Floating-type nuclear power generation system

Abstract

Disclosed is a floating-type nuclear power generation system capable of advantageously countering core meltdown. The present disclosure is a floating-type nuclear power generation system comprising: a nuclear reactor; a turbine generator that is driven by steam generated by the heat of the nuclear reactor; and a floating body in which the nuclear reactor and the turbine generator are disposed and which is moored on the sea. The floating body has, on the lower side of the nuclear reactor, a core catcher, the lower side of which is filled with ballast water in a ship-bottom ballast tank formed, in a double hull structure, at the bottom portion of the floating body.

Description

Floating nuclear power generation system

[0001] The present invention relates to a floating nuclear power generation system.

[0002] Nuclear power generation systems have been proposed not only in land-based configurations but also in floating configurations that float on the sea (see, for example, Patent Documents 1 to 3).

[0003] JP-A No. 63-151898 JP-A No. 63-151899 JP-A No. 52-149589

[0004] Buongiorno, J. et al. "The Offshore Floating Nuclear Plant Concept." Nuclear Technology 194.1 (2016) Earthquake response characteristics of floating structures for floating nuclear power plants (part 2) - Vertical seismic isolation characteristics of a floater with an air chamber at the bottom - Central Research Institute of Electric Power Industry, Yutaka Hagiwara et al., August 1, 1987

[0005] In nuclear power generation systems, a core meltdown accident is something that must be avoided at all costs. Therefore, even if all cooling means of the system are lost, it is necessary to attempt to inject water such as seawater. In the case of land-based nuclear power generation systems, attempting to use seawater to counter a core meltdown clearly requires the power of pumps, etc. In this regard, if a nuclear power generation system is floating on the sea, it would seem to have an advantage over land-based nuclear power generation systems in terms of using seawater to counter a core meltdown. However, if a land-based nuclear power generation system is simply floating on the sea, it cannot use seawater advantageously.

[0006] Therefore, the present application discloses a floating nuclear power generation system that can advantageously resist core meltdown.

[0007] In order to solve the above problems, the present invention provides a core catcher below the reactor, the underside of which is filled with ballast water from a bottom ballast tank formed on the bottom of the floating body by a double hull structure.

[0008] In detail, the present invention is a floating nuclear power generation system comprising a nuclear reactor, a turbine generator driven by steam generated by the heat of the reactor, and a float on which the nuclear reactor and the turbine generator are arranged and which is moored at sea, the float having a core catcher below the reactor, the underside of which is filled with ballast water from a bottom ballast tank formed in the bottom part of the float by a double hull structure.

[0009] In the above-mentioned floating nuclear power generation system, the underside of the core catcher, which is placed below the reactor, is filled with ballast water from the bottom ballast tank formed in the bottom part of the float due to the double hull structure of the float. Because the float of a floating nuclear power generation system is much larger than the reactor, the bottom ballast tank of the float also contains a large amount of ballast water. Therefore, even if the molten core falls into the core catcher due to a core meltdown, the molten core can be cooled by ballast water via the core catcher. Therefore, it can be said that such a floating nuclear power generation system is advantageously able to withstand a core meltdown.

[0010] The core catcher may be made of steel and include a steel plate that forms the bottom of the containment vessel in which the reactor is housed, and a heat transfer plate that is installed upright in the bottom ballast tank on the underside of the steel plate. Steel is strong and has excellent heat transfer properties. Therefore, if the core catcher is made of such steel plate and heat transfer plate, even if the molten core falls into the core catcher due to a core meltdown, the molten core can be effectively cooled by ballast water via the core catcher.

[0011] The floating nuclear power generation system may also have a communication valve that allows water around the float to flow into the containment vessel. In such a floating nuclear power generation system, even in a situation where water is lost from the containment vessel, the communication valve can be opened to allow water around the float to flow into the containment vessel. Therefore, such a floating nuclear power generation system can minimize the loss of water in the containment vessel, which could lead to a core meltdown. Therefore, such a floating nuclear power generation system can be said to be advantageous in countering a core meltdown.

[0012] The floating nuclear power generation system may further include a sinking means for sinking the float. In such a floating nuclear power generation system, the reactor can be sunk together with the float by sinking the float. Therefore, in such a floating nuclear power generation system, the loss of water in the containment vessel, which may lead to a core meltdown, can be minimized. Therefore, it can be said that such a floating nuclear power generation system is advantageously able to counter a core meltdown.

[0013] The floating nuclear power generation system described above can advantageously withstand a core meltdown.

[0014] FIG. 1 is a schematic diagram showing the arrangement of equipment in a floating nuclear power generation system according to an embodiment. FIG. 2 is a schematic diagram showing the system configuration of a floating nuclear power generation system according to an embodiment. FIG. 3 is a diagram showing how a floater changes direction. FIG. 4 is a diagram illustrating an example of a state when a tsunami hits the floating nuclear power generation system. FIG. 5 is a diagram showing an example of a dust removal device provided in the floating nuclear power generation system 1. FIG. 6 is a diagram showing the IC / PCCS pool from the side. FIG. 7 is a diagram showing the IC / PCCS pool from above. FIG. 8 is a diagram showing how a molten core falls from the bottom of a pressure vessel. FIG. 9 is an explanatory diagram regarding the flooding function of a containment vessel. FIG. 10 is an explanatory diagram regarding the sinking function of a floating nuclear power generation system.

[0015] The following describes an embodiment of the present invention. The embodiment described below is one aspect of the present invention and does not limit the technical scope of the present invention.

[0016] <Outline of Equipment Layout> Fig. 1 is a schematic diagram showing the layout of equipment in a floating nuclear power generation system 1 according to an embodiment. Fig. 1(A) shows the layout of various equipment provided in the floating nuclear power generation system 1 as viewed from above. Fig. 1(B) shows the layout of various equipment provided in the floating nuclear power generation system 1 as viewed from the side.

[0017] The floating nuclear power generation system 1 is a floating power generation system that can be floated on the sea. Therefore, the floating nuclear power generation system 1 includes a float 2. As can be seen from FIG. 1A , the float 2 is a streamlined float. However, the float 2 is not a vessel intended for autonomous navigation on the sea. The float 2 floats on the sea while being moored in order to transmit the electricity generated by the floating nuclear power generation system 1 to land. To reduce resistance to tidal currents, the float 2 is moored at only one end in the longitudinal direction and floats on the sea with the other end unmoored. Therefore, the float 2 floats on the sea like a windsock. That is, when the float 2 is subjected to a tidal current, the moored portion of the float 2 naturally faces upstream of the tidal current as it floats on the sea.

[0018] Since the float 2 has such a streamlined shape, in this embodiment, for convenience, the moored portion of the float 2 in the longitudinal direction will be referred to as the "bow side," and the unmoored portion will be referred to as the "stern side." Therefore, in Fig. 1, the left side of the page is the "bow side," and the right side of the page is the "stern side." Also, Fig. 1(B) shows the internal configuration of the floating nuclear power generation system 1 as seen from the port side of the float 2.

[0019] In this embodiment, a streamlined float 2 is exemplified, but the float 2 may be a non-streamlined float. The float 2 used in the floating nuclear power generation system 1 may be, for example, a cylindrical float that is circular in top view, a rectangular parallelepiped float that is square in top view, or any other float of various shapes.

[0020] As shown in FIG. 1 , the floating nuclear power generation system 1 includes a reactor 3 disposed near the center of a float 2, and a turbine generator 4 disposed closer to the bow than the reactor 3. The reactor 3 generates steam by boiling water with heat generated by nuclear fission. The turbine generator 4 generates electricity by rotating a generator with a steam-driven turbine. Note that in this embodiment, a boiling water reactor (BWR) floating nuclear power generation system 1 that drives the turbine generator 4 with steam from the reactor 3 is illustrated as an example, but the floating nuclear power generation system 1 may also be, for example, a pressurized water reactor (PWR) or may use various other types of reactors.

