JP2012255660A - Powerless reactor cooling system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powerless reactor cooling system in which a core can be cooled continuously until decay heat is reduced sufficiently and a reactor is automatically stopped perfectly even without power/fuel or human support from the outside.SOLUTION: A steam turbin 13 is operated by steam generated inside a reactor pressure vessel 1, the steam after operating the steam turbin 13 is heat-exchanged with external air and condensed by cooling means 14, and a condensed liquid is returned into the reactor pressure vessel 1 by a condensate liquid pump 16 driven by the steam turbin 13. The cooling means 14 includes a fin tube type heat exchange device 31 and a cooling tower 32 in a base isolation structure. The cooling tower 32 includes a plurality of legs 32a which are arranged in such a manner that a fluid can pass between the legs, and a tower body 32b which is supported at a predetermined height by the legs 32a. The tower body 32b includes the heat exchange device 31 in its lower part and a funnel 32c for exhausting heated external air above the heat exchange device 31.

Description

  The present invention relates to an unmanned and unpowered nuclear reactor cooling system for cooling a nuclear power plant nuclear reactor whose power supply from the outside is stopped.

The accident at the Fukushima Daiichi nuclear power plant that occurred in March 2011 overturned the theory that no serious nuclear accident would occur. Until now, it has been said that "the radioactive material produced by fission of uranium in a nuclear reactor is confined by five walls so as not to affect the outside of the power plant." In other words,
・ First wall: Hard pellets made of earthenware, baked and hardened uranium ・ Second wall: Durable metal fuel cladding tube containing the pellet ・ Third wall: Sturdy, fuel-filled Steel Reactor Pressure Vessel • Fourth Wall: Reactor containment vessel made of reinforced concrete with high-tightness steel lining containing the reactor pressure vessel and important equipment • Fifth Wall: It is a reactor building made of thick concrete that covers the outermost side. As you know, this “myth” was destroyed in the accident at the Fukushima Daiichi nuclear power plant. In the accident at the Fukushima Daiichi NPS, the reactor core was damaged, and a large amount of radioactivity was released to the atmosphere by blow-off of the core gas. Even in April 2011, one month after the accident, there was still a possibility of leaking water, and more than 400 tons of radioactive water was discharged into the environment every day.

  This accident was triggered by a long-term blackout due to the earthquake and tsunami, and the core collapsed due to the decay heat of the core. In other words, if a long-term blackout occurs, accidents at the Fukushima Daiichi nuclear power plant may occur at all nuclear power plants. For example, if for some reason the power transmission is stopped for a long time, or if a person becomes unable to approach the nuclear power plant due to large-scale radioactive contamination at the neighboring nuclear power plant, the supply of fuel and operating personnel to the emergency power generation facility is cut off. It was proved that nuclear reactors could easily be destroyed without natural disasters. In addition, in a nuclear power plant where multiple nuclear reactors are located, if one of the reactors is destroyed and high-contaminated radioactivity enters the environment, workers cannot enter the nuclear power plant for a long time. There is a possibility of core collapse in all other nuclear reactors.

  Conventional power generation facilities, such as thermal power plants, automatically shut down when equipment is damaged or when there are no operating personnel, and without further refueling, there is no further negative impact on the environment. However, nuclear power plants always have operating personnel, and all safety systems are designed on the assumption that power is supplied from the outside.

  Not only is external power supply indispensable for cold shutdown of a nuclear reactor, but core cooling over a long period of time is necessary to maintain it. When the reactor is stored as it is, the time until the core is not destroyed even if nothing is done is as long as 10 to 30 years after the reactor shutdown. In the meantime, it is highly conceivable that the power supplied to the reactor and operators will be lost due to a major disaster. The conventional nuclear reactor does not assume such a case. In other words, in order to collapse the nuclear reactor, it is only necessary to shut off the external power supply so that no one enters the nuclear reactor for more than one week. The Fukushima Daiichi NPS proved this through natural disasters such as earthquakes and tsunamis.

  A conventional nuclear power plant emergency core shutdown system operates as follows. When the nuclear reactor is brought to an emergency stop, first, control rods are inserted into the core to stop the fission reaction (criticality) of the fuel. Since this operation is driven by compressed gas, no external power is required. When the turbine is brought to an emergency stop, the decay heat of the fuel rods cannot be removed, so the emergency core cooling system (ECCS) is operated and boric acid water or the like is injected into the core to perform initial core cooling. Normally, the core is cooled using an external power source or a diesel emergency power source, and stabilized in a cold shutdown state where the core is 100 ° C. or lower. However, even after the cold shutdown, it is necessary to continue cooling the reactor with residual heat removal equipment using seawater, and external power is indispensable during that time.

  In the case of a boiling water nuclear power plant (BWR) such as the Fukushima Daiichi nuclear power plant, if the supply of power is stopped during an emergency shutdown of the reactor, the reactor isolation cooling facility is activated. This is to drive the turbine with high-pressure steam generated by decay heat, condense the drive steam in the suppression chamber, and cool the water in the suppression chamber by injecting it into the core with power from the turbine (for example, Patent Document 1). This system does not require an external power supply, but automatically stops because the steam does not condense when the water in the suppression chamber becomes hot. The reactor isolation cooling system is considered to be operable for about 10 hours to 2 days at Unit 2 of the Fukushima Daiichi Nuclear Power Station.

  In the case of a pressurized water reactor (PWR), if the supply of power is stopped during an emergency shutdown of the reactor, there is no cooling facility for isolating the reactor, so the residual heat removal facility (RHRS) is activated by the diesel emergency power source and the core Cool down.

JP 2005-172482 A

  Conventional nuclear power plant emergency core shutdown systems have a problem in that the cooling of the core stops when the supply of external power is stopped, and when the reactor isolation cooling facility and the diesel emergency power supply stop. When cooling of the core stops, the reactor becomes high temperature and high pressure due to decay heat, core steam is released from the safety valve to the environment, and further, water is depleted and the core melts. Existing reactors are premised on that even if the power is shut down, the power will be restored within about 10 hours and the residual heat removal equipment can be driven. An accident occurs.

