JPH09304586A - Boiling water nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a boiling water nuclear power plant capable of propecly performing daily load follow-up operation without varying the thermal efficiency of turbine. SOLUTION: In the case of performing short time daily load follow-up operation for a few hours to one day, reactivity control is done at first with control rods, then the steam extraction rate at a steam extractor 16 is controlled with a steam extraction controller 17 to respond to the fluctuation of reactivity due to the fluctuation of xenon so that the steam flow supplied to the turbine 4 is specific one according to the target load. According to this steam extraction rate, feed water temperature is raised with a feed water heater 18 for controlling feed water temperature and power control operation is attained by controlling this feed water temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiling water nuclear power plant in which the control rod insertion position in a nuclear reactor is adjusted to adjust the reactivity so as to perform daily load following continuous rotation.

[0002]

2. Description of the Related Art Generally, a boiling water nuclear power plant is constructed as shown in FIG. The main steam generated in the core 2 of the nuclear reactor 3 is guided to the high-pressure turbine 4, and the steam that has finished its work in the high-pressure turbine 4 is guided to the low-pressure turbine 6 through the moisture separation heater 5 installed downstream thereof. Get burned.
The generator 7 is given a driving force by the high-pressure turbine 4 and the low-pressure turbine 6 to generate electricity. The steam that has finished its work in the low-pressure turbine 6 is condensed in the condenser 8 and returned to water.

Water from the condenser 8 is guided to a condensate tank 10 by a condensate pump 9, and further a plurality of low pressure feed water heaters 11 are provided.
Water is supplied to the reactor 3 through a to 11d, the water supply pump 12, and a plurality of high-pressure water supply heaters 13a and 13b. The high-pressure feed water heater 13 heats the feed water using the steam extracted from the high-pressure turbine 4 and the waste water of the moisture separation heater 5 as a heat source.
The low-pressure feed water heater 11 heats the feed water upstream of the high-pressure feed water heater 13 using the steam extracted from the low-pressure turbine 6 as a heat source. Further, the feed water pump 12 pressurizes the low-pressure feed water to raise the pressure to the reactor pressure.

By extracting a part of the steam from the high pressure turbine 4 and the low pressure turbine 6 to raise the temperature of the feed water,
The amount of heat dissipated in the condenser 8 is reduced. This allows
Thermal efficiency is improved. Such a thermal cycle is called a regeneration cycle and is commonly used in boiling water nuclear power plants. In such a heat cycle, control is performed to keep the temperature of the feed water constant during the output operation.

In a boiling water nuclear power plant,
Output adjustment (hereinafter referred to as daily load following operation) may be performed once to several times a day. When performing the daily load follow-up operation, in a normal method, a control rod pattern that is a target output is determined, and the control rod is operated in a relatively short time of about several minutes so as to obtain the control dedicated pattern. After that, until the equilibrium concentration of xenon in the reactor 3 is reached, the output adjustment due to the influence of the xenon is performed by adjusting the core recirculation flow rate.

For example, when the reactor power is increased, the xenon concentration initially becomes low, and the reactivity of the core increases.
After that, when the xenon concentration increases to the equilibrium concentration, the reactivity decreases. Since such a xenon effect occurs and the reactor output fluctuates, the adjustment is performed by adjusting the core recirculation flow rate.

[0007]

However, since it is necessary to adjust the output every day load operation and it is necessary to consider the adjustment of the recirculation flow rate due to the influence of the xenon effect.
Controlling the recirculation flow rate becomes complicated. In particular, in a natural circulation type boiling water nuclear power plant, since there is no recirculation device for recirculating the coolant of the reactor, the output adjustment is generally made only by the control rods.

When performing daily load follow-up operation in a natural circulation type boiling water reactor, it is necessary to adjust the output only with control rods. Therefore, the control including the increase / decrease in reactivity due to the increase / decrease in xenon should be 6-8. It is difficult to carry out continuously over a long period of time. That is, a fine position adjusting capability is required for adjusting the control rod, and the position must be controlled continuously. Therefore, driving had to be extremely complicated. Further, in this case, there is a problem that a costly control rod drive device capable of fine position adjustment is essential.

