JP7664152B2 - Nuclear Power Plant - Google Patents

Description

The present invention relates to a nuclear power plant that performs throttled extraction operation (CT), which instantaneously reduces the amount of extraction steam used to heat the feedwater heater in response to a load following command (output increase) from the demand side to increase the turbine work load (generator output).

In order to prevent global warming, the proportion of total electricity generation that is accounted for by renewable energies (such as solar power generation and wind power generation) that do not produce _CO2 during power generation is increasing.
Conventionally, nuclear power plants have played a role in steadily supplying a nearly constant amount of electricity by operating at a constant rated thermal output.
However, as the amount of renewable energy, which is highly dependent on weather and therefore has unstable power generation, increases in the future, it is expected that there will be an increasing need for load-following operation, which flexibly changes electrical output in response to power requests from the grid (grid requests) resulting from fluctuations in power demand and renewable energy.

From the viewpoint of preventing fuel damage, nuclear power plants cannot take measures to increase the thermal power output of the reactor core in response to system demands that exceed the rated thermal power output (100%).
To meet such system demands, a method is required to increase the amount of power generation by momentarily increasing the amount of steam flowing into the power generation turbine. Specifically, the amount of extracted steam to the feedwater heater installed on the feedwater line to heat the low-temperature feedwater after condensation in the condenser is temporarily reduced, and the amount of steam flowing into the turbine is increased. This type of operation is called throttled extraction operation (CT).

A typical nuclear power plant is equipped with multiple feedwater heaters and multiple extraction lines, and methods for controlling them to perform CT are well known (see, for example, Patent Document 1).

JP 2017-194312 A

The above-mentioned Patent Document 1 describes, as a conventional technique, a method for controlling the output of a nuclear power plant by controlling the valve openings of a plurality of bleed valves provided on a plurality of bleed lines using a bleed valve control device (see FIG. 11 of Patent Document 1).
However, the range of output increase that can be controlled by the CT is only the amount of extracted steam to the feed water heater, and there is no means for increasing output beyond this amount in response to load change requests.

The present invention was made in consideration of this background, and aims to provide a nuclear power plant that can expand the output control range of throttled extraction operation (CT), which instantaneously reduces the amount of extraction steam used to heat the feedwater heater in response to a load following command (output increase) from the demand side, thereby increasing the turbine work volume (generator output).

The above and other objects of the present invention, as well as the novel features of the present invention, will become apparent from the description of this specification and the accompanying drawings.

The nuclear power plant of the present invention is a nuclear power plant including a nuclear reactor, a turbine driven by steam generated in the reactor, a generator driven by the turbine to generate electric power, a condenser for condensing exhaust steam from the turbine, a feedwater heater for heating the condensed water condensed in the condenser with extraction steam, an extraction line installed between the reactor and the condenser for supplying a portion of the steam generated in the reactor as extraction steam to the feedwater heater, a bleeding valve for adjusting the flow rate of the bleeding line, and a control unit for controlling the opening degree of the bleeding valve.
The nuclear power plant of the present invention has three operation modes: a first operation mode in which the generator output is operated at a constant level; a second operation mode in which the generator output is adjusted to follow the load; and a third operation mode in which the generator output is operated at a constant level. One of the three operation modes is selected for operation.
In addition, in the nuclear power plant of the present invention, in the second operation mode, the valve opening of the bleed valve is smaller than the valve opening of the bleed valve in the first operation mode, and the valve opening of the bleed valve is adjusted by control of the control unit so that the output of the generator follows the load, and in the third operation mode, the valve opening of at least some of the bleed valves is set to a larger value than in the first operation mode by control of the control unit.

According to the nuclear power plant of the present invention described above, one of three operation modes including a third operation mode in which the valve opening degree of at least some of the air bleed valves is set to a larger degree than that of the first operation mode is selected, and operation is performed.
In the third operating mode, the valve opening of at least some of the bleed valves is set to a large value. Therefore, when transitioning from the third operating mode to the second operating mode, the control range of the valve opening of the bleed valves can be made larger compared to when transitioning from the first operating mode.
This makes it possible to expand the output control range of the extraction throttle operation (CT), which instantaneously reduces the extraction steam for heating the feedwater heater and increases the turbine work (generator output) in response to a load following command (output increase) from the demand side.

Note that issues, configurations, and advantages other than those described above will become clear from the explanation of the embodiments below.

1 is a system diagram of a nuclear power plant according to a first embodiment of the present invention. FIG. 2 is a schematic diagram of an operation mode recording device for the nuclear power plant of FIG. 1. FIG. 2 is a schematic diagram of a normal operation state recording device of the nuclear power plant of FIG. 1. FIG. 2 is a schematic configuration diagram of a heat balance changing device of the nuclear power plant of FIG. 1. FIG. 2 is a schematic configuration diagram of a bleed valve control device of the nuclear power plant of FIG. 1. FIG. 4 is a system diagram of a nuclear power plant according to a second embodiment of the present invention. FIG. 7 is a schematic diagram of a normal operation state recording device of the nuclear power plant of FIG. 6. FIG. 7 is a schematic configuration diagram of a heat balance changing device of the nuclear power plant of FIG. 6. FIG. 7 is a schematic configuration diagram of a bleed valve control device of the nuclear power plant of FIG. 6.

Below, an embodiment of a nuclear power plant according to the present invention will be described with reference to the drawings. In each embodiment, similar parts are given the same reference numerals and duplicated explanations will be omitted. Note that each figure is merely a schematic illustration to allow a sufficient understanding of the present invention, and the present invention is not limited in any way to the contents below and the contents shown in the drawings, and can be modified or combined as desired within the scope that does not significantly impair the effects of the present invention.

The nuclear power plant of the present invention is a nuclear power plant including a nuclear reactor, a turbine driven by steam generated in the reactor, a generator driven by the turbine to generate electric power, a condenser for condensing exhaust steam from the turbine, a feedwater heater for heating the condensed water condensed in the condenser with extraction steam, an extraction line installed between the reactor and the condenser for supplying a portion of the steam generated in the reactor as extraction steam to the feedwater heater, a bleeding valve for adjusting the flow rate of the bleeding line, and a control unit for controlling the opening degree of the bleeding valve.
That is, the nuclear power plant of the present invention is configured to be able to execute throttling operation (CT) by controlling the valve opening of the extraction valve that adjusts the flow rate in the extraction line.

