Fuel debris take-out method and fuel debris take-out system

Abstract

To take out fuel debris in an underwater environment by submerging a part of a nuclear facility suffering from a severe accident in water and shielding radiation with water.SOLUTION: A fuel debris take-out method includes: building a water gate 82 that communicates with the inside of a nuclear facility in which fuel debris 7 is generated due to a severe accident and that opens and closes at a position lower than the height of a surface 99 of water storage present in at least part of the inside of the nuclear facility; storing water up to a position higher than the position where the water gate 82 opens and closes and building a water storage tank 81 on the outside of the nuclear facility; when taking out the fuel debris 7 from the inside of the nuclear facility, causing a cutting device 72 to enter the inside of the nuclear facility from the water storage tank 81 through an opening of the water gate 82 to cut the fuel debris 7 inside the nuclear facility; conveying, by a conveying device 71, cut pieces of the fuel debris generated from the cutting performed by the cutting device 72 in the water of the water storage tank 81; and accommodating, by an accommodating device 77, the cut pieces conveyed by the conveying device 71 in a waste container 23 in the water of the water storage tank 81.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a decommissioning technique for a nuclear reactor that has suffered a severe accident. [Background technology]

[0002] In the event of a severe accident, including a core meltdown, at a boiling water nuclear power plant, the reactor containment vessel and reactor pressure vessel are damaged, making dismantling work extremely difficult in a flooded state. Furthermore, the high radiation levels inside the reactor building and the low water level make it difficult to identify damaged areas and repair water leaks. In such cases, fuel debris must be removed and the reactor building dismantled in an air environment. However, much of the dismantling work must be performed remotely, and measures must be taken to prevent the leakage of radioactive dust produced during cutting work during dismantling. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6960170 [Patent Document 2] Patent No. 5757222 [Patent Document 3] Patent No. 6186980 [Patent Document 4] Patent No. 7070998 [Patent Document 5] Patent No. 7071003 [Patent Document 6] Utility Model Registration No. 3196318 [Patent Document 7] Patent No. 5961572 Summary of the Invention [Problem to be solved by the invention]

[0004] Various technologies have been known in the past. For example, the fuel debris treatment method described in Patent Document 1 aims to settle ultra-high specific gravity muddy water containing barite, solidify the fuel debris, and store it. However, no consideration is given to a method for removing nuclear fuel material or radioactive material from the area where it remains.

[0005] Furthermore, the flooding methods for a containment vessel described in Patent Documents 2 and 3 assume that there is a damaged area in the containment vessel, but that it is difficult to identify the damaged area, and so all of the space is filled with concrete. Since a large amount of radioactive waste will be generated, a watertight structure is constructed upstream of the anticipated damaged area, and the containment vessel is then flooded. This flooding method has the problem of requiring a large amount of work to be performed inside the reactor building, which is highly radioactive.

[0006] Furthermore, the reactor building flooding devices in Patent Documents 4 and 5 have a bottom constructed underground below the reactor building, and physically isolate the entire reactor building while flooding it. This is a very good concept as it reduces the risk of contaminated water leaking into the environment, but there are issues with this, such as the increased amount of work required, and in particular the need to construct an underground shield tunnel.

[0007] Furthermore, the nuclear reactor decommissioning support facility in Patent Document 6 constructs a pool that covers all of the multiple reactor buildings, and submerges the entire reactor buildings. However, there are issues such as the difficulty of constructing the bottom of the pool, the large scale of the pool, and the extremely large amount of water that the pool can hold.

[0008] Furthermore, the nuclear fuel processing method in Patent Document 7 pulverizes fuel debris by at least one of the following processes: heat treatment, mechanical fragmentation, electrical fragmentation, oxidation, reduction, and halogenation. However, no consideration is given to a method for removing nuclear fuel material or radioactive material from the area where it remains.

[0009] An embodiment of the present invention has been made in consideration of these circumstances, and aims to submerge part of a nuclear facility that has suffered a severe accident in water, shield it from radiation with water, and remove fuel debris in an underwater environment. [Means for solving the problem]

[0010] A fuel debris removal method according to an embodiment of the present invention includes constructing a water gate that leads to the inside of a nuclear facility where fuel debris has been generated due to a severe accident and that opens and closes at a position lower than the water level of stored water present in at least a part of the inside of the nuclear facility, constructing a water tank outside the nuclear facility that is connected to the water gate and stores water up to a position higher than the position at which the water gate opens and closes, and when removing the fuel debris from inside the nuclear facility, inserting a cutting device from the water tank into the inside of the nuclear facility through the opening of the water gate to cut the fuel debris inside the nuclear facility, transporting the pieces of the fuel debris cut by the cutting device through the water in the water tank with a transport device, and storing the cut pieces transported by the transport device in a waste container within the water in the water tank with a storage device. [Effects of the Invention]

[0011] According to an embodiment of the present invention, a portion of a nuclear facility that has suffered a severe accident can be flooded, the water can provide radiation shielding, and fuel debris can be removed in an underwater environment. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view showing the reactor building from which fuel debris is removed in the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the connection between the water tank and the containment vessel. [Figure 3] FIG. 2 is a cross-sectional view showing a reactor containment vessel being perforated by a cutting device. [Figure 4] A cross-sectional view showing the containment vessel from which fuel debris is removed. [Figure 5] FIG. 10 is a cross-sectional view showing a reactor building from which fuel debris is removed in the second embodiment. [Figure 6]Cross-sectional view showing the connection between the water tank and the reactor building. [Figure 7] FIG. 1 is a cross-sectional view showing a reactor building being drilled by a cutting device. [Figure 8] A cross-sectional view showing the reactor building from which fuel debris is removed. DETAILED DESCRIPTION OF THE INVENTION

[0013] (First embodiment) Hereinafter, embodiments of a fuel debris retrieval method and a fuel debris retrieval system will be described in detail with reference to the drawings. Note that the scale of each component shown in the drawings may be changed as appropriate to facilitate understanding.

[0014] Reference numeral 1 in Fig. 1 denotes a reactor building included in a nuclear facility. This reactor building 1 is a facility of a nuclear power plant that has suffered a severe accident, and decommissioning work is being carried out therein. The fuel debris retrieval system 100 of the first embodiment is used in this reactor building 1 to mainly retrieve fuel debris 7 that has fallen to the bottom of the reactor containment vessel 4. A fuel debris retrieval method is carried out using this fuel debris retrieval system 100.

[0015] In the fuel debris retrieval method, all processes of cutting, transporting, and accommodating the fuel debris 7 are carried out while the fuel debris 7 remains submerged in water. In other words, the work of retrieving the fuel debris 7 can be carried out while shielding it from radiation with water.

[0016] In the event of a severe accident, the fuel assemblies in the reactor melt due to overheating of the nuclear fuel, resulting in a so-called meltdown. The molten nuclear fuel leaks from the reactor pressure vessel 5 contained inside the reactor containment vessel 4. The reactor containment vessel 4 is also damaged by the increased pressure inside. Because the fuel debris 7 containing the molten nuclear fuel is highly radioactive, even remotely operated robots may malfunction due to the effects of radiation if the work of removing the fuel debris 7 is attempted using the partial submersion method. There is also a risk of workers being exposed to radiation.

[0017] In the process of removing the fuel debris 7 from the reactor building 1, the fuel debris retrieval system 100 transports the fuel debris 7 and stores it in a waste container 23. If the fuel debris 7 to be removed can be surrounded by water, the water can shield it from radiation. Furthermore, inside the reactor building 1, there are many other highly radioactive areas in addition to the fuel debris 7, and these also need to be submerged when being removed. Therefore, the fuel debris retrieval system 100 submerges at least a portion of the reactor building 1 and the reactor containment vessel 4. Note that there may already be stored water inside the reactor containment vessel 4 due to the cooling water injected after the severe accident.

[0018] 1 shows the overall configuration of the fuel debris retrieval system 100. The fuel debris retrieval system 100 comprises, for example, a water gate 82, a water tank 81, a cutting device 72, a transport device 71, and a storage device 77. Furthermore, the fuel debris retrieval system 100 comprises components incidental to these.

[0019] The floodgate 82 leads to the interior of the nuclear facility where fuel debris 7 has been generated due to a severe accident, and is constructed to open and close at a position lower than the height of the water surface 99 (Figure 3) of the reservoir water present in at least a part of the interior of the nuclear facility.