On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 62-138794 discloses that a natural circulation type nuclear power plant can follow a load depending on the feed water temperature. That is, the output control is performed by the feed water temperature, and the feed water temperature is controlled by the turbine bleed air to adjust the reactivity and the load following operation is performed. However, in this method, since the bleed air from the middle of the turbine is used, the reheat amount changes, the heat amount discarded in the condenser fluctuates, and the electric output also fluctuates. Therefore, there is a problem that the control of the feed water temperature causes a variation in the electric output, which makes the output control more complicated.

An object of the present invention is to obtain a boiling water nuclear power plant that can appropriately perform daily load following operation without changing the thermal efficiency of the turbine.

[0011]

According to the invention of claim 1, there is provided an extraction device for extracting a part of main steam supplied from the reactor to the turbine, and a feed water supplied to the reactor by extraction from the extraction device. It is equipped with a feed water heater for controlling the feed water temperature to be heated, and an extraction control device that controls the extraction amount in the extraction device so that the flow rate of steam supplied to the turbine becomes a constant steam flow rate corresponding to the target load. is there.

According to the first aspect of the present invention, when the daily load follow-up continuous rotation for a short time of several hours to about one day is performed, the reactivity is first adjusted by the control rod, and the reactivity is subsequently increased / decreased with the increase of xenon. For the increase and decrease of, the amount of air extracted by the air extraction device is controlled so that the flow rate of steam supplied to the turbine becomes a constant flow rate of steam corresponding to the target load, and the output adjustment operation is performed by adjusting the supply water temperature. .

According to a second aspect of the present invention, in the first aspect of the invention, the unit for inserting the control rod during the daily load following operation is 1/20 or more of the effective fuel portion, and the circulation of the coolant in the reactor is natural circulation. It's something that you do.

According to the second aspect of the present invention, the control unit insertion unit is set to 1/20 or more of the fuel effective portion to simplify the structure and reduce the cost of the control unit driving device.

[0015] The invention of claim 3 is claim 1 or claim 2.
In one embodiment, one or a plurality of feed water temperature control water heaters are provided, and only the uppermost stage feed water temperature control water feed heater is a mixed-type feed water heater in which feed water and extraction steam are directly mixed. Other than that, the feed water heater for controlling the feed water temperature is a heat exchange type feed water heater in which the feed water and the extracted steam exchange heat in a non-contact manner.

In the invention of claim 3, at least one of the feed water heaters for controlling the feed water temperature is a mixed feed water heater of a type in which the feed water and the extracted steam are directly mixed, and the heat energy of the extracted steam is efficiently supplied. In order to prevent heat loss by returning all to the water supply, and not to affect the reheat amount on the turbine side.

According to a fourth aspect of the present invention, there is provided the first or second aspect.
In the invention of, one or a plurality of water supply temperature control water supply heater is provided, the water supply temperature control water supply heater is a heat exchange type water supply heater in which the water supply and sleeve steam are non-contact heat exchange, The drain water from the feed water heater for controlling the feed water temperature at the most upstream stage is mixed with the feed water by the drain pump.

In the invention of claim 4, the drain water of the heat exchange type feed water heater at the final stage is mixed with the feed water by the drain pump, and all the heat energy of the extracted steam is efficiently returned to the feed water without heat loss. And the amount of reheat on the turbine side is not affected.

[0019]

Embodiments of the present invention will be described below. FIG. 1 is a configuration diagram showing a first embodiment of the present invention. The first embodiment is different from the conventional example shown in FIG. 5 in that a bleed device 16 for bleeding part of the main steam supplied from the reactor 3 to the turbine 4 and a bleed air from the bleed device 16. The feed water temperature control feed water heater 18 for heating the feed water supplied to the reactor 3 by means of the bleeding device 16 so that the steam flow rate supplied to the turbine 4 will be a constant steam flow rate corresponding to the target load. Extraction control device 1 for controlling the amount
7 is provided. Other configurations are the same as those of the conventional example shown in FIG. 5, and therefore, the same components are denoted by the same reference numerals and description thereof will be omitted.