  The present invention has been made paying attention to such a problem, and even if there is no external power, fuel, or human support, the decay heat is sufficiently reduced until the reactor automatically shuts down completely. The objective is to provide an unmanned and unpowered reactor cooling system that can keep cooling the core.

  In order to achieve the above object, an unmanned / unpowered reactor cooling system according to the present invention is an unmanned / unpowered reactor cooling system for cooling a nuclear power plant nuclear reactor whose power supply from outside is stopped. A steam turbine that is operated by steam generated inside the reactor pressure vessel, cooling means that heat-exchanges the steam after operating the steam turbine with outside air and condenses, and is driven by the steam turbine. And a condensate pump for returning the liquid condensed by the cooling means to the inside of the reactor pressure vessel.

  The unmanned / unpowered reactor cooling system according to the present invention is preferably configured to operate when the external power supply is stopped and the reactor isolation cooling facility or the diesel emergency power supply is stopped. The unmanned / unpowered reactor cooling system according to the present invention cools and condenses the steam generated inside the reactor pressure vessel by heat exchange with the outside air by the cooling means, and condenses the condensed liquid in the reactor pressure vessel. By returning to the inside, the reactor core can be cooled. By maintaining a cooling cycle in which the steam generated inside the reactor pressure vessel is cooled by outside air and returned, the core can be continuously cooled. Air is used for cooling, and seawater is not used.

  The unmanned / unpowered reactor cooling system according to the present invention can drive a condensate pump that returns the liquid condensed by the cooling means to the inside of the reactor pressure vessel by a steam turbine, so that power supply from the outside and Even without an emergency power source, the cooling cycle can be maintained, and the core can be continuously cooled. Further, since the cooling cycle is maintained without any human operation, the core can be continuously cooled. The cooling cycle can be maintained until the reactor core is sufficiently cooled and no steam is generated inside the reactor pressure vessel, and the reactor core can be cooled unattended until the reactor is automatically shut down completely. . As described above, the unmanned / unpowered reactor cooling system according to the present invention is used until the decay heat is sufficiently reduced and the reactor is automatically completely stopped even without external power, fuel, and human support. During this time, the core can continue to be cooled.

  In the unmanned / unpowered reactor cooling system according to the present invention, the cooling means for cooling the steam by exchanging heat with the outside air can be configured with a relatively simple structure. It is difficult to cool the steam stably for a long time.

  In the unmanned / unpowered reactor cooling system according to the present invention, the steam turbine includes a high-pressure turbine that operates when a heat generation amount inside the reactor pressure vessel is larger than a predetermined heat generation amount, and the reactor pressure vessel And a condensate pump having a high-pressure pump driven by the high-pressure turbine and a low-pressure pump driven by the low-pressure turbine. It is preferable.

  In this case, since the steam turbine is used in a range in which the calorific value inside the reactor pressure vessel changes greatly from the start of operation until the reactor core is cooled and the reactor automatically stops completely, the calorific value The condensate pump can be driven efficiently by dividing into a high-pressure turbine that operates efficiently when the heat generation amount is large and a low-pressure turbine that operates efficiently when the heat generation amount is small. Further, by dividing the condensate pump into a high-pressure pump and a low-pressure pump according to the capabilities of the high-pressure turbine and the low-pressure turbine, respectively, the condensed liquid can be efficiently returned to the inside of the reactor pressure vessel. Note that the steam turbine and the condensate pump may each be composed of three or more turbines and pumps according to the amount of heat generated inside the reactor pressure vessel.

  The unmanned / unpowered reactor cooling system according to the present invention preferably includes a solar power generation device provided so that the condensate pump can be driven when the steam turbine stops operating. In this case, even when the steam turbine stops operating for some reason, the condensate pump can be driven by the solar power generation device, and the core can be continuously cooled. Further, even when the amount of heat generated inside the reactor pressure vessel decreases and the steam turbine stops operating, the core can be continuously cooled until the reactor is completely stopped. As a result, the risk of core melting can be avoided, and safety can be improved.

  An unmanned and unpowered reactor cooling system according to the present invention is disposed at a position higher than the reactor pressure vessel, and is driven when the steam turbine stops operating, and generates steam generated inside the reactor pressure vessel. It is preferable to have a thermosiphon cooling device configured to exchange heat with outside air to condense and return the condensed liquid to the inside of the reactor pressure vessel. In this case, even when the steam turbine or the condensate pump is stopped for some reason, the core can be continuously cooled by the thermosiphon cooling device. In addition, even when the steam turbine or condensate pump stops operating due to a decrease in the amount of heat generated inside the reactor pressure vessel or a failure of the cooling means, the core is cooled until the reactor stops completely. You can continue. As a result, the risk of core melting can be avoided, and safety can be improved.

  In the unmanned / unpowered reactor cooling system according to the present invention, the cooling means includes a heat exchange device and a cooling tower, and the heat exchange device includes a plurality of conduits through which the steam passes, and an outer surface of each conduit. And fins provided to increase the area in contact with the outside air, and the cooling tower is a seismic isolation structure, and a plurality of legs that are spaced apart from each other so that fluid can pass between each other And a tower main body supported at a predetermined height from the installation surface by each leg, the tower main body having the heat exchange device disposed in a lower portion thereof, and the steam and heat above the heat exchange device. You may have the chimney part for discharging | emitting the external air warmed by exchange.

  In this case, since the cooling tower has a seismic isolation structure, damage due to the earthquake can be prevented. Each leg is spaced from each other so that fluid can pass between each other, and the tower body is supported by each leg at a predetermined height from the installation surface. This can prevent damage to the tower body and heat exchanger due to the tsunami. The tower body is preferably arranged at a position higher than the height at which the tsunami reaches. In addition, a water-permeable and breathable protective fence is provided to prevent debris and the like by passing fluid around each leg in order to prevent rubble and the like washed away by the tsunami from hitting each leg. It is preferable to be provided.

  Also, in this case, since the outside air heated by exchanging heat with steam in the heat exchange device rises and is discharged through the chimney, new outside air for cooling can be sucked into the heat exchange device, Cooling efficiency can be increased. The cooling efficiency can be further enhanced by the fins provided in the heat exchange device. In the heat exchange device, it is preferable that each conduit is arranged so that the vapor flows from the top to the bottom so that the condensed liquid can be efficiently collected. The heat exchange device preferably has a pressure sensor and a shut-off valve for blocking steam from entering the conduit when leakage or blockage occurs in the conduit. The heat exchange device is an air-cooled cooling facility using natural convection and has a feature that does not require external power such as a blower or coolant such as seawater.