Furthermore, the nuclear power plant of the present invention has three operation modes: a first operation mode in which the generator output is operated at a constant level; a second operation mode in which the generator output is adjusted to follow the load; and a third operation mode in which the generator output is operated at a constant level. One of the three operation modes is selected for operation.
In addition, in the nuclear power plant of the present invention, in the second operation mode, the control unit controls the valve opening of the bleed valves so that the output of the generator follows the load, and in the third operation mode, the control unit controls the valve opening of at least some of the bleed valves to be larger than in the first operation mode.
That is, in the nuclear power plant of the present invention, in addition to the first and second operation modes which are similar to the operation modes executed in a nuclear power plant which executes a conventional throttled extraction operation (CT), a third operation mode in which the valve opening degree of at least a part of the bleed valves is set to a large state is added.

According to the configuration of the nuclear power plant of the present invention, one of three operation modes is selected and operation is performed, including a third operation mode in which the valve opening degree of at least some of the air bleed valves is set to a larger degree than in the first operation mode.
In the third operating mode, the valve opening of at least some of the bleed valves is set to a large value. Therefore, when transitioning from the third operating mode to the second operating mode, the control range of the valve opening of the bleed valves can be made larger than when transitioning from the first operating mode.
This makes it possible to expand the output control range of the extraction throttle operation (CT), which instantaneously reduces the extraction steam for heating the feedwater heater and increases the turbine work (generator output) in response to a load following command (output increase) from the demand side.

In the above-mentioned configuration of the nuclear power plant, the control unit may be configured to have an operation mode recording device for retaining the state of the operation mode, a normal operation state recording device for recording the output of the generator and the valve opening of the bleed valve when operating in either the first operation mode or the third operation mode, a heat balance change device having a function of increasing the valve opening of the bleed valve and changing the operation mode to the third operation mode when a command to change the adjustment range of the output of the generator is input when operating in the first operation mode, and a function of returning the valve opening of the bleed valve to the state in the first operation mode and changing the operation mode to the first operation mode when a command to change the adjustment range of the output of the generator is input when operating in the third operation mode, and a bleed valve control device for adjusting the valve openings of the plurality of bleed valves when a command to adjust the output of the generator is input when operating in the second operation mode.
That is, in the case of this configuration, when a command to change the adjustment range of the output of the generator is inputted by the heat balance change device, the valve opening of the bleed valve is increased or decreased, and the operation mode is changed from one of the first operation mode and the third operation mode to the other. As a result, when a command to change the adjustment range of the output of the generator is inputted, the valve opening of the bleed valve is specifically changed, and the operation mode can be switched between the first operation mode and the third operation mode.

In a nuclear power plant having this configuration, the bleed valve control device can be further configured to control the valve openings of the multiple bleed valves to be multiplied by a constant when adjusting the valve openings of the multiple bleed valves in response to a command to adjust the output of the generator.
As a result, the valve openings of the multiple air bleed valves are adjusted by controlling the valve openings of the multiple air bleed valves to be multiplied by a constant, so that the bleed air amount can be adjusted and the generator output can be adjusted with a relatively simple configuration and method.

In the configuration of the nuclear power plant described above, the bleed valve may be composed of two types of valves, a first bleed valve and a second bleed valve, the first bleed valve has the same valve opening in the first operation mode and the third operation mode, and the second bleed valve has a larger valve opening in the third operation mode compared to the first operation mode.
This makes it possible to expand the output control range of the bleed throttle operation (CT) to the sum of the valve opening of the first bleed valve in the first and third operation modes and the change in the valve opening of the second bleed valve between the first and third operation modes. Therefore, it becomes possible to expand the output control range more than the output control range possible with only the first bleed valve or only the second bleed valve.

In the nuclear power plant having this configuration, the first bleed valve is set to a fully open state in the first operation mode and the third operation mode, and the second bleed valve is set to a fully closed state in the first operation mode, and the control unit can be configured to have a heat balance change device having a function of bringing the second bleed valve to a fully open state and changing the operation mode to the third operation mode when a command to change the adjustment range of the output of the generator is input in the first operation mode, and a function of bringing the second bleed valve to a fully closed state and changing the operation mode to the first operation mode when a command to change the adjustment range of the output of the generator is input in the third operation mode, and a bleed valve control device for adjusting the valve openings of the multiple bleed valves when a command to adjust the output of the generator is input while operating in the second operation mode.
That is, in the case of this configuration, when a command to change the adjustment range of the output of the generator is inputted by the heat balance change device, the valve opening of the second bleed valve is increased or decreased, and the operation mode is changed from one of the first operation mode and the third operation mode to the other. As a result, when a command to change the adjustment range of the output of the generator is inputted, the valve opening of the second bleed valve is specifically changed, and the operation mode can be switched between the first operation mode and the third operation mode.
In the case of this configuration, the first bleed valve is in a fully open state in both the first operating mode and the third operating mode, and the second bleed valve changes its valve opening from one of a fully closed state and a fully open state to the other when switching between the first operating mode and the third operating mode.
This makes it possible to simplify the control of the valve opening degrees of the first and second bleed valves when switching between the first and third operating modes.
In addition, since the second bleed valve changes its valve opening from one of the fully closed state and the fully open state to the other, the change in valve opening between the first and third operation modes can be made large, so that it is not necessary to increase the designed heat exchange capacity of the heat exchanger of the feed water heater, thereby reducing the cost of the feed water heater compared to when the second bleed valve is not provided.
Furthermore, since the control of the valve opening degree of the first bleed valve and the second bleed valve can be simplified and the cost of the feed water heater can be reduced, the equipment configuration of the nuclear power plant can be rationalized.

In a nuclear power plant having this configuration, two extraction lines for supplying extraction steam to one feed water heater may be connected, and a second extraction valve may be provided in the extraction line supplying steam of a higher temperature, and a first extraction valve may be provided in the extraction line supplying steam of a lower temperature.
This makes it possible to increase the amount of change in the energy of the bleed steam caused by opening and closing the second bleed valve, making it possible to further reduce the designed heat exchange capacity of the heat exchanger of the feed water heater.

In the above-described configuration of the nuclear power plant, in the third operation mode, the valve openings of at least some of the bleed valves are set to a larger value than in the first operation mode, i.e., the valve openings of all the bleed valves are set to a larger value, or the valve openings of some of the plurality of bleed valves are set to a larger value.
In the third operating mode, the valve opening of at least some of the bleed valves is set to a larger value compared to the first operating mode. Therefore, when transitioning from the third operating mode to the second operating mode, the adjustment range of the valve opening of the bleed valves can be made larger than when transitioning from the first operating mode.

