JPH02244000A - Method and device for controlling nuclear power plant - Google Patents

Abstract

PURPOSE:To prevent the fall of a water level down to the reactor scram set value of a BWR by inserting a selected control rod into the core to drop the reactor output when a feed water pump trips. CONSTITUTION:A feed water pump trip detector 17 is inputted with the state quantity measured in association with the feed water pump, detects the trip and outputs a trip signal S4. A recirculation rate controller 13 is inputted with signal S4 and the reactor water level measured by a water level detector 8 and outputs a run-back signal S7 of a recirculation pump 15 when the AND circuit conditions of the reactor water level La (water level about 20 to 30cm below the ordinary level) and the signal S4 hold. A controller 28 outputs a limit request signal S5 and a selected control rod insertion request signal S6 when the signals S4 and S7 are inputted thereto. A control rod controller 20 is inputted with the signal S6 and inserts the selected prescribed control rod 22 into the core. The reactor output is dropped in this way until the reactor water level rises and is held constant at a certain level. The reactor scram is thus averted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a nuclear power plant control method and its control device, and is particularly applicable to boiling water reactors and suitable for avoiding reactor scrams. This invention relates to a nuclear power plant control method and its control device.

(Prior art) A conventional boiling water reactor has two turbine-driven water pumps (referred to as T/D-RFP) and two motor-driven water pumps.
It has two water supply pumps (referred to as M/D-RFP). During normal operation, two T/D-RFPs are driven;
The M/D-RFPs are in a standby state. 2 T/D-
If one of the RFPs trips, two
M/D-RFP is activated. However, if M/D-RFP is not started for some reason, one T
/D-RFP has only about 55% of the water supply capacity, so
Water supply flow to the reactor pressure vessel is insufficient. For this reason, the reactor water level continues to drop, and the water level may drop to a predetermined reactor water level, leading to a reactor scram.

To avoid this situation, recirculation flow controllers
The feedwater pump trip signal and the reactor water level La signal are taken in to run back the recirculation pump. The runback of the recirculation pump reduces the reactor output and prevents the 3yX child reactor water level from dropping.

At the same time, the water supply control signal, which is the output of the water supply controller performing three-element control, is limited to 68% of its signal level.
For example, when a water supply control signal with a water supply flow rate of 100% is output from the water supply controller, the water supply control signal becomes a control signal with a water supply flow rate of 68%. Specifically, T/D-RFP with a rated capacity of 55%,
It will operate at 68% capacity. This control is performed by the output of the water pump trip detector. Other water supply pumps that do not trip are transiently placed in a runner-out operation state. By limiting the water supply request signal, tripping of other water supply pumps due to bon run-out is avoided. If the other running water pump trips again,
Leading to a reactor scram.

In addition, conventionally, one T/D-RFP in operation was 68%
Even if the reactor is operated at capacity, the recirculation bomb runback will cause the reactor output to drop in an extremely short period of time (approximately 1 minute) to a reactor outlet corresponding to 55% of the feedwater flow rate.

[Problem to be solved by the invention]

Recently, expansion of the power control range at rated output using core flow rate control, that is, expansion of the operating range, has been studied. It has been newly discovered that the following problem occurs when the operating range is expanded in the conventional example described above. In operating conditions with low core flow rate and high reactor power, if one T/D-RFP trips and the M/D-RFP is not activated, the reactor is activated by recirculation bomb runback for the lower core flow rate. The amount of decrease in output is small, and there is a possibility that the output decrease will not reach the level of the reactor output commensurate with the water supply capacity of the water supply pump being driven. This prevents the reactor water level from recovering and leads to a reactor scram. Figure 7 is.

The characteristics when the operating range is expanded in the conventional example are shown.

An object of the present invention is to provide a method for controlling a nuclear power plant and a control device for the same, which can expand the operating range in a state where the possibility of reactor scram is low.

[Means to solve the problem]

The above objectives can be achieved by inserting selective control rods into the reactor core when the feedwater pump trips.