  The unmanned / unpowered reactor cooling system according to the present invention includes the reactor pressure vessel and the nuclear power generator turbine so as to guide the steam generated inside the reactor pressure vessel to the cooling means through the steam turbine. A steam pipe connected in the middle of the pipe connecting the pipe, a condensing pipe provided to guide the liquid condensed by the cooling means to the inside of the reactor pressure vessel, and a steam turbine capable of generating electricity. Generator, a battery for storing electricity generated by the generator, and the steam pipe, and when the inside of the reactor pressure vessel exceeds a predetermined temperature, the steam is guided to the steam pipe. You may have the comprised branch valve.

  In this case, surplus electricity other than the electric power for driving the condensate pump can be stored in the battery. The electricity stored in the battery can be used as a power source for the reactor control room, various sensors and controllers. In addition, after the power supply from the outside was stopped, and the reactor isolation cooling facility and the diesel emergency power supply were stopped, the temperature inside the reactor pressure vessel rose due to the decay heat of the core and exceeded the predetermined temperature. When the steam inside the reactor pressure vessel is guided to the steam pipe by the branch valve, the steam turbine, the cooling means, etc. can be automatically operated to cool the core.

  According to the present invention, even if there is no external power, fuel, or human assistance, it is possible to continue cooling the core until the decay heat is sufficiently reduced and the reactor is automatically completely shut down. -A powerless reactor cooling system can be provided.

1 is a side view showing an overall configuration of an unmanned / unpowered reactor cooling system according to a first embodiment of the present invention. It is a graph which shows the decay | disintegration heat of the core after a nuclear reactor shutdown, and the time change of the accumulated energy. It is a block diagram which shows the isolation machine room of the unmanned unpowered reactor cooling system shown in FIG. It is a side view which shows the cooling means of the unmanned unpowered reactor cooling system shown in FIG. It is the (a) front view and (b) side view which show the heat exchange apparatus of the unmanned unpowered reactor cooling system shown in FIG. It is a side view which shows the thermosiphon type cooling device of the unmanned unpowered reactor cooling system shown in FIG. It is a perspective view which shows the non-powered heat exchanger of the unmanned and non-powered reactor cooling system shown in FIG. It is a side view which shows the whole structure of the unmanned and unpowered reactor cooling system of the 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 7 show an unmanned and unpowered reactor cooling system according to a first embodiment of the present invention.
As shown in FIG. 1, an unmanned / unpowered reactor cooling system 10 is an unmanned / unpowered reactor cooling system for cooling a nuclear reactor of a boiling water nuclear power plant (BWR) in which power supply from the outside is stopped. It is. The unmanned / powerless reactor cooling system 10 includes a steam pipe 11, a branch valve 12, a steam turbine 13, a cooling means 14, a condensing pipe 15, a condensate pump 16, a generator 17, a battery 18, a solar power generation device 19, and a thermostat. A siphon type cooling device 20 and a control unit 21 are provided.

  FIG. 2 shows an estimated amount of decay heat released from the core after the Fukushima Daiichi NPS No. 2 (electric power output 784 MW), which is a BWR, is stopped, and its accumulated energy. As shown in FIG. 2, since the reactor isolation cooling facility operates for about 10 hours immediately after an emergency stop, the unmanned / unpowered reactor cooling system 10 needs to cool the heat dissipation amount of 15 MW after about 10 hours. . Further, the decay heat after 10 years is 100 kW, and after 30 years it is 30 kW. Therefore, it is necessary to operate with such a small amount of heat. In other words, the unmanned / unpowered reactor cooling system 10 is a reliable system that handles heat from low power 10 to 30 years later, from high output immediately after shutdown of the reactor isolation cooling facility, and operates unattended. There must be. In the meantime, it is necessary to operate without external power or fuel supply.

  As shown in FIG. 1, the steam pipe 11 is provided in the middle of a main steam pipe 3 that connects a reactor pressure vessel 1 housed in a containment vessel in a reactor building and a nuclear power generator turbine 2 in the turbine building. It is connected. The steam pipe 11 is provided to guide the steam generated inside the reactor pressure vessel 1 to the cooling means 14 through the steam turbine 13.

  The branch valve 12 is provided in the steam pipe 11 at a position close to the main steam pipe 3 connecting the reactor pressure vessel 1 and the nuclear power generator turbine 2. The branch valve 12 is configured to open the inlet of the steam pipe 11 and guide the steam inside the reactor pressure container 1 to the steam pipe 11 when the inside of the reactor pressure container 1 exceeds 200 ° C.

  The steam turbine 13 is configured to operate with steam generated inside the reactor pressure vessel 1 and passing through the steam pipe 11. As shown in FIG. 3, the steam turbine 13 includes a high-pressure turbine 13a that operates when the amount of heat generated in the reactor pressure vessel 1 is greater than 1 MW, and the amount of heat generated in the reactor pressure vessel 1 is less than 1 MW. And a low-pressure turbine 13b operating in The high pressure turbine 13 a and the low pressure turbine 13 b are connected to the steam pipe 11 in parallel. The high-pressure turbine 13a is preferably made of the same specifications as the reactor isolation cooling equipment turbine.

  In the steam turbine 13, when the amount of heat generated in the reactor pressure vessel 1 is reduced to 1 MW, the valve is automatically switched so that the steam that has flowed to the high-pressure turbine 13a flows to the low-pressure turbine 13b. In the example shown in FIG. 2, about one year after the emergency stop, the high pressure turbine 13a is switched to the low pressure turbine 13b. In addition, the low-pressure turbine 13b needs to operate for about 10 years without repair until the amount of heat generated in the reactor pressure vessel 1 reaches about 100 kW. The high-pressure turbine 13a and the low-pressure turbine 13b are preferably configured to give priority to robustness and reliability capable of non-repair operation rather than efficiency.

