JPH07306296A - Method and system for controlling output of abwr - Google Patents

Abstract

PURPOSE:To make a smooth transition of single load operation in the station without sacrifice of thermal soundness of fuel in the reactor by tripping a predetermined number of internal pumps upon abrupt closure of a steam control valve due to load interruption of a generator and then inserting selective control rods quickly. CONSTITUTION:An output controller 1 takes in a turbine bypass valve quick open signal 5, a steam control valve quick open signal 6, and a reactor core state signal 7 upon load interruption of a generator. The signals 5, 6 are fed to a bypass decision circuit 3 where a decision is made whether a turbine bypass valve was fully opened within a predetermined time. If it was not opened, a reactor scram command signal 8 is outputted and a turbine bypass valve non-full open signal 9 is delivered to a number of tripping pump operating unit 4. The operating unit 4 determines the number of recirculation pumps to be tripped based on the signals 6, 7 and outputs a recirculation pump trip command signal 10. When the bypass valve is not fully opened within a predetermined time, a recirculation pump step trip command signal 11 and a selective control rod quick insertion command signal 12 are outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power control method and apparatus for a boiling water nuclear power plant, and more particularly to an ABWR (Advanced) having a recirculation pump having a small inertia time constant.
The present invention relates to an output control method and apparatus suitable for shifting to a single load operation in a plant when the load of a boiling water reactor is lost.

[0002]

2. Description of the Related Art FIG. 7 is a schematic configuration diagram of a conventional boiling water nuclear power plant. In FIG. 7, 14 is a reactor, 15 is a steam control valve, 16 is a turbine bypass valve, 1
7 is a turbine, 18 is a condenser, 19 is a generator, 20 is a water supply pump, 21 is a control rod, 22 is a selective control rod, and 23 is a recirculation pump. Now when the loss of generator load occurs,
The steam control valve 15 is suddenly closed to reduce the overspeed of the turbine 17, and the turbine bypass valve 16 is rapidly opened to allow surplus steam to flow directly to the condenser 18. The speed request signal 29 from the main controller 24 is sent to the variable frequency power supply device 25 via the changeover switch 27, and the power supply frequency 30 of the recirculation pump 23 is controlled by the variable frequency power supply device 25. The rotation speed is controlled according to the load demand.

However, when a load loss occurs, the power load unbalance relay 26 operates and the changeover switch 2
7, the variable frequency power supply 25 is connected to the recirculation pump runback speed signal generator 28. This runback speed signal generator 28 takes in the reactor output signal 31 at the time of load loss, calculates the fast runback speed, the pump speed drop width by the fast runback, and the slow runback speed to determine the runback pattern. , And outputs the runback speed request signal 32 to the variable frequency power supply device 25 via the changeover switch 27. As a result, the recirculation pump 23
Are all run back to prevent the neutron flux from rising due to pressure fluctuations in the reactor 14 when the steam control valve 15 is rapidly closed. Further, a predetermined selection control rod 22 of the control rods 21 is rapidly inserted, the output of the nuclear reactor 14 is lowered together with the runback of the recirculation pump, and the predetermined single load operation is performed.

As a conventional technique in which a high speed runback and a low speed runback are combined, there is one described in Japanese Patent Laid-Open No. 59-190697.

[0005]

The conventional technique shown in FIG. 7 is an ordinary boiling water nuclear power plant (BWR), whereas in recent years, an improved nuclear power plant called ABWR has been constructed. There is. The ABWR feature is that instead of the external recirculation pump shown in FIG.
As shown in FIG. 5, an internal pump 53 is arranged around the reactor core shroud 52 housed in the reactor pressure vessel wall 51. As shown in FIG. 9, it is usual that ten or twelve internal pumps 53 are arranged on a concentric circle, and the rotation of each internal pump 53 is controlled by a motor 54.

In such an ABWR, it is necessary to develop a technique for smoothly shifting to a single load operation in the plant when the generator load is lost. However, compared with the conventional external recirculation pump, an internal pump type is used. The inertial time constant of the recirculation pump is small and the above-mentioned conventional technique cannot be applied as it is.

