purpose of the present invention is to provide an 1tI device.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention performs governor-free operation of the turbine using the governor-free operation aiIII system when the fluctuation cycle of turbine load fluctuation is short and the fluctuation range is small, and other than this Regarding load fluctuations, reactor output control operation is performed by reactor output control, and the load setting device receives load commands from the automatic frequency 1i11 control signal (AFC signal) and base load signal (DPC signal) from the central power dispatch center. The feature is that the load is automatically set based on the value, and the turbine generator output is made to follow the fluctuation of this load command value.

[Embodiments of the invention]

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

FIG. 1 is a block diagram showing the overall configuration of an embodiment of a load following control device for a boiling water nuclear power plant according to the present invention, and reference numeral 1 in the figure indicates a boiling water nuclear reactor. A reactor core 2 is housed in the reactor 1 in a state where it is submerged with reactor water, and the reactor water is heated by the reaction heat of the nuclear fuel loaded into the reactor core 2 to generate steam. Reactor 1 has main steam pipe 3
The main steam generated in the reactor 1 is introduced to the turbine 4 through the main steam pipe 3 to do work, and the turbine power generator (not shown) is directly connected to the output shaft 5 of the turbine 4. The system is designed to drive the machine, waste electricity, and supply electricity to a power system (not shown).

A main steam control valve 6 is attached to the main steam pipe 3 near the main steam inlet of the turbine 4 to adjust the amount of steam flowing into the turbine 4.

A turbine bypass pipe 7 is connected midway through the main steam 13 on the upstream side of the main steam control valve 6, and the other end of the turbine bypass pipe 7 is connected to a bypass valve 8 midway through which the turbine 4 condenses. It is connected to the container 9. The turbine bypass valve 8 opens when the load on the turbine 4 is significantly reduced.
A decrease in the main steam inflow to the turbine 4 is directly bypassed to the condenser 9 to control a sudden rise in pressure within the reactor 1.

In addition, the reactor water in the reactor 1 is forcedly circulated to the reactor core 2 by the recirculation pump 10, and steam is effectively generated.
By changing the core coolant flow m, the reactor thermal output (amount of generated steam) is adjusted to M all L.

The pump speed of the recirculation pump 1o is controlled by the MG upper set 1, and the control is executed based on the set value set by the recirculation flow rate vJtll system 12.

The boiling water nuclear power plant configured in this manner further includes a pressure control system A that controls the pressure of the reactor 1 to always maintain it at a predetermined pressure, and a pressure control system A that controls the pressure of the reactor 1 to always maintain it at a predetermined pressure, and a pressure control system A that prevents the turbine 4 from overspeeding. A turbine control system B that appropriately controls the rotation speed of the turbine 4, a governor free operation control system C that controls the opening of the main steam control valve 6, and a reactor power control system that controls the core flow rate in the reactor 1. The pressure control system A is provided with a pressure detector 13 on the turbine inlet side of the main steam pipe 3 for detecting the turbine inlet pressure. The turbine inlet pressure detected by the pressure detector 13 is inputted as a turbine inlet pressure signal 13A to the pressure comparator 14, where the pressure setting device 1
5 is compared with the pressure setting value set in step 5, the deviation from the setting value is calculated, and is inputted to the pressure control @ position 16 as a pressure deviation signal 14A. In this pressure control device [16, this pressure deviation signal 14A is converted into the valve opening degrees of the main steam control valve 6 and the turbine bypass valve 8, respectively, and a pressure regulation signal 1 is obtained.
6A, which is output via an adder 17 to a low value priority circuit 18 and a servo adder 19, respectively. A control signal from the turbine control system B is also input to the low value priority circuit 18, but the pressure control system A, which normally has a low value,
The pressure adjustment signal 16A is given priority and input to the main steam control valve servo 20 and the turbine bypass valve servo 21 via the servo adder 19, respectively. The main steam control valve servo 20 and the turbine bypass valve servo 21 control the openings of the main steam control valve 6 and the turbine bypass valve 8 so that the pressure deviation from the pressure setting value becomes a predetermined value. Thereby, the pressure inside the nuclear reactor 1 is always maintained at a predetermined value.

