JPS6046242B2 - Reactor - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a nuclear reactor.

[Background of the invention]

In conventional boiling water reactors, the cooling water that flows from the turbine condenser to the reactor pressure vessel is heated by directing the steam produced by the turbine to the feed water heater.

In this type of feed water heating method, if the steam generated in the reactor pressure vessel during reactor startup or shutdown bypasses the turbine and goes directly to the turbine condenser, the cooling water generated by the steam generated from the turbine is The low-temperature cooling water condensed by the turbine condenser is injected into the reactor pressure vessel at a low temperature by the feedwater pump. Therefore, at the time of reactor startup, the reactor pressure is at a high temperature that is approximately the same as the temperature of the cooling water in the reactor pressure vessel before the water supply pump supplies cooling water to the reactor pressure vessel. The water supply piping (for example, a nozzle) in the vessel is cooled to a low temperature as soon as the water supply pump is activated and the low temperature cooling water in the turbine condenser is injected.

Also, when the reactor was shut down, the water supply piping, through which high-temperature cooling water heated by the steam generated by the turbine, was flowing.
When the steam supply to the turbine is stopped, the cooling water is not heated by the steam drawn from the turbine, so the low temperature cooling water drawn from the turbine condenser flows, and the temperature immediately becomes low. As described above, in conventional boiling water reactors, there is a possibility that the temperature change in the water supply piping within the reactor pressure vessel becomes large during startup and shutdown of the reactor.

[Object of the invention] The present invention enables accurate detection of the supply status of extracted steam from the turbine to the feed water heater during startup and shutdown of the reactor, and significantly suppresses thermal shock to the water supply pipes inside the reactor vessel. The goal is to provide a nuclear reactor that can.

[Summary of the invention]

The features of the present invention are that a second bleed pipe is provided to guide the steam in the reactor vessel to the feedwater heater without going through the turbine, an on-off valve is provided in the second bleed pipe, and a first bleed pipe that connects the turbine and the feedwater heater is provided. A first control means is provided for detecting the pressure in the air bleed pipe and opens and closes the on-off valve based on this pressure, and a pressure control valve is provided in the second air bleed pipe downstream of the on-off valve to control the pressure in the second air bleed pipe. A second control means is provided for detecting the pressure and operating the pressure control valve based on this pressure to control the pressure of steam flowing through the second bleed pipe to a predetermined pressure.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings, but first, operating characteristics in a conventional boiling water reactor will be described with reference to FIGS. 1 and 2.

In Fig. 1, 1 is the reactor pressure vessel of the boiling water reactor, 2 is the main steam pipe through which the steam generated in the reactor pressure vessel 1 passes, and 3 is the steam regulator that adjusts the amount of steam to the turbine 4. The valve 5 is a bypass valve that bypasses the turbine 4 and regulates the amount of steam reaching the turbine condenser 8, and the reference numeral 6 is a bypass pipe through which the steam bypassed by the turbine 4 flows.

The steam extracted from the turbine 4 is supplied to the high temperature side of the feedwater heater 10 through the extraction pipe 7 and then recovered to the turbine condenser 8 .

The turbine condenser 8 condenses and cools the steam discharged from the turbine 4 by means of a turbine condenser cooling system 9. The low temperature cooling water obtained by condensing the steam is supplied to the water supply pipe 12.
The water passes through the feed water heater 10 and is heated by steam supplied from the bleed pipe 7. After that, the cooling water is supplied to the water supply pump 11
The pressure of the water is raised by the reactor water supply pipe 13 and the water supply sprinkler pipe 14 to lead into the reactor pressure vessel 1 . FIG. 2 shows changes in the state of each part of such a boiling water reactor when the reactor is started.

In FIG. 2, the horizontal axis shows elapsed time and time, and the vertical axis shows changes in the state of each part.

In FIG. 2, characteristics A, B, and C indicate the steam pressure in the reactor pressure vessel 1, the turbine output, and the turbine rotation speed, respectively, at the time of reactor startup.

Here, the turbine output is the electrical output of a generator (not shown) connected to the turbine 4. Also, the characteristic D,
E and F indicate the water supply flow rate, the amount of steam extracted from the turbine 4, and the temperature of the reactor water supply pipe 13, respectively. When starting up the reactor, first, the reactor output is increased with the steam control valve 3 and bypass valve 5 closed.

