JP2007232396A - Nuclear power plant and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure quickly a core thermal margin, when a core coolant flow rate or a core output is fluctuated resulting from a disturbance or the like, in a nuclear power plant equipped with a natural circulation type BWR. <P>SOLUTION: When the core coolant flow rate is decreased or increased, a core pressure is controlled properly by increasing or decreasing the opening of at least either of a steam control valve 16 of a turbine system and a turbine bypass valve 26 based on a set value of the core pressure outputted from a controller 34 by using a measured value of the core coolant flow rate or measured values of the core coolant flow rate and the core output. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nuclear power plant, and in particular, a control method for quickly ensuring the safety of a natural circulation boiling water light water reactor (hereinafter abbreviated as BWR) in which a coolant is naturally circulated by a density difference between inside and outside of a core. About.

  In general, the BWR can be roughly classified into a forced circulation type and a natural circulation type according to the circulation method of the coolant (cooling water). Most BWRs currently in operation are forced circulation BWRs that forcibly circulate coolant in the core using the power of a recirculation pump or a reactor internal pump. In this forced circulation type BWR, in order to ensure the safety of operation, the core coolant flow rate is controlled by controlling the number of revolutions of the pump to ensure an appropriate core thermal margin. On the other hand, in recent years, a natural circulation type BWR that does not have these pumps has been studied in order to simplify the plant. Regarding the natural circulation type BWR, many examples including Patent Document 1 have been made so far. In the natural circulation type BWR, there is no means for adjusting the core coolant flow rate by the pump like the forced circulation type BWR, and the control width of the core coolant flow rate by the water level control or the like is smaller than that in the forced circulation type BWR. Therefore, as a control method for ensuring the thermal margin of the core, a method of reducing the core output by inserting the control rod while keeping the operating pressure constant has been studied.

Japanese Patent Laid-Open No. 2003-130982

  By the way, in the natural circulation type BWR, when the core coolant flow rate is temporarily reduced or the core output is increased due to fluctuations in the temperature of the coolant in the reactor, there is a disturbance during normal operation that does not lead to a transient event. When this occurs, it is conceivable to ensure driving safety by inserting a control rod and reducing the output while keeping the operating pressure constant as described above. However, since the insertion speed of the control rod is slow except during scram, considering the time delay from the fluctuation of the core coolant flow rate and the core power to the insertion of the control rod, the control It is difficult to quickly secure the thermal margin.

  The present invention is for solving the above-mentioned problems, and in a nuclear power plant equipped with a natural circulation type BWR, when a core coolant flow rate or a core output fluctuates, a thermal margin of the core is quickly secured. An object of the present invention is to provide a nuclear power plant and a control method for the nuclear power plant.

  In order to achieve the above object, a nuclear power plant according to the present invention has a core coolant flow rate sensor for measuring a core coolant flow rate, and a set value of the core pressure as an input of a measured value of the core coolant flow rate sensor. When the core coolant flow rate decreases, the core pressure is reduced based on the set value from the controller, and when the core coolant flow rate increases, And configured to increase the core pressure.

  Further, the nuclear power plant according to the present invention inputs a core coolant flow sensor for measuring the core coolant flow rate, a core output sensor for measuring the core power, and measured values of the core coolant flow sensor and the core output sensor. And a control device that outputs the minimum limit power ratio output from the calculation device and outputs the set value of the core pressure as an input, and controls when the minimum limit power ratio decreases. When the core pressure is decreased based on the set value from the reactor and the minimum limit power ratio is increased, the core pressure is increased based on the set value from the controller.

  In the nuclear power plant of the present invention, the set value of the core pressure is output by the measured value of the core coolant flow rate sensor or the minimum limit output ratio obtained by using the measured values of the core coolant flow rate sensor and the core output sensor. Based on this set value, the core pressure is quickly controlled when the core coolant flow rate decreases or increases. Particularly in the control of the core pressure, when the core pressure is decreased, an increase in the core coolant flow rate, a decrease in the core power, and an increase in the minimum limit power ratio can be achieved simultaneously.

  In order to achieve the above object, a nuclear power plant control method according to the present invention includes a controller that receives a measured value of the coolant flow rate of the core as an input and outputs a set value of the core pressure as an output. Is decreased, the core pressure is decreased based on the set value from the controller, and when the core coolant flow rate is increased, the core pressure is increased based on the set value from the controller.