[0020] The water tank 81 is connected to the water gate 82, stores water up to a position higher than the position at which the water gate 82 opens and closes, and is constructed outside the nuclear facility. The water tank 81 is a structure such as a wall structure made of plate material designed only for water storage, a concrete structure with a metal lining, a double structure, a tank structure, or a hull structure.

[0021] 3, the water gate 82 of the first embodiment is constructed on the side of the reactor containment vessel 4 included in the nuclear facility. In addition, the cutting device 72 is provided in the water tank 81. This cutting device 72 extends from the water tank 81 to the fuel debris 7 present inside the reactor containment vessel 4.

[0022] As shown in Fig. 4, when removing fuel debris 7 from inside the nuclear facility, the cutting device 72 enters the inside of the nuclear facility through the opening of the water gate 82 from the water tank 81 and cuts up the fuel debris 7 inside the nuclear facility. The transport device 71 transports the cut pieces of the fuel debris 7 cut by the cutting device 72 in the water of the water tank 81. The storage device 77 stores the cut pieces transported by the transport device 71 in the waste container 23 in the water of the water tank 81.

[0023] As shown in Figure 1, the structure of a reactor building 1 above an operation floor 2 has been dismantled and removed. The reactor building 1 is a reinforced concrete structure. A reactor containment vessel 4 is located inside the reactor building 1. The reactor containment vessel 4 is composed of a main body 4a, a pressure suppression chamber 4b, and a head 4c. A reactor pressure vessel 5 is located inside the reactor containment vessel 4. The reactor pressure vessel 5 is composed of a main body shell 5a, a head 5b, a reactor substructure 5c, and a head insulation material (not shown). The reactor pressure vessel 5 is supported on the bottom of the main body 4a of the reactor containment vessel 4 via a pedestal 6. Fuel debris 7 that fell from the reactor pressure vessel 5 due to a core meltdown has accumulated at the bottom of the main body 4a of the reactor containment vessel 4. A boiling water reactor (BWR) is shown as an example here.

[0024] The fuel debris retrieval system 100 may be configured to stop water leakage points in the containment vessel 4 with fine particles (fine particle deposition layer 8b) and store water at the bottom of the main body 4a of the containment vessel 4 to the extent that the fuel debris 7 is submerged. For example, when it is desired to increase the water level inside the containment vessel 4, an injection device 21 is used.

[0025] The fuel debris retrieval system 100 includes an injector 21 that injects a microparticle dispersion liquid 8 containing microparticles into a nuclear facility. The fuel debris retrieval system 100 further includes configurations associated with these components.

[0026] Furthermore, when removing fuel debris 7 from inside a nuclear facility where a water leak has occurred due to a severe accident, the fuel debris removal system 100 seals the leak with fine particles that have a specific gravity greater than that of water, and floods at least a portion of the nuclear facility.

[0027] The injection device 21 injects the microparticle dispersion 8 into the internal space of the nuclear facility where the leak location exists, and forms a microparticle deposition layer 8b by accumulating microparticles until the level is higher than the leak location. The injection device 21 also raises the water level of the water stored inside the nuclear facility to submerge the sluice gate 82. Note that if the water level of the water stored inside the nuclear facility is sufficiently high, the injection of the microparticle dispersion 8 by the injection device 21 may be omitted. In other words, the configuration of the injection device 21 may be omitted in the fuel debris retrieval system 100.

[0028] In a reactor where a severe accident has occurred, it may be difficult to identify the leak location. In such cases, the height of the leak location can be predicted from information such as the water level (height) of the water stored inside the reactor containment vessel 4 and design drawings of the reactor. The design drawings include, for example, a system diagram of the reactor and a piping route diagram. The injector 21 injects the microparticle dispersion 8 until it reaches this predicted height, forming a microparticle sediment layer 8b. It is sufficient that at least the height of the leak location can be predicted.

[0029] Furthermore, a reinforced concrete skeleton (not shown) exists on the outside (outer surface) of the containment vessel 4. Here, the outside of the containment vessel 4 is not in direct contact with the skeleton, and a template (not shown) exists between the outside of the containment vessel 4 and the skeleton. A gap (not shown) exists between the outside of the containment vessel 4 and the template. Furthermore, openings constituted by penetrations for piping (not shown) or the like are provided in the template and the reinforced concrete skeleton. The fuel debris retrieval system 100 may also inject the microparticle dispersion liquid 8 into these gaps and openings to form a microparticle deposition layer 8b. This makes it possible to stop leakage points related to the gaps and openings.

[0030] The microparticles contain at least barite as a weighting material, and optionally at least bentonite as a thickener. The microparticles are deposited without solidifying, and are a water-stopping material with fluidity. The blending ratio of materials such as barite and bentonite is adjusted in advance so that the microparticles have such properties. The deposited microparticles can be made to flow again by applying vibration. In other words, even in a location where a microparticle deposition layer 8b has already formed, applying vibration can wash away the microparticle deposition layer 8b. Note that modes of applying vibration include modes of stirring.

[0031] The fine particle deposition layer 8b has fluidity, and various devices can access the fuel debris 7 even when the fuel debris 7 is buried in the fine particle deposition layer 8b. In other words, in the following explanation, the state in which the fuel debris 7 is buried in the fine particle deposition layer 8b and the state in which the fuel debris 7 is submerged are almost the same state and have the same meaning.

[0032] The fuel debris retrieval system 100 first drills a hole in the side surface of the main body 4a of the containment vessel 4 to form a drilled section 19. The side surface of the main body 4a of the containment vessel 4 may be dissolved with a predetermined chemical solution such as sulfuric acid. Next, the fuel debris retrieval system 100 injects a particulate dispersion 8 into the containment vessel 4 through the drilled section 19 to form a particulate deposition layer 8b in which particulates are deposited inside the main body 4a of the containment vessel 4. If another path such as a penetration (not shown) in the containment vessel 4 already exists, the particulate dispersion 8 may be injected through that path.

[0033] At this point, water is injected into the containment vessel 4 up to a height that submerges the perforated section 19. The fuel debris 7 is then removed while it is submerged in water. When removing the fuel debris 7 underwater, sediments may be stirred up during the cutting work for removal, and the cutting powder may turn into colloids, causing the water to become cloudy and spread. By draining the water near such dismantling work areas and transferring it to a separate water purification facility, the diffusion of colloidal particles containing radioactive materials into the water can be prevented.

[0034] The fuel debris retrieval system 100 also drills the pressure suppression chamber 4b to form a drilled section 27. Next, the fuel debris retrieval system 100 injects a particulate dispersion 8 into the pressure suppression chamber 4b through the drilled section 27 to form a particulate deposition layer 8b in which particulates are deposited in the pressure suppression chamber 4b. Furthermore, the pressure suppression chamber 4b is filled with water, and water is injected into the containment vessel 4 to a height that submerges the drilled section 19. Then, the fuel debris 7 is retrieved while it is submerged in water.

[0035] A first cover building 3 is arranged around the reactor building 1. The first cover building 3 is constructed on the ground near the reactor building 1 and extends over the reactor building 1. A ventilation and air conditioning system (not shown) is arranged in this first cover building 3 to purify and ventilate the air inside. Note that the first cover building 3 may be configured to have a shielding function to shield the interior from radiation, taking into account the ease of work in the surrounding area.

[0036] A water tank 81 is constructed near the outside of the reactor building 1. This water tank 81 is constructed, for example, in the ground near the first cover building 3 or in the ground dug down to ensure the required water depth. This water tank 81 has a double structure. In addition, the double structure part of the water tank 81 is provided with a water leakage sensor (not shown) that can detect water leakage.

[0037] The water tank 81 is a pool that is open at the top. Because the water tank 81 is configured as a pool, workers can approach the water surface 99 of the water tank 81 to perform work. For example, the workers can access various devices that are placed underwater in the water tank 81.

[0038] The water tank 81 may be a tank that is closed off and sealed at the top. If the water tank 81 is a tank, it may be provided with a device that adjusts the air pressure or water pressure inside it as needed. If the water tank 81 is a tank, it may be provided with a top cover member or the like to facilitate transportation and handling of the device, and the top of the tank may be structured to be openable and closable.

[0039] In addition, a second cover building 3a is hung over the water tank 81. A ventilation and air conditioning system (not shown) is installed in this second cover building 3a to purify and ventilate the air inside.