An object of the present invention is to provide an output control method and apparatus for smoothly shifting to a single load operation in a plant when a generator load is lost without impairing the thermal soundness of fuel in a nuclear reactor.

[0008]

In the ABWR having a plurality of internal pumps, a predetermined number of internal pumps are immediately tripped when the steam control valve is suddenly closed due to load interruption of the generator. This is achieved by rapid insertion of selective control rods and runback of the remaining internal pumps after the required time.

The above-mentioned object is also to immediately trip the predetermined first partial number of internal pumps when the steam control valve is suddenly closed due to the load cutoff of the generator and to quickly insert the selection control rod, and immediately after that, immediately bypass the turbine bypass. When the valve does not open suddenly, it is achieved by tripping and scramming the predetermined second partial number of the remaining internal pumps.

[0010]

The function of the present invention will be described.

A problem when the load of the generator is cut off is an increase in neutron flux caused by an increase in reactor pressure when the steam control valve is rapidly closed. Depending on the size of the rising width of this neutron flux,
It could lead to a reactor scrum. Therefore, in the present invention, by tripping a predetermined number of internal pumps when the generator load is cut off, the reactor core flow rate is decreased, and the void ratio in the reactor is increased to increase the negative charge reactivity. Suppress the rise of neutron flux.
By selecting the optimum number of pump trips according to the reactor power and reactor core flow rate, unnecessary recirculation pump trips can be avoided and the time required for restarting the recirculation pumps can be shortened.

Further, in the present invention, from the viewpoint of the stability of the nuclear reactor, the unstable region of the nuclear reactor is avoided by fast-running back the pump that has not been tripped, but the thermal soundness of the fuel inside the nuclear reactor is improved. In order to protect the performance, a runback is performed after a required time from the pump trip, so that it is possible to stably shift the reactor to the in-house single load operation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sequence diagram showing an ABWR output control method according to an embodiment of the present invention. In the present embodiment, it is assumed that ten internal pump type recirculation pumps are arranged (see FIG. 9). In the present embodiment, when the steam control valve abrupt closing signal is generated due to the load interruption of the generator, the selection control rod is inserted and two of the 10 recirculation pumps are immediately tripped. This 2
The units are two of the recirculation pumps placed on the concentric circles, which are intended for the shaft. If you trip three,
By setting the recirculation pump at the position divided into three around the axis (if it is not divisible by an integer, it is the pump closest to the position divided into three), so that the core flow can be kept uniform in the reactor. . It should be noted that the number of vehicles to be tripped immediately may be one. Then, after the time T2 seconds when the plant output decreases and the core flow rate decreases due to the insertion of the selective control rod and the recirculation pump trip, the remaining eight recirculation pumps are run back, and the pump speed is set to 40%, for example. When the turbine bypass valve does not open suddenly while the above control is performed by the steam control valve abrupt closing signal, a predetermined partial number of the eight units that have run back, for example, two recirculation pumps are tripped (step trip). ) And scram the reactor. If the total number of pumps that have tripped immediately and pumps that have stepped trips is, for example, four, these four will be located at the position divided into four around the axis of the concentric pumps, or at each of these positions. Use a near pump.

FIG. 2 is a block diagram of an output control device for implementing the output control method described with reference to FIG. In FIG. 2, no output signal is output from the output control device 1 during normal operation. When the generator load is cut off, the turbine bypass valve rapid open signal 5, steam control valve rapid close signal 6 and core state signal 7 (reactor output, reactor core flow rate not shown here)
Take in. The turbine bypass valve rapid opening signal 5 is input to the bypass determination circuit 3 together with the steam control valve rapid closing signal 6. The bypass determination circuit 3 determines whether or not the turbine bypass valve 16 is fully opened within a predetermined time when the generator load is cut off, and when the turbine bypass valve 16 is not fully opened within the predetermined time, the reactor. The scram command signal 8 is output, and further, the turbine bypass valve not fully opened signal 9 is output to the trip number computing unit 4.

