JPH0441800B2 - - Google Patents

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 is particularly suitable for use when the range of load fluctuation is small and the fluctuation cycle is short. The present invention relates to a load following control device for a boiling water nuclear power plant that follows the load by so-called governor-free operation.

[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, power demand has large seasonal, daytime, and nighttime fluctuations, as well as small load fluctuations at all times.In order to keep the frequency of the power system constant in response to these load fluctuations, the power supply of this power system is On the other hand, a power plant controls its electrical output.
So-called grid automatic frequency control (AFC) is being implemented.

Therefore, if the supply share of nuclear power plants in the electric power system continues to increase 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 electric power system at night will be necessary. Is required. This is because thermal power plants, which have traditionally been responsible for automatic frequency control of the electric power system, stop operating in response to the drop in power demand at night, and output adjustment that takes part in automatic frequency control of the electric power system is required. This is because the amount decreases.

FIG. 5 shows an example of the distribution of output control on the power plant side regarding such load fluctuations in the power system.
In other words, the vertical axis shows the magnitude of load fluctuation, and the horizontal axis shows the cycle of load fluctuation.For load fluctuations that have a longer cycle than fluctuation cycle B (for example, about 15 minutes) and have a large fluctuation range, , performs appropriate daily output adjustments based on instructions from a central power dispatch control center (not shown) of the power system. This is described in detail in ``Load Follow Automation Device for Nuclear Power Plant'' (published in Japanese Unexamined Patent Publication No. 55-20404) for which the applicant of this patent has already filed a patent application. Also, the fluctuation period A
(for example, approximately 20 seconds) to B, the required output adjustment amount is usually calculated by an automatic control device in the central power dispatch control room of the power system, and this is used to control the frequency control within the power system. It is distributed to the participating power plants in appropriate proportions and transmitted as an AFC mid-feed signal. Each power plant that receives this signal adjusts its output based on this signal. Regarding this automatic frequency control (AFC) device for boiling water type nuclear power generation plants, for example, the applicant of this patent has applied for a patent for ``Output control device for boiling water type nuclear power generation plants (published in Japanese Patent Application Laid-Open No. 59-54997). detailed in.

For high-frequency components with a fluctuation period A or less, each power plant responds to so-called governor-free operation by controlling the opening of the turbine inlet governor valve (main steam control valve). In this governor-free operation, the turbine generator rotation speed is compared with a set value, the deviation is fed back to the turbine, and the opening of the turbine inlet governor valve (main steam control valve) is controlled so that this deviation becomes zero. However, conventional nuclear power plants did not perform governor-free operation. However, due to the circumstances mentioned above,
Today, governor-free operation is required even in nuclear power plants. Furthermore, when performing this governor-free operation, it is desirable that sufficient consideration be given especially to cooperation with automatic frequency control (AFC) operation.

By the way, the characteristic of governor-free operation is that it targets load fluctuations with a relatively short fluctuation cycle as shown in Figure 5, and at the same time, the range of fluctuation is relatively small, and the required output adjustment is is small. Therefore, in a boiling water nuclear power plant, when performing governor-free operation using 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, output adjustment is not necessary. Not necessarily necessary.

Figures 6 and 7 show the reactor pressure in a boiling water nuclear power plant when the main steam flow rate to the turbine increases or decreases for a short time without recirculation flow rate control or power adjustment by control rod operation. (Kg/cm ² ) and thermal output (% rating). As shown in FIG. 6, when the main steam flow rate (%) to the turbine is increased by a small amount and for a short period of time, the reactor pressure decreases in a quadratic curve. 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 7, even when the main steam flow rate (%) to the turbine is reduced by a small amount and for a short period of time, the reactor pressure increases in a quadratic curve. , the thermal output hardly changes at the initial stage, indicating that a decrease in reactor pressure has a small effect on the thermal output.

Therefore, from the above, if the fluctuation period of load fluctuation is relatively short, for example about 20 seconds or less, and the fluctuation range is small,
By utilizing the inertia of the reactor system, governor-free operation can be performed without causing large fluctuations in the thermal output of the reactor. In other words, in general, in boiling water nuclear power plants, when the turbine steam flow rate, or load increases, the reactor pressure decreases and steam bubbles (voids) in the reactor core increase, and the negative reactivity effect of these steam bubbles causes Although an adverse response occurs in which the reactor output decreases, it was confirmed that such an adverse response does not need to be taken into account if it is limited to short-term load fluctuations.

