JP2815591B2 - Recirculation pump protector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a protection device for a recirculation pump.

[Conventional technology]

FIG. 4 shows an outline of a configuration example of a nuclear power plant. As shown in the figure, a two-phase flow of water and steam generated in a nuclear reactor 1 is separated into steam and water by a steam separator 2. The mixed water of the condensed water and the feedwater from the feedwater pump 3 is led to the recirculation pump 5 through the down pipe 4, where the pressure is increased and returns to the nuclear power 1 again. The number of recirculation pumps 5 varies depending on the scale of the power plant and the capacity of the recirculation pump 5, but it is better to provide a plurality of small-capacity pumps than one large-capacity pump when one recirculation pump fails. In general, a plurality of reactors are provided because they are advantageous in securing the core flow rate. In this example of the nuclear power plant, two recirculation pumps 5A and 5B are provided. The steam separated by steam in the steam separator 2 is recovered as condensed water in the condenser 7 after the steam turbine 6 is rotated, and is pressurized by the feed water pump 3 and supplied to the steam separator 2. . In general, a plurality of water supply pumps 3 are provided for risk distribution. In this example, two of the three water supply pumps are for regular use and one is for spare use. During high-power operation, when a trip occurs in both the service water supply pumps 3A and 3B and a loss of water supply flow occurs, such as when the backup water supply pump 3C fails to start, a subcooling at the inlet side of the recirculation pump is performed. When the recirculation pump 5 is operated at a high speed as it is, cavitation is generated. Therefore, the conventional device is disclosed in
As described in Japanese Patent No. 154697, when a loss of the feedwater flow rate occurs, the recirculation pumps 5A and 5B are tripped at the same time to prevent the occurrence of cavitation of the recirculation pumps 5A and 5B. I was In FIG.
(8A, 8B) is a recirculation pump flow rate detector, 9 is a manifold, 10 is a feedwater control valve, 11 is a generator, and 12 is a feedwater flow rate detector.

FIG. 5 shows a conventional example of a protection device for a recirculation pump. As shown in the drawing, when detecting that the supply water flow has decreased, the supply water flow decrease detector 13 transmits a supply water flow decrease signal 14. When the recirculation pump control device 15 receives the feed water flow rate reduction signal 14, it sends a recirculation pump trip signal 16 to recirculation pump power circuit breakers 17 (17A, 17A).
B) Open. Since the required NPSH of the recirculation pumps 5A and 5B decreases with a decrease in the rotation speed of the recirculation pumps 5A and 5B, cavitation can be prevented.

On the other hand, the trip of the recirculation pump 5 (5A, 5B) causes a sudden decrease in the flow rate of the coolant flowing through the reactor, that is, the recirculation flow rate, resulting in a severe thermal condition. Therefore, it is necessary to immediately stop the reactor. A recirculation pump flow detector 8 (8A, 8B) is installed on the discharge side of the recirculation pump 5, and when the recirculation pump flow decrease detection circuit 18 (18A, 18B) detects a decrease in the flow of the recirculation pump 5, , Recirculation pump flow drop signal 19
(19A, 19B) is transmitted to the safety protection logic circuit 20 to scramble the reactor.

By the way, when the recirculation pumps 5A and 5B trip at the same time, the rate of decrease in the recirculation flow rate is large and the user has to wait until the recirculation pump flow rate low signal 19 is transmitted, so that a sufficient thermal margin cannot be obtained. For this reason, the recirculation power supply breaker disconnection signal
When the 21 (21A, 21B) was transmitted, the reactor was supposed to scram ahead. In the same figure, 22 (22
(A, 22B) is a service bus, and 23 is a reactor scram signal.

[Problems to be solved by the invention]

The above prior art has the following problem in that the recirculation pump power circuit breaker disconnection signal must be used for a reactor scram signal which must be secured for safety. That is, the reactor scram signal that needs to be secured for safety is (A) separation and independence, (B) multiplicity, (C) seismic resistance (A
(D) or higher), and (d) it is required to satisfy the respective requirements of the soundness confirmation testability during operation. The recirculation pump power circuit breaker disconnection signal is transmitted by the operation of an auxiliary contact attached to the recirculation pump power circuit breaker. The auxiliary contact is like a position switch that mechanically detects that the recirculation pump power circuit breaker has been opened, and cannot be actually operated during operation to confirm that the function is sound. Also, since the recirculation pump is a regular system, the recirculation pump power circuit breaker is designed to be an earthquake-resistant C class.
That is, since the recirculation pump power circuit breaker disconnection signal does not satisfy the above requirements (c) and (d),
It is not desirable to use it as a reactor scram signal that needs to be secured for safety.

