Control system of nuclear power plant, control method of nuclear power plant, and nuclear power plant

Abstract

To provide a control system of nuclear power plant capable of precisely controlling the target water supply temperature, a control method of nuclear power plant, and a nuclear power plant.SOLUTION: The control system of a nuclear power plant controls a nuclear power plant including: a nuclear reactor; a condenser that converts steam generated in the nuclear reactor back into water: a feedwater heater that heats the water returned by the condenser; and a piping located downstream of the condenser and upstream of the feedwater heater or a drain pump that returns drain water from the feedwater heater to the equipment. The control system also includes: a feedwater temperature control unit that controls the feedwater temperature of the feedwater heater; and a target water supply temperature setting unit that outputs a water supply temperature command value. The feedwater temperature control unit controls the pump output of the drain pump based on the water supply temperature command value and the water supply temperature measurement value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control system for a nuclear power plant, a control method for a nuclear power plant, and a nuclear power plant. [Background technology]

[0002] In preparation for the large-scale introduction of renewable energy and the decommissioning of thermal power plants, there is an increasing need for daily output adjustments at nuclear power plants to adapt to fluctuations in solar power generation and demand throughout the entire operating cycle, and improvements in output adjustment technology are expected. In particular, the main output adjustment methods for boiling water reactors include core output adjustments by control rod operation and recirculation flow control. When core output adjustments are performed at the end of the operating cycle, the excess reactivity deficiency of the fuel rods must be compensated for by controlling the feedwater temperature.

[0003] Controlling the feedwater temperature requires operating equipment on the BOP (Balance of Plant) side. Prior art related to feedwater temperature control is shown in Patent Document 1. Patent Document 1 describes the method of controlling feedwater temperature as follows: "An extraction flow control valve is installed on the extraction pipe that extracts steam from the steam system and sends it to the feedwater heater, a feedwater temperature measuring instrument is installed at the outlet of the feedwater heater, and an extraction flow controller is provided that receives the feedwater temperature measurement value and the feedwater temperature set value as inputs and outputs a request for the opening of the extraction flow control valve." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-133723 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, in order to control the feedwater temperature to a target value, the opening of an extraction flow control valve (hereinafter referred to as the extraction valve) is operated to adjust the flow rate of extraction steam supplied to a high-pressure feedwater heater. However, extraction steam is saturated steam and easily transitions from gas phase to liquid phase with slight changes in pressure and temperature, making fine flow rate adjustments difficult. This poses a challenge in that it is difficult to accurately adjust the feedwater temperature relative to the target value. Furthermore, when the extraction valve is throttled to lower the feedwater temperature, the reduced amount of extraction steam flows into the turbine. This raises concerns about an increase in turbine rotation speed.

[0006] An object of the present invention is to provide a control system for a nuclear power plant, a control method for a nuclear power plant, and a nuclear power plant that are capable of controlling the feedwater temperature with high accuracy relative to a target feedwater temperature. [Means for solving the problem]

[0007] The nuclear plant control system of the present invention controls a nuclear plant having a nuclear reactor, a condenser that converts steam generated in the reactor back into water, a feedwater heater that heats the water returned by the condenser, and a drain pump that returns drain water from the feedwater heater to piping or equipment located downstream of the condenser and upstream of the feedwater heater, and is characterized in that it comprises a feedwater temperature control unit that controls the feedwater temperature of the feedwater heater, and a target feedwater temperature setting unit that outputs a feedwater temperature command value, and the feedwater temperature control unit controls the pump output of the drain pump based on the feedwater temperature command value and the feedwater temperature measurement value.

[0008] Alternatively, the present invention provides a method for controlling a nuclear plant, which controls a nuclear plant including a nuclear reactor, a condenser that converts steam generated in the reactor back into water, a feedwater heater that heats the water returned by the condenser, and a drain pump that returns drain water from the feedwater heater to piping or equipment located downstream of the condenser and upstream of the feedwater heater, and is characterized in that the pump output of the drain pump is controlled based on a target feedwater temperature command value and a measured feedwater temperature value.

