JP2005091291A - Super-critical pressure water cooled nuclear power plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure cooling of core fuel during supply pump trip accidents in a super-critical water cooled nuclear power plant and suppress the transport of radioactive material to a condenser. <P>SOLUTION: The nuclear power plant has a reactor 1 using super-critical water as coolant, turbines 4, 5 which are supplied with steam obtained in the reactor 1 through a main steam pipe 2, a condenser 6 condensing steam exhausted from the turbines, a condensate pump 7 for returning condensate obtained in the condenser 6 to the reactor 1, first supply water heaters 10, 11 arranged in between the discharge side of the condensate pump 7 and the reactor 1, making supply water by heating condensate water by extracting from the turbines 4 and 5, a second supply water heater 14 arranged in between the first supply water heaters 10, 11, further heating supply water passed through the first supply water heaters 10, 11 by extracting from the main steam extraction pipe 13 branched from the main steam pipe 2, and a recirculation pump 15 for returning drain water of extraction steam from the main steam pipe 2 coming out of the second supply water heater 14. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a supercritical water-cooled nuclear power plant using supercritical water as a coolant, and more particularly to a supercritical water-cooled nuclear power plant with main steam extraction and its recirculation system.

  FIG. 7 shows an example of a conventionally considered supercritical water cooling nuclear power plant (see Patent Document 1). High-temperature and high-pressure (about 220 atm., 500 ° C. or higher) steam generated in the nuclear reactor 1 passes through the main steam pipe 2 and is guided to the high-pressure turbine 4 via the main steam stop valve 3. The steam that has worked in the high-pressure turbine 4 enters the low-pressure turbine 5, and after further work here, it is condensed in the condenser 6 to become low-temperature and low-pressure condensate. The condensate is boosted to a supercritical pressure by the condensate pump 7 and the feed water pump 8, and is supplied to the reactor 1 through the feed water pipe 9.

  During this time, the supply and condensate is heated in the low-pressure feed water heater 10 and the high-pressure feed water heater 11 by steam extracted from part of the exhaust from the high-pressure turbine 4 and the low-pressure turbine 5. At this time, the following coolant flows in the nuclear reactor 1. That is, as shown in FIG. 9, the coolant guided to the nuclear reactor 1 by the water supply pipe 9 passes through the lower plenum 24, and the entire amount thereof is heated by the core 25 and flows into the upper plenum 26 as steam. . The total amount of this steam flows out of the reactor 1 through the main steam pipe 2. As described above, the supercritical water cooling nuclear power plant is a once-through type system in which the entire amount of coolant entering the nuclear reactor flows out of the nuclear reactor.

Such a once-through supercritical water-cooled nuclear power plant requires a dedicated start-up system that is not found in conventional light water reactors (startup system). FIG. 8 shows a typical startup system configuration. When the output is low, the main steam switching valve 18 is closed, and the fluid at the reactor outlet is guided to the flash tank 22 through the main steam extraction pipe. Here, the fluid is separated into steam and water, and the steam is sent to the high-pressure turbine 4 through the main steam supply pipe 17 at the time of startup. The remaining drain water is sent to the condenser 6 through the flash tank drain line 23 and mixed with the condensed water of the turbine exhaust to become condensate. When the reactor power increases and the retained enthalpy of the reactor outlet fluid exceeds the retained enthalpy of the steam supplied from the flash tank 22, the main steam switching valve 18 is opened to supply the main steam directly from the reactor outlet. .
JP 2002-31694 A

  In the nuclear reactor having such a configuration, when an accident that trips the feed water pump 8 occurs, the operation speed of the feed water pump 8 is reduced in time according to its inertia, and the driving force of the coolant is also lowered accordingly. For this reason, the coolant flowing into the nuclear reactor 1 gradually decreases, and eventually its total flow rate is lost. Since the supercritical water-cooled nuclear power plant is a once-through system, this accident also eliminates the flow of the coolant that cools the core 24, and the cooling of the core 24 deteriorates.

  The conventional supercritical water cooling nuclear power plant has the following problems in the event of a feed water pump trip accident. That is, as described above, in the supercritical pressure water-cooled nuclear power plant, which is a once-through system, the feedwater pump is the driving source for the coolant flow in the reactor. The total amount of material flow can be lost, which can impair core fuel cooling.