In FIG. 1, an extraction device 16 is installed between the outlet of the nuclear reactor 3 and the high pressure turbine 4, and the high pressure turbine 4
The extraction amount is controlled by the extraction control device 17 so that the main steam injected into the exhaust gas reaches a target value determined by the daily load.

The extracted main steam is supplied to the feed water temperature control feed water heater 18 through the extraction pipe 19. The feed water heater 18 for controlling the feed water temperature is the high-pressure feed water heater 1 at the final stage.
A mixed feed water heater of a type installed between the downstream of 3b and the inlet of the nuclear reactor 3 and in which feed water and extracted steam are directly mixed is used. That is, the feed water heater 1 for controlling the feed water temperature
In 8, the feed water from the high pressure feed water heater 13b at the final stage is mixed with the extracted main steam, and the feed water is further heated. Then, the heated water supply is supplied to the nuclear reactor 2. A steam injector may be used as the feed water heater 18 for controlling the feed water temperature.

Here, the steam pressure of the reactor 3 during the output operation is controlled to about 70 atm, and the main steam temperature at the reactor outlet is about 280 ° C., which is the saturation temperature of 70 atm. Therefore, the upper temperature limit at the outlet of the feed water temperature control feed water heater 18 is set so that the fuel assembly output does not exceed the limit output. That is, the limit output of the reactor 3 decreases as the feed water temperature increases. Therefore, the fuel assembly output is set so as not to exceed the limit output in consideration of the power density of the reactor 3, the core flow rate, the limit output characteristic of fuel, and the like. To do. The condition temperature is, for example, about 220 ° C. as in the conventional case.

The lower limit of the temperature of the outlet of the feed water heater 18 for controlling the feed water temperature is set to a value corresponding to the reactivity adjustment width required to follow the load. The reactivity of xenon at 100% output is 3% Δ
It is about k, and the increase and decrease range of the xenon reactivity becomes about 0.5% Δk at most for a load increase of 10%, that is, for an electric output increase of 10%. Since the sensitivity of the change in the core reactivity due to the change in the feed water temperature is 0.01% Δk / ° C, the control range of the feed water temperature may be at most 50 ° C, and the lower limit of the temperature in this case is 170 ° C.

Next, the case where the daily load follow-up continuous rotation is performed for a short time of several hours to about one day will be described. FIG. 2 is a characteristic diagram showing a change in each process amount with respect to a control operation when the output is increased by 10% as the daily load tracking.

The reactor output (heat output) is constant before the output is increased, and the electric output of the generator 7 is also constant. When the control rod is rapidly pulled out to the target reactivity by the daily load follow-up control, the reactor output after operating the control rod rises in a short time. The steam to the turbine 4 is increased at the same speed as the rising speed of the reactor output. The amount of water supply will also be increased at the same speed as the rising speed of the reactor output. As a result, the amount of extracted steam extracted for controlling the feed water temperature also rises at the same speed as the rising speed of the reactor output.

After the reactor power rises for a relatively short time, the xenon concentration changes because the concentration of iodine, which is the parent nuclide of xenon, is lower than the equilibrium concentration and the xenon disappearance speed increases after the reactor power increases. , Then the concentration temporarily decreases. Then, after reaching the minimum value, it gradually increases, and equilibrium is achieved in a state where the concentration is higher than before the output increase. This xenon change time is about 6 hours. The negative change in reactivity due to xenon is proportional to the xenon concentration.

The reactor output in the section where the xenon concentration is changing is kept substantially constant by the feed water temperature control by extraction air. During this time, a change in the feed water temperature is given to just cancel the reactivity of xenon. That is, when the reactivity of xenon is positive, the feed water temperature is high, and when it is negative, it is low. Further, the flow rate of the extracted steam during this period is such that the extracted air is larger than the equilibrium value while the xenon reactivity is positive, and the outlet enthalpy of the reactor 3 increases. The feedwater temperature seen from the reactor 3 is rising at this time, and the enthalpy of feedwater is increasing. The heat output of the nuclear reactor 3 is almost constant, so that the difference between the enthalpy at the outlet of the nuclear reactor 3 and the enthalpy of feed water is constant.

