JPH01114798A - Load follow-up method for nuclear power plant - Google Patents

Abstract

PURPOSE:To suppress the excess increase of neutrons at the time of a load follow-up operation so that the scram of a nuclear reactor is prevented and the safe operation is continued by generating the correction signal based on the deviation signal between a reference neutron flux value and a measured neutron flux value when the reference neutron value is exceeded. CONSTITUTION:A recirculation flow rate control system controls an MG set via a reference speed request limiter 17, a speed controller 18, a scoop pipe position regulator 19, etc., by the correction signal obtd. by correcting the deviation of the output of a main controller 16 from the reference value of the neutron flux signal by a corrector 30 and regulates further the recirculation flow rate by controlling the speed of a recirculation pump, thereby suppressing the excessive increase of the neutron fluxes. The corrector 30 is constituted of a filter 31, an adder 32 for determining the deviation signal between the neutron flux signal and the reference value, a limiter 33 and a series dynamic operation compensator 34. The reference value is the value which exists above the value obtd. by superposing a stationary noise width on the rated value of the standardized neutron flux and below the scram level of the reactor.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a load following method in a boiling water nuclear power plant, and particularly relates to a load following method in a nuclear power plant that suppresses an excessive rise in neutron flux. .

(Prior Art) A conventional boiling water nuclear power plant control system will be explained with reference to FIG.

In the boiling water reactor 1, light water is used as a coolant and a moderator. When this coolant passes through the fuel assembly of the reactor core 2, it absorbs the heat generated by nuclear fission of uranium in the fuel and becomes steam. Thus, the steam generated in the reactor 1 is transferred to a steam separator 4. It passes through a steam dryer 5 and is led from a pressure vessel 6 to a turbine 8 via a main steam pipe 7. The steam that has done work in the turbine 8 becomes condensed water in the condenser 9, and is transferred to the feed water heater 10. The water is returned to the reactor pressure vessel 6 via the water supply pump 11.

In general, control rods 3 are used to make large changes in output such as when starting or stopping a reactor, to adjust the output distribution, and to compensate for long-term changes in core reactivity due to fuel combustion, and recirculation is used to follow up the output in response to load fluctuations. This is done using a flow control system.

The recirculation flow rate is driven by the recirculation pump 12;
The recirculation flow rate control system adjusts the recirculation flow rate by changing the power frequency of the induction motor that drives the recirculation pump 12 and changing the pump rotation speed. The recirculation flow rate control system 20 includes a variable frequency generator 13 and a drive motor 1.
4 and a fluid coupling 15 between them, and a main controller 16 for controlling the recirculation pump MG set. It is composed of a speed request limiter 17, a speed controller 18, and a scoop pipe position adjuster 19.

Further, the pressure control system 22 attempts to control the pressure of the nuclear reactor 1 at a constant level by operating a control valve 26 so that the amount of steam flowing to the turbine 8 matches the amount of steam generated in the reactor core.

Conventional nuclear plant load tracking methods involve coordinating the recirculation control system and the pressure control system 22. When the load deviation is positive, a rise command is given to the recirculation flow controller to increase the reactor output by increasing the core flow rate, while the pressure set point regulator 21 commands the pressure control system 22 to open the turbine steam control valve. The feedforward circuit 27 attempts to improve the initial response of the plant output by transiently extracting the steam flow rate. It is configured to compensate by In addition, 23 is a control valve servo, 2
4 is a pressure sensor, 25 is a turbine steam stop valve, 28 is a turbine bypass valve, 29 is a main steam isolation valve, and 30 is a relief safety valve.

(Problem to be solved by the invention) By the way, when increasing the load setting to increase the plant output, ``increase in load deviation → increase in main controller output signal → increase in recirculation pump speed → increase in core flow rate → Decrease in core average void fraction→
The process of increasing reactivity → increasing neutron flux → increasing heat flow rate → increasing core average void fraction → decreasing reactivity → decreasing neutron flux leads to settling. Accompanied by a shoot.

On the other hand, the control constants of the main controller 16, pressure set point regulator 21, and feedforward circuit 27 that control the plant output are normally adjusted so as to maximize load following ability while ensuring plant stability. One of the important variables for this stability index is neutron flux.

