JPS61223596A - Recirculating flow controller - 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 [Field of Application of the Invention] The present invention relates to a recirculation flow rate control device for a boiling water nuclear power plant, and particularly to a control method when a momentary power outage occurs in the power supply of a recirculation pump motor.

[Background of the invention]

One method for controlling the output of a nuclear couplant is to control the core flow rate by controlling the speed of a recirculation pump. Previously, the speed control of this recirculation pump was controlled by MG Sets)? Recently, however, studies have been underway to use a static inverter power source instead of the MG superset.

Compared to the conventional MO top set, the static inverter power supply is a) Expected to be economical; b) The installation area of the equipment is small; C) good controllability, d) Good responsiveness; It has advantages such as

However, the biggest weakness of static inverter power supplies is that they are directly affected by voltage fluctuations in the power supply system, making it difficult to continue operation in the event of a momentary power outage (hereinafter referred to as a "momentary power outage"). If the recirculation pump speed suddenly increases when the system voltage is restored after the t1 instantaneous power outage occurs, this may lead to a rapid increase in the core flow rate and, in turn, a rapid increase in the neutron flux, which may lead to a reactor scram.

On the other hand, in the case of the MG upper set, the mechanical inertia of the companion flywheel attached to the MG upper set allows a constant supply of power to the recirculation pump motor even if a momentary power failure occurs in the power supply system. I can do it.

In the case of a stationary inverter power source, it is possible to add electrical inertia, but this would require very large DC power supply equipment and capacitors, making it impractical.

[Purpose of the invention]

The purpose of the present invention is to provide a boiling water nuclear power plant in which the recirculation flow rate is controlled by a stationary inverter, when the reactor output decreases due to an instantaneous power outage (overshoot of neutron flux).
? It is an object of the present invention to provide a recirculation flow rate control device that quickly increases the output again while suppressing the output.

[Summary of the invention]

Next, in order to clarify the features of the present invention, new findings regarding the problems of the above-mentioned prior art will be explained in more detail with reference to FIG. FIG. 4 is a schematic diagram of a conventional recirculation flow rate control device using a static inverter.

The output of the nuclear reactor 1 is controlled by changing the recirculation flow rate with a recirculation pump 3. The recirculation pump drive motor 4 uses a static inverter 11 as a power source, and the rotation speed of the recirculation pump 30 is controlled by adjusting the output frequency of the static inverter 11 in accordance with a request signal 10 from the recirculation flow rate control device 6. . The output change request signal is given manually or as an output from the turbine controller 5 to the main controller 7 of the recirculation flow rate controller 6, via the M/A operator 8 and the compensator 9.
It is output to the stationary inverter 11 as a recirculation pump rotation speed request signal 10. The static inverter 11 converts the electric power received from the regular bus 12 into alternating current power at a frequency matching the recirculation pump rotation speed request signal 10 and supplies it to the recirculation pump drive motor 4 . Recirculation pump 3 from this trap
is operated at a rotational speed according to the output request, and the output of the nuclear reactor 1 is controlled.

In the above system, when an instantaneous power outage occurs in the service bus 12, the power to the recirculation pump drive motor 4 is temporarily lost, and the rotational speed of the recirculation pump 30 decreases. A static inverter has excellent controllability because it does not have mechanical inertia like an MG top set, but at the same time, even in the event of a temporary power loss such as a momentary power outage, the rotational speed of the recirculation pump 3 remains constant. There is a problem with a significant decline. In addition, when the power is restored afterwards, the pump rotation speed increases rapidly according to the pump rotation speed request signal of the recirculation flow rate control device, so the coolant core flow rate in the reactor core 2 fluctuates, and the neutron flux also fluctuates. Become,
There was a possibility that a scram would occur due to the high neutron flux when the core flow rate increased.

Conventionally, to deal with this problem, a static inverter 11
An upper limit function for the rate of change was provided to limit the rate of increase in pump speed. In this example, the upper limit of the rate of change needs to be very small so that the neutron flux does not overshoot the rated value when the pump speed increases after an instantaneous power outage occurs.

In this case, after the neutron flux suddenly decreases due to an instantaneous power outage, it takes a long time to return to the rated value again, which increases the impact on the power transmission system and causes a bigger problem compared to the MO top-set type. was.

A series of these plant transient changes will be explained with reference to FIG. The solid line indicates the case where no countermeasures are taken, and the dotted line indicates the case where conventionally considered countermeasures are taken.