[Effect]

By inserting selective control rods, the reactor output can be significantly reduced when the feed water pump trips.

It is possible to prevent the reactor water level from decreasing to the scram set value.

〔Example〕

A control device for a nuclear power plant, which is a preferred embodiment of the present invention applied to a boiling water nuclear power plant, will be described below with reference to FIG.

First, an overview of boiling water nuclear power plants will be explained. Steam generated within the reactor pressure vessel 1 is led to the turbine 3 through the main steam pipe 2, and after rotating the turbine 3, is condensed in the condenser 4 and returned to water. This water is supplied to the water supply pump 5A as cooling water.

5B, 5G, 5D, etc., and is returned to the reactor pressure vessel l via the water supply pipe 6. The water supply pumps 5A and 5B are turbine-driven, and each has a capacity that can supply 55% of the water supply flow rate.

Water supply pumps 5C and 5D are motor-driven and have approximately 27.5
It has the capacity to supply a water supply flow rate of 20%.

The recirculation pump 15 is installed in a recirculation pipe connected to the reactor pressure vessel 1 . Cooling water is supplied into the core 21 by driving the recirculation pump 15 .

7 is the liquid level of cooling water in the reactor pressure vessel 1, and 22
is the control rod. A water level detector 8 is provided in the reactor pressure vessel 1 . A flow rate detector 10 for detecting the flow rate of water supply is provided in the water supply pipe 6, and a flow rate detector 11 for detecting the flow rate of steam is provided in the main steam pipe 2, respectively.

The feed water controller 1 inputs the reactor water level detected by the water level detector 8, the feed water flow rate detected by the flow rate detector 10, and the steam flow rate detected by the flow rate detector 11, and based on these values, the conventional Control of the water supply flow rate 1, for example, the rotational speed of the water supply pumps 5A and 5B, is carried out using the well-known three-element control system. During normal operation of the nuclear reactor (for example, at 100% rated output operation), two turbine-driven water pumps 5A and 5B are driven. At this time, the motor-driven water supply pumps 5C and 5D are on standby as standby machines.

The output signal (water supply control signal) Sl of the water supply controller 12 is input to the signal limiter 19. The function of the signal limiter 19 is shown in FIG. 2 in terms of hardware. That is, the signal limiter 19 includes opening/closing means 23, 24, and 25 and limiters 26 and 27 connected in parallel. Opening/closing means 2
Input terminals 3 to 25 are connected to the water supply controller 12. The limiters 26 and 27 are arranged in parallel, with the limiter 26 being connected to the output end of the switching means 24 and the limiter 27 being connected to the output end of the switching means 25. The output ends of the restrictors 26 and 27 are connected to the output end of the opening/closing means 23. The opening/closing means 23 is opened by the input of a trip signal 84 that is output when the water supply pump trip detection device 17 detects a trip of the water supply pump.

The opening/closing means 23 is also opened by inputting the restriction request signal S6 output by the control device 28.

When the trip signal S4 and the restriction request signal SR are not input, the opening/closing means 23 is closed. The opening/closing means 24 is closed by the input of the trip signal S4 and is engaged when the limit request signal S3 is input or when the trip signal S4 and the limit request signal S6 are not input. The opening/closing means 25 is
(control) is closed when the request signal S6 is input, and is opened when the signal is not input. Such a signal limiter 19 can also be configured by a program using a computer such as a microprocessor. Water supply control No. 4 outputted from the signal limiter 19 is used to control a predetermined water supply pump. It can also be said that the water supply controller 12 and the signal limiter 19 constitute a water supply control device.

The feedwater pump trip detection device 17 detects the rotational speed of the feedwater pump and the oil/steam flow rate (T) supplied to the pump drive turbine.
/D-RFP), the current supplied to the motor, ! A measured state quantity related to the water pump, such as pressure (in the case of M/D-RFP), is input to detect a water pump trip. The water supply pump trip detection device 17 outputs a trip signal S4 when detecting a trip of the water supply pump. Trip signal S4 is communicated to recirculation flow controller 13, signal limiter 19 and controller 28.

