JPH0631774B2 - Recirculation flow controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Use of the Invention] The present invention relates to a boiling water nuclear plant (hereinafter referred to as BWR).
The present invention relates to a recirculation flow rate control system, and more particularly to a recirculation flow rate control device having a protection function against a sudden increase in the recirculation flow rate and a sudden increase in the reactor output due to an abnormality in the recirculation flow rate control system or the components of the recirculation system.

[Background of the Invention]

In the conventional BWR recirculation flow rate control device, the recirculation flow rate may suddenly increase or decrease due to erroneous input to the control system, erroneous operation of the control system, failure of the recirculation system constituent devices such as the MG set rake pipe operator, etc. obtain. In particular, when the recirculation flow rate increases sharply, the neutron flux increases, and in some cases,
May lead to high neutron scrum. An abnormal rise in neutron flux can adversely affect fuel integrity,
Moreover, when a neutron flux high scrum occurs, there is a problem that the operating rate of the plant decreases. Therefore, in order to prevent a rapid increase in the recirculation flow rate, the following device has been devised.

For example, in the apparatus shown in Japanese Patent Laid-Open No. 54-62490, M
A limiter for changing the limit value according to the neutron flux signal is provided before the speed controller of the G set generator. In this device, if the input signal to the controller increases abnormally due to an operator's mistaken operation, etc., limit the speed request signal entering the controller to prevent an abnormal sudden increase in the recirculation flow rate. You can However, this technique cannot cope with a malfunction of the control system or a rapid increase in the recirculation flow rate due to a failure of the components of the recirculation system.

Further, in the device disclosed in Japanese Patent Laid-Open No. 53-90591, the output signals of the control systems of two recirculation loops are compared, and when the difference is large, the recirculation flow rate is fixed. This device is effective for control system malfunction during automatic operation in which the input signals to the two-loop control system are equal. However, this device does not take measures against a control system malfunction during manual operation in which the inputs to the two-loop control system are set separately, or a sudden increase in the recirculation flow rate due to a failure of the components of the recirculation system. .

On the other hand, the power supply to the recirculation pump / motor and the rotation speed of the MG set generator are taken in to obtain the recirculation pump / motor speed increase rate (acceleration). There are those that make a judgment and generate a fail-safe operation such as a recirculation pump or trip.

However, in general, the relationship between the increase rate of the recirculation flow rate (acceleration of the recirculation pump / motor) and the increase rate of the reactor output (neutron flux) differs depending on the output state of the reactor (control rod state). . Also, reactor operation is generally limited by the rate of power increase, not by the rate of recirculation flow rate increase. That is, the determination as to whether or not it is abnormal should be made based on the rate of increase in output (neutron flux). Therefore, this technique has a problem that it is not possible to accurately determine whether or not there is an abnormality. Further, the limit value of the power increase rate may change significantly depending on the power level of the nuclear reactor, but this point has not been recognized by this technique.

[Object of the Invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to detect an abnormal increase in the recirculation flow rate due to an erroneous input to the recirculation flow rate control system, an erroneous operation of the control system, and a failure of the recirculation component equipment with high accuracy and early. , A recirculation flow rate control device that prevents the expansion of abnormal disturbance even when the limit value of the output increase rate changes with the output level by generating the protection operation and improves the operating rate of the plant by avoiding the reactor scrum Is to provide.

[Outline of Invention]

In order to achieve the above object, the rate of increase of the recirculation pump flow rate using the measurement value of the neutron flux in the core of the boiling water reactor and the measurement value of the rotation speed of the recirculation pump that circulates water in the core. In the recirculation flow rate control device having means for detecting anomalies, a function generator that obtains a limit value for determining the neutron flux increase rate anomaly according to the level change of the measurement value related to the neutron flux is anomaly detection. It is provided in the means. Moreover, when the generator rotation speed still increases after a certain period of time, a pump trip signal is output to prevent an abnormal increase in neutron flux.

Example of Invention

 Hereinafter, the present invention will be described in detail with reference to examples.

FIG. 1 is a block diagram showing the configuration of the first embodiment device together with a conventional recirculation system and a recirculation flow rate control system.