At this time, the steam pressure within the reactor pressure vessel 1 rises to 100% as shown by characteristic A in FIG. Further, the temperature of the reactor water supply pipe 13 is regarded as the saturation temperature of the steam pressure in the reactor pressure vessel 1, and increases as shown in characteristic F as the steam pressure increases. Next, after the steam pressure in the reactor pressure vessel 1 reaches 100%, the steam control valve 3 is opened and the turbine rotational speed is increased to 100% as shown in characteristic C. Steam that has passed through the turbine 4 flows into the turbine condenser 8 and is cooled and condensed by the turbine condenser cooling system 9. Since the steam control valve 3 is opened and the feed water pump 11 is started to supply cooling water into the reactor pressure vessel 1, the feed water flow rate increases as shown in characteristic D. At this time, as shown in characteristic E, there is no amount of steam extracted from the turbine 4 until the turbine output increases, and the cooling water condensed in the turbine condenser 8 is heated by the feed water heater 10. It is injected into the reactor pressure vessel 1 without being injected into the reactor pressure vessel 1.
Therefore, the temperature of the reactor water supply pipe 13 immediately drops to the temperature of the cooling water. When the circuit breaker connecting the generator and the power system is turned on and the opening degree of the steam control valve 3 is increased to increase the turbine output (electrical output) as shown in characteristic B 7, the steam passing through the turbine 4 increases, turbine 4
The amount of steam extracted from the reactor pressure vessel 1 begins to increase as shown in characteristic E, the extracted steam begins to flow to the high temperature side of the feedwater heater 10, and the temperature of the cooling water introduced into the reactor pressure vessel 1 rises.

As a result, the temperature of the reactor water supply pipe increases as shown in characteristic F as the turbine output increases. As the turbine output increases, it is necessary to increase the flow rate of steam to be supplied to the turbine 4, so as shown in characteristic D, the flow rate of water supply is increased from the middle. As described above, when the reactor is started, the temperature change in the reactor water supply pipe 13 becomes large as shown by characteristic F.

Therefore, a large thermal shock is applied to the reactor water supply pipe 13. The state change when the reactor is shut down is the opposite of the state change described above, and the temperature change in the reactor water supply pipe 13 is similarly large.

In conventional once-through boilers, in order to prevent cooling water pipes within the boiler from burning out, it is necessary to flow cooling water at a minimum flow rate when starting the boiler until the required steam conditions are obtained. In order to increase the boiler thermal efficiency at this time, a method is adopted in which all of the steam generated by the once-through boiler is not guided to the turbine condenser for cooling, but a portion is guided to the feed water heater to heat the water fed to the boiler. is taken. In the case of a boiling water reactor, there is no startup method that allows a minimum flow rate to flow as in the once-through boiler described above, and since the purpose of the present invention is to alleviate temperature changes in the piping inside the reactor, once-through boilers are not used. This is different from the case of

In other words, the present invention takes into consideration heating the cooling water when the amount of steam extracted from the turbine is small. FIG. 3 shows an embodiment of the invention.

In this figure, the same reference numerals as in FIG. 1 indicate the same parts, so the description of these parts will be omitted. A high pressure switch 15, a low pressure switch 16, and a check valve 17 are installed in the bleed pipe 7.

A remote operated valve 22, a pressure control valve 20, a check valve 19, and a pressure regulator 18 are installed in a steam pipe 21 that connects the main steam pipe 2 and the bleed pipe 7. Next, the operating state of this embodiment will be explained based on FIG. 4.

In FIG. 4, characteristics A-F are the same as those shown in FIG. 2, and characteristic G represents the steam pressure in the steam pipe 21 at point G shown in FIG.