[0040] Note that a member having a shielding function may be provided in the second cover building 3a. For example, a shielding wall made of reinforced concrete having a shielding function, or a shielding wall that stores water inside, may be provided in the second cover building 3a. In this way, radiation generated inside the first cover building 3 can be shielded so as not to leak to the outside.

[0041] To provide the water tank 81, an opening is formed in a part of the wall of the reactor building 1 near the water tank 81. Also, a predetermined area of ​​obstacles or concrete framework (not shown) around a hatch (not shown) at the loading entrance of the main body 4a of the reactor containment vessel 4 is dismantled and removed using remotely controlled heavy machinery (not shown). Then, near the water tank 81, the outer steel surface of the main body 4a of the reactor containment vessel 4 is exposed.

[0042] The fuel debris retrieval system 100 also includes a water treatment facility 43 installed outside the first cover building 3. The water treatment facility 43 includes a water storage container 43a, transfer devices 46a, 46b, and 46c, a filter 48, and transfer pipes 47a, 47b, and 47c. The transfer devices 46a, 46b, and 46c are, for example, pumps.

[0043] The transfer piping 47c extends from the torus room 32 at the bottom of the basement floor of the reactor building 1 (nuclear facility) to the water storage container 43a. The suction port of the transfer piping 47c is provided in the basement floor of the reactor building 1. The transfer device 46c is provided on the transfer piping 47c. By driving the transfer device 46c, the water in the torus room 32 is transferred to the water storage container 43a.

[0044] The transfer pipe 47b extends from the water tank 81 to the water storage container 43a. The transfer device 46b is provided on the transfer pipe 47b. When the transfer device 46b is driven, the water in the water tank 81 is transferred to the water storage container 43a.

[0045] The water storage container 43a stores water discharged from the torus chamber 32 and the water storage tank 81 by the respective transfer devices 46b, 46c. The water storage container 43a is covered with a reinforced concrete skeleton. Note that the water storage container 43a may be covered with a third cover building (not shown) instead of the reinforced concrete skeleton.

[0046] Transfer piping 47a extends from water storage container 43a to water storage tank 81. Transfer device 46a and filter 48 are provided on transfer piping 47a. By driving transfer device 46a, water in water storage container 43a is transferred to water storage tank 81. The transferred water is purified by filter 48.

[0047] The side surface of the main body 4a of the containment vessel 4 is perforated to form a perforated section 19. An isolation room 20 is arranged adjacent to this perforated section 19. An injection device 21 is arranged near the isolation room 20 and inside the first cover building 3.

[0048] The injector 21 has a function of injecting the microparticle dispersion 8 into the inside of the reactor containment vessel 4. The injector 21 injects the microparticle dispersion 8 into the inside of the pedestal 6 through the isolation room 20, the perforated portion 19, and the opening 28 of the pedestal 6. The injector 21 includes a water injection pump. The opening 28 of the pedestal 6 is, for example, an existing opening such as a carry-in port (not shown) of a control rod drive mechanism. The injector 21 also has a function of draining the supernatant liquid 8a from inside the main body 4a of the reactor containment vessel 4. In other words, the injector 21 includes a discharge device (drainage pump).

[0049] The supernatant liquid 8a is water separated from the microparticle dispersion liquid 8. The water in the water tank 81 may contain the supernatant liquid 8a. Furthermore, the supernatant liquid 8a inside the containment vessel 4 may contain the water in the water tank 81.

[0050] A tube bundle 22 consisting of a plurality of tubes for injecting the microparticle dispersion liquid 8 is provided inside the main body 4a of the reactor containment vessel 4. Also provided is an isolation tube 26 that passes through a perforated portion 27 drilled in the pressure suppression chamber 4b.

[0051] The injection device 21 injects the microparticle dispersion 8 into the pressure suppression chamber 4b through the perforated portion 27 to form a microparticle deposition layer 8b inside the pressure suppression chamber 4b. The injection device 21 may also inject the microparticle dispersion 8 into the space outside the pressure suppression chamber 4b (torus chamber 32) to form the microparticle deposition layer 8b outside the pressure suppression chamber 4b.

[0052] Furthermore, a predetermined drilling device (not shown) forms a drilled portion 29 in the floor surface 33 of the first floor of the reactor building 1. An isolation pipe 26 is provided in this drilled portion 29. The tip of the isolation pipe 26 is attached to the outer surface of the pressure suppression chamber 4b by a rubber seal or by welding. Furthermore, the predetermined drilling device forms a drilled portion 27 in the pressure suppression chamber 4b. This drilled portion 27 is disposed inside the isolation pipe 26 and is isolated. In other words, the gas or liquid flowing out from the inside of the pressure suppression chamber 4b is isolated by the isolation pipe 26.

[0053] A tube bundle 30 consisting of a plurality of tubes for injecting the microparticle dispersion 8 is arranged inside the pressure suppression chamber 4b of the reactor containment vessel 4. The tube bundle 30 is arranged through an isolation pipe 26. The base end of the tube bundle 30 is connected to the injection device 21.

[0054] The tube bundle 30 can also drain the supernatant liquid 8a of the microparticle dispersion liquid 8. Furthermore, the tube bundle 30 is connected to a ventilation and air conditioning system (not shown) that removes radioactive materials. This ventilation and air conditioning system purifies the gas inside the reactor containment vessel 4. Furthermore, the isolation pipe 26 is connected to the ventilation and air conditioning system that removes radioactive materials in order to treat radioactive dust generated during the drilling work.

[0055] A tube bundle 31 consisting of a plurality of tubes for injecting the microparticle dispersion liquid 8 is disposed inside the torus chamber 32. The tube bundle 31 is disposed through a perforated portion 29 in the floor surface 33 of the first floor of the reactor building 1. The base end of the tube bundle 31 is connected to the injector 21. The tube bundle 31 can also drain the supernatant liquid 8a. The tube bundle 31 is also connected to a ventilation and air conditioning system (not shown) that removes radioactive materials. The ventilation and air conditioning system purifies the gas inside the torus chamber 32.

[0056] An isolation room 20 is arranged on the side of the containment vessel 4 so as to be in close contact with its main body 4a. A drilling section 19 is formed inside this isolation room 20. To treat radioactive dust generated during the drilling work, the isolation room 20 is equipped with a ventilation and air conditioning system (not shown) that removes radioactive materials. This ventilation and air conditioning system purifies the gas inside the isolation room 20.

[0057] In addition, when the perforated portion 29 in the floor surface 33 of the first floor of the reactor building 1 and the opening 28 in the pedestal 6 are formed in advance, isolation devices (not shown) may be installed to isolate each of these parts. These isolation devices may be provided with ventilation and air conditioning equipment (not shown).

[0058] An injection device 21 is also disposed inside the first cover building 3. Furthermore, a tube bundle 22 consisting of a plurality of tubes for injecting the microparticle dispersion liquid 8 and draining the supernatant liquid 8a is also disposed inside the first cover building 3. The tube bundle 22 passes through the isolation room 20 and the perforated section 19, and extends from an opening 28 of the pedestal 6, which is the entrance for the control rod drive mechanism, into the inside of the pedestal 6.

[0059] When the microparticle dispersion 8 is injected from the tube bundle 22, the microparticles, having a higher specific gravity than water, gradually settle and accumulate downward, forming a microparticle sediment layer 8b inside the containment vessel 4. When the height of the upper surface of this microparticle sediment layer 8b exceeds the height of the leak point and the leak point is covered with the microparticle sediment layer 8b, a watertight effect is achieved. Then, the water level inside the containment vessel 4 rises. Note that the leak point includes the entrance and exit of the piping that leads to the internal space of the containment vessel 4. In other words, the entrance and exit of the piping that already existed before the severe accident may also become a leak point.

[0060] For example, if the water leakage stops at the height of the first floor 33 of the reactor building 1 and a rise in the water level commensurate with the injection amount and the space volume is observed, the injection device 21 injects clean water instead of the microparticle dispersion liquid 8. In addition, the gas inside the reactor containment vessel 4 is purified by an air conditioning system (not shown).

[0061] It should be noted that the fuel debris retrieval system 100 does not need to have a drainage function if the leakage point can be watertight by injecting the microparticle dispersion liquid 8 into the reactor containment vessel 4 only once. For example, even if water remains at the bottom of the main body 4a of the reactor containment vessel 4, microparticles will accumulate, and a microparticle accumulation layer 8b can be formed.