In the figure, 1 is a nuclear reactor, 2 is a core, 3 is a jet pump, and 4 is a recirculation pump. The recirculation pump 4 is driven by a pump motor 5, which
The power source is the generator 6. The generator 6 is connected to the drive motor 8 via the fluid coupling 7, and the frequency of the generator 6 can be changed by adjusting the slip of the fluid coupling 7 by the rake pipe operating device 9. On the other hand, in the recirculation flow control system,
Main controller or manual generator speed request signal 10
Is input to a speed controller 12 that performs a proportional-plus-integral operation via a limiter 11, and this output signal is sent to a scoop tube manipulator 9 via a random back generator 13 and a function generator 14.
Sent to. Further, the output signal of the rotation speed measuring device 15 of the generator 6 is input to the adder 1601 as a feedback signal.

The device 17 of the present embodiment uses signals from the neutron flux measuring device 18 and the generator rotational speed measuring device 15 provided in the core as input signals. The neutron flux measurement signal φ (t) is
After removing the high frequency noise component with the low pass filter 1901,
Guided to the differentiator 2001. Output signal of differentiator 2001 (t)
Is compared with a value ₀ set in advance in the comparator 2101 based on the limit value of the increase rate of the reactor output. The output signal of the comparator 2101 is "1" when (t)> ₀ ... (1), and "0" otherwise. This signal is led to the AND gate 2201.

On the other hand, the generator speed signal ω (t) is the low-pass filter 1
After removing the high frequency noise component at 902, it passes through the differentiator 2002, is converted into the rotation speed increase rate (t), and then is guided to the comparator 2102. The comparator 2102 outputs '1' if (t)> ε ₀ ... (2), and outputs '0' otherwise. Here, ε ₀ is a positive number close to zero, and is a value set in advance for determining whether or not ω (t) is increasing.

The signal of the comparator 2101 is also guided to the AND gate 2201. Here, when the input signals of the AND gate 2201 both become "1", the runback command signal is sent to the runback generator 13
Sent to.

On the other hand, the runback command signal '1' is the time delay circuit 2301.
Through the AND gate 2202. AND gate
2202 also receives the signal from the comparator 2102 as an input signal,
When both of these signals become "1", the recirculation pump trip signal is sent to the circuit breaker 24. This allows
The power supply 25 of the drive motor 8 is disconnected and the recirculation pump
Trip occurs. Here, the time delay Δt in the time delay circuit 2301 is set in advance by analysis by a reactor dynamic characteristic analysis program or the like.

FIG. 2 is a flow chart showing the operation of the apparatus of this embodiment. In this device, the neutron flux increase rate (t) is continuously set to _0.
Compared to. Here, ₀ is a value set based on the limit value of the neutron flux (output) increase rate necessary for maintaining the integrity of the fuel. When φ (t) exceeds this value, it is determined that the neutron flux increase rate is abnormal. On the other hand, the rate of increase in generator speed
(t) is continuously compared with the set value ε ₀ (a positive number near zero), and it is determined whether or not the generator speed is increasing. In this device, when the neutron flux increase rate (t) is abnormally high and the generator rotational speed ω (t) is increasing, that is, (t)> ₀ , and (t)> ε ₀ ...... (3 In the case of), a recirculation pump / ramback signal is generated.
With this runback signal, the runback generator installed after the speed controller forcibly limits the upper limit of the signal from the controller to a low level (corresponding to the minimum pump speed), so the signal to the rake pipe operator is , The pump speed decreases rapidly. However, this is a case of an error due to an erroneous input to the controller or a malfunction of the controller, and in the case of an error due to a failure of the recirculation system components such as the rake pipe operator,
The pump speed may continue to increase after the runback.

In order to cope with such a situation, the present apparatus again determines whether the generator rotation speed increase rate (t) is (t + Δt)> ε ₀ (4) after the time Δt has elapsed from the generation of the random signal. It is determined whether or not the generator rotation speed ω (t) is increasing. And, in spite of the occurrence of the backlash, ω
If (t) continues to increase, generate a recirculation pump trip signal. As a result, even if the pump speed abnormally rises due to a failure of the recirculation system components, the MG
By forcing the set drive motor power off, the recirculation pump speed can be reduced and an abnormal increase in neutron flux can be discouraged.