[0009] Alternatively, the nuclear plant of the present invention comprises a nuclear reactor, a condenser that converts steam generated in the reactor back into water, a feedwater heater that heats the water returned by the condenser, and a drain pump that returns drain water from the feedwater heater to piping or equipment located downstream of the condenser and upstream of the feedwater heater, and further comprises a feedwater temperature control unit that controls the feedwater temperature of the feedwater heater, and a target feedwater temperature setting unit that outputs a feedwater temperature command value, and the feedwater temperature control unit controls the pump output of the drain pump based on the feedwater temperature command value and the feedwater temperature measurement value. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a control system for a nuclear power plant, a control method for a nuclear power plant, and a nuclear power plant that are capable of controlling the feedwater temperature with high accuracy relative to a target feedwater temperature. [Brief explanation of the drawings]

[0011] [Figure 1] 1 shows a nuclear power plant and a control system according to a first embodiment. [Figure 2] FIG. 3 is a block diagram of a recirculation flow rate control unit according to the first embodiment. [Figure 3] FIG. 2 is a diagram showing the operating range of reactor power and reactor recirculation pump power according to the first embodiment. [Figure 4] FIG. 3 is a block diagram of a target feedwater temperature setting unit according to the first embodiment. [Figure 5] FIG. 2 is a block diagram of a water supply temperature control unit according to the first embodiment. [Figure 6] 3 is an example of the results of supply water temperature control according to the present invention related to the first embodiment. [Figure 7] 10 is a nuclear power plant and control system equipped with a bypass pipe to a condenser according to a second embodiment. [Figure 8] 10 is a nuclear power plant and control system according to a second embodiment, which is provided with a bypass pipe to a low-pressure feedwater heater drain pipe. [Figure 9] 10 shows a nuclear power plant and a control system according to a third embodiment. [Figure 10] FIG. 10 is a block diagram of a drain water level control unit according to a third embodiment. [Figure 11] FIG. 10 is a block diagram of a supply water temperature control unit according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] In an embodiment of the present invention, in a nuclear power plant equipped with a nuclear reactor, a condenser, and a feedwater heater, automatic switching from control using a reactor recirculation pump to control including feedwater temperature control using a bleed valve and / or a drain pump is possible to achieve power adjustment, particularly at the end of an operating cycle. The drain pump adjusts the amount of drain water returning to the piping or equipment between the feedwater heater, the condenser, and the reactor or steam generator. Furthermore, a feedwater temperature control method with excellent control accuracy is proposed. A feedwater temperature command value is output based on the power-flow map (PF map) of the recirculation flow control system. Based on the command value of the feedwater temperature control unit, large feedwater temperature deviations are accommodated by operating the bleed valve, and small feedwater temperature deviations are accommodated by operating the high-pressure drain pump. This allows for automatic control, maintains the control range for the feedwater temperature, and improves control accuracy.

[0013] In order to achieve automatic control of switching output adjustments, in the control of a nuclear power plant in an embodiment for implementing the present invention, the target feedwater temperature setting unit obtains recirculation flow rate command values ​​before and after the restriction based on the PF map of the recirculation flow rate control system, and outputs a feedwater temperature command value to the feedwater temperature control unit so that the difference between the two is small.

[0014] Furthermore, in order to achieve highly accurate feedwater temperature control, in the control of a nuclear power plant according to an embodiment of the present invention, the feedwater temperature deviation between the rated temperature and the target temperature (a large feedwater temperature deviation over a long period) is controlled by operating the extraction valve, and the feedwater temperature deviation that is small over a short period compared to the large feedwater temperature deviation over a long period, which occurs when the feedwater temperature is controlled by operating the extraction valve from the rated temperature to the target temperature, (a small feedwater temperature deviation over a short period) is controlled by adjusting the output of the high-pressure drain pump. Alternatively, the feedwater temperature deviation that can be controlled only by the high-pressure drain pump is controlled only by adjusting the output of the high-pressure drain pump. Alternatively, in order to suppress an increase in turbine rotation speed during feedwater temperature control, a lower limit is set for the opening of the extraction valve, and the extraction valve is operated within that range, and if further feedwater temperature control is required, the high-pressure drain pump is operated.

[0015] Since large deviations in feedwater temperature over a long period are controlled by operating the bleed valve, and small deviations over a short period are controlled by the high-pressure drain pump, high-precision feedwater temperature control is possible.Alternatively, by controlling the feedwater temperature with the high-pressure drain pump in addition to controlling the bleed valve, the amount of bleed throttle can be reduced, and an increase in turbine rotation speed can be suppressed.Furthermore, in boiling water nuclear power plants, output adjustment is possible, especially at the end of the operating cycle.