[0062] Furthermore, when the microparticle dispersion liquid 8 is first introduced, water may already have accumulated in a portion of the containment vessel 4, and this water may dilute the microparticle dispersion liquid 8. In such cases, a specified drainage device (not shown) is added to the fuel debris retrieval system 100. Then, the injection of the microparticle dispersion liquid 8, settling, and discharge of the supernatant liquid 8a are repeated. In this way, the amount of accumulated microparticles increases. By increasing the amount of accumulated microparticles, it is possible to stop water from leaking from multiple leaking points lined up in the height direction of the containment vessel 4.

[0063] Furthermore, even if the water cannot be completely stopped, the leak will fall into the basement floor, and the water in the basement floor will be sent to the water storage container 43a by the transfer device 46c. Then, water is poured from the water storage container 43a into the water tank 81 and the containment vessel 4. In such a case, a flow occurs from the water storage tank 81 to the containment vessel 4. Therefore, it is possible to suppress the diffusion of radioactive materials into the water storage tank 81 into which clean water is poured. Furthermore, if the amount of circulating water increases, the water may be transferred to a separately installed contaminated water treatment facility (not shown).

[0064] As shown in Fig. 2, the water tank 81 is in contact with the side surface of the main body 4a of the reactor containment vessel 4. A water gate 82 is constructed at this contacting portion. The water gate 82 is kept airtight and watertight, and can be opened and closed by remote control.

[0065] The water gate 82 is disposed at the end of the water tank 81. The entire periphery of the opening of the water gate 82 is welded to the surface of the main body 4a of the reactor containment vessel 4. Alternatively, the entire periphery of the opening of the water gate 82 is fixed in intimate contact with the surface of the main body 4a of the reactor containment vessel 4.

[0066] The water gate 82 is connected to the inside of the reactor containment vessel 4, and opens and closes at a position lower than the water level (height) of the stored water inside the reactor containment vessel 4. In other words, the water gate 82 is positioned so that when it is opened, its opening is located at a position lower than the water level (height) of the stored water.

[0067] The water gate 82 is configured so that the water level at which its opening is submerged is maintained even when it is fully opened. In this way, the gas phase of the reactor containment vessel 4 does not flow toward the second cover building 3a (water tank 81) through the water gate 82. In other words, the gas phase of the reactor containment vessel 4 and the gas phase of the second cover building 3a can be isolated. Therefore, during the work of removing fuel debris 7, dust inside the reactor containment vessel 4 does not leak toward the second cover building 3a.

[0068] Furthermore, ventilation and air conditioning equipment (not shown) is connected to the reactor containment vessel 4, the reactor building 1, the first cover building 3, and the second cover building 3a to purify the gas inside these buildings. These ventilation and air conditioning equipment ensure that the air pressure inside the reactor containment vessel 4 is lowest, and that the air pressure decreases in the order of the reactor building 1, the first cover building 3, and the second cover building 3a. In this way, even if the top of the opening of the water gate 82 is exposed to the air, dust inside the reactor containment vessel 4 will not leak through the opening of the water gate 82 toward the second cover building 3a.

[0069] The fuel debris removal system 100 makes the air pressure in the gas phase space (internal space) on the side of the nuclear facility where the fuel debris 7 was generated, separated by the water gate 82, lower than the air pressure in the gas phase space (the internal space of the second cover building 3a or the atmosphere) on the side of the water tank 81 located outside the nuclear facility. In this way, in the unlikely event that the water gate 82 is not submerged, the gas on the side of the water tank 81 will flow into the inside of the nuclear facility, preventing dust from inside the nuclear facility from leaking toward the second cover building 3a.

[0070] Furthermore, when the floodgate 82 is opened, water flows from the water tank 81 to the reactor containment vessel 4, so that when the floodgate 82 is open, the water level inside the reactor containment vessel 4 and the water tank 81 can be kept the same.

[0071] If leakage occurs at the connection between the water gate 82 and the main body 4a of the reactor containment vessel 4 due to an earthquake or the like, the leaking water will flow through a floor drain hole (not shown) or a floor penetration hole (not shown) and fall into the basement floor of the reactor building 1. This falling water will be transferred to the water storage vessel 43a by the transfer device 46c.

[0072] As shown in FIG. 1, various devices are arranged in the water storage tank 81 for storing the removed cut pieces (not shown) in the waste container 23 underwater, closing the lid, decontaminating, and carrying them out.

[0073] A carry-in room 69 is provided near the water tank 81. This carry-in room 69 is connected to the second cover building 3a. The carry-in room 69 is equipped with material handling equipment (not shown) inside. The material handling equipment is provided for temporarily locating a cutting device 72 for removing the fuel debris 7. The material handling equipment includes lifting devices such as cranes and hoists. An airtight door 73 is also provided at the bottom of the carry-in room 69. This airtight door 73 is provided to allow equipment to enter the water tank 81. An airtight door 73a is also provided at the side of the carry-in room 69. This airtight door 73a is provided to allow equipment to enter the interior of the second cover building 3a.

[0074] To construct the water tank 81, it is first necessary to form an opening in the wall of the reactor building 1. When forming this opening, a seismic evaluation of the reactor building 1 is performed, and the reactor building 1 may be seismically reinforced as necessary.

[0075] As shown in FIG. 3, the cutting device 72 has at its tip a device for performing at least one of the cutting processes of thermal cutting, mechanical cutting, electrical cutting, laser cutting, gas cutting, and cutting by chemical dissolution.

[0076] For example, the cutting device 72 has a base 14, a support rod 15, and a cutting unit 16. The cutting unit 16 is provided at the tip of the support rod 15. The support rod 15 is a rod-shaped member having a hollow pipe-like interior. The cut pieces cut out by the cutting unit 16 can be transported through the inside of the support rod 15. In other words, the cutting device 72 also functions as part of the transport device 71.

[0077] The base portion 14 is provided on the water tank 81. The base portion 14 supports the base end of the support rod 15. The base portion 14 has a driving device (not shown) such as a motor for controlling the forward and backward movement of the support rod 15 and for changing the angle θ up, down, left, and right.

[0078] 4, the support rod 15 enters the inside of the containment vessel 4 horizontally from the water gate 82 and changes the angle θ with the base 14 as a fulcrum. The cutting unit 16 at the tip of the support rod 15 accesses the area inside the containment vessel 4 where the fuel debris 7 exists. In addition, by tilting the tip of the support rod 15 so that it faces upward, the cutting unit 16 can also access the bottom of the reactor pressure vessel 5.

[0079] For example, when the floodgate 82 is open, the cutting device 72 can move straight ahead or backward. Furthermore, the cutting device 72 can change the angle of inclination θ of the support rod 15 up, down, left, or right. The cutting device 72 can also cut the fuel debris 7 with the cutting unit 16. The cutting device 72 can also cut structures that obstruct movement to the fuel debris 7. Cutting modes of the cutting device 72 include excavation and crushing.

[0080] The cutting device 72 is, for example, a boring machine. The support rod 15 is, for example, a boring rod. The cutting unit 16 is, for example, a boring bit. The boring machine includes a diamond core boring machine, a spindle boring machine, a rotary boring machine, a rotary percussion drill, etc.

[0081] The cutting device 72 may be a device other than a boring machine. For example, the cutting unit 16 may be a welding machine, a laser output device, a burner, or a chemical injector. The cutting device 72 may also be a device that combines the above-mentioned configurations.

[0082] When the cutting unit 16 shreds the lumps of fuel debris 7, detached pieces are generated. The pieces are particles or small chunks such as excavated pieces, dross, slag, slag, spatter, and burrs. These pieces are transported from inside the containment vessel 4 through a water gate 82 to a water tank 81. The pieces are transported by methods such as underwater suction, a belt conveyor, a screw feeder, vibrating transport, scooping, pushing transport, towing transport, and caterpillar transport. The pieces are then collected in the water of the water tank 81.

[0083] Fig. 1 shows an example of underwater suction. The transport device 71 is, for example, a transport pump that sucks in the cut pieces along with the water. This transport device 71 sucks water mixed with the cut pieces from the cutting device 72 via a transport hose 78, and classifies the water in a cyclone separator 74. Relatively large cut pieces are then collected in a collection container 75, and small cut pieces are collected in a filter 76. These cut pieces are then stored in a waste container 23 underwater. The waste container 23 has its lid 23a closed underwater, and is then transported to the outside by a container transport facility 24.

