Nuclear facility flooding device and nuclear facility flooding method

Abstract

A nuclear facility suffering from a severe accident is submerged to shield radiation with water, and the nuclear facility is dismantled in an underwater environment.SOLUTION: A nuclear facility submergence device 1 includes a bottom boundary that suppresses outflow of water flowing downward from a nuclear reactor building 2 that is decommissioned by submerging at least a nuclear reactor containment vessel 4, and the bottom boundary includes at least one of a frozen-soil impervious wall 29 constructed by freezing ground below the nuclear reactor building 2, a cut-off deposition layer 38 in which fine particles are deposited, or an ice block constructed by freezing water stored in a basement of the nuclear reactor building 2.SELECTED DRAWING: Figure 11

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] If a severe accident, including a core meltdown, occurs at a boiling water nuclear power plant, damaging the containment vessel and reactor pressure vessel, dismantling the reactor building under flooded conditions is extremely difficult. Furthermore, the high radiation levels inside the reactor building and the low water level make it difficult to identify the 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 generated during cutting work during dismantling. On the other hand, if the leaks can be sealed, the reactor well can be flooded, allowing dismantling work to be carried out from above the reactor building. [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 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 processing 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 measures to prevent leakage of radioactive materials into and outside the reactor building that may occur during processing of the solidified fuel debris.

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

[0006] Furthermore, the reactor building flooding devices in Patent Documents 4 and 5 have a base constructed underground below the reactor building, and physically isolate the entire reactor building while flooding it. While this is an excellent concept as it reduces the risk of contaminated water leaking into the environment, it does not take into account the risk that the amount of contaminated water stored will increase, or that the reactor building itself will deteriorate over time and collapse or fall off due to the effects of an earthquake or other disaster. In order for this to be viable, the buildings around the reactor building would need to be demolished first.

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

[0009] A nuclear facility flooding device according to an embodiment of the present invention includes a bottom boundary that floods at least the reactor containment vessel to suppress the outflow of water flowing downward from the reactor building being decommissioned, and the bottom boundary includes at least one of a frozen soil water barrier constructed by freezing the ground below the reactor building, a water-stopping sediment layer made of accumulated fine particles, or an ice block constructed by freezing water stored in the basement of the reactor building. [Effects of the Invention]

[0010] According to an embodiment of the present invention, a nuclear facility that has suffered a severe accident can be submerged, the water can be used to shield radiation, and the nuclear facility can be dismantled in an underwater environment. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a plan view showing a nuclear facility flooding device according to a first embodiment. [Figure 2] AA cross section of Figure 1 showing a nuclear facility flooding device. [Figure 3] BB cross section of Figure 1 showing the nuclear facility flooding device. [Figure 4] A cross-section of a reactor building with a moat around it. [Figure 5] A cross-section of the reactor building while a shield tunnel is being constructed underground. [Figure 6] FIG. 10 is a cross-sectional view showing the reactor building with the main wall portion constructed. [Figure 7] Cross-section showing the shield tunnel during construction. [Figure 8] Cross-sectional view showing the shield tunnel with the bottom liner constructed. [Figure 9] FIG. 10 is a cross-sectional view showing a frozen state of the bottom of the reactor building according to the second embodiment. [Figure 10] A plan view showing the frozen soil impermeable wall installation around the reactor building. [Figure 11] FIG. 10 is a cross-sectional view showing a freeze impermeable wall at the bottom of a reactor building according to Modification 1. [Figure 12] FIG. 10 is a plan view showing the frozen soil impermeable wall installation around the reactor building of Modification 2. [Figure 13] FIG. 10 is a plan view showing the frozen soil impermeable wall installation around the reactor building of Modification 3. [Figure 14] FIG. 10 is a cross-sectional view showing a frozen state of the bottom of the reactor building of Modification 4. [Figure 15] FIG. 10 is a plan view showing the installation of frozen soil impermeable walls around the reactor building of Modified Example 5. [Figure 16] FIG. 10 is a plan view showing the installation of frozen soil impermeable walls around the reactor building of variant 6. [Figure 17] FIG. 20 is a cross-sectional view showing the frozen state of the bottom of the reactor building of Modification 7. [Figure 18] FIG. 20 is a cross-sectional view showing the frozen state of the bottom of the reactor building of Modification 8. [Figure 19] FIG. 13 is a plan view showing the installation of frozen soil impermeable walls around the reactor building of Variant 9. [Figure 20] FIG. 10 is a cross-sectional view showing a nuclear facility flooding device according to a third embodiment. [Figure 21] FIG. 20 is a cross-sectional view showing a nuclear facility flooding device according to a tenth modification. [Figure 22] FIG. 19 is a cross-sectional view showing a nuclear facility flooding device according to an eleventh modification. DETAILED DESCRIPTION OF THE INVENTION

[0012] (First embodiment) Hereinafter, embodiments of a nuclear facility flooding device and a nuclear facility flooding method will be described in detail with reference to the drawings. First, a first embodiment will be described with reference to Figures 1 to 8. Note that the scale of each component shown in the drawings may be changed as appropriate to facilitate understanding.

[0013] Reference numeral 1 in Fig. 1 denotes a nuclear facility flooding device of the first embodiment. This nuclear facility flooding device 1 floods a reactor containment vessel 4 installed in a nuclear power plant, and in the unlikely event that a large amount of water leaks from inside the reactor containment vessel 4, it also prevents water from leaking into the surrounding area of ​​a reactor building 2. The first embodiment illustrates an example of a mode in which decommissioning work is carried out on a nuclear power plant that has suffered a severe accident.

[0014] As shown in Figures 1 to 3, the reactor building 2 is a building made of reinforced concrete. Inside it are a reactor pressure vessel 3 that houses the reactor, and a reactor containment vessel 4 that houses the reactor pressure vessel 3. Other facilities such as a pressure suppression chamber 5 are also provided. Here, a boiling water reactor (BWR) is shown as an example, in which the reactor containment vessel 4 and the torus chamber pressure suppression chamber 5 are provided as separate bodies.

[0015] In the event of a severe accident, the fuel assemblies in the reactor melt due to overheating of the nuclear fuel, resulting in what is known as a meltdown. The molten nuclear fuel leaks from the reactor pressure vessel 3. The reactor containment vessel 4 is also damaged by the increased internal pressure. Because fuel debris containing molten nuclear fuel is highly radioactive, even remotely operated robots may malfunction due to the effects of radiation if the partial submersion method is used to remove the fuel debris.

[0016] If the inside of the reactor containment vessel 4 could at least be filled with water, the water would be able to shield against radiation. However, it would be difficult to repair damaged areas of the reactor containment vessel 4.

[0017] Therefore, the nuclear facility flooding apparatus 1 is provided with a huge water tank 7 that accommodates the entire reactor building 2. The water tank 7 may be any water tank that covers at least the lower part of the reactor building 2.

[0018] The water tank 7 can accommodate at least the lower part of the reactor building 2 and store water inside. Even if a large amount of water leaks from the reactor containment vessel 4, the water tank 7 can store the leaked water so that it does not leak into the surrounding area of ​​the site.

[0019] The water tank 7 is made up of a bottom boundary and a side boundary. The bottom boundary is a structure that prevents water from flowing downward from the reactor building 2, where decommissioning is performed by submerging at least the reactor containment vessel 4. The side boundary is a structure that surrounds the periphery of the reactor building 2 and prevents water that leaks from the reactor containment vessel 4 from flowing out. Decommissioning work is performed with at least the reactor containment vessel 4 submerged.

[0020] The water tank 7 of the first embodiment includes a main wall 8 that surrounds the periphery of the reactor building 2, an auxiliary wall 9 that surrounds the periphery of the main wall 8, a bottom 10 constructed underground where the reactor building 2 is erected, and a ceiling 11 that covers the upper part of the reactor building 2. This ceiling 11 is dome-shaped. Note that the ceiling 11 may also be flat.