In actual operation, when the output is not changed for a while, it is desirable to adopt the first operation mode so that the time spent operating in the first operation mode is the longest.
When the adjustment range of the opening degree of the extraction valve is expanded before the operation mode is changed to the second operation mode, the operation mode is changed from the first operation mode to the third operation mode. However, when the plan to switch to the second operation mode is canceled for a while due to a change in schedule, it is desirable to return from the third operation mode to the first operation mode. In the third operation mode, the opening degree of the extraction valve is made larger than in the first operation mode, so that the amount of extraction steam increases and the amount of steam going to the turbine decreases accordingly, which reduces the efficiency of the power generation relative to the output of the reactor, and therefore the operation mode is not suitable for long-term operation.

Next, we will explain a specific embodiment of the nuclear power plant of the present invention.

(First embodiment)
FIG. 1 is a system diagram of a nuclear power plant according to a first embodiment of the present invention.

As shown in FIG. 1, the nuclear power plant of this embodiment includes a reactor pressure vessel (RPV) 1, a high-pressure turbine 4, a moisture separator 5, a low-pressure turbine 6, a condenser 7, a generator 8, and multiple feedwater heaters 11, 12, 13, and 14.

A reactor pressure vessel (RPV) 1 contains a reactor core 2 .
In addition, the reactor pressure vessel 1 is connected to a high-pressure turbine 4 , a moisture separator 5 , and a low-pressure turbine 6 via a main steam line 3 .
A condenser 7 is installed downstream of the low-pressure turbine 6. The condenser 7 is connected to the reactor pressure vessel 1 by a feedwater line 15. On the feedwater line 15, a condensate pump 9, a plurality of feedwater heaters (a first stage feedwater heater 11, a second stage feedwater heater 12, a third stage feedwater heater 13, and a fourth stage feedwater heater 14), and a feedwater pump 10 are installed.
The high-pressure turbine 4 and the low-pressure turbine 6 are connected to a generator 8. Note that in Fig. 1, the connection between the high-pressure turbine 4 and the generator 8 is omitted.

The moisture separator 5 is connected to the shell side of the heat exchanger of the third stage feed water heater 13 via a condensate discharge line 17 .
The main steam line 3 branches between the high-pressure turbine 4 and the moisture separator 5, and the branched line is connected to the shell side of the heat exchanger of the fourth stage feedwater heater 14 via an extraction line 24 to the fourth stage feedwater heater and an extraction valve 25 to the fourth stage feedwater heater.
Three lines branch off from the low pressure turbine 6. The first line from the left is connected to the shell side of the third stage feedwater heater 13 via an extraction line 22 to the third stage feedwater heater and an extraction valve 23 to the third stage feedwater heater. The second line from the left is connected to the shell side of the second stage feedwater heater 12 via an extraction line 20 to the second stage feedwater heater and an extraction valve 21 to the second stage feedwater heater. The third line from the left is connected to the shell side of the heat exchanger of the first stage feedwater heater 11 via an extraction line 18 to the first stage feedwater heater and an extraction valve 19 to the first stage feedwater heater. The shell sides of the heat exchangers of these feedwater heaters 13, 12, and 11 are connected to the condenser 7 via a drain line 16.

As control devices for controlling the valve openings of the extraction valve 19 to the first stage feedwater heater, the extraction valve 21 to the second stage feedwater heater, the extraction valve 23 to the third stage feedwater heater, and the extraction valve 25 to the fourth stage feedwater heater, there are provided an extraction valve control device 34, a heat balance changing device 35, a normal operation state recording device 36, and an operation mode recording device 38. An input/output connection mechanism 43 connects the inputs and outputs of the four devices 34, 35, 36, and 38.
The bleed valve control device 34, the heat balance changing device 35, the normal operation state recording device 36, and the operation mode recording device 38 provided in the input/output connection mechanism 43 constitute the above-mentioned control unit for controlling the valve opening of the bleed valve in the nuclear power plant of the present invention.

In addition, the input/output connection mechanism 43 is connected to external input signals, including information on the valve opening degree of the extraction valve 19 to the first stage feedwater heater 11, the extraction valve 21 to the second stage feedwater heater 12, the extraction valve 23 to the third stage feedwater heater 13, and the extraction valve 25 to the fourth stage feedwater heater 14, a generator output adjustment command 39, a generator output adjustment range change command 40, and a generator output 42.

Below, we will explain a specific method for expanding the output control range during extraction throttle operation (CT) in the nuclear power plant of this embodiment, in which the extraction steam is instantaneously reduced to heat the feedwater heater and increase the turbine work (generator output).

Steam generated in the reactor core 2 is sent to a high-pressure turbine 4 and a low-pressure turbine 6 via a main steam line 3, and the work of rotating the turbine blades is converted into electricity via a generator 8 and sent to the grid. After completing its work in the low-pressure turbine 6, the steam is cooled by seawater or the like in a condenser 7 to become low-temperature condensed water. The low-temperature condensed water is sent to a feedwater line 15, heated and raised in temperature as it passes through a number of feedwater heaters 11, 12, 13, and 14, pressurized by a condensate pump 9 and a feedwater pump 10, and then returned to the reactor pressure vessel 1.
A portion of the feed water returned to the reactor pressure vessel 1 becomes steam in the core 2 and is sent again to the turbines 4 and 6, so that the system diagram shown in FIG. 1 forms a closed loop related to steam and feed water.

Hot, humid steam is supplied to the shell side of the heat exchanger of the feedwater heater to heat the feedwater passing through the tube side of the heat exchanger.
In this embodiment, the steam after passing through the high-pressure turbine 4 is supplied to the shell side of the heat exchanger of the fourth stage feedwater heater 14 via an extraction line 24 to the fourth stage feedwater heater and an extraction valve 25 to the fourth stage feedwater heater.
Similarly, three extraction steam lines from the low-pressure turbine 6 are supplied to the third stage feedwater heater 13 via an extraction line 22 to the third stage feedwater heater and an extraction valve 23 to the third stage feedwater heater, to the second stage feedwater heater 12 via an extraction line 20 to the second stage feedwater heater and an extraction valve 21 to the second stage feedwater heater, and to the shell side of the heat exchanger of the first stage feedwater heater 11 via an extraction line 18 to the first stage feedwater heater and an extraction valve 19 to the first stage feedwater heater.
The steam (condensed water) condensed by heat exchange with low-temperature feed water in the heat exchanger is sent to the condenser 7 via a drain line 16 and becomes part of the feed water.