  As shown in FIGS. 1 and 4, the cooling means 14 includes a heat exchange device 31 and a cooling tower 32. As shown in FIG. 5, the heat exchanging device 31 includes a fin-tube heat exchanger, and is provided on a plurality of conduits 31 a through which steam passes, and on the outer surface of each conduit 31 a in order to increase the area in contact with the outside air. And fins 31b. In a specific example shown in FIG. 5, the heat exchange device 31 is configured as a unit having 1 × 2 m flat fins 31 b arranged at a pitch of 30 mm, a ventilation cross section of 2 × 2 m, and 6 steps and a height of about 7 m. ing. The fin 31b is made of a galvanized steel plate or a galvalume steel plate and has a thickness of 1 mm. In consideration of strength and external impact, the lowermost and uppermost fins 31b have a thickness of 3 mm. The fin 31b may be made of aluminum in consideration of thermal characteristics and weight, but aluminum is considered to be more suitable because it burns in a large-scale fire. Each conduit 31a passing through the fin 31b has a diameter of 30 mm.

  Further, the heat exchange device 31 has a steam header 31c and a condensate header 31d. The heat exchanger 31 is connected to a steam header 31c disposed at the upper end of each conduit 31a and a condensate header 31d disposed at the lower end of each conduit 31a. In the heat exchange device 31, the steam header 31 c is connected to the steam pipe 11, and the condensate header 31 d is connected to the condensing pipe 15. The heat exchanging device 31 introduces the steam after operating the steam turbine 13 from the steam pipe 11 to the steam header 31c, branches it to each conduit 31a, and flows it from the top to the bottom. It is designed to condense by heat exchange. Further, the heat exchange device 31 collects the condensed liquid in the condensate header 31 d and guides it to the condensing pipe 15.

  Moreover, the heat exchange apparatus 31 is comprised from several units by making the some conduit | pipe 31a into one unit, and has the pressure sensor 31e and the cutoff valve 31f for every unit. When a leak or blockage occurs in the conduit 31a in a unit, the heat exchange device 31 senses an abnormality in the pressure of the conduit 31a, and the shutoff valve 31f blocks the entry of steam into the unit. It has become. Since decay heat decreases with the passage of time, it is considered that it is not necessary to pass steam through all the conduits 31a in the later stage of cooling. Therefore, according to the decrease in steam, several conduits 31a are connected by shutoff valves 31f. It may be configured to block.

  As shown in FIG. 4, the cooling tower 32 is installed on the base of a base isolation structure, and has a plurality of legs 32a and a tower body 32b. The legs 32a are arranged at intervals from each other so that fluid can pass between them. The tower body 32b is supported at a predetermined height from the installation surface by each leg portion 32a. The tower main body 32b is provided with a heat exchanging device 31 at the lower portion, and has a chimney portion 32c above the heat exchanging device 31 for exhausting outside air heated by exchanging heat with steam by a chimney effect. The tower body 32b is installed at a position higher than the height that the tsunami is supposed to reach so as to prevent damage to the heat exchange device 31 due to the tsunami. In the example shown in FIG. 4, it is installed so that the air intake at the lower part of the heat exchange device 31 is approximately 10 m above the ground. The chimney 32c has a height of approximately 30 m from the top of the heat exchange device 31.

  The cooling tower 32 is provided with a protective fence 32d around the legs 32a for preventing debris and the like from passing around the legs 32a so as to prevent the rubble and the like washed away by the tsunami from hitting the legs 32a and being damaged. Yes. In the cooling tower 32, protective fences 32 d for protecting the heat exchanging device 31 from scattered matter, falling objects, and the like are also installed at the upper and lower portions of the heat exchanging device 31. Further, the cooling tower 32 has a radioactive gas purification device 32e that purges the non-condensable gas contained in the vapor, purifies the radioactivity, and releases it to the atmosphere.

  In addition, it is preferable that the cooling means 14 has the intensity | strength which can be used without repair for 30 years, and can also endure an earthquake, the scattered matter from the outside, etc. It is preferable that the heat exchange device 31 is designed with a sufficient size. Since the heat exchange device 31 expands and contracts depending on the temperature, it is preferable that the heat exchange device 31 is installed with a sufficient gap in the vertical direction.

  As shown in FIG. 1, the condensing pipe 15 connects the condensate header 31 d of the heat exchange device 31 and the reactor pressure vessel 1 so as to guide the liquid condensed by the cooling means 14 to the inside of the reactor pressure vessel 1. Is provided. The steam pipe 11 and the condensing pipe 15 have a structure that can cope with the shaking of the cooling tower 32 due to an earthquake or the like at a connection point with the cooling means 14.

  As shown in FIGS. 1 and 3, the condensate pump 16 is provided in the middle of the condensing pipe 15 and is driven by the steam turbine 13 to return the liquid condensed by the cooling means 14 to the inside of the reactor pressure vessel 1. It is configured as follows. The condensate pump 16 has a large high-pressure pump 16a driven by the high-pressure turbine 13a and a small low-pressure pump 16b having a small flow rate driven by the low-pressure turbine 13b. The high pressure pump 16 a and the low pressure pump 16 b are connected to the condensing pipe 15 in parallel. Note that the high-pressure pump 16a and the low-pressure pump 16b preferably have a configuration that prioritizes robustness and reliability capable of non-repair operation over efficiency. Moreover, since the high pressure pump 16a and the low pressure pump 16b have a low pressure in the inlet environment and easily generate cavitation, it is preferable to devise an inducer or the like.

  The generator 17 is configured to be capable of generating power by the steam turbine 13, and includes a high-pressure generator 17a connected from the high-pressure turbine 13a via the high-pressure pump 16a, and a low-pressure generator 17b connected to the low-pressure turbine 13b. Yes. The battery 18 is connected to the high voltage generator 17a and the low voltage generator 17b, and is configured to store electricity generated by the high voltage generator 17a and the low voltage generator 17b. The low pressure pump 16b is driven by electricity generated by the low pressure generator 17b by the low pressure turbine 13b and stored in the battery 18. The battery 18 stores surplus electricity other than the electric power for driving the low-pressure pump 16b, and can be used as a power source for the reactor central control room 4, the radioactive gas purification device 32e, various sensors, a controller, and the like.