[0021] The floating nuclear power generation system 1 includes various types of equipment in addition to the float 2, reactor 3, and turbine generator 4 described above. The floating nuclear power generation system 1 includes, for example, reactor equipment areas 5 and 7, a pit 6, and a fuel pool 8 around the reactor 3. The floating nuclear power generation system 1 also includes a desalination plant 9, an IC / PCCS pool 10, various equipment areas 12, a living area 13, and a waste treatment room 24, which are arranged aft of the reactor 3. The floating nuclear power generation system 1 also includes a condensate storage tank 14 arranged between the reactor 3 and the turbine generator 4. The floating nuclear power generation system 1 also includes a laydown area 18 and an ancillary equipment area 19, which are arranged near the bow of the float 2. A main transformer 20 and an auxiliary boiler 21 are installed in the ancillary equipment area 19. The floating nuclear power generation system 1 also includes a diesel fuel tank 23 on the deck near the bow of the float 2. The floating nuclear power generation system 1 also includes a bow ballast tank 25, a bottom ballast tank 26, a stern ballast tank 27, and a side ballast tank 28 for controlling the attitude of the float 2.

[0022] The reactor equipment areas 5 and 7 are equipped with various types of reactor equipment that are installed outside the containment vessel of the reactor 3. The equipment that is installed in the reactor equipment areas 5 and 7 includes, for example, pumps and valves of various reactor cooling equipment such as an emergency core cooling system and a residual heat removal system, pumps and valves of a pool water cooling system that cools the fuel pool, compressed air equipment for control, ventilation and air conditioning equipment, an emergency diesel generator that serves as an emergency power source, DC power supply equipment using storage batteries, and various other equipment.

[0023] The pit 6 is a pit for temporarily storing various items during periodic inspections and refueling. Examples of items to be stored in the pit 6 include a steam separator and a steam dryer that are placed above the nuclear fuel inside the reactor 3.

[0024] The fuel pool 8 is a pool for storing unused or spent nuclear fuel. The nuclear fuel for the reactor 3 is in the form of fuel assemblies. For this reason, the fuel pool 8 is provided with racks for storing the fuel assemblies at appropriate intervals. In addition, a fuel exchange machine for transferring the fuel assemblies between the reactor 3 and the fuel pool 8 is provided above the fuel pool 8.

[0025] The desalination device 9 is a device that desalinates seawater. Because the floating nuclear power generation system 1 is used while floating on the sea, it is not possible to obtain freshwater that is almost free of salt from rivers, as is the case with facilities on land. For this reason, the floating nuclear power generation system 1 is equipped with the desalination device 9 that removes salt from seawater to desalinate it, in order to secure reactor cooling water and various other types of water. Various methods, such as reverse osmosis and evaporation, can be used as the desalination method for the desalination device 9.

[0026] An IC heat exchanger and a PCCS heat exchanger are arranged in the IC / PCCS pool 10. The IC heat exchanger is an isolation condenser (IC) facility that cools the reactor 3 when the containment vessel is placed in an isolated state due to a loss of all AC power or the like. The PCCS heat exchanger is a passive containment cooling system (PCCS) facility that cools the steam released into the containment vessel in the event of a severe accident or the like.

[0027] The various equipment area 12 is provided with a central control room for operating the floating nuclear power generation system 1, an entrance / exit control room for controlling entry / exit to the radiation controlled area, and various other equipment. The emergency diesel generator and DC power supply equipment described above may be provided in the various equipment area 12 instead of the reactor equipment areas 5 and 7.

[0028] The living area 13 is provided with living facilities for the operators and others staying on the floating nuclear power generation system 1. Examples of the living facilities include private rooms with berths, a dining room with cooking equipment, bathing facilities, recreational facilities, and various other facilities.

[0029] Various facilities for treating radioactive waste are installed in the waste treatment room 24. Examples of radioactive waste to be treated in the waste treatment room 24 include liquid waste such as wastewater generated in radiation controlled areas and miscellaneous solid waste such as waste materials generated in various operations. These wastes are reduced in volume in the waste treatment room 24 by evaporation and concentration, compression, incineration, or the like, and stored within the float 2 before being transported from the float 2.

[0030] The condensate storage tank 14 is a tank that stores water that can be supplied to the reactor 3. The condensate storage tank 14 is connected to the condenser of the turbine generator 4 and an emergency core cooling system, and is used to replenish water to the condenser during normal operation and to inject water into the reactor 3 in an emergency.

[0031] The laydown area 18 is a work space for disassembling and inspecting various large equipment such as the turbine generator 4. The laydown area 18 is on the same floor as the operating floor for the turbine generator 4, and large equipment can be easily transported using crane equipment installed above the operating floor.

[0032] Various types of auxiliary equipment, such as a main transformer 20 and an auxiliary boiler 21, are arranged in the auxiliary equipment area 19. The main transformer 20 is a transformer for stepping up the voltage of the electricity generated by the turbine generator 4 to the voltage of the power grid. The auxiliary boiler 21 is a boiler that generates steam using heat generated by burning diesel oil.

[0033] The floating nuclear power generation system 1 is moored on the sea by an anchor chain 22 attached to the bow side of the float 2. As described above, when the floating nuclear power generation system 1 is subjected to a tidal current, it floats on the sea with the moored part naturally facing upstream of the tidal current. For this reason, the submarine cable for connecting the floating nuclear power generation system 1 to the onshore power grid is suspended from near the bow of the float 2 toward the seabed, similar to the anchor chain 22. For this reason, it is reasonable to place the main transformer 20 for stepping up the electricity generated by the turbine generator 4 to the voltage of the power grid near the bow of the float 2, close to the submarine cable, as shown in Figure 1.

[0034] Furthermore, the auxiliary boiler 21 is used to provide steam for the ground of the turbine generator 4 and to heat the steam equipment around the turbine when the floating nuclear power generation system 1 starts up. For this reason, it is reasonable to arrange the auxiliary boiler 21 near the turbine generator 4.

[0035] For this reason, the floating nuclear power generation system 1 employs a configuration in which the main transformer 20 and the auxiliary boiler 21 are arranged in an auxiliary equipment area 19 provided on the bow side of the float 2. Furthermore, the floating nuclear power generation system 1 employs a configuration in which a light oil tank 23 for storing light oil to be supplied to the auxiliary boiler 21 is arranged above the auxiliary equipment area 19. Note that in addition to the main transformer 20 and the auxiliary boiler 21, switching equipment such as a line switch (LS) for opening and closing the electrical connection between the submarine cable and the main transformer 20 may also be installed in the auxiliary equipment area 19.

[0036] The bow ballast tank 25, the bottom ballast tank 26, the stern ballast tank 27, and the side ballast tank 28 are tanks for receiving ballast water for controlling the attitude of the float 2. The ballast water in the bow ballast tank 25, the bottom ballast tank 26, and the stern ballast tank 27 can also be used as seawater for cooling the reactor 3 in an emergency in the floating nuclear power generation system 1. Water can be injected into the bow ballast tank 25, the bottom ballast tank 26, and the stern ballast tank 27 naturally by the water pressure of seawater, for example, by opening a water intake provided on the bottom of the float 2. A pump or the like may also be used for water injection, if necessary. Water can be discharged from the bow ballast tank 25, the bottom ballast tank 26, and the stern ballast tank 27 using a pump or an ejector.

[0037] The outline of the equipment layout of the floating nuclear power generation system 1 according to this embodiment has been described above, but the above-described equipment layout is only an example, and other equipment layouts may be adopted. Next, an outline of the system configuration of the floating nuclear power generation system 1 will be described.

[0038] <Outline of System Configuration> Fig. 2 is a schematic diagram showing the system configuration of the floating nuclear power generation system 1 according to the embodiment. The floating nuclear power generation system 1 is mainly composed of a reactor system R and a turbine system T. The reactor 3 described above is a main component of the reactor system R. Furthermore, the turbine generator 4 described above is a main component of the turbine system T.