During normal operation of a nuclear power plant, the amount of steam flowing into the turbines 4 and 6, the amount of extracted steam to the feedwater heaters 11, 12, 13, and 14, the amount of heating of the feedwater in the feedwater heaters 11, 12, 13, and 14, etc. are kept constant, i.e., the plant is operated in a steady state.

Conventional nuclear power plants that perform throttled operation (CT) are operated by switching between two operation modes: an operation mode in which the output is constant during normal operation, and an operation mode in which the output of the generator is adjusted to follow the load.
In contrast, the nuclear power plant of this embodiment employs the following three operation modes, and is operated by switching between these operation modes.
Operation mode 1 is a normal operation mode in which the output of the generator is constant.
Operation mode 2 is an operation mode in which the output of the generator is adjusted to follow the load.
Operation mode 3 is a normal operation mode in which the output of the generator is constant, but the opening degree of the bleed valves 19, 21, 23, and 25 is larger than in operation mode 1.

Figure 2 shows a schematic diagram of the operation mode recording device 38 of the nuclear power plant in Figure 1. In Figure 2, each step S11 to S13 of the process performed by the operation mode recording device 38 and the operation mode recorder 38A within the operation mode recording device 38 are shown in a block diagram.

An operation mode 41 is input to the operation mode recording device 38 shown in Fig. 2. When a currently operating operation mode is set, a signal indicating the set operation mode is input as the operation mode 41. When no operation mode is set, the operation mode 41 is not input.
In step S11, it is determined whether or not the operation mode 41 has been input. If the operation mode 41 has been input (No), the process proceeds to step S12, and if the operation mode 41 has not been input (Yes), the process proceeds to step S13.
In step S13, the operation mode 41 is set to the operation mode 1, which is the initial value when no operation mode exists, and the process proceeds to step S12.
In step S12, it is determined whether or not the operation mode is 2, and if the operation mode is not 2 (Yes), the process proceeds to the operation mode recorder 38A. However, if the operation mode is 2 (No), no processing is performed.
The operation mode recorder 38A records the state of the operation mode (operation mode 1 or operation mode 3) as a recorded value 41s, and outputs the recorded value 41s of that state from the operation mode recorder 38 to the outside.
The operation mode 41, the details of which will be described later, is overwritten by the heat balance change device 35 shown in Fig. 4 or the bleed valve control device 34 shown in Fig. 5. Every time the operation mode 41 is overwritten, the recorded value 41s of the operation state is changed by the operation mode recording device 38 shown in Fig. 2.

Next, FIG. 3 shows a schematic diagram of the normal operating state recording device 36 of the nuclear power plant in FIG. 1. In FIG. 3, step S21 of the process performed by the normal operating state recording device 36 and the normal operating state recorder 36A within the normal operating state recording device 36 are shown in a block diagram.

1. The normal operating state recording device 36 shown in FIG. 3 receives the generator output 42 and the valve openings of the four bleed valves 19, 21, 23, and 25 shown in FIG.
In step S21, it is determined whether or not the operation mode is 2, and if the operation mode is not 2 (Yes), the process proceeds to the normal operation state recorder 36A. However, if the operation mode is 2 (No), nothing is executed.
The normal operating condition recorder 36A records the valve openings of the four bleed valves 19, 21, 23, 25 and the generator output 42 as recorded values 19s, 21s, 23s, 25s, 42s, and outputs the recorded values from the normal operating condition recorder 36 to the outside.

Next, FIG. 4 shows a schematic diagram of the heat balance change device 35 of the nuclear power plant in FIG. 1. In FIG. 4, steps S31 to S35 of the processing performed by the heat balance change device 35 are shown in a block diagram.

A generator output adjustment range change command 40 and a recorded value 41s of the operation mode are input to the heat balance change device 35 shown in FIG.
In step S31, the operation mode is determined. If the operation mode is 1, the process proceeds to steps S32 and S33, and if the operation mode is 3, the process proceeds to steps S34 and S35.
In step S32, the valve openings of the bleed valves 19, 21, 23, and 25 are changed to full open, and the changed valve openings are output to the outside of the heat balance change device 35.
In step S33, the operation mode is changed to operation mode 3, and the changed operation mode 41 is output to the outside of the heat balance change device 35.
In step S34, the valve openings of the extraction valves 19, 21, 23, and 25 are changed to the valve openings in operation mode 1 (normal operation), and the changed valve openings are output to the outside of the heat balance change device 35.
In step S35, the operation mode is changed to operation mode 1, and the changed operation mode 41 is output to the outside of the heat balance change device 35.

Next, FIG. 5 shows a schematic diagram of the bleed valve control device 34 of the nuclear power plant in FIG. 1. In FIG. 5, steps S41 to S45 of the process performed by the bleed valve control device 34, as well as the subtraction unit and multiplication unit, are shown in a block diagram.

5 receives the generator output adjustment command 39, the recorded value 42s of the generator output, and the recorded value 41s of the operation mode. Then, the difference (39-42s) between the generator output adjustment command 39 and the recorded value 42s of the generator output is calculated.
In step S41, the operation mode is determined from the input operation mode record value 41s. If the operation mode is 1, the process proceeds to step S42, and if the operation mode is 3, the process proceeds to step S43.
In step S42, the previously calculated difference is plotted on the horizontal axis of a graph, and a bleed valve opening magnification that corresponds to the difference on the graph is calculated. The calculated bleed valve opening magnification is multiplied by the recorded valve opening values 19s, 21s, 23s, and 25s of each bleed valve during normal operation in an individual calculator for each bleed valve, to calculate the changed valve opening. The calculated valve openings are output to the outside of the bleed valve control device 34.
In step S43, the previously calculated difference is plotted on the horizontal axis of a graph, and the bleed valve opening magnification corresponding to the difference in the graph is calculated. The calculated bleed valve opening magnification is multiplied by the recorded values 19s, 21s, 23s, and 25s of the valve opening during normal operation of each bleed valve in an individual calculator for each bleed valve, to calculate the changed valve opening. The calculated valve openings are output to the outside of the bleed valve control device 34. Note that step S43 is the same operation as step S42, but the graph showing the relationship between the difference and the bleed valve opening magnification is different.
In step S44, it is determined whether the generator output adjustment command 39 has been input, and if it has been input (Yes), the process proceeds to step S45. If it has not been input (No), no processing is performed.
In step S45, the operation mode is changed to the operation mode 2, and the changed operation mode 41 is output to the outside of the bleed valve control device 34.