[0016] Hereinafter, examples of the present invention will be described in detail with reference to the drawings. Note that the same components are designated by the same reference numerals, and if a description is redundant, that description may be omitted. Furthermore, the present invention is not limited to the following embodiments. Although the present embodiment will be described using a boiling water reactor, it can also be applied to other reactor systems such as a pressurized water reactor. [Example]

[0017] 1 is a diagram showing a nuclear power plant 1 and a control system 2 in Example 1. The nuclear power plant 1 mainly includes a nuclear reactor 101, a condenser 105 that converts steam generated in the nuclear reactor 101 back into water, and a feedwater heater that heats the water returned by the condenser 105. The nuclear power plant 1 also includes a high-pressure turbine group 102 consisting of one or more high-pressure turbines, a moisture separator heater 103, a low-pressure turbine group 104 consisting of one or more low-pressure turbines, a high-pressure feedwater heater group 106 consisting of one or more high-pressure feedwater heaters, a low-pressure feedwater heater group 107 consisting of one or more low-pressure feedwater heaters, a steam extraction valve 108, a high-pressure drain pump 109, and a temperature sensor 110.

[0018] The extraction valve 108 is a control valve that adjusts the flow rate of extracted steam flowing from the high-pressure turbine into the high-pressure feedwater heater, and one or more are provided in the nuclear plant 1. By controlling and narrowing the opening of the extraction valve 108, the flow rate of the extracted steam, which is the heating source for the high-pressure feedwater heater, is reduced, and the feedwater temperature can be lowered.

[0019] The high-pressure drain pump 109 returns drain water discharged from the high-pressure feedwater heater to the feedwater piping between the high-pressure feedwater heater group 106 and the low-pressure feedwater heater group 107. In other words, this drain pump adjusts the amount of drain water returned to the piping or equipment between the feedwater heater, the condenser, and the reactor or steam generator, and returns drain water from the feedwater heater to the piping or equipment located downstream of the condenser 105 and upstream of the feedwater heater. In the first embodiment, the pump has the function of adjusting the amount of drain water being sent by adjusting the pump output. The drain water discharged from the high-pressure feedwater heater group 106 has a higher temperature than the feedwater heated by the low-pressure feedwater heater group 107. Therefore, the feedwater temperature can be lowered by reducing the amount of drain water returned to the feedwater piping.

[0020] The control system 2 is composed of a generator output control unit 111, a recirculation flow rate control unit 112, a target feedwater temperature setting unit 113, and a feedwater temperature control unit 114, and sends operation commands to the extraction valve and high-pressure drain pump to control the feedwater temperature.

[0021] The generator output control unit 111 is called an Automatic Power Regulator System (APR), and sends operation commands to a Recirculation Flow Control System (RFC) and a Rod Control and Information System (RC&IS) to adjust the electrical output to the target level.

[0022] The recirculation flow rate control unit 112 represents a recirculation flow rate control system, which controls the recirculation flow rate by adjusting the pump output of a reactor recirculation pump (not shown) in the reactor 101 in order to control the target reactor power.

[0023] FIG. 2 shows a block diagram of the recirculation flow rate control unit 112. It receives a load request deviation 201 from the generator output control unit 111 and calculates a recirculation flow rate command value (before limit) 204 by PI control using an RFC proportional gain 202 and an RFC integral gain 203. At this time, the command value is prevented from exceeding the constraint of the maximum flow rate of the reactor recirculation pump. For this purpose, the map shown in FIG. 3 is used. This map indicates the operable range of reactor power and reactor recirculation pump output, and is called a PF map 205. Using this PF map 205, a limit is set on the recirculation flow rate command value (before limit) 204 so that it falls within the operating range. If the recirculation flow rate command value (before limit) 204 exceeds the operating range, a recirculation flow rate command value (after limit) 206 is output, with the excess amount cut off.

[0024] The target feedwater temperature setting unit 113 uses PI control to calculate a feedwater temperature that can compensate for the insufficient reactivity caused by recirculation flow rate control alone when controlling to the target reactor power. A block diagram of the target feedwater temperature setting unit 113 is shown in Figure 4. It receives a recirculation flow rate command value (before restriction) 204 and a recirculation flow rate command value (after restriction) 206 from the recirculation flow rate control unit 112, and performs PI control using a temperature setting unit proportional gain 301 and a temperature setting unit integral gain 302 to minimize the deviation between the two, and sets upper and lower limits using upper and lower temperature constraint limits 303. Through the above control, the feedwater temperature command value 304 can be corrected every time so that it can track the target reactor power.