[0039] The reactor system R containing the reactor 3 is equipped with various facilities such as a containment vessel 3A, nuclear fuel 3B, control rods 3C, a recirculation pump 3D, and a pressure vessel 3E. The turbine system T containing the turbine generator 4 is equipped with various facilities such as a condenser 4C, circulating water piping 4D, a circulating water pump 4E, and a feedwater pump 4F in addition to the turbine 4A and generator 4B that constitute the turbine generator 4.

[0040] The containment vessel 3A is a vessel that contains a pressure vessel 3E that contains nuclear fuel 3B and the like, and plays a role in containing radioactive materials that are released from the pressure vessel 3E in the event of a meltdown accident or the like in the reactor 3. The containment vessel 3A may be made of concrete, or may be made of the same steel material that constitutes the floater 2. The containment vessel 3A contains the pressure vessel 3E that contains the reactor 3 in its center, and has an upper dry well 3M formed above the pressure vessel 3E and a lower dry well 3N formed below the pressure vessel 3E. The containment vessel 3A also has a suppression pool 3H around the lower dry well 3N.

[0041] The pressure vessel 3E is a container that contains nuclear fuel 3B and the like, and serves to contain water and steam for cooling the reactor 3. Several hundred nuclear fuel 3B are arranged in the center of the pressure vessel 3E in the form of fuel assemblies, thereby forming the main body of the reactor 3. Control rods 3C that can be moved up and down by a drive mechanism provided at the bottom of the pressure vessel 3E are inserted into the gaps between the fuel assemblies in the main body of the reactor 3. When the control rods 3C are withdrawn from the reactor 3 and the reactor 3 reaches a critical state, the reactor 3 continues to generate heat. Furthermore, when the control rods 3C are inserted into the reactor 3 and the reactor 3 reaches a subcritical state, the heat generation from the reactor 3 gradually decreases.

[0042] A recirculation pump 3D is provided in the pressure vessel 3E. The recirculation pump 3D is responsible for removing heat from the reactor 3 and controlling the reactor power output by forcibly circulating water, which serves as reactor coolant, in the liquid phase within the pressure vessel 3E. Note that the floating nuclear power generation system 1 of this embodiment is assumed to be an advanced boiling water reactor (ABWR), and therefore in FIG. 2 the recirculation pump 3D is provided in the pressure vessel 3E, but the floating nuclear power generation system 1 is not limited to this. The floating nuclear power generation system 1 may have a recirculation system in which the recirculation pump and circulation piping are arranged outside the pressure vessel 3E, for example.

[0043] A main steam pipe 3L is connected to the pressure vessel 3E to send steam generated in the pressure vessel 3E to the turbine generator 4 of the turbine system T. Since the main steam pipe 3L is a pipe connecting the inside and outside of the containment vessel 3A, main steam isolation valves 3J and 3K are provided near penetrations of the containment vessel 3A to enable isolation of the containment vessel 3A. A safety relief valve 3F is provided midway along the main steam pipe 3L to prevent the internal pressure of the pressure vessel 3E from becoming excessive when the main steam isolation valves 3J and 3K are closed. The end of an exhaust pipe 3G downstream of the safety relief valve 3F is located in a suppression pool 3H.

[0044] The turbine 4A and generator 4B that make up the turbine generator 4 are connected by a common rotating shaft. The turbine 4A has a structure in which an impeller is housed within a casing. A condenser 4C is provided below the turbine 4A to condense the steam that passes through the turbine 4A. The condenser 4C contains a number of narrow tubes that form part of the circulating water piping 4D, which connects a water intake located below the waterline on the exterior surface of the float 2 to a water outlet. The condenser 4C condenses the steam using the cold heat of seawater pumped by a circulating water pump 4E located on the circulating water piping 4D. Therefore, the pressure difference between the steam supplied from the reactor 3 through the main steam pipe 3L and the pressure inside the condenser 4C applies power to the impeller to rotate the generator 4B. This rotates the generator 4B and generates electricity. The condensed water condensed in the condenser 4C is then fed back into the pressure vessel 3E via a feedwater piping 4G by a feedwater pump 4F.

[0045] Note that Figure 2 merely shows an outline of the reactor system R and the turbine system T, and in reality, a wide variety of equipment is installed. For example, important equipment such as a steam control valve and a turbine bypass valve is installed near the turbine 4A of the main steam pipe 3L. The turbine bypass valve may be capable of 100% bypass, sending the entire amount of main steam at rated output directly to the condenser 4C without passing through the turbine 4A, or it may have a lower bypass capacity. In addition, important equipment such as a feedwater flow control valve, a condensate demineralizer, and a feedwater heater is installed in the feedwater piping 4G. Furthermore, piping for an emergency core cooling system is installed inside and outside the containment vessel 3A. The turbine 4A is a combination of a high-pressure turbine and multiple low-pressure turbines.

[0046] 2 shows only one system of each device, the devices of the floating nuclear power generation system 1 are multiplexed. For example, there are multiple circulating water pumps 4E and multiple feedwater pumps 4F.

[0047] In the reactor system R, the position of the control rod 3C is adjusted so that the reactor 3 maintains a predetermined reactor output. In the turbine system T, the opening of the steam control valve is adjusted so that the turbine generator 4 maintains a predetermined rotation speed, and the feedwater flow rate of the feedwater pump 4F is adjusted so that the reactor 3 maintains a predetermined water level. With this configuration, the floating nuclear power generation system 1 transmits thermal energy generated by the nuclear reaction in the reactor 3 as electrical energy to the power grid via the generator 4B, which is synchronized with the grid frequency.

[0048] The above is an overview of the system configuration of the floating nuclear power generation system 1 according to this embodiment. Next, each characteristic part of the floating nuclear power generation system 1 will be described in detail.

[0049] <Matters Related to the Shape of the Float 2> As described above, the floating nuclear power generation system 1 according to this embodiment uses a streamlined float 2. Since the floating nuclear power generation system 1 is used while moored at sea, the decay heat of the reactor 3 can be removed stably over a long period of time by using the surrounding seawater, thereby greatly improving safety.

[0050] For example, the Russian Academic Lomonosov, which has a nuclear power plant mounted on a ship-type barge, began commercial operation in 2020 as an example of an offshore floating nuclear power plant. In Japan, designs for installing nuclear power plants on floating flat barges were also considered in the 1990s. However, in ship-type and flat barge-based nuclear power plants, the reactor is located above sea level, similar to land-based nuclear power plants. Therefore, using seawater to cool the reactor in ship-type and flat barge-based nuclear power plants requires power from electricity, engines, and other sources for pumping. Therefore, maintaining stable cooling over a long period of time poses a challenge, as it requires external replenishment of electricity and fuel.

[0051] To overcome this challenge, Professor Buongiorno and his colleagues at the Massachusetts Institute of Technology (MIT) have proposed a design that incorporates a nuclear reactor system into a cylindrical floating structure used for offshore oil drilling. However, the cylindrical floating structure proposed by MIT places the nuclear reactor at the bottom and the steam turbine and generator at the top. The steam turbine and generator are heavy objects. Therefore, it is difficult to realize a structure that supports such heavy objects at the top. Furthermore, because the cylindrical floating structure is roughly circular when viewed from above, manufacturing it in a standard horizontal shipbuilding dock creates dead space within the dock, resulting in poor manufacturing efficiency. Furthermore, a structure with a nuclear reactor at the bottom and a steam turbine and generator at the top has challenges, such as a draft several times deeper than that of a large ship, making it difficult to manufacture.