[0021] In this first embodiment, the bottom boundary is formed by the bottom portion 10. Furthermore, the main wall portion 8 and the auxiliary wall portion 9 form the side boundary.

[0022] Additionally, decommissioning work equipment such as a crane 12 is provided inside the nuclear facility flooding apparatus 1. The crane 12 may be supported by the main wall portion 8, or a dedicated support structure (not shown) may be constructed separately inside the main wall portion 8, and the crane 12 may be supported by this support structure.

[0023] The main wall 8 has a height from the ground 13, i.e., a vertical dimension (L) that allows at least the lower part of the reactor containment vessel 4 to be submerged. For example, the vertical dimension (L) of the main wall 8 (side boundary) is at least the same as the vertical dimension (L) of the reactor containment vessel 4. A support wall 40 that supports the ceiling 11 is provided on the upper part of the main wall 8.

[0024] In the first embodiment, the inside of the reactor containment vessel 4 is flooded with water, and the height (water level) of the reservoir water 6 is maintained at a position slightly lower than the operation floor.

[0025] The nuclear facility flooding device 1 includes a transfer device 25. When water that has leaked from the reactor containment vessel 4 accumulates in the basement of the reactor building 2, the transfer device 25 transfers the accumulated water to the reactor containment vessel 4.

[0026] For example, water leaks due to accidents and aging may exist inside the reactor building 2. Also, water may leak inside the main wall 8. This leaked water is injected into the reactor containment vessel 4 via the transfer device 25 and transfer piping 26 through the reactor well 27. For example, two systems of transfer devices 25 and transfer piping 26 are provided in one reactor building 2. The transfer device 25 is, for example, a pump.

[0027] The upper end of the main wall portion 8 is set to an appropriate height. For example, if the reactor containment vessel 4 is flooded and all the water leaks out of the reactor containment vessel 4, the upper end of the main wall portion 8 should be higher than the water level stored inside the main wall portion 8.

[0028] The upper part of the reactor building 2, that is, the part above the so-called operation floor, is removed in advance. Then, water 6 is stored in the reactor well 27 on the operation floor of the reactor building 2, the pool consisting of the equipment pool and the fuel storage pool, and the reactor containment vessel 4.

[0029] For example, the water level of the water reservoir 6 stored inside the containment vessel 4 is set to the level of the operation floor. The operation floor does not have to be submerged. In other words, the water level of the water reservoir 6 may be set to a position slightly lower than the operation floor.

[0030] The main wall 8 and the auxiliary wall 9 are constructed on the ground 13 (basement) on which the reactor building 2 is erected. First, a moat 14 that is circular in plan view is constructed around the reactor building 2. The main wall 8 and the auxiliary wall 9 are constructed along this moat 14. The reactor building 2 has a quadrangular shape in plan view. The diameter of the main wall 8 is approximately the same length as the diagonal of the reactor building 2 in plan view. Depending on the shapes of the main wall 8 and the auxiliary wall 9, the moat 14 may have a rectangular shape or a rectangular shape with rounded corners in plan view.

[0031] The main wall portion 8 and the auxiliary wall portion 9 are formed so that their lower portions are thicker than their upper portions. The lower portions of the main wall portion 8 and the auxiliary wall portion 9 are constructed underground, and their upper portions are constructed above ground. The thickness of the above-ground portion is thinner than the thickness of the underground portion.

[0032] There may be a case where the water 6 stored in the reactor containment vessel 4 leaks on a large scale, moves into the water tank 7, and then leaks from the main wall 8. Even in this case, the auxiliary wall 9 and the moat 14 are provided, so that the water 6 can be prevented from spreading further to the outside.

[0033] The height of the auxiliary wall portion 9 is lower than that of the main wall portion 8. A connecting portion 15 is provided to connect the main wall portion 8 and the auxiliary wall portion 9 to each other. In this way, the main wall portion 8 can be reinforced by the auxiliary wall portion 9.

[0034] The main wall 8 and auxiliary wall 9, which form the side boundary, are constructed from prestressed concrete. In other words, the side boundary is a wall constructed using prestressed concrete. In this way, cracks in the main wall 8 and auxiliary wall 9 can be prevented.

[0035] Prestressed concrete is concrete that has been pre-stressed. Steel is used to place the concrete in a compressive state before a load is applied, preventing the concrete from developing tensile stresses when subjected to a load. Alternatively, prestressed concrete is concrete in which the tensile stresses that develop in the concrete are controlled.

[0036] As shown in FIG. 1, the main wall portion 8 has a circular shape in a plan view. The auxiliary wall portion 9 also has a circular shape in a plan view and is provided concentrically with the main wall portion 8. Alternatively, instead of being circular, both may have a rectangular shape or a rectangular shape with rounded corners. A steel wall liner 16 is constructed on the inner peripheral surface of the main wall portion 8. This makes it possible to prevent water leakage. The wall liner 16 is formed by welding multiple steel plates together.

[0037] As shown in Figures 2 and 3, the bottom 10 is constructed by a shield tunnel 17. The shield tunnel 17 is a tunnel constructed using the shield construction method. For example, a cylindrical (or box-shaped) shield machine 18 (Figure 5) temporarily supports the tunnel wall behind the tunnel face and moves forward while excavating the tunnel face. Blocks (segments) are placed behind the shield machine 18 to reinforce the tunnel wall. The blocks can be mass-produced in a factory.

[0038] In this way, the portion that will become the bottom 10 of the tank 7 can be easily constructed underground. For example, the bottom 10 can be constructed using multiple shield tunnels 17 that are constructed side by side in the horizontal direction. The shield tunnels 17 can be used to construct the bottom 10 that spreads out in a plane.

[0039] A steel bottom liner 19 is constructed inside the shield tunnel 17. This prevents the water 6 stored in the water tank 7 from leaking out from the bottom 10. The bottom liner 19 is formed by welding together a number of steel plates.

[0040] The lower end of the wall liner 16 and the periphery of the bottom liner 19 are joined together to form a huge cylindrical water tank 7. The wall liner 16 and the bottom liner 19 prevent water from leaking out.

[0041] The shield tunnel 17 is constructed using a rectangular shield machine 18 (Fig. 5). Therefore, the shield tunnel 17 has a square shape in cross section (Fig. 7). By arranging the square-shaped shield tunnels 17 horizontally, it is possible to construct a flat, integrated bottom 10.

[0042] In the first embodiment, it is desirable that the reactor containment vessel 4 is not affected by changes over time and that its structure be maintained even during an earthquake. Therefore, the nuclear facility flooding device 1 is provided with a connecting structure 28 that connects the main wall portion 8, which is the side boundary, to the reactor building 2. The connecting structure 28 separates the reactor containment vessel 4 from the ground and causes it to sit on the bottom 10 of the water tank 7. The connecting structure 28 provides seismic reinforcement, and maintains the structure of the reactor containment vessel 4 even during an earthquake. Thus, the flooded state inside the reactor containment vessel 4 can be maintained even during an earthquake.

[0043] Next, a nuclear facility flooding method according to the first embodiment will be described. First, buildings around the reactor building 2 are removed. For example, various structures such as a turbine building 39 (FIG. 9) and a chimney are installed around the reactor building 2. After these structures are removed, only the reactor building 2 remains.

[0044] Next, a trench 14 is formed around the reactor building 2. Furthermore, supports 20 are installed along the trench 14 (FIG. 4). At this time, the ground where the trench 14 is to be installed freezes, forming frozen soil.

[0045] Furthermore, instead of freezing the ground, a water-stopping material with an extremely low coefficient of permeability may be poured without gaps, and then a water-stopping sediment layer 38 (FIG. 20) described below may be constructed.

[0046] The fine particles forming the water-blocking sedimentary layer 38 have a specific gravity greater than that of water, and contain at least barite as a weighting agent and at least bentonite as a thickener. The water-blocking sedimentary layer 38 is constructed using a fine particle dispersion containing such fine particles.

