JPH0631812B2 - Pump cavitation prevention device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a pump cavitation prevention device for a boiling water reactor equipped with a plurality of recirculation pumps and jet pumps.

(Prior Art) Generally, in a boiling water reactor, as shown in FIG. 5, an atom forcibly circulating a reactor coolant 3 through a jet pump 2 arranged on the inner circumference of a reactor pressure vessel 1 is used. A furnace coolant recycle system is provided.

Reactor coolant recirculation systems are usually installed independently in parallel 2
Each loop is equipped with a recirculation pump 5, which is driven by an electric motor 4, and controls the output of the reactor by adjusting the flow rate of the coolant 3 circulated by the recirculation pump 5. is doing.

To adjust the flow rate of the recirculation pump 5, as shown in FIG. 5, the speed request signal 8 output from the speed controller 7 is input to the variable frequency power supply 9 according to the set value stored in the speed setter 6 in advance, It is implemented by increasing or decreasing the frequency of the power source to control the rotation speed of the electric motor 4.

When the reactor is operating at rated power, the two recirculation pumps 5a, 5b are rotating at 100% rated speed. In this case, as shown in FIG. 6, the core flow rate of the coolant 3 with respect to the reactor output is sufficiently large, and the recirculation pump 5 is operated at an operation point P ₂ distant from the cavitation region A ₂ of the jet pump 2. Therefore, the cavitation of the jet pump 2 does not occur.

However, if one recirculation pump 5a trips, the core flow rate will be halved even if the remaining one recirculation pump 5b is operated at 100% rated speed, and as shown in FIG. The operating point P ₁ of the pump 5b enters the cavitation area A ₁ of the jet pump in the operating loop.

Therefore, cavitation occurs in the jet pump,
The vibration may damage the jet pump within a short time.

On the other hand, the coolant 3 may flow back through the loop on the side of the recirculation pump 5a that has tripped and stopped, causing the recirculation pump 5a to rotate in the reverse direction and causing damage.

In order to prevent the jet pump 2 and the recirculation pump 5 from being damaged due to the trip of the recirculation pump 5 as described above, when a trip occurs in the recirculation pump 5, the recirculation pump 5b being operated by the operator is used. After confirming the operating state, the automatic / manual switching contact 10 is switched from the automatic side A to the manual side M to shut off the speed command from the speed setter 6.
The rotational speed of the recirculation pump 5b in operation is manually reduced to a predetermined set value at which cavitation does not occur by the speed command output from the runback setting device 11.

(Problems to be solved by the invention) However, the runback operation procedure for lowering the rotation speed is described in detail in the operation manual, etc., but when the recirculation pump trips, the corresponding operation and confirmation items for each system However, the operation is complicated due to the rapid construction of the robot, and the operation for avoiding cavitation may be delayed.
In addition, a more advanced technique is required to perform an optimum runback operation.

That is, when the rotation speed is suddenly reduced to a predetermined set value, a large disturbance may be applied to the reactor output, the water level in the reactor, and the like, leading to a plant trip. Restoring a plant trip requires a great deal of time and labor, and in particular, stopping a highly public nuclear plant such as a nuclear power plant has a considerable impact on society.

On the other hand, when the rotational speed is gradually reduced with a minute change amount, the tripped recirculation pump may reversely rotate for a long time and be damaged, or the jet pump in operation may be damaged by cavitation.

The present invention has been made to solve the above-mentioned problems, and when the recirculation pump trips, the cavitation generation region of the jet pump arranged in the other operation side loop is monitored, and the recirculation pump Pump cavitation prevention for boiling water reactors that reliably prevents damage to stopped recirculation pumps and jet pumps during operation by automatically running back the rotation speed to a specified limit value that avoids cavitation regions The purpose is to provide a device.