  In addition, the nuclear power plant control method according to the present invention includes a calculation device that outputs a measured value of the coolant flow rate of the core and a measured value of the core output as inputs, and a minimum limit output ratio as an input. A controller that outputs the set value of the core pressure, and when the minimum limit power ratio decreases, the core pressure is reduced based on the set value from the controller, and when the minimum limit power ratio increases The core pressure is increased based on the set value from the reactor.

  In the method for controlling a nuclear power plant according to the present invention, the set value of the core pressure is output by the measured value of the core coolant flow rate or the minimum limit output ratio obtained by using the measured values of the core coolant flow rate and the core output. Based on this set value, the core pressure is quickly controlled when the core coolant flow rate decreases or increases. Particularly in the control of the core pressure, when the core pressure is decreased, an increase in the core coolant flow rate, a decrease in the core power, and an increase in the minimum limit power ratio can be achieved simultaneously.

  According to the present invention, an increase in the core coolant flow rate, a decrease in the core power, and an increase in the minimum critical power ratio can be achieved at the same time by reducing the core pressure, so that the safety of the reactor can be secured quickly. . In particular, even when the core coolant flow rate or the core output fluctuates due to disturbance or the like, the thermal margin of the core can be secured quickly.

  Hereinafter, embodiments of a nuclear power plant and a control method thereof according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing an overall configuration of a first embodiment of a nuclear power plant provided with a natural circulation type BWR and its control system according to the present invention.

  As shown in FIG. 1, the nuclear power plant according to the present embodiment includes a natural circulation type BWR 1 and a turbine system 2 connected thereto. The natural circulation type BWR 1 has a core 6 in which a fuel rod assembly 4 in which a plurality of fuel rods are aligned and a control rod 5 that is inserted into or extracted from a gap between the fuel rod assemblies 4 to control the reactivity of the core. The reactor pressure vessel 7 is included. Although not shown, a control rod drive mechanism that drives the control rod 5 in the reactor core 6 so that it can be inserted and removed in the vertical direction is provided below the reactor pressure vessel 7. The control rod adjusts the reactor power, that is, the core power.

  A cylindrical shroud 8 is disposed in the reactor pressure vessel 7 so as to surround the core 6. An ascending flow path for the coolant to rise is formed inside the shroud 8, and a downcomer 13, which is a descending flow path for the coolant to descend, is formed in the gap between the shroud 8 and the reactor pressure vessel 7. Is formed. A chimney 9, which is a device for increasing the natural circulation flow rate, is installed in the upper part of the core, and a steam separator 11 and a steam dryer 12 are provided above the chimney 9.

  The turbine system 2 has a main steam pipe 14 connected to the reactor pressure vessel 7 and a water supply pipe 15 for supplying a coolant. The steam generated in the reactor, that is, the reactor pressure vessel 7 is supplied to the main steam pipe 14. The main steam pipe 14 is connected to a high-pressure turbine 17 via a steam control valve 16 connected to the main steam pipe 14, and further connected to a low-pressure turbine 19 via a moisture separator or a moisture separation superheater 18. The steam control valve 16 is an adjustment valve that adjusts the amount of steam flowing from the main steam pipe 14 into the high-pressure turbine 17. Reference numeral 20 denotes a generator connected to the low-pressure turbine 19.

  A condenser 21 that condenses steam discharged from the low-pressure turbine 19 via an extraction line is installed at the outlet of the low-pressure turbine 19, and a low-pressure feed water heater 22, a feed water pump 23, and the like are disposed downstream of the condenser 21. A high-pressure feed water heater 24 is installed. A water supply pipe 15 is connected to the outlet of the high-pressure water heater 24.

  The main steam pipe 14 is provided with a turbine bypass pipe 27 that is branched and directly connected to the condenser 21 via the turbine bypass valve 26. The turbine bypass pipe 27 is a bypass passage that extracts a part of the steam from the main steam pipe 14 on the upstream side of the steam control valve 16 and supplies the steam to the condenser 21. The turbine bypass valve 26 is an adjustment valve that adjusts the amount of steam that is on the bypass flow path and passes through the turbine bypass pipe 27.

  On the downstream side of the condenser 21, that is, in the middle of the feed pipe 15 from the condenser 21 to the reactor pressure vessel 7, a low-pressure feed water heater 22 that sequentially heats the feed water supplied from the condenser 21, At least one or more feed water pumps 23 that pressurize the feed water and supply it to the reactor pressure vessel 7 and a high-pressure feed water heater 24 that heats the feed water are arranged.