However, as shown in FIG. 8, for example, when the period of load fluctuation is around the boundary A between the governor free operating region and the automatic frequency control (AFC) 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), When operating near the rated output, it can cause false alarms if combined with the noise inherent to the neutron flux. Also,
In automatic frequency control (AFC) operation, the reactor output is often controlled by the AFC request signal before controlling the turbine steam flow rate, so the occurrence of reverse neutron flux response in the governor-free operation region is automatically This complicates the response in the transition region to the frequency control operation region. Therefore, in such a case, it is desirable to keep the neutron flux constant during governor free operation.

[Purpose of the invention]

The present invention was made in view of the above-mentioned circumstances, and
It is an object of the present invention to provide a load following control device for a boiling water nuclear power plant that reliably follows the turbine load request while improving the reverse response of neutron flux due to fluctuations in the turbine steam flow rate.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention performs governor-free operation of the turbine when the fluctuation period of turbine load fluctuation is short and the fluctuation range is small, and furthermore, during this governor-free operation, the turbine is not operated again. The system is characterized in that the neutron flux within the reactor is kept constant by a circulation flow rate control system, the turbine generator output reliably follows the load fluctuations, and the reverse response of the neutron flux is improved.

[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. The nuclear reactor 1 is connected to a turbine 4 via a main steam pipe 3, and the main steam generated in the reactor 1 is introduced into the turbine 4 via the main steam pipe 3 to do work, and the output shaft 5 of the turbine 4 generates electricity by driving a turbine generator (not shown) directly connected to
Power is supplied 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 in the main steam pipe 3 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 is restored. It is connected to a water container 9. The turbine bypass valve 8 opens when the load on the turbine 4 is significantly reduced, and bypasses the reduced amount of main steam flowing into the turbine 4 directly to the condenser 9, thereby controlling a sudden rise in pressure within the reactor 1. do.

In addition, the reactor water in the reactor 1 is forcedly circulated to the reactor core 2 by the recirculation pump 10 to effectively generate steam, and by changing the core coolant flow rate, the reactor thermal output (amount of generated steam) is increased. It's in control. The pump speed of the recirculation pump 10 is controlled by an MG set 11, and the control is executed based on a set value set by a recirculation flow rate control 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 turbine control system that appropriately controls the rotation speed of the turbine. The pressure control system A includes a pressure detector 13 on the turbine inlet side of the main steam pipe 3 to detect the turbine inlet pressure. The turbine inlet pressure detected by this pressure detector 13 is the turbine inlet pressure signal 1
3A to the pressure comparator 14, where:
It is compared with the pressure setting value set by the pressure setting device 15, a deviation from the setting value is calculated, and is inputted to the pressure control device 16 as a pressure deviation signal 14A. In this pressure control device 16, this pressure deviation signal 14A
, the main steam control valve 6 and the turbine bias valve 8
The pressure adjustment signal 16 is converted into the valve opening degree of
A is formed and outputted 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,
The pressure adjustment signal 16A of the pressure control system A, which normally has a low value, is prioritized and input to the main steam control valve servo 20 and the servo adder 19, respectively. Main steam control valve servo 20 and turbine bypass valve servo 2
1, the main steam control valve 6 and the turbine bias valve 8 are operated so that the pressure deviation from the pressure setting value becomes a predetermined value.
Opening control is performed. 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.
and the rotational speed (frequency) of a turbine generator (not shown). The rotation speed of the turbine 4 detected by the turbine speed detector 22 is sent to the speed comparator 2 as a turbine speed signal 22B.
3, and is compared with the speed setting value set by the speed setting device 24 to calculate the deviation. This speed deviation signal 23B is input to the speed adder 25, where the load setting bias generator 26
The load setting bias and load setting value outputted from the load setting device 27 are added to form a turbine load request signal 25B, which is output to the bias subtractor 28 and the low value priority circuit 18, respectively. . As described above, the pressure adjustment signal 16A from the pressure control system A is also input to the low value priority circuit 18, but since the turbine load request signal 25B of the turbine control system B is already biased,
Usually, the pressure adjustment signal 16A having a low value is given priority, and the pressure adjustment signal 16A is outputted to each servo 20, 21 with priority, respectively. This is to give priority to the pressure control system A over the turbine control system B, since generally there is always a positive feedback on the influence of pressure changes in the reactor system on the output.