Since static inverters have almost no inertia, the recirculation pump speed decreases significantly during momentary power outages. In the solid line where no countermeasures are taken, the pump speed increases quickly after power is restored, so the neutron flux rises rapidly, leading to a high neutron flux scram.

On the other hand, if a strict rate of change limit is set in the stationary inverter 11 to limit the rate of increase in pump speed,
The recirculation pump speed increases more slowly and the neutron flux increases more slowly, avoiding scrams. However, in this method, the return of the reactor output to the initial value is slow, so the amount of loss in the generator output is large, which has a large impact on the power transmission system.

In addition, if the neutron flux and main steam flow rate signals are fed back for control, this overshoot of the neutron flux can be suppressed to some extent, but this method has problems with the detection accuracy of the feedback signal and noise 'contamination. ,
The problem is that the system becomes complicated due to the addition of noise filters and PI controllers.

Therefore, as a countermeasure to this problem, there has been a need for a simple method for quickly restoring the output when the power is restored from an instantaneous power failure.

In order to solve the problems of the prior art described above, the present invention detects the occurrence of an instantaneous power failure in the power supply system using a bus low voltage relay, determines the duration of the instantaneous failure, and based on the determination result, recirculates the power supply system. The speed request signal of the flow control system is once runback to a predetermined value, and after the plant parameters such as neutron flux are stabilized, the run pack is reset. This is the result of noting that the response of neutron flux to changes in core flow rate is very sensitive, so the rate of change in power must be limited.

In the present invention, the speed request signal of the recirculation flow rate control system is once runbacked to the extent that neutron flux overshoot at the time of restoration of power is not a problem, and after the plant parameters are stabilized with the output, the runpack is reset. , proposes a two-step recovery method that returns the output to the level before the power outage. With this measure, it is possible to increase the pump speed increase rate when power is restored.1. Output will be restored quickly.

[Embodiments of the invention]

Next, one embodiment of the present invention will be described in more detail with reference to FIGS. 1 to 3.

FIG. 1 is a schematic diagram of a boiling water nuclear power plant including a turbine control system, a nuclear reactor, and a recirculation flow control system from which the recirculation flow control system of the present invention receives signals.

The coolant circulating in the reactor 1 is pressurized by the recirculation pump 3 controlled by the recirculation flow rate control device 6, and is sent to the reactor core 2 through the jet pump, where it absorbs the heat of the nuclear reaction and boils, eliminating voids. It rises as it occurs. The water is then separated into saturated water and steam by a steam separator, and the saturated water descends through the pressure vessel, mixes with the feed water again, and returns to the jet pump. - 10,000, the steam passes through the main steam line 13, is regulated by the turbine steam control valve 14, and flows into the turbine 15,
After performing mechanical work, the water is condensed back into water in the condenser 18 and is again supplied to the reactor. Mechanical work in the turbine 15 is converted into electrical output by a generator 16 and transmitted to the power system 12.

Next, regarding the turbine steam flow rate, the opening degree of the turbine steam control valve 14 is controlled so as to keep the turbine inlet pressure measured by the main steam pressure detector constant.

The main steam pressure adjustment circuit 52 performs this control, and as a result of increasing (decreasing) the reactor output by controlling the recirculation flow rate, the steam pressure 53 increases (decreases) from the set value 54. , the regulator valve 14 is opened (closed) to increase (reduce) the turbine output in an attempt to keep the steam pressure 53 constant.

If the steam pressure 53 rises further and the pressure rise cannot be suppressed even if the control valve 14 is opened, the turbine bypass valve 1
7 is opened to dump steam directly into the condenser 18, thereby suppressing a rise in steam pressure.

As described above, the opening degree of the turbine steam control valve 14 is controlled by a command from the main steam pressure regulation circuit 52 during normal operation. When the rotational speed of the turbine generator 16 exceeds a set value due to a sudden load reduction, etc., the opening degree of the turbine steam control valve 14 is changed in priority to a control command from the turbine speed/load control circuit 57 that detected the rotational speed. reduce and prevent turbine acceleration. However, the command from the speed/load control circuit 57 closes the control valve 14 only when the turbine rotational speed 19 exceeds the set value and is at 9 o'clock.

The difference between the output from the main steam pressure adjustment circuit 52 and the value obtained by subtracting the bias component 58 from the speed/load control circuit 57 is given to the recirculation control device 7 as a load deviation signal St between the requested load and the actual load. During steady operation, the load deviation signal S1 becomes zero, and an equilibrium state is maintained. On the other hand, load deviation signal S
If 1 is not zero, the recirculation flow rate is changed to make it zero. Note that when the selector switch 25 is turned on the terminal 26A, the signal S1 from the turbine control device 5 is inputted to enter automatic operation, and when the switch 25 is turned on the terminal 26B, the signal S manually set from the console is inputted.

is input and manual operation starts.