On the other hand, the recirculation pump flow rate detector is designed to be of the earthquake-proof A class, and has four detectors per recirculation pump. Can be checked during operation.
Furthermore, by adding a simulation signal to the input side of the recirculation pump flow rate decrease detection circuit, the soundness of the recirculation pump flow rate decrease detection circuit can be confirmed during operation. Therefore, the recirculation pump flow rate reduction signal is obtained from the above-mentioned required requirements (a) to (d).
Are all satisfied.

The present invention has been made in view of the above points, and even when the recirculation pump cavitation prevention interlock is activated when the feedwater flow is lost, the reactor is scrambled by the recirculation flow reduction signal to reduce the thermal margin. It is an object of the present invention to provide a protection device for a recirculation pump which can be sufficiently taken.

[Means for Solving the Problems] The object of the present invention is to provide a protection device provided with means for sequentially tripping or decelerating a plurality of recirculation pumps at predetermined time intervals when the supply flow rate is lost. Is achieved by

[Action]

Since the protection device is provided with means for sequentially tripping or decelerating a plurality of recirculation pumps at predetermined time intervals when the supply water flow is lost, the protection device can be moderated in the rate of decrease in the coolant flowing through the reactor. As a result, it is no longer necessary to scram the reactor in advance with the recirculation pump trip signal, and it is possible to detect a decrease in the flow rate of the recirculation pump and scram the reactor to obtain a sufficient thermal margin. .

〔Example〕

Hereinafter, the present invention will be described based on the illustrated embodiments.
FIG. 1 shows an embodiment of the present invention. The same parts as those in the related art are denoted by the same reference numerals, and the description thereof will be omitted.
In this embodiment, the protection device is formed by providing the protection device with means for sequentially tripping or decelerating the plurality of recirculation pumps 5A and 5B at predetermined time intervals when the supply water flow is lost. By doing so, the rate of decrease of the coolant flowing through the reactor can be reduced, and it is not necessary to scram the reactor in advance with the recirculation pump trip signals 16A and 16B. Even if the cavitation prevention interlock is activated, the recirculation flow reduction signal, that is, the recirculation pump flow reduction signal 19A, 19B
Thus, it is possible to obtain a protection device for a recirculation pump that enables scram of nuclear power and sufficient thermal margin.

That is, when the feed water flow rate decrease signal 14 is transmitted, the recirculation pump 5A is first tripped and the timer 24 is started at the same time. The recirculation pump 5B continues to operate and trips when a time set in advance by the timer 24 has elapsed. FIG. 2 shows a conventional example, that is, the recirculation pumps 5A and 5A when the feedwater flow is lost.
The case where B is tripped at the same time is defined as Case I. In this embodiment, the recirculation pump 5A is tripped first when the water supply flow rate is lost, and the recirculation pump 5B is tripped after a lapse of a predetermined time (in this case, 2 seconds). In case II, the horizontal axis indicates time, and the vertical axis indicates the recirculation pump flow rate and the recirculation flow rate, and shows how the recirculation pump flow rate and the recirculation flow rate change in each case. In the figure, the recirculation flow rate is the flow rate of the coolant flowing into the reactor,
This is the sum of the discharge flow rates of 5A and 5B, and 100 on the vertical axis is a rating.

As is clear from FIG. 2, Case II is better than Case I.
The decrease in the recirculation flow rate is more gradual. Also, Case II
Then, after the tripping, the flow rate of the recirculation pump 5A is changed from the recirculation pump 5B, which continues to operate, to the manifold 9 (see FIG. 4).
Case I due to the coolant being pushed in via
Decreases faster than Accordingly, the flow rate reduction signal of the recirculation pump 5A in Case II is transmitted earlier than in Case I.

From the above, in case II, the decrease in the recirculation flow rate is more gradual and the reactor scram signal is transmitted earlier, so that the thermal margin of the reactor can be increased and the recirculation pump power circuit breaker disconnection signal Does not need to be a scrum signal. The same effect can be obtained even if the recirculation pump is decelerated to a rotation speed that does not cause cavitation, instead of tripping the recirculation pump.