On the other hand, the turbine load request signal 25B input to the bias subtracter 28 is once again removed from the added bias by the speed adder 25, and then input to the pressure set value regulator 29 and the high frequency filter 30, respectively. be done. This pressure set value regulator 29
The system adjusts the pressure set value input to the pressure comparator 14 as appropriate, stops the reactor pressure compensation function by the pressure control system A, and causes the turbine control system B to control the rotational speed of the turbine 4 during that time. However, it is closely related to the pressure control device 16,
Since it is extremely difficult to adjust the control constant of the pressure set value regulator 29, it is not reliable and 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. 5 are removed. For load fluctuations in the high frequency region shorter than the fluctuation period A, the load is followed by governor-free operation, and in the low frequency region longer than the fluctuation period A, as shown in Figure 5, automatic frequency control and daily This is to share the responsibility for output adjustment. The high frequency turbine speed deviation signal 30c of the high frequency component extracted by the high frequency filter 30 is transmitted to the limiter 3.
1 and the recirculation flow rate controller 33, and the limiter 31 limits the amplitude to the required width, suppressing the turbine load request to below the limit allowed by the inertia of the reactor system (for example, several percent rated output). Adjust as follows,
A governor free operation request signal 31c is formed and outputted 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 and 21 respectively control the valve opening degrees of the main steam control valve 6 and the turbine bias 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 period 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 the pressure set value changer 32, the governor free operation request signal 31c
In response, a pressure setting value change signal 32c is output to the pressure comparator 14 to change the pressure setting value of the pressure setting device 15 in a direction that allows continued governor-free operation. 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 change and a required transfer function. For example, a first-order lag can be used as the required transfer function.

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

On the other hand, the turbine load request signal 30c input to the recirculation flow rate controller 33 is converted into a recirculation flow rate setting value of the recirculation flow rate control system 12, and is converted into a recirculation flow rate setting value of the recirculation flow rate control system 12 as a feed forward signal 33d. 12. The recirculation flow rate 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 keeps the neutron flux in the reactor 1 constant. to hold. The effect of the reverse response compensation of the neutron flux by this recirculation flow rate control system 12 is
As shown in the figure. FIG. 2 shows an example of the reverse response of the neutron flux when fluctuations in the turbine steam flow rate occur at the period of the transition region between the governor free operation region and the automatic frequency control operation region, for example, at a period of about 20 seconds. According to Fig. 2, compared to the conventional example shown in Fig. 8, the fluctuation range of neutron flux fluctuation is reduced to about 70% in peak-to-peak value, and the relationship between turbine steam flow rate and neutron flux is reduced to approximately 70%. The reverse response has also been improved.

Note that in the above embodiment, a signal that has been sufficiently adjusted for neutron flux control is output to the recirculation flow rate control system 12 as the feed forward signal 33d, but the output adjustment range due to governor free operation is In particular, when the range of variation in neutron flux is expected to be large, such as when increasing the boundary period A or when increasing the boundary period A further, it is possible to perform feedback control on the neutron flux signal. The embodiment shown in FIG. 3 is one example,
A feedback circuit is newly installed to feed back the neutron flux signal detected in the reactor 1 to the recirculation flow control system 12.

That is, the main difference between this embodiment and the embodiment shown in FIG. At the same time, the feedforward signal 33d output from the recirculation flow rate controller 33 is sent to the MG set
The reason is that it is configured to output to. In FIG. 3, the same parts as those in FIG. 1 are given the same reference numerals, and the explanation of the overlapping parts will be omitted.

The noise filter 34 removes noise specific to neutrons, and converts the neutron flux signal 36f of the average output monitor output from the neutron detector 36 that detects the neutron flux inside the reactor 1 into equivalent to the electrical output of the power generation plant. This conversion factor can be easily calculated using a process computer for evaluating the core performance of this power plant. The output signal from this noise filter 34 is transmitted to the neutron flux controller 3.
5, and at this input point, it is compared with the set value e for the base load of the power plant, its deviation is calculated, and its output signal 35f is output to the recirculation flow control system 12, and the recirculation Adjust flow setpoint.