[Structure of Invention]

(Means for Solving Problems) A pump cavitation prevention device for a boiling water reactor according to the present invention forcibly circulates a reactor coolant through a jet pump arranged on the inner circumference of a reactor pressure vessel. Multiple recirculation pumps, trip detection circuit that detects the trip status of the recirculation pumps, and trip signal from the trip detection circuit to select the reactor output / core flow curve that corresponds to the number of recirculation pumps in operation The monitoring circuit that monitors the presence or absence of pump cavitation by comparing the selected reactor power / core flow curve with the feedwater flow rate signal and the core flow rate signal, and the pump cavitation generation signal from the monitoring circuit or the trip signal An interlock circuit that outputs the run-back command of the recirculation pump, and the re-circulation pump that is operating during the run-back command. The speed control device lowers the rotation speed of the pump to a predetermined speed limit that avoids the cavitation region.This speed control device changes the recirculation pump according to the speed setting signal from the speed setting device during automatic operation. A speed controller that outputs a speed request signal to the frequency power supply, an automatic / manual switching contact arranged between the speed setting device and the speed controller, and a run side on the manual side terminal of the automatic / manual switching contact. A runback setting device connected via a back contact, the automatic / manual switching contact and the runback contact are configured to operate according to a runback command, and the runback setting device includes a runback contact. The manual setting device provided in the bypass circuit, the tracking contact provided on the tracking line on the primary side of the manual setting device, and the command ram counter on the secondary side of the manual setting device. And a command contacts provided on said tracking contact and command contact is characterized by being configured to operate by runback command.

(Operation) In the pump cavitation prevention device for a boiling water reactor having the above-described configuration, the trip signal of the recirculation pump output from the trip detection circuit is transmitted to the monitoring circuit and the interlock circuit.

In the monitoring circuit, the reactor power / core flow curve corresponding to the number of recirculation pumps in operation excluding the recirculation pump that has tripped and stopped is selected, and the curve shape and feedwater flow rate signal and core flow rate signal are selected. In comparison, monitor whether the current driving condition has reached the cavitation area,
If it has arrived, a runback area arrival signal is output to the interlock circuit.

The interlock circuit detects that the flow rate distribution of the coolant in the reactor is unbalanced by the runback region arrival signal or the trip signal, and outputs a runback command to the speed control device.

Based on the runback command, the speed control device automatically lowers the rotation speed of the recirculation pump in operation to a predetermined speed limit that avoids the cavitation region.

In this way, the reactor power / core flow curve corresponding to the number of recirculation pumps in operation is constantly compared with the operation state, and when the operation point reaches the pump cavitation generation region, or at least one recirculation When the pump trips, a runback command is issued from the interlock circuit, and the operating recirculation pump is automatically runback by the operation of the speed control device.

Therefore, damage due to cavitation of the jet pump and damage due to reverse rotation of the recirculation pump that has tripped and stopped can be prevented, and the labor load of the operator required for the runback operation can be significantly reduced.

(Embodiment) Next, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a pump cavitation prevention device for a boiling water reactor according to the present invention, and the same elements as those of the conventional example shown in FIG.

The pump cavitation prevention device for a boiling water reactor according to the present embodiment includes a plurality of recirculation pumps 5a, 5b, ... For forcedly circulating a coolant through a jet pump arranged inside the reactor pressure vessel. , Recirculation pumps 5a, 5b ... Are connected to a trip detection circuit 12 for detecting the trip state.

As shown in FIG. 1, the trip detection circuit 12 includes a variable frequency power source 9 as a drive source of each recirculation pump 5a, 5b ...
The recirculation pumps 5a, 5b ... By detecting the open / closed state of the contacts of the input circuit breakers 13a, 13b.
Configured to detect trips.

As shown in FIG. 2, the trip detection circuit 12 has an AND circuit 14 that performs a logical product operation on trip signals from the recirculation pumps 5a to 5n, and further includes a NOT circuit 15, AND circuits 16 and 17. Is connected to the OR circuit 18 via an OR circuit, a trip of at least one recirculation pump is detected, an imbalance in the operating state of the remaining recirculation pump 5 occurs, and the core flow rate distribution of the coolant 3 is uneven. Then, the trip signal 12a is output.