  In the natural circulation type BWR 1, the gas-liquid two-phase coolant heated in the core 6 and partially boiled to become steam flows through the chimney 9 in an upward flow, and the steam-water separator 11 and the steam dryer 12 Separated. Of the separated vapor, the vapor in the vapor phase is sent to the main vapor pipe 14 and the high temperature water in the liquid phase is recirculated water. The recirculated water and the coolant in the upward flow flowing through the core 6 and the chimney 9 are separated by the shroud 8 and do not mix with each other. The recirculated water flows as a downward flow, mixed with the feed water supplied from the feed water nozzle 25 of the feed water pipe 15 on the way, and supplied from the lower part of the core 6 after passing through the lower plenum 26.

  In the reactor pressure vessel 7, the volume density of the gas-liquid two-phase rising fluid flowing in the chimney 9 is smaller than the liquid single phase, and the volume density of the descending fluid (coolant) outside the chimney 9 is high. Due to the difference, the coolant is naturally circulated.

  On the other hand, the steam sent from the reactor pressure vessel 7 to the main steam pipe 14 is guided to the high-pressure turbine 17 through the steam control valve 16, and further to the low-pressure turbine 19 through the moisture separator or the moisture separation superheater 18. The generator 20 connected to the low-pressure turbine 19 is rotated to generate power.

  The steam that has rotated the low-pressure turbine 19 is introduced into the condenser 21 through the extraction line and condensed. The cooling water (condensate) condensed in the condenser 21 is returned to the reactor pressure vessel 7 from the feed water pipe 15 by the feed water pump 23. The cooling water (condensate) from the condenser 21 is heated to an appropriate temperature by the low-pressure feed water heater 22 and the high-pressure feed water heater 23 in the middle of the feed water pipe 15.

  In this embodiment, the flow rate sensor 31 for measuring the core coolant flow rate, the output sensor 32 for measuring the core output, and the MCPR calculation device for calculating and outputting the MCPR value from the core flow rate and the core output. (So-called MCPR computer) 33, a control device having a pressure controller 34 for inputting the MCPR from the MCPR calculation device 33 and outputting a set value of the core pressure, and a core pressure sensor 35 for measuring the core pressure 36 is provided. The definition of MCPR will be described later.

  That is, a flow rate sensor 31 that measures the coolant flow rate of the core 6 and an output sensor 32 that measures the core output are installed inside the reactor pressure vessel 7. As the output sensor 32, for example, a sensor that measures the core power by measuring the thermal balance or neutron flux of the core can be used. Actually, the flow rate can be measured by a pressure difference (differential pressure) between the upper and lower sides of the core support plate 35 provided in the lower part of the core. In this example, the core power can be calculated from the value of the neutron flux sensor that is the output sensor 32 inserted from the bottom of the core. Methods other than those described above may be used for measuring the core flow rate and core power.

  In the control device 36, the measured value of the core flow rate by the flow sensor 31 and the measured value of the core output by the output sensor 32 are input to the MCPR calculation device 33. The MCPR calculation device 33 calculates the MCPR value from the core flow rate and the core output, and outputs the MCPR calculation result. The MCPR increases as the core flow rate increases and the core power decreases, and the thermal margin of the core increases as the MCPR value increases.

  The MCPR value is not limited to the method of calculating from two measured values (input signals) of the core flow rate and the core output. For example, since MCPR also depends on the core pressure, as shown in FIG. 1, the measured value of the core pressure by the core pressure sensor 35, the measured value of the core flow rate by the flow sensor 31, and the measurement of the core output by the output sensor 32. There is also a method in which three measured values (input signals) are input to the MCPR calculation device 33 and the MCPR value is calculated from the core pressure, the core flow rate, and the core output. The core pressure can be measured, for example, with a pressure gauge serving as the pressure sensor 35 installed in the upper dome portion of the reactor pressure vessel 7. The core pressure value measured by the pressure sensor 35 is also input to the pressure controller 32.

  The MCPR value output from the MCPR calculation device 33 is input to the pressure controller 34, and the pressure set value is evaluated in the pressure controller 34. The set value evaluated inside the pressure controller 34 is compared with the core pressure measured by the core pressure sensor 35, and a valve opening request signal is sent to the steam control valve 16 and the turbine bypass valve 26, and Send the rotation speed request signal. By the respective valve opening request signals from the pressure controller 34, the opening of the steam control valve 16 and the opening of the turbine bypass valve 26 are controlled, and the core pressure is controlled. That is, when the MCPR decreases, the core pressure decreases. Here, the valve opening request signal is input to at least one of the steam control valve 16 and the turbine bypass valve 26, that is, one or both of them, so that proper control of the core pressure is performed. Further, even if the water supply amount from the water supply pump 23 is controlled by the rotation speed request signal from the pressure controller 34 and the core pressure is controlled, a constant water supply amount can be supplied to the reactor pressure vessel 7.