FIG. 3 and FIG. 4 are diagrams showing the effects of the device of this embodiment, and respectively show the changes over time in the neutron flux and pump rotational speed when a failure occurs in the recirculation system constituent equipment. FIG. 3 shows the conventional control system, and FIG. 4 shows the case where the apparatus of this embodiment is used.

As shown in FIG. 3, when the conventional control system is used, if the recirculation pump rotation speed increases due to equipment failure, the void ratio in the core decreases and a positive reactivity is applied. Then, the neutron flux increases rapidly. As a result, neutron flux high scrum may occur as shown in the figure.

On the other hand, as shown in FIG. 4, in the apparatus of this embodiment, when the neutron flux increase rate becomes abnormally high, as described above, first,
A random signal is generated. In the case of an abnormality due to an erroneous input to the control system or an erroneous operation of the controller, an abnormal increase in pump speed and neutron flux can be stopped by this randomization. However, if the cause of the abnormality is a device failure, the pump speed continues to increase even after the occurrence of the backlash. Therefore, the present apparatus outputs the pump trip signal after the time Δt has elapsed from the generation of the random signal. As a result, increases in pump speed and neutron flux are suppressed as shown in the figure. As described above, according to the present device, it is possible to suppress the fluctuation of the neutron flux and to avoid the neutron-high scrum that occurs when the recirculation flow rate is abnormally rapidly increased.

FIG. 5 is a circuit diagram showing the configuration of the second embodiment device.
In the figure, 26 is a neutron flux signal φ (t), 27 is a generator rotation speed signal ω (t), 1903 and 1904 are reduced passage filters, 290
1, 2902 is an arithmetic unit, 2103, 2104 are comparators, 2203, 2204 are AND gates, 2302 is a time delay circuit, 2801 is a function generator, function generator 2801, an arithmetic unit 2901 for calculating the change rate of the signal. , 2902, the configuration is the same as that of the first embodiment device.

Currently, regarding the operation of a nuclear reactor, in the method recommended for preventing fuel damage, it is necessary to change the limit value of the output increase rate according to the value of the output (linear power density) depending on the fuel combustion history. . As an example, when the output is about 50% or more, the control value of the output increase rate changes to about 1% / hr, and when it is less than about 30% / hr.

In the apparatus of the present embodiment, in order to deal with the change in the output level of the limit value of the output increase rate, using the function generator 2801, the set value for the output increase rate abnormality determination in the comparator 2103.
₁ is changed according to the level of neutron flux φ (t) (output). With this function generator 2801, even when it is necessary to change the limit value of the output increase rate according to the output level, this device accurately detects an abnormal increase in the recirculation flow rate or output, and It is possible to early generate the protection operation of. As a result, even when the limit value of the output increase rate changes depending on the output level, it is possible to prevent the expansion of disturbance or avoid scrum.

In the comparator 2104 of this embodiment, the comparison signal set value ε
_{As the value 1} , a value determined in advance by analysis or the like is used to determine the high rate of increase in the generator rotation speed.

FIG. 6 shows an arithmetic unit 2901 used in the apparatus of this embodiment.
2 is a circuit diagram showing a configuration of 2902. FIG. Input signal φ as shown
The (t) 30 is taken in by the AD converter 31 at the sampling period Δt _S and is guided to the shift register 32. Of the data stored in the shift register, the first (n + 1) (φ (t), ..., φ (t−n)) and the last (n + 1) (φt−N + n), ..., φ (t -N))
Are added in adders 3301 and 3302, respectively, and the results are multiplied by 1 / (n + 1) in multipliers 3401 and 3402, respectively. The outputs of these multipliers 3401 and 3402 are the time average values of the signal φ at the times when the time (N−n) Δt _S differs. These output signals are the adder 3303.
And subtracted by 1 / {(N−n) Δ in the multiplier 3403.
It is multiplied by t _S } and output. This output is the time (N-
n) Corresponds to the average rate of change of signal φ in Δt _S. That is, this arithmetic unit functions like a differentiator.