Special. The value H indicates the steam pressure inside the extraction pipe 7 at point H shown in FIG. Furthermore, characteristic 1 indicates the steam flow rate within the steam pipe 21. When the reactor is started, the temperature and pressure increasing operation of the reactor is started (time T). That is,
The reactor output is increased while keeping the steam control valve 3 and bypass valve 5 closed. At this time, the steam pressure within the reactor pressure vessel 1 rises to 100% as shown by characteristic A in FIG.
Furthermore, the temperature of the water supply pipe inside the reactor is regarded as the saturation temperature of the steam pressure inside the reactor pressure vessel, and rises as shown in characteristic F. Remotely operated valve 22 is engaged entirely by a signal from low pressure switch 16. That is, the low pressure switch 16 issues a signal that completely controls the remote operated valve 22 when the internal steam pressure at point H of the bleed pipe 7 falls below a certain value (set pressure). At the time of reactor startup, the pressure at point H is naturally lower than the set pressure of the low pressure switch 16, so the remotely operated valve 22 is open. For this reason, the reactor pressure vessel 1
The steam generated is passed through the steam pipe 21 to the feed water heater 1.
0. Because of the check valve 17, this steam does not flow back through the extraction pipe 7 and into the turbine 4. In order to prevent the level of cooling water in the reactor pressure vessel 1 from dropping due to steam outflow and maintain it at a predetermined level, the water supply pump 11 is activated for a period of time T. Cooling water is supplied from the condenser 8 to the reactor pressure vessel 1 through the water supply pipe 12. The cooling water flowing through the water supply pipe 12 is heated by the steam supplied from the steam pipe 21 in the water supply heater 10.The steam is condensed in the water supply heater 10, becomes drain water, and is sent to the condenser 8. Between time T and time, the steam discharged from the reactor pressure vessel 1 is
Steam piping 21, feed water heater 10 (steam is connected to feed water heater 10)
Since the water is condensed into water at the feedwater heater 10 and thereafter, it flows in a closed loop connecting the condenser 8, the water supply piping 12, and the reactor pressure vessel 1. The pressure at point G is
As shown by characteristic G in FIG. 4, it increases as the steam pressure (characteristic A in FIG. 4) increases from time t1 to time t1.

However, the pressure at point G remains constant after time. This operation is performed by the pressure regulator 18 and the pressure control valve 20, and the pressure regulator 18 adjusts the opening degree of the pressure control valve 20 so that the pressure at point G is constant.
That is, when the steam pressure in the steam pipe 21 between the check valve 19 and the pressure control valve 20 is lower than the set pressure (pressure value at point G at time t1), the pressure regulator 18 closes the pressure control valve. When the pressure at point G exceeds the set pressure, the opening of pressure control valve 20 is decreased to adjust the pressure at point G to the set pressure. Pressure regulator 18
The set pressure of the steam set in is equal to the pressure of the steam extracted from the turbine 4 from then on. The pressure regulator 18 and the pressure control valve 20 have a function of supplying steam at a predetermined pressure or lower to the feedwater heater 10 through the steam pipe 21 and preventing the feedwater heater 10 from being damaged. The pressure resistance of the feed water heater 10 is designed to withstand the pressure of the steam pipe connected from the turbine 4 to the extraction pipe 7. Since the steam extracted from the turbine is extracted after performing some work in the turbine 4, the pressure of the extracted steam is considerably lower than the steam pressure in the main steam pipe 2. Even before the time when steam is extracted from the turbine 4, the steam pressure in the reactor pressure vessel 1 before time t1 is:
Time i! 11T. Since the pressure is lower than the pressure of the extracted steam discharged from the turbine 4 to the extraction pipe 7 after time t1, the steam pressure in the reactor pressure vessel 1 is applied almost unchanged to the feedwater heater 10 before time t1. . However, after time t1, reactor pressure vessel 1
That is, the pressure of the steam in the main steam pipe 2 becomes higher than the pressure of the steam extracted from the turbine 4 after the time. This high-pressure steam flows through the pressure control valve 20.
If the steam is directly applied to the feed water heater 10 via the steam pipe 21 without being depressurized in the steam pipe 21, the feed water heater 10 will be damaged.
In this embodiment, the opening degree of the pressure control valve 20 is gradually reduced from time ζ to the time when the steam pressure in the reactor pressure vessel 1 reaches 100%.
The opening degree of the pressure control valve 20 is kept constant as long as there is no pressure fluctuation from the time when the steam pressure in Since the pressure at point G is suppressed to the set pressure, the feed water heater 10 will not be damaged. Time T.