Now, in FIG. 1, the portion surrounded by dotted lines is the function added by the present invention. 21 is a busbar low voltage detector for detecting a voltage drop on the busbar; 23 is a stationary inverter output frequency detector; 27 is a recirculation pump speed request runback command circuit; 29 is a recirculation pump speed request upper limit value setter; 3
0 is a recirculation pump speed request runback setter, 31 is a runback setting value switching circuit, and 32 is a low value priority circuit.

The recirculation pump speed request runback command circuit 17 receives the detection signal 22 of the busbar low voltage detector 21, the output signal 24 of the static inverter output frequency detector 22, the output signal of the low value priority circuit 32, and its own It takes in the output signal as a parameter and sends the necessary commands.

During normal operation, the signal 28 from the recirculation pump speed request runback command circuit 27 puts the runback signal switching circuit 31 into the pump speed request upper limit value setter 29 side. Therefore, the signal of the pump speed request upper limit value is input to the low value priority circuit 32. The speed request signal 10 from the compensator 9 is
It is compared with this upper limit value. In this case, the lower value is
Speed request signal 10 from compensator 9 is transmitted to static inverter 1
1 is input. That is, the speed of the recirculation pump 3 will be controlled as in the conventional system.

Next, we will explain the behavior when a momentary power outage occurs and there is a hole.

Even if a momentary power outage occurs during plant operation, if the power outage time is short, the amount of decrease in recirculation pump speed is small, so it is possible to immediately return the output to the level before the momentary power outage occurred. However, as the power outage increases, the amount of decrease in pump speed increases, and in order to return the output to the level before the instantaneous power outage, it is necessary to limit the speed increase rate of the pump to a small value using the static inverter 11, which slows down the return of output. This was a factor.

Therefore, in the present invention, a power outage is detected by a bus low voltage detector 21 consisting of a low voltage relay, etc., and when the power outage continues for a specified time or more, a runback setting value is set according to a signal 28 from a pump speed request runback command circuit 27. The switching circuit 31 is switched to the pump speed request runback setting device 30 side.

As a result, the low value priority circuit 32 uses the runback setting device 3.
A signal of 0 is input. Speed request signal 1 at the exit of compensator 9
0 is maintained at the value before the instantaneous power failure, but the final speed request signal 33 is limited to a value equal to or less than the runback setting value selected by the low value priority circuit 13.

Therefore, even if the pump speed increases again when power is restored,
The runback will not rise above the set value.

The run pack setting value is predetermined so that the neutron flux overshoot due to the increase in pump speed at the time of power restoration does not reach the scram level, and the restriction on the pump speed increase rate in the stationary inverter 11 can be significantly relaxed. That is, the output can be quickly restored to the run pack setting value.

Next, a control method for recovering the output from the runback setting value to the output before the instantaneous power failure will be explained.

Overshoots in neutron flux, main steam flow rate, etc. subside a few seconds after the pump speed reaches the runpack setpoint, and the plant begins to settle. Here, the recirculation pump speed request runback command circuit 27 receives the recirculation pump speed request signal 33. Static inverter output frequency signal 24. The recirculation pump speed request runback command signal 28 is used to determine the settling state of the plant, and the runback set value switching circuit 3
1 and input the speed request signal upper limit value 29 to the low value priority circuit 32. As a result, the speed request signal 10 from the compensator 9 is input to the static inverter 11, so that the recirculation pump speed increases again and returns to the speed before the instantaneous power failure. Since the difference between the run pack setting value 30 and the rated speed is small, even when the rated output is restored, scrams and the like due to neutron flux overshoot will not occur due to the increase in pump speed during this period.

Here, the setting logic of the runback setting value 30 will be explained. The runback setting value is set to satisfy the following two requirements.

■ When returning the pump speed when power is restored, set a value that will not cause scram due to neutron flux overshoot even if the rate of change of the static inverter is greatly restricted and the output is quickly restored.

■ To prevent a scram from occurring due to neutron flux overshoot when the pump speed increases from the runback setting value to the speed at rated output, set the value as close to the speed at rated output as possible.

Next, the logic of the recirculation pump speed request runback command circuit 27 will be explained with reference to FIG.

