Control method and control device

Abstract

To provide a nuclear power plant control method that can increase generation of power in a nuclear power plant so as to cope with a sudden increase in load and a sudden reduction in the amount of supplied power.SOLUTION: A control method includes the steps of: determining whether to perform load response drive of temporarily increasing generation of power in accordance with a reduction in power supplied from a nuclear power plant or an increase in load; when determining to perform the load response drive, reducing the amount of steam extracted from a steam turbine; when determining to perform the load response drive, starting up an external power supply; determining the connection timing to connect the external power supply to an electric power system; when the connection timing is reached, connecting the external power supply to the electric power system; determining the timing to return the amount of extraction; when the returning timing is reached, returning the amount of extraction so as to prevent output of a nuclear reactor from increasing beyond a prescribed value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a control method and a control device.

Background Art

[0002] In recent years, the proportion of renewable energy in the total generated electric power has been increasing, and the situation where the instability of the frequency of the power grid cannot be avoided has occurred. For example, in a power generation system, when a rapid load increase or a decrease in the power supply amount occurs, since the power supply from the power generation system cannot catch up immediately, the grid frequency temporarily decreases. When the grid frequency decreases, a rapid output increase request is made to the power generation system side. The short-term load response immediately after fluctuations such as load, which responds to this output increase request, is called primary response, and the load response that maintains that state is called secondary response. Generally, nuclear power plants do not have a function to respond to rapid output fluctuations, and until now, thermal power plants have been responsible for primary response and secondary response. Therefore, the proportion of thermal power generation in the total generated electric power cannot be reduced below a certain level, and there is a limit to the decarbonization of society.

[0003] Patent Document 1 discloses a condensate throttling operation in a steam power plant that generates electricity by driving a steam turbine with high-temperature and high-pressure steam generated from a steam generation source such as a boiler or a nuclear reactor. By rapidly reducing the flow rate of the condensate supplied to the deaerator, the extraction steam from the steam turbine is reduced, and accordingly, the output of the steam turbine is increased. However, the output increase by the condensate throttling operation is temporary and cannot be maintained. In addition, different from a thermal power plant, a nuclear power plant has a limitation that it cannot operate beyond the rated output of the nuclear reactor. Therefore, by increasing the amount of steam supplied to the steam turbine by increasing the output of the nuclear reactor, it is not possible to compensate for the output after the output temporarily increased by the condensate throttling operation has decreased.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-134054 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Nuclear power plants are also required to operate in a way that rapidly increases power generation in response to sudden increases in load or sudden decreases in power supply.

[0006] This disclosure provides a control method and a control device that can solve the above-mentioned problems. [Means for solving the problem]

[0007] The control method of the present disclosure is a control method for a nuclear power plant comprising a nuclear reactor and a steam turbine driven by steam directly generated by the nuclear reactor or steam indirectly generated by heat exchange with the heat of the nuclear reactor, wherein the power generated by driving the steam turbine is supplied to a power grid, the method comprising: determining whether or not to perform load response operation to temporarily increase the power generated in response to a decrease in the power supplied from the nuclear power plant or an increase in the load; if it is determined that load response operation should be performed, reducing the amount of steam extracted from the steam turbine; if it is determined that load response operation should be performed, starting up an external power supply; determining the timing for connecting the external power supply to the power grid; when the timing for connecting arrives, connecting the external power supply to the power grid; determining the timing for returning the amount of extracted steam; and when the timing for returning the amount of extracted steam arrives, returning the amount of extracted steam so that the output of the nuclear reactor does not rise above a specified value.

[0008] The control device of the present disclosure is a control device for a nuclear power plant comprising a reactor and a steam turbine driven by steam directly generated by the reactor or steam indirectly generated by heat exchange with the heat of the reactor, and which supplies power generated by driving the steam turbine to a power grid, and comprises means for determining whether or not to perform load response operation to temporarily increase the power generated in response to a decrease in the power supplied from the nuclear power plant or an increase in the load; means for reducing the amount of steam extracted from the steam turbine when it is determined that load response operation should be performed; means for determining the timing for connecting an external power source started based on the determination to perform load response operation to the power grid; means for determining the timing for returning the amount of steam extracted; and means for returning the amount of steam extracted so that the output of the reactor does not rise above a specified value when the timing for returning the amount of steam extracted arrives. [Effects of the Invention]

[0009] According to the control method and control device described above, it is possible to rapidly increase the power generated by a nuclear power plant in response to a sudden increase in load or a sudden decrease in power supply. [Brief explanation of the drawing]

[0010] [Figure 1] This is a system diagram showing an example of a nuclear power plant according to the embodiment. [Figure 2] This figure shows an example of the time-dependent changes in system frequency and output related to load-response operation in the embodiment. [Figure 3] This figure illustrates the control of load-response operation according to the embodiment. [Figure 4] This flowchart shows an example of control for load-response operation according to the embodiment. [Figure 5] This is a diagram illustrating another example of a nuclear power plant according to the embodiment. [Modes for carrying out the invention]

[0011] <Embodiment> The load response control described herein will be explained below with reference to the drawings. (composition) Figure 1 is a system diagram showing an example of a nuclear power plant according to an embodiment. The nuclear power plant 1 of this embodiment includes a reactor 10, a steam generator 12, a steam turbine 20, a generator 50, an external power supply 70, a control device 100, etc. The reactor 10 and the steam generator 12 are connected by a flow path 11 for circulating primary cooling water, and primary cooling water that cools the reactor 10 circulates through this flow path 11. The steam generator 12 exchanges heat between the primary cooling water circulating in the flow path 11 and the secondary cooling water (condensate) flowing through the steam turbine 20, thereby heating the secondary cooling water and generating steam.