Next, the operation of the nuclear power plant of this embodiment will be described with reference to FIGS.
First, the operation during normal bleed throttle operation (CT) will be described, and then the operating principle of CT with an expanded output control range according to this embodiment will be described.

When a system request, i.e., a generator output adjustment command 39 is input to the bleed valve control device 34 shown in FIG. 5, it is determined in step S44 that the input has been received, and in step S45 the operation mode is changed to operation mode 2, and the difference from the generator output 42s during steady operation (generator output increase range) is calculated.
In the normal CT, the operation mode 41s during normal operation is 1 (operation mode 1), and the difference signal is transmitted to step S42 in Fig. 5. In step S42, the difference signal is input and an opening rate multiplier to be multiplied with the opening rate of the air bleed valve is calculated based on the graph. The "a" in the graph in step S42 represents the maximum generator output increase that can be controlled by the normal CT.
When the difference is a, the opening magnification is 0. When the difference is negative or 0, the opening magnification is 1.0. When 0<difference<a, the opening magnification corresponds to the straight line on the graph.
The maximum generator output increase can be evaluated as the maximum generator output increase obtained by fully closing the four bleed valves 19, 21, 23, 25 from the valve openings 19s, 21s, 23s, 25s during normal operation. The bleed valve opening magnification calculated from the difference is multiplied by the bleed valve openings 19s, 21s, 23s, 25s during normal operation recorded in the normal operation state recording device 36, thereby narrowing the bleed valve openings and realizing an increase in power generation equivalent to the generator output adjustment command 39. This allows the generator output to be increased to "rated output + a".

Next, the operating principle of the CT with an expanded output control width in this embodiment will be described.
In order to increase the range of increase in the output of the CT, the nuclear power plant of this embodiment is provided with the heat balance changing device 35 shown in Figs.
When the operation mode recorded value 41s=1 (operation mode 1), if a generator output adjustment range change command 40 is input to the heat balance change device 35, a command signal is propagated from step S31 to steps S32 and S33 in Fig. 4. As a result, in step S32, the valve openings of the four extraction valves 19, 21, 23, 25, the valve openings of which were controlled so as to obtain the amount of extracted steam required in operation mode 1, are fully opened, and in step S33, the operation mode is switched from operation mode 1 to operation mode 3.
When the four extraction valves 19, 21, 23, 25 are fully opened, the steady state of the system (the amount of steam flowing into the turbine, the amount of extracted steam to the feedwater heater, the amount of heating of the feedwater in the feedwater heater, etc.) changes in the operation mode in which the generator output is operated at a constant (normal operation), but the nuclear power plant is stabilized in a new steady state (steady state 2) by the action of the control system of the nuclear power plant.

When the generator output adjustment range change command 40 is input to the heat balance change device 35 in the operation mode 3, the operation mode is returned from the operation mode 3 to the operation mode 1 in step S35, and the valve opening of the extraction valve is also returned to the state of the operation mode 1 in step S34.
That is, the heat balance change device 35 has a function of switching between the operation mode 1 and the operation mode 3 using the generator output adjustment range change command 40 as a trigger.

The state of operation mode 3 is recorded as recorded value 41s by operation mode recording device 38 in FIG. 2. In addition, the valve openings 19, 21, 23, and 25 of the four fully open bleed valves and the generator output 42 in steady state 2 are recorded as recorded values 19s, 21s, 23s, 25s, and 42s in operation state recorder 36A in normal operation state recording device 36 in FIG. 3.

In this state, when a generator output adjustment command 39 is input to the bleed valve control device 34 shown in FIG. 5, the operation mode is switched to operation mode 2 in step S45, and a difference signal (generator output increase amount signal) is propagated to step S43, similarly to the normal CT.
In the operation mode 3, the valve openings of the four bleed valves 19, 21, 23, 25 are larger than in the normal state, so the maximum increase in generator output obtained by fully closing the bleed valves increases from a to a+b.
That is, as shown in the system diagram of FIG. 1, by using four devices (a bleed valve control device 34, a heat balance changing device 35, a normal operation state recording device 36, and an operation mode recording device 38), it is possible to increase the generator output increase range during CT from a to a+b.

According to the nuclear power plant of this embodiment, in the operation mode 3, the valve openings of the extraction valves 19, 21, 23, and 25 are set to a state in which they are larger than in the operation mode 1. Therefore, when the operation mode is shifted from the operation mode 3 to the operation mode 2 (an operation mode in which the output of the generator is adjusted to follow the load), the control width of the valve openings of the extraction valves 19, 21, 23, and 25 can be made larger than when the operation mode is shifted from the operation mode 1.
This makes it possible to expand the output control range of the throttled exhaust operation (CT) in response to a load following command (output increase) from the demand side.

Second Embodiment
FIG. 6 is a system diagram of a nuclear power plant according to a second embodiment of the present invention.
7 shows a schematic configuration diagram of the normal operation state recording device 36 of the nuclear power plant of FIG. 6, and FIG. 9 shows a schematic configuration diagram of the extraction valve control device 34 of the nuclear power plant of FIG.

The nuclear power plant of the second embodiment differs from the nuclear power plant of the first embodiment in that four more extraction lines (26, 28, 30, 32) for supplying extraction steam to the four feedwater heaters 11, 12, 13, 14 are added in addition to the four lines (18, 20, 22, 24) in the first embodiment, and in that second extraction valves 27, 29, 31, 33 are added on the four added extraction lines in addition to the four extraction valves (herein referred to as first extraction valves) 19, 21, 23, 25 in the first embodiment.
Hereinafter, in the second embodiment, the bleed lines 18, 20, 22, 24 similar to those in the first embodiment will be referred to as first bleed lines, and the added bleed lines 26, 28, 30, 32 will be referred to as second bleed lines.

The locations where the four additional second extraction lines 26, 28, 30, and 32 extract steam from the turbines 4 and 6 or the main steam line 3 are upstream (higher temperature side) of the first extraction lines 18, 20, 22, and 24 that are common to FIG. 1.

In addition, the four second bleed valves 27, 29, 31, and 33 are maintained in a fully closed state during operation mode 1.

Here, a schematic diagram of the normal operating state recording device 36 of the nuclear power plant in FIG. 6 is shown in FIG. 7. In FIG. 7, step S51 of the process performed by the normal operating state recording device 36 and the normal operating state recorder 36A within the normal operating state recording device 36 are shown in a block diagram.