A monitoring circuit 19 and an interlock circuit 20 are connected to the secondary side of the trip detection circuit 12 as shown in FIG.

The monitoring circuit 19 uses the reactor output / core flow rate curves 21a and 21b for each number of recirculation pumps 5 that operate as shown in FIG.
Of the feed water flow rate signal 22 and the core flow rate signal 23, and the reactor power / core flow rate curves 21a and 21b.
In comparison with the above, it has storage comparison circuits 25a and 25b for monitoring whether or not the current operation point of the recirculation pump 5 has reached the cavitation generation region. Further, monitoring switching contacts 24a and 24b for selecting a reactor output / core flow rate curve as a reference for comparison by the pump trip signal 12a are provided at the input portions of the memory comparing circuits 25a and 25b.

An interlock circuit 20 is provided on the secondary side of the monitoring circuit 19, and the interlock circuit 20 outputs the runback area arrival signals 27a and 27b and the pump trip signal output from the monitoring circuit 19 as illustrated in FIG. When an AND circuit 28 for logically operating 12a and an OR circuit 29 are connected to each other and a runback region is reached while two recirculation pumps 5 are operating, or any one recirculation pump The runback command 30 is output when the vehicle 5 trips and reaches the runback area.

A speed controller 31 is provided on the secondary side of the interlock circuit 20. For example, as shown in FIG. 1, the speed control device 31 uses a speed setting signal 32 from the speed setting device 6 during automatic operation.
The speed controller 7 for outputting the speed request signal 8 to the variable frequency power source 9b of the recirculation pump 5b, and the automatic / manual switching provided between the speed setter 6 and the speed controller 7. The contact 10 and a runback setter 11 connected to the manual side terminal of the automatic / manual switching contact 10 via a runback contact 33. The automatic / manual switching contact 10 and the runback contact 33 are runbacks. It is configured to operate according to the command 30.

Further, a manual setting device 34 is provided in a circuit that bypasses the runback contact 33, and a tracking contact 36 is provided on a tracking line 35 on the primary side thereof, while a command contact 37 is provided on a command line 37 on the secondary side. It is provided.
Then, the tracking contact 36 and the command contact 38
Are configured to operate according to a runback command 30.

Next, the operation of the pump cavitation prevention device according to this embodiment will be described.

The operating state of the nuclear reactor is constantly monitored by the monitoring circuit 19 shown in FIG. That is, the operation point of the reactor is grasped by two operation parameter signals of the reactor feed water flow rate signal 22 and the core flow rate signal 23, and these operation parameter signals are stored for each number of recirculation pumps operating. By comparing with the power / core flow rate curve, it is monitored whether or not the operating point has reached the cavitation areas A ₁ and A ₂ set in the curve area.

When the driving point reaches the cavitation area A ₁ or A ₂ and the runback operation is required, the runback area arrival signal 27a or 27b is output to the interlock circuit 20 shown in FIG.

On the other hand, when the trip detection circuit 12 shown in FIG. 2 detects that one of the recirculation pumps 5 has tripped from the open / closed state of the contact of the input circuit breaker 13 of the recirculation pump 5, It is detected that the core flow rate distribution of the coolant 3 is non-uniform due to the imbalance of the operating state, and the trip signal 12 a is output to the interlock circuit 20 and the monitoring circuit 19.

The trip signal 12a from the trip detection circuit 12 causes the monitoring switching contact 24a of the monitoring circuit 19 shown in FIG.
24b is switched.