[0025] In this way, the recirculation flow rate control unit 112 outputs not only the recirculation flow rate command value (after restriction) 206 but also the recirculation flow rate command value (before restriction) 204, and the target feedwater temperature setting unit 113 performs PI control so as to reduce the deviation between the two, thereby making it possible to automatically calculate and control the feedwater temperature capable of compensating for the reactivity that is insufficient when controlling to the target reactor power by recirculation flow rate control alone. That is, it becomes possible to automatically switch from control using only the reactor recirculation pump to control including feedwater temperature control using a bleeding valve and / or a high-pressure drain pump.

[0026] The feedwater temperature control unit 114 issues operation commands to the plant equipment to control the feedwater temperature. A block diagram of the feedwater temperature control unit 114 is shown in Figure 5. It receives a feedwater temperature command value 304 from the target feedwater temperature setting unit 113, and also acquires a feedwater temperature measurement value 401 measured by a temperature sensor 110 installed at the outlet of the high-pressure feedwater heater in the high-pressure feedwater heater group 106. It then calculates the deviation between the feedwater temperature command value 304 and the feedwater temperature measurement value 401 and sends it to a feedwater temperature deviation analysis unit 402. The feedwater temperature deviation analysis unit 402 records and accumulates the feedwater temperature deviation, and calculates and outputs large long-term feedwater temperature deviations 403 and small short-term feedwater temperature deviations 404 based on the change trend of the deviation.

[0027] The calculations in the feedwater temperature deviation analysis unit 402 are performed by frequency analyzing past feedwater temperature fluctuations using a Fourier transform based on device performance information such as the controllable temperature range, cycle, and control speed of the bleed valve 108 and the high-pressure drain pump 109, and separating the long-cycle components from the short-cycle components. As an example of the calculation, the feedwater temperature deviation analysis unit 402 calculates the feedwater temperature deviation between the rated temperature and the target temperature as a large long-cycle feedwater temperature deviation 403, and a small short-cycle feedwater temperature deviation 404 that is a deviation component smaller than the feedwater temperature deviation between the rated temperature and the target temperature that occurs when the feedwater temperature is controlled by operating the bleed valve to change the temperature from the rated temperature to the target temperature (the deviation between the feedwater temperature command value 304 and the feedwater temperature measurement value 401 that cannot be fully controlled by operating the bleed valve). Here, the rated temperature refers to the feedwater temperature before control, and the target temperature refers to the final target feedwater temperature after control (see Figure 6).

[0028] Although an example has been described in which a large long-period feedwater temperature deviation 403 and a small short-period feedwater temperature deviation 404 are calculated, it is also possible to output only the small short-period feedwater temperature deviation 404 if the feedwater temperature deviation (of the order of several degrees Celsius) can be controlled only by the high-pressure drain pump 109. In this case, the feedwater temperature can be accurately controlled only by the high-pressure drain pump 109 without using a bleed valve, so the amount of bleed throttling can be reduced and an increase in turbine rotation speed can be suppressed.

[0029] In order to reduce the large feedwater temperature deviation 403 over a long period, PI control is performed using the bleed valve opening proportional gain 405 and the bleed valve opening integral gain 406, and upper and lower limits are set by the upper and lower limit restrictions 407 of the bleed valve opening constraint, and a bleed valve opening command value 408 is set.

[0030] In order to reduce the small feedwater temperature deviation 404 in a short period, PI control is performed using a pump output proportional gain 409 and a pump output integral gain 410, upper and lower limits are set by upper and lower limit limits 411 of the pump output constraints, and a high-pressure drain pump output command value 412 is set.

[0031] In the feedwater temperature control unit 114, it is desirable to adjust the opening of the air bleed valve 108 and the output of the high-pressure drain pump 109 by PI control so as to reduce the deviation between the feedwater temperature command value and the feedwater temperature measurement value. By outputting the opening adjustment of the air bleed valve 108 and the pump output of the high-pressure drain pump 109 by PI control, the feedwater temperature measurement value 401 can be corrected every time so that it can follow the feedwater temperature command value 304.