The number-of-trips calculator 4 receives the turbine bypass valve not fully open signal 9, the steam control valve abrupt close signal 6 and the core state signal 7 as input, determines the number of trips of the recirculation pump, and determines the tripping recirculation pump. Recirculation pump trip command signal 10 is output to each corresponding variable frequency power supply. If the turbine bypass valve 16 does not fully open within the predetermined time T1, the number of staged trips of the recirculation pump is determined, and the recirculation pump is supplied to the variable frequency power supply device corresponding to the recirculation pump to be staged tripped. The step trip command signal 11 is output. Further, the output control device 1 outputs the selection control rod rapid insertion command signal 12 using the steam control valve rapid closing signal 6. Further, the steam control valve rapid closing signal 6 input to the output control device 1 is output as a recirculation pump high speed runback command signal 13 via a delay circuit 2 which delays the input signal by a predetermined time T2.

FIG. 3 shows the output control device 1 of FIG.
It is a block diagram when applying. In FIG. 3, the output control device 1 receives the turbine bypass valve rapid opening signal 5, the steam control valve rapid closing signal 6 and the core state signal 7 as inputs, and recirculates pump trip command signal 10 and selection control rod rapid insertion command signal 12 And the recirculation pump high-speed runback command signal 13 is output, but when the turbine bypass valve 16 does not fully open within the predetermined time T1, the output control device 1 further outputs the reactor scram command signal 8, the recirculation pump. The step trip command signal 11 is output.

The reactor protection device 33 receives the reactor scrum command signal 8 and the selection control rod rapid insertion command signal 12 as input signals, and quickly inserts the control rod 21 to perform the scrum operation, or rapidly selects the selection control rod 22. Insert it. The main controller 24 receives the recirculation pump high speed runback command signal 13 as an input signal and outputs the high speed runback signal 34 to each of the plurality of variable frequency power supply devices 25. The recirculation pump 23 is run at high speed. Further, the variable frequency power supply device 25 is
The recirculation pump trip command signal 10 and the recirculation pump stage trip command signal 11 output from the output control device 1 are used as inputs, and the power receiving / interrupting circuit (not shown in the figure) in the variable frequency power supply device 25 is opened. Recirculation pump 23
To trip or step.

Next, the setting of the number of recirculation pump trips when the generator load is cut off will be described. There are the following four points to consider in setting. (1) Minimize the number of trips. (2) It is possible to suppress an abnormal increase in neutron flux due to fluctuations in reactor pressure during rapid closing of the steam control valve to below a predetermined limit value (for example, 110%). (3) Abnormal increase in reactor water level due to increase in voids caused by rapid decrease in recirculation flow rate, given limit value (eg 30 cm)
The following can be suppressed. (4) The thermal conditions of the fuel in the reactor should not become strict due to the increase of voids accompanying the rapid decrease of the recirculation flow rate.

When the number of recirculation pumps 23 to be tripped is reduced, the rate of reduction of the recirculation flow rate decreases and the rate of increase of voids in the reactor decreases.
As a result, the increase in neutron flux is large. Therefore, it is necessary to properly set the number of trips of the recirculation pump 23 necessary for suppressing the increase of the neutron flux to be equal to or less than the limit value.

FIG. 4 shows the relationship between the number of trips of the recirculation pump 23 and the maximum neutron flux when the generator load is cut off. In FIG. 4, it can be seen that it is necessary to trip at least one recirculation pump 23 if the maximum neutron flux limit is 110% or less. However, FIG.
Is the relationship in a certain part where the burnup of the fuel in the reactor is constant, and the maximum neutron flux also changes when the burnup changes. Here, in order to sufficiently suppress the rise in the neutron flux, the number of trips of the recirculation pump 23 is increased. However, when the number of trips is large, the number of trips is sharply increased due to a sharp decrease in the recirculation flow rate. The rise in the reactor water level becomes large. Therefore, the upper limit of the number of trips of the recirculation pump 23 that trips when the generator load is cut off must be set appropriately.