On the other hand, the feed forward signal 33d from the recirculation flow rate controller 33 is not input to the recirculation flow rate control system 12 as in the embodiment shown in FIG.
It is input to MG set 11. Therefore, the MG set 11 is set by the feed forward signal 33d.
The input voltage of the motor 10a for driving the recirculation pump 10, that is, the driving torque of the motor 10a for driving the recirculation pump 10, is adjusted by directly controlling the excitation current of the generator. This allows the recirculation flow rate to be adjusted without using the MG set 11.
The recirculation flow rate can be quickly adjusted regardless of the response delay of the MG set 11. FIG. 4 shows the effect of the inverse response compensation of the neutron flux according to this embodiment. Figure 4 shows an example of the reverse response of the neutron flux when fluctuations in the turbine steam flow rate occur at the period of the transition region between the governor free operating region and the automatic frequency control operating region, for example, at a period of about 20 seconds. . According to FIG. 4, the inverse response of the neutron flux in the embodiment shown in FIG. 1 has been further improved, the fluctuation width of the neutron flux fluctuation has been further improved to a small extent, and load fluctuations can be followed well. I understand.

〔Effect of the invention〕

As explained above, the present invention allows the turbine to follow the load fluctuation by governor-free operation when the fluctuation period of the turbine load fluctuation is relatively short and the fluctuation width is small, During operation, the neutron flux inside the reactor was kept constant by a recirculation flow control system. Therefore, according to the present invention, it is possible to reliably and quickly follow load fluctuations while improving the reverse response of neutron flux.

[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 shows fluctuations in turbine steam flow rate in the embodiment shown in FIG. 1. FIG. 3 is a block diagram showing the overall configuration of another embodiment of the present invention, and FIG. 4 is an example of the inverse response of the neutron flux, etc. of the embodiment shown in FIG. 3. Figure 5 is a graph showing a general load fluctuation curve of an electric power system along with an example of sharing power plant output control. Figures 6 and 7 are a graph showing a nuclear reactor system in a typical boiling water nuclear power plant. FIG. 8 is a graph for explaining the inverse response of neutron flux in a conventional boiling water nuclear power plant. 10...Recirculation pump, 11...MG set, 12
... Recirculation flow control system, 28 ... Bias subtractor, 2
8B...Turbine load request signal, 30...High frequency filter, 30c...High frequency turbine speed deviation signal, 3
1...Limiter, 31c...Governor free operation request signal, 32...Pressure set value change device, 32c...Pressure set value change signal, 33...Recirculation flow rate controller, 33d...
Feed forward signal, 34... noise filter, 35... neutron flux controller, 36... neutron flux detector.

Claims (1)

[Claims] 1. A pressure control system that controls the reactor pressure of the boiling water reactor to always maintain it at a predetermined pressure, a turbine control system that appropriately controls the rotation speed of the turbine, and appropriately controls the recirculation flow rate within the reactor. In a boiling water nuclear power plant having a recirculation flow rate control system, the governor free operating region is determined from the turbine speed deviation signal obtained by removing the load setting bias from the turbine load request signal in the turbine control system. A high-frequency filter extracts a high-frequency component and outputs a high-frequency turbine speed deviation signal, and the amplitude of this high-frequency turbine speed deviation signal is appropriately limited and adjusted to the required output adjustment amount to form a governor free operation request signal, which is transmitted as described above. A limiter applied to the pressure adjustment signal of the pressure control system, and a pressure that changes the required pressure setting value of the pressure control system in response to the governor free operation request signal and stops the reactor pressure compensation function by the pressure control system. a setpoint changer; and a recirculation flow setpoint adjuster for converting the high frequency turbine load request signal into a recirculation flow setpoint of the recirculation flow control system, the governor free controller being applied to the pressure adjustment signal. The opening degree of the main steam control valve is controlled by the operation request signal to make the turbine generator output follow the load fluctuation, and the recirculation flow rate set value of the feedforward signal output from the recirculation flow rate set value regulator is A load following control device for a boiling water nuclear power plant, characterized in that the recirculation flow rate is controlled by the above to compensate for fluctuations in reactor output due to governor-free operation of the main steam control valve.