[0012] The steam turbine 20 comprises a high-pressure steam turbine 21, a main steam stop valve 22, a steam control valve 23, a moisture separator 24, moisture separator heaters 25 and 26, a low-pressure steam turbine 27, a reheat steam stop valve 28, an interset valve 29, a condenser 30, a condensate pump 31, a deaerator water level control valve 32, a low-pressure first feedwater heater 33, a low-pressure second feedwater heater 34, a low-pressure third feedwater heater 35, a low-pressure fourth feedwater heater 36, a deaerator 37, a main feedwater pump 38, a feedwater booster pump 39, and a high-pressure sixth feedwater heater 3A.

[0013] The steam generator 12 and the high-pressure steam turbine 21 are connected via a main steam pipe L1. The steam generated by the steam generator 12 is supplied to the high-pressure steam turbine 21 through the steam pipe L1. The main steam pipe L1 is equipped with a main steam stop valve 22 and a steam control valve 23. By closing the main steam stop valve 22, the supply of steam from the steam generator 12 to the high-pressure steam turbine 21 is cut off. By adjusting the opening of the steam control valve 23, the flow rate of steam supplied from the steam generator 12 to the high-pressure steam turbine 21 is controlled.

[0014] The outlet side of the high-pressure steam turbine 21 and the moisture separator 24 are connected via a steam pipe L2. The moisture separator 24 separates the moisture contained in the steam exhausted by the high-pressure steam turbine 21. The separated steam is supplied to the moisture separator heater 25, and the separated moisture is supplied to the deaerator 37 via a drain pipe L21. The moisture separator heater 25 is connected to the high-pressure steam turbine 21 via a steam pipe L3. In the moisture separator heater 25, the steam supplied from the high-pressure steam turbine 21 via the steam pipe L3 reheats the steam supplied from the moisture separator 24 and separates the moisture. The separated moisture and the moisture cooled and condensed by heat exchange in the moisture separator heater 25 are supplied to the high-pressure sixth feedwater heater 3A via a drain pipe L22. The steam after moisture separation and heating in the moisture separator heater 25 is supplied to the moisture separator heater 26. The moisture separator heater 26 is connected to the steam generator 12 via a steam pipe L4. In the moisture separation heater 26, the steam supplied from the moisture separation heater 25 is heated by the steam supplied through the steam pipe L4, and moisture is separated. The separated moisture and the moisture cooled and condensed by heat exchange in the moisture separation heater 26 are supplied to the high-pressure sixth feedwater heater 3A via the drain pipe L23.

[0015] The steam, after moisture separation and heating in the moisture separation heater 26, is supplied to the low-pressure steam turbine 27 via the steam pipe L5. The steam pipe L5 is equipped with a reheat steam stop valve 28 and an interset valve 29. Closing the reheat steam stop valve 28 cuts off the supply of steam to the low-pressure steam turbine 27. The flow rate of steam supplied to the low-pressure steam turbine 27 is controlled by adjusting the opening of the interset valve 29. The low-pressure steam turbine 27 is connected to a generator 50. The low-pressure steam turbine 27 is rotationally driven by the steam supplied from the moisture separation heater 26, which drives the generator 50. The electricity generated by driving the generator 50 is supplied to the power grid 60. The power grid 60 is equipped with a frequency meter 61 for measuring the grid frequency.

[0016] The steam used to drive the low-pressure steam turbine 27 is supplied to the condenser 30. The condenser 30 returns the steam discharged from the low-pressure steam turbine 27 back into water. The condenser 30 and the steam generator 12 are connected by a condensate line L6. The condensate line L6 is equipped with a condensate pump 31, a deaerator water level control valve 32, a low-pressure first feedwater heater 33, a low-pressure second feedwater heater 34, a low-pressure third feedwater heater 35, a low-pressure fourth feedwater heater 36, a deaerator 37, a main feedwater pump 38, a feedwater booster pump 39, and a high-pressure sixth feedwater heater 3A, in this order from the condenser 30 to the steam generator 12. The condensate generated in the condenser 30 is sequentially sent by the condensate pump 31 to the low-pressure first feedwater heater 33, the low-pressure second feedwater heater 34, the low-pressure third feedwater heater 35, and the low-pressure fourth feedwater heater 36. The low-pressure first feedwater heater 33 is connected to the low-pressure steam turbine 27 via an extraction pipe L7. The condensate sent to the low-pressure first feedwater heater 33 is heated by the extracted steam supplied through the extraction pipe L7. The condensate heated in the low-pressure first feedwater heater 33 is supplied to the low-pressure second feedwater heater 34. The low-pressure second feedwater heater 34 is connected to the low-pressure steam turbine 27 via an extraction pipe L8. The condensate sent to the low-pressure second feedwater heater 34 is heated by the extracted steam supplied through the extraction pipe L8 and supplied to the low-pressure third feedwater heater 35. Similarly, the low-pressure third feedwater heater 35 and the low-pressure fourth feedwater heater 36 are connected to the low-pressure steam turbine 27 via extraction pipes L9 and L10, respectively, and the condensate sent to the low-pressure third feedwater heater 35 and the low-pressure fourth feedwater heater 36 is heated by extracted steam supplied through extraction pipes L9 and L10, respectively. The condensate heated in the low-pressure second feedwater heater 34 is supplied to the low-pressure third feedwater heater 35, and the condensate heated in the low-pressure third feedwater heater 35 is supplied to the low-pressure fourth feedwater heater 36. The condensate heated in the low-pressure fourth feedwater heater 36 is supplied to the deaerator 37.