The recirculation flow rate controller 13 inputs the trip signal S4 and the reactor water level measured by the water level detector 8.

A runback signal for the recirculation pump 15 is output when the AND condition of the reactor water level La and the trip signal S4 is satisfied. The set reactor water level La does not reach the actual reactor water level when one water pump (T/D-RFP) is tripped and the standby unit (M/D-RFP) is not activated.
In addition, the recirculation Bonplan pack is designed to avoid a reactor scram due to low reactor water level in the event of standby engine failure. The reactor water level La is approximately 20% lower than the normal water level.
It is standard to set the value lower than ~30 (!l). During normal operation of a nuclear power plant, the recirculation flow rate controller 13 responds to the reactor output change request output from the turbine control device (not shown). The variable frequency power supply device 14 inputs a signal and outputs a control signal to control the rotation speed of the recirculation pump 15 according to the signal.
A runback signal or a control signal output from the recirculation pump 15 is input, and a signal corresponding to the input signal is output to the recirculation pump 15. In this way, the recirculation pump 1''5 is limited to the required rotation speed, and the flow rate of cooling water (core flow rate) supplied to the reactor core 21 is adjusted.

The IIJ# device 28 outputs a restriction request signal S8 and a selected control rod insertion request signal S6. This function will be explained below. The control device 28 includes an interlock shown in FIG. The control device 28 outputs a trip signal S4.
, the recirculation bomb runback signal, the reactor water level measured by the water level detector 8 and the feedwater flow rate measured by the flow rate detector 10 are input.

The control device 28 includes AND circuits 29, 30 and 31.

Judgment units 32 and 33, timer 36, and signal generation unit 34
and 35. The determination unit 32 determines that the water supply flow rate is a predetermined value (
For example, the determination unit 33 determines whether the reactor water level is equal to or higher than a predetermined value Lb, and outputs "1" if it is equal to or higher than a predetermined value. Outputs "1" if The predetermined value Lb of the reactor water level is set to a value lower than the normal water level and higher than the reactor water level La at which the recirculation bomb runback signal is output (
The signal generator 34 outputs a limit request signal S5 (usually set at about 10 cm below the normal water level). The signal generator 35 outputs a 1 selection control insertion request signal S8.

The selected control rod insertion request signal S6 is input to the control rod control device 2o.

The control rod control device 20 drives the control rods 22 based on an operator's operation command, and rapidly inserts the selected control rod 22 when the selected control rod insertion request signal S8 is input.

During normal operation of the boiling water reactor, the switching means 23 of the signal limiter 19 is closed and the other switching means 24 and 25 are open. Therefore, the water supply control signal S1 output from the water supply controller 12 is output from the signal limiter 19 as it is.

Next, a case will be described in which the water supply pump 5B of the two water supply pumps 5A and 5B in operation trips and the water supply pumps 5C and 5D on standby do not start for some reason. The water supply pump trip detection device 17 is connected to the water supply pump 5B.
Detects the trip and outputs a trip signal S4. In the signal limiter 19, the opening/closing means 23 and 25 are opened and the intervening means 24 is closed.The water supply controller signal Ss is inputted to the limiter 26 via the opening/closing means 24. The water supply control signal 81 requesting a 100% water supply flow rate becomes the water supply control signal s2 requesting a 68% water supply flow rate, and the water supply control signal 81 requests a 68% water supply flow rate.
is output from. The driven water supply pump 5A is rotated based on the water supply control signal S2 so as to discharge a water supply flow rate of 68%, which is larger than the rated capacity of 55%. The water supply pumps 5A and 5B, which have a rated capacity of 55%, can be operated at 68% for a short time. Due to the action of the signal limiter 19, the water supply flow rate is reduced as shown in FIG. 4(A). The recirculation flow rate controller 13 outputs a recirculation bomb run back signal when the trip signal S4 is input and the reactor water level reaches the "reactor water level low" level. When this signal is output, the rotation speed of the recirculation pump 15 decreases rapidly.