[0032] FIG. 6 shows an example of the results of feedwater temperature control according to this embodiment. When a temperature command value 501 is sent from target feedwater temperature setting unit 113, the chart shows the changes in feedwater temperature when controlled by only the bleed valve operation, when controlled by only the high-pressure drain pump, and when controlled by both. When controlled by only the bleed valve operation, as shown in temperature measurement value (only bleed valve operation) 502, the target temperature is reached, but the control accuracy is poor and the temperature command value 501 does not follow. When controlled by only the high-pressure drain pump, as shown in temperature measurement value (only high-pressure drain pump operation) 503, the control accuracy is good and the temperature command value 501 follows, but the temperature control width is narrow and the target temperature is not reached. In contrast, when controlled by both the bleed valve and the high-pressure drain pump, the target temperature is reached and the temperature command value 501 follows, as shown in temperature measurement value (combined operation of the bleed valve and high-pressure drain pump) 504.

[0033] According to the first embodiment described above, the feedwater temperature can be controlled accurately by controlling the large feedwater temperature deviation component with a long cycle by operating the extraction valve, and controlling the small feedwater temperature deviation component with a short cycle by using the high-pressure drain pump. Also, by controlling the high-pressure drain pump in addition to controlling by operating the extraction valve, the amount of extraction throttling can be reduced, and an increase in turbine rotation speed can be suppressed. Furthermore, in a boiling water nuclear power plant, output adjustment at the end of the operation cycle becomes possible.

[0034] Furthermore, the highly accurate core power control, i.e., feedwater temperature control, described in the above-described first embodiment makes it possible to respond to requests for more accurate power adjustment from the power grid side. The system includes a feedwater temperature control unit 114 that controls the feedwater temperature of the feedwater heater, and a target feedwater temperature setting unit 113 that outputs a feedwater temperature command value 304, and the feedwater temperature control unit 114 controls the pump output of the drain pump based on the feedwater temperature command value 304 and the feedwater temperature measurement value 401, thereby enabling highly accurate feedwater temperature control relative to the target feedwater temperature.

[0035] In the first embodiment, the nuclear power plant 1 is described as including the high-pressure turbine group 102, the moisture separator heater 103, the low-pressure turbine group 104, the high-pressure feedwater heater group 106, and the low-pressure feedwater heater group 107. However, the nuclear power plant 1 may not have the moisture separator heater 103 and may be configured with either the high-pressure turbine group 102 or the low-pressure turbine group 104, and either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107. In this case, the high-pressure drain pump 109 returns the drain water discharged from either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107 to the feedwater piping between the either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107 and the condenser 105. [Example]

[0036] In Example 2, a method is described for keeping the drain water level of the high-pressure feedwater heater within a limit value by installing a bypass pipe in a nuclear power plant that discharges drain water to a condenser when a steam extraction valve and a high-pressure drain pump are operated in combination to control the feedwater temperature.

[0037] 7 is a diagram showing a nuclear power plant 1 and a control system 2 in Example 2. In the nuclear power plant 1, a bypass pipe 115 that discharges drain water to the condenser 105 is provided in the pipe from the high-pressure feedwater heater group 106 to the high-pressure drain pump 109. Bypass pipe 115 makes it possible to lower the output of the high-pressure drain pump 109 and discharge the reduced amount of drain back to the feedwater pipe directly to the condenser 105, thereby suppressing fluctuations in the drain water level of the high-pressure feedwater heater.

[0038] Although the nuclear power plant 1 has been described as including the high-pressure turbine group 102, the moisture separator heater 103, the low-pressure turbine group 104, the high-pressure feedwater heater group 106, and the low-pressure feedwater heater group 107, the nuclear power plant 1 may not have the moisture separator heater 103 and may be configured with either the high-pressure turbine group 102 or the low-pressure turbine group 104, and either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107. In this case, the high-pressure drain pump 109 returns the drain water discharged from either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107 to the feedwater piping between the either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107 and the condenser 105. Furthermore, as shown in the nuclear power plant 1 of Figure 8, even in an equipment configuration in which the bypass piping 116 connected to the drain piping of the low-pressure feedwater heater merges with the piping from the low-pressure feedwater heater group 107 to the condenser 105, the reduced amount of drain return can be similarly discharged to the condenser 105.

[0039] According to the second embodiment described above, by providing a bypass pipe for discharging the reduced amount of reflux drain water to the condenser, fluctuations in the drain water level of the high-pressure feedwater heater can be suppressed. [Example]

[0040] In Example 3, a method is described for keeping the drain water level of a high-pressure feedwater heater within a limit value by using a control system that coordinates control of the air extraction valve and drain discharge valve when using a high-pressure drain pump to control the feedwater temperature.