MCPR is defined as follows.
MCPR = Min. (Output at which fuel temperature rises due to film boiling / Current output)
Min. Means the minimum value calculated for all fuel assemblies.
In general, the thermal margin of the BWR is evaluated by an index called the minimum limit output ratio (= MCPR) defined above.

  FIG. 2 shows the change in the void ratio at the top of the core due to the change in the core pressure. The evaluation in FIG. 2 shows an example in which the pressure during rated operation is 7.0 MPa and the core exit void ratio is 80%. In order to simplify the calculation, the void ratio at the core outlet is shown, but the tendency of the void ratio to change with the core pressure is the same inside the core. When the core pressure is decreased, the boiling point of water decreases, and the density difference between the gas and liquid increases, so the void ratio increases. As the void ratio increases, the neutron moderation ability decreases and the reactor power decreases.

  Next, FIG. 3 shows changes in the coolant density difference inside and outside the shroud (= average coolant density outside the shroud−average coolant density inside the shroud) due to changes in the core pressure. As shown in FIG. 2, decreasing the core pressure increases the void fraction, but increasing the void fraction means increasing the volume of the gas phase with a lower density, so the average coolant density inside the shroud decreases. . Since the coolant outside the shroud is compressed water, the density hardly changes even if the pressure changes. Therefore, when the core pressure is decreased, the coolant density difference inside and outside the shroud increases.

  Since the natural circulation of the coolant is caused by the difference in the coolant density inside and outside the shroud as described above, when the coolant density difference inside and outside the shroud increases, the natural circulation amount, that is, the core coolant flow rate increases. Further, in general, the value of MCPR increases as the core pressure decreases.

  During the operation of the reactor, there is a possibility that the feed water flow rate and feed water temperature will fluctuate due to disturbances such as fluctuations in generator load. When the feed water flow varies, the core flow varies, and when the feed water temperature varies, the core output varies. If these fluctuations are small, there is no particular problem, but if the core flow rate is greatly reduced or the core output is greatly increased, the MCPR margin may be excessively reduced.

  If it is a forced circulation type BWR equipped with a recirculation pump or a reactor internal pump, it is possible to maintain the MCPR margin appropriately by increasing the number of revolutions of the pump, but in the case of a natural circulation type BWR In the prior art, a control method for inserting a control rod to lower the core output has been studied. However, since output control by inserting control rods is slow in response, it is necessary to keep a large MCPR margin during rated operation when using conventional techniques.

  On the other hand, in the present embodiment, a control method is adopted in which the core pressure set point is decreased when the MCPR decreases. In order to decrease the core pressure, the opening of the steam control valve 16 and / or the opening of the turbine bypass valve 26 may be increased by a signal output from the pressure controller 34. The MCPR increases due to the decrease in the core pressure, the thermal margin of the core increases, and safety is ensured. When the core pressure decreases, the feed water flow rate increases. Therefore, when it is desired to keep the feed water flow rate constant, the rotation speed of the feed water pump 23 is simultaneously reduced by a signal output from the pressure controller 34.

  A control method according to the present embodiment will be described. When the core coolant flow rate decreases or the MCPR decreases, the opening of at least one of the steam control valve 16 or the turbine bypass valve 26 is increased by the valve opening request signal from the pressure controller 34 to increase the core pressure. Decrease. At this time, at the same time, by the pump speed request signal from the pressure controller 34, the feed water flow rate is reduced by reducing the rotation speed of at least one of the feed pumps having one or more stages, and the core coolant flow rate is kept constant. Keep on. Further, when the core coolant flow rate increases or the MCPR increases, the opening of at least one of the steam control valve 16 or the turbine bypass valve 26 is decreased to increase the core pressure. At this time, at the same time, by the pump speed request signal from the pressure controller 34, the feed water flow rate is increased by increasing the rotation speed of at least one stage of the feed pumps having one or more stages, and the core coolant flow rate is kept constant. Keep on. As a result, the core pressure is controlled, the core power is controlled, and the safe operation of the reactor is ensured.

  According to the nuclear power plant according to the first embodiment, as described above, when the core coolant flow rate or the core output greatly fluctuates due to the disturbance, for example, the core coolant flow rate greatly decreases or the core output greatly increases. When the thermal margin is reduced, the core safety can be achieved by reducing the core pressure, which is the factor that increases the safety margin, which is the core power reduction, core coolant flow rate increase, and MCPR increase. Can be secured quickly.