[0047] The microparticle dispersion contains water and microparticles with a specific gravity greater than that of water. This microparticle dispersion can be used to build a watertight structure that stops water leaks. When the microparticle dispersion is injected, the microparticles, which have a specific gravity greater than that of water, gradually settle and accumulate downward, forming a watertight sediment layer 38. This watertight sediment layer 38 is the watertight structure.

[0048] Next, the shield machine 18 is lowered to the bottom of the trench 14 to prepare for excavation. Once the shield machine 18 has been positioned, excavation begins.

[0049] Next, a shield tunnel 17 is constructed by a shield machine 18 (FIGS. 5 and 6). Here, multiple shield tunnels 17 may be constructed by one shield machine 18 moving back and forth, or multiple shield machines 18 may be lined up and proceed simultaneously to construct multiple shield tunnels 17.

[0050] As the shield machine 18 advances, the surrounding soil freezes, forming frozen soil. Alternatively, instead of freezing the ground, a water-stopping material with an extremely low coefficient of permeability may be poured tightly into the ground, and then a water-stopping sediment layer 38 (FIG. 20), which will be described later, may be constructed. This prevents groundwater from entering during excavation and construction work, and prevents the surrounding ground from collapsing.

[0051] As shown in Figure 7, when a shield tunnel 17 is constructed, extra trenches 21 are provided around it. The extra trenches 21 are provided so that the extra trenches 21 of multiple shield tunnels 17 overlap. For example, some areas (D) of the extra trenches 21 overlap. In this way, the shield tunnels 17 can be arranged closely together.

[0052] The blocks that make up the shield tunnel 17 may be made of concrete or steel. A plurality of pillars 22 extending in the vertical direction are provided inside the shield tunnel 17. These pillars 22 may be provided during excavation by the shield machine 18, or may be added after the shield tunnel 17 is constructed. These pillars 22 can reinforce the shield tunnel 17. The pillars 22 may be joined together to form a wall.

[0053] Next, a bottom liner 19 is constructed inside the shield tunnel 17. As shown in Figure 8, some of the side blocks that make up the shield tunnel 17 are removed to form openings 23. Adjacent shield tunnels 17 are then connected to each other through these openings 23. Intermediate floors 24 are also provided inside the shield tunnel 17. A large number of steel plates are laid on the upper surfaces of these intermediate floors 24 and welded together to construct the bottom liner 19.

[0054] The rectangular shape of the shield tunnel 17 makes it easier for workers to work inside it. The pillars 22 and the bottom liner 19 may also be welded together.

[0055] Next, the main wall 8 and the auxiliary wall 9 are constructed along the moat 14 around the reactor building 2 (FIG. 6).

[0056] Then, a wall liner 16 is constructed over the entire inner peripheral surface of the main wall 8 (FIG. 1). The lower end of the wall liner 16 and the peripheral edge of the bottom liner 19 are welded to each other.

[0057] Next, the shoring 20 installed in the trench 14 is removed (FIGS. 5 and 6). Note that the shoring 20 may be used as a reinforcing material for the main wall portion 8 and the auxiliary wall portion 9 without being removed.

[0058] Next, the reactor building 2 and the main wall 8 are connected by a connecting structure 28 (FIGS. 2 and 3). This connecting structure 28 provides earthquake-resistant reinforcement. The connecting structure 28 may also have a vibration isolation damper (not shown). The vibration isolation damper can suppress vibrations transmitted from the main wall 8 to the reactor building 2 in the event of an earthquake.

[0059] Next, decommissioning work equipment such as a crane 12 is placed inside the nuclear facility flooding apparatus 1 (Fig. 3). Furthermore, a ceiling 11 is constructed above the main wall 8 (Fig. 3).

[0060] Next, a transfer device 25 and transfer piping 26 are installed to take the accumulated water from the basement of the reactor building 2 and transfer it into the reactor containment vessel 4. Then, with the reactor well 27 and the reactor containment vessel 4 submerged, the leaking water from the reactor containment vessel 4 is transferred into the reactor containment vessel 4, and decommissioning work can be started with the water level maintained.

[0061] It is sufficient that at least the reactor containment vessel 4 is submerged. In this way, when the covers of the reactor containment vessel 4 and the reactor pressure vessel 3 are opened, radiation can be shielded by water, making it easier to remove the fuel debris. In other words, the fuel debris can be removed by submersion. Furthermore, the dismantling of the reactor containment vessel 4 and the reactor pressure vessel 3 may also be performed by submersion.

[0062] Although the embodiment shows the construction of the bottom 10 of the nuclear facility flooding device 1 after a severe accident has occurred, other embodiments are also possible. For example, when a new nuclear power plant is constructed, the bottom 10 may be constructed underground in advance.

[0063] Although the nuclear equipment flooding apparatus 1 is used in the decommissioning work of a nuclear power plant where a severe accident has occurred, other embodiments are also possible. For example, the nuclear equipment flooding apparatus 1 may be used in the decommissioning work of a nuclear power plant where a severe accident has not occurred.

[0064] Although the main wall portion 8 and the auxiliary wall portion 9 are circular in plan view, other shapes are also possible. For example, the main wall portion 8 and the auxiliary wall portion 9 may be elliptical in plan view, or may be a racetrack shape that combines arcs and straight lines in plan view. The main wall portion 8 and the auxiliary wall portion 9 may also be rectangular in shape to match the planar shape of the reactor building 2. For example, the main wall portion 8 may be constructed so that the inner surface of the main wall portion 8 is in contact with or close to the outer wall of the reactor building 2, resulting in the main wall portion 8 being rectangular in plan view. In this way, the extent of expansion of water leakage from the reactor containment vessel 4 in the unlikely event of an accident can be minimized.

[0065] Although the shield tunnel 17 having a square cross section is constructed using a rectangular shield machine 18, other configurations are also possible. For example, a shield tunnel 17 having a circular cross section may be constructed using a circular shield machine.

[0066] Although the main wall portion 8 and the auxiliary wall portion 9 are constructed from prestressed concrete, other configurations are also possible. For example, the main wall portion 8 and the auxiliary wall portion 9 may be made of steel. Furthermore, the main wall portion 8 and the auxiliary wall portion 9 may be constructed from reinforced concrete.

[0067] For example, the main wall 8 and the auxiliary wall 9, which are the side boundary, may be constructed using a hull structure. In other words, the side boundary is a wall constructed using a hull structure. Note that the side boundary may be constructed using both prestressed concrete and a hull structure.

[0068] A hull structure (steel hull structure) is a structure (steel structure) that imitates the structure of a ship's hull. In particular, a hull structure is a structure in which at least one steel plate separates a space containing water from a space containing air, and this steel plate is reinforced with a frame connected to it so that it can withstand water pressure. For example, the side boundary is constructed using double hull structure manufacturing technology. In other words, the hull structure is a structure in which at least two steel plates separate the internal and external spaces of the side boundary, and this steel plate is reinforced with a frame connected to it so that it can withstand water pressure.

[0069] Specifically, the side boundary is made up of four layers of plate-shaped steel members in its thickness direction. For example, the side boundary is made up of one plate-shaped steel member that forms the outer surface of the tank 7, one plate-shaped steel member that forms the inner surface of the tank 7, and two plate-shaped steel members placed in the center in the thickness direction. This creates a side boundary with two additional layers of double hull structure.

[0070] A sealed space is formed inside the hull structure serving as the side boundary, which makes it possible to prevent the water stored in the water tank 7 from leaking out.

[0071] The hull structure serving as the side boundary is internally divided into multiple compartments. Each compartment is surrounded by plate steel members and frame steel members. Each compartment is an independently sealed, enclosed space. In this way, even if a crack occurs in the hull structure, water leaking from the crack will be contained within one compartment, preventing the leaked water from spreading to other compartments or outside the hull structure.

[0072] According to the first embodiment, a part of the reactor building 2 is housed in the water tank 7, which is capable of storing water inside, and therefore, even if there is a leak from the submerged reactor containment vessel 4, the leaked water is prevented from spreading to the surrounding area. Furthermore, dismantling of nuclear facilities in connection with the decommissioning of a reactor that has suffered a severe accident can be carried out in a submerged state, and radiation can be shielded by water, thereby reducing the radiation exposure of workers.