As described above, according to the present embodiment, when the feedwater flow rate is lost, a plurality of or the recirculation pumps are sequentially tripped with a time delay, so that the rate of decrease in the coolant flowing through the reactor can be reduced. It is no longer necessary to scram the reactor in advance with the recirculation pump trip signal, and a sufficient thermal margin can be obtained by detecting a decrease in the flow rate of the recirculation pump and scramming the reactor.

FIG. 3 shows another embodiment of the present invention. In the present embodiment, the protection device is used as a protection device, and a standby power supply device for a protection device
A determination circuit 26 is provided to sequentially trip or decelerate the plurality of recirculation pumps 5A and 5B connected to the standby power supply device 25 when used. In this case as well, the plurality of recirculation pumps 5A and 5B are successively tripped or decelerated, so that the same operation and effect as in the above case can be obtained.

That is, the recirculation pump power supply devices 27A and 27B are connected to the service buses 22A and 22B via the recirculation pump power supply breakers 17A and 17B, respectively. The backup power supply device 25 is provided as a backup when one of the recirculation pump power supply devices 27A and 27B fails, and is connected to the service buses 22A and 22B by backup power supply breakers 28A and 28B. However, in a normal state, the standby power circuit breaker 28A is closed and 28B is open.
The recirculation pump power supplies 27A, 27B and the backup power supply 25 and the recirculation pumps 5A, 5B are connected by power switches 29A, 29B, 29C, 29D, and normally the power switches 29A and 29D are closed,
29B and 29C are open. For example, if the recirculation pump power supply device 27A fails, the recirculation pump power circuit breaker 17A is opened by a failure signal and the power switch 2
9A is opened, 29B is closed and recirculation pump 5A is set to standby power supply 2
Connect to 5. Even if the recirculation pump power supply 27B fails, the recirculation pump 5B is connected to the backup power supply 25 in the same manner, but in this case, the two recirculation pumps 5A, 5A,
Since 5B is connected and the load balance is deteriorated, an operation of switching the standby power supply device 25 to the service bus 22B is performed.

When the feedwater flow rate is lost, the signal of the feedwater flow rate detector 12 decreases, and the feedwater flow rate decrease signal 14
Is transmitted. The recirculation pump control device 15A issues a recirculation pump trip signal 16
Send A to open the recirculation pump power breaker 17A. When the feedwater flow rate reduction signal 14 is transmitted, the timer 24 starts operating, and when a preset time has elapsed, a signal is sent to the recirculation pump control device 15B. The recirculation pump controller 15B sends a recirculation pump trip signal 16B to open the recirculation pump power breaker 17B. The above is the operation in the case where the supply water flow rate is lost during the normal operation, that is, when the operation is performed using the recirculation pump power supply devices 27A and 27B. Next, an operation in the case where either the recirculation pump power supply device 27A or 27B fails and a water supply flow rate loss occurs during operation using the backup power supply device 25 will be described.

The case where the recirculation pump power supply device 27B breaks down is taken as an example. In this case, the state of the power supply switches 29A to 29D is 29A closed, 2
9B is open, 29C is closed, 29D is open. The states of the recirculation pump power circuit breakers 17A and 17B are 17A closed and 17B open. The standby power circuit breaker 28A is open and 28B is closed. Therefore the recirculation pump
5B is driven by the backup power supply 25, and the backup power supply 25 is supplied with power from the service bus 22B. When the feedwater flow rate is lost, the recirculation pump 5A first trips as in the normal operation. After the time set in the timer 24 elapses,
The recirculation pump control device 15B transmits a trip signal 16B, but there is no particular change in the state because the recirculation pump power circuit breaker 17B has already been opened. The judgment circuit 26 is a standby power supply
It is determined whether 25 is connected to any of the recirculation pumps 5A and 5B, and if it is connected to the recirculation pump 5A, the determination signal 30 is transmitted immediately when the feedwater flow rate reduction signal 14 is transmitted, and the standby power controller 31 Then, the standby power breakers 28A and 28B are opened via the standby power trip signal 32. Further, when connected to the recirculation pump 5B, after the supply water flow rate reduction signal 14 is transmitted, the determination signal 30 after the elapse of the same time as the time preset in the timer 24 is output.
To open the standby power circuit breakers 28A and 28B. It is determined whether the standby power supply device 25 is connected to the recirculation pump 5A or connected to the recirculation pump 5B in the open / close state of the power supply switches 29B and 29C. The recirculation pump flow rate decrease detection circuit 18 monitors the case of the recirculation pump flow rate detector 8 and, when the recirculation pump flow rate decreases, a recirculation pump flow rate decrease signal.
19 is sent to the safety protection logic circuit 20 to scram the reactor. In the figure, 33A and 33B are power switches 29B and 2
9C is an open / closed state signal.