FIG. 7 is a circuit diagram showing the configuration of the third embodiment device.
As shown in the figure, the neutron flux signal φ (t) 26 and the generator rotation speed signal ω (t) 27 are taken in the present apparatus. The neutron flux signal φ (t) is guided to the calculator 35 directly or via the function generator 2802. The rotation speed signal ω (t) is also input to the calculator 35. Here, the function generator 2802 deals with the case where the limit value of the output increase rate differs depending on the output level, and the limit value _{2 of the} neutron flux increase rate is calculated from the value of the neutron flux signal φ (t). Ask for. In addition, the calculator 35
Is to compute the limit value ₂ of the generator rotational speed increase rate corresponding to the limit value ₂ of the neutron flux increase.

This limit value ₂ and rotation speed signal ω (t)
905, the signal (t) processed by the differentiator 2003 is compared with the comparator 2105
In the case of (t)> ₂ (5), the rake signal "1" is generated.

Also, this '1' signal is passed through the time delay circuit 2303,
It is led to the AND gate 2205. The signal from the comparator 2106 is also input to the AND gate 2205. Comparator 21
In 06, the rotation speed increase rate (t) is compared with a positive set value close to zero (preset in consideration of the accuracy of the comparator) ε _2, and (t)> ε ₂ (6) In the case, "1" is output, and in other cases, "0" is output. The AND gate 2205 generates a pump trip signal when all of these input values are "1".

FIG. 8 is a diagram showing the contents of processing in the computing unit 35. From what is generally called a flow rate control curve (which gives the relationship between the output and the recirculation flow rate), the recirculation flow rate and the generator rotational speed ω are shown. It is obtained by using the relationship of. The curves in the figure are
Supports different control rod patterns.

The computing unit 35 first determines the current operating point as shown in the figure using the neutron flux signal φ (t) and the generator rotational speed signal ω (t). Next, using the limit value ₂ of the neutron flux increasing rate which is the output of the function generator 2802 (amount of increase per unit time), as shown in the figure, the increase rate of the corresponding generator speed limit ₂
And output.

FIG. 9 is a flowchart showing the operation of this device. As shown in the figure, in the present device, the neutron flux signal φ (t) is used to obtain the limiting value ₂ of the neutron flux increase rate according to the output level. Next, the neutron flux signal φ (t),
Using the generator speed signal ω (t) and ₂ , the limit value ₂ of the speed increase rate is obtained. And (t) and ₂
Are compared, and if the rotation speed exceeds the limit value, a rake signal is sent to the rake operation device. As a result, the position of the rake tube is fixed and the increase in the number of rotations is stopped. However, when the flow rate is abnormally increased due to a failure of the components of the recirculation system, the rotation speed may continue to increase even if the lock signal is generated. To handle this situation,
In the device of this embodiment, the time Δ
After t _{2 has} elapsed, the rotational speed increase rate signal (t + Δt) is compared with ε _2, and if the rotational speed is increasing despite the lock signal, a recirculation pump trip signal is generated. As a result, the power of the MG set drive motor is turned off and off, the pump speed is reduced, and an increase in neutron flux can be prevented. It should be noted that the recirculation pump trip can also be used to turn off the generator field circuit or the damper. Therefore, the same operation can be realized even if the trip signal of the present device is guided to the field magnet or the dumper.

FIG. 10 is a diagram showing the effect of the device of the present embodiment, and shows changes in the neutron flux and the pump rotation speed when an abnormality such as a rapid increase in recirculation flow rate due to a malfunction of the speed controller occurs.

In the device of the present embodiment, since the rake signal of the rake pipe is issued when the increasing rate of the generator rotational speed exceeds the control value, the pump rotational speed and the neutron flux are suppressed from increasing as shown in the figure.
On the other hand, in the case of the conventional control system, the neutron flux rapidly increases, and a neutron flux high scrum may occur as shown in the figure. As described above, by using the present device, it is possible to suppress the abnormal fluctuation of the neutron flux to a small level and to avoid the neutron flux high scrum which may occur.

As described above, this device, after the lock signal is generated,
When the number of revolutions continues to increase, a pump trip is generated, so that the same effect as above can be obtained even when the flow rate is abnormally increased due to a failure of the recirculation system constituent device.

FIG. 11 is a block diagram showing an example in which the devices of the first, second, and third embodiments are applied to a plant having a recirculation system using an inverter. In the figure, 1 is a reactor, 2 is a core part, 36 is a recirculation pump, 37 is a pump / motor, 40
Is a recirculation control system. In this plant, unlike the plant with MG set, the rotation speed of the pump / motor is
It is adjusted by changing the power supply frequency to the pump / motor by the inverter 38. Inverter drive circuit 39
Controls the thyristor in the inverter 38.