6. The normal operation state recording device 36 shown in FIG. 7 receives the generator output 42 and the valve openings of the eight bleed valves 19, 21, 23, 25, 27, 29, 31, and 33 shown in FIG.
In step S51, it is determined whether or not the operation mode is 2, and if the operation mode is not 2 (Yes), the process proceeds to the normal operation state recorder 36A. However, if the operation mode is 2 (No), no processing is performed.
The normal operation state recorder 36A records the valve openings of the eight bleed valves 19, 21, 23, 25, 27, 29, 31, and 33 and the generator output 42 as recorded values 19s, 21s, 23s, 25s, 27s, 29s, 31s, 33s, and 42s, and outputs the recorded values from the normal operation state recorder 36 to the outside.

Next, FIG. 8 shows a schematic diagram of the heat balance change device 35 of the nuclear power plant in FIG. 6. In FIG. 8, steps S61 to S65 of the processing performed by the heat balance change device 35 are shown in a block diagram.

Similar to the heat balance change device 35 of the first embodiment shown in FIG. 4, the heat balance change device 35 shown in FIG. 8 receives a generator output adjustment range change command 40 and a recorded value 41s of the operation mode.
In step S61, the operation mode is determined. If the operation mode is 1, the process proceeds to steps S62 and S63, and if the operation mode is 3, the process proceeds to steps S64 and S65.
In step S 62 , the valve openings of the second bleed valves 27 , 29 , 31 , and 33 are changed to full open, and the changed valve openings are output to the outside of the heat balance change device 35 .
In step S63, the operation mode is changed to operation mode 3, and the changed operation mode 41 is output to the outside of the heat balance change device 35.
In step S 64 , the valve openings of the second bleed valves 27 , 29 , 31 , and 33 are changed to fully closed, and the changed valve openings are output to the outside of the heat balance change device 35 .
In step S65, the operation mode is changed to operation mode 1, and the changed operation mode 41 is output to the outside of the heat balance change device 35.

Next, FIG. 9 shows a schematic diagram of the bleed valve control device 34 of the nuclear power plant in FIG. 6. In FIG. 9, steps S71 to S74 of the process performed by the bleed valve control device 34, as well as the subtraction unit and multiplication unit, are shown in a block diagram.

9 receives a generator output adjustment command 39 and a recorded value 42s of the generator output. Then, the difference (39-42s) between the generator output adjustment command 39 and the recorded value 42s of the generator output is calculated.
In step S71, the previously calculated difference is plotted on the horizontal axis of a graph, and a bleed valve opening magnification that corresponds to the difference on the graph is calculated. The calculated bleed valve opening magnification is multiplied by the recorded valve opening values 19s, 21s, 23s, and 25s of each first bleed valve in an individual calculator for each bleed valve, to calculate the changed valve opening. The calculated valve openings are output to the outside of the bleed valve control device 34.
In step S72, the previously calculated difference is plotted on the horizontal axis of a graph, and the bleed valve opening magnification corresponding to the difference in the graph is calculated. The calculated bleed valve opening magnification is multiplied by the recorded values 27s, 29s, 31s, and 33s of the valve opening during normal operation of each second bleed valve in an individual calculator for each bleed valve, to calculate the changed valve opening. The calculated valve openings are output to the outside of the bleed valve control device 34. Note that step S72 differs from step S71 in the graph showing the relationship between the difference and the bleed valve opening magnification.
In step S73, it is determined whether the generator output adjustment command 39 has been input, and if it has been input (Yes), the process proceeds to step S74. If it has not been input (No), no processing is performed.
In step S74, the operation mode is changed to the operation mode 2, and the changed operation mode 41 is output to the outside of the bleed valve control device 34.

By adopting such a configuration, the nuclear power plant of this embodiment has the following improvements over the nuclear power plant of the first embodiment:

In the first embodiment, in order to increase the amount of output increase during CT, the valve openings of the four first bleed valves 19, 21, 23, 25 during the generator output constant operation mode (normal operation) are maintained in a state other than the full open state (intermediate opening state), and when the operation mode is switched to operation mode 3, the valve openings of the four first bleed valves are changed to the full open state, thereby expanding the amount of generator output increase during CT during load following operation (generator output adjustment operation mode (load following)).
However, when this method of increasing the output increase is adopted, even when the four first bleed valves 19, 21, 23, 25 are fully open, the fully condensed steam (condensed water) needs to be sent to the condenser 7 via the drain line 16, so the designed heat exchange capacities of the four feedwater heaters 11, 12, 13, 14 need to be designed to be larger in anticipation of the possibility that the four first bleed valves will be fully open. Therefore, in the constant generator output operation mode (normal operation), i.e., when the valve openings of the four first bleed valves 19, 21, 23, 25 are in an intermediate opening state, the heat exchange amounts of the four feedwater heaters 11, 12, 13, 14 are less than the design specifications (design heat exchange capacities), resulting in the disadvantage that the feedwater heaters during constant thermal output operation (steady operation) have excessive specifications.

In contrast, in this embodiment, by adding four second bleed lines 26, 28, 30, 32 and four second bleed valves 27, 29, 31, 33 to guide high-temperature steam to the feed water heater, the drawback of the feed water heater being over-specified is eliminated and the control of the bleed valves can be simplified.

In order to demonstrate the above advantages, the operating principle of a CT with an expanded output control width according to this embodiment will be described below.
Incidentally, the operation mode recording device 38 can be realized by the operation mode recording device 38 having the configuration shown in FIG. 2, as in the first embodiment, so a description of the operation will be omitted.

When the operation mode recorded value 41s=1 (operation mode 1), if the generator output adjustment range change command 40 is input to the heat balance change device 35, a command signal is propagated from step S61 to step S62 and step S63 in Fig. 8. As a result, in step S62, the valve openings of the four second bleed valves 27, 29, 31, 33 that were in a fully closed state in operation mode 1 are changed to a fully open state, and in step S63, the operation mode is switched from operation mode 1 to operation mode 3.
By fully opening the four second extraction valves 27, 29, 31, 33, the steady state of the system (the amount of steam flowing into the turbine, the amount of extracted steam to the feedwater heater, the amount of heating of the feedwater in the feedwater heater, etc.) in the operation mode in which the generator output is operated at a constant (normal operation) changes, but as in the first embodiment, the nuclear power plant transitions to a new steady state (steady state 2') due to the action of the control system of the nuclear power plant.
In this embodiment, when transitioning to the steady state 2', high-temperature steam is added by changing the second bleed valves 27, 29, 31, 33 from fully closed to fully open, instead of adjusting the valve opening (steam flow rate) of the first bleed valves 19, 21, 23, 25. This is the difference between the present embodiment and the first embodiment.