[0073] Furthermore, by constructing a circulation system using the transfer device 25 and transfer piping 26 to inject water leaking from the containment vessel 4 into the containment vessel 4, the water level in the containment vessel 4 can be maintained in a flooded state.

[0074] (Second embodiment) Next, a second embodiment and its modified examples will be described with reference to Figures 9 to 19. 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.

[0075] Figure 9 is a cross-sectional view showing the reactor building 2 and its surroundings. The reactor building 2 is constructed on land close to the sea 60, that is, on the coast. For example, the left side of the page in Figure 9 is the mountain side, and the right side of the page in Figure 9 is the sea side.

[0076] The ground on which the reactor building 2 is located is made up of layers of permeable layers through which groundwater easily permeates and impermeable layers through which groundwater does not easily permeate. The permeable layers and impermeable layers are layered alternately. For example, there is an upper permeable layer 50 near the surface, an upper impermeable layer 51 below that, a lower permeable layer 52 below that, and a lower impermeable layer 53 below that.

[0077] A wide-area frozen soil impermeable wall 33 and a sea-side impermeable wall 34 have been constructed around and near the reactor building 2. The wide-area frozen soil impermeable wall 33 and the sea-side impermeable wall 34 have been constructed by vertically excavating from the ground surface to a depth where the lower impermeable layer 53 exists.

[0078] The wide-area frozen soil impermeable wall 33 is constructed to surround the reactor building 2 and the surrounding buildings. The buildings surrounding the reactor building 2 include, for example, a turbine building 39, other buildings, chimneys, piping, and other structures.

[0079] The sea-side impermeable wall 34 is constructed in a location facing the sea 60, that is, along the coast. The sea-side impermeable wall 34 is a structure that is not a frozen soil impermeable wall.

[0080] The wide-area frozen soil impermeable wall 33 and the sea-side impermeable wall 34 are conventionally known structures, and therefore detailed explanations thereof will be omitted.

[0081] The nuclear facility flooding device 1 of the second embodiment includes a specified frozen soil impermeable wall 29. The specified frozen soil impermeable wall 29 is constructed by vertically excavating from the ground surface to a depth where the upper impermeable layer 51 exists.

[0082] The specific frozen soil impermeable wall 29 is a frozen soil impermeable wall that is different from the wide-area frozen soil impermeable wall 33. The specific frozen soil impermeable wall 29 is constructed at a position closer to the reactor building 2 than the wide-area frozen soil impermeable wall 33. The specific frozen soil impermeable wall 29 is constructed at a position close to the reactor building 2 and the turbine building 39. The specific frozen soil impermeable wall 29 may also be constructed directly below the reactor building 2 and the turbine building 39.

[0083] In addition, a water tank 7 is constructed that can accommodate the entire reactor building 2 and that can submerge at least a portion of the reactor building 2 by storing water therein.

[0084] The water tank 7 of the second embodiment includes a main wall portion 8, an auxiliary wall portion 9, and a specified frozen soil impermeable wall 29. As in the first embodiment, a transfer device 25 and transfer piping 26 are provided to take in stagnant water in the basement of the reactor building 2 and transfer it into the reactor containment vessel 4. A circulation system is constructed to inject water leaking from the reactor containment vessel 4 into the reactor containment vessel 4, thereby maintaining the water level in the reactor containment vessel 4 in a flooded state.

[0085] In this second embodiment, it is not necessary to dismantle and remove all of the buildings around the reactor building 2. Furthermore, the walls or floors of the buildings around the reactor building 2 may be used as the main wall 8 and the auxiliary wall 9. Furthermore, the water tank 7 may be constructed by taking waterproofing measures for the penetrations in the walls or floors through which components such as pipes pass.

[0086] Also, the second embodiment does not require a bottom 10 (FIG. 2) to be constructed underground where the reactor building 2 is erected.

[0087] The main wall 8 and auxiliary wall 9 may also be constructed on the ground 13 on which the reactor building 2 is built. The main wall 8 and auxiliary wall 9 may also be constructed from the lowest basement inside or outside of surrounding buildings to an appropriate height, which is a height that can receive a large amount of water leaking from the reactor containment vessel 4.

[0088] The space between the main wall portion 8 and the auxiliary wall portion 9 is formed as a moat 14. The shape of the moat 14 may be arbitrary. The moat 14 only needs to have an appropriate height (depth) of the auxiliary wall portion 9 so that it can catch water leaking from the main wall portion 8.

[0089] The thickness of the main wall portion 8 and the auxiliary wall portion 9 may be such that they will not be significantly deformed or damaged when they contain the maximum amount of anticipated leaked water.

[0090] In the second embodiment, instead of constructing the bottom 10 (FIG. 2) using a shield tunnel 17, the basement of the reactor building 2 is frozen to construct the bottom boundary. In other words, the bottom boundary includes an ice block constructed by freezing water stored in the basement of the reactor building 2. This ice block prevents water from flowing out of the basement of the reactor building 2 and blocks groundwater from flowing into the basement of the reactor building 2.

[0091] In this second embodiment, the bottom boundary is formed by ice blocks in the basement of the reactor building 2. Note that a specific frozen soil impermeable wall 29 may be included in the bottom boundary. Furthermore, the main wall portion 8 and the auxiliary wall portion 9 form a side boundary.

[0092] When constructing the specified frozen soil impermeable wall 29, first, the ground 13 is excavated by boring, and freezing pipes 30 are inserted into the holes. Then, coolant is supplied to the freezing pipes 30, which freezes the moisture contained in the ground around the freezing pipes 30, causing the ground to become frozen and hard. Multiple freezing pipes 30 are installed in the ground at equal intervals, and the surrounding frozen ground is connected to each other, thereby constructing the specified frozen soil impermeable wall 29. The specified frozen soil impermeable wall 29 only needs to be in a state that at least prevents the passage of water. The moisture contained in the ground is, for example, groundwater flowing through the ground.

[0093] A freezing pipe header 55 is provided at the top of each freezing pipe 30, i.e., at the surface portion. A frozen soil impermeable wall line 31 is connected to these freezing pipe headers 55. The frozen soil impermeable wall line 31 is connected to a freezing plant 32 that supplies coolant.

[0094] In this way, the specified frozen soil impermeable wall 29 is constructed by supplying coolant from the freezing plant 32 to freezing pipes 30 that are installed near the wall surface or by drilling into the ground from inside and outside the reactor building 2. The specified frozen soil impermeable wall 29 prevents leakage of water stored in the reactor containment vessel 4.

[0095] FIG. 10 shows an example of the arrangement of freezing pipes 30, frozen soil impermeable wall lines 31, and freezing plants 32. For example, the explanation will be given assuming that the bottom of FIG. 10 is the mountain side and the top of FIG. 10 is the sea side. Four reactor buildings 2 (R / B) are lined up on the site of one power plant. Of the four reactor buildings 2, three are targeted for fuel debris removal. Each of the three reactor buildings 2 is contained in a main wall section 8 (water tank 7). FIG. 10 shows an example in which two systems of frozen soil impermeable wall lines 31 are installed for each reactor building 2: one inside the reactor building 2 and one outside, including surrounding buildings.

[0096] To reduce radiation exposure to workers, the freezing plant 32 is located away from the reactor building 2. The frozen soil impermeable wall line 31 circulates coolant at temperatures of several tens of degrees below freezing.

[0097] A plurality of freezing pipes 30 are arranged at predetermined intervals around the periphery of the reactor building 2 or from the inside and outside of surrounding buildings, so as to surround the outside of the reactor building 2. For example, a plurality of freezing pipes 30 are arranged so as to surround the reactor building 2 and a turbine building 39. Furthermore, a plurality of freezing pipes 30 are arranged inside the above, in the area of ​​the reactor building 2. The outer plurality of freezing pipes 30 are supplied with coolant from a freezing plant 32 on the mountain side. The inner plurality of freezing pipes 30 are supplied with coolant from a freezing plant 32 on the sea side.