That is, when the control operation for load following is performed, the core reactivity changes for several hours due to the subsequent transient fluctuation of the xenon concentration. For example, when the output is increased, the xenon concentration initially decreases and a positive reactivity occurs, and the xenon concentration gradually approaches the equilibrium concentration higher than before the output change, and a negative reaction is added. At this time, when the extraction control for keeping the steam going to the turbine 4 constant is performed, the increase in the main steam amount due to the transient output increase increases the extraction steam, and the heat input of the extraction water temperature control feed water heater 18 increases. Increase to increase the feedwater temperature.

When the feed water temperature increases, a negative reactivity is added to the nuclear reactor 3, and the nuclear reactor output autonomously settles down to a thermal output corresponding to the amount of steam going to the turbine 4 side. Even if the xenon concentration change continuously changes with time, the steam to the turbine 4 side is constant and changes so as to keep the reactor output and the electric output constant. No reactivity adjustment is required. Even when the output is decreased, the action is only reversed, and the control operation for the fluctuation of the xenon concentration is unnecessary.

According to the first embodiment, the generator 7
In order to increase the electric output of the control rod, the control rod is first operated by the amount corresponding to the output change and is not operated thereafter, and thereafter, only the extraction steam is controlled so that the steam flow rate supplied to the turbine 4 is constant. Good. As described above, in a reactor having a feedwater temperature control system that does not affect the turbine thermal efficiency, particularly in a natural circulation type reactor that does not have a recirculation system, control rod operation can be minimized to follow the load. Needless to say, similar control can be performed in the forced circulation furnace by providing a similar system.

Further, since the operation of the control rod is minimized, the influence of distorting the power distribution of the core is small and the operation with a large thermal margin is possible. At the time of load following, it is clear that the only operation required after the control operation is the adjustment of the bleed air amount, and the parameters to be controlled are greatly reduced compared to the control rod, which facilitates the control. This facilitates operator's operation and reduces the burden.

As described above, in the first embodiment, part of the main steam before the turbine inlet is extracted to regulate the supply steam to the turbine 4 at a constant level, and the extracted steam is used for controlling the feed water temperature. It is injected into the feed water heater 18 to adjust the feed water temperature. That is, when performing load follow-up operation for a short time of several hours to about one day, first adjust the reactivity with the control rod, and then increase or decrease the reactivity with the increase or decrease of xenon. Perform the operation to maintain the output constant by adjusting with the heater.

Therefore, it is possible to perform a load following operation for a short time of several hours to about one day without changing the thermal efficiency of the turbine, and it is possible to perform a simple and easy output adjusting operation.

Next, a second embodiment of the present invention will be described. In the second embodiment, the insertion unit of the control rod during the daily load following operation is set to 1/20 or more of the effective fuel portion. As a result, the reactor is cooled by the natural circulation system, and the coolant flow rate equivalent to that of the forced circulation reactor is secured.

The control rod operation at the time of output fluctuation during daily load following operation is performed only at the beginning of output adjustment. Furthermore, the reactivity is controlled by a control drive device that is similar to the forced circulation type boiling water reactor with a recirculation device. In a forced circulation type boiling water reactor, a positioning ability of at least about 1/25 of the normal core effective length is sufficiently practical, and in a natural circulation reactor, the effective core length is usually about 80% of that of the forced circulation reactor. Therefore, when applied to a natural circulation furnace, it is possible to achieve sufficient control at about 1/20.

That is, in the second embodiment, the reactor is cooled by the natural circulation reactor system. In this case, since the coolant is circulated only by the head difference due to the water level,
A design is applied to maintain a sufficient coolant flow rate by reducing the core effective height to reduce the pressure loss in the core 2.

In the second embodiment, the height of the core 2 is set to about 80% of the height used in the forced circulation furnace, and the circulation flow rate is secured to be almost the same as the flow rate used in the forced circulation. . Therefore, the effective core height of a natural circulation reactor is 80% of the 3.7 m used in the forced circulation reactor.
Of about 3 m. Further, in this case, the load following is performed by both the control rod and the feed water temperature similar to those shown in the first embodiment. The required control rod insertion unit length is about the same as the control rod insertion unit used in the conventional recirculation reactor, about 15 cm.
It should be about. Therefore, the effective height of the core 2 is 3
In the case of m, the insertion unit is about 1/20 of the effective core height, and sufficient output control is possible.