  As shown in FIGS. 1 and 3, the steam turbine 13, the condensate pump 16, the generator 17, and the battery 18 are robust sealed containers that can withstand earthquakes, tsunamis, scattered matters from the outside, and the like. It is preferable to be stored in the isolation machine room 22 and to be arranged underground. In this case, it is preferable that the steam pipe 11 and the condensing pipe 15 have a flexible structure in which a portion arranged in the basement can mitigate vibration caused by an earthquake. In addition, in order to prevent the isolated machine room 22 from becoming hot due to steam from the core, frictional heat from the steam turbine 13 and the condensate pump 16, etc., a heat pipe 22a etc. is installed in the ground to keep the room at a constant temperature. Is preferably maintained. The control of the various valves is preferably basically pressure control while avoiding the use of electronic / electrically driven parts with low long-term reliability. When the heat generation amount of the core decreases, condensation may occur in the steam pipe 11 and clogging may occur. Therefore, a bypass line 23 that allows only liquid to pass is provided between the outlet of the low-pressure turbine 13b and the inlet of the low-pressure pump 16b. It is preferable.

  As shown in FIG. 1 and FIG. 3, the solar power generation device 19 is provided with a solar cell panel attached to the south surface of the cooling tower 32, and the battery 18 can be charged with the generated power. The solar cell panel is preferably installed in a sufficient area so that it can perform its function even on a cloudy day. The solar power generation device 19 can drive the condensate pump 16 via the battery 18 even when the operation of the steam turbine 13 is stopped.

  As shown in FIGS. 1 and 6, the thermosiphon cooling device 20 is disposed on the roof of the reactor building, which is higher than the reactor pressure vessel 1. As shown in FIG. 6, the thermosiphon cooling device 20 includes a steam pipe 33 branched from a main steam pipe 3 that connects a reactor pressure vessel 1 and a nuclear power generator turbine 2, and each non-powered heat exchanger. Distributor 34, shutoff valve 35, steam check valve 36, pressure gauge 37, non-powered heat exchanger 38, condensed water check valve 39, shutoff valve 40, condensed water dispersed in 38. It has a collection pipe 41 and a pipe 42 connected to the reactor pressure vessel 1. Further, a vacuum pump pipe 43 branched from the main steam pipe 3 connecting the reactor pressure vessel 1 and the nuclear power generator turbine 2, a small vacuum pump 44, a radiation removal filter 45, and an exhaust chimney 46 are provided. is doing.

  As shown in FIG. 7, the non-powered heat exchanger 38 includes a natural convection fin 38a and a condensing pipe 38b welded to the natural convection fin 38a. The non-powered heat exchanger 38 is made of iron (made of steel), and is subjected to anticorrosion treatment by galvanized plating and paint. The non-powered heat exchanger 38 is preferably coated with a white paint so as to prevent overheating due to sunlight and easily recognize rust. The non-powered heat exchanger 38 is expected to be pierced by corrosion during operation. For this reason, the non-powered heat exchanger 38 is temporarily shut off by the shut-off valve 35 for what seems to have been corroded by the pressure gauge 37, and is permanently shut off after confirming an increase in pressure. ing.

  The thermosyphon cooling device 20 is driven when the operation of the steam turbine 13 is stopped, and the steam generated inside the reactor pressure vessel 1 is condensed by exchanging heat with the outside air by the non-powered heat exchanger 38. The liquid is returned to the inside of the reactor pressure vessel 1 by gravity. The thermosiphon cooling device 20 operates as follows. First, the boiling point of the cooling water of the fuel rod is set to a maximum of 80 ° C. (vapor pressure 0.5 atm (absolute pressure)), and the inside of the steam pipe 33 is always kept at a negative pressure. The steam emitted from the steam pipe 33 is branched to each zero-gravity heat exchanger 38, condensed by a condensing pipe 38b with natural convection fins 38a, and returned to water. The water is collected by the condensed water collecting pipe 41 and flows into the core using gravity. Note that the thermosiphon cooling device 20 may be configured to cool the fuel in the spent fuel pool without power and keep the cold state.

  Further, the thermosyphon cooling device 20 is configured to always exhaust non-condensable gas generated by nuclear reaction or leakage in the core through the radiation removal filter 45 by the vacuum pump 44 from the exhaust chimney 46. From the exhausted gas, iodine, cesium, and other radioactive substances are removed. In addition, it is thought that generation | occurrence | production of hydrogen by a radiation is very small when the thermosiphon type cooling device 20 operates. In the thermosiphon cooling device 20, a vacuum pump 44, a pressure gauge 37, and a shut-off valve 35 are operated by a battery 18. In addition, the thermosiphon cooling device 20 except that the non-condensable gas accumulated therein is sometimes vented by the vacuum pump 44, and the pressure is monitored to close the leaky non-powered heat exchanger 38. Does not require external energy.

  In a specific example shown in FIG. 7, the non-powered heat exchanger 38 has a size of about 5 × 5 × 5 m, a weight of about 37 tons, a natural convection fin 38 a having a thickness of 1 mm and an area of 5 × 3 m. And a condensing pipe 38b formed by welding 50 mm pipes to natural convection fins 38a at intervals of 360 mm. In this case, the exchange heat quantity of the non-powered heat exchanger 38 is obtained as follows.

The condensation temperature is set as T _w = 80 ° C. The natural convection fin 38a is approximated as a parallel plate channel having a thickness b = 50 mm, a height H = 3 m, and a width W = 5 m. The number of fins is n = 100. It is assumed that the interval between the condensing pipes 38b is P = 360 mm, and a substantially similar heat transfer coefficient is exhibited even in a rectangular channel. The average heat transfer coefficient of the isothermal vertical parallel plate channel is estimated to be h = 3.10.

The natural convection fin 38a is a fin having a fin height P / 4. When the thermal conductivity of steel is k = 42.8 W / mK, the periphery of the fin is 2H, and the fin thickness is t = 1 mm, the fin efficiency is 0.73. Therefore, the exchange heat quantity Q _s of one unit of the non-powered heat exchanger 38 is
It becomes. That is, a single non-powered heat exchanger 38 can remove heat of 272 kW. As shown in FIG. 2, Fukushima Daiichi Nuclear Power Station Unit 2 has a core calorific value of about 100 kW and a condensed water amount of 0.05 liter / s in 10 years after the reactor shutdown. For this reason, even if it is assumed that the steam turbine 13 stops operating after 10 years and the zero gravity heat exchanger operates, the core can be cooled if two or three units are installed with a margin.