[0017] The deaerator 37 is connected to the high-pressure steam turbine 21 via the extraction pipe L11. In the deaerator 37, the moisture supplied to the deaerator 37 via the drain pipe L21 and the condensate supplied from the low-pressure fourth feedwater heater 36 are heated and deaerated by the extraction steam supplied through the extraction pipe L11. The deaerated condensate is stored in the deaerator 37. The deaerator water level control valve 32 adjusts the water level of the condensate stored in the deaerator 37. The deaerator water level control valve 32 is, for example, a pneumatic valve and can be quickly closed. Further, a water level gauge 371 for measuring the stored water level is provided in the deaerator 37.

[0018] Between the deaerator 37 and the steam generator 12, in order from the upstream side in the condensate flow direction, a main feedwater pump 38, a feedwater booster pump 39, and a high-pressure sixth feedwater heater 3A are installed. The main feedwater pump 38 and the feedwater booster pump 39 send the condensate from the deaerator 37 to the steam generator 12 via the high-pressure sixth feedwater heater 3A. The high-pressure sixth feedwater heater 3A is connected to the high-pressure steam turbine 21 via the extraction pipe L12. The high-pressure sixth feedwater heater 3A heats the moisture supplied via the drain pipes L22 and L23 and the condensate supplied from the deaerator 37 with the extraction steam supplied through the extraction pipe L12. The heated condensate (the secondary cooling water described above) is heated by heat exchange with the primary cooling water in the steam generator and becomes steam. The condensate that has become steam circulates through the paths described so far and drives the generator 50.

[0019] The external power source 70 is, for example, a synchronous diesel generator that generates electricity when the external power supply to the nuclear power plant 1 stops. In the nuclear power plant 1, multiple emergency diesel generators are provided in consideration of redundancy as a power source for operating the safety system equipment in an emergency. These diesel generators have a large capacity and are not normally used. In this embodiment, these emergency power sources are utilized as the external power source 70. The external power source 70 is configured not only to supply power to the safety system equipment of the nuclear power plant 1 in an emergency but also to be able to connect (merge) to the power grid 60 via the power line 71 by closing the circuit breaker 72.

[0020] The control device 100 controls the nuclear power plant 1. For example, the main steam stop valve 22, the steam control valve 23, the reheater steam stop valve 28, the intercept valve 29, the deaerator water level control valve 32, the condensate pump 31, the main feed water pump 38, and the feed water booster pump 39 are connected to the control device 100 and are controlled by the control device 100. The control device 100 includes a data acquisition unit 101, a determination unit 102, a control unit 103, and a storage unit 104.

[0021] The data acquisition unit 101 is configured to include various input interfaces, switches, buttons, input devices such as keyboards, etc. The data acquisition unit 101 is connected to a frequency meter 61, a water level meter 371, an external power source 70, etc., and acquires the system frequency of the power system 60 measured by the frequency meter 61, the water level of the deaerator 37 measured by the water level meter 371, and information indicating the operating status of the external power source 70 (for example, the rotational speed of a synchronous generator, etc.). In addition, the data acquisition unit 101 acquires information input by the user using the input device. The data acquisition unit 101 records the various acquired information in the storage unit 104.

[0022] The determination unit 102 determines whether to execute a load response operation using the information acquired by the data acquisition unit 101. Here, the load response operation is an operation that controls the output of the nuclear power plant 1 so as to be able to respond to fluctuations in the frequency of the power system 60 and fluctuations in power demand. Specifically, it is an operation that rapidly increases the output when the load connected to the power system 60 increases or the power supplied from the nuclear power plant 1 to the power system 60 decreases. For example, when the power supply frequency measured by the frequency meter 61 drops below a predetermined threshold value, the determination unit 102 determines to execute the load response operation.

[0023] When the determination unit 102 determines that load response operation should be performed, the control unit 103 controls the nuclear power plant 1 and performs load response operation. Load response operation consists of a primary response, which is a short-term load response, and a secondary response, which maintains the output increase caused by the primary response. For example, the control unit 103 increases the output by condensate throttling operation, which will be described later (primary response). Subsequently, the control unit 103 maintains the increased output state by starting the external power supply 70 and connecting it to the power grid 60 (secondary response). The control unit 103 also has a timer for measuring time. The memory unit 104 stores information acquired by the data acquisition unit 101, thresholds necessary for load response operation, and other such information.

[0024] The control device 100 is composed of a computer. The control device 100 includes an input interface included in the data acquisition unit 101, an external storage device that stores programs for realizing the functions of the determination unit 102 and the control unit 103, a CPU that executes these programs, and a main memory where the execution results of the CPU are stored. The storage unit 104 corresponds to the external storage device and the main memory in this case. The control device 100 also performs control other than load response operation, but the description of functions related to other control is omitted in this specification.