On the other hand, the turbine control system B includes a turbine speed detector 22 on the output shaft 5 of the turbine 4 to detect the rotational speed (frequency) of the turbine 4 and a turbine generator (not shown). The rotational speed of the turbine 4 detected by the turbine speed detector 22 is input to the speed comparator 23 as a turbine speed signal 22B, where it is compared with the speed setting value set by the speed setting device 24 to determine the deviation. is calculated. This speed deviation signal 23B is input to the speed adder 25, where the load setting bias generator 26 and the load setting device 2
The load setting bias and load setting value output from 7 are
are added together to form a turbine load request signal 25B, which is output to bias subtractor 28 and low value priority circuit 18, respectively. As mentioned above, the pressure adjustment signal 16A from the pressure control system A is also input to the low value priority circuit 18, but the turbine load request signal 2 of the turbine control system B is also input to the low value priority circuit 18.
5B is heavily biased, the low-value pressure adjustment signal 16A usually takes priority, and the pressure adjustment signal 16A is output to each servo 20, 21 with priority, respectively. This is to give priority to the pressure control system over the turbine control system B, since generally there is always a positive feedback to the influence of pressure changes in the reactor system on the output.

On the other hand, bias subtraction! The turbine load request signal 25B inputted to the pressure setting value regulator 25 is once again removed from the added bias in the speed adder 25.
9 and the high frequency filter 30 of the governor free operation MtIl system C. This pressure set value regulator 2
Step 9 appropriately adjusts the pressure set value input to the pressure comparator 14 to stop the reactor pressure compensation function by the pressure ill system A, and in the meantime, controls the rotation speed of the turbine 4 by the turbine control system B. However, since it is closely related to the pressure control device 16 and it is extremely difficult to adjust the control constant of the pressure set value regulator 29, the reliability is not high.
It is hardly used in actual plants.

Further, high frequency components in the governor free operation region are extracted from the turbine load request signal 28B input to the high frequency filter 30, and cycles (low frequency components) longer than the load fluctuation cycle A shown in FIG. 6 are removed. This is the fluctuation period A
For load fluctuations in the high frequency region shorter than A, the load is followed by governor free operation, and for low frequency regions with a longer period than the fluctuation period A, automatic frequency control and daily output adjustment are used, as shown in Figure 6. It is. The high-frequency turbine speed deviation signal 30G, which is a high-frequency component extracted by the high-frequency filter 30, is input to a limiter 31 and a recirculation flow rate controller 33, and the limiter 31 limits its amplitude to a required width to meet the turbine load requirement. is adjusted to be below the limit allowed by the inertia of the reactor system (for example, several percent rated output), and a governor free operation request signal 31c is formed and output to the adder 17 and the pressure set value changer 32, respectively. . The signal obtained by adding the pressure adjustment signal 16A and the governor free operation request signal 31C in the adder 17 is sent to the main steam control valve servo 20 and the turbine bypass valve servo via the low value priority circuit 18 and the servo adder 19, respectively. 21 and 21, respectively. These servos 20.21 respectively control the valve opening degrees of the main steam control valve 6 and the turbine bypass valve 8 in accordance with the load request of the governor free operation request signal 31c, and make the output of the turbine 4 follow the load fluctuation. . By the way, when the fluctuation cycle of this load fluctuation is about 20 seconds, when the opening degree control of both valves 6 and 8 is performed, the reactor pressure fluctuates.

As a result, the pressure detector 13 of the pressure control system A detects this pressure fluctuation, and the reactor pressure compensation function of the pressure control system A operates so that the deviation from the pressure setting value is set to a predetermined value, and the governor-free operation is activated. Load following effectiveness is lost over time.

Therefore, in response to the governor free operation request signal 31C, the pressure set value changer 32 transmits a pressure set value change signal 32C to the pressure comparator to change the pressure set value of the pressure setting device 15 in a direction in which the governor free operation can be continued. Output to 14.

That is, the pressure set value changer 32 appropriately forms the pressure set value change signal 32c using a coefficient for converting the load request of the turbine load request signal 31C into a pressure set value and a required transfer function. For example, a -order lag can be used as the transfer function.

In addition, when performing the above-mentioned governor free operation, the use of the pressure set value regulator 29 is stopped and the high frequency filter 30 is
, limiter 31, and pressure setting value changer 32.

On the other hand, the turbine load request signal 30G input to the recirculation flow ff1llll device 33 of the reactor power control system is converted to the recirculation flow m setting value of the reactor power control system 12, and the feedforward signal 33d It is output to the reactor power control system 12 as The reactor power control system 12 appropriately controls the pump speed of the recirculation pump 10 via the MG set 11 based on the recirculation flow rate set value of the feedforward signal 33d, and maintains the neutron flux in the reactor 1 constant. do.

Regarding the control of neutron flux, a signal that has been sufficiently adjusted and confirmed is output to the reactor power output liiwJ system 12 as a feedforward signal 33d. A
When it is expected that the fluctuation range of the neutron flux will increase, such as when the neutron flux is further increased, it is possible to perform feedback control on the neutron flux signal. Therefore, a feedback circuit is provided to feed back the neutron flux signal detected in the reactor 1 to the reactor power control system 12.