[0052] Therefore, the floating nuclear power generation system 1 of this embodiment employs a streamlined float 2, and nuclear power generation equipment such as a nuclear reactor 3 and a turbine generator 4 is disposed inside the float 2, which has a double hull structure similar to that of a large tanker. In the floating nuclear power generation system 1 of this embodiment, as shown in FIG. 1(B), the reactor 3 is disposed below the seawater surface. This makes it possible to realize a passive heat exchange system with seawater that does not require power from electricity, engines, or the like, which is not possible with ships or flat-plate barges. The passive heat exchange system realized in the floating nuclear power generation system 1 of this embodiment will be described in detail later.

[0053] As mentioned above, the floating body 2 is moored on the sea by the anchor chain 22, and therefore floats like a windsock. Figure 3 shows how the floating body 2 changes direction. When the floating body 2 receives a tidal current, it floats on the sea with its bow, moored by the anchor chain 22, naturally facing upstream of the tidal current. As a result, the streamlined shape of the floating body reduces resistance, making it possible to minimize the tension applied to the anchor chain 22.

[0054] The floating nuclear power generation system 1 has several advantages due to the streamlined float 2, in addition to the aforementioned reduction in resistance to tidal currents when moored. For example, the streamlined shape of the float 2 allows for maximum utilization of the space within a typical horizontal shipbuilding dock when manufacturing the floating nuclear power generation system 1, thereby enabling efficient manufacturing of the floating nuclear power generation system 1. In other words, by using multiple cranes in the shipbuilding dock, it becomes possible to simultaneously perform manufacturing work near the reactor 3 and manufacturing work near the turbine generator 4. Furthermore, manufacturing the floating nuclear power generation system 1 at a centralized manufacturing base such as a shipbuilding dock can be expected to improve manufacturing quality and reduce manufacturing costs. Because the floating nuclear power generation system 1 can be transported by sea, it can be easily exported to countries bordering the sea. Therefore, exporting floating nuclear power generation systems 1 manufactured at a centralized manufacturing base by sea offers advantages in both quality and cost compared to establishing manufacturing bases around the world.

[0055] Another advantage of the floating nuclear power generation system 1 due to the use of a streamlined float 2 is the ease of loading and unloading materials at sea. That is, with a streamlined float 2, the port and starboard sides are generally linear, making it easy for other ships to moor alongside the port or starboard side. If a ship can moor alongside the port or starboard side of the float 2, cargo can be transferred with the linear sides touching each other, facilitating the transfer of, for example, food for operators, diesel fuel consumed by the auxiliary boiler 21 and emergency diesel generator, chemicals used for water quality control, casks storing nuclear fuel, and various other maintenance parts.

[0056] Another advantage of the floating nuclear power generation system 1 due to the adoption of a streamlined float 2 is the layout advantage of various facilities of the floating nuclear power generation system 1, such as the reactor 3 and the turbine generator 4. In the floating nuclear power generation system 1, steam generated in the reactor 3 is sent to the turbine generator 4, and the electricity generated by the turbine generator 4 is transformed by the main transformer 20 and sent to the undersea cable. In a floating nuclear power generation system 1 in which each facility is interconnected in this manner, it is more rational to arrange the reactor 3, turbine generator 4, and main transformer 20 in order. In this regard, the streamlined float 2 makes it possible to arrange the reactor 3, turbine generator 4, and main transformer 20 in this order from the stern to the bow. Furthermore, the streamlined float 2 makes it possible to position the turbine generator 4 so that its rotation axis is aligned along the longitudinal direction of the float 2, as shown in FIG. 2 . This eliminates the possibility of the turbine blade flying toward the reactor 3, even in the unlikely event of a turbine missile occurring, in which a turbine blade breaks off during rotation. In addition, the floating nuclear power generation system 1 employs a casing that is strong enough to prevent the turbine blades from penetrating it, to prevent turbine missiles from occurring.

[0057] <Matters Related to Mooring of Float 2> Next, we will describe characteristic features provided in the floating nuclear power generation system 1 for mooring the streamlined float 2. Because the floating nuclear power generation system 1 employs a configuration in which the streamlined float 2 is moored, it is equipped with a device for controlling the attitude of the float 2 by itself. An example of a device for controlling the attitude of the float 2 is a thruster. If the float 2 is equipped with an electric screw thruster that can freely rotate the propulsion direction, it becomes possible to freely change the direction of the float 2 around the mooring part and to control the position of the float 2. Furthermore, if the float 2 is equipped with a thruster, it becomes possible to continue to maintain the float 2 in a fixed position when the anchor chain 22 breaks.

[0058] Furthermore, a circulating water pump 4E, for example, can be used as a device for independently controlling the attitude of the float 2. The circulating water pump 4E is a pump that supplies seawater to the condenser 4C, which has the largest cooling capacity of any nuclear power generation facility. Therefore, the circulating water pump 4E has the largest capacity of any pump provided in the floating nuclear power generation system 1, and depending on the arrangement of the water intake and discharge ports of the circulating water piping 4D, the float 2 can be moved at sea. Therefore, in the floating nuclear power generation system 1 of this embodiment, as shown in Figure 3, a circulating water system is provided so that a circulating water pump 4EL provided in a circulating water pipe 4D connecting the port-side intake 4DSL and the starboard-side discharge outlet 4DHR sends seawater from the port side to the starboard side, and a circulating water pump 4ER provided in a circulating water pipe 4D connecting the starboard-side intake 4DSR and the port-side discharge outlet 4DHL sends seawater from the starboard side to the port side. During normal times when the direction (attitude) of the float 2 is left to the tidal current, the flow rate of the circulating water pump 4EL and the flow rate of the circulating water pump 4ER are balanced so that the water is sent symmetrically by the circulating water pump 4E. When it is desired to move the float 2 to the port side, the flow rate of the circulating water piping 4D is adjusted so that the flow rate of the circulating water pump 4EL is greater than the flow rate of the circulating water pump 4ER. When it is desired to move the float 2 to the starboard side, the flow rate of the circulating water piping 4D is adjusted so that the flow rate of the circulating water pump 4ER is greater than the flow rate of the circulating water pump 4EL. The flow rate of the circulating water piping 4D can be adjusted, for example, by adjusting the opening of a flow control valve provided on the turbine generator 4 or by stopping the circulating water pump 4ER. Controlling the direction of the float 2 by adjusting the flow rate in this manner is effective not only for changing direction around the mooring parts but also for correcting positional deviation of the float 2.

[0059] In addition to the circulating water pump 4E, other devices for independently controlling the attitude of the float 2 include, for example, a reactor auxiliary cooling seawater pump (RSW) for a reactor building cooling water system (RCW) and a turbine auxiliary cooling seawater pump (TSW) for a turbine building cooling water system (TCW). In the floating nuclear power generation system 1 of this embodiment, like the circulating water pump 4E, the reactor auxiliary cooling seawater pump and the turbine auxiliary cooling seawater pump can also be used for position control. The floating nuclear power generation system 1 of this embodiment has multiple reactor auxiliary cooling seawater pumps and multiple turbine auxiliary cooling seawater pumps, one of which pumps seawater from the port side to the starboard side, and the other seawater pump pumps from the starboard side to the port side. Therefore, if the flow rate of each seawater pump is adjusted according to the position of the float 2, it is possible to correct the positional deviation of the float 2.

[0060] The floating nuclear power generation system 1 of this embodiment is assumed to have three low-pressure turbines as the turbines 4A. Two circulating water pipes 4D are connected to each of the three condensers 4C disposed below each low-pressure turbine for multiplexing. Therefore, FIG. 3 illustrates six circulating water pipes 4D and circulating water pumps 4E (4EL, 4ER). However, the floating nuclear power generation system 1 of this embodiment is not limited to this. The circulating water pipes 4D and circulating water pumps 4E may be arranged symmetrically, and may be, for example, four or fewer, or eight or more. While FIG. 3 illustrates the water intake 4DSL and the water discharge 4DHL arranged close to each other, they may be arranged spaced apart from each other or with their opening directions alternating, such as toward the side and downward of the float 2, to prevent short-circuiting.