[0084] The container transport equipment 24 includes a carry-in device and an elevator device. The container transport equipment 24 drains water from the waste container 23. The carry-in device is, for example, a belt conveyor. The elevator device is, for example, an elevator for transporting the waste container 23 out of the water. The container transport equipment 24 also includes a decontamination device, a floor transport device, a surface survey, additional decontamination equipment, an unloading room with a ceiling opening / closing hatch, and a crane. The container transport equipment 24, for example, lifts the waste container 23 from the unloading room with a crane and transports it outside.

[0085] A plurality of storage devices 77 are provided inside the second cover building 3a. At least one storage device 77 is required. These storage devices 77 are, for example, cranes. These storage devices 77 are used to transport the collection container 75, the filter 76, the waste container 23, and the lid 23a. The storage devices 77 are also used to transport various pieces of equipment inside the pool, such as lifting tools and gripping tools. The storage devices 77 are also used when disassembling and assembling the cyclone separator 74.

[0086] 2 shows a connection between the main body 4a of the reactor containment vessel 4 and the water tank 81. A portion of the concrete framework around the main body 4a of the reactor containment vessel 4 has been removed in advance using remotely controlled heavy machinery (not shown).

[0087] The water gate 82 has a water gate plug 83, an opening / closing mechanism 84, and a pressing mechanism (not shown). The water gate 82 is closed by the water gate plug 83. The water gate plug 83 has a sealing member. The water gate plug 83 may be a water stop plug that expands at least in part to close the opening. By closing the water gate 82 with the water gate plug 83, the connection portion between the water tank 81 and the main body 4a of the reactor containment vessel 4 can be closed airtight and watertight.

[0088] The water gate 82 has a fixed structure with the main body 4a of the reactor containment vessel 4. For example, the water gate 82 has a welded joint 85. The water gate 82 is fixed to the surface of the reactor containment vessel 4 by this welded joint 85. The fixing structure of the water gate 82 may be a fixing structure that maintains airtightness and watertightness by using a single or double or more resin seals or waterstop materials.

[0089] The water gate 82 is carried in through an opening in the reactor building 1 to be connected to the reactor containment vessel 4. At that time, the water gate 82 is fixed in a cantilevered manner to the bottom of the water tank 81. In this way, it is possible to prevent load from being applied to the first floor 33 of the reactor building 1 or to the reactor containment vessel 4 after the water gate 82 is connected. In addition, the water tank 81, the first cover building 3, and the second cover building 3a are connected to each other in an airtight manner.

[0090] 3 shows the state in which the water tank 81 is filled with water. After this water filling, the water gate plug 83 is opened. Then, the cutting device 72 drills a hole in the main body 4a of the reactor containment vessel 4 through the opening of the water gate 82. After the main body 4a of the reactor containment vessel 4 is opened, the cutting device 72 further advances. Note that this water gate plug 83 may have a shielding function to shield radiation from the reactor building 1.

[0091] Figure 4 shows the cutting device 72 moving straight and cutting the fuel debris 7. The support rod 15 of the cutting device 72 moves straight, and the cutting unit 16 at its tip cuts the fuel debris 7. The support rod 15 that moves straight may have a telescopic mechanism, or it may move straight by connecting and adding tubes or rods. This straight movement may be performed by a mechanism installed in the cutting device 72, or it may be performed by a machine or a worker from the loading room 69 (Figure 1) installed in the water tank 81.

[0092] According to the first embodiment, the water tank 81 is constructed so as to expand the submerged area when the fuel debris 7 to be removed is submerged. Then, by using water, the water tank 81 and the high-dose area of ​​the reactor containment vessel 4 (reactor building 1) can be made watertight and airtight. Furthermore, by providing a water gate 82 with a submerged opening at a position below the water surface 99 of the water tank 81, various devices can be inserted into the reactor containment vessel 4 through the opening of the water gate 82.

[0093] Furthermore, it is possible to stop water leakage points in a flooded environment, collect, store and purify the leaked water, and circulate the water between the water tank 81 and the reactor building 1. Then, the water level inside the reactor containment vessel 4 (reactor building 1) and the water tank 81 can be maintained, and the fuel debris 7 can be removed while it is submerged.

[0094] Furthermore, since the cutting device 72 has a straight support rod 15, the cutting unit 16 can be pressed against the fuel debris 7. In other words, a pressing force can be applied in the axial direction (longitudinal direction) of the support rod 15. Therefore, compared to devices such as a robot arm having multiple joints, even if the diameter of the support rod 15 is small, a larger force can be applied to the tip of the support rod 15 than with a robot arm. This makes it easier for the cutting unit 16 to cut the fuel debris 7 and destroy the structure, while keeping the opening of the water gate 82 small. Furthermore, since the support rod 15 extends from near the outside of the opening of the water gate 82, the swing range of the support rod 15 can be increased, and the accessible range of the tip of the support rod 15 inside the reactor containment vessel 4 (reactor building 1) can be increased.

[0095] Furthermore, by providing the base portion 14 to the water tank 81, the weight of the cutting device 72 can be supported by the bottom of the water tank 81. Furthermore, by supporting a portion of the load near the water gate 82 of the water tank 81 in a cantilever state, the load acting on the inside of the reactor building 1 can be reduced and a large amount of the load can be supported outside the reactor building 1. Therefore, the weight of the cutting device 72 does not need to be applied to the reactor containment vessel 4 and the reactor building 1, and the effort required to reinforce the reactor containment vessel 4 and the reactor building 1 can also be saved.

[0096] (Second embodiment) Next, a second embodiment will be described. Note that the same components as those shown in the above-described embodiment will be assigned the same reference numerals and redundant description will be omitted.

[0097] 5, in the second embodiment, a water tank 80 is constructed that accommodates at least a portion of the reactor building 1 and that fills with water to submerge at least a lower portion of the reactor building 1. The water tank 80 has an outer wall 37 that surrounds the periphery of the reactor building 1. The inside of the outer wall 37 is filled with water, causing a portion of the reactor building 1 to be submerged.

[0098] The water gate 82 of the second embodiment is constructed on the side of a reactor building 1 included in a nuclear facility. The cutting device 72 is provided in a water tank 81. This cutting device 72 extends from the water tank 81 to the fuel debris 7 present inside the reactor building 1.

[0099] Furthermore, a pit 42 is formed on the outer periphery of the reactor building 1. However, the pit 42 does not necessarily have to be provided. Therefore, part of the basement structure of the reactor building 1 is exposed to the ground surface. A foundation 86 of the outer wall 37 is constructed near the pit 42, and the outer wall 37 is constructed on the foundation 86. The outer wall 37 may be a wall structure made of plate material that is designed only for water storage, a concrete structure with a metal lining, a double structure, a tank structure, a hull structure, or other structure that has a shielding function.

[0100] Furthermore, water leakage can be prevented by placing a predetermined member or water-stopping material between the outer wall 37 and the reactor building 1. Furthermore, since there is a possibility that groundwater may flow into the bottom of the pit 42, a transfer device 46d and transfer piping 47d are provided to transfer the stored water in the pit 42 to water treatment equipment 43. However, since there is a possibility that water from the reactor building 1 may also flow into the pit 42, the concentration of radioactive materials contained in the water in the pit 42 is measured and monitored, and then appropriate water treatment is carried out within the site, which is a radiation controlled area.

[0101] Next, the microparticle dispersion 8 is poured into the water tank 80, and a microparticle deposition layer 8b is formed by depositing the microparticles on the bottom of the water tank 80. Furthermore, water is poured into the water tank 80 up to at least a predetermined height of the containment vessel 4. Then, with at least the bottom of the containment vessel 4 submerged in water, the fuel debris 7 is removed.

[0102] Even if the amount of water leakage from the containment vessel 4 is reduced by injecting the microparticle dispersion liquid 8 and the bottom of the containment vessel 4 is flooded, it may not be possible to completely stop water leakage from the surface of the containment vessel 4. Also, an external event such as a large-scale earthquake may occur. In that case, equipment such as the containment vessel 4 in the reactor building 1 that has deteriorated due to the severe accident may be damaged, and water stored in this equipment may leak outside the containment vessel 4. Furthermore, the amount of leakage may increase.