[0098] These freezing pipes 30 construct the specified frozen soil impermeable wall 29. For example, a plurality of freezing pipes 30 are arranged at predetermined intervals from the wall to the floor of the basement of the reactor building 2. These freezing pipes 30 freeze the stagnant water in the basement into ice blocks. In other words, the ice blocks in the basement of the reactor building 2 are constructed using the freezing pipes 30 that construct the specified frozen soil impermeable wall 29.

[0099] The reactor building 2 and surrounding buildings are undergoing environmental improvements, such as area decontamination. Then, freezing work will begin in areas where the installation of the frozen soil impermeable wall lines 31 and the placement of the freezing pipes 30 have been completed. This will prevent groundwater from flowing into the reactor building 2, and will also allow the water to be contained in the basement of the reactor building 2 even if it leaks from the reactor containment vessel 4.

[0100] Also provided are a transfer device 25 and transfer piping 26 that take in water from the basement of the reactor building 2 and transfer the water to the containment vessel 4 via the reactor well 27. In the case of this second embodiment, it is assumed that the water intake section (not shown) that takes in water from the basement of the reactor building 2 will freeze. Therefore, to prevent the water intake section from freezing, a predetermined range from the water intake section to the inlet of the reactor well 27 via the transfer device 25 is heated and insulated, thereby taking measures to prevent freezing. In this way, even if the accumulated water in the reactor building 2 freezes, the water intake section will not freeze. In addition, the water intake section has a pit-like shape. In this way, leaked water from the containment vessel 4 can be collected in the pit and efficiently transferred.

[0101] The second embodiment differs from the first embodiment in that it is not necessary to remove buildings around the reactor building 2. Also, a freezing plant 32 is installed. Furthermore, instead of constructing a shield tunnel 17 (FIG. 2), a frozen soil impermeable wall line 31 is constructed.

[0102] Furthermore, by implementing the second embodiment prior to the first embodiment, it is possible to suppress the inflow of groundwater into the basement of the reactor building 2 even during the construction period of the side boundary and bottom boundary in the first embodiment. This reduces the amount of contaminated water, and further reduces the risk of contaminated water leaking from the reactor building 2 into the groundwater.

[0103] This eliminates the need to first remove buildings around the reactor building 2. Also, since there is no need to excavate the ground directly below the reactor building 2, it is possible to improve ground stability in the event of an earthquake during construction. Furthermore, there is no risk of on-site workability when constructing a structure in the ground below the reactor building 2.

[0104] On the other hand, simply freezing the basement of the reactor building 2 leaves the reinforced concrete structure directly below the reactor containment vessel 4 as a water permeation path. Therefore, to block groundwater and water leakage from the reactor building 2, a specific frozen soil impermeable wall 29 with an extremely low permeability coefficient is constructed, and this specific frozen soil impermeable wall 29 is used to surround the reactor building 2 from the ground below.

[0105] Fig. 11 shows Modification 1. For example, the left side of Fig. 11 is the mountain side, and the right side of Fig. 11 is the sea side. Modification 1 illustrates a specified frozen soil impermeable wall 29 that collectively covers the ground directly below the reactor building 2 and surrounding buildings.

[0106] The bottom boundary of Modification 1 is a specified frozen soil impermeable wall 29 constructed by freezing the ground below the reactor building 2. For example, a specified frozen soil impermeable wall 29 constructed from the mountain side, a specified frozen soil impermeable wall 29 constructed from the sea side, and a specified frozen soil impermeable wall 29 constructed between the reactor building 2 and the turbine building 39 are provided. The lower end portion of the specified frozen soil impermeable wall 29 is constructed from the ground surface to a depth where the lower permeable layer 52 exists.

[0107] A portion of the specified frozen soil impermeable wall 29 is constructed along the lower permeable layer 52. Because the lower permeable layer 52 has an abundant amount of groundwater, it can be frozen efficiently, and a strong specified frozen soil impermeable wall 29 can be constructed.

[0108] The specified frozen soil impermeable walls 29 constructed from the mountain side and the sea side are constructed in a diagonal direction from the periphery of the reactor building 2 toward the bottom of the reactor building 2. Note that the diagonal direction includes not only a linear direction but also a slightly curved direction. The lower end portions of the specified frozen soil impermeable walls 29 constructed from the mountain side and the sea side intersect with each other underground. In Variation 1, the bottom boundary is formed by the specified frozen soil impermeable walls 29.

[0109] To reduce worker exposure to radiation, a freezing plant 32 is located away from the reactor building 2. A frozen soil impermeable wall line 31 is routed from this freezing plant 32. The frozen soil impermeable wall line 31 is connected to a freezing pipe header 55 provided at the top of each freezing pipe 30.

[0110] Coolant at several tens of degrees below freezing is supplied to each freezing pipe 30 from the freezing plant 32 via the frozen soil impermeable wall line 31. The ground containing groundwater around the freezing pipes 30 then freezes, and a specific frozen soil impermeable wall 29 is constructed.

[0111] For example, the ground is excavated by boring from both the mountain side and the sea side of the reactor building 2 so as to form a curved shape in cross section. The borings are drilled at predetermined intervals to form multiple holes. Then, the freezing pipes 30 are arranged in accordance with the drilled holes.

[0112] Furthermore, the water tank 7 of Modification 1 is constructed over a wide area covering the entire reactor building 2 and turbine building 39. The water tank 7 includes a main wall 8, an auxiliary wall 9, and a ceiling 11. The ceiling 11 is constructed so as to cover the entire area from the reactor building 2 to the turbine building 39.

[0113] A sub-drain 35 is constructed near the turbine building 39. If the sub-drain 35 detects a predetermined concentration of radioactive material, it drains the water inside the reactor containment vessel 4 to the outside of the reactor building 2.

[0114] Figure 12 shows variant 2. For example, the description will be given assuming that the bottom side of the page in Figure 12 is the mountain side and the top side of the page in Figure 12 is the sea side. This variant 2 shows the arrangement of multiple freezing pipes 30 that collectively surround four reactor buildings 2. Four reactor buildings 2 are lined up within the site of one power plant. All of the reactor buildings 2 are targets for fuel debris removal. In addition, the four reactor buildings 2 are housed together in one main wall section 8 (water tank 7).

[0115] For example, a plurality of freezing pipes 30 are provided to surround four reactor buildings 2. One freezing plant 32 is provided to supply coolant to these freezing pipes 30. Also, only one frozen soil impermeable wall line 31 is required.

[0116] In particular, the placement of these items is checked taking into consideration the spatial dimensions, the ambient radiation dose, the transportation of equipment, and the placement, and consideration is given to environmental improvement through decontamination and removal of obstructions as necessary.The placement is also planned so that the freezing pipes 30 can be placed within a specified interval.

[0117] In this modification 2, a plurality of freezing pipes 30 for constructing a specified frozen soil impermeable wall 29 are arranged at predetermined intervals. A plurality of freezing pipes 30 buried diagonally from one side (e.g., the mountain side) of the reactor building 2 and a plurality of freezing pipes 30 buried diagonally from the other side (e.g., the sea side) are arranged so that they intersect underground (intersect in a cross-sectional view). Note that it is not necessary for all freezing pipes 30 to intersect, and it is sufficient that at least a portion of the freezing pipes 30 intersect. Furthermore, modes in which freezing pipes 30 intersect include modes in which the freezing pipes 30 are connected, joined, or adjacent to each other.

[0118] Figure 13 shows a third modified example. For example, the description will be given assuming that the lower side of the page in Figure 13 is the mountain side and the upper side of the page in Figure 13 is the sea side. This third modified example shows the arrangement of multiple freezing pipes 30 that collectively surround two reactor buildings 2. Four reactor buildings 2 are lined up within the site of one power plant. All of the reactor buildings 2 are targets for fuel debris removal. In addition, the two reactor buildings 2 are housed together in one main wall section 8 (water tank 7). In the example of Figure 13, two main wall sections 8 (water tanks 7) are provided.