[0061] Another example of a device for changing the direction of the float 2 is a tugboat. By permanently tethering a tugboat to the float 2, not only can the direction of the float 2 be changed, but also, for example, in the event of an emergency in the sea area where the floating nuclear power generation system 1 is installed, the anchor chain 22 can be cut and the floating nuclear power generation system 1 can be quickly moved. Examples of emergencies that may occur in a specific sea area include the occurrence of a natural disaster such as an undersea volcanic eruption, and the occurrence of an armed attack by terrorists or the military. In response to an armed attack targeting the floating nuclear power generation system 1, it is desirable to take measures such as, for example, setting up an area within a predetermined distance from the floating nuclear power generation system 1 that restricts the entry of ships and other vessels to monitor maritime traffic, or setting up a torpedo defense net around the floating nuclear power generation system 1 to prevent the approach of torpedoes and suspicious ships.

[0062] If the direction of the float 2 can be changed, the following measures can be taken, for example. Figure 4 is a diagram illustrating the state when a tsunami hits the floating nuclear power generation system 1. Figure 4(A) shows the floating nuclear power generation system 1 as seen from above, and Figure 4(B) shows the floating nuclear power generation system 1 as seen from the side.

[0063] For example, as shown in Fig. 4(A), assume that the tidal current is flowing downward and to the right on the page of Fig. 4. In this case, the floating nuclear power generation system 1 moored by the anchor chain 22 floats due to the tidal current in the state indicated by symbol P1 in Fig. 4(A), that is, with the bow of the floater 2 facing upward and to the left. In this state, assume that, for example, an earthquake or typhoon occurs centered on the left side of the page of Fig. 4, causing a tsunami to flow to the right.

[0064] If the floating nuclear power generation system 1 receives this tsunami with the bow of the float 2 facing upward and left, the floating nuclear power generation system 1 will receive the tsunami from the port side of the float 2. Therefore, the floating nuclear power generation system 1 may tilt to the starboard side due to the tsunami received from the port side of the float 2. On the other hand, if the generation of the tsunami is detected and the direction of the float 2 is immediately started to change, and the state shown by symbol P2 in FIG. 4(A) is reached, that is, the state in which the bow of the float 2 is directed to the left, the floating nuclear power generation system 1 will receive the tsunami from the bow side of the float 2. Therefore, the floating nuclear power generation system 1 can minimize the possibility of the float 2 tilting to either the port side or the starboard side. In the floating nuclear power generation system 1, since the float 2 is long from bow to stern, even if a tsunami hits the bow side of the float 2, the floating nuclear power generation system 1 will hardly tilt in the fore-and-aft direction as shown in Figure 4 (B).

[0065] Although Fig. 4 illustrates the floating nuclear power generation system 1 relatively close to land, it is preferable that the floating nuclear power generation system 1 be moored offshore at a distance of tens of kilometers or more from land. As shown in Fig. 4(B), tsunamis have the tendency to become gradually larger as they approach land in shallow waters. For this reason, if the floating nuclear power generation system 1 is moored offshore at a distance of tens of kilometers or more from land in deep waters, it is possible to relatively reduce the size of the tsunami that the floating nuclear power generation system 1 receives, although this depends on the topography of the seabed.

[0066] A suitable distance from land for mooring the floating nuclear power generation system 1 is, for example, 30 km or more. If the floating nuclear power generation system 1 is moored at sea 30 km or more from land, no residential area will be within the area required for evacuation planning under Japanese law. In other words, even if a large-scale accident were to occur at the floating nuclear power generation system 1, it is unlikely that residents on land would need to evacuate.

[0067] Incidentally, it is preferable to provide a dust removal device for removing debris (seaweed, jellyfish, small fish, waste, etc.) from the seawater at the intake port that takes in the seawater used in the floating nuclear power generation system 1. Therefore, in the floating nuclear power generation system 1, dust removal devices are provided at the intake ports 4DSL, 4DSR of the circulating water piping 4D and at the intake port of the reactor auxiliary cooling seawater system that supplies cold heat to auxiliary machinery around the reactor 3. Figure 5 is a diagram showing an example of a dust removal device provided in the floating nuclear power generation system 1.

[0068] As shown in FIG. 5, the dust removal device 29 includes a dust removal pit 29A, an inlet 29C, a cyclone 29D, a settling tank 29E, a discharge door 29G, and an outlet 29H.

[0069] The dust removal pit 29A is a space provided on the bottom or side of the float 2 and is constantly filled with seawater surrounding the float 2. A cyclone 29D is provided in the center of the dust removal pit 29A. The cyclone 29D is located at the open end of an outlet 29H connected to a seawater system pump, such as the circulating water pump 4E. The cyclone 29D has a conical interior shape and an inlet 29C that opens tangentially at its outermost diameter. Therefore, when the seawater system pump is operated while the dust removal pit 29A is filled with seawater and seawater is sucked into the outlet 29H, the seawater flowing in from the inlet 29C generates a spiral water flow within the cyclone 29D. The spiral water flow causes debris D, which has a greater specific gravity than seawater, to be centrifuged within the cyclone 29D and settle into a sedimentation tank 29E provided below the cyclone 29D. An openable discharge door 29G is provided at the bottom of the settling tank 29E. Therefore, by opening the discharge door 29G as needed, the debris D accumulated in the settling tank 29E can be discharged from the settling tank 29E. If the water intake is provided at the bottom of the float 2, the water intake will be located at a depth of, for example, approximately 80 to 100 meters, depending on the displacement of the float 2, making it less likely to suck in debris that is abundant near the sea surface. By combining this with the effect of preventing large amounts of migratory fish from entering using the torpedo protection net described above, it is possible to minimize the amount of debris that enters the water intake.

[0070] The dust removal device 29 is provided with a strainer 29F that prevents relatively large debris D from flowing into the dust removal pit 29A. The dust removal device 29 is also provided with a strainer 29B that prevents relatively large debris D from flowing into the inlet 29C. Therefore, debris D that is not suitable for centrifugation can be removed by the strainer 29F or the strainer 29B.

[0071] The floating nuclear power generation system 1 is not limited to one equipped with such a dust removal device 29. The floating nuclear power generation system 1 may be one using, for example, a dust removal device that rotates an endless screen (traveling screen) or other types of dust removal devices.

[0072] <Matters Related to Core Cooling> Next, the core cooling equipment provided in the floating nuclear power generation system 1 will be described. During normal operation, the reactor 3 is cooled by cold heat from the condenser 4C, but during normal shutdown or emergency shutdown, the reactor 3 is cooled by various cooling equipment other than the condenser 4C. The cooling equipment used in an emergency for the reactor 3 is called an emergency core cooling system (ECCS), and is composed of various cooling equipment such as a high-pressure water injection system, an isolation cooling system, and a low-pressure water injection system. Here, particularly characteristic matters of the various cooling equipment provided in the floating nuclear power generation system 1 will be described.

[0073] As described above, the floating nuclear power generation system 1 is equipped with an emergency condenser and a passive containment vessel cooling system. Because the floating nuclear power generation system 1 is a floating body floating on the sea, it is possible to significantly improve safety by stably removing decay heat from the reactor 3 over a long period of time using surrounding seawater. For this reason, the floating nuclear power generation system 1 is capable of inflowing seawater into the IC / PCCS pool 10. When seawater is allowed to flow into the IC / PCCS pool 10, cooling can be continued by the natural circulation force due to the density difference of the seawater. For this reason, the floating nuclear power generation system 1 has the IC / PCCS pool 10 arranged as follows.

[0074] Fig. 6 is a side view of the IC / PCCS pool 10. Fig. 7 is a top view of the IC / PCCS pool 10. Fig. 6 shows the positional relationship between the IC / PCCS pool 10 and the pressure vessel 3E in the direction of sea level.