As a safety measure at the time of this water supply pump trip, the following can be considered, for example.
(1) The reactor scram is activated by detecting a feed water pump trip, and the reactor output is quickly reduced.
(2) Detect the feed water pump trip and activate the alternative feed water system to secure the core coolant flow rate.
(3) The rate of decrease in the coolant flow rate is reduced by giving the water pump a large inertia.

  With the measures listed here, there is a technically unavoidable time delay in detecting feed pump trips, scram operation and alternative water system activation, so it is essential to give the water pump some degree of inertia. .

  10 and 11 show temporal changes in the coolant flow rate 51 of the core, the reactor thermal output 52, and the fuel cladding tube temperature 53 at the time of a feedwater pump trip accident. In these figures, it is assumed that the reactor scram and the alternative feed water system start up, but in FIG. 10, the feed water pump has sufficient inertia to compensate for the delay in the start time of the scram operation and the alternative feed water system. FIG. 11 shows a case where the inertia of the feed water pump is insufficient. That is, in FIG. 10, the coolant flow rate 51 in the core decreases relatively slowly after the feed water pump trip, whereas in FIG. 11, the coolant flow rate 51 in the core decreases rapidly after the feed water pump trip. As a result, the cladding tube surface temperature 53 is suppressed to a certain value in FIG. 10, but the cladding tube surface temperature 53 is rapidly increased in FIG. At this time, there is a high possibility that the integrity of the core will be impaired, such as melting of the fuel rods and damage to the cladding tube.

  In general, a nuclear power plant is required to have a higher output than a thermal power plant, but if the speed of the feed water pump increases as the scale of the plant increases and the coolant flow rate increases, Since coast-down time is shortened, more and more inertia is required. When large inertia is required beyond the enlargement of the feed pump for the existing supercritical pressure thermal power plant, it is necessary to add unnecessary equipment (emergency equipment) such as a flywheel during normal operation. , Increase the construction cost of the plant.

  Further, in the configuration of a typical starting system shown in FIG. 8, the drain water separated by the flash tank 22 flows directly into the condenser 6. Since the radioactive material contained in the coolant is likely to move to the water phase, a large amount of the radioactive material in the coolant is carried to the condenser 6 at the start-up, increasing the radiation dose around the condenser 6 and There is a risk of increasing the amount of exposure.

Accordingly, a first object of the present invention is to provide a supercritical water cooling nuclear power plant that can ensure cooling of core fuel in the event of a feedwater pump trip accident without adding emergency equipment such as a flywheel. It is.
A second object of the present invention is to provide a supercritical water cooling nuclear power plant that suppresses the transfer of radioactive material to a condenser.

  The present invention is directed to the above object, and the invention according to claim 1 is a reactor in which supercritical pressure water is used as a coolant, and steam obtained in the reactor is supplied through a main steam pipe. A turbine driven by the steam, a condenser for condensing steam discharged from the turbine to produce condensate, and a condensate pump for returning the condensate obtained by the condenser to the reactor And at least one first feed water heater disposed between the discharge side of the condensate pump and the nuclear reactor, wherein the condensate is heated by extraction from the turbine to produce feed water. A feed water heater and a second feed water heater disposed between the first feed water heater and the nuclear reactor, wherein the first feed water is extracted from a main steam extraction pipe branched from the main steam pipe. The second feed water heater for further heating the feed water from the feed water heater And a recirculation pump for returning drain water extracted from the main steam pipe exiting the second feed water heater to a nuclear reactor. .

  The invention according to claim 5 is a reactor using supercritical pressure water as a coolant, a turbine supplied with steam obtained in the reactor through a main steam pipe, and driven by the steam, A condenser for condensing steam discharged from the turbine to produce condensate, a condensate pump for returning the condensate obtained by the condenser to the reactor, and a discharge side of the condensate pump; A first feed water heater disposed between nuclear reactors, the first feed water heater configured to heat the condensate by extraction from the turbine to produce feed water; and the first feed water A supercritical pressure water-cooled nuclear power plant, comprising: a steam injector that feeds water supplied from the heater to the nuclear reactor driven by extraction from a main steam extraction pipe branched from the main steam pipe is there.