  As shown in FIGS. 1 and 3, the control unit 21 is accommodated in a completely sealed container independent of the isolation machine room 22, and is disposed underground. The control unit 21 can be driven by an external power source, the battery 18 of the isolation machine room 22, and the solar power generation device 19, and has a backup power source, and finally drives for a certain time even when all the power sources are cut off. It is configured to The control unit 21 includes a communication system for wirelessly transmitting various measuring instruments and their data, a wired communication system for transmitting driving signals for valves and the like, and manual operation, and a control computer. The control unit 21 can automatically execute a final shutdown sequence when all the functions of the cooling system are stopped 30 years after the reactor shutdown.

The unmanned / powerless reactor cooling system 10 operates as follows.
If the reactor is shut down for some reason, the control rod will go up and the criticality will stop. When the main steam pipe 3 connecting the core and the turbine 2 for nuclear power generator and the water supply pipe are cut off and electric power is obtained from the outside or when the emergency power supply is operating, the emergency core cooling device is activated and the emergency Cool down. Furthermore, the seawater from the outside is circulated in the heat exchanger in the residual heat removal facility, and the core is cooled by exchanging heat with the core water. When power is not available, the reactor isolation cooling system is activated to cool the core until the water in the pressure control chamber becomes hot and saturated. After the cooling of the reactor core is stopped, the unmanned / unpowered reactor cooling system 10 is activated.

  In the example shown in FIG. 2, the decay heat after 10 hours of critical shutdown is about 15 MW. Therefore, the unmanned / unpowered reactor cooling system 10 has a maximum cooling capacity of 30 MW with a margin. Is preferred. If the emergency power supply is interrupted while the reactor isolation cooling system is operating, a part of the steam is drawn from the main steam pipe 3 into the steam turbine 13 of the unmanned / unpowered reactor cooling system 10 by bypass. It is also possible to secure electric power in the main reactor central control room 4 by generating power.

  The core temperature immediately after the reactor isolation cooling facility is shut down is estimated to be about 100 ° C. at the saturation temperature of the suppression chamber, but then the pressure rises due to decay heat and rises to 200 ° C. and 15 atm. At that time, the branch valve 12 branched from one system of the main steam pipe 3 is opened, and the steam flows into the steam pipe 11. When the unmanned / powerless reactor cooling system 10 is not operating, the steam pipe 11 and the condensation pipe 15 are filled with nitrogen of 1 atm (absolute pressure) or more so that no explosion occurs even when steam containing hydrogen flows in. Take measures. In addition, since the initial steam contains a relatively large amount of radioactivity and hydrogen, the upper part of the cooling tower 32 is provided with an initial radioactive gas removing device in addition to the radioactive gas purifying device 32e, and hydrogen explosion occurs. It is preferable not to get up.

  The steam that has flowed into the steam pipe 11 drives the high-pressure turbine 13 a and flows into the heat exchange device 31 of the cooling means 14. At this time, the temperature of the steam is set to be lowered to about 150 ° C. by adiabatic expansion in the high-pressure turbine 13a. In this process, a maximum turbine output of 5 MW is obtained. The steam that has flowed into the cooling means 14 is condensed by exchanging heat with air through the conduit 31a of the fin-tube heat exchanger 31. The air heated by the steam obtains buoyancy in the cooling tower 32 and is discharged outside. The air at the inlet of the heat exchange device 31 is sucked by the buoyancy. That is, the cooling tower 32 becomes a chimney and introduces cooling air.

  When the inlet air temperature is 40 ° C., the condensation temperature of the conduit 31a is 150 ° C. (4.5 atm), and the average temperature of the fins 31b is 100 ° C., the heat dissipation amount per unit of the fin 31b shown in FIG. Therefore, approximately 25 units are required to absorb 30 MW of heat. At this time, the inlet diameter of the heat exchange device 31 is about 12 m.

  The condensed water is returned to the core through one system of the main water supply pipe by a high-pressure pump 16a directly connected to the high-pressure turbine 13a. The flow rate of water at the beginning of operation is about 14 liters / second. Since the power for feeding the condensed water is about 30 kW, the output of the high-pressure turbine 13a has a sufficient margin. The generator 17 is rotated by the surplus energy, and can be used to charge the battery 18 of the isolation machine room 22 and the battery of the control unit 21 and to secure the power source of the reactor central control room 4, thereby maintaining the soundness of the system. be able to. While the high-pressure turbine 13a is operating, the turbine inlet pressure is kept at 15 atm and operated. One year later, when the heating value of the core decreases to about 1 MW, the steam flow path is switched to the low-pressure turbine 13b.

  The flow rate of the condensed water when switched to the low-pressure turbine 13b is 0.5 liter / second. The set pressure of the low-pressure turbine 13b is set to 2 atm at 120 ° C. The reason why the vapor pressure is always set higher than the atmospheric pressure is to prevent hydrogen explosion due to air entering the core. Further, the performance of the heat exchange device 31 is maintained by continuously taking out the non-condensed gas with the vacuum pump and the radioactive gas purification device 32e installed at the upper part of the cooling tower 32. The low-pressure generator 17b connected to the low-pressure turbine 13b is connected to the battery 18 and drives a small low-pressure pump 16b with the electric power to inject condensed water into the reactor. At this stage, power is not supplied to the reactor central control room 4 or the like. The water lost in these processes is supplied from the reactor water tank to the reactor core. The low-pressure turbine 13b is operated until 10 years after the core heating value reaches 100 kW. In the latter half of the period, the steam does not reach the heat exchanging device 31 and condenses, so the condensed water is supplied to the low pressure pump 16 b through the bypass line 23.

  After that, in the case of independent operation, the battery 18 is charged by the solar power generation device 19 installed in the cooling tower 32, and the core water injection is continued by the low-pressure pump 16b. When the low-pressure pump 16b stops operating, the core cooling is continued by the thermosiphon cooling device 20 installed above the reactor. When the reactor core calorific value is reduced to 30 kW after 30 years and the reactor is automatically shut down, all valves are closed and fuel rods are taken out or the reactor building is completely closed. This shut-out sequence is executed by the control unit 21 using the power of the battery 18.