[0075] 6 and 7 , an emergency condenser 30A and a PCCS heat exchanger 30D are disposed in the IC / PCCS pool 10 (the PCCS heat exchanger 30D is not shown in FIG. 6 due to space limitations). The IC / PCCS pool 10, in which the emergency condenser 30A and the PCCS heat exchanger 30D are disposed, is higher than the reactor core C. The IC / PCCS pool 10 is provided with a communication valve 10A for communicating with the side ballast tank 28, communication valves 10B and 10C for communicating with the periphery (sea) of the floating body 2, and an atmosphere release pipe 10D for communicating with the atmosphere. The emergency condenser 30A is connected to the inside of the pressure vessel 3E via a pipe 30B connected to the vicinity of the upper part of the pressure vessel 3E and a pipe 30C connected to the vicinity of the lower part of the pressure vessel 3E.

[0076] The IC / PCCS pool 10 is normally filled with fresh water. Even if the floating nuclear power generation system 1 experiences a loss of AC power, the reactor 3 can be cooled by the emergency condenser 30A by opening the pipes 30B and 30C. The IC / PCCS pool 10 also has a path for connecting to the condensate storage tank 14. Therefore, even if the floating nuclear power generation system 1 experiences a loss of AC power and the fresh water in the IC / PCCS pool 10 decreases, the reactor 3 can continue to be cooled by the fresh water stored in the condensate storage tank 14. However, if the loss of AC power continues even after the fresh water in the IC / PCCS pool 10 and the condensate storage tank 14 decreases due to boiling, there may be a case where the reactor 3 cannot be continuously cooled by fresh water. Even in such a case, the floating nuclear power generation system 1 can fill the IC / PCCS pool 10 with ballast water by opening the communication valve 10A. Furthermore, in the floating nuclear power generation system 1, by opening the communication valves 10B and 10C, it is possible to fill the IC / PCCS pool 10 with seawater around the float 2. If the IC / PCCS pool 10 is filled with either fresh water or seawater, it is possible to continue cooling the core C using the isolation condenser 30A. Note that the floating nuclear power generation system 1 has valves at appropriate locations for allowing seawater to flow from around the float 2 into the side ballast tanks 28, so that even if the seawater in the side ballast tanks 28 decreases, it can be replenished as needed.

[0077] The floating nuclear power generation system 1 according to this embodiment is not limited to the configuration in which the isolation condenser 30A condenses steam in the pressure vessel 3E and the PCCS heat exchanger 30D condenses steam in the containment vessel 3A. The isolation condenser 30A, which is used to cool the core C when the primary system boundary is intact, and the PCCS heat exchanger 30D, which is used to cool the containment vessel 3A when the primary system boundary is damaged, may complement or exchange each other's functions by switching the system configuration by opening and closing valves. That is, the isolation condenser 30A may be connected to the upper part (upper dry well 3M) and lower part (suppression pool 3H) of the containment vessel 3A by opening and closing valves. Furthermore, the PCCS heat exchanger 30D may be connected to the upper part and lower part of the pressure vessel 3E by opening and closing valves. The valves for switching the system configuration may be motor-operated valves using a DC power source or manual valves.

[0078] Furthermore, in the floating nuclear power generation system 1, there is a difference in elevation between the communicating valves 10B and 10C. Therefore, convection occurs in the seawater in the IC / PCCS pool 10 heated by the isolation condenser 30A due to a difference in seawater density caused by a temperature difference, but the difference in elevation between the communicating valves 10B and 10C is expected to have the effect of naturally replacing the seawater in the IC / PCCS pool 10 with the seawater around the floating body 2.

[0079] Note that salt deposition on the surfaces of the isolation condenser 30A and the PCCS heat exchanger 30D may reduce heat exchange capacity. Therefore, when seawater is introduced into the IC / PCCS pool 10, it is preferable to prevent salt deposition due to evaporation of the seawater. Salt deposition can be suppressed by preventing boiling of seawater (the generation of voids) on the heat exchange surfaces of the isolation condenser 30A and the PCCS heat exchanger 30D. Therefore, in order to suppress the temperature rise of the seawater in the IC / PCCS pool 10, it is preferable to use large-diameter valves for the communication valves 10A, 10B, and 10C. For example, using large-diameter valves for the communication valves 10B and 10C makes it easier for the seawater in the IC / PCCS pool 10 to be replaced with seawater around the floating body 2, thereby suppressing the temperature rise of the seawater in the IC / PCCS pool 10 as much as possible. Furthermore, when seawater is used to cool the emergency condenser 30A or the PCCS heat exchanger 30D, such salt precipitation may occur. Therefore, it is preferable to attempt cooling with fresh water in the initial stage immediately after an emergency shutdown of the reactor 3 when the decay heat is relatively large, and then start cooling with seawater when the amount of fresh water has decreased due to evaporation, etc., and the decay heat of the reactor 3 has also decreased.

[0080] As described above, the floating nuclear power generation system 1 is provided with various facilities for facilitating cooling with seawater, taking advantage of the floating structure compared to land-based nuclear power plants. Therefore, it can be said that the floating nuclear power generation system 1 can stably remove decay heat from the reactor 3 for a long period of time by using the surrounding seawater. The function of using seawater by opening the communication valves 10A, 10B, 10C can be used not only in the IC / PCCS pool 10 but also in, for example, the fuel pool 8.

[0081] The design concept of introducing seawater into the IC / PCCS pool 10 can also be applied to a pressurized water reactor. For example, if the floating nuclear power generation system 1 is a pressurized water reactor, seawater is introduced into the secondary side of the steam generator, which exchanges heat between the primary cooling system in which the reactor is installed and the secondary cooling system in which the turbine is installed, instead of the condensate of the secondary cooling system. This makes it possible to cool the coolant of the primary cooling system with the seawater introduced into the secondary side of the steam generator, even if the condensate of the secondary cooling system is lost.

[0082] <Matters Related to Accident Countermeasures> Next, we will explain the accident countermeasure facilities provided in the floating nuclear power generation system 1. As mentioned above, the floating nuclear power generation system 1 is provided with sufficient facilities for cooling the reactor 3, but various measures are also taken in anticipation of the unlikely event of a serious accident, as described below.

[0083] <Core Catcher> Figure 8 shows the molten core falling from the bottom of the pressure vessel 3E. When the reactor core melts in the nuclear reactor 3, the bottom of the pressure vessel 3E may be damaged, causing the molten core to fall below the pressure vessel 3E, as shown in Figure 8. If the molten core falls below the pressure vessel 3E, the structural materials of the float 2 below the pressure vessel 3E will be heated. However, as described above, the float 2 has a double-hull structure, and a bottom ballast tank 26 is provided at the bottom of the float 2. Furthermore, a number of heat transfer plates 26B are attached to the underside of the steel plate 26A of the float 2, which forms the bottom of the lower dry well 3N. Therefore, the steel plate 26A is firmly reinforced by the heat transfer plates 26B. Although Figure 8 illustrates the interior of the bottom ballast tank 26 as being partitioned by the heat transfer plates 26B, water ports are provided at various locations in the heat transfer plate 26B for circulating ballast water. Therefore, the ballast water can flow freely within the bottom ballast tank 26 without being obstructed by the heat transfer plate 26B.

[0084] The bottom surface of the lower dry well 3N, which is formed by the steel plates 26A and the heat transfer plates 26B, functions as a core catcher. The steel plates 26A and the heat transfer plates 26B are in contact with the ballast water in the bottom ballast tank 26. Therefore, the bottom of the lower dry well 3N functions as a heat sink for dissipating heat to the ballast water in the bottom ballast tank 26. Therefore, if the molten core falls from the pressure vessel 3E due to a core meltdown, the heat of the molten core that has fallen from the pressure vessel 3E is transferred to the ballast water in the bottom ballast tank 26 via the steel plates 26A and the heat transfer plates 26B.