  That is, when the thermal margin decreases, the core void ratio can be increased by increasing the core pressure, and the core coolant flow rate can be increased to decrease the core power. As a result, the thermal margin of the core can be secured quickly, and safety can be secured quickly.

  Thereafter, when the disturbance converges and the MCPR recovers, the operating pressure set point is increased and the opening of the steam control valve 16 and / or the turbine bypass valve 26 is decreased, contrary to the previous operation. Increase the pressure to the core pressure during rated operation. When the rotation speed control of the feed water pump 23 is also performed at the same time, the rotation speed of the feed water pump 23 is also increased.

  The above embodiment may be used at all times during rated operation, but may be used as part of an interlock (safety device) for ensuring safety. In this embodiment, an example in the case of using as a part of an interlock is shown. In FIG. 4, the conceptual diagram of the pressure set point at the time of MCPR change and a core pressure change is shown.

  When used as part of an interlock, some variation in MCPR is allowed and pressure control is not performed. The MCPR is provided with a lower limit threshold 41, and the core pressure is reduced only when the MCPR falls below the lower limit threshold 41 (from time t2). When the core pressure is decreased and the disturbance is converged, the MCPR gradually increases (time t3 to t4). When MCPR increases, it is necessary to return the core pressure to the core pressure 42 during the rated operation. When the core pressure is increased, contrary to the case where the core pressure is decreased, the core power increase, the core coolant flow rate decrease, and the MCPR decrease occur at the same time. A value 43 is provided, and when the MCPR exceeds the upper limit threshold value 43, the core pressure is increased (from time t4 to time t5). MCPR also returns to the rated value 44 at time t5 when the core pressure returns to the rated pressure 42. As is apparent from FIG. 4, the upper limit of the control range of the core pressure is the core pressure (rated pressure 42) during rated operation.

  Regarding the core coolant flow rate, as in the case of the MCPR, a threshold value (lower threshold value) smaller than the value at the rated operation is provided, and the core only when the core coolant flow rate falls below this lower threshold value. The pressure can be reduced. In addition, a threshold value (upper limit threshold value) greater than the value at rated operation is set for the core coolant flow rate, and the core pressure is decreased only when the core coolant flow rate is below the lower limit threshold value, and the upper limit threshold value is reached. The core pressure can be increased after the value is exceeded. When the core pressure returns to the rated pressure, the core coolant flow rate also returns to the rated value.

  FIG. 5 shows the control logic of this embodiment. First, the MCPR calculation device 33 receives the measured value signals P1 and P2 of the core coolant flow rate sensor 31 and the core output sensor 32, respectively. The MCPR calculation device 33 evaluates the MCPR from the core coolant flow rate and the core output, and sends the evaluation result (that is, the MCPR calculated value signal P3) to the pressure controller 34. On the other hand, a core pressure measurement value signal P 4 measured by the core pressure sensor 35 is sent to the pressure controller 34.

In the pressure controller 34, first, in step S1, it is evaluated whether or not the current MCPR is below a threshold value 41 (see FIG. 4) that is a lower limit.
When it is below, it progresses to step S4 and decreases a core pressure setting value.
If the MCPR is not below the lower limit threshold 41, the process proceeds to step S2 to evaluate whether the MCPR is above the upper limit threshold 43 (see FIG. 4).
If the upper limit threshold value 43 is exceeded, the process proceeds to step S3, and it is evaluated whether or not the current core pressure is lower than the rated core pressure 42 (see FIG. 4).
If the current core pressure is lower than the rated core pressure, the process proceeds to step S6, and the core pressure set value is increased to gradually return the core pressure to the rated core pressure.
In cases other than the above, that is, when the MCPR does not exceed the upper limit threshold value 43 in step S2 and when the current core pressure is not lower than the rated core pressure in step S3, the process proceeds to step S5, Leave the core pressure setpoint unchanged.
The pressure set value evaluated inside the pressure controller 34 (that is, the pressure set value signal P5 based on the pressure set value decrease, the pressure set value deferment, and the pressure set value increase) is the steam control valve 16, the turbine bypass valve 26, and the water supply. It is sent to the pump 23, the core pressure is adjusted, and one control is completed. Here, the pressure set value signal P5 output from the pressure controller 34 includes a valve opening request signal to the steam control valve 16, a valve opening request signal to the turbine bypass valve 26, and the rotation speed to the feed pump 23. A request signal is included.
The input signal of the MCPR calculator 33 in FIG. 5 may add the core pressure in addition to the core flow rate and the core output.
Although not shown in FIG. 5, the pressure set value evaluated inside the pressure controller 34 is actually compared with the current core pressure, and if the pressure set value is larger than the core pressure, the steam control valve is used. 16 or a valve opening request signal in a direction to decrease the opening of the turbine bypass valve 26, and if the pressure set value is smaller than the core pressure, a valve opening request in a direction to increase the opening of the steam control valve 16 or the turbine bypass valve 26. Send a signal.