[0041] Fig. 9 is a diagram showing a nuclear power plant 1 and a control system 2 in Example 3. In the nuclear power plant 1 in Fig. 9, a water level sensor 117 is attached to the drain tank of the high-pressure feedwater heater group 106, and a drain discharge valve 118 is also provided to adjust the amount of drain discharged from the drain tank.

[0042] The control system 2 is configured as shown in Figure 1 with the addition of a drain water level control unit 119. A block diagram of the drain water level control unit 119 is shown in Figure 10. An operation command is given to the air extraction valve and the drain discharge valve so as to reduce the deviation between the drain water level setting value 601 of the high-pressure feed water heater and the drain water level measurement value 602 measured by the water level sensor 117. Here, the drain water level setting value 601 may be set to the standard water level at the time of design, or may be input manually from a computer, or may be input by some other method.

[0043] PI control is performed using a discharge valve opening proportional gain 603 and a discharge valve opening integral gain 604 so that the deviation between the drain water level set value 601 and the drain water level measurement value 602 is small, and upper and lower limits are set by an upper limit limit 605 and a lower limit limit 606 of the drain discharge valve opening constraints, and a drain discharge valve opening command value is set.

[0044] In a state where the discharge valve opening cannot be narrowed down even though the drain water level has not been adjusted to the drain water level set value due to the lower limit value restriction 606, the drain water level is controlled by narrowing the bleed valve opening. PI control is performed using a bleed valve opening proportional gain 609 and a bleed valve opening integral gain 610 so as to reduce the deviation between a discharge valve opening command value 607 and a discharge valve opening command value 608 before the lower limit value restriction, and upper and lower limits are set by upper and lower limit restrictions 611 to set a bleed valve opening command value 612. It is desirable to output the discharge valve opening command value 607 and the bleed valve opening command value 612 by PI control. By outputting the discharge valve opening command value 607 and the bleed valve opening command value 612 by PI control, the drain water level measurement value 602 can be corrected every time so as to follow the drain water level set value 601. With the above control, for example, if the drain water level rises due to a reduction in the output of the high-pressure drain pump and the drain water level measurement value 602 becomes larger than the drain water level setting value 601, a command is first issued to open the discharge valve, and if the water level still does not decrease, a command is issued to throttle the air bleed valve.

[0045] According to the above-described third embodiment, even if the output of the high-pressure drain pump is reduced and the drain return volume decreases, the opening of the extraction valve is narrowed to reduce the amount of steam flowing into the high-pressure feed water heater, and the drain discharge valve is opened to discharge the drain water, thereby suppressing fluctuations in the drain water level of the high-pressure feed water heater.

[0046] In the third embodiment, the nuclear power plant 1 is described as including the high-pressure turbine group 102, the moisture separator heater 103, the low-pressure turbine group 104, the high-pressure feedwater heater group 106, and the low-pressure feedwater heater group 107. However, the nuclear power plant 1 may not have the moisture separator heater 103 and is configured with either the high-pressure turbine group 102 or the low-pressure turbine group 104, and either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107. In this case, the high-pressure drain pump 109 returns the drain water discharged from either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107 to the feedwater piping between the either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107 and the condenser 105. [Example]

[0047] In the fourth embodiment, a method will be described in which a high-pressure drain pump is used in addition to the control of the feedwater temperature by the bleed valve in order to suppress an increase in turbine rotation speed when throttling the bleed air to control the feedwater temperature.

[0048] 11 shows a block diagram of the feedwater temperature control unit 114 in the fourth embodiment. In order to reduce the deviation between the feedwater temperature command value 304 and the feedwater temperature measurement value 401, PI control is performed using an extraction valve opening proportional gain 701 and an extraction valve opening integral gain 702, and upper and lower limits are set by an upper limit limit 703 and a lower limit limit 704 to set an extraction valve opening command value 705. In this case, by changing the value of the lower limit limit 704, the minimum opening of the extraction valve can be adjusted, and therefore the increase in turbine flow rate due to throttling of the extraction valve can also be adjusted.