[0119] For example, there are multiple freezing pipes 30 surrounding the two reactor buildings 2 on the left side of the page, and multiple freezing pipes 30 surrounding the two reactor buildings 2 on the right side of the page. Two freezing plants 32 are provided to supply coolant to the freezing pipes 30 on the left and right sides of the page, respectively. In addition, two frozen soil impermeable wall lines 31 are provided.

[0120] Fig. 14 shows Modification 4. For example, the left side of the paper in Fig. 14 is the mountain side, and the right side of the paper in Fig. 14 is the sea side.

[0121] The bottom boundary of Modification 4 is a specified frozen soil impermeable wall 29 constructed by freezing the ground below the reactor building 2. For example, a specified frozen soil impermeable wall 29 constructed from the mountain side and a specified frozen soil impermeable wall 29 constructed between the reactor building 2 and the turbine building 39 are provided. The lower end portion of the specified frozen soil impermeable wall 29 is constructed from the ground surface to a depth where the lower permeable layer 52 exists.

[0122] This variation 4 omits the configuration of the specific frozen soil impermeable wall 29 constructed from the sea side of variation 1 (Fig. 11). This reduces construction costs and running costs for maintaining the frozen soil, and shortens the construction period.

[0123] Figure 15 shows variant 5. For example, the description will be given assuming that the bottom side of the page in Figure 15 is the mountain side and the top side of the page in Figure 15 is the sea side. This variant 5 corresponds to the arrangement of variant 4 (Figure 14) described above, and shows an arrangement of multiple freezing pipes 30 that collectively surround two reactor buildings 2. Four reactor buildings 2 are lined up within the site of one power plant. All of the reactor buildings 2 are targets for fuel debris removal. In addition, the two reactor buildings 2 are housed together in one main wall section 8 (water tank 7). In the example of Figure 15, two main wall sections 8 (water tanks 7) are provided.

[0124] For example, there are multiple freezing pipes 30 surrounding the two reactor buildings 2 on the left side of the page, and multiple freezing pipes 30 surrounding the two reactor buildings 2 on the right side of the page. Two freezing plants 32 are provided to supply coolant to the freezing pipes 30 on the left and right sides of the page, respectively. In addition, two frozen soil impermeable wall lines 31 are provided.

[0125] Fig. 16 shows Modification 6. For example, the explanation will be given assuming that the lower side of Fig. 16 is the mountain side and the upper side of Fig. 16 is the sea side. Modification 6 corresponds to the arrangement of Modification 4 (Fig. 14) described above, and shows an arrangement of multiple freezing pipes 30 that collectively surround each reactor building 2.

[0126] Four reactor buildings 2 are lined up within the site of one power plant. Of the four reactor buildings 2, three are the targets for fuel debris removal. Each of the three reactor buildings 2 is contained within a main wall section 8 (water tank 7). Figure 16 shows an example in which a frozen soil impermeable wall line 31 and a freezing plant 32 are installed for each reactor building 2.

[0127] Fig. 17 shows Modification 7. For example, the left side of Fig. 17 is the mountain side, and the right side of Fig. 17 is the sea side. Modification 7 illustrates a specified frozen soil impermeable wall 29 that covers the entire ground directly below the reactor building 2.

[0128] The bottom boundary of Variation 7 is a specified frozen soil impermeable wall 29 constructed by freezing the ground below the reactor building 2. For example, a specified frozen soil impermeable wall 29 constructed from the mountain side and a specified frozen soil impermeable wall 29 constructed from between the reactor building 2 and the turbine building 39 are provided. The lower end portions of the specified frozen soil impermeable walls 29 intersect underground. The specified frozen soil impermeable walls 29 are constructed diagonally downward from the ground surface. The specified frozen soil impermeable walls 29 are constructed so as to be slightly curved.

[0129] Fig. 18 shows Modification 8. For example, the left side of Fig. 18 is the mountain side, and the right side of Fig. 18 is the sea side. Modification 8 illustrates a specified frozen soil impermeable wall 29 that covers the entire ground directly below the reactor building 2.

[0130] The bottom boundary of Variation 8 is a specified frozen soil impermeable wall 29 constructed by freezing the ground below the reactor building 2. For example, a specified frozen soil impermeable wall 29 constructed from the mountain side and a specified frozen soil impermeable wall 29 constructed from between the reactor building 2 and the turbine building 39 are provided. The lower end portions of the specified frozen soil impermeable walls 29 intersect underground. The specified frozen soil impermeable walls 29 are constructed in a straight line, diagonally downward from the ground surface. In this way, the area excavated by boring is linear, making excavation easier.

[0131] Figure 19 shows variant 9. For example, the description will be given assuming that the bottom side of the paper in Figure 19 is the mountain side and the top side of the paper in Figure 19 is the sea side. This variant 9 corresponds to the arrangement of variant 7 (Figure 17) or variant 8 (Figure 18) described above, and shows an arrangement of multiple freezing pipes 30 that collectively surround each reactor building 2.

[0132] Four reactor buildings 2 are lined up within the site of one power plant. Of the four reactor buildings 2, three are the targets for fuel debris removal. Each of the three reactor buildings 2 is contained within a main wall section 8 (water tank 7). Figure 19 shows an example in which a frozen soil impermeable wall line 31 and a freezing plant 32 are installed for each reactor building 2.

[0133] According to the second embodiment and its modified example, there is no need to remove buildings surrounding the reactor building 2. Furthermore, portions of the ground directly below the reactor building 2 remain unexcavated, improving ground stability and reducing the risk of on-site workability associated with excavation, including during earthquakes.

[0134] (Third embodiment) Next, a third embodiment and its modified examples will be described with reference to Figures 20 to 22. Note that the same components as those shown in the above-described embodiments will be assigned the same reference numerals and redundant description will be omitted.

[0135] 20 to 22 are cross-sectional views showing the reactor building 2 (R / B) and the surrounding turbine building 39 (T / B). The reactor building 2 is constructed on the coast. For example, the left side of the pages of FIGS. 20 to 22 will be the mountain side, and the right side of the pages of FIGS. 20 to 22 will be the sea side.

[0136] 20 shows an example of the third embodiment. A water tank 7 is constructed to accommodate the entire reactor building 2 and to allow at least a portion of the reactor building 2 to be submerged by storing water therein. The water tank 7 includes a main wall portion 8, an auxiliary wall portion 9, and a water-stopping sediment layer 38 on which fine particles are deposited.

[0137] For example, a water-stopping sediment layer 38 made of a water-stopping material, a filler, and fine particles is provided at the bottom of the water tank 7, which reduces the rate at which water permeates from the bottom.

[0138] In this third embodiment, the bottom boundary is formed by a water-stopping deposition layer 38 in which fine particles are deposited. Furthermore, the main wall portion 8 and the auxiliary wall portion 9 form side boundaries.

[0139] Furthermore, since the removal of fuel debris and the like is required as soon as possible, fine particles that are easy to remove are injected into the inside of the containment vessel 4 and deposited as a water-stopping sediment layer 38.

[0140] In the third embodiment, the distribution of the underground strata at the location where the reactor building 2 is built is measured, the distribution of the upper impermeable layer 51, which is a mudstone layer with a low permeability coefficient, is determined, and the main wall section 8 and auxiliary wall section 9 surrounding the periphery of the reactor building 2 are constructed.

[0141] The main wall 8 has a vertical dimension that allows the reactor building 2 to be submerged. Furthermore, the inside of the water tank 7 surrounded by the main wall 8 is flooded. The inside of the main wall 8 is filled with a predetermined filling material before being flooded. Furthermore, equipment for injecting water into and draining water from the water tank 7 may be provided.

[0142] The bottom portion of the water tank 7, that is, the portion surrounded by the main wall portion 8, is filled with a water-stopping material having an extremely low coefficient of permeability without any gaps, and then a water-stopping sediment layer 38 is constructed.