  FIG. 6 shows a second embodiment of a nuclear power plant including a natural circulation type BWR and its control system according to the present invention. The nuclear power plant according to the present embodiment is configured by excluding the rotation speed of the feed water pump 23 from the control items of the first embodiment. That is, from the pressure controller 34 of the control device 36, the output valve opening request signals are respectively input to the steam control valve 16 and the turbine bypass valve 26. The output controller 34 does not output a rotation speed request signal for controlling the rotation speed of the water supply pump 23. The other configuration is the same as that of the first embodiment in FIG.

  In the present embodiment, when the core pressure is lowered when the MCPR is decreased and the rotation speed of the feed water pump 23 is not changed, the pressure difference between the outlet pressure of the feed water pump 23 and the core pressure increases, so that the feed water flow rate increases. . When this embodiment is used for the purpose of ensuring safety, since the increase in the feed water flow rate is on the safe side, the rotation speed of the feed water pump need not be controlled when the increase in the feed water flow rate is allowed. In addition, the feed water flow rate is originally determined by the thermal balance inside the reactor separately from the MCPR, so even if the rotation speed of the feed water pump 23 is controlled by a control system different from the pressure control of the present embodiment. good.

  According to the nuclear power plant according to the second embodiment, as in the first embodiment, the valve opening that is output from the pressure controller 34 even when the core coolant flow rate or the core output fluctuates greatly due to disturbance. The degree request signal is input to the steam control valve 16 and the turbine bypass valve 26, and the opening degree of the steam control valve 16 and / or the opening degree of the turbine bypass valve 26 is controlled, and the core pressure can be reduced. This makes it possible to ensure the safety of the core quickly.

  FIG. 7 shows a third embodiment of a nuclear power plant including a natural circulation type BWR and its control system according to the present invention. The nuclear power plant according to the present embodiment omits the MCPR calculation device 33 of the first embodiment, and two measured values are the core coolant flow rate from the flow rate sensor 31 and the core pressure from the pressure sensor 35. Thus, each measured value is inputted to the pressure controller 34. The other configuration is the same as that of the first embodiment shown in FIG.

  In the forced circulation BWR, the core output is controlled by controlling the core coolant flow rate, thereby improving the operability of the plant. According to the nuclear power plant of the third embodiment, even in a natural circulation furnace, the core pressure is controlled by controlling the opening of the steam control valve 16 and / or the turbine bypass valve 26 with an output signal from the pressure controller 34. Thus, the core coolant flow rate can be controlled, and safety can be secured quickly and the operability of the plant can be improved. That is, in the case of continuous operation, the core power can be controlled without using control of the control rod, so that the operability of the plant is improved.

  In FIG. 7, similarly to the second embodiment of FIG. 6, it is possible to prevent the rotation speed request signal for controlling the rotation speed of the feed water pump 23 from being output from the pressure controller 34. In this case, the rotation speed of the feed water pump 23 is not changed.

  FIG. 8 shows a fourth embodiment of a nuclear power plant including a natural circulation type BWR and its control system according to the present invention. The nuclear power plant according to the present embodiment is configured by adding the operation of the control rod 5 to the control items of the first embodiment. That is, a control rod drive signal is output from the pressure controller 34, and this control rod drive request signal is supplied to the control rod drive device 37 that drives the control rod 5 to control the control rod 5. The other configuration is the same as that of the first embodiment in FIG.

  The fourth embodiment can be used for two purposes. The first purpose is to use it for ensuring the safety of the nuclear reactor as in the first embodiment. The second purpose is simply for use in controlling the core flow rate.

In the case of the first purpose of use, when the core pressure is reduced, the opening of the steam control valve 16 and / or the turbine bypass valve 26 is controlled by the valve opening request signal from the pressure controller 34 to reduce the core pressure. At the same time, the control rod 5 is inserted by the control rod drive request signal from the pressure controller 34 to further reduce the core power. As a result, the safety margin can be increased and the safety can be ensured more reliably.
Further, when the core pressure is increased, the core pressure is increased by controlling the opening of the steam control valve 16 and / or the turbine bypass valve 26 by the valve opening request signal from the pressure controller 34, and the core output is increased. In order to suppress (reduce) the amount, the control rod 5 is inserted together with the increase in the core pressure. These two methods may be combined.