As described above, with respect to the control drive unit, the control drive insertion unit is set to 1/20 or more of the fuel effective portion to simplify the structure and reduce the cost of the control drive unit.

Next, a third embodiment of the present invention will be described. FIG. 3 is a plant configuration diagram showing a third embodiment of the present invention. The third embodiment is the same as the first embodiment shown in FIG.
In the embodiment, three feed water temperature control feed water heaters 31, 32, 33 are provided, and only the feed water temperature control feed water heater 31 in the uppermost stage is used to directly mix feed water and extracted steam. And the other feed water temperature control feed water heaters 32 and 33 are heat exchange feed water heaters for exchanging heat between the feed water and the extracted steam in a non-contact manner.

In FIG. 3, the three feed water temperature control water heaters 31, 32, 33 are referred to as an upstream feed water heater 31, a midstream feed water heater 32, and a downstream feed water heater 33, respectively, from the upstream side of the feed water. The feed water heater 31 is a mixed feed water heater. The three feed water heaters 31 and 3 for controlling the feed water temperature
2, 33, it is set so that the water supply can be increased up to about 50 ° C. Exhaust drain 34 of the downstream feed water heater 33
Is injected into the midstream feed water heater 32 as a heating source, and the exhaust drain 35 serves as a heating source for the upstream feed water heater 31. Further, since the upstream feed water heater 31 is a mixed type heater, there is no exhaust drain.

Generally, a normal feed water heater has a maximum of 3 in one stage.
Since there is an ability to increase the feed water temperature of about 0 ° C., when the normal feed water heater is applied, the control range of the feed water temperature can be realized up to about 90 ° C. with three units. Thus, even if there are a plurality of feed water heaters for controlling the feed water temperature, the most upstream feed water heater 31
By using a mixed type, there is no exhaust and no heat loss. Further, since the fluctuation of the heat quantity is not transmitted to the turbine side, the fluctuation of the turbine thermal efficiency due to the fluctuation of the extraction air flow is eliminated. Therefore, electric output control becomes easy.

In the third embodiment, an example in which the number of feed water heaters for controlling the feed water temperature is three has been shown, but in principle the same effect can be obtained if the uppermost stream is a mixed type. It is clear that as the number of feed water heaters is increased, the feed water temperature control range can be increased. As described above, in the third embodiment, there is no change in thermal efficiency and the amount of steam input to the turbine is kept constant, so that the amount of power generation can also be kept constant.

Next, a fourth embodiment of the present invention will be described. FIG. 4 is a plant configuration diagram showing a fourth embodiment of the present invention. The fourth embodiment is provided with three feed water temperature control heaters 41, 42, 43 for controlling the feed water temperature.
The water heaters 41, 42, 43 for controlling the water temperature of the stand are heat exchange water heaters for exchanging heat between the water and the sleeve steam in a non-contact manner, and the water heater 41 for controlling the water temperature at the most upstream stage. The drain water from (4) is mixed with the feed water by the drain pump 44.

In FIG. 4, three feed water temperature control feed water heaters are respectively provided from the upstream side of the feed water to the upstream feed water heaters 4
1. A middle-stream feed water heater 42 and a downstream feed water heater 43 are provided, and a drain pump 44 is installed upstream of the upstream feed water heater 41 so as to increase the pressure of the exhaust drain and mix it with the feed water to the upstream feed water heater 13b. In addition, these feed water heaters 41, 42,
All 43 are heat exchange type feed water heaters. With these three water heaters 41, 42, 43, water can be supplied at a maximum temperature of approximately 50 ° C.
It is set to be able to rise.

The exhaust drain 45 of the downstream feed water heater 43 is injected into the midstream feed water heater 42 as a heating source, and the exhaust drain 46 becomes a heating source of the upstream feed water heater 41.
The exhaust drain of the upstream feed water heater 41 is the drain pump 4
4 is mixed with the water supply.

Also in the case of the fourth embodiment, since all the thermal energy of the extracted steam is returned to the feed water, the same effect as that of the third embodiment can be obtained. Further, in the fourth embodiment, since the feed water heaters 41, 42, 43 are all heat exchange type and the drain pump 44 is provided, it can be realized only by the device which is currently in practical use.