Generally, when making the above adjustment, if the neutron flux peak value has little margin with respect to the reactor scram level due to the neutron flux height,
There is a risk that neutron flux will rise excessively due to parameter changes, pressure fluctuations, or core flow rate fluctuations, leading to unnecessary reactor scrams. As a result, the reactor scram level due to the high neutron flux is adjusted to have sufficient margin to prevent such unnecessary reactor scrams from occurring.

A problem arises in that the load following function is set at a lower level than the original function.

The present invention has been made in view of the above circumstances, and its purpose is to provide a load following method for a nuclear power plant that can prevent reactor scram and continue stable operation by suppressing excessive rise in neutrons during load following operation. It is in.

[Structure of the invention]

(Means and effects for solving the problems) In order to achieve the above object, the present invention provides a load following method for a boiling water nuclear power plant equipped with a recirculation control system and a pressure control system, based on neutron flux standards. A value is set, and when this neutron flux reference value is exceeded, a signal based on the deviation signal between this reference value and the neutron flux measurement value is used as a correction signal, and this correction signal is configured to suppress an excessive increase in neutron flux. It is characterized by this.

According to the load following method for a nuclear power plant of the present invention, by setting a neutron flux reference value, when there is a margin in the reactor scram level, operation is carried out by maximizing the capacity of the output controller. By making corrections based on the deviation signal between the neutron flux and the measured neutron flux values, the intensity of the correction can be increased as the reactor scram level is approached.

(Example) Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention. This figure shows a case where the above-mentioned correction is made to the command value to the recirculation flow rate control system. Note that the same parts as in FIG. 7 will be described with the same reference numerals.

The recirculation flow rate control system 20 compares the output of the main controller 16 with a signal obtained by correcting the deviation signal between the neutron flux signal and the reference value by a corrector 30.A speed demand limiter 17, a speed controller 18, and a scoop tube position adjuster 19 is configured to control the MG upper set and further control the recirculation pump speed to adjust the recirculation flow rate. An example of the corrector 30 is a filter 31
an adder 32 for obtaining a deviation signal between the neutron flux signal and the reference value.
, a limiter 33, and a series dynamic characteristic compensator 342, such as a lead/lag compensator.

The filter 31 is for cutting high frequency noise of the neutron flux signal, and may have a short time constant. The standard value of neutron flux is set below the reactor scram level with sufficient margin. That is, this reference value is a value that is above the value obtained by superimposing the steady nozzle width on the normalized rated value of neutron flux and below the reactor scram level.

Next, the operation of this embodiment will be explained.

Now, the response of the plant when a load deviation occurs will be explained using FIG. According to this embodiment, the solid line (
As shown in 4), the neutron flux reaches the reactor scram level Q.
Does not reach 1. That is, load set point increases → main controller output increases → recirculation pump speed increases → core flow rate increases → core average void fraction decreases → reactivity increases → neutron flux increases →
Neutron flux exceeds the standard value → Recirculation pump speed reduction command by the corrector of the present invention → Decrease in the rate of increase in core flow rate → Dividing the neutron flux reduction reference value → Output of the corrector becomes zero → Excessive neutron flux is reduced by the process of setting can suppress the rise in

However, in the conventional method, the neutron flux increases and reaches the reactor scram level Q1, as shown by the broken line (b) in FIG. Solid lines (c) and (d) represent the core flow rate and main steam flow rate, respectively.

On the other hand, when no load deviation occurs, the output of the corrector 30 is zero and the control equipment does not perform any unnecessary operations. Furthermore, during load following operation with a low output as the reference output, the neutron flux does not exceed the reference value even if the contact width is the same, so the load following ability can be utilized to the maximum.

Furthermore, since the neutron flux does not increase for the descending command, the load following ability can be utilized to the maximum.

FIG. 3 shows a schematic configuration diagram of a second embodiment of the present invention, and this figure shows the case where the above-mentioned correction is made to the command value to the main steam control valve. It should be noted that the same parts as those in FIGS. 1 and 7 already explained will be described with the same reference numerals.

As shown in FIG. 3, there is a conventional pressure control system that feeds back the main steam pipe pressure to stabilize the reactor pressure and turbine inlet pressure, and a corrector based on the deviation signal between the neutron flux signal and the reference value according to the present invention. It is composed of.

An example of the corrector 30 of this embodiment includes a filter 31, an adder 32 for obtaining a deviation signal between a neutron flux signal and a reference value, a limiter 33, and a series dynamic characteristic compensator 34, such as a lead/lag compensator.