For example, when one of the two recirculation pumps 5 is tripped, the monitoring switching contacts 24a and 24b are switched to the b side ON by the trip signal 12a, and the feed water flow rate signal 22 and the core flow rate signal 23 are It is input to the memory comparison circuit 25b that stores the reactor output / core flow rate curve 21b when one pump is operating. The input operation parameter signal is compared with the reactor power / core flow rate curve 21b,
It is monitored whether or not the driving point reaches the cavitation area A ₁ set in the curved area.

On the other hand, during the normal operation in which the pump trip does not occur, the monitoring switching contacts 24a and 24b are always kept a-side ON, and the reactor output / core flow rate curve 21a and the above operating parameter signal when two recirculation pumps 5 are operated. Are compared, and the approaching state of the driving point to the cavitation area A ₂ is constantly monitored.

In this way, based on the reactor power / core flow rate curve corresponding to the number of operating recirculation pumps 5, the adequacy of the operating points of the reactor and the presence / absence of reaching the cavitation generation region of the jet pump 2 are constantly monitored and operated. When the point reaches the cavitation area A ₁ or A ₂ , a runback command 30 according to the condition of the interlock circuit 20 shown in FIG. 4 is output to the speed control device 31.

The runback command 30 turns on the runback contact 33 of the speed control device 31, and the automatic / manual switching contact 10
Is switched to the manual side b, and the speed setting command signal 39 is output from the runback setting device 11.

The speed setting command signal 39 is sent from the speed controller 7 to the speed request signal 8
Is input to the variable frequency power source 9b of the recirculation pump 5b on the operation loop side, and the rotation speed of the electric motor 4b is automatically run back to a predetermined value by reducing the frequency of the power source.

Therefore, the damage due to the cavitation of the jet pump 2 and the damage due to the reverse rotation of the recirculation pump 5 which has stopped due to the trip are prevented, and the labor burden of the operator, which is required for the conventional manual runback operation, is significantly reduced. It can be reduced.

Here, the level of the speed setting command signal 39 output from the runback setting device 11 is the level of the tripped recirculation pump 5
a is a rotation speed that gives a core flow rate that does not cause reverse rotation, and as shown in FIG. 7, the recirculation corresponding to the operation point P _L preset to avoid the cavitation region A ₁ of the jet pump 2. The rotation speed of the pump 5 is set.

When the runback command 30 is output, the manual setting device 3
Command contact 38 provided on command line 37 of No. 4 is OFF
Therefore, the command signal 40 from the manual setting device 34 is cut off during the runback operation. At the same time, the manual setting device 3
Since the tracking contact 36 provided on the tracking line 35 of No. 4 is turned on, the manual setting device 34 tracks the output of the runback setting device 11.

With this configuration, the setting of the rotation speed of the recirculation pump 5 in the manual setting device 34 can be made to substantially match the current rotation speed. Therefore, after the runback operation is completed, the manual setting device 34 is switched to the operation of the recirculation pump. Even in the case of performing the above, it becomes possible to operate the recirculation pump without causing a rapid change in the core flow rate.

The runback command 30 from the interlock circuit 20
Without operating the speed control device 31 by the alarm 41
It can also be configured to operate only.

〔The invention's effect〕

As described above, according to the pump cavitation prevention device of the present invention, the comparison between the reactor power / core flow curve and the operation parameter signal corresponding to the number of recirculation pumps in operation is always executed, When the operating point reaches the cavitation area, or when at least one recirculation pump trips, a runback command is output from the interlock circuit and the operation of the speed control device causes the recirculation pump in the operation side loop to cavitation. It will automatically run back to a predetermined speed limit to avoid the area.

Therefore, damage due to cavitation of the jet pump and damage due to reverse rotation of the stopped recirculation pump can be prevented, and manual laborious runback operation for the recirculation pump of the operation side loop can be omitted, which results in labor burden on the operator. It is possible to greatly improve the safety and operating characteristics of a nuclear power plant by significantly reducing the above.