[0103] Furthermore, even if the water leaking outside the containment vessel 4 is circulated back into the containment vessel 4 via the water treatment equipment 43 and the water tank 81, deterioration and damage may occur due to the amount of water leakage exceeding the design assumption. In addition, if the amount of water leakage is too large, the required capacity for draining water from the reactor building 1, the capacity for injecting water into the containment vessel 4, or the capacity for injecting water into the water tank 81 may become excessive, and the circulation system design may not be viable. Furthermore, even if the circulation system design is viable, it is possible that a water flow that interferes with the work of retrieving fuel debris 7 may occur in the work area.

[0104] Furthermore, it is known that there is high-dose equipment inside the reactor building 1 in addition to the reactor containment vessel 4, and dismantling this high-dose equipment in the air is expected to expose workers to radiation, so it is not desirable to perform work in an air environment.

[0105] In order to solve these various problems, the fuel debris retrieval system 100 of the second embodiment is equipped with a water tank 80. This fuel debris retrieval system 100 can minimize the amount of water leakage into the environment outside the reactor building 1. Furthermore, by forming a fine particle sediment layer 8b in the basement floor of the reactor building 1 and inside the containment vessel 4, water leakage from the bottom of the water tank 80 can be prevented, and at least the lower part of the reactor building 1 can be submerged in water by the water tank 80.

[0106] For example, a fine particle sediment layer 8b has accumulated on the bottom of the water tank 80, the bottom of the main body 4a of the reactor containment vessel 4, and the basement floor of the reactor building 1. An exterior wall drain outlet 65 is formed in the exterior wall 37. A drain pipe 66 extends from this exterior wall drain outlet 65. A plurality of exterior wall drain outlets 65 and drain pipes 66 are provided. For example, the drain pipe 66 consists of an upper drain pipe 66a and a lower drain pipe 66b, and is also provided in the basement floor of the reactor building 1.

[0107] The water treatment equipment 43 is disposed near the outside of the outer wall 37. The water treatment equipment 43 is a controlled area facility that confines radioactive materials. The drainage pipe 66 is connected to the water treatment equipment 43 via an on-off valve (not shown).

[0108] In the first embodiment described above, a transfer pipe 47c (FIG. 1) having a suction port is arranged in the basement of the reactor building 1 in order to guide water leaking into the reactor building 1. In contrast, the second embodiment differs in that by closing an on-off valve (not shown) of the drainage pipe 66, at least the lower part of the reactor building 1 can be submerged in a water tank 80, making it possible to store water inside the outer wall 37.

[0109] A fine particle sediment layer 8b is deposited on the bottom between the reactor building 1 and the containment vessel 4, and between the outer wall 37 and the reactor building 1. Furthermore, gaps that are leakage points may exist at the bottom of these areas, but the deposition of the fine particle sediment layer 8b makes it possible to minimize the need for waterproofing treatment in the gaps during work to connect the reactor building 1 to the containment vessel 4.

[0110] Measures to prevent overflow must be taken to flood at least the lower part of the reactor building 1. To prevent overflow, an upper drainage pipe 66a and a lower drainage pipe 66b are provided so that the water tank 80 does not exceed its designed maximum storage capacity.

[0111] The water treatment equipment 43 connected to the upper drainage piping 66a and the lower drainage piping 66b purifies water. In addition, a transfer piping 47a and a transfer device 46a are provided for transferring purified water from the water storage container 43a of the water treatment equipment 43 to the water storage tank 81. For example, the purified water is transferred in accordance with the evaporation of water from inside the reactor building 1 or from the water storage tank 81, or the amount of water leakage from the reactor containment vessel 4. In addition, if the amount of circulating water increases, it may be transferred to a separately installed contaminated water treatment equipment (not shown).

[0112] A particle treatment facility 47 is disposed near the outside of the outer wall 37 as a controlled area facility for confining radioactive materials. The particle treatment facility 47 includes an injection device 21. The injection device 21 injects water into the interior of the outer wall 37.

[0113] As in the first embodiment, the injection device 21 includes tube bundles 22, 30, and 31. The injection device 21 has a drainage function and a function of injecting the microparticle dispersion liquid 8.

[0114] Before injecting the microparticle dispersion liquid 8 into the bottom of the torus chamber 32, the injector 21 uses its water injection function to flush the torus chamber 32. For example, clean water is injected into the torus chamber 32 from a predetermined injection pipe (not shown) of the tube bundle 31. Then, the wastewater from the torus chamber 32 is transferred to the water treatment facility 43. In this way, radioactive materials present at the bottom of the torus chamber 32 can be removed or at least reduced.

[0115] Next, the injector 21 injects the microparticle dispersion 8 to a position below the floor surface 33 of the first floor of the reactor building 1. Note that the injector 21 may inject the microparticle dispersion 8 after a buffer material (not shown) is injected, cast, or placed inside the reactor building 1. The method of injecting the microparticle dispersion 8 into the reactor containment vessel 4 is the same as in the first embodiment described above.

[0116] Furthermore, the first cover building 3 is constructed on top of the outer wall 37 in the vicinity of the reactor building 1, and is suspended over the reactor building 1 so as to straddle the upper part thereof.

[0117] In order to provide the water tank 81, an opening is formed in a part of the outer wall 37 near the water tank 81. Furthermore, it is necessary to form an opening in the reactor building 1. When forming these openings, a seismic evaluation of the reactor building 1 and the outer wall 37 is performed, and the reactor building 1 and the outer wall 37 may be seismically reinforced as necessary.

[0118] As shown in Figure 6, the water tank 81 is connected to the outer wall 37 by welding or the like so as to maintain airtightness and watertightness, and is in contact with the side of the reactor building 1. A water gate 82 is constructed near the part that is in contact with the outer wall 37. The water gate 82 maintains airtightness and watertightness between the water tank 81 and the outer wall 37, and can be opened and closed by remote control. It is not necessary for the reactor building 1 and the water tank 81 to be in contact with each other. It is sufficient that the water tank 81 is at least connected to the outer wall 37.

[0119] The water gate 82 is disposed at the end of the water tank 81. The entire periphery of the opening of the water gate 82 is fixed to the opening of the outer wall 37 so as to maintain airtightness and watertightness. In addition, the entire periphery of the opening of the water gate 82 is fixed to the wall of the reactor building 1. Alternatively, the entire periphery of the opening of the water gate 82 is fixed in close contact with the wall of the reactor building 1.

[0120] The water gate 82 is connected to the inside of the reactor building 1 (water tank 80). Then, the water tank 81 is filled with water. Here, as shown in Figures 7 and 8, the water level (height) of the stored water inside the reactor containment vessel 4 is raised. The water level inside the reactor containment vessel 4 may be higher than, the same as, or lower than the water level of the water tank 81. However, the water level inside the reactor containment vessel 4 is set to a position at least higher than the upper end of the opening of the water gate 82. Note that the water level inside the reactor containment vessel 4 here includes the water level of the water tank 80.

[0121] The water level of the containment vessel 4 is adjusted appropriately by the air pressure inside the reactor containment vessel 4. For example, if the air pressure inside the reactor containment vessel 4 is made lower than the air pressure inside the second cover building 3a, the water level of the reactor containment vessel 4 can be made higher than the water level of the water tank 81. Furthermore, if the water tank 81 is configured as a sealed tank, the water level of the reactor containment vessel 4 can be made lower than the water level of the water tank 81 by making the air pressure inside the reactor containment vessel 4 higher than the air pressure inside the water tank 81. Furthermore, if the water tank 81 is a tank, a top cover member or the like is provided for transportation and handling of the equipment, and the top of the tank is structured so that it can be opened and closed. Note that the air pressure of the first cover building 3 (water tank 80) may be adjusted instead of the reactor containment vessel 4 referred to here.

[0122] The water gate 82 opens and closes at a position lower than the water level (height) of the stored water inside the reactor containment vessel 4. In other words, the water gate 82 is positioned so that when it is opened, its opening is located at a position lower than the water level (height) of the stored water.

[0123] In this way, even when the floodgate 82 is fully opened, the water level can be maintained so that the opening is submerged. Therefore, the gas phase of the containment vessel 4 does not flow toward the second cover building 3a through the floodgate 82. In other words, the gas phase of the containment vessel 4 and the gas phase of the second cover building 3a can be isolated. Therefore, during the work of removing fuel debris 7, dust inside the containment vessel 4 does not leak toward the second cover building 3a.