In this embodiment, the average temperature of the steam supplied to each of the feed water heaters 11, 12, 13, and 14 is increased, as compared with the nuclear power plant of the first embodiment.
Generally, the heat exchange amount of a heat exchanger is proportional to the difference between the temperature of the fluid on the shell side (steam temperature) and the temperature of the fluid on the tube side (feedwater temperature). Therefore, in this embodiment, the heat exchange amount in the feedwater heater can be increased without using a feedwater heater with a large heat exchange capacity as shown in the first embodiment.
Due to the above-mentioned effects, in this embodiment, it is possible to reduce the installation costs of the feed water heater.

When the generator output adjustment range change command 40 is input to the heat balance change device 35 in the operation mode 3, the operation mode is returned from the operation mode 3 to the operation mode 1 in step S65, and the valve opening of the second bleed valve is also returned to the state in the operation mode 1 (fully closed state) in step S64.
That is, the heat balance change device 35 has a function of switching between the operation mode 1 and the operation mode 3 using the generator output adjustment range change command 40 as a trigger.
Comparing Figure 4 with Figure 8, in Figure 4, it is necessary to control the four bleed valves to an intermediate opening state at the branching of operation mode 3 (step S34), whereas in Figure 8, it is only necessary to control the four second bleed valves to a fully closed state. Therefore, this embodiment has the advantage that the valve control at the time of switching the operation mode can be simplified.

The state of operation mode 3 is recorded as recorded value 41s by operation mode recording device 38 in FIG. 2. In addition, the valve openings of the eight bleed valves 19, 21, 23, 25, 27, 29, 31, 33 that are in the fully open state and the generator output 42 in steady state 2' are recorded as recorded values 19s, 21s, 23s, 25s, 27s, 29s, 31s, 33s, 42s in operation state recorder 36A in normal operation state recording device 36 in FIG. 7.

In this state, when a generator output adjustment command 39 is input to the bleed valve control device 34 shown in FIG. 9, the operation mode is switched to the operation mode 2 in step S74, similarly to the normal CT and the first embodiment.
In this embodiment, unlike the first embodiment, there is no branching related to the operation mode in the bleed valve control device 34, and instead, control of the first bleed valves (control of the four valves on the upper side of FIG. 9 ) and control of the second bleed valves (control of the four valves on the lower side of FIG. 9 ) are performed simultaneously.

In this embodiment, valve opening and closing control is performed using the first bleed valves 19, 21, 23, and 25. In Fig. 9, the generator output increase obtained by changing the valve opening of the first bleed valve from the fully open state to the fully closed state is denoted as a.
Then, only when the value of the difference signal between the generator output adjustment command 39 and the generator output 42s is larger than a, in addition to the first bleed valve, the valve openings of the second bleed valves 27, 29, 31, 33, which change the fully closed state to the fully open state when increasing the output increase range during CT, are also controlled. In Figure 9, the generator output increase range obtained by changing the valve opening of the second bleed valve from the fully open state to the fully closed state is denoted as c.
For both the first and second bleed valves, a bleed valve opening magnification corresponding to the generator output increase width (difference) is calculated, and by multiplying this by the bleed valve openings 19s, 21s, 23s, 25s, 27s, 29s, 31s, and 33s of the steady-state bleed valves recorded in the normal operation state recording device 36, the bleed valve openings during load following operation are calculated, and the valve openings of the eight bleed valves are adjusted. This makes it possible to increase the generator output to "rated output + a + c".

As described above, in the nuclear power plant of this embodiment, compared to the first embodiment, four second bleed lines 26, 28, 30, 31 and second bleed valves 27, 29, 31, 33 must be added to supply high-temperature steam to the feedwater heater. However, there is no need to increase the design heat exchange capacity of the feedwater heater, which reduces the cost of the feedwater heater and simplifies the control method for the first bleed valve and the second bleed valve, thereby streamlining the equipment configuration.

According to the nuclear power plant of this embodiment, the valve openings of the second bleed valves 27, 29, 31, 33 are fully open in operation mode 3 and fully closed in operation mode 1, and the valve openings of the second bleed valves 27, 29, 31, 33 are large in operation mode 3. Therefore, when the operation mode is shifted from operation mode 3 to operation mode 2 (an operation mode in which the output of the generator is adjusted to follow the load), the control range of the valve openings of all the bleed valves (the first bleed valve and the second bleed valve) can be made larger than when the operation mode is shifted from operation mode 1.
This makes it possible to expand the output control range of the throttled exhaust operation (CT) in response to a load following command (output increase) from the demand side.

Furthermore, as described above, the nuclear power plant of this embodiment can reduce the cost of the feedwater heater and simplify the control method for the first and second bleed valves, thereby streamlining the equipment configuration.

(Modification)
In each of the above-described embodiments, the feed water heater is provided in four stages, and in the first embodiment, one extraction line is connected to each of the feed water heaters 11, 12, 13, and 14, while in the second embodiment, two extraction lines are connected to each of the feed water heaters 11, 12, 13, and 14.
In the nuclear power plant of the present invention, the number of stages of feedwater heaters and the number of extraction lines connected to each feedwater heater are not limited to the numbers in each embodiment, and may be other numbers.
As long as one or more feed water heaters and one or more extraction lines are provided, the present invention can be applied to operate the plant in three operating modes, namely, the first operating mode, the second operating mode, and the third operating mode.

In each of the above-described embodiments, in Figs. 5 and 9, the opening degree multiplication factors used to obtain the valve opening degrees of the four air bleed valves are set to the same multiplication factor.
On the other hand, taking into consideration differences in the temperature of the bleed steam in each bleed line, it is also possible to weight and multiply each of a plurality of bleed valves by giving a coefficient to each bleed valve.
In addition, when changing the valve opening degrees of a plurality of air bleed valves, the timing for opening and closing the air bleed valves may be either such that all the air bleed valves are opened and closed simultaneously, or such that the air bleed valves are opened and closed sequentially starting from the air bleed valve on the high temperature side or the air bleed valve on the low temperature side.