  The supercritical water-cooled nuclear power plant of the present invention has a coolant recirculation loop driven by a recirculation pump and a steam injector, and ensures the flow of coolant to the reactor core when a feedwater pump trip occurs. The core can be cooled. Moreover, the cost for constructing the recirculation loop can be kept low. Further, by using the feed water heater installed in the recirculation loop as part of the starting system, further cost reduction can be achieved. In addition, since radioactive contamination of the condenser can be suppressed, an increase in worker exposure can be suppressed. Therefore, according to the present invention, safety is improved without deteriorating the economic efficiency of the supercritical water cooling nuclear power plant.

  Embodiments of a supercritical water cooling nuclear power plant according to the present invention will be described below with reference to FIGS. Here, parts common or similar to those in the prior art are denoted by common reference numerals, and redundant description is omitted.

FIG. 1 is a conceptual diagram of a supercritical water cooling nuclear power plant according to a first embodiment of the present invention. The supercritical water cooling nuclear power plant according to the present embodiment is configured as follows. That is, between the high-pressure feed water heater 11 and the nuclear reactor 1, a feed water heater 14 is installed that uses steam extracted from the main steam pipe 2 through the main steam extraction pipe 13 as a heating source. The extracted steam after heating the feed water is condensed and becomes drain water of the feed water heater 14. The drain water is returned to the water supply pipe 9 by the recirculation pump 15 and supplied to the nuclear reactor 1 again.
The high-pressure feed water heater 11 normally has a three-stage configuration, but is reduced by one stage in the present embodiment. The feed water heater 14 performs the feed water heating function for one stage.

  With such a configuration, a coolant recirculation loop of reactor 1 → main steam pipe 2 → main steam extraction pipe 13 → feed water heater 14 → recirculation pump 15 → feed water pipe 9 → reactor 1 is formed. . Even in the event of a water supply pump trip accident, the coolant can be circulated to the core 24 as long as a recirculation loop using the recirculation pump 15 as a drive source exists. The number of high-pressure feed water heating stages is the same as before, but without adding emergency equipment such as flywheels to the feed water pump, the flow of coolant that can compensate for the delay in the operation of the scrum and the start-up delay in the alternative feed water system is reduced. This can be ensured by the recirculation loop of the embodiment.

  Further, the recirculation pump 15 has a capacity of about 10% of the core flow rate, and the lift is about the pressure difference between the reactor inlet and outlet (several tens to several hundred kPa), so compared with the feed water pump (100% flow rate, lift 27 MPa). , Significantly smaller. Therefore, the economical negative influence by adding the recirculation pump 15 is small.

  FIG. 2 is a conceptual diagram of a supercritical water cooling nuclear power plant according to the second embodiment of the present invention. The supercritical water cooling nuclear power plant according to the present embodiment is configured as follows. That is, in the configuration of FIG. 1, a feed water heater drain tank 16 for temporarily holding drain water from the feed water heater 14 is installed between the feed water heater 14 and the recirculation pump 15.

  Even if the feed water heater 14 does not function and the main steam is not condensed at the time of abnormality such as cooling water being held in the additional feed water heater drain tank 16 of the present embodiment and loss of the feed water flow rate, the inside of the drain tank 16 Since the cooling water can be sent to the reactor 1 by the recirculation pump 15, the core flow rate is secured. Since the drain tank 16 is a simple container, the increase in cost is small. Moreover, the plant safety is improved despite the small increase in cost.

  FIG. 3 is a conceptual diagram of a supercritical water cooling nuclear power plant according to the third embodiment of the present invention. The supercritical water cooling nuclear power plant according to the present embodiment is configured as follows. That is, in the configuration of FIG. 1, the feed water heater 14 is used as a flash tank that is a part of the start-up system necessary at the start-up. A flash tank is a device that boiles high-pressure high-temperature water by reducing the pressure below the saturation pressure for that temperature, and is used in thermal power plants and the like.

  The feed water heater 14 is a shell-and-tube type heat exchanger having a heat transfer tube and a cylinder that accommodates the heat transfer tube. Steam from the main steam extraction pipe 13 flows through the cylinder side, and water supply flows through the heat transfer pipe. It is configured as follows.