According to the fourth embodiment, all the heat quantities of the extracted air are controlled by the feed water temperature control feed water heaters 41, 42 and 4.
3 is taken into the inside of the turbine 3, and does not affect the heat balance of the feedwater heaters 13 and 11 belonging to the turbine side. Further, since there is no change in thermal efficiency and the amount of steam input to the turbine 4 is kept constant, the amount of power generation can also be kept constant. Further, since the mixed feed water heater is not used, maintenance is easy. Therefore, manufacturing cost and maintenance cost can be reduced.

Here, the temperature of the feed water injected into the feed water temperature control feed water heater is made independent of the output of the reactor by making the amount of extracted steam used for the feed water heater extracted from the middle of the turbine proportional to the feed water amount. You may make it fixed.
This makes it possible to easily and easily control the feed water temperature by the extraction steam while keeping the feed water condition injected into the feed water temperature control feed water heater constant.

[0049]

As described above, according to the present invention, the extraction device for extracting the main steam from the nuclear reactor and the feed water heating for controlling the feed water temperature for heating the temperature of the feed water by the extraction amount from the extraction device. It is possible to perform load following operation without deteriorating the thermal characteristics of the core simply by providing a reactor and adjusting the amount of air extracted from the air extraction device. Moreover, the operation at the time of load following can be simplified, the burden on the operator can be reduced, and the operation with a large thermal margin can be performed. In addition, a simple control rod having a large control insertion unit can be used, and the number of parts is small and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a plant configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a change in each process amount with respect to a control operation when an output is increased by 10% as a daily load following in the first embodiment of the present invention.

FIG. 3 is a plant configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a plant configuration diagram showing a fourth embodiment of the present invention.

FIG. 5 is a plant configuration diagram showing a conventional example.

[Explanation of symbols]

 2 Core 3 Reactor 4 High Pressure Turbine 5 Moisture Separation Heater 6 Low Pressure Turbine 7 Generator 8 Condenser 9 Condensate Pump 10 Condensate Tank 11 Low Pressure Water Heater 12 Water Pump 13 High Pressure Water Heater 16 Extractor 17 Extraction Control device 18 Feed water heater for controlling feed water temperature 19 Extraction pipe 31 Upstream feed water heater 32 Midstream feedwater heater 33 Downstream feedwater heater 34, 35 Exhaust drain 41 Upstream feedwater heater 42 Midstream feedwater heater 43 Downstream feedwater heater 44 Drain Pump 45, 46 Exhaust drain

Claims (4)

[Claims] 1. In a boiling water nuclear power plant in which a control rod insertion position is adjusted in a nuclear reactor to adjust reactivity to perform daily load following continuous rotation, a main unit supplied from the nuclear reactor to a turbine. A bleeding device for bleeding a part of steam, a feed water temperature control feed water heater for heating feed water supplied to the reactor by bleeding from the bleed device, and a steam flow rate supplied to the turbine to a target load. A boiling water nuclear power plant, comprising: a bleed control device that controls the bleed amount in the bleed device so that a corresponding constant steam flow rate is obtained. 2. The unit for inserting the control rod during the daily load following operation is set to 1/20 or more of the effective fuel portion, and the circulation of the coolant of the nuclear reactor is performed by natural circulation. The boiling water nuclear power plant according to Item 1. 3. A mixed-type water supply system in which one or a plurality of water supply temperature control water heaters are provided, and only the most upstream water supply temperature control water supply heater is used to directly mix the water supply with the extracted steam. 3. A heater, and a feed water heater for controlling the feed water temperature other than that is a heat exchange type feed water heater for exchanging heat with the feed water and the extraction steam in a non-contact manner. Boiling water nuclear power plant. 4. A heat exchange type feed water heater provided with one or a plurality of feed water temperature control feed water heaters, wherein the feed water temperature control feed water heater exchanges heat between the feed water and sleeve steam in a non-contact manner. The boiling water nuclear power plant according to claim 1 or 2, wherein the drain water from the feed water heater for controlling the feed water temperature at the uppermost stage is mixed with the feed water by a drain pump.