[0025] Next, the load response operation according to this embodiment will be described with reference to Figures 2 and 3. Figure 2 shows an example of the temporal changes in system frequency and output related to load response operation in the embodiment. Figure 2, upper G21, shows the change in system frequency of power system 60 during load response operation, and figure 22, lower G22, shows the change in output of nuclear power plant 1 during load response operation. In upper G21, the vertical axis represents power frequency (Hz), and the horizontal axis represents time. In lower G22, the vertical axis represents generated power (W), and the horizontal axis represents time. The same position on the vertical axis in upper G21 and lower G22 represents the same time. When the frequency of power system 60 falls below the rated frequency by a threshold Δf or more at time t1, the determination unit 102 determines to perform load response operation. Then, the control unit 103 starts primary response (time t1). When primary response starts, the output rapidly increases by ΔL(w). As explained below, the primary response involves, for example, condensate throttling (an operation that reduces the flow rate of condensate supplied to the deaerator 37 by throttling the deaerator water level control valve 32), but this operation can only be performed for a certain period of time (for example, within 5 minutes). If condensate throttling can no longer be performed, the output, which has increased by ΔL, will decrease. Therefore, the control unit 103 starts a secondary response using the external power supply 70 within the time when condensate throttling can be performed (for example, at time t2). When the output increases by ΔL due to the primary response, the secondary response performs output control to maintain this output increase of ΔL. This compensates for sudden increases in load and decreases in power supply. Also, as shown in Figure G21 above, the grid frequency recovers due to the increase in output of the nuclear power plant 1 due to the primary and secondary responses.

[0026] Figure 3 is a diagram illustrating the control of load-response operation according to the embodiment. The upper part of Figure 3, G31, shows the output fluctuation of the generator 50, and the lower part, G32, shows the output fluctuation of the external power supply 70. In the upper parts G31 and G32, the vertical axis shows the magnitude and direction (increase or decrease) of the output fluctuation, and the horizontal axis shows time. The control unit 103 starts condensate throttling operation at time t1. Condensate throttling operation is an operation that reduces the flow rate of condensate supplied from the condenser 30 to the deaerator 37 via the low-pressure first feedwater heater 33 to the low-pressure fourth feedwater heater 36 by rapidly closing the opening of the deaerator water level control valve 32 to a predetermined opening. When the flow rate of condensate flowing through the low-pressure first feedwater heater 33 to the low-pressure fourth feedwater heater 36 decreases, the flow rate of extracted steam that heats the condensate in the heaters 33 to 36 naturally decreases. The heaters 33 to 36 are devices that cool the steam with condensate and return it to water. In heaters 33-36, the extracted steam from the low-pressure steam turbine 27 cools and turns into water, reducing its volume. This process of drawing in new steam from the low-pressure steam turbine 27 and supplying it is automatically and continuously repeated, thus supplying extracted steam from the low-pressure steam turbine 27 to heaters 33-36. When the deaerator water level control valve 32 closes suddenly, the flow rate of condensate decreases, reducing the amount of steam that returns to water in heaters 33-36, thus reducing the amount of extracted steam drawn from the low-pressure steam turbine 27. A decrease in the amount of extracted steam drawn from the low-pressure steam turbine 27 increases the amount of steam in the low-pressure steam turbine 27, thus increasing the output of the low-pressure steam turbine 27. This also increases the amount of power generated by the generator 50. However, when the flow rate of condensate supplied from the condenser 30 to the deaerator 37 decreases, the water level in the deaerator 37 drops. If the water level in the deaerator 37 drops too low, the main feedwater pump 38 and feedwater booster pump 39 may be damaged by swirling vortices. However, if the water level in the deaerator 37 is kept low enough so that it does not drop too low, the flow rate of the supplied condensate and the flow rate of the extracted steam will remain constant, which will not lead to an increase in the output of the low-pressure steam turbine 27. Furthermore, if the water level in the deaerator 37 is kept low, it will not be possible to respond by "condensate throttling operation" if it is necessary to increase the output during that time, which is undesirable.Therefore, the deaerator water level control valve 32 must be opened to increase the condensate flow rate and restore the water level in the deaerator 37 before the water level in the deaerator 37 drops too low. Also, if the flow rate of condensate supplied to the deaerator 37 is increased rapidly at this time, the amount of extracted steam from the low-pressure steam turbine 27 will increase. As a result, the amount of steam that the steam turbine 20 (low-pressure steam turbine 27) takes in from the steam generator 12 will increase, which may exceed the rated output of the reactor 10. The output of the reactor is to be controlled so as not to exceed the rated output as stipulated by law. Therefore, the control unit 103 ends the primary response by returning the condensate flow rate to prevent the reactor output from exceeding the rated output and slowly restoring the water level in the deaerator 37. For example, at time t3, the control unit 103 slowly opens the deaerator water level control valve 32 by a predetermined opening angle greater than the opening angle at the start of the primary response, and maintains that opening angle for a while, thereby restoring the water level at a rate that does not affect the reactor output.

[0027] When the primary response is initiated at time t1 due to condensate throttling, the control unit 103 begins preparing for the secondary response. Specifically, as shown in Figure 3, lower G32, the control unit 103 waits for a predetermined time T1 before starting the external power supply 70. The reason for waiting for time T1 is that there is a possibility that the grid frequency will return to the normal range during this time. If the grid frequency returns to normal during the waiting period, the secondary response can be canceled. Also, since it takes several minutes for the external power supply 70 to be started and ready to connect to the power grid 60, the external power supply 70 is started when the primary response begins to prepare for the secondary response. Once the external power supply 70 is started and the rotational speed of the diesel generator reaches a predetermined value, the system is connected to the power grid 60 (secondary response). It is desirable to connect to the power grid 60 before the water level in the deaerator 37 reaches the lower limit. The time t3 in Figure 3, upper diagram G31, is, for example, a certain time before the water level in the deaerator 37 drops to the lower limit, and a certain time after the connection of the external power supply 70 (or a time when the external power supply 70 is in a state where it can be connected, even before it is actually connected). After the connection of the external power supply 70, the output of the external power supply 70 is controlled by adjusting the fuel supplied to the diesel generator, etc., so that the sum of the output of the generator 50 (the output tends to decrease because the condensate flow rate is restored after the condensate throttling operation is completed) and the output of the external power supply 70 is maintained at the output of the generator 50 during primary response execution (to be equal to the load). This makes it possible to implement load response operation in the nuclear power plant 1 to respond to rapid frequency fluctuations and load fluctuations in the power grid 60, which was conventionally handled by thermal power plants.