[0085] If the molten core falling from the bottom of the pressure vessel 3E were to come into direct contact with a large amount of water, there is a risk of a steam explosion or the generation of a large amount of hydrogen. Therefore, when attempting to inject water into the molten core, it is necessary to take measures such as limiting the amount of water injected to an appropriate amount. However, it is not easy to control the amount of water injected while a severe accident such as a core meltdown is progressing.

[0086] In this regard, in the floating nuclear power generation system 1 of this embodiment, the steel plates 26A and heat transfer plates 26B that form the bottom of the lower dry well 3N function not only as a core catcher but also as a heat sink for dissipating heat to the ballast water in the bottom ballast tank 26. Therefore, the molten core that falls to the bottom of the lower dry well 3N is stably cooled and solidified, and then deposited as fuel debris. Furthermore, in this cooling method, the molten core does not come into direct contact with a large amount of water, so there is a low possibility of a steam explosion or the generation of a large amount of hydrogen.

[0087] Furthermore, in the floating nuclear power generation system 1 of this embodiment, the pedestal supporting the pressure vessel 3E is made of steel, so that heat from the molten core in the pressure vessel 3E is also transferred to the suppression pool 3H via the pedestal. As such, in the floating nuclear power generation system 1 of this embodiment, even in the event of a core meltdown, passive countermeasures against the molten core are implemented, utilizing the water in the bottom ballast tank 26 and the water in the suppression pool 3H. Note that, in order to minimize the impact of the pedestal coming into contact with fuel debris, a cylindrical bulkhead may be installed inside the pedestal, and heat from the fuel debris may be transferred to the suppression pool 3H via a heat transfer tube or the like. If such a bulkhead and heat transfer means are provided, the integrity of the pedestal can be maintained even in the unlikely event of a core meltdown.

[0088] <Flooding Function of Containment Vessel 3A> Figure 9 is an explanatory diagram of the flooding function of the containment vessel 3A. The floating nuclear power generation system 1 is designed so that the reactor 3 is located below sea level. For this reason, the floating nuclear power generation system 1 is provided with a function to fill the containment vessel 3A with seawater. That is, the floating nuclear power generation system 1 is provided with a seawater inlet pipe 3AP that connects the inside of the containment vessel 3A with the surroundings (sea) of the float 2. A seawater inlet valve 3AV is provided midway along the seawater inlet pipe 3AP.

[0089] Under normal conditions, the seawater inlet valve 3AV is closed, and as shown in FIG. 9A, seawater does not flow into the containment vessel 3A. If an accident occurs and all means for injecting water into the pressure vessel 3E are lost, the seawater inlet valve 3AV is opened. When the seawater inlet valve 3AV is opened, seawater around the float 2 flows into the containment vessel 3A. As described above, the reactor 3 is located below sea level. Therefore, by opening the seawater inlet valve 3AV, most of the containment vessel 3A is filled with seawater, as shown in FIG. 9B, enabling indirect cooling of the reactor core C inside the pressure vessel 3E from outside the pressure vessel 3E. In order to evacuate the air inside the containment vessel 3A when filling it with seawater, the floating nuclear power generation system 1 is provided with two seawater inlet pipes 3AP, one above the other. As a result, in the initial state when seawater begins to flow into the containment vessel 3A, the upper seawater inlet pipe 3AP serves as an air vent path, and the air inside the containment vessel 3A is discharged. When the containment vessel 3A is filled with seawater, the containment vessel 3A becomes flooded. Note that a vent valve other than the seawater inlet valve 3AV may be provided to vent the air inside the containment vessel 3A. A filter vent device for removing radioactive materials contained in the air may be provided along the air vent path.

[0090] <Sinking Function of Floating Nuclear Power Generation System 1> Fig. 10 is an explanatory diagram of the sinking function of the floating nuclear power generation system 1. The floating nuclear power generation system 1 has a function of sinking the float 2. The float 2 can be sinking by, for example, opening a valve that connects the inside and outside of the float 2, destroying the bottom of the vessel, or filling the inside of the float 2 with seawater by various other methods.

[0091] Because the floating nuclear power generation system 1 is configured to float on the sea, if all means for injecting water into the pressure vessel 3E are lost due to some kind of accident, the floating nuclear power generation system 1 may be sunk, for example, as shown in FIG. 10(A). If the floating nuclear power generation system 1 is sunk, the reactor 3 can be cooled with seawater. If it is desired to raise the floating nuclear power generation system 1 from the seabed, a floating float F is prepared for floating the floating nuclear power generation system 1, as shown in FIG. 10(B), when several years have passed since the floating nuclear power generation system 1 was sunk and the decay heat of the reactor 3 has become sufficiently small. The floating float F is a hollow body with a sealed structure, and it is possible to inject seawater into the floating float F and to drain the seawater from the inside of the floating float F.

[0092] After preparing such a floating float F, seawater is poured into the floating float F above the floating nuclear power generation system 1 that is submerged on the seabed, as shown in Figure 10(C), and the floating float F is submerged on the seabed. Then, the floating float F is connected to the floating nuclear power generation system 1. Next, the seawater inside the floating float F is discharged. Once the seawater inside the floating float F is discharged, the buoyancy of the floating float F causes the floating float F to rise to the sea surface together with the floating nuclear power generation system 1. This makes it possible to attempt various disposal methods, such as dismantling the floating nuclear power generation system 1 and removing the nuclear fuel.

[0093] In this way, even if the floating nuclear power generation system 1 were to encounter a situation where it were unable to inject water into the reactor 3, it would be possible to use the above-mentioned various functions that take advantage of the floating design to cool the reactor 3 with seawater and sufficiently prevent radioactive materials from being released from the reactor 3. Therefore, it is possible to use nuclear energy more safely than in land-based nuclear power plants.

[0094] The present application also includes the following additional matters.

[0095] <First Supplementary Group> <Supplementary Note 1> A floating nuclear power generation system comprising: a nuclear reactor; a turbine generator driven by steam generated by heat from the nuclear reactor; a float on which the nuclear reactor and the turbine generator are disposed; and a thruster for controlling the position of the float, wherein the float is a streamlined or rectangular parallelepiped float that is square when viewed from above, and is moored by an anchor chain only at the bow side of one end in the longitudinal direction, and a submarine cable connecting from a switchgear of the float to a seabed near the bow of the float for transmitting power from the float to an onshore power grid. <Supplementary Note 2> The floating nuclear power generation system according to Supplementary Note 1, wherein the turbine generator is arranged closer to the bow of the float in the longitudinal direction than the nuclear reactor. <Supplementary Note 3> The floating nuclear power generation system according to Supplementary Note 2, further comprising a main transformer arranged closer to the bow of the float than the turbine generator in the longitudinal direction of the float. <Supplementary Note 4> The floating nuclear power generation system according to any one of Supplementary Notes 1 to 3, wherein the turbine generator is disposed so that the rotation axes of the turbine and the generator are aligned along the longitudinal direction of the float. <Effects of the First Supplementary Note Group> When a nuclear power generation system is floated on the sea, it can be disposed on the coast within several kilometers of land, offshore approximately tens of kilometers from land, or in the open ocean approximately hundreds of kilometers from land. When a nuclear power generation system is disposed on the coast of the sea, it is very close to land, making it easy to transmit electricity and transport materials. However, because the seabed is shallower in coastal areas than offshore, the wave height of tsunamis that arrive in the event of an earthquake is higher than offshore. Furthermore, if a nuclear power generation system is disposed offshore close to land, there is a possibility that residents on land may be forced to evacuate in the event of a serious accident at the nuclear power generation system. On the other hand, installing a nuclear power generation system in the ocean several hundred kilometers from land would require laying long distances of undersea cables for power transmission, and would not be practical because it would be difficult to transport materials. Therefore, taking all of these factors into consideration, it is preferable to install a floating nuclear power generation system offshore, some distance from land. However, offshore, far from land, the currents are often stronger and more varied in direction than in coastal areas.Therefore, when a floating nuclear power generation system is deployed offshore, it is essential to ensure the stability of the float against tidal currents. The floating nuclear power generation system of the first supplementary group is stable against tidal currents.