The flow rate of cooling water supplied to the core 21 decreases to a flow rate corresponding to 20% of the recirculation pump rotation speed. Since the reactor power also sharply decreases, the main steam flow rate discharged from the reactor pressure vessel 1 by the recirculation Bonplan pack rapidly decreases as shown in FIG. 4(B). As shown in FIG. 4(C), the recirculation bomb runback also suppresses the drop in the reactor water level, and the reactor water level eventually begins to increase.

When the control device 28 inputs the trip signal S4 and the recirculation bomb run back signal, the AND circuit 29 changes to logic [1].
Output. Since the measured water supply flow rate is 68%,
The determination unit 32 outputs logic "1". The timer 36 operates to AND the logic "1" when the AND circuit 29 outputs the logic "1" one minute after the AND condition of the trip signal S4 and the recirculation Bonrun back signal is satisfied. to the circuit 30. At this time, since the determination unit 32 also outputs the logic TIJ as described above, the AND circuit 30
outputs logic “1” to the signal generator 34. The signal generating unit 34 generates a restriction request signal SI when logic “1” is input.
! Output l. In the signal limiter 19, the opening/closing means 23 and 24 are opened and the opening/closing means 25 is closed. The water supply control signal S1 outputted from the water supply controller 12 and requesting 100% water supply flow rate is input to the limiter 27 via the opening/closing means 25 and becomes the water supply control signal S3 requesting 55% water supply flow rate, and the water supply control signal S1 outputs from the water supply controller 12 and requests 55% water supply flow rate. Signal limiter 1 as control signal S3
Output from 9. Since the rotation speed of the water supply pump is controlled based on this water supply control signal S8, the reactor pressure vessel 1
The flow rate of water supplied to the area is limited to 55% or less.

The determination unit 32 outputs the logic rlJ when the reactor water level becomes equal to or higher than Lb, as shown in FIG. 4(C). The AND circuit 31 is configured such that the AND circuit 30 and the determination unit 33 have a logic “1”.
”, a logic “1” is output to the signal generator 35. The signal generator 35 outputs a selected control rod insertion request signal S8 when the logic "1" is input. The control rod control device 20 receives the signal and inserts a predetermined selected control rod into the reactor core. By inserting the selective control rods, the reactor output decreases and the main steam flow rate decreases as shown in FIG. 4(B).

By limiting the water supply flow rate to 55% using the water supply control signal S8, the reactor water level is temporarily lowered to below Lb as shown in FIG. 4(C). However, the reactor water level begins to rise due to the insertion of the selective control rods and is kept constant at a certain level. Therefore, the reactor water level is
Reactor scram can be avoided without descending to the scram setting level.

In this example, even if one feedwater pump trips and the standby pump does not start up under low core flow rate and high output (for example, 100% rated output) operation state when the operating range is expanded, recirculation pump back-up is possible. Insufficient reactor power reduction width can be compensated for by inserting one selected control rod. Therefore, in this embodiment, even if the water supply pump trips when the operating range of the nuclear reactor is expanded, a reactor scram can be reliably avoided.

That is, in this embodiment, it is possible to expand the operating range (expanding the operating range in which the reactor output can be controlled at a constant level by core flow rate control) in a state where the possibility of reactor scram is small. Note that the reduction in reactor power due to recirculation bomb runback and the reduction in reactor power due to selective control rod insertion are functionally different as follows. The recirculating bomb runback transiently increases voids within the reactor core 21, resulting in a rise in the reactor water level. Insertion of selective control rods transiently lowers the reactor water level in order to reduce voids in the reactor core 21.If the insertion of the zero-selective control rods precedes the recirculation bomb runback, the reactor water level will drop. There is a possibility that this could lead to a reactor scram.