FIG. 5 shows the relationship between the number of trips of the recirculation pump 23 and the rising range of the reactor water level when the generator load is cut off. In FIG. 5, if the upper limit of the rising range of the reactor water level is limited to 30 cm, the maximum number of recirculation pumps 23 that can be tripped is four.

From the above results, the number of recirculation pumps 23 that can actually trip is limited to a maximum of four.
The recirculation pump that trips from inside the stand and the recirculation pump that trips in stages are set. That is, there are four combinations of the number of trips and the number of stepped trips: 1 to 3 units, 2 to 2 units, 3 to 1 unit, and 4 to 0 units.

From the above combinations, it is necessary to select a combination having the smallest number of trips according to the core state. Here, the core state is determined by the magnitude of the reactor power and the reactor core flow rate. Also, what must be considered here is the thermal soundness of the fuel in the reactor described above. The change rate (ΔMCPR) of the minimum limit power ratio (MCPR) is an index for measuring the thermal soundness of the fuel in the nuclear reactor. If the number of trips of the recirculation pump is constant, the thermal conditions tend to become more severe as the power output becomes higher and the core flow rate becomes lower.
This is because the cooling capacity inside the reactor decreases due to the recirculation flow rate, and it is necessary to reduce the number of trips on the low core flow rate side.

FIG. 6 is a flow chart showing an embodiment of the processing procedure in the trip number calculator 4 of FIG.
First, in step 1, the turbine first stage post-pressure and the jet pump total flow rate are constantly monitored, and the values when the power load unbalance relay 26 is operating are taken in as the reactor output and the reactor core flow rate when a load interruption occurs. In step 2,
The optimum value of the number of trips is determined as a relation between the reactor output and the reactor core flow rate at the time of load shedding, which is obtained by analysis and is stored in advance.

From the number of trips at this time, the number of stepped trips is determined, and in step 3, the number of trips and the number of stepped trips determined in step 2 are recirculated pump trip command signal 10 and recirculated pump stage trip command signal 11 respectively. As a variable frequency power supply 25,
A signal from the variable frequency power supply 25 causes the recirculation pump 23 to trip or step.

[0026]

EFFECTS OF THE INVENTION According to the present invention, the number of recirculation pumps that trip when the load of the generator is cut off, regardless of the state of the reactor such as reactor output, is minimized and the rise of neutron flux is effectively suppressed. Thus, there is an effect that the output can be stably reduced and the operation can be shifted to the predetermined single load operation.

[Brief description of drawings]

FIG. 1 shows a sequence diagram of an output control method according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an output control device according to an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram in which the output control device of FIG. 2 is applied to an ABWR plant.

FIG. 4 is a diagram showing the relationship between the number of trips of a recirculation pump and the maximum neutron flux when load shedding occurs during 100% output operation.

FIG. 5 is a diagram showing the relationship between the number of trips of the recirculation pump and the reactor water level rise width when load shedding occurs during 100% output operation.

FIG. 6 is a flowchart showing an example of a processing procedure in the trip number calculator of FIG.

FIG. 7 shows a schematic configuration diagram of a boiling water nuclear power plant according to a conventional control method.

FIG. 8 is a reactor cross-sectional view showing the internal pump arrangement position of the ABWR.

FIG. 9 is a plan view showing an internal pump arrangement position of the ABWR.

[Explanation of symbols]

1 ... Output control device, 2 ... Delay circuit, 3 ... Bypass determination circuit, 4 ... Trip number calculator, 5 ... Turbine bypass valve rapid opening signal, 6 ... Steam control valve rapid closing signal, 7 ... Core state signal, 8 ... Reactor scrum command signal, 9 ... Turbine bypass valve not fully open signal, 10 ... Recirculation pump trip command signal, 11 ... Recirculation pump stage trip command signal, 12 ...
Selection control rod rapid insertion command signal, 13 ... Recirculation pump high speed runback command signal, 23, 53 ... Internal pump type recirculation pump.