[0096] <Second Supplementary Group> <Supplementary Note 1> A floating nuclear power generation system comprising: a nuclear reactor, a turbine generator driven by steam generated by heat of the reactor, a float on the sea on which the nuclear reactor and the turbine generator are disposed, and a circulating water pump that supplies cooling water to a condenser that condenses steam that has passed through the turbine of the turbine generator, wherein the circulating water pump comprises: a first circulating water pump that delivers cooling water discharged from the float in a first direction when the float is viewed from above, and a second circulating water pump that delivers cooling water discharged from the float in a second direction opposite to the first direction when the float is viewed from above. <Supplementary Note 2> A floating nuclear power generation system according to Supplementary Note 1, wherein the flow rates of the first circulating water pump and the second circulating water pump are adjusted according to the position of the float. <Supplementary Note 3> The floating nuclear power system according to Supplementary Note 1, wherein the float has a streamlined shape when viewed from above and is moored only at the bow side of one end in the longitudinal direction, the first circulating water pump is responsible for feeding cooling water to be discharged to the starboard side of the float, and the second circulating water pump is responsible for feeding cooling water to be discharged to the port side of the float. <Supplementary Note 4> The floating nuclear power system according to Supplementary Note 1, further comprising a seawater pump for at least one of a reactor auxiliary cooling system and a turbine auxiliary cooling system, and the flow rate of the seawater pump is adjusted according to the position of the float. <Supplementary Note 5> The floating nuclear power system according to any one of Supplements 1 to 4, wherein the float is moored by an anchor chain provided on the bow side. <Supplementary Note 6> The floating nuclear power system according to Supplementary Note 5, wherein the float is moored by an anchor chain provided on the bow side. <Effects of the Second Supplementary Group> When a nuclear power generation system is floated on the sea, it can be placed on the coast within a few kilometers of land, offshore about tens of kilometers from land, or in the open sea about hundreds of kilometers from land. When a nuclear power generation system is placed on the coast of the sea, it is very close to land, making it easy to transmit electricity and transport materials. However, because the seabed is shallower in coastal areas than offshore, the wave height of a tsunami that arrives in the event of an earthquake is higher than offshore.Furthermore, if a nuclear power generation system is located offshore close to land, there is a possibility that residents on land may be forced to evacuate in the event of a serious accident at the nuclear power generation system. On the other hand, installing a nuclear power generation system in the open ocean several hundred kilometers from land would require laying long-distance submarine cables for power transmission, making it difficult to transport materials, making this unrealistic. Therefore, taking all of these factors into consideration, it is preferable to install a floating nuclear power generation system offshore, somewhat away from land. When a floater is moored at sea, it will be located downstream of the moorings relative to the tidal current. However, if a tsunami occurs due to a low pressure system or an earthquake, it may arrive from a direction different from the tidal current. Therefore, when a floating nuclear power generation system is moored offshore, it is preferable to make the float's position controllable. The floating nuclear power generation system of the second supplementary group above allows for control of the float's position.

[0097] <Third Supplementary Group> <Supplementary Note 1> A floating nuclear power generation system comprising: a nuclear reactor; a turbine generator driven by steam generated by heat from the reactor; a float on which the nuclear reactor and the turbine generator are disposed and moored at sea; a condenser that condenses steam generated in a pressure vessel or a containment vessel in which the reactor is located in an emergency using cold heat from stored water and returns the condensate to the pressure vessel or the containment vessel; and a water storage section for storing the stored water, wherein at least a bottom of the water storage section is set lower than the waterline of the float and wherein a communication valve is provided for allowing water around the float to flow in directly or indirectly. <Supplementary Note 2> A floating nuclear power generation system according to Supplementary Note 1, wherein the float has at least side ballast tanks formed on side portions of the float by a double hull structure, and the water storage section has as the communication valve a first communication valve that communicates the inside of the water storage section with the side ballast tank. <Supplementary Note 3> The floating nuclear power generation system according to Supplementary Note 1, wherein the water storage section has, as the communication valve, a second communication valve that allows water around the float to flow into the water storage section. <Supplementary Note 4> The floating nuclear power generation system according to any one of Supplements 1 to 3, wherein the condenser is installed at a position on the float that is at least higher than the reactor. <Effects of the Third Supplementary Note Group> When a nuclear power generation system is floated on the sea, the float is surrounded by the sea, which is an environment that is inherently advantageous for cooling the reactor. However, the reactor is tightly protected by a containment vessel or the like to prevent radioactive materials from being released into the environment. For this reason, even if a land-based nuclear power generation system is simply floated on the sea, the advantage of the float being surrounded by the sea cannot be utilized for cooling the reactor. The floating nuclear power generation system according to the above-mentioned Third Supplementary Note Group makes it possible to utilize the advantages of the float for cooling the reactor.

[0098] R. Reactor system: T. Turbine system: F. Floating float: C. Reactor core: D. Garbage: 1. Floating nuclear power generation system: 2. Float: 3. Reactor: 4. Turbine generator: 5. Reactor equipment area: 6. Pit: 7. Reactor equipment area: 8. Fuel pool: 9. Desalination plant: 10. IC / PCCS pool: 12. Various equipment areas: 13. Living area: 14. Condensate storage tank: 18. Laydown area: 19. Ancillary equipment area: 20. Main transformer: 21. Auxiliary boiler: 22. Anchor chain: 23. Light oil tank: 24. Waste treatment room: 25. Bow ballast tank: 26. Bottom ballast tank: 27. Stern ballast tank: 28. Side ballast tank: 29. Dust removal device: 30. Emergency condenser system: 3A. Containment vessel: 3B. Nuclear fuel: 3C. Control rods: 3D. Recirculation pump: 3E. Pressure vessel: 3 F... Safety relief valve: 3G... Exhaust pipe: 3H... Suppression pool: 3J... Main steam isolation valve: 3K... Main steam isolation valve: 3L... Main steam pipe: 3M... Upper dry well: 3N... Lower dry well: 4A... Turbine: 4B... Generator: 4C... Condenser: 4D... Circulating water piping: 4E... Circulating water pump: 4F... Feedwater pump: 4G... Feedwater piping: 3AP... Seawater inlet pipe: 3AV... Seawater inlet valve: 4DS... Intake: 4DH Water outlet: 10A, connecting valve: 10B, connecting valve: 10C, connecting valve: 10D, atmospheric release pipe: 26A, steel plate: 26B, heat transfer plate: 29A, dust removal pit: 29B, strainer: 29C, inlet: 29D, cyclone: ​​29E, settling tank: 29F, strainer: 29G, discharge door: 29H, outlet: 30A, emergency condenser: 30B, piping: 30C, piping: 30D, heat exchanger for PCCS

Claims

1. A floating nuclear power generation system comprising: a nuclear reactor; a turbine generator driven by steam generated by the heat of the reactor; and a float on which the nuclear reactor and the turbine generator are disposed and which is moored at sea, wherein the float has a core catcher below the reactor, the underside of which is filled with ballast water from a bottom ballast tank formed in the bottom part of the float by a double hull structure.

2. The floating nuclear power generation system according to claim 1, wherein the core catcher is made of steel and comprises a steel plate forming the bottom portion of the containment vessel in which the reactor is housed, and a heat transfer plate erected in the bottom ballast tank on the underside of the steel plate.

3. The floating nuclear power generation system according to claim 1, further comprising a communication valve that allows water around the float to flow into the containment vessel.

4. A floating nuclear power generation system according to any one of claims 1 to 3, further comprising a sinking means for sinking the float.

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