  In the case of the second usage purpose, when the core pressure is decreased, the control rod drive request signal is used to pull out the control rod 5 for suppressing the decrease in the core output to suppress the change in the core output. That is, the control rod 5 is pulled out to reduce the core power reduction amount due to the core pressure reduction. Similarly, when the core pressure is increased, the control rod 5 is inserted by a control rod drive request signal in order to suppress an increase in the core output.

  Note that the control by the control rod added in the fourth embodiment can be used in addition to the control method of each embodiment described above.

  Although the above-described embodiments have been described on the assumption that they are used during rated operation, the present invention can be applied in the same manner even when the reactor is started up.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows 1st Embodiment of the nuclear power plant which concerns on this invention, and its control system. It is a graph which shows the void ratio change of the core upper part by a core pressure change. It is a graph which shows the coolant density difference change inside and outside a shroud by core pressure change. It is a conceptual diagram of the pressure set point and core pressure change at the time of MCPR change. It is a control logic figure of a 1st embodiment of the present invention. It is a schematic block diagram which shows 2nd Embodiment of the nuclear power plant which concerns on this invention, and its control system. It is a schematic block diagram which shows 3rd Embodiment of the nuclear power plant which concerns on this invention, and its control system. It is a schematic block diagram which shows 4th Embodiment of the nuclear power plant which concerns on this invention, and its control system.

Explanation of symbols

  1 ... Natural circulation type BWR 2 ... Turbine system 4 ... Fuel rod assembly 5 ... Control rod 6 ... Core reactor 7 ... Reactor pressure vessel 8 ... Shroud 9 ... Chimney , 11 steam separator, 12 ... steam dryer, 13 ... downcomer, 14 ... main steam pipe, 15 ... water supply pipe, 16 ... steam control valve, 17 ... high pressure turbine, 18 ... moisture Separation superheater, 19 ... Low pressure turbine, 21 ... Condenser, 22 ... Low pressure feed water heater, 23 ... Feed pump, 24 ... High pressure feed water heater, 26 ... Turbine bypass valve, 27 ... Turbine Bypass pipe, 31 ... Flow sensor, 32 ... Output sensor, 33 ... MCPR calculation device, 34 ... Pressure controller, 35 ... Pressure sensor, 36 ... Control device,

Claims (18)