[0028] (operation) Figure 4 is a flowchart showing an example of load response operation control according to the present invention. The data acquisition unit 101 acquires the system frequency from the frequency meter 61 (step S1). The data acquisition unit 101 outputs the system frequency to the determination unit 102. Next, the determination unit 102 determines whether or not to perform load-response operation (step S2). The determination unit 102 determines to perform load-response operation if the system frequency has fallen by a predetermined value Δf or more from the rated frequency, and to not perform load-response operation otherwise. If the determination unit 102 determines not to perform load-response operation (step S2; No), the flowchart in Figure 4 ends.

[0029] If the determination unit 102 determines that load response operation should be performed (step S2; Yes), the control unit 103 executes load response operation. First, the control unit 103 reduces the amount of extracted steam (step S3). For example, the control unit 103 reduces the flow rate of condensate supplied from the condenser 30 to the deaerator 37 to 30-50% of the amount before the rapid closing by performing a condensate throttling operation, which rapidly closes the opening of the deaerator water level control valve 32 to a predetermined opening. As a result, the amount of steam extracted from the low-pressure steam turbine 27 naturally decreases, and the flow rate of steam flowing through the steam turbine 20 increases. This increases the output of the steam turbine 20 and the output of the generator 50 (primary response). Also, due to the rapid closing of the deaerator water level control valve 32, the water level in the deaerator 37 gradually decreases. Next, the external power supply 70 is started (step S4). For example, the control unit 103 or the operator starts the emergency generator of the nuclear power plant 1. The external power supply 70 may be started after waiting for a predetermined time (e.g., 30 seconds) after the control to reduce the extraction volume has started. If the system frequency recovers during this waiting period, the extraction volume may be slowly restored and the load response operation may be terminated without starting the external power supply.

[0030] Next, the control unit 103 determines the timing for connecting the external power supply 70 to the power system 60 (step S5). For example, the control unit 103 determines to connect the external power supply 70 to the power system 60 when it is ready to be connected. Specifically, the control unit 103 determines to connect the external power supply 70 to the power system 60 when its rotational speed stabilizes and exceeds the synchronous speed corresponding to the system frequency. Also, for example, the control unit 103 determines to connect the activated external power supply 70 to the power system until the generated power, which temporarily increased due to the decrease in the extraction volume, decreases (for example, up to 5 minutes after the start of the decrease in the extraction volume). More specifically, the control unit 103 determines to connect the external power supply 70 to the power system 60 before the water level in the deaerator 37 reaches the lower limit. This is because when the water level in the deaerator 37 reaches the lower limit, the opening of the deaerator water level control valve 32 begins to return, so the external power supply 70 is connected to the power system 60 by then to prepare for a decrease in the output of the steam turbine 20. If it is determined that the external power supply 70 will not be connected to the power grid 60 (Step S5; No), the system waits until the time to connect it arrives. If it is determined that the external power supply 70 will be connected to the power grid 60 (Step S5; Yes), the external power supply 70 is connected to the power grid 60 (Step S6). For example, the control unit 103 or the operator closes the circuit breaker 72 to connect the external power supply 70 to the power grid 60. Next, the output of the nuclear power plant 1 is adjusted (Step S7). For example, the control unit 103 or the operator controls the output of the external power supply 70 so that the sum of the power generated by the steam turbine 20 and the power supplied by the external power supply 70 reaches a predetermined target value. Connecting the external power supply 70 to the power grid 60 and adjusting the output corresponds to the secondary response.

[0031] Next, the control unit 103 determines the timing to return the extraction volume (step S8). For example, the control unit 103 determines to return the extraction volume when the condensate water level in the deaerator 37, as acquired by the data acquisition unit 101 from the water level gauge 371, reaches the lower limit. Alternatively, the control unit 103 determines to return the extraction volume when the connection of the external power supply 70 to the power system 60 is completed. Completion of the connection may be determined by the operator inputting a connection completion signal to the control device 100, or by the control unit 103 detecting the open / closed state of the circuit breaker 72, for example. Alternatively, even without actually connecting, the control unit 103 may determine to return the extraction volume when the rotational speed allows for connection of the external power supply 70. If it is not determined to return the extraction volume (step S8; No), the control unit waits until the timing to return the extraction volume arrives. If it is determined to return the extraction volume (step S8; Yes), the control unit 103 performs control to return the extraction volume (step S9). Here, if the deaerator water level control valve 32, which was reduced to a predetermined opening in step S3, is rapidly opened to restore the water level in the deaerator 37, the amount of extracted steam will increase. As a result, the amount of steam pulled from the steam generator 12 to the steam turbine 20 will increase, which may cause the output of the reactor 10 to exceed its rated output. Therefore, the control unit 103 slowly opens the deaerator water level control valve 32 to a predetermined opening to slowly restore the water level in the deaerator 37. By slowly restoring the water level in the deaerator 37, the increase in the amount of steam pulled from the steam generator 12 to the steam turbine 20 can be suppressed, and the output increase of the reactor 10 can be suppressed. For example, the control unit 103 opens the deaerator water level control valve 32 to an opening that is a predetermined value larger than the opening before slowly reducing the amount of extracted steam, and maintains that state to slowly restore the water level in the deaerator 37. The control unit 103 then maintains the opening degree for water level restoration until the water level in the deaerator 37 returns to the level before the amount of extracted air was reduced. Once the water level in the deaerator 37 returns to its original level, the control unit 103 returns the opening degree of the deaerator water level control valve 32 to the opening degree before the amount of extracted air was reduced.