Therefore, the selective control rods are inserted after the recirculation pump runback (preferably after the reactor water level has recovered to a predetermined value, e.g. Lb, by the recirculation pump runback) or in parallel with the recirculation pump brushback. 8 In this example, the reactor water level is reduced to L by executing recirculation bomb runback.
This is an example in which the selection control rod is inserted after recovery to b.

6 with the reactor output reduced by selective control rod insertion.
When one water pump 5A is operated for a long time (for example, over 1 minute) to obtain a water supply flow rate of 8%, the water pump 5A is tripped to prevent runout. However, in this embodiment, the limit request signal S5
Since the water supply flow rate is again restricted at , it is possible to prevent the running water pump 5A from running out even by inserting a selective control rod. Since the runout of the pump is limited by the second limit value (55%) which is lower than the first limit value (68%, for example), the water supply pump 5A can be driven for a long time to supply water. This is because the second limit value is the rated capacity of the water pump 5A, and the value is preferably set to be less than or equal to the rated capacity of the water pumps 5A and 5B.

If the limit value of the signal limiter 19 at the time when the trip signal S4 is generated is set to the second limit value, even if the feed water flow rate decreases too much and recirculation bomb runback is performed, the reactor water level will not reach the scram setting. There is a possibility that the value may drop. The first limit value needs to be larger than the rated capacity of the water pump (T/D-RFP) within the allowable range.

Other embodiments of the present invention will be described below.The configuration of this embodiment will be explained based on FIGS. 5 and 6.

Most of this embodiment is the same as the embodiment of FIG. In this embodiment, a control device 40 is used in place of the control device 19 of the previous embodiment. 39 is an output detector (neutron detector).

The interlock of the control bag @40 will be explained with reference to FIG. The control device 40 includes determination units 32 and 41, and a signal generation unit 34.
, 35, timer 36, OR circuit 42, and AND circuit 4
The 1 determining unit 41 having the output voltage 3 inputs the output of the output detector 39 and outputs a logical ``1'' when the reactor output becomes equal to or higher than a predetermined value. The OR circuit 42 includes the determination unit 32 and the M
/D-RFP deactivation signal is input. AND circuit 43
is the trip signal S4. The output of the OR circuit 42 and the output of the determination section 41 are input. Among the interlocks of the control device 40, the parts having the same symbols as the control device 28 are the same as those of the control device 28.
It has the same function as the corresponding part of . M/D-RFP
Non-starting of the water supply pumps 5C and 5D is detected by a water pump non-starting detector (not shown). The water pump trip detection device 17 can be used as a water pump non-start detector. This is because the water pump trip detection device 17 can also detect the stopped state of the water pump.

The OR circuit 42 outputs a logic "1" when the 1 determining section 32 outputs a logic "1" or when the M/D-RFP in the standby state is not activated. The AND circuit 43 outputs the logic rlJ when the trip signal 84 and the logic "1" which is the output of the OR circuit 42 and the determination unit 41 are input. This logic "1" is transmitted to signal generators 34 and 35.

However, if the AND circuit 43 is still outputting the logic "1" one minute later due to the action of the timer 36, this logic "1" is transmitted to the signal generating section 35. Signal generator 3
4 and 35 are the selected control rod insertion request signal Ss and the restriction request signal SI! by inputting logic "1". Output.

This embodiment provides the same effects as the previously described embodiments. This embodiment is an example in which the recirculation bomb runback by the recirculation flow rate controller 13 and the insertion of the selected control rod are started at the same time. This is because the same judgment as recirculating Bon Runback,
The control device 40 includes a determination as to whether or not the AND condition is established between the short trip signal S4 and the reactor water level La or lower.

The determination unit 41 determines that the current reactor output detected by the output detector 39 is greater than or equal to the reactor output corresponding to the 55% water supply flow rate, that is, it is not possible to operate one water supply pump 5A in operation for a long time. This is to determine that the situation is impossible. By providing the determination section 41, the selective control rod can be inserted only when necessary.