That is, the neutron flux signal detected in the reactor 1 is returned to the reactor power control system 12 via the noise filter 34 and the neutron flux controller 35, and the load setting device 27
The load setting signal 27d output from the neutron flux controller 3
It was configured to output to 5.

The noise filter 34 removes noise specific to neutrons, and also removes the neutron flux signal 36 of the average output monitor output from the neutron detector 36 that detects the neutron flux in the reactor 1.
This converts f into the electrical output equivalent of the power plant, and this conversion factor can be easily calculated using a process calculator for evaluating the core performance of the power plant. The output signal from this noise filter 34 is input to a neutron flux controller 35 that performs a PI operation to improve the initial response of the generator output, and at the input point of this neutron flux controller 35, a load is output from the load setting device 27. It is compared with the setting signal 27d,
The deviation is calculated, and the deviation signal 35f is output to the reactor power control system 12 to adjust the recirculation flow II setting value.

The speed of the recirculation pump 10 is controlled based on the thus adjusted recirculation flow mountain setting value, and the reactor power of the nuclear reactor 1 is controlled. As a result, the output of the turbine generator that receives the furnace output as input follows the load setting value set by the load setting device 27.

By the way, the load setting signal 27d is a load command value inputted to the load setting device 27 from a central power dispatch center (not shown),
That is, it is formed from the sum of the DPC signal and the FC signal. Of course, the load setting device 27 is as shown in Fig. 2 (
Adding a base load signal (DPC signal) i configured as shown in A) and an automatic frequency control signal (AFC signal) transmitted from a central power dispatch center (not shown) and an automatic frequency control signal (AFC signal) using a load adder 27a. The load is set according to the following. However, for the AFC signal pair, an AFC signal compensator 27b for improving signal response,
The load adder 27 sequentially passes through the change rate and amplitude controller 27C for controlling the load change rate and amplitude to the required load change rate and amplitude allowed from the core of the reactor 1 and the plant operating state.
input to a. DP added by load adder 27a
The C signal 1 and the AFC signal j1, that is, the load setting value, are sent to the neutron flux controller 35 as the load setting signal 27d.
and the speed adder 25, respectively.

The load setter @27d input to the speed adder 25 is converted into a turbine load request signal 25B, and then output to the high frequency filter 30 via the bias subtracter 28.

As described above, the high frequency filter 3o extracts the high frequency component in the governor free operation region from the human input signal and removes the other low frequency components, so that it is removed from the AFC signal. However, in order to improve the initial response to the AFC signal, the characteristics of the high frequency filter 30 may be changed so as to pass the peripheral components of the AFC signal with the period shown in FIG.

In addition to the constant value, the DPC signal has a period of 8 as shown in Fig. 6 in order to adjust the daily output of the power plant.
The above-mentioned slow daily output 14M signal may be used.

In addition, the high frequency filter 30 is provided with an 0N-OFF switch or a changeover switch, and this 0N-OFF switch is turned OFF when the governor free operation control system C is not operated.
Alternatively, a bandpass filter (
(not shown), and the governor free operation may be stopped.

Furthermore, in the embodiment shown in FIG.
5, the output 27d of the load setting device is used as is, but instead of the output 27d of the load setting device, the output 27d of the load setting device and the turbine speed deviation 23B are used.
The operation described above is exactly the same even if the signal 28B, which is the sum of

Furthermore, in the above embodiment, the load setting device 27 is controlled by the AFC signal and the DPC signal from the intermediate supply, but instead of the DPC signal from the intermediate supply, an arbitrary signal with time as an independent variable can be used. It can also be controlled by the output from the load pattern generator. FIG. 2(B) shows an example of a load pattern.

Next, a case will be described in which, for example, the load request value of the DPC signal i (basic load signal) decreases.

When the DPC signal signal load requirement value decreases, the load setting signal 27d also decreases.

The load setting signal 27 inputted to the neutron flux controller 35
d is compared with the output of the noise filter 35 at the input point of the neutron flux control t121i35, and the output of the reactor power control system 1
2 is a deviation signal 35f that reduces the current recirculation outflow.
is input. As a result, the reactor power control system 12 adjusts the recirculation pump 10 to reduce the current recirculation outflow.
Performs speed control. As a result, the pressure inside the nuclear reactor 1 decreases, the neutron flux also decreases, and the generator output follows the DPC signal well.

On the contrary, even if the DPC signal signal angle load request value increases, by simply changing the control direction from the case where the load request value eventually decreases, the turbine generator output can be adjusted to load fluctuations. Follow.

3 to 5 show the main parameters in the reactor 1 when various system frequency fluctuations (load fluctuations) occur in this embodiment, that is, the turbine steam flow ff1T (
%), neutron flux N (%) and reactor pressure P<Kg/c
Examples of responses for i') are shown below.