[0032] In the above explanation, the primary response was performed by condensate throttling operation by adjusting the opening of the deaerator water level control valve 32. However, as shown in Figure 5, the nuclear power plant 1' may be configured with extraction volume control valves 40 to 45 in the extraction pipes L7 to L12, respectively. The control unit 103 may then reduce the extraction volume from the steam turbine 20 by lowering the opening of the extraction volume control valves 40 to 45 to a predetermined opening in step S3, and then in step S9, it may control the extraction volume control valves 40 to 45 to slowly return to their original openings so as not to cause an increase in the output of the reactor 10, thereby performing the primary response. Alternatively, in step S7, the output of the steam turbine 20 may be adjusted (within a range that does not cause an increase in the output of the reactor 10) by adjusting the opening of the steam control valve 23 in addition to the external power supply 70.

[0033] (effect) In general, nuclear power plants cannot increase output by increasing the amount of steam supplied from the steam generator to the steam turbine, as the reactor output must be kept within its rated output. Therefore, load response operation (primary response, secondary response) that can respond to sudden load changes or fluctuations in grid frequency cannot be implemented. In contrast, in this embodiment, load response operation can be achieved by utilizing the emergency generators provided in nuclear power plants 1 and 1' and combining them with condensate throttling operation.

[0034] In the above embodiment, the case where the nuclear power plant 1 is a pressurized water reactor (PWR) was described as an example, but the control method and control device of this embodiment can also be applied to a boiling water reactor (BWR). That is, the nuclear power plant 1 may have a configuration in which the steam turbine 20 is driven by steam directly generated in the reactor (BWR), instead of a configuration in which the steam turbine 20 is driven by steam indirectly generated by heat exchange with primary cooling water heated by the reactor 10 (PWR).

[0035] As described above, several embodiments relating to this disclosure have been explained, but all of these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0036] <Note> The control methods and control devices described in each embodiment can be understood, for example, as follows.

[0037] (1) A control method according to the first embodiment is a control method for a nuclear power plant comprising a reactor and a steam turbine driven by steam directly generated by the reactor or steam indirectly generated by heat exchange with the heat of the reactor, wherein the power generated by driving the steam turbine is supplied to a power grid, comprising: a step of determining whether or not to perform load response operation to temporarily increase the power generated in response to a decrease in the power supplied from the nuclear power plant or an increase in the load; a step of reducing the amount of steam extracted from the steam turbine if it is determined that load response operation should be performed; a step of starting an external power supply if it is determined that load response operation should be performed; a step of determining the timing to connect the external power supply to the power grid; a step of connecting the external power supply to the power grid when the timing to connect arrives; a step of determining the timing to return the amount of extracted steam; and a step of returning the amount of extracted steam when the timing to return the amount of extracted steam arrives so as not to cause the output of the reactor to rise above a specified value. This enables load-response operation, which rapidly increases the power generated by a nuclear power plant in response to a sudden increase in load or a sudden decrease in power supply.

[0038] (2) The control method relating to the second embodiment is the control method of (1), wherein the nuclear power plant comprises a condenser that generates condensate from steam discharged by the steam turbine, and a deaerator that heats and deaerates the condensate generated by the condenser, and in the step of reducing the extraction amount, the opening degree of a condensate flow rate control valve (deaerator water level control valve 32) that adjusts the flow rate of the condensate supplied from the condenser to the deaerator, which is located downstream of the steam turbine, is reduced to a predetermined opening degree. This allows for the execution of the primary response in load response operation.

[0039] (3) A control method relating to the third embodiment is the control method of (1) to (2), wherein the nuclear power plant is equipped with a heater that heats the condensate produced from the steam discharged by the steam turbine with steam extracted from the steam turbine, and in the step of reducing the amount of extracted steam, the opening degree of an extraction amount control valve that adjusts the amount of steam extracted from the steam turbine to the heater is reduced to a predetermined opening degree. This allows for the execution of the primary response in load response operation.

[0040] (4) The control method relating to the fourth aspect is the control method of (2), wherein in the step of reducing the extraction amount, the flow rate of the condensate is reduced to 30-50% by reducing the opening degree of the condensate control valve. This allows for the execution of the primary response in load response operation.

[0041] (5) The control method relating to the fifth aspect is the control method of (2), wherein in the step of returning the extraction amount, the condensate control valve is kept open at a recovery opening that is a predetermined value greater than the opening before the extraction amount was reduced. This allows the water level in the deaerator to be restored while suppressing the increase in reactor output.

[0042] (6) The control method according to the sixth embodiment is the control method of (5), wherein in the step of returning the extraction amount, the recovery opening of the condensate control valve is maintained until the water level of the deaerator returns to the water level before the extraction amount was reduced. This allows the primary response to be terminated and the operating state to return to the state before load response operation.