For this plant, the power supply frequency measuring device 41 of the inverter is used in place of the generator speed signal, and the trip signal is supplied to the inverter 42 or the breaker 43.
To the run-back generator of the control system 40, and the frequency lock signal (corresponding to the scoop tube lock signal) to the frequency lock circuit of the inverter drive circuit 39.
When output respectively, the first, second and third embodiment devices 44
Can be applied. Further, these examples can be similarly applied to a plant using an internal pump.

〔The invention's effect〕

As described above, according to the present invention, in a BWR plant, the recirculation flow rate is abnormally increased due to an erroneous input to the recirculation flow rate control system, a malfunction of the control system, a failure of components of the recirculation system, and the like. It is possible to suppress the fluctuation of the neutron flux when the limit value of the rate of increase changes with the output level, and to avoid the neutron flux high scrum. Therefore, when the recirculation flow rate control device of the present invention is used, safety is improved and the effect of preventing a decrease in operating rate due to scrum is great.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention,
FIG. 2 is a flow chart showing its operation, FIGS. 3 and 4 are diagrams showing its effect, FIG. 5 is a circuit diagram showing the configuration of the second embodiment, and FIG. 6 is an operation used in it. FIG. 7 is a circuit diagram showing the configuration of the third embodiment, FIG. 7 is a circuit diagram showing the processing contents in the arithmetic unit used therein, and FIG. 10 is a flowchart showing the operation of the embodiment.
FIG. 11 is a diagram showing the effect, and FIG. 11 is a block diagram showing an example in which the first to third embodiments are applied to a plant using an inverter. DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Core part, 3 ... Jet pump, 4 ... Recirculation pump, 5 ... Pump / motor, 6 ... Generator, 7 ... Fluid coupling, 8 ... Drive motor, 9 ... Scoop pipe operating device, 10 ...
Generator speed request signal, 11 ... Limiter, 12 ... Speed controller, 13 ... Ranbak generator, 14 ... Function generator, 15
... Rotation speed measuring device, 1601 ... Adder, 17 ... First embodiment detection device, 18 ... Neutron flux measuring device, 1901, 1902, 1903, 1904
… Low-pass filter, 2001, 2002, 2003… Differentiator, 210
1, 2102, 2103, 2104, 2105, 2106 ... Comparator, 2201, 220
2, 2203, 2204, 2205 ... AND gate, 2301, 2302, 230
3 ... Time delay circuit, 24 ... Shatter breaker, 25 ... Power supply, 26
… Neutron flux signal, 27… Generator speed signal, 2801, 2802
... Function generator, 2901, 2902 ... Operation unit, 30 ... Signal, 31
... AD converter, 32 ... shift register, 3301, 3302,
3303 ... adder, 3401, 3402, 3403 ... multiplier, 35 ... arithmetic unit, 36 ... recirculation pump, 37 ... pump / motor, 38
... Inverter, 39 ... Inverter drive circuit, 40 ... Recirculation flow control system, 41 ... Power supply frequency measuring device, 42 ... Power supply,
43 ... Shiya breaker, 44 ... 1st-3rd Example apparatus.

Claims (2)

[Claims] 1. An abnormality in the rate of increase of the recirculation pump flow rate is determined by using a measurement value related to the neutron flux in the core of a boiling water reactor and a measurement value related to the rotational speed of a recirculation pump for circulating water in the core. In the recirculation flow rate control device having a means for detecting, the abnormality detecting means is provided with a function generator for obtaining a limit value for determining the neutron flux increase rate abnormality according to the level change of the measurement value related to the neutron flux. A recirculation flow rate control device characterized in that 2. The means for detecting an abnormality in the rate of increase in the recirculation pump flow rate, when detecting an abnormality in the rate of increase in the recirculation pump flow rate, issues a protection operation for fixing or decreasing the rotational speed of the recirculation pump. The recirculation flow rate control according to claim 1, further comprising a circuit for instructing a trip operation for disconnecting the pump drive source when the rotation speed of the recirculation pump continues to increase even after a lapse of a certain time. apparatus.