Without providing the determination unit 41, the control device 40 is configured to input logic “1” to the signal generation units 34 and 35 when the AND condition of the trip signal S4 and the output of the OR circuit 42 is satisfied. Also, it is possible to expand the operating range in a state where the possibility of reactor scram obtained in each of the above-described embodiments is small.

More specifically, the trip signal S4 and the reactor water level below a predetermined value (judgment unit 3
The control device 40 may be configured to output the selective control rod insertion request signal S6 and the restriction request signal S6 when the AND condition of (determination in step 2) is established.This also reduces the possibility of the above-mentioned reactor scram. It is possible to expand the operating range due to the low The establishment of the AND condition of the trip signal S4 and the reactor water level below a predetermined value is a requirement for the recirculation flow rate controller 13 to output the recirculation bomb run back signal.

For this reason, the input of each input signal to the AND circuit 43 and the installation of the AND circuit 43 are stopped, and the recirculation bomb runback signal output from the recirculation flow rate controller 13 is taken in and the signal S
Even if the control device 40 is configured to output signals 11 and Ss, the effects of the embodiment shown in FIG. 1 can be obtained.

〔Effect of the invention〕

According to the present invention, expansion of the operating range through core flow rate control can be achieved while reducing the possibility of reactor scram.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a control device for a nuclear power plant which is a preferred embodiment of the present invention, FIG. 2 is a detailed block diagram of the signal limiter shown in FIG. 1, and FIG. 3 is a block diagram of the control device 28 of FIG. An explanatory diagram showing the interlock of one T/D-RF P
An explanatory diagram showing the characteristics of the embodiment of FIG. 1 when the M/D-RFP trips and does not start, FIG. 5 is a configuration diagram of another embodiment of the present invention, and FIG. 6 is a diagram showing the characteristics of the embodiment of FIG. FIG. 7 is an explanatory diagram showing the interlock of the control device 40, and FIG. 7 is an explanatory diagram showing the characteristics of the conventional example when the operating range is assumed to be expanded. 1... Reactor pressure vessel, 2... Main steam pipe, 5A~5
D... Water supply pump, 8... Water level detector, 10.11
...Flow rate detector, 12...Water supply controller, 13...
Recirculation flow rate controller, 15... Recirculation pump, 17...
・Water pump trip detection device, 19... Signal limiter, 28° 40... Control device. 26.27...Restrictor Diagram Diagram Diagram Current Water Supply Pump Torisoge Hunt Dark Diagram Diagram Water Supply Pump Trip Time

Claims (1)

[Claims] 1. A method for controlling a nuclear power plant including a plurality of water supply pumps that supply water to a nuclear reactor, and a plurality of control rods inserted into the core of the nuclear reactor; A method for controlling a nuclear power plant, comprising detecting a trip and inserting a selective control rod into the reactor core when the water pump trips. 2. Detecting a trip of a feed water pump that supplies water to a nuclear reactor, and upon detecting this trip, causing a recirculation pump that supplies coolant into the core of the nuclear reactor to run back;
A method for controlling a nuclear power plant, comprising inserting selected control rods into the reactor core in parallel with or after the runback of the recirculation pump. 3. means for detecting a trip of the water pump; a control means for outputting a selective control rod insertion signal when the trip is detected and the reactor water level drops below a predetermined value; and a control means for outputting a selective control rod insertion signal based on the selective control rod insertion signal. and control rod control means for inserting selective control rods. 4. Water supply control means for outputting a water supply control signal, wherein the control means for outputting the selected control rod insertion signal outputs a restriction signal based on the detection of the trip and the decrease of the reactor water level below the predetermined value. 4. The control device for a nuclear power plant according to claim 3, further comprising means for outputting the water supply control signal and for limiting the level of the water supply control signal based on the output of the limit signal.