In the second embodiment described above, the first bleed valve is in the fully open state in both the first operation mode and the third operation mode, and the second bleed valve is in the fully closed state in the first operation mode and in the fully open state in the third operation mode.
The valve opening states of the first bleed valve and the third bleed valve in each of the first and third operation modes may be configured in other ways.
For example, as described above, it is possible to set the first bleed valve to the same valve opening in the first and third operation modes, and the second bleed valve to a state in which the valve opening is larger in the third operation mode compared to the first operation mode. In this case, the output control width of the bleed throttle operation (CT) can be expanded to the sum of the valve opening of the first bleed valve in the first and third operation modes and the change in the valve opening of the second bleed valve between the first and third operation modes. Therefore, it becomes possible to expand the output control width beyond the output control width possible with only the first bleed valve or only the second bleed valve.
Also, for example, it is possible to consider a case where the first bleed valve is fully opened in both the first and third operation modes as in the second embodiment, and the second bleed valve is opened to a different degree from that in the second embodiment. In this case, a large amount of bleed steam can be secured by the first bleed valve being fully opened in the first operation mode, so that it is not necessary to increase the designed heat exchange capacity of the feed water heater, and the cost of the feed water heater can be reduced.
Also, for example, it is possible to consider a case where the first bleed valve has the same valve opening in the first and third operation modes, and the second bleed valve has the same valve opening as in the second embodiment. In this case, the first bleed valve has the same valve opening, and the second bleed valve changes between a fully closed state and a fully open state, so that it is possible to simplify the method of controlling the first bleed valve and the second bleed valve.

The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments and examples have been described in detail to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all of the configurations described.

1: Reactor pressure vessel (RPV), 2: Core, 3: Main steam line, 4: High pressure turbine, 5: Moisture separator, 6: Low pressure turbine, 7: Condenser, 8: Generator, 9: Condensate pump, 10: Feedwater pump, 11: First stage feedwater heater, 12: Second stage feedwater heater, 13: Third stage feedwater heater, 14: Fourth stage feedwater heater, 15: Feedwater line, 16: Drain line, 1 7: condensate discharge line, 18: (first) extraction line to the first stage feedwater heater, 19: (first) extraction valve to the first stage feedwater heater, 20: (first) extraction line to the second stage feedwater heater, 21: (first) extraction valve to the second stage feedwater heater, 22: (first) extraction line to the third stage feedwater heater, 23: (first) extraction valve to the third stage feedwater heater, 24: (first) extraction line to the fourth stage feedwater heater (1) bleed line to the heater, 25: (1) bleed valve to the 4th stage feed water heater, 26: 2nd bleed line to the 1st stage feed water heater, 27: 2nd bleed valve to the 1st stage feed water heater, 28: 2nd bleed line to the 2nd stage feed water heater, 29: 2nd bleed valve to the 2nd stage feed water heater, 30: 2nd bleed line to the 3rd stage feed water heater, 31: 2nd bleed valve to the 3rd stage feed water heater, 32: 2nd bleed line to the 4th stage feed water heater, 33: 2nd bleed valve to the 4th stage feed water heater, 34: bleed valve control device, 35: heat balance change device, 36: normal operating state recording device, 38: operating mode recording device, 39: generator output adjustment command, 40: generator output adjustment range change command, 41: operating mode, 42: generator output, 43: input/output connection mechanism

Claims (6)

A nuclear reactor,
a turbine driven by steam generated in the nuclear reactor;
a generator driven by the turbine to generate electric power;
a condenser for condensing exhaust steam from the turbine;
a feed water heater that heats the condensed water condensed by the condenser with extracted steam;
an extraction line that is installed between the reactor and the condenser and that supplies a portion of the steam generated in the reactor to the feed water heater as the extraction steam;
A bleed valve for adjusting the flow rate of the bleed line;
A control unit for controlling a valve opening degree of the air bleed valve;
A nuclear power plant comprising:
the nuclear power plant has three operation modes, namely, a first operation mode in which the output of the generator is kept constant, a second operation mode in which the output of the generator is adjusted to follow a load, and a third operation mode in which the output of the generator is kept constant, and one of the three operation modes is selected to perform operation;
In the second operation mode, a valve opening degree of the bleed valve is smaller than a valve opening degree of the bleed valve in the first operation mode, and the valve opening degree of the bleed valve is adjusted by control of the control unit so that an output of the generator follows a load.
the third operation mode is controlled by the control unit to set a valve opening degree of at least a part of the air extraction valves to a larger value than in the first operation mode. The control unit includes an operation mode recording device for retaining the state of the operation mode, a normal operation state recording device for recording the output of the generator and the valve opening of the bleed valve when the control unit is operated in either the first operation mode or the third operation mode, a heat balance change device having a function of increasing the valve opening of the bleed valve and changing the operation mode to the third operation mode when a command to change the adjustment range of the output of the generator is input in the first operation mode, and a function of returning the valve opening of the bleed valve to the state in the first operation mode and changing the operation mode to the first operation mode when a command to change the adjustment range of the output of the generator is input in the third operation mode, and a bleed valve control device for adjusting the valve opening of the plurality of bleed valves when a command to adjust the output of the generator is input when the control unit is operated in the second operation mode. The nuclear power plant according to claim 2, wherein the bleed valve control device controls the valve openings of the plurality of bleed valves by multiplying the valve openings of the plurality of bleed valves by a constant when adjusting the valve openings of the plurality of bleed valves in response to a command to adjust the output of the generator. The bleed valve is composed of two types of valves, a first bleed valve and a second bleed valve.
the first bleed valve has the same valve opening degree in the first operation mode and the third operation mode;
2. The nuclear power plant according to claim 1, wherein the second bleed valve is set to a state in which the valve opening degree is larger in the third operation mode than in the first operation mode. In the first operation mode and the third operation mode, the first bleed valve is in a fully open state,
In the first operating mode, the second bleed valve is fully closed,
5. The nuclear power plant according to claim 4, wherein the control unit comprises: a heat balance change device having a function of fully opening the second bleed valve and changing to the third operation mode when a command to change an adjustment range of an output of the generator is input in the first operation mode, and a function of fully closing the second bleed valve and changing to the first operation mode when a command to change an adjustment range of the output of the generator is input in the third operation mode; and a bleed valve control device for adjusting valve openings of the plurality of bleed valves when a command to adjust the output of the generator is input while operating in the second operation mode. The nuclear power plant according to claim 4, wherein two of the extraction lines that supply the extraction steam are connected to one of the feed water heaters, the second extraction valve is provided on the extraction line that supplies the higher temperature steam, and the first extraction valve is provided on the extraction line that supplies the lower temperature steam.

Images