[0049] When the bleeding valve opening cannot be reduced due to the lower limit 704 even though the target value of the feedwater temperature has not been reached, the feedwater temperature is controlled by adjusting the output of the high-pressure drain pump. PI control is performed using a pump output proportional gain 707 and a pump output integral gain 708 so as to reduce the deviation between a bleeding valve opening command value 705 and a bleeding valve opening command value 706 before the lower limit is set, and upper and lower limits are set by upper and lower limit limits 709 of the pump output constraints, and a high-pressure drain pump output command value 710 is set. It is desirable to output the bleeding valve opening command value 705 and the high-pressure drain pump output command value 710 using PI control. By outputting the bleeding valve opening command value 705 and the high-pressure drain pump output command value 710 using PI control, the measured feedwater temperature value 401 can be corrected every time so as to follow the feedwater temperature command value 304.

[0050] According to the fourth embodiment described above, by using both the bleed valve and the high-pressure drain pump when controlling the feedwater temperature, it is possible to suppress an increase in the turbine rotation speed more effectively than when controlling using only the bleed valve.

[0051] In the fourth embodiment, the nuclear power plant 1 is described as including the high-pressure turbine group 102, the moisture separator heater 103, the low-pressure turbine group 104, the high-pressure feedwater heater group 106, and the low-pressure feedwater heater group 107. However, the nuclear power plant 1 may not have the moisture separator heater 103 and may be configured with either the high-pressure turbine group 102 or the low-pressure turbine group 104, and either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107. In this case, the high-pressure drain pump 109 returns the drain water discharged from either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107 to the feedwater piping between the either the high-pressure feedwater heater group 106 or the low-pressure feedwater heater group 107 and the condenser 105.

[0052] Although the embodiments of the present invention have been described above using a boiling water reactor as an example, the present invention can also be applied to pressurized water reactors and fast reactors if they are provided with high-pressure drain piping that returns water to the extraction piping and feedwater piping. [Explanation of symbols]

[0053] 1...Nuclear plant, 2...Control system, 101...Nuclear reactor, 102...high-pressure turbine group, 103...moisture separator heater, 104...low-pressure turbine group, 105...condenser, 106...high-pressure feedwater heater group, 107...low-pressure feedwater heater group, 108...bleed valve, 109...high-pressure drain pump, 110...temperature sensor, 111... generator output control unit, 112... recirculation flow rate control unit, 113... target feedwater temperature setting unit, 114...feedwater temperature control unit, 115...bypass piping connected to the condenser, 116...Bypass piping connected to the drain piping of the low-pressure feedwater heater; 117...water level sensor, 118...drain discharge valve, 119...drain water level control unit, 201...Load request deviation, 202...RFC proportional gain, 203...RFC integral gain, 204...Recirculation flow rate command value (before restriction), 205...PF map, 206...Recirculation flow rate command value (after restriction), 301...Temperature setting unit proportional gain, 302...Temperature setting unit integral gain, 303...Upper and lower limit of temperature constraint, 304...supply water temperature command value, 401...supply water temperature measurement value, 402...supply water temperature deviation analysis unit, 403...Large supply water temperature deviation over a long period, 404...Small supply water temperature deviation over a short period, 405... Bleed valve opening proportional gain, 406... Bleed valve opening integral gain, 407...Upper and lower limits of the bleed valve opening restriction, 408...Bleed valve opening command value, 409... Pump output proportional gain, 410... Pump output integral gain, 411...Upper and lower limit limits of pump output constraints, 412...High-pressure drain pump output command value, 501...Temperature command value, 502...Temperature measurement value (only for bleed valve operation), 503...Temperature measurement value (high pressure drain pump operation only), 504...Temperature measurement value (combined operation of bleed valve and high-pressure drain pump), 601...Drain water level setting value, 602...Drain water level measurement value, 603...Discharge valve opening proportional gain, 604...Discharge valve opening integral gain, 605...upper limit value limit, 606...lower limit value limit, 607...discharge valve opening command value, 608...Discharge valve opening command value before lower limit value restriction, 609... Bleed valve opening proportional gain, 610... Bleed valve opening integral gain, 611...upper and lower limit limits, 612...exhaust valve opening command value, 701... Bleed valve opening proportional gain, 702... Bleed valve opening integral gain, 703...upper limit value limit, 704...lower limit value limit, 705...exhaust valve opening command value, 706...Bleed valve opening command value before lower limit value restriction, 707... Pump output proportional gain, 708... Pump output integral gain, 709...Upper and lower limit, 710...High-pressure drain pump output command value.