  The above process is the worst case scenario assumed when there are no workers for 10 or 30 years. In practice, maintenance inspection is often performed during the operation process. Moreover, if the power supply is restored, the original core cooling equipment can be operated.

  In this way, the unmanned / unpowered reactor cooling system 10 cools and condenses the steam generated inside the reactor pressure vessel 1 through heat exchange with the outside air by the cooling means 14 and condenses the condensed liquid. By returning to the inside of the pressure vessel 1, the core of the nuclear reactor can be cooled. By maintaining a cooling cycle in which the steam generated in the reactor pressure vessel 1 is cooled by outside air and returned, the core can be continuously cooled.

  The unmanned / unpowered reactor cooling system 10 can drive the condensate pump 16 that returns the liquid condensed by the cooling means 14 to the inside of the reactor pressure vessel 1 by the steam turbine 13. Even without an emergency power source, the cooling cycle can be maintained and the core can be continuously cooled. Further, since the cooling cycle is maintained without any human operation, the core can be continuously cooled. The cooling cycle can be maintained until the core is sufficiently cooled and no steam is generated inside the reactor pressure vessel 1, and the core can continue to be cooled until the reactor is automatically completely shut down. In this way, the unmanned / unpowered reactor cooling system 10 is capable of reducing the decay heat and reducing the atomic energy without the need for external power, fuel, or human assistance if the main equipment of the reactor is operating. The core can continue to cool until the furnace is automatically shut down. The unmanned / powerless reactor cooling system 10 can be installed not only in a newly installed reactor but also in an existing reactor.

  The unmanned / powerless reactor cooling system 10 is a steam turbine in a range in which the amount of heat generated inside the reactor pressure vessel 1 changes greatly from the start of operation until the reactor core is cooled and the reactor is automatically completely stopped. 13 is used, the condensate pump is divided by dividing the steam turbine 13 into a high-pressure turbine 13a that operates efficiently when the calorific value is large and a low-pressure turbine 13b that operates efficiently when the calorific value is small. 16 can be driven efficiently. Further, by dividing the condensate pump 16 into the high pressure pump 16a and the low pressure pump 16b according to the capabilities of the high pressure turbine 13a and the low pressure turbine 13b, the condensed liquid can be efficiently returned to the inside of the reactor pressure vessel 1. Can do.

  In the unmanned / powerless reactor cooling system 10, the cooling means 14 that cools the steam by exchanging heat with the outside air can be configured with a relatively simple structure, so that the cooling means 14 is not easily damaged or broken down. It is possible to cool the steam stably for a long time. Since the cooling tower 32 has a seismic isolation structure, damage due to the earthquake can be prevented. Since each leg part 32a is arrange | positioned mutually spaced apart so that a fluid can pass between each other, and the tower main body 32b is supported by the predetermined height from the installation surface by each leg part 32a, each leg part 32a. A tsunami flows between them, and damage to the tower body 32b and the heat exchange device 31 due to the tsunami can be prevented. Moreover, since the outside air heated by exchanging heat with steam in the heat exchange device 31 rises and is discharged through the chimney 32c, new outside air for cooling can be sucked into the heat exchange device 31, Cooling efficiency can be increased. Thus, the heat exchange device 31 can cause natural convection by the heat of condensation of steam and cool the core, and is effective for long-term decay heat removal without power.

  The unmanned / powerless reactor cooling system 10 can drive the condensate pump 16 by the solar power generator 19 even when the steam turbine 13 stops operating for some reason, and continues to cool the core without power. be able to. Further, even when the amount of heat generated inside the reactor pressure vessel 1 decreases and the steam turbine 13 stops operating, the solar core can be continuously cooled by the solar power generator 19 until the reactor is completely stopped. As a result, the risk of core melting can be avoided, and safety can be improved.

  Further, the unmanned / unpowered reactor cooling system 10 continues to cool the core almost unpowered by the thermosiphon cooling device 20 even when the steam turbine 13 or the condensate pump 16 stops operating for some reason. Can do. Further, even when the steam turbine 13 or the condensate pump 16 stops operating due to a decrease in the amount of heat generated inside the reactor pressure vessel 1 or a failure of the cooling means 14, the thermosiphon cooling device 20 The core can continue to cool until the reactor is completely shut down. As a result, the risk of core melting can be avoided, and safety can be improved.

FIG. 8 shows an unmanned and unpowered reactor cooling system 50 according to the second embodiment of the present invention.
As shown in FIG. 8, the unmanned / unpowered reactor cooling system 50 is an unmanned / unpowered reactor cooling system for cooling a reactor of a pressurized water nuclear power plant (PWR) whose power supply from the outside is stopped. is there. The unmanned / powerless reactor cooling system 50 includes a steam pipe 11, a branch valve 12, a steam turbine 13, a cooling means 14, a condensing pipe 15, a condensate pump 16, a generator 17, a battery 18, a solar power generation device 19, and a thermostat. A siphon type cooling device 20 and a control unit 21 are provided.

  The embodiment of the unmanned / unpowered reactor cooling system 50 is substantially the same as the unmanned / unpowered reactor cooling system 10 of the first embodiment of the present invention, except that the reactor type is different. For this reason, in the following description, the same code | symbol is attached | subjected to the structure same as the unmanned and unpowered reactor cooling system 10 of the 1st Embodiment of this invention, and the overlapping description is abbreviate | omitted.

  In the case of a pressurized water reactor (PWR), since there is no cooling facility for reactor isolation, the residual heat removal facility (RHRS) 5 is operated for initial core cooling. When the core stops urgently, the control rods are lowered and the core criticality is stopped. When the core is temporarily lost, the emergency core low customer facility (ECCS) is activated and boric acid water or the like is injected into the core. Thereafter, the residual heat removal equipment 5 is activated after the heat generation in the core is reduced. When there is no external power source, the ECCS and the residual heat removal facility 5 operate with an emergency power source such as a diesel emergency power source. The unmanned / unpowered reactor cooling system 50 operates when the external power supply and the emergency power supply stop operating and the residual heat removal equipment 5 stops and the pressure inside the reactor rises.