[0043] (7) The control method relating to the seventh aspect is the control method of (2), wherein in the step of reducing the extraction amount, the condensate control valve is rapidly closed to a predetermined first opening, and in the step of returning the extraction amount, the condensate control valve is opened to a predetermined second opening at a speed such that the output of the reactor does not rise above a specified value. This allows for the primary response to be executed while suppressing the increase in reactor output.

[0044] (8) The control method according to the eighth aspect is the control method according to (1) to (7), wherein in the step of determining whether or not to perform load response operation, it is determined that the generated power should be increased when the frequency of the power system falls below a predetermined value. This allows for the determination of whether or not to perform load-response operation.

[0045] (9) The control method relating to the ninth aspect is the control method of (1) to (8), wherein the external power supply is a synchronous generator, and in the step of determining the timing for connecting the external power supply to the power system, it is determined that the power supply should be connected to the power system when the rotational speed of the generator exceeds a predetermined value. This allows an external power supply to be connected to the power grid, enabling secondary response to be performed.

[0046] (10) The control method according to the tenth embodiment is the control method according to (1) to (9), wherein in the step of determining the timing of connecting the external power supply to the power system, it is determined that the power generated by the steam turbine, which has temporarily increased by reducing the amount of steam extracted, should be connected to the power system before the power is reduced. This makes it possible to perform a secondary response even in nuclear power plants where it is not possible to perform a secondary response by increasing the output of the steam generator 12.

[0047] (11) The control method according to the eleventh aspect is the control method according to (1) to (10), wherein in the step of determining the timing for connecting the external power supply to the power system, it is determined that the connection should be made to the power system before the water level in the deaerator reaches the lower limit. This prevents the failure of downstream pumps that may occur due to a drop in the water level of the deaerator.

[0048] (12) The control method according to the 12th embodiment is the control method according to (1) to (11), wherein in the step of determining the timing for returning the extraction amount, it is determined to return the extraction amount when the water level in the deaerator reaches the lower limit. This prevents the failure of downstream pumps that may occur due to a drop in the water level of the deaerator.

[0049] (13) The control method relating to the 13th aspect is the control method of (1) to (12), wherein in the step of determining the timing for returning the extraction amount, it is determined that the extraction amount should be returned when the connection of the external power supply to the power system is completed. This allows the output, which was temporarily increased by the primary response, to be maintained.

[0050] (14) The control method according to the 14th embodiment is the control method according to (1) to (13), wherein in the step of starting the external power supply, the external power supply is started after waiting for a predetermined time after starting the control to reduce the amount of extracted air by the step of reducing the amount of extracted air, and in the step of determining the timing of connecting the external power supply to the power system, it is determined that the power system will be connected before a predetermined time limit (for example, the time until the water level of the deaerator 37 reaches the lower limit) has elapsed during which the control to reduce the amount of extracted air can be continued. This allows the system to respond using only the primary response when system load fluctuations are very short-lived, preventing the unnecessary activation of the external power supply. Furthermore, by switching to output compensation using the external power supply within the time the primary response can be maintained, the output required for load response operation can be maintained.

[0051] (15) A control method according to the 15th embodiment is the control method according to (1) to (14), further comprising the step of adjusting the output of the nuclear power plant after the start of the decrease in the extraction amount, wherein in the adjusting step, the opening degree of a steam control valve that adjusts the steam flow rate supplied to the steam turbine and / or the output of the external power supply are controlled so that the sum of the power generated by the steam turbine and the power supplied by the external power supply becomes a predetermined target value. This allows the output, which was temporarily increased by the primary response, to be maintained.

[0052] (16) The control method relating to the 16th aspect is the control method of (1) to (15), wherein the external power source is an emergency generator of a nuclear power plant. This allows for the effective use of multiple high-capacity emergency generators that are normally not used and are installed in nuclear power plants.

[0053] (17) A control device according to the 17th embodiment is a control device for a nuclear power plant comprising a reactor and a steam turbine driven by steam directly generated by the reactor or steam indirectly generated by heat exchange with the heat of the reactor, and which supplies power generated by driving the steam turbine to a power grid, comprising: means for determining whether or not to perform load response operation to temporarily increase the power generated in response to a decrease in the power supplied from the nuclear power plant or an increase in the load; means for reducing the amount of steam extracted from the steam turbine when it is determined that load response operation should be performed; means for determining the timing for connecting an external power source started based on the determination to perform load response operation to the power grid; means for determining the timing for returning the amount of steam extracted; and means for returning the amount of steam extracted so that the output of the reactor does not rise above a specified value when the timing for returning the amount of steam extracted arrives. [Explanation of Symbols]

[0054] 1, 1'... Nuclear power plant, 10... Nuclear reactor, 12... Steam generator, 21... High-pressure steam turbine, 22... Main steam stop valve, 23... Steam control valve, 24... Moisture separator, 25, 26... Moisture separator heater, 27... Low-pressure steam turbine, 28... Reheat steam stop valve, 29... Interset valve, 30... Condenser, 31... Condenser pump, 32... Deaerator water level control valve, 33... Low-pressure No. 1 feedwater heater, 34... Low-pressure No. 2 feedwater heater, 35... Low-pressure No. 3 feedwater heater, 36... Low-pressure No. 4 feedwater heater, 37 deaerator, 371 water level gauge, 38 main feedwater pump, 39 feedwater booster pump, 3A high-pressure feedwater heater No. 6, 40-45 extraction volume control valve, 50 generator, 60 power system, 61 frequency meter, 70 external power supply, 71 power line, 72 circuit breaker, 100 control device, 101 data acquisition unit, 102 judgment unit, 103 control unit, 104 memory unit, L1-L5 steam pipe, L6 condensate line, L7-L12 extraction pipe