Thus, according to the present embodiment, since the circuit for determining the recirculation pump connected to the backup power supply is provided,
Even when a spare power supply is used, the protection operation for preventing the cavitation of the recirculation pump when the supply water flow rate is lost can be appropriately performed.

〔The invention's effect〕

As described above, according to the present invention, even if the recirculation pump cavitation prevention interlock is activated when the feedwater flow rate is lost, the reactor can be scrammed by the recirculation pump flow rate reduction signal, and sufficient thermal margin can be obtained. Thus, even if the recirculation pump cavitation prevention interlock is activated when the feedwater flow rate is lost, the reactor can be scrammed with a low recirculation flow signal to achieve sufficient thermal margin. A protection device for the circulation pump can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment of a protection device for a recirculation pump according to the present invention, and FIG. 2 is a characteristic showing the relationship between the time, the recirculation pump flow rate, and the recirculation flow rate between the embodiment and the conventional example. FIGS. 3 (a) and 3 (b) show another embodiment of the protection device for the recirculation pump according to the present invention, wherein (a) is an explanatory diagram, (b) is a decision logic diagram of a decision circuit, and FIG. FIG. 4 is an explanatory view showing a configuration of a nuclear power plant to which the present invention is applied, and FIG. 5 is an explanatory view of a conventional protection device for a recirculation pump. 1 ... Reactor, 5 (5A, 5B) ... Recirculation pump, 13 ...
Feedwater flow drop detector, 15 (15A, 15B) ... Recirculation pump controller, 17A, 17B ... Recirculation pump power circuit breaker, 22 (2
2A, 22B) ... regular bus, 24 ... timer, 25 ... standby power supply, 26 ... determination circuit, 27A, 27B ... recirculation pump power supply.

Claims (4)

(57) [Claims] 1. A plurality of recirculation pumps connected to different service buses via recirculation pump power circuit breakers, respectively, for supplying mixed water to a nuclear reactor, and preventing the recirculation pumps from being calibrated when supply water flow is lost. Supply water flow rate decrease detector for detecting a decrease in the supply water flow rate, and a protection device for a recirculation pump provided with a plurality of recirculation pump control devices each receiving a signal from the detector and controlling the recirculation pump respectively 3. The recirculation pump protection device according to claim 1, further comprising means for sequentially tripping or decelerating the plurality of recirculation pumps at predetermined time intervals when the feedwater flow rate is lost. 2. The recirculation pump according to claim 1, wherein one of the recirculation pumps is stopped or decelerated when the feedwater flow rate is lost, and the flow rate of the stopped or decelerated recirculation pump falls below a predetermined value. 2. The protection device for a recirculation pump according to claim 1, wherein the repetition pump is stopped or decelerated at times to prevent cavitation. 3. The recirculation pump protection device according to claim 1, wherein said plurality of recirculation pumps are prevented from tripping or decelerating at the same time due to a single failure or single malfunction of equipment. . 4. A plurality of recirculation pumps connected to different service buses via a recirculation pump power circuit breaker and a recirculation pump power supply, respectively, for supplying mixed water to the reactor, and a cavitation when the feedwater flow rate is lost. A feedwater flow rate decrease detector for detecting a decrease in the feedwater flow rate, a plurality of recirculation pump control devices each receiving a signal from the detector to control the recirculation pump, and the plurality of recirculation pump power supplies A protection device for a recirculation pump provided with a backup device in the case of failure of any of the devices, wherein the protection device includes a plurality of recirculation pumps connected to the backup power device when the backup power device is used. A protection device for a recirculation pump, comprising a measuring circuit for sequentially tripping or decelerating the circulation pump.