  First, steam is generated by lowering the pressure of the core from 14 MPa or more to a saturation pressure of 7 MPa by blowdown. At that time, it is necessary to take out steam through the gas-liquid separator 6 so that the high-temperature and high-pressure water is gas-liquid separated. Further, after the pressure of the steam is reduced to 2 MPa by a pressure regulating valve, the high pressure turbine 13a is driven by the steam and the condensed water is circulated. It should be noted that the operating pressure of the condensate pump 16 is higher than that of the unmanned / unpowered reactor cooling system 10 in order to feed the condensed water to the high pressure core.

  The residual heat removal equipment 5 is driven by the electric power of the high pressure generator 17a connected to the high pressure turbine 13a. In addition, since a steam will not generate | occur | produce when a nuclear reactor cools with the residual heat removal equipment 5, the residual heat removal equipment 5 will not operate | move. When the residual heat removal equipment 5 stops, the pressure in the reactor rises again to generate steam, and the unmanned / unpowered reactor cooling system 50 operates. Since the unmanned / unpowered nuclear reactor cooling system 50 moves intermittently in this way, one system of the residual heat removal equipment 5 is configured to operate intermittently in accordance with this. When the decay heat of the core is settled and the initial cooling is completed, the core cooling is continued only by the unmanned / non-powered reactor cooling system 50. When the cooling water in the core decreases, water is injected from the emergency water supply system.

  Even when the ECCS and the residual heat removal equipment 5 do not operate for some reason, it is necessary to cool the core only by the unmanned / non-powered reactor cooling system 50. Since the decay heat immediately after the reactor core is stopped is large, the cooling capacity (for example, 30 MW) of the unmanned / unpowered reactor cooling system 50 may be exceeded. In this case, the steam branched from the core is partially bypassed, and the steam in the furnace is blown off to the environment via the emergency steam discharger 7. Before releasing to the environment, it is necessary to reduce the emitted radioactivity as much as possible with an emergency purification device filled with water and sand. Since no core damage has occurred at this point, the release of radioactivity into the environment is considered to be limited. This blow-off is at most 10 hours. Water lost in the blow-off is injected into the core from the emergency water supply system. This emergency blow-off device may be installed as a backup when the reactor cooling device for BWR isolation does not operate.

DESCRIPTION OF SYMBOLS 1 Reactor pressure vessel 2 Nuclear power generator turbine 3 Main steam pipe 4 Reactor central control room 10 Unmanned and unpowered reactor cooling system 11 Steam pipe 12 Branch valve 13 Steam turbine 13a High pressure turbine 13b Low pressure turbine 14 Cooling means 15 Condensation Pipe 16 Condensate pump 16a High pressure pump 16b Low pressure pump 17 Generator 17a High pressure generator 17b Low pressure generator 18 Battery 19 Solar power generation device 20 Thermosiphon cooling device 21 Control unit 22 Isolation machine room 22a Heat pipe 23 Bypass line 31 Heat exchanger 31a Conduit 31b Fin 31c Steam header 31d Condensate header 31e Pressure sensor 31f Shut-off valve 32 Cooling tower 32a Leg 32b Tower body 32c Chimney 32d Protective fence 32e Radioactive gas purification 33 Steam pipe 34 Distributor 35 Shut-off valve 36 Steam check valve 37 Pressure gauge 38 Powerless heat exchanger 39 Condensate check valve 40 Shut-off valve 41 Condensate collection pipe 42 Pipe 43 Vacuum pump pipe 44 Vacuum pump 45 Radiation Performance removal filter 46 Exhaust chimney

Claims (6)

An unmanned and unpowered reactor cooling system for cooling a nuclear power plant nuclear reactor whose power supply from the outside is stopped,
A steam turbine that is operated by steam generated inside the reactor pressure vessel;
Cooling means for condensing the steam after operating the steam turbine by exchanging heat with outside air;
A condensate pump driven by the steam turbine and returning the liquid condensed by the cooling means to the inside of the reactor pressure vessel;
An unmanned and unpowered nuclear reactor cooling system. The steam turbine includes a high pressure turbine that operates when a heat generation amount inside the reactor pressure vessel is larger than a predetermined heat generation amount, and a heat generation amount inside the reactor pressure vessel that is smaller than the predetermined heat generation amount. A low-pressure turbine that operates,
The unmanned / unpowered reactor cooling system according to claim 1, wherein the condensate pump includes a high-pressure pump driven by the high-pressure turbine and a low-pressure pump driven by the low-pressure turbine.   The unmanned / unpowered reactor cooling system according to claim 1, further comprising a solar power generation device provided so that the condensate pump can be driven when the steam turbine stops operating.   It is arranged at a position higher than the reactor pressure vessel, and is driven when the steam turbine stops operating.The steam generated inside the reactor pressure vessel is condensed by exchanging heat with the outside air, and the condensed liquid is The unmanned / unpowered reactor cooling system according to any one of claims 1 to 3, further comprising a thermosiphon cooling device configured to return to the inside of the reactor pressure vessel. The cooling means has a heat exchange device and a cooling tower,
The heat exchange device includes a plurality of conduits through which the steam passes, and fins provided on the outer surface of each conduit to increase an area in contact with outside air,
The cooling tower has a seismic isolation structure, a plurality of legs arranged at intervals from each other so that fluid can pass between each other, and a tower main body supported at a predetermined height from the installation surface by each leg. The tower body has a chimney for discharging the outside air heated by exchanging heat with the steam above the heat exchange device. The unmanned / unpowered nuclear reactor cooling system according to any one of claims 1 to 4. A steam pipe connected in the middle of a pipe connecting the reactor pressure vessel and the nuclear power generator turbine so as to guide the steam generated inside the reactor pressure vessel to the cooling means through the steam turbine;
A condensing pipe provided to guide the liquid condensed by the cooling means to the inside of the reactor pressure vessel;
A generator provided so as to be able to generate power by the steam turbine;
A battery for storing electricity generated by the generator;
A branch valve provided in the steam pipe and configured to guide the steam to the steam pipe when the inside of the reactor pressure vessel exceeds a predetermined temperature;
The unmanned / unpowered reactor cooling system according to claim 1, wherein the unmanned / unpowered reactor cooling system is provided.