Claims (14)

[Claims] 1. An AB having a plurality of internal pumps
In the WR, when the steam control valve is suddenly closed due to the load cutoff of the generator, a certain number of internal pumps are immediately tripped and the selection control rod is rapidly inserted, and the remaining internal pumps are run back after the required time. An output control method for an ABWR, comprising: 2. An AB having a plurality of internal pumps
In WR, when the steam control valve suddenly closes due to generator load cutoff, the specified first partial number of internal pumps is immediately tripped and the selection control rod is rapidly inserted, and immediately after that, the turbine bypass valve opens rapidly. If not, an ABWR output control method is characterized in that a predetermined second partial number of the remaining internal pumps is tripped and scrammed. 3. An AB having a plurality of internal pumps
In WR, when the steam control valve suddenly closes due to generator load cutoff, the specified first partial number of internal pumps is immediately tripped and the selection control rod is rapidly inserted, and immediately after that, the turbine bypass valve opens rapidly. If not, trip the specified second part of the remaining internal pumps and scram, and when the turbine bypass valve opens rapidly, run back the remaining internal pumps after the required time after the steam control valve closes rapidly. An output control method for an ABWR, comprising: 4. The required time according to claim 1 or 3, wherein the required time is a time until the plant output is reduced and the core flow rate is reduced due to the rapid insertion of the selective control rod and the partial trip of the internal pump. ABWR output control method. 5. The output control method for an ABWR according to claim 3, wherein the predetermined first partial number and / or the predetermined second partial number is changed to an arbitrary number according to the core state. 6. The output control method for an ABWR according to claim 5, wherein the total of the predetermined first partial number and the predetermined second partial number is set to a constant number. 7. The internal pump according to claim 1, wherein the total number of internal pumps is 10, and the number of trips immediately when the steam control valve is suddenly closed is 2. ABWR output control method. 8. The output control method for an ABWR according to claim 3, wherein the predetermined second partial number is two. 9. The internal pump to be tripped according to any one of claims 1 to 8, is the most internal pump arranged concentrically at a position equally divided by the number of trips around the shaft. An output control method for an ABWR, characterized in that the internal pumps are located close to each other. 10. A equipped with a plurality of internal pumps
In the BWR, a means for immediately tripping a specified number of internal pumps when the steam control valve is suddenly closed due to generator load cutoff, and a selection control rod is rapidly activated when the steam control valve is suddenly closed due to generator load cutoff. An output control device for an ABWR, comprising: means for inserting the means; and means for running back the remaining internal pumps after a required time has passed since the steam control valve was closed abruptly. 11. A having a plurality of internal pumps
In BWR, a means for immediately tripping a predetermined first partial number of internal pumps when the steam control valve is suddenly closed due to generator load cutoff, and a selective control rod when the steam control valve is rapidly closed due to generator load cutoff And a means for causing a predetermined second partial number of the remaining internal pumps to trip and scram when the turbine bypass valve does not open immediately after the steam control valve is closed suddenly. An output control device for an ABWR, characterized in that 12. A having a plurality of internal pumps
In the BWR, a means for immediately tripping the predetermined first partial number of the internal pumps when the steam control valve is suddenly closed due to the load interruption of the generator, and a means for rapidly inserting the selection control rod when the steam control valve is rapidly closed, When the turbine bypass valve does not open immediately after the steam control valve closes rapidly, a means for tripping and scramming the specified second partial number of the remaining internal pumps, and steam when the turbine bypass valve opens rapidly. An output control device for an ABWR, comprising: means for running back the remaining internal pumps after a required time has elapsed from the sudden closing of the control valve. 13. The time required according to claim 10 or 12, wherein the required time is a period until the plant output is reduced and the core flow rate is reduced due to the rapid insertion of the selective control rod and the partial trip of the internal pump. AB
WR output control device. 14. The output control device for an ABWR according to claim 12, further comprising means for changing the predetermined first partial number and / or the predetermined second partial number to an arbitrary number according to a core state.