  When starting the supercritical water cooling nuclear power plant, first, the feed water pump 8 is used to boost the cooling water to the supercritical pressure. Thereafter, the control rod is pulled out and the cooling water is heated in the nuclear reactor 1. When the temperature of the cooling water is equal to or lower than the set temperature, the cooling water discharged from the reactor 1 is transferred to the reactor 1 through a recirculation loop (main steam extraction pipe 13, feed water heater 14, recirculation pump 15, feed water pipe 9). return. When the temperature reaches a set temperature (usually 280-290 ° C.) or higher, steam is generated by boiling under reduced pressure in the feed water heater 14 (functioning as the flash tank). By opening the main steam stop valve 3, the steam generated on the trunk side of the feed water heater 14 flows to the turbines 4 and 5 via the main steam supply pipe 17 at the time of startup, and the turbine is started. When the reactor outlet temperature reaches the rated temperature, the main steam switching valve 18 is opened to send the main steam directly to the turbines 4 and 5. The drain water of the feed water heater 14 generated by the boiling under reduced pressure is returned to the nuclear reactor 1 by the recirculation pump 15 and the feed water pipe 9.

  According to such a configuration, the function of the flash tank that has been conventionally installed only for activation can be provided by the feed water heater 14. In addition, the drain water in the flash tank that has conventionally flowed into the condenser 6 returns to the reactor 1, and the radioactivity contained in the drain water does not go to the condenser 6. Therefore, it is possible to prevent activation from flowing into the condenser 6 while rationalizing the startup device and improving the economic efficiency, thereby improving safety.

  FIG. 4 is a conceptual diagram of a supercritical water cooling nuclear power plant according to the fourth embodiment of the present invention. The supercritical water cooling nuclear power plant according to the present embodiment is configured as follows. That is, in the configuration of FIG. 3, the feed water heater 14 is disposed inside the storage container 19. With this arrangement, a coolant (water phase) containing radioactivity can be confined in the containment vessel 19. Therefore, it is not necessary to manage the turbine building including the condenser 6 as a radiation management area. There is no increase in worker exposure.

  FIG. 5 is a conceptual diagram of a supercritical water-cooled nuclear power plant according to the fifth embodiment of the present invention. The supercritical water cooling nuclear power plant according to the present embodiment is configured as follows. That is, in the configuration of FIG. 1, instead of the feed water heater 14 and the recirculation pump 15, a steam injector 20 that operates using the extraction steam from the main steam extraction pipe 13 as a drive source is installed, thereby heat exchange with the supply water As well as the driving force of the recirculation loop. Since the steam injector 20 is a static device, further improvement in reliability can be expected. Moreover, since the roles of the feed water heater 14 and the recirculation pump 15 can be performed by a single device, the economic efficiency can be expected.

  FIG. 6 is a conceptual diagram of a supercritical water-cooled nuclear power plant according to the sixth embodiment of the present invention. The supercritical water cooling nuclear power plant according to the present embodiment is configured as follows. That is, in the configuration of FIG. 5, the buffer tank 21 is installed between the high-pressure feed water heater 11 and the steam injector 20. By installing the buffer tank 21, the cooling water in the buffer tank 21 can be sent to the reactor by the steam injector 20 in the event of an abnormality such as a tripping of the water supply pump, so that the core flow rate is secured. Since the buffer tank 21 is a simple container, the increase in cost is small. Therefore, the plant safety is improved in spite of a small increase in cost.