- During the period t1, as mentioned above, steam is supplied to the feedwater heater 10 through the steam piping 21, so the flow rate of the feedwater to the reactor pressure vessel 1, the pressure at point G, the steam flow rate at point G, and the reactor As shown in FIG. 4, the temperature of the internal water supply pipe 13 changes to a characteristic D as the steam pressure inside the reactor pressure vessel 1 increases.
, G, l and F. As time elapses, the pressure increase at point G is suppressed by the pressure control valve 20 as described above, so the steam flow rate at point G is kept constant.

Therefore, after time t1, the water supply flow rate (characteristic D in FIG. 4) and the reactor water supply pipe temperature (characteristic F in FIG. 4) are held constant for a predetermined period. Time steam control valve 3
The reactor pressure vessel 1 is gradually opened and steam generated within the reactor pressure vessel 1 is supplied to the turbine 4.

By supplying this steam, the rotational speed of the turbine 4 increases as shown by characteristic C in FIG. 4 and reaches 100% after a while.
Since steam is supplied to the turbine 4 through the steam control valve 3, the reactor pressure vessel 1 needs to generate a corresponding amount of steam. For this reason, the water supply flow rate also increases as shown by characteristic D in FIG. 4 over time. The pressure at point H increases as shown by characteristic H in FIG. 4 as the steam control valve 3 opens and the turbine 4 begins to rotate and the amount of steam supplied to the turbine 4 increases. In the range from time ζ to ζ, the rotation speed of the turbine 4 is constant and the steam flow rate supplied to the turbine 4 is also kept constant, so the feed water flow rate and the pressure at point H are also the same as the characteristic D and the pressure at point H in FIG. It becomes constant like H. Although steam does not flow in the bleed pipe 7 upstream of the check valve 17, the bleed pipe 7 communicates with the turbine 4. Therefore, even if no steam is flowing, the pressure is applied almost unchanged to point H at the steam extraction position of the turbine 4. At a predetermined time after the turbine 4 has rotated, the bypass valve 5 is completely closed. At time ζ, the circuit breaker connecting the generator to the power grid is closed.

The electricity generated by the generator is transmitted to the power grid. As the circuit breaker is closed, the opening degree of the steam control valve 3 is increased, and the fourth
The turbine output is increased so that it reaches 100% in time as shown in characteristic B in the figure. Along with this, the water supply flow rate and the pressure at point H also increase as shown by characteristics D and H in Figure 4).
However, the pressure at point G and the steam flow rate at point G are held constant based on the functions of pressure regulator 18 and pressure control valve 20. Turbine output (electrical output) as shown in characteristic B
When the pressure is increased, the amount of steam passing through the turbine 4 increases, and as described above, the pressure at point H, where the pressure at the extraction position of the turbine 4 is applied, increases as shown by characteristic H.

However, when the pressure at point G is higher than the pressure at point H,
No flow of steam 9 from the turbine 4 to the bleed pipe 7 occurs. When the pressure at point H reaches the set value of the high pressure switch 15,
High pressure switch 15 issues a signal to fully close remotely operated valve 22. As a result, by inputting that signal, the remote operated valve 2
2 is completely closed, and the steam flow rate at point G becomes zero. The pressure setting of the high pressure switch 15 is higher than the pressure setting of the low pressure switch 16. The remote operated valve 22 is opened by inputting the output signal of the low pressure switch 16, and is opened by inputting the output signal of the low pressure switch 16.
It is closed by inputting the output signal of 5. As a result of the pressure at point H becoming higher than the pressure at point G, the amount of extracted steam flowing from the turbine 4 through the extraction pipe 7 increases as shown by characteristic E in FIG. 4.