The filter 31 is for cutting high frequency noise of the neutron flux signal, and may have a short time constant. The reference value of neutron flux is set above the value obtained by superimposing the steady-state noise width on the normalized rated value of neutron flux, and below with sufficient margin for the reactor scram level, and the dead band width of the limiter is set at this value. The standard value is the upper limit.

Furthermore, if appropriate control constants are set, a similar effect can be obtained even when a correction signal is applied to the pressure set point.

Next, the operation of this embodiment will be explained.

Now, the response of the plant when a load deviation occurs will be explained using FIG. According to this embodiment, the solid line (4
), the neutron flux does not reach the reactor scram level Q4. In other words, the load set point increases in a stepwise manner→
Increase in main controller output → Increase in recirculation pump speed → Increase in core flow rate → Decrease in core average void fraction → Increase in reactivity → Increase in neutron flux → Neutron flux exceeds the reference value → Adjustment valve by the corrector of the present invention Through the process of opening command → pressure decrease → increase in core average void fraction → decrease in reactivity → decrease in neutron flux → dividing the reference value → settling, it is possible to suppress the excessive increase in neutron flux, and also to open the control valve. The steam flow rate can be taken out and the quick solubility of the plant output can be met. Also,
When the steam control valve is opened, the retained steam is released, which causes the reactor pressure to drop, but this changes to the safe side as there is a margin for the reactor high scram level. On the other hand, in the conventional system, the neutron flux increases and reaches the reactor scram level (e), as shown by the broken line (b) in Figure 4. The solid line (c) shows the core flow rate, the solid line (d) shows the main steam flow rate, the solid line (e) shows the reactor pressure, and Q□ is the reactor scram level of the reactor pressure.

As described above, according to this embodiment, it is possible to suppress an excessive increase in neutron flux, and as the plant output, by opening the control valve, the steam flow rate can be taken out to satisfy the initial rapid solubility.

On the other hand, when no load deviation occurs, the output of the corrector is zero, and the control equipment does not perform any unnecessary operations. Furthermore, during load following operation with a low output as the reference output, the neutron flux does not exceed the reference value even if the contact width is the same, so the load following ability can be utilized to the maximum. Furthermore, since the neutron flux does not increase for the descending command, the load following ability can be utilized to the maximum.

FIG. 5 is a configuration diagram of a third embodiment of the present invention, in which a thyristor power supply is used as the variable frequency power supply of the first embodiment, and the command to the recirculation flow rate control system 20 is shown in FIG. This is a case where the above-mentioned correction is applied to the value.

This embodiment is comprised of a lead/lag speed controller 18 that dynamically compensates the signal of the main controller 16, and a correction device 30 based on a deviation signal between a neutron flux signal and a reference value according to the present invention. - Then, the output signal of the speed controller 18 is converted by the inverter 35 to perform set control on the MO, thereby adjusting the recirculation flow rate. An example of the corrector 30 includes a filter 31, an adder 32 for obtaining a deviation signal between the neutron flux signal and a reference value, a limiter 33, and a series dynamic characteristic compensator 34, such as a lead/lag compensator.

The filter 31 is for cutting high frequency noise of the neutron flux signal, and may have a short time constant. The reference value of neutron flux is set above the value obtained by superimposing the steady-state noise width on the normalized rated value of neutron flux, and below with sufficient margin for the reactor scram level, and the dead band width of the limiter is set at this value. The standard value is the upper limit.

Next, the operation of this embodiment will be explained.

Now, when a load deviation occurs, the plant response is as follows. i.e. the load set point increases →
Increase in main controller output → Increase in recirculation pump speed → Increase in core flow rate → Decrease in core average void fraction → Increase in reactivity → Increase in neutron flux → Neutron flux exceeds the reference value → Recirculation by the corrector of the present invention Excessive increase in neutron flux can be suppressed through the following process: pump speed reduction command → reduction in core flow rate increase → dividing the neutron flux reduction reference value → zero output of the corrector → settling.

On the other hand, when no load deviation occurs, the output of the corrector is zero and the control equipment does not perform any unnecessary operations. Furthermore, during load following operation with a low output as the reference output, the neutron flux does not exceed the reference value even if the contact width is the same, so the load following ability can be utilized to the maximum. Furthermore, since the neutron flux does not increase for the descending command, the load following ability can be utilized to the maximum.