Claims

1. A nuclear reactor and a condenser that converts the steam generated in the reactor back into water; a feedwater heater that heats the water returned by the condenser; a drain pump that returns drain water from the feed water heater to a pipe or device located downstream of the condenser and upstream of the feed water heater, a feed water temperature control unit that controls the feed water temperature of the feed water heater; a target feedwater temperature setting unit that outputs a feedwater temperature command value, a feedwater temperature control unit that controls a pump output of the drain pump based on the feedwater temperature command value and the feedwater temperature measurement value;

2. A control system for a nuclear power plant further comprising: a turbine; and a bleeding valve that adjusts a flow rate of bleeding air from the turbine to the feedwater heater, the control system comprising:

2. The control system for a nuclear power plant according to claim 1, wherein the feedwater temperature control unit also controls the opening of the extraction valve based on the feedwater temperature command value and the feedwater temperature measurement value.

3. 2. The nuclear power plant control system according to claim 1, a target feedwater temperature setting unit that acquires a recirculation flow rate command value before restriction to an operable range of a recirculation flow rate control system and a recirculation flow rate command value after restriction, and outputs the feedwater temperature command value so as to reduce the deviation between the two.

4. 4. The nuclear power plant control system according to claim 3, 10. A control system for a nuclear power plant, wherein the feedwater temperature command value is output by PI control.

5. 3. The nuclear power plant control system according to claim 2, a feedwater temperature control unit that controls the opening of the extraction valve and the pump output of the drain pump by PI control so as to reduce a deviation between the feedwater temperature command value and the feedwater temperature measurement value.

6. 3. The nuclear power plant control system according to claim 2, a control system for a nuclear power plant, characterized in that a deviation between the rated temperature and the target temperature of the feed water heater is reduced by manipulating the opening of the extraction valve, and a deviation that is small compared to the deviation between the rated temperature and the target temperature, which occurs when manipulating the opening of the extraction valve from the rated temperature to the target temperature, is reduced by manipulating the pump output of the drain pump.

7. 2. The nuclear power plant control system according to claim 1, a bypass pipe to the condenser connected midway through a drain pipe through which drain water discharged from the feed water heater passes;

8. 3. The nuclear power plant control system according to claim 2, The nuclear power plant may further include, instead of the turbine, a high-pressure turbine group including one or more high-pressure turbines, a moisture separator heater, and a low-pressure turbine group including one or more low-pressure turbines, Instead of the feedwater heater, a high-pressure feedwater heater group including one or more high-pressure feedwater heaters and a low-pressure feedwater heater group including one or more low-pressure feedwater heaters are provided; The extraction valve controls the extraction flow rate from the high-pressure turbine group to the high-pressure feedwater heater, The drain pump adjusts the amount of drain water returning from the high-pressure feedwater heater to the feedwater piping, A control system for a nuclear power plant, characterized in that a bypass pipe is connected to a drain pipe through which drain water discharged from the group of low-pressure feed water heaters passes, midway through the drain pipe through which drain water discharged from the high-pressure feed water heaters passes.

9. 3. The nuclear power plant control system according to claim 2, a drain tank of the feed water heater is provided with a water level sensor; and a drain discharge valve is provided in a drain pipe through which drain water discharged from the feed water heater passes; a drain water level control unit that acquires a drain water level measurement value of the drain tank of the feed water heater from the water level sensor and controls the opening degree of the extraction valve and the drain discharge valve based on the drain water level measurement value and a drain water level setting value.

10. 10. The nuclear power plant control system according to claim 9, The drain water level control unit controls the openings of the air extraction valve and the drain discharge valve by PI control so as to reduce the deviation between the drain water level measurement value and the drain water level setting value.

11. A nuclear reactor and a condenser that converts the steam generated in the reactor back into water; a feedwater heater that heats the water returned by the condenser; a drain pump that returns drain water from the feed water heater to a pipe or device located downstream of the condenser and upstream of the feed water heater, A method for controlling a nuclear power plant, comprising controlling the pump output of the drain pump based on a target feedwater temperature command value and a measured feedwater temperature value.

12. A nuclear reactor and a condenser that converts the steam generated in the reactor back into water; a feedwater heater that heats the water returned by the condenser; a drain pump that returns drain water from the feed water heater to a pipe or device located downstream of the condenser and upstream of the feed water heater, a feed water temperature control unit that controls the feed water temperature of the feed water heater; a target feedwater temperature setting unit that outputs a feedwater temperature command value, The nuclear power plant, wherein the feedwater temperature control unit controls the pump output of the drain pump based on a feedwater temperature command value and a feedwater temperature measurement value.

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