[0124] Before constructing the outer wall 37, the water tank 81, and the water gate 82, a sealant that maintains airtightness may be applied or sprayed onto the inner and outer surfaces of the walls around the openings of the reactor building 1. This makes it possible to weatherseal any penetration cracks in the concrete frame of the reactor building 1 that may occur in the event of a severe accident. This makes it possible to maintain airtightness inside the reactor building 1, and makes it possible to raise the water level inside the reactor building 1 even if the water level outside the reactor building 1 is low.

[0125] When the opening of the reactor building 1 is submerged, the gas phase inside the reactor building 1 does not flow toward the second cover building 3a through the opening of the reactor building 1 when the water gate 82 is fully opened. In other words, the gas phase inside the reactor building 1 and the gas phase in the second cover building 3a can be isolated. Therefore, during the work of removing fuel debris 7, dust inside the reactor building 1 does not leak toward the second cover building 3a.

[0126] Furthermore, ventilation and air conditioning equipment (not shown) is connected to the reactor containment vessel 4, the reactor building 1, the first cover building 3, and the second cover building 3a to purify the gas inside these buildings. These ventilation and air conditioning equipment ensure that the air pressure inside the reactor containment vessel 4 is lowest, and that the air pressure decreases in the order of the reactor building 1, the first cover building 3, and the second cover building 3a. In this way, even if the top of the opening of the water gate 82 is exposed to the air, dust inside the reactor containment vessel 4 will not leak through the opening of the water gate 82 toward the second cover building 3a.

[0127] 5, a pit 42 is constructed near the reactor building 1. However, the construction of the pit 42 is not essential. The water that falls into the pit 42 is transferred to the water storage container 43a via the transfer pipe 47d by the driving force of the transfer device 46d.

[0128] The water storage container 43a stores water discharged by the transfer devices 46b and 46d from the basement floor of the reactor building 1 (nuclear facility) and the water storage tank 81. The transfer device 46a transfers the water stored in the water storage container 43a to the water storage tank 81.

[0129] FIG. 6 shows the connection between the reactor building 1, water tank 81, and exterior wall 37. Part of the concrete framework around the reactor building 1, together with part of the exterior wall 37, has been removed in advance using remotely controlled heavy machinery (not shown). However, these do not have to be removed in advance. The water gate 82 has an opening / closing mechanism 84 and a pressing mechanism (not shown) for the water gate plug 83. When the water gate 82 is closed, it can isolate the connection between the water tank 81 and the water tank 80 (reactor building 1, reactor containment vessel 4) in an airtight and watertight manner.

[0130] The water gate 82 has a connection structure with at least one of the reactor building 1 or the outer wall 37. For example, the water gate 82 is fixed to the wall surface of at least one of the reactor building 1 or the outer wall 37 with a connection material such as concrete or adhesive. The connection structure of the water gate 82 may be a connection structure that maintains airtightness and watertightness by using a single or double or more resin seal or waterstop material. The outer frame of the water gate 82 is connected to at least one of the reactor building 1 or the outer wall 37 by welding or other method.

[0131] 7 shows the state in which the water tank 81 is filled with water. After this water filling, the water gate plug 83 is opened. Then, the cutting device 72 drills holes in the frame of the reactor building 1 and the main body 4a of the reactor containment vessel 4 through the opening of the water gate 82. After the main body 4a of the reactor containment vessel 4 is opened, the cutting device 72 further advances.

[0132] As in the first embodiment, the cutting device 72 includes a base portion 14, a support rod 15, and a cutting unit 16. The cutting unit 16 is provided at the tip of the support rod 15.

[0133] The base portion 14 is provided on the water tank 81. The base portion 14 supports the base end of the support rod 15. The base portion 14 has a driving device (not shown) such as a motor for controlling the forward and backward movement of the support rod 15 and for changing the angle θ up, down, left, and right.

[0134] The support rod 15 enters the reactor building 1 horizontally from the water gate 82 and changes the angle θ with the base 14 as a fulcrum. Then, the cutting unit 16 at the tip of the support rod 15 accesses the area inside the reactor building 1 where the fuel debris 7 exists.

[0135] Figure 8 shows the cutting device 72 moving straight and cutting the fuel debris 7. The support rod 15 of the cutting device 72 moves straight, and the cutting unit 16 at its tip cuts the fuel debris 7. The support rod 15 that moves straight may have a telescopic mechanism, or it may move straight by connecting and adding tubes or rods. This straight movement may be performed by a mechanism installed in the cutting device 72, or it may be performed by a machine or a worker from the loading room 69 (Figure 5) installed in the water tank 81.

[0136] An additional extension wall (not shown) may be constructed on the outer wall 37 (FIG. 5). In other words, the outer wall 37 can be constructed in two or more stages.

[0137] For example, after the fuel debris 7 is removed from the containment vessel 4, a new extension wall (not shown) may be constructed on the outer wall 37 (FIG. 5), thereby raising the height of the entire outer wall 37. The water level in the water tank 81 may then be raised, deepening the water depth. For example, the height of the work floor of the water tank 81 may be raised, deepening the water tank 81, thereby raising the water level inside the extended outer wall 37. In this way, it becomes possible to flood the bottom of the reactor pressure vessel 5 or the fuel debris 7 around the control rod drive mechanism housing. In this way, the work of removing and transporting the fuel debris 7 from the flooded portion can be carried out underwater, improving work efficiency.

[0138] According to the second embodiment, it is expected that exposure to radiation can be reduced and work efficiency can be improved in the work of retrieving fuel debris over a wide area inside the reactor building 1. Furthermore, if the structures outside the reactor containment vessel 4 are highly radioactive, highly radioactive materials such as fuel debris 7 may remain inside and outside the system. Even in such cases, underwater work can be performed by flooding.

[0139] Furthermore, the outer wall 37 is configured to be stackable. Therefore, after a certain height range of the reactor building 1 is removed, an additional outer wall 37 can be constructed upward to raise the water level inside. In this way, the fuel debris 7 can be removed not only from the bottom of the pedestal 6, but also from the bottom of the reactor pressure vessel 5 or around the control rod drive mechanism housing.

[0140] The present invention has been described above based on the first and second embodiments, but the configuration applied in any of the embodiments may be applied to other embodiments, and the configurations applied in each embodiment may be combined.

[0141] In the above-described embodiment, the nuclear facility includes various devices installed in a nuclear power plant, such as the reactor building 1, the reactor well 9, the reactor containment vessel 4, the reactor pressure vessel 5, the pressure suppression chamber 4b, the pedestal 6, the vent pipe 68, the control rod drive mechanism, and the reactor core. The nuclear facility may also be a part of the fuel debris retrieval system 100. For example, the nuclear facility includes the outer wall 37.

[0142] In the above-described embodiment, the manner in which a microparticle deposition layer 8b is formed to seal off the leaking area includes not only the manner in which a microparticle deposition layer 8b is formed inside the room in which the leaking area is located to seal off the water, but also the manner in which a microparticle deposition layer 8b is formed outside the room in which the leaking area is located to seal off the water.

[0143] In the above-described embodiment, flooding includes submerging the equipment from which the fuel debris 7 is to be removed and structures to be removed that obstruct access when removing the fuel debris 7. Flooding also includes filling the interior of the equipment to be removed with water when removing the fuel debris 7. Furthermore, flooding also includes submerging the highly radioactive parts of the equipment to be removed to a depth at which the radiation level is sufficiently attenuated when removing the fuel debris 7.

[0144] In the above embodiment, the cutting device 72, the transporting device 71, and the storing device 77 are configured separately, but one device may have the functions of cutting, transporting, and storing.

[0145] Furthermore, in the above-described embodiment, the transportation device 71 transports the cut pieces of fuel debris 7 by sucking them together with water. In other words, the water flow (water pressure) of the pump is used to transport the cut pieces of fuel debris 7. However, the transportation device 71 may have a different configuration. For example, the cut pieces of fuel debris 7 may be placed in a designated basket, and the basket may be transported using a ropeway system using wire ropes.

[0146] Alternatively, a device such as an autoslope placed underwater in the water tank 81 may transport the cut pieces of fuel debris 7. Alternatively, an underwater heavy machinery placed underwater in the water tank 81 may transport the cut pieces of fuel debris 7.