[0143] The microparticles that form the water-stopping sediment layer 38 have a specific gravity greater than that of at least water, contain at least barite as a weighting material, and contain at least bentonite as a thickener, and the water-stopping sediment layer 38 is constructed using a microparticle dispersion containing the microparticles.

[0144] The microparticle dispersion contains water and microparticles with a specific gravity greater than that of water. This microparticle dispersion can be used to build a watertight structure that stops water leaks. When the microparticle dispersion is injected, the microparticles, which have a specific gravity greater than that of water, gradually settle and accumulate downward, forming a watertight sediment layer 38. This watertight sediment layer 38 is the watertight structure.

[0145] The fine particles are a water-stopping material that accumulates without solidifying and has fluidity. The blending ratio of materials such as barite and bentonite is adjusted in advance so that the fine particles have this property. The accumulated fine particles can be made to flow again by applying vibration. In other words, even in a location where a water-stopping sediment layer 38 has already formed, the water-stopping sediment layer 38 can be washed away by applying vibration. Note that modes of applying vibration include modes of stirring.

[0146] The water-blocking sediment layer 38 has fluidity, and various devices can access the fuel debris even when it is buried in the water-blocking sediment layer 38. In other words, in the following explanation, the state in which fuel debris is buried in the water-blocking sediment layer 38 and the state in which fuel debris is submerged are almost the same state and have the same meaning.

[0147] The fine particles may also be a combination of fine particles with different particle sizes, including two or more of barite, bentonite, polymer, nuclide adsorbent (adsorbent that adsorbs radioactive materials), and boric acid. These fine particles maintain fluidity after deposition. The deposited fine particles can be re-fluidized by applying vibration.

[0148] The third embodiment differs from the first embodiment in that it is not necessary to dismantle and remove buildings around the reactor building 2 when constructing the water tank 7. Also, the reactor building 2 and the ground 13 inside and around the buildings around it are enclosed by the main wall 8. A water-stopping sediment layer 38 is constructed in this enclosed area by depositing water-stopping material, filler material, and fine particles, thereby implementing water-stopping measures using a bottom boundary and constructing the water tank 7. Also, in the first embodiment, there is no need for the bottom 10 (FIG. 2) constructed underground at the location where the reactor building 2 is constructed.

[0149] Furthermore, after investigating the depth distribution of the underground ground strata, the ground is excavated until it reaches an upper impermeable layer 51, such as a mudstone layer, which has a low permeability coefficient. A wide-area frozen soil impermeable wall 33 is constructed in a lower permeable layer 52, such as a sandstone layer, which has a relatively high permeability coefficient. Furthermore, a land-side impermeable wall 48 is constructed using concrete materials, steel plates, water-stopping materials, etc. near the reactor building 2 and turbine building 39. This minimizes changes in ground stability due to underground ground excavation and suppresses the infiltration rate of the upper impermeable layer 51, which is a mudstone layer.

[0150] The space between the main wall portion 8 and the auxiliary wall portion 9 is formed as a moat 14. Water leaking from the main wall portion 8 is caught in the moat 14. As long as an appropriate height of the auxiliary wall portion 9 is ensured, the shape of the moat 14 may be any shape.

[0151] The thickness of the main wall portion 8 and the auxiliary wall portion 9 may be such that they will not be significantly deformed or damaged when they contain the maximum amount of anticipated leaked water.

[0152] Water is stored in a saturated state at the bottom of the water tank 7 due to the concrete material, water-stopping material, filler material, and fine particles. A basin zone (unsaturated zone) may be formed at the top of the main wall 8. This reduces the amount of water stored in the water tank 7 and the risk of water leakage. Furthermore, the amount of water permeating through components such as the water-stopping material or filler material is reduced, which slows down the water permeation rate.

[0153] Furthermore, if there is a gap between the main wall 8 on the mountain side upstream of the groundwater and the ground, a microparticle dispersion primarily made of bentonite may be supplied to the gap. Here, the microparticle dispersion may be supplied while being stirred inside the gap. By continuously supplying the microparticle dispersion to the gap, the microparticles can be dispersed along the waterway in the permeable layer along the flow of groundwater. This may result in the microparticles remaining in the permeable layer, suppressing the infiltration rate.

[0154] In the third embodiment, the leak location is waterproofed with fine particles having a specific gravity greater than that of water, and at least a portion of the nuclear facility is flooded. For example, an injection device (not shown) injects a fine particle dispersion into the internal space of the nuclear facility where the leak location is located, and forms a water-stopping deposition layer 38 in which the fine particles are deposited to a height higher than the leak location. The fine particles contain at least barite as a weighting material, and optionally at least bentonite as a thickener. The fine particles 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 fine particles have such properties.

[0155] The water tank 7 of the third embodiment is provided with a gantry 42 instead of the above-mentioned ceiling portion 11 (FIG. 3), and the nuclear facility flooding device 1 of the third embodiment is provided with an airtight structure 43. For example, the airtight structure 43 is suspended from the gantry 42 so that the lower part thereof is submerged, or the airtight structure 43 is floated above the water surface, thereby creating a water-sealed gas-phase containment space.

[0156] For example, a gantry 42 is arranged on the outside of the main wall portion 8. This gantry 42 does not necessarily need to ensure airtightness. However, an airtight structure 43 is suspended from this gantry 42. Inside the airtight structure 43, work equipment 45 (work machinery) for dismantling and removal, such as a crane 12, is suspended via a vertical lifting device 44. By submerging the lower end of the airtight structure 43 in water, a water seal can maintain airtightness inside and outside the airtight structure 43.

[0157] 21 shows Modification 10. In this Modification 10, an airtight structure 43, a floating structure 46, and a water volume reduction structure 47 are arranged according to the fuel debris removal work.

[0158] Not only is there water inside the water tank 7, but a floating structure 46, which is a ship-shaped structure, is also placed inside the water tank 7. The floating structure 46 is a structure that allows work equipment used in the decommissioning work to float on the water stored in the water tank 7 in a state where it can be moved horizontally. Note that the floating structure 46 can be submerged by pouring water into the inside of the floating structure 46.

[0159] Furthermore, the floating structure 46 has a structure that can seal the water contained therein. Water that does not contain radioactive materials is filled into the floating structure 46 in advance, and after sealing, the floating structure 46 is floated in the water tank 7, thereby isolating the inside of the floating structure 46 from the radioactive materials inside the water tank 7. Therefore, an increase in the water inside the water tank 7, that is, an increase in contaminated water, can be prevented.

[0160] The airtight structure 43 is a dome-shaped structure that is floated on the water stored in the water tank 7 by a floating structure 46 and covers the air layer area above the water tank 7 to maintain airtightness.

[0161] That is, in the tenth modification, instead of the up-and-down lifting device 44 (FIG. 20) suspended from the gantry 42, a floating structure 46 is attached to the bottom of the airtight structure 43. The airtight structure 43 floats on the water surface, and can maintain airtightness inside and outside the airtight structure 43.

[0162] The water storage volume reduction structure 47 is a container that traps a gas phase inside. If the water storage volume reduction structure 47 is sinkable, it will sit in a predetermined location. Furthermore, if the water storage volume reduction structure 47 becomes neutrally buoyant, it will float in the water, allowing the amount of water stored in the water tank 7 to be reduced without placing a load on the structure.

[0163] In cases where the water volume reduction structure 47 tends to float due to the balance between its own weight and buoyancy, a flat top can provide a foothold for work. In addition, equipment for injecting water into the water volume reduction structure 47 and discharging water from the water volume reduction structure 47 may be provided. This equipment makes it possible to adjust the weight and buoyancy of the floating structure 46, allowing the floating structure 46 to move within the water tank 7. In the example of Figure 21, the water volume reduction structure 47 is seated on the turbine building 39.

[0164] If an upper impermeable layer 51, which is a low-permeability mudstone layer, exists and it is confirmed that a certain amount of groundwater is flowing into this upper impermeable layer 51, existing boreholes 54 on the mountain side, which is upstream of the groundwater, or equivalent new boreholes 54 are drilled at specified intervals. Then, fine particles made primarily of bentonite are supplied into the boreholes 54. The fine particles are supplied while being stirred to prevent accumulation. The fine particles are supplied into the ground and suppress the infiltration rate of the groundwater.