1 is a schematic system diagram showing a first embodiment of a supercritical water cooling nuclear power plant according to the present invention. The schematic system diagram which shows 2nd Embodiment of the supercritical pressure water cooling nuclear power plant which concerns on this invention. The schematic system diagram which shows 3rd Embodiment of the supercritical pressure water cooling nuclear power plant which concerns on this invention. The schematic system diagram which shows 4th Embodiment of the supercritical pressure water cooling nuclear power plant which concerns on this invention. The schematic system diagram which shows 5th Embodiment of the supercritical pressure water cooling nuclear power plant which concerns on this invention. The schematic system diagram which shows 6th Embodiment of the supercritical pressure water cooling nuclear power plant which concerns on this invention. Schematic system diagram of a conventional supercritical water cooling nuclear power plant. FIG. 2 is a schematic sectional elevation view showing a conventional supercritical water reactor. The schematic system diagram including the starting system of the conventional supercritical water cooling nuclear power plant. The graph showing the time change of the main parameters at the time of the feed water pump trip accident when the inertia of a feed water pump is comparatively large in the conventional supercritical water cooling nuclear power plant. The graph showing the time change of the main parameter at the time of the feed water pump trip accident when the inertia of a feed water pump is comparatively small in the conventional supercritical water cooling nuclear power plant.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Main steam piping, 3 ... Main steam stop valve, 4 ... High pressure turbine, 5 ... Low pressure turbine, 6 ... Condenser, 7 ... Condensate pump, 8 ... Feed water pump, 9 ... Feed water piping, DESCRIPTION OF SYMBOLS 10 ... Low pressure feed water heater (2nd feed water heater), 11 ... High pressure feed water heater (2nd feed water heater), 12 ... Alternative feed water system pump, 13 ... Main steam extraction piping, 14 ... Feed water heater ( (First feed water heater), 15 ... recirculation pump, 16 ... additional feed water heater drain tank, 17 ... main steam supply pipe at startup, 18 ... main steam switching valve, 19 ... containment vessel, 20 ... steam injector, 21 ... buffer tank, 22 ... flash tank, 23 ... flash tank drain line, 24 ... lower reactor plenum, 25 ... reactor core, 26 ... upper reactor plenum.

Claims (6)

A reactor using supercritical pressure water as a coolant,
A turbine supplied with steam obtained in the nuclear reactor through a main steam pipe and driven by the steam;
A condenser for condensing steam discharged from the turbine to produce condensate;
A condensate pump for returning the condensate obtained in the condenser to the reactor;
At least one first feed water heater disposed between a discharge side of the condensate pump and a nuclear reactor, wherein the feed water is heated to extract the condensate by extraction from the turbine to produce feed water. And
A second feed water heater disposed between the first feed water heater and the reactor, wherein the first feed water heater is extracted by extraction from a main steam extraction pipe branched from the main steam pipe. A second feed water heater for further heating the feed water that has exited;
A recirculation pump for returning drain water from the main steam pipe exiting the second feed water heater to the reactor;
A supercritical water-cooled nuclear power plant characterized by comprising:   The supercritical pressure water-cooled nuclear power plant according to claim 1, wherein the drain water is temporarily held between the drain water outlet exiting the second feed water heater and the recirculation pump. A supercritical water cooling nuclear power plant characterized by further comprising a tank. In the supercritical water-cooled nuclear power plant according to claim 1,
The second feed water heater is a shell-and-tube type heat exchanger having a heat transfer tube and a body for housing the heat transfer tube,
The steam supplied to the second feed water heater through the main steam extraction pipe is configured to flow on the trunk side, and the feed water flows in the heat transfer pipe,
Start-up main steam supply pipe for returning at least a part of the steam that has entered the trunk side of the second feed water heater through the main steam extraction pipe to the downstream side of the branch point of the main steam extraction pipe of the main steam pipe When,
A main steam switching valve disposed between a branch point of the main steam pipe and the main steam extraction pipe and a confluence of the main steam supply pipe at start-up;
Further comprising
The trunk side of the second feed water heater is configured to function as a flash tank,
Supercritical pressure water cooled nuclear plant characterized by   The supercritical pressure water-cooled nuclear power plant according to claim 1, further comprising a containment vessel that accommodates the nuclear reactor, the second feed water heater, and a recirculation pump. plant. A reactor using supercritical pressure water as a coolant,
A turbine which is supplied with steam obtained in the reactor through a main steam pipe and is driven by the steam;
A condenser for condensing steam discharged from the turbine to produce condensate;
A condensate pump for returning the condensate obtained in the condenser to the reactor;
At least one first feed water heater disposed between a discharge side of the condensate pump and a nuclear reactor, wherein the feed water is heated to extract the condensate by extraction from the turbine to produce feed water. And
A steam injector that drives the feed water that has exited the first feed water heater by extraction from the main steam extraction pipe branched from the main steam pipe, and sends it to the reactor;
A supercritical water cooling nuclear power plant characterized by comprising: The supercritical pressure water-cooled nuclear power plant according to claim 5, further comprising a buffer tank that temporarily holds feed water between the first feed water heater and the steam injector. Pressure water cooled nuclear power plant.

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