[0147] Furthermore, an underwater drone placed underwater in the water tank 81 may transport cut pieces of the fuel debris 7. Note that this underwater drone may be guided by a wire stretched underwater in the water tank 81.

[0148] Alternatively, an Archimedes pump placed underwater in the water tank 81 may transport the cut pieces of the fuel debris 7. Alternatively, the scraping function of a water wheel may be used to transport the cut pieces of the fuel debris 7.

[0149] A seesaw-like device may be placed underwater in the water tank 81, and the upper and lower positions of both ends of the seesaw may be swapped, causing a cut piece of fuel debris 7 located at one end to move to the other end.

[0150] Furthermore, a screen device (sifter) that uses tilt and vibration to transport pulverized material may transport cut pieces of fuel debris 7.

[0151] Furthermore, a long carpet may be laid in the water of the water tank 81, and the cut pieces of the fuel debris 7 may be placed on this carpet, and then the carpet may be rolled up to transport the cut pieces of the fuel debris 7.

[0152] Alternatively, a net placed underwater in the water tank 81 may capture and transport the cut pieces of fuel debris 7. Alternatively, a dozer-type device using an underwater cylinder may capture and transport the cut pieces of fuel debris 7.

[0153] Furthermore, the manner in which the fuel debris 7 is removed includes grabbing the fuel debris 7 and grabbing and pulling out the fuel debris 7. For example, the manner in which the fuel debris 7 is removed includes pinching and pulling out the fuel debris 7 with a grab bucket, or scooping up the fuel debris 7 in a straight line with heavy machinery such as a shovel.

[0154] The water tanks 81 may be constructed at two or more locations around the reactor building 1. The fuel debris 7 removal work may be carried out from several directions. For example, if a water tank 81 is constructed on the south side of the reactor building 1, other water tanks 81 may be constructed on the east and west sides. Alternatively, one water tank 81 may be constructed only on the south side of the reactor building 1, and water gates 82 may be constructed at three locations on the south, east, and west sides of the reactor building 1. Three routes may be constructed from one water tank 81, branching into three and connecting to the three water gates 82. In constructing the branched routes, the roles of the cutting process and the process of transporting the cut pieces or pulverized material may be assigned to each route.

[0155] In the above-described embodiments, the singular does not necessarily mean to limit the number to one, and the singular may mean a plural number.

[0156] Note that one cutting device 72 may have multiple support rods 15 and multiple cutting units 16. For example, multiple support rods 15 may extend from one base portion 14, and a cutting unit 16 may be provided at the tip of each support rod 15. Furthermore, multiple cutting devices 72 may be arranged in one sluice gate 82.

[0157] Although the above-described embodiment exemplifies a form applied to the decommissioning of a boiling water reactor (BWR), other forms are also possible. For example, the above-described embodiment may be applied to the decommissioning of an advanced boiling water reactor (ABWR), a pressurized water reactor (PWR), or a graphite-moderated boiling water pressure tube reactor (RBMK).

[0158] According to at least one of the embodiments described above, the floodgate 82 is constructed to open and close at a position lower than the water level 99 of the reservoir water present in at least a part of the interior of the nuclear facility. This allows a part of the nuclear facility that has suffered a severe accident to be flooded, the water to shield radiation, and the fuel debris 7 to be removed in the underwater environment.

[0159] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and modifications thereof are intended to be included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0160] 1...Reactor building, 2...Operation floor, 3...First cover building, 3a...Second cover building, 4...Reactor containment vessel, 4a...Main body, 4b...Pressure suppression chamber, 4c...Head, 5...Reactor pressure vessel, 5a...Main body shell, 5b...Head, 5c...Reactor lower structure, 6...Pedestal, 7...Fuel debris, 8...Fine particle dispersion, 8a...Supernatant, 8b...Fine particle deposition layer, 9...Reactor well, 14...Base, 15...Support rod, 16...Cutting unit, 19...Drilling section, 20...Isolation room, 21...Injection device, 22...Tube bundle, 23...Waste container, 23a...Cover, 24...Container transfer equipment, 26...Isolation tube, 27...Drilling section, 28...Opening, 29...Drilling section, 30...Tube bundle, 31...Tube bundle, 32...Torus room, 33...Floor surface, 37...exterior wall, 42...pit, 43...water treatment equipment, 43a...water storage container, 46a, 46b, 46c, 46d...transfer device, 47...particle treatment equipment, 47a, 47b, 47c, 47d...transfer piping, 65...exterior wall drain outlet, 66...drainage piping, 66a...upper drainage piping, 66b...lower drainage piping, 68...vent pipe, 69...loading room, 71...transportation equipment, 72...cutting device, 73...airtight door, 73a...airtight door, 74...cyclone separator, 75...collection container, 76...filter, 77...containment device, 78...transport hose, 80...water tank, 81...water storage tank, 82...water gate, 83...water gate plug, 84...opening / closing mechanism, 85...welded joint, 86...foundation, 99...water surface, 100...fuel debris removal system.

Claims

1. constructing a water gate that leads to the inside of a nuclear facility where fuel debris has been generated due to a severe accident and that opens and closes at a position lower than the water level of reservoir water present in at least a part of the inside of the nuclear facility; a water tank connected to the water gate, storing water up to a position higher than the position at which the water gate opens and closes, and constructed outside the nuclear facility; When removing the fuel debris from inside the nuclear facility, a cutting device is inserted into the inside of the nuclear facility from the water tank through the opening of the water gate to cut the fuel debris inside the nuclear facility; a transport device transporting the cut pieces of the fuel debris cut by the cutting device in the water of the water tank; a storage device that stores the cut pieces transported by the transport device in a waste container in the water of the water storage tank; Fuel debris removal method.

2. When removing the fuel debris from the nuclear facility where a water leakage site has occurred due to the severe accident, the leakage site is sealed off using a microparticle dispersion containing at least microparticles with a specific gravity greater than that of water, and the water level of the stored water inside the nuclear facility is raised to submerge the water gate. The fuel debris removal method according to claim 1.

3. The microparticles include at least barite as a weighting material and at least bentonite as a thickening agent. The fuel debris removal method according to claim 2.

4. forming a particulate deposition layer in an internal space of the nuclear facility where the leak location exists, by depositing the particulates until the particulates reach a height higher than the leak location; The fuel debris removal method according to claim 2 or 3.

5. constructing the water gate on a side of a reactor containment vessel included in the nuclear facility; The cutting device is provided in the water tank, and the cutting device extends from the water tank to the fuel debris present inside the reactor containment vessel. The fuel debris removal method according to claim 1 or 2.

6. the cutting device has a base, a support rod, and a cutting unit; the base portion provided on the water tank supports the support rod; the support rod enters the reactor containment vessel from the water gate in a horizontal direction and changes its angle with the base portion as a fulcrum; the cutting unit at the tip of the support rod accesses an area inside the containment vessel where the fuel debris is present; The fuel debris removal method according to claim 5.

7. constructing the water gate on a side of a reactor building included in the nuclear facility; The cutting device is provided in the water tank, and the cutting device extends from the water tank to the fuel debris present inside the reactor building. The fuel debris removal method according to claim 1 or 2.

8. the cutting device has a base, a support rod, and a cutting unit; the base portion provided on the water tank supports the support rod; the support rod enters the reactor building from the water gate in a horizontal direction and changes its angle with the base portion as a fulcrum; the cutting unit at the tip of the support rod accesses an area inside the reactor building where the fuel debris is present; The fuel debris removal method according to claim 7.

9. The air pressure in the internal space of the nuclear facility across the water gate is made lower than the air pressure on the side of the water tank. The fuel debris removal method according to claim 1 or 2.

10. a water gate that leads to the inside of a nuclear facility where fuel debris has been generated due to a severe accident and is constructed to open and close at a position lower than the water level of reservoir water present in at least a part of the inside of the nuclear facility; a water tank connected to the water gate, storing water up to a position higher than the position at which the water gate opens and closes, and constructed outside the nuclear facility; a cutting device that enters the inside of the nuclear facility from the water tank through the opening of the water gate and cuts the fuel debris inside the nuclear facility when removing the fuel debris from inside the nuclear facility; a transport device that transports the pieces of the fuel debris cut by the cutting device in the water of the water tank; a storage device that stores the cut pieces transported by the transport device in a waste container in the water of the water storage tank; Equipped with Fuel debris removal system.

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