[0165] Before the water-stopping material, filler, and fine particles are poured, a floating structure 46 may be placed to ensure an underwater environmental space that these filler materials cannot enter.

[0166] Figure 22 shows Modification 11. Modification 11 illustrates an embodiment in which a water tank 7 is constructed using a main wall portion 8, and a waterproof sediment layer 38 is deposited over almost the entire water tank 7. Water 6 is stored only in the area where fuel debris removal work will be carried out. Then, work equipment is inserted through the stored water 6, and fuel debris removal work is carried out in the underwater environment.

[0167] Fine particles are deposited in spaces where fuel debris and other debris must first be removed, such as inside the reactor building 2. The deposited fine particles are easily liquefied by applying vibration. Then, during the fuel debris removal work, water is injected while the fine particles are removed, creating an underwater environment. To manage these water levels, equipment is installed to appropriately inject and drain water.

[0168] The third embodiment differs from the first embodiment in that it does not require the removal of buildings around the reactor building 2. Also, instead of placing a shield machine 18 (FIG. 5), a plant for supplying water-stopping material, filler material, and microparticle dispersion liquid is placed. Furthermore, injection lines for water-stopping material, etc., injection and drainage pipes are placed, and obstacles and a boat-shaped structure are placed. After the decommissioning work equipment is placed, water transfer equipment is placed. Furthermore, water-stopping material, filler material, and microparticle dispersion liquid are introduced, and water is stored.

[0169] Meanwhile, the impact of water infiltration from the bottom of Reactor Building 2 and surrounding buildings will need to be evaluated, and if necessary, partial removal of the ground directly below will be required after the demolition of the surrounding buildings.

[0170] According to the third embodiment and its modifications, there is no need to first remove buildings around the reactor building 2. In addition, there is no need to excavate the ground directly below the reactor building 2, eliminating the risk of on-site workability when constructing the hull structure on the ground below the reactor building 2, including the risk of ground stability during earthquakes during construction.

[0171] The present invention has been described above based on the first to third embodiments and each modified example, 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.

[0172] For example, the bottom boundary may include all of the components of the bottom 10, the specific frozen soil impermeable wall 29, the water-blocking sediment layer 38, and the ice blocks. Also, the bottom boundary may be constructed by mixing at least two of these components.

[0173] The nuclear facility flooding method described above illustrates an example in which each step is performed in series, but the order of steps is not necessarily fixed, and the order of some steps may be reversed. Also, some steps may be performed in parallel with other steps. Furthermore, the above description covers at least some of the steps of the nuclear facility flooding method, and other steps may be included in the nuclear facility flooding method.

[0174] In the above-described embodiment, the nuclear facility includes various devices installed in a nuclear power plant, such as the reactor building 2, the reactor well 27, the shield plug, the reactor pressure vessel 3, the reactor containment vessel 4, the pressure suppression chamber 5, the pedestal, the vent pipe, the control rod drive mechanism, and the reactor core. The nuclear facility may also be a part of the nuclear facility flooding device 1. For example, the nuclear facility includes a main wall portion 8.

[0175] In the above-described embodiment, "submerging" includes submerging the equipment to be dismantled. "Submerging" also includes filling the interior of the equipment to be dismantled with water. "Submerging" also includes submerging the highly radioactive parts of the equipment to be dismantled to a depth at which the radiation level is sufficiently attenuated.

[0176] 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).

[0177] According to at least one embodiment described above, the bottom boundary allows a nuclear facility that has suffered a severe accident to be submerged, the water to shield radiation, and the nuclear facility to be dismantled in an underwater environment.

[0178] 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]

[0179] 1...nuclear facility flooding device, 2...reactor building, 3...reactor pressure vessel, 4...reactor containment vessel, 5...pressure suppression chamber, 6...water storage, 7...water tank, 8...main wall section, 9...auxiliary wall section, 10...bottom, 11...ceiling section, 12...crane, 13...ground, 14...trench, 15...connecting section, 16...wall liner, 17...shield tunnel, 18...shield machine, 19...bottom liner, 20...shoring, 21...excess trench section, 22...column section, 23...opening, 24...intermediate floor, 25...transfer device, 26...transfer piping, 27...reactor well, 28...connecting structure Body, 29...specific frozen soil impermeable wall, 30...frozen pipe, 31...frozen soil impermeable wall line, 32...frozen plant, 33...wide-area frozen soil impermeable wall, 34...sea-side impermeable wall, 35...sub-drain, 38...water-stopping sediment layer, 39...turbine building, 40...support wall section, 42...platform, 43...airtight structure, 44...upper and lowering device, 45...work equipment, 46...floating structure, 47...water storage volume reduction structure, 48...land-side impermeable wall, 50...upper permeable layer, 51...upper impermeable layer, 52...lower permeable layer, 53...lower impermeable layer, 54...borehole, 55...frozen pipe header, 60...sea.

Claims

1. A bottom boundary is provided to suppress the outflow of water flowing downward from the reactor building to be decommissioned by flooding at least the reactor containment vessel, the bottom boundary includes at least one of a frozen soil impermeable wall constructed by freezing the ground below the reactor building, a water-stopping sedimentary layer in which fine particles are deposited, or an ice block constructed by freezing water stored in the basement of the reactor building; Nuclear facility flooding device.

2. a side boundary that surrounds the reactor building and suppresses outflow of water leaked from the reactor containment vessel to the outside; The side boundary is a wall constructed using at least one of prestressed concrete and hull structure. The nuclear facility flooding device according to claim 1.

3. the side boundary has at least the same vertical dimension as the reactor containment vessel; a connecting structure that connects the side boundary and the reactor building; The nuclear facility flooding device according to claim 2.

4. a water tank is constructed that is composed of the bottom boundary and the side boundary, that can accommodate the entire reactor building, and that can submerge at least a portion of the reactor building by storing water therein; The nuclear facility flooding device according to claim 2.

5. A floating structure is provided that floats on the water stored in the water tank in a state in which work equipment used in the decommissioning work can be moved horizontally. The nuclear facility flooding device according to claim 4.

6. a dome-shaped airtight structure that is floated on the water stored in the water tank by the floating structure and that covers an air layer area above the water tank to maintain airtightness; The nuclear facility flooding device according to claim 5.

7. a transfer device that transfers accumulated water to the reactor containment vessel when water leaking from the reactor containment vessel accumulates in the basement of the reactor building; The nuclear facility flooding device according to any one of claims 1 to 6.

8. the bottom boundary includes the frozen soil impermeable wall, the frozen soil impermeable wall is constructed obliquely from the periphery of the reactor building toward below the reactor building, The nuclear facility flooding device according to any one of claims 1 to 6.

9. the bottom boundary includes the frozen soil impermeable wall, A plurality of frozen pipes for constructing the frozen soil impermeable wall are arranged at predetermined intervals, A plurality of the freezing pipes buried obliquely from one side of the reactor building and a plurality of the freezing pipes buried obliquely from the other side are arranged so as to intersect underground. The nuclear facility flooding device according to any one of claims 1 to 6.

10. the bottom boundary includes the water-blocking deposit layer; the fine particles have a specific gravity greater than that of at least water, contain at least barite as a weighting material, and contain at least bentonite as a thickening agent; The water-blocking deposition layer is constructed using a microparticle dispersion containing the microparticles. The nuclear facility flooding device according to any one of claims 1 to 6.

11. A bottom boundary including at least one of a frozen soil impermeable wall constructed by freezing the ground below the reactor building, a water-stopping sedimentary layer made of accumulated fine particles, or an ice block constructed by freezing water stored in the basement of the reactor building suppresses the outflow of water flowing downward from the reactor building, At the very least, the reactor containment vessel will be flooded and decommissioned. Methods for flooding nuclear facilities.

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