In a control method of a nuclear power plant equipped with a natural circulation boiling water light water reactor in which a coolant circulates naturally due to a coolant density difference in a nuclear reactor, and a turbine system,
It has a controller that takes the measured value of the core coolant flow rate as input and outputs the set value of core pressure
When the core coolant flow rate decreases, the opening degree of at least one of the steam control valve and the turbine bypass valve that adjusts the steam amount to the turbine of the turbine system based on the set value output from the controller is increased. Reduce the core pressure,
When the core coolant flow rate increases, the core pressure is increased by decreasing the opening of at least one of the steam control valve or the turbine bypass valve based on the set value output from the controller. A method for controlling a nuclear power plant. When the core coolant flow rate is decreased, the core pressure is reduced based on the set value output from the controller, and the rotation speed of at least one or more of the feed pumps of the turbine system is reduced,
When the core coolant flow rate is increased, the core pressure is increased based on the set value output from the controller, and the rotation speed of at least one of the feed water pumps is increased. The method for controlling a nuclear power plant according to claim 1. In a control method of a nuclear power plant equipped with a natural circulation boiling water light water reactor in which a coolant circulates naturally due to a coolant density difference in a nuclear reactor, and a turbine system,
A calculation device that takes the measured value of the coolant flow rate of the core and the measured value of the core power as input and outputs the minimum critical power ratio;
A controller having the minimum limit output ratio as an input and a set value of the core pressure as an output,
When the minimum limit output ratio decreases, the opening degree of at least one of the steam control valve and the turbine bypass valve that adjusts the steam amount to the turbine of the turbine system based on the set value output from the controller is increased. Reduce the core pressure,
When the minimum limit output ratio increases, the opening of at least one of the steam control valve or the turbine bypass valve is decreased based on a set value output from the controller to increase the core pressure. A method for controlling a nuclear power plant. When the minimum limit output ratio is reduced, the core pressure is reduced based on the set value output from the controller, and the rotational speed of at least one or more of the feed pumps of the turbine system is reduced,
When the minimum limit output ratio increases, the core pressure is increased based on the set value output from the controller, and the rotation speed of at least one or more of the feed water pumps is increased. A method for controlling a nuclear power plant according to claim 3.   2. The method of controlling a nuclear power plant according to claim 1, wherein when the core pressure is decreased or increased, the control power is further controlled by inserting and removing control rods from the core.   4. The method of controlling a nuclear power plant according to claim 3, wherein when the core pressure is reduced or increased, the control power is further controlled by inserting / removing control rods into / from the core. The core coolant flow rate has a lower threshold that is smaller than the value during rated operation,
2. The nuclear power plant control method according to claim 1, wherein the core pressure is decreased only when the value falls below the lower threshold. The core coolant flow rate has a lower threshold that is smaller than the value during rated operation and an upper threshold that is greater than the value during rated operation.
Reduce the core pressure only when below the lower threshold,
The nuclear power plant control method according to claim 1, wherein the core pressure is increased after the upper limit threshold is exceeded. The minimum limit output ratio has a lower threshold that is smaller than the value during rated operation,
The nuclear power plant control method according to claim 3, wherein the core pressure is decreased only when the value falls below the lower threshold. The minimum limit output ratio has a lower threshold that is smaller than the value during rated operation and an upper threshold that is greater than the value during rated operation.
Reduce the core pressure only when below the lower threshold,
The nuclear power plant control method according to claim 3, wherein the core pressure is increased after the upper limit threshold is exceeded.   4. The control of a nuclear power plant according to claim 3, wherein a measured value of the core coolant flow rate, a measured value of the core power, and a measured value of the core pressure are used as input signals to the computer that outputs the minimum limit power ratio. Method. In a nuclear power plant equipped with a natural circulation boiling water light water reactor in which the coolant circulates naturally due to a difference in coolant density in the nuclear reactor, and a turbine system,
A core coolant flow sensor for measuring the coolant flow rate in the core;
A controller that takes the measured value of the core coolant flow sensor as an input and outputs the set value of the core pressure as an output;
When the core coolant flow rate decreases, the opening degree of at least one of the steam control valve and the turbine bypass valve that adjusts the steam amount to the turbine of the turbine system based on the set value output from the controller is increased. Reduce the core pressure,
When the core coolant flow rate increases, the opening of at least one of the steam control valve or the turbine bypass valve is decreased based on the set value output from the controller to increase the core pressure. A nuclear power plant characterized by When the core coolant flow rate is decreased, the core pressure is reduced based on the set value output from the controller, and the rotation speed of at least one or more of the feed pumps of the turbine system is reduced,
When the core coolant flow rate increases, the core pressure is increased based on the set value output from the controller, and the rotation speed of at least one of the feed water pumps is increased. The nuclear power plant according to claim 12. In a nuclear power plant equipped with a natural circulation boiling water light water reactor in which the coolant circulates naturally due to a difference in coolant density in the nuclear reactor, and a turbine system,
A core coolant flow sensor for measuring the coolant flow rate in the core;
A core power sensor for measuring the core power;
A calculation device that outputs the minimum limit output ratio by using the measured values of the core coolant flow rate sensor and the core output sensor as inputs; and
A controller that outputs the set value of the core pressure with the minimum limit output ratio output from the calculation device as an input;
When the minimum limit output ratio decreases, the opening degree of at least one of the steam control valve and the turbine bypass valve that adjusts the steam amount to the turbine of the turbine system based on the set value output from the controller is increased. Reduce the core pressure,
When the minimum limit output ratio increases, the opening of at least one of the steam control valve or the turbine bypass valve is decreased based on the set value output from the controller to increase the core pressure. A nuclear power plant characterized by When the minimum limit output ratio is reduced, the core pressure is reduced based on the set value output from the controller, and the rotational speed of at least one or more of the feed pumps of the turbine system is reduced,
When the minimum limit output ratio increases, the core pressure is increased based on the set value output from the controller, and the rotation speed of at least one of the feed water pumps is increased. The nuclear power plant according to claim 14.   13. The nuclear power plant according to claim 12, wherein when the core pressure is decreased or increased, the control rod is further inserted into and removed from the core to control the core power.   15. The nuclear power plant according to claim 14, wherein when the core pressure is decreased or increased, the control rod is further controlled to be inserted into and removed from the core to control the core output.   15. The nuclear power plant according to claim 14, wherein a measured value of the core coolant flow rate, a measured value of the core power, and a measured value of the core pressure are used as an input signal of a computer that outputs the minimum limit power ratio.

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