In particular, when a runback command is output, the manual setter tracks the output of the runback setter, so the rotational speed setting of the recirculation pump in the manual setter is almost the same as the current rotational speed. Therefore, even if the recirculation pump is operated by switching to the manual setting device after the runback operation is completed, it is possible to operate the recirculation pump without causing a sudden change in the core flow rate. Become.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a pump cavitation prevention device according to the present invention, FIG. 2 is a circuit diagram showing a configuration of a trip detection circuit in FIG. 1, and FIG. 3 is a monitoring circuit in FIG. FIG. 4 is a circuit diagram showing the configuration, FIG. 4 is a circuit diagram showing the configuration of the interlock circuit in FIG. 1, FIG. 5 is a system diagram showing a flow rate adjusting mechanism around a conventional recirculation pump, and FIG. FIG. 7 is a graph showing the relationship between the core flow rate and the reactor power when the recirculation pump is operated and the cavitation region of the jet pump. FIG. 7 is the relationship between the core flow rate and the reactor power when one recirculation pump is operated and It is a graph which shows the cavitation area | region of a jet pump. 1 ... Reactor pressure vessel, 2 ... Jet pump, 3 ...
Reactor coolant, 4, 4a, 4b ... Power supply, 5, 5a,
5b ... Recirculation pump, 6 ... Speed setter, 7 ... Speed controller, 8 ... Speed request signal, 9, 9a, 9b ... Variable frequency power source, 10 ... Automatic / manual switching contact, 11 ... … Runback setting device, 12 …… Trip detection circuit, 12a…
... Trip signal, 13, 13a, 13b ... Input breaker, 14 ... AND circuit, 15 ... NOT circuit, 16,
17 ... AND circuit, 18 ... OR circuit, 19 ... Monitoring circuit, 20 ... Interlock circuit, 21, 21a, 21
b …… Reactor power / core flow curve, 22 …… Supply water flow signal,
23 ... Core flow rate signal, 24a, 24b ... Monitoring switching contact, 25a, 25b ... Memory comparison circuit, 27a, 27b
...... Runback area arrival signal, 28 …… AND circuit, 2
9 ... OR circuit, 30 ... runback command, 31 ... speed control device, 32 ... speed setting signal, 33 ... runback contact, 34 ... manual setting device, 35 ... tracking line, 36 ... Tracking contact, 37 ... command line, 38 ... command contact, 39 ... speed setting command signal, 4
0 ...... command signals, 41 ...... warning _device, A 1, _{A 2} ...... cavitation _{region, P 1, P 2, P} L ...... operation point.

Claims (1)

[Claims] 1. A plurality of recirculation pumps for forcibly circulating a reactor coolant through a jet pump arranged inside the reactor pressure vessel, and a trip detection circuit for detecting a trip state of the recirculation pumps. , The reactor output / core flow curve corresponding to the number of recirculation pumps in operation is selected by the trip signal from the trip detection circuit, and the selected reactor output / core flow curve and feedwater flow signal and core flow signal are selected. By comparison, a monitoring circuit that monitors the occurrence of pump cavitation, an interlock circuit that outputs a runback command for the recirculation pump by the pump cavitation generation signal from the monitoring circuit or the above trip signal, and the operation by the above runback command Speed control to reduce the rotation speed of the recirculation pump inside to a predetermined speed limit to avoid the cavitation region This speed control device includes a speed controller that outputs a speed request signal to a variable frequency power source of a recirculation pump in response to a speed setting signal from the speed setter during automatic operation, and the speed setting device described above. The automatic / manual switching contact arranged between the controller and the speed controller, and the runback setting device connected to the manual side terminal of the automatic / manual switching contact via the runback contact. The manual switching contact and the runback contact are configured to operate according to a runback command, and the runback setting device is a manual setting device that is arranged in a circuit that bypasses the runback contact and the tracking of the primary side of the manual setting device. The tracking contact provided on the line and the command contact provided on the command line on the secondary side of the manual setting device are provided. Pump cavitation preventing device being characterized in that configured to work.