FIG. 6 shows a configuration diagram of a fourth embodiment of the present invention.
This figure shows a case where an internal pump having a drive unit inside the pressure vessel is adopted instead of the recirculation control system when the recirculation pump/jet pump of the first embodiment is used.6 This embodiment It is composed of a main controller 16, a core flow rate controller 36, and a corrector 30 based on a neutron flux signal and a reference value deviation signal. After the output signal of the main controller 16 is corrected by the corrector 30, the output signal is further corrected by the core flow controller 3.
6 and then converted by the inverter 35, the MG
upper set control, thereby adjusting the recirculation flow rate. Examples of the corrector 30 include a filter 31, an adder 32 for obtaining a deviation signal between a neutron flux signal and a reference value, and a limiter 33.
, a series dynamic characteristic compensator 34, for example, a lead/lag compensator.

The filter 31 is for cutting high frequency noise of the neutron flux signal, and may have a short time constant. The reference value of neutron flux is set above the value obtained by superimposing the steady-state noise width on the normalized rated value of neutron flux, and below with sufficient margin for the reactor scram level, and the dead band width of the limiter is set at this value. The standard value is the upper limit.

Next, the operation of this embodiment will be explained.

First, when a load deviation occurs, the following process occurs.

Load set point increases → main controller output increases → internal pump rotation speed increases → core flow rate increases → core average void fraction decreases → reactivity increases → neutron flux increases → neutron flux exceeds standard value → main With the compensator of the invention, an excessive increase in neutron flux can be suppressed through the process of issuing an internal pump rotational speed reduction command → decreasing the rate of increase in core flow rate → dividing the neutron flux decrease reference value → zero output of the compensator → settling.

On the other hand, when no load deviation occurs, the output of the corrector is zero and the control equipment does not perform any unnecessary operations. Furthermore, during load following operation with a low output as the reference output, the neutron flux does not exceed the reference value even if the contact width is the same, so the load following ability can be utilized to the maximum. Furthermore.

Regarding the descending command, the neutron flux does not increase, so the load following ability can be utilized to the maximum.

〔Effect of the invention〕

As explained above, the load following method for a nuclear power plant of the present invention provides the following effects.

■ At low power, when the neutron flux is at the reactor scram level, the load following ability can be utilized to its fullest extent.

■ Compensation works only when the load deviation is positive, and the load following ability can be utilized to the maximum when the load deviation is negative.

■ The time constant of the filter for cutting noise in the neutron flux can be kept small, allowing a high-speed response and making it possible to avoid unnecessary reactor scrams.

(4) There is no shift in plant output due to sensitivity deterioration of the neutron flux detector.

■ By operating the main steam control valve, it is possible to not only suppress neutron flux but also achieve high-speed output response.

■ The structure is simple, and it can be realized with not only a digital control device but also an analog control device, and it is easy to improve conventional control devices.

■ During load following operation, it is possible to prevent reactor scram and continue stable operation while suppressing excessive increases in neutron flux, and it is possible to follow system load fluctuations and significantly increase the operating rate of nuclear plants.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the first embodiment of the present invention, and FIG. 2 is a configuration diagram of the first embodiment of the present invention.
FIG. 3 is a block diagram of the second embodiment of the present invention, FIG. 4 is a diagram showing the response of the plant variables in FIG. 3, and FIG. FIG. 6 is a block diagram of the fourth embodiment of the present invention, and FIG. 7 is a schematic block diagram of a conventional boiling water nuclear power plant control system. 1... Nuclear reactor, 2... Reactor core, 7... Main steam pipe. 8...Turbine, 12...Recirculation pump. 13... Variable frequency generator, 16... Main controller.

Claims (4)

[Claims] (1) In the load tracking method of a boiling water nuclear power plant equipped with a recirculation control system and a pressure control system, a neutron flux reference value is set, and when this neutron flux reference value is exceeded, this reference value and neutron flux A load following method for a nuclear power plant, characterized in that a signal based on a deviation signal from a measured value is used as a correction signal, and the correction signal is configured to suppress an excessive increase in neutron flux. (2) The neutron flux reference value is a value obtained by superimposing a stationary noise width on a standardized neutron flux rating value, the load following method for a nuclear power plant according to claim 1. (3) The method of following claim 1, wherein the correction signal controls a recirculation pump speed, a core flow rate, or a recirculation flow rate. (4) The load following method for a nuclear power plant according to claim 1, wherein the correction signal is sent to a pressure setting device, a speed controller, or a core flow rate controller.