When the extracted steam from the turbine 4 is supplied to the feed water heater 10, the steam temperature at the extracted position of the turbine 4 will be lower than the temperature at the junction of the main steam pipe 2 and the steam pipe 21 due to the work done by the turbine 4. The temperature of the steam decreases slightly below the temperature of the steam, so the time T
After 5, the temperature of the cooling water heated by the feed water heater 10 is slightly lower than before. For this reason, the temperature of the reactor water supply pipe 13 becomes slightly lower after time T5 than before, as shown by characteristic F in FIG. However, this amount of temperature fluctuation does not apply a large thermal shock to the reactor water supply pipe 13 as in the conventional case, and does not impair the safety of the reactor water supply pipe 13 in any way. As mentioned above, even in a state where turbine bleed air cannot be expected as a fluid on the feedwater heater 10 side, such as during reactor startup, feedwater heating can be performed using steam from the main steam pipe 2, so the reactor The temperature change in the inner water supply pipe 13 will not be large.

According to this embodiment, since the steam pressure in the extraction piping 7 is detected, the supply state of the extraction steam from the turbine 4 to the feed water heater 10 can be accurately detected. Moreover, the opening/closing operation of the remotely operated valve 22 can be appropriately performed depending on the supply state of the turbine bleed steam.

At the time of starting up the nuclear reactor as described above, the low steam pressure set by the low pressure switch 16 of the bleed pipe 7 can be detected with high accuracy, and the remote ζ operating valve 22 can be appropriately opened. As a result, extracted steam can be appropriately supplied to the feedwater heater 10 through the steam piping 21, and temperature fluctuations in the feedwater at the start-up time when the feedwater flow rate is increased from zero as in the past are significantly suppressed. Thermal shock is significantly reduced. In addition, the bleed pipe 7 set by the high pressure switch 15
The high steam pressure can be detected with high accuracy, and the remotely operated valve 22 can be appropriately closed. Therefore, when the steam piping reactor is shut down, the above-mentioned state change is reversed, and similarly, the temperature change in the reactor water supply pipe 13 does not become large. When the reactor is shut down, it is possible to accurately measure that the steam pressure in the bleed piping 7 has fallen to the value set by the high pressure switch 15 as described above, and to appropriately switch to the supply of bleed steam through the steam piping 21. be able to. Therefore, temperature fluctuations in the feed water during reactor shutdown, where the feed water flow rate is reduced to zero, are significantly suppressed, and the original temperature is reduced. Thermal shock to which the child reactor water supply pipe 13 is subjected is significantly reduced. [Effects of the Invention] According to the present invention, the supply state of extracted steam from the turbine to the feedwater heater can be detected with high accuracy, and the supply route of the extracted steam to be supplied to the feedwater heater can be determined based on the supply state of the turbine extracted steam. Can be switched appropriately.

Temperature fluctuations in the feed water during startup and shutdown of the reactor are significantly suppressed, and the thermal shock applied to the water supply pipes inside the reactor vessel is significantly reduced.

[Brief explanation of drawings]

Figure 1 is a system diagram of a conventional boiling water reactor, and Figure 2 is a system diagram of a conventional boiling water reactor.
FIG. 3 is a system diagram of a boiling water reactor which is a preferred embodiment of the present invention, and FIG. It is a characteristic diagram which shows the state change of each part of Example. 1... Reactor pressure vessel, 2... Main steam piping, 4... Turbine, 7... Bleed piping, 8... Turbine recovery Water device, 10...Water heater, 12...Water supply piping, 13...
Reactor water supply piping, 15... High pressure switch,
16...Low pressure switch, 18...Pressure regulator, 20...Pressure control valve, 21...
・Steam piping, 22...Remotely operated valve.

Claims (1)

[Claims] 1. A reactor vessel, a turbine, a feedwater heater, a steam pipe that guides steam generated in the reactor vessel to the turbine, and a water supply pipe that guides cooling water into the reactor vessel via the feedwater heater. and a first bleed pipe that guides steam extracted from the turbine to the feed water heater,
A second bleed pipe is provided to guide steam in the reactor vessel to the feed water heater without going through the turbine, an on-off valve is provided in the second bleed pipe, and the pressure in the first bleed pipe is detected. A first control means for opening and closing the on-off valve based on pressure is provided, a pressure control valve is provided in the second air bleed pipe downstream of the on-off valve, and a pressure control valve is provided in the second air bleed pipe to detect the pressure in the second air bleed pipe. A nuclear reactor characterized in that a second control means is provided for controlling the pressure of steam flowing through the second bleed pipe to a predetermined pressure by operating the pressure control valve based on pressure.