Figure 3 shows an example of the response of the main parameters of the reactor 1 when only governor free operation is performed in which the opening degree of the main steam control valve 6 is controlled. , shows the case of a rectangular wave with an amplitude of ±1.5%. In this case, compared to the conventional example shown in FIG. 9, the fluctuation width of the neutron flux N is also narrowed to a small extent, and its reverse response is also improved, resulting in the highest vapor flow rate of 1! The auxiliary period also fluctuates approximately corresponding to the period of 20 seconds of system frequency fluctuation, indicating that the load followability is good.

On the other hand, FIG. 4 shows an example of each response of the main parameters of the reactor 1 when the AFC signal signal system is input to the load setter 27 and the nuclear power plant is operated only under automatic frequency control. This shows the case of a rectangular wave with a period of 120 seconds (signal system frequency fluctuation) and an amplitude of ±5%. Even in this case, the fluctuation range of the neutron flux N (%) is also comparable to the amplitude of the AFC signal, and the load followability of the turbine steam flow rate (%) is also good.

In addition, Fig. 5 shows the system frequency fluctuation (period 20) shown in Fig. 3.
4. Examples of responses are shown when the AFC signal period (120 seconds, amplitude ±1.5%) is superimposed on the AFC signal system shown in FIG. 4 (120 seconds, amplitude ±5%). In this case as well, the fluctuation range of the neutron flux N (%) is almost the same as when only the AFC signal is applied,
The load followability of turbine steam Rm (%) is also good.

〔Effect of the invention〕

As explained above, the present invention automatically sets the load of the load setting device based on the sum of the automatic frequency control signal from the central power dispatch center and the base load signal at the same time as performing governor-free operation. The turbine generator output was made to follow the fluctuation of the value.

Therefore, according to the present invention, each operation mode of governor free operation, AFC operation, and daily output adjustment operation can be easily operated individually or in any combination according to the appropriate demands of the power system, and this allows control of the system frequency. It is very effective in doing so. Furthermore, since the turbine generator output of the nuclear power plant can be automatically made to follow the load command value from the central power dispatch center, the burden on plant operators can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the load following control device for a boiling water nuclear power plant according to the present invention, and FIG. 2(A) is a load setting in the embodiment shown in FIG. 1. A block diagram showing the configuration of the device, Figure 2 (B) is the first
Figures 3 through 5 are graphs showing examples of the response of the main parameters of the reactor to various load fluctuations in the embodiment shown in Figure 1. The figure is a graph showing a typical load fluctuation curve of an electric power system along with an example of sharing power plant output control. Figures 7 and 8 respectively explain the inertia of the atomic system in a typical boiling water nuclear power plant. FIG. 9 is a graph showing an example of the response of the main parameters of a conventional nuclear reactor to load fluctuations in the peripheral area to the boundary in FIG. 10... Recirculation pump, 11... MG set, 12
... Reactor power control system, 27 ... Load setting device, 27
a... Load adder, 27b... AFC signal compensator,
27C... Rate of change and amplitude limiter, 27d... Load setting signal, 28... Bias subtractor, 28B...
Turbine load request signal, 30...high frequency filter, 3
0c... High frequency turbine speed deviation signal, 31... Limiter, 31c... Governor free operation request signal, 32...
...Pressure set value changer, 32c...Pressure set value change signal, 33...Recirculation flow rate controller, 33 (1...Feed forward signal, 34...Noise filter, 35
...Neutron flux controller, 36...Neutron flux detector. Applicant's agent Hisashi Hatano Figure 6 Figure 8

Claims (1)

[Claims] 1. A reactor power control system that controls the reactor output to a predetermined value by controlling the core flow rate of a boiling water reactor, and the output of the load setting device and the turbine rotation speed deviation or system frequency. A device that controls a turbine control valve by the output of a high-frequency filter that extracts the high-frequency component of the sum of the deviation, that is, the high-frequency component of the load request value, and a device that performs gain/phase compensation on the output of the high-frequency filter and adds it to the pressure setting value of the pressure control device. and the load setting device is configured to be automatically set by a signal given from the outside, so that the turbine generator output automatically follows fluctuations in the load request value. Features: Load following control device for boiling water nuclear power plants. 2. The signals given from the outside are the automatic frequency control signal and base load signal from the central dispatch center, and the automatic frequency control signal is controlled by a signal compensator to improve response and the required load change rate and load change width. The load following device for a boiling water nuclear power plant according to claim 1, wherein the load follower for a boiling water nuclear power plant is added to the base load signal after sequentially passing through a rate of change for limiting and an amplitude limiter. 3. The load following device for a boiling water nuclear power plant according to claim 1, wherein the externally applied signal is generated by a load pattern generator.