A drop in the bus voltage is detected by the bus low voltage detector 21, and a timer determines that the power outage has continued for a predetermined period of time or more, and issues a runback command for the recirculation pump speed request signal. A self-hold is applied to this word so that the runback continues even if the bus voltage is restored. The runback setting value is input to the low value priority circuit 32' by this runback command signal.

Next, when the recirculation pump speed request runback command signal 28 is being output and the deviation between the recirculation pump speed request signal 33 and the static inverter output frequency signal 24' becomes small, the recirculation pump It is determined that the speed has gradually returned to the runback set value.

After that, a timer is used to provide a delay of several seconds to determine that the plant parameters have stabilized, and this signal is used to reset the runback.

The configuration and logic of the runback command circuit shown in FIGS. 1 and 2 are just examples, and the determination may be made based on the rotational speed of the recirculation pump 3, the flow rate of the recirculation loop, or the deviation of the speed request signal 10.
Data on neutron flux and main steam flow rate for a certain period of time is constantly acquired, and the degree of stabilization of plant parameters is determined from the variation in the data.

FIG. 3 shows the plant response when the power is restored from an instantaneous power failure when the present invention is implemented. The solid line shows the case where the present invention is implemented, and the dotted line shows the case where the conventional measure of strictly limiting the rate of change of the static inverter 11 is taken.

During rated output operation, a momentary power outage occurs and the recirculation pump speed decreases significantly. After power is restored, the recirculation pump speed is set to inverter 11.
However, since the speed request signal is runback, scram due to neutron flux overshoot is avoided, and once the output of the runback setting is reached, Heading towards stabilization. After a few seconds, the runback is reset based on how well the plant has settled, and the recirculation pump speed increases again, restoring the output to the level before the momentary power failure. According to the present invention, the restriction on the rate of change of the inverter can be significantly relaxed, so that the recirculation pump speed can be restored at the time of power restoration, that is, the reactor output can be quickly and easily restored. According to FIG. 3, it is clear that the output recovery is much faster than in the conventional system.

〔Effect of the invention〕

According to the present invention, in a recirculation flow rate control device using a static inverter power supply device, even if a momentary power outage occurs, it is possible to restart safely and quickly and easily recover the once reduced reactor output. , enhance the brand's driving reliability,
Operation rate can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the recirculation flow rate control device according to the present invention together with a nuclear reactor, turbine, etc., FIG. 2 is a flowchart showing the logic of the recirculation pump speed request signal runback command circuit, and FIG. Fig. 4 shows a block diagram of a conventional example of a recirculation flow control device using a static inverter, and Fig. 5 shows a case where an instantaneous power outage occurs in the conventional example. FIG. DESCRIPTION OF SYMBOLS 1... Nuclear reactor, 2... Core, 3... Recirculation pump, 4... Recirculation pump drive motor, 5... Turbine control device, 6... Recirculation flow rate control device, 7 ...Main controller, 8...M/A operation device, 9...Compensator, 10.
...Pump rotation speed request signal, 11...Stationary inverter, 12...Common system bus, 13...Main steam line,
14...Turbine steam control valve, 15...Turbine,
16... Generator, 17... Turbine bypass valve, 1
8...Condenser, 19...Yuichi bottle rotation speed, 20...
-Static inverter output frequency, 21...Bus bar low voltage detector, 22...Bus bar low voltage detection signal, 23...Static inverter output frequency detector, 24...Static inverter output signal, 25 ...Automatic manual changeover switch,
26...Terminal, 27...Recirculation pump speed request run bank command circuit, 28...Runback command signal, 29
... Recirculation pump speed request signal upper limit value setter, 30.
...Runback setting device, 31...Runback setting value switching circuit, 32...Low value priority circuit, 33...Pump speed request signal.

Claims (1)

[Claims] 1. In a recirculation flow control device for a nuclear power plant having a static inverter for controlling the speed of a recirculation pump in a nuclear reactor, bus voltage is detected and the duration of the momentary power outage exceeds a specified value. It includes a runback command circuit that sometimes runs back the recirculation pump speed request signal to a predetermined value, reducing the inverter's restriction on the recirculation pump speed change rate when power is restored, and quickly increasing the reactor output. A recirculation flow control device characterized by a recirculation flow control device. 2. In claim 1, the runback command circuit monitors the pump speed request signal, the inverter output signal, and its own runback command, and after the recirculation pump speed has recovered to the runback set value, A recirculation flow control device characterized by determining the settling of plant parameters, resetting a runback, and restoring a pump speed to a value before a momentary power outage.