Claims

1. A control method for a nuclear power plant comprising a nuclear reactor and a steam turbine driven by steam directly generated by the nuclear reactor or steam indirectly generated by heat exchange with the heat of the nuclear reactor, wherein the power generated by driving the steam turbine is supplied to the power grid, The steps include determining whether or not to perform load-response operation to temporarily increase the generated power in response to a decrease in the power supplied from the nuclear power plant or an increase in the load, When it is determined that the load response operation will be performed, the steps include reducing the amount of steam extracted from the steam turbine, If it is determined that the aforementioned load response operation should be performed, the steps include starting the external power supply, The steps include determining the timing for connecting the external power supply to the power system, When the timing for connection arrives, the steps include connecting the external power supply to the power system, The step of determining the timing for returning the aforementioned extraction amount, When the timing to return the extraction amount arrives, the process includes the step of returning the extraction amount so that the reactor output does not rise above a specified value, A control method having

2. The nuclear power plant comprises a condenser that generates condensate from the steam discharged by the steam turbine, and a deaerator that heats and deaerates the condensate generated by the condenser. In the step of reducing the amount of extracted air, The opening degree of the condensate flow control valve, which adjusts the flow rate of the condensate supplied from the condenser located downstream of the steam turbine to the deaerator, is reduced to a predetermined opening degree. The control method according to claim 1.

3. The nuclear power plant is equipped with a heater that heats the condensate produced from the steam discharged by the steam turbine with steam extracted from the steam turbine. In the step of reducing the amount of extracted air, The opening degree of the extraction volume control valve, which adjusts the amount of steam extracted from the steam turbine to the heater, is reduced to a predetermined opening degree. The control method according to claim 1.

4. In the step of reducing the amount of extracted air, By reducing the opening of the condensate flow control valve, the condensate flow rate is reduced to 30-50%. The control method according to claim 2.

5. In the step of returning the amount of extracted air, The condensate control valve is kept open at a recovery opening that is a predetermined value greater than the opening before the extraction volume was reduced. The control method according to claim 2.

6. In the step of returning the amount of extracted air, The recovery opening of the condensate control valve is maintained until the water level in the deaerator returns to the level before the extraction amount is reduced. The control method according to claim 5.

7. In the step of reducing the amount of extracted air, the condensate control valve is rapidly closed to a predetermined first opening degree. In the step of returning the extraction volume, the condensate control valve is opened to a predetermined second opening degree at a rate such that the reactor output does not rise above a specified value. The control method according to claim 2.

8. In the step of determining whether or not to perform the load response operation, When the frequency of the power system falls below a predetermined value, it is determined that the generated power should be increased. The control method according to claim 1 or claim 2.

9. The aforementioned external power supply is a synchronous generator, In the step of determining the timing for connecting the external power supply to the power system, When the rotational speed of the generator exceeds a predetermined value, it is determined that the system should be connected to the power grid. The control method according to claim 1 or claim 2.

10. In the step of determining the timing for connecting the external power supply to the power system, By reducing the amount of steam extracted, it is determined that the power generated by the steam turbine, which has temporarily increased, will decrease before the power grid is connected. The control method according to claim 1 or claim 2.

11. In the step of determining the timing for connecting the external power supply to the power system, It is determined that the power system will be connected before the water level in the deaerator reaches the lower limit. The control method according to claim 2.

12. In the step of determining the timing for returning the aforementioned extraction amount, When the water level in the deaerator reaches the lower limit, it is determined that the extraction volume should be returned. The control method according to claim 2.

13. In the step of determining the timing for returning the aforementioned extraction amount, When the connection of the external power supply to the power system is completed, it is determined that the extraction amount should be returned. The control method according to claim 1 or claim 2.

14. In the step of starting the external power supply, After starting the control to reduce the extraction volume by the step of reducing the extraction volume, wait for a predetermined time and then start the external power supply. In the step of determining the timing for connecting the external power supply to the power system, It is determined that the system will be connected to the power grid before a predetermined time limit has elapsed during which the control to reduce the amount of extracted air can be continued. The control method according to claim 1 or claim 2.

15. The further step is to adjust the output of the nuclear power plant after the reduction in the extraction volume has begun, In the aforementioned adjustment step, The opening degree of the steam control valve that adjusts the steam flow rate supplied to the steam turbine and / or the output of the external power supply are controlled so that the sum of the power generated by the steam turbine and the power supplied by the external power supply reaches a predetermined target value. The control method according to claim 1 or claim 2.

16. The aforementioned external power source is an emergency generator for a nuclear power plant. The control method according to claim 1 or claim 2.

17. A control device for a nuclear power plant comprising a nuclear reactor and a steam turbine driven by steam directly generated by the nuclear reactor or steam indirectly generated by heat exchange with the heat of the nuclear reactor, wherein the control device supplies the power generated by driving the steam turbine to the power grid, Means for determining whether or not to perform load-response operation to temporarily increase the generated power in response to a decrease in the power supplied from the nuclear power plant or an increase in the load, When it is determined that the load response operation will be performed, means for reducing the amount of steam extracted from the steam turbine, A means for determining the timing of connecting the external power supply, which has been activated based on the determination to perform the aforementioned load response operation, to the power system, Means for determining the timing for returning the aforementioned extraction amount, When the timing to return the extraction amount arrives, means for returning the extraction amount so that the reactor output does not rise above a specified value, A control device having

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