Method for dismantling the upper core structure

Abstract

To improve work efficiency. [Solution] A method for dismantling an upper core structure, comprising an upper core plate and a plurality of upper core support columns connecting an upper core plate, the method comprising: removing the anti-rotation mechanism of the connecting portion that connects the upper core support column to the upper core support plate while the upper core structure is placed inside a reactor vessel containing water; lifting the upper core support plate so that the upper core structure, together with the upper core support column connected to the upper core support plate via the connecting portion and the upper core plate connected to the upper core support column, is moved to a work space outside the reactor vessel; removing the connecting portion in the work space; and separating the upper core support plate from the upper core support column and transporting it.

Description

Technical Field

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[0001] The present disclosure relates to a method for disassembling an upper core structure.

Background Art

[0002] Patent Document 1 describes a method for disassembling a nuclear power plant for which decommissioning measures have been determined. In this disassembling method, in order to suppress the period during which the working pool is filled with water, the removal and disassembly work of the in-vessel structure is started before the completion of the removal of the fuel from the fuel storage pool.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, a nuclear reactor has many members with a high radiation dose (dose), including the in-vessel structure which is an internal structure. Therefore, when disassembling a nuclear reactor, it often touches members with a high dose, resulting in many restrictions on the working time and working place. Therefore, when disassembling a nuclear reactor while suppressing the influence of radiation, it is desired to improve workability.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a method for disassembling an upper core structure capable of suppressing the influence of radiation and improving workability.

Means for Solving the Problems

[0006] To solve the above problems, the method for dismantling an upper core structure according to the present disclosure is a method for dismantling an upper core structure comprising an upper core plate, an upper core support plate positioned vertically above the upper core plate, and a plurality of upper core support columns connecting the upper core plate and the upper core support plate, the method comprising: removing the anti-rotation mechanism of the connecting portion that connects the upper core support column to the upper core support plate while the upper core structure is positioned inside a reactor vessel containing water; lifting the upper core support plate so that the upper core structure, together with the upper core support column connected to the upper core support plate via the connecting portion and the upper core plate connected to the upper core support column, is moved to a work space outside the reactor vessel; removing the connecting portion in the work space; and separating the upper core support plate from the upper core support column and transporting it. [Effects of the Invention]

[0007] According to the method for dismantling the upper core structure described herein, the effects of radiation can be suppressed and work efficiency can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a longitudinal cross-sectional view showing a pressurized water reactor according to the embodiment. [Figure 2] This is a schematic diagram showing a pressurized water reactor, with water stored inside and its reactor vessel lid removed, positioned inside a pool within the reactor building according to the embodiment. [Figure 3] This is a perspective view showing the upper core structure according to the embodiment. [Figure 4] This is a longitudinal cross-sectional view showing the upper core structure according to the embodiment. [Figure 5] This diagram shows the positional relationship between the upper core support plate and the upper core support column with respect to the upper core plate according to the embodiment. [Figure 6] This is a flowchart illustrating a method for dismantling the upper core structure according to the embodiment. [Figure 7]This figure shows the state after raising the water level in the reactor building before moving the upper core structure according to the embodiment. [Figure 8] This figure shows the state after the water level in the reactor building has been lowered following the relocation of the upper core structure according to the embodiment. [Figure 9] This figure shows an example of the configuration of a device for raising the upper core support column of the embodiment. [Modes for carrying out the invention]

[0009] The following describes embodiments for implementing the method of dismantling the upper core structure according to this disclosure, with reference to the attached drawings. However, this disclosure is not limited to these embodiments.

[0010] <Embodiment> (nuclear reactor) Figure 1 is a longitudinal cross-sectional view showing a pressurized water reactor 1, which is the reactor to be dismantled according to this embodiment. The reactor is a pressurized water reactor 1 (PWR) that uses light water as a reactor coolant and neutron moderator to create high-temperature, high-pressure water that does not boil throughout the entire core, sends this high-temperature, high-pressure water to a steam generator to generate steam through heat exchange, and sends this steam to a turbine generator to generate electricity.

[0011] As shown in Figure 2, the pressurized water reactor 1 is located inside the reactor building pool 100. The reactor building pool 100 has a space where cooling water (water) can be stored. The reactor building pool 100 in this embodiment has a first cavity 110 in which the pressurized water reactor 1 is located, and a second cavity 120 located adjacent to the first cavity 110. The first cavity 110 has a first floor surface 111 in which workers can walk. The first floor surface 111 has a recess in which the pressurized water reactor 1 is housed. The second cavity 120 has a second floor surface 121 that is recessed from the first floor surface 111. In other words, the second floor surface 121 is located vertically Dv below the first floor surface 111. As a result, the second cavity 120 is formed as a space that is recessed vertically Dv lower than the first cavity 110. Furthermore, the first cavity 110 and the second cavity 120 are provided with workspaces where parts can be placed when dismantling the pressurized water reactor 1. Specifically, these workspaces are formed by a portion of the first floor surface 111 and a portion of the second floor surface 121.

[0012] As shown in Figures 1 and 2, the pressurized water reactor 1 of this embodiment comprises a reactor vessel 2, a control rod drive unit 3, an upper core structure 5, and a lower core structure 6.

[0013] The reactor vessel 2 has a reactor vessel body 21 and a reactor vessel lid 22 (upper mirror) so that internal reactor structures can be inserted inside. The reactor vessel 2 is positioned inside a hole formed to be recessed from the first floor surface 111. The reactor vessel 2 is positioned so that a portion of it (specifically the reactor vessel lid 22) protrudes from the first floor surface 111.

[0014] The reactor vessel body 21 can be opened at the top by removing the reactor vessel head 22. The lower part of the reactor vessel body 21 has a cylindrical shape closed by a hemispherical bottom mirror. At the upper part of the reactor vessel body 21, an inlet nozzle 23 (inlet plenum) for supplying light water (coolant) as primary cooling water (water) and an outlet nozzle 24 (outlet plenum) for discharging light water are formed. Further, the reactor vessel body 21 has a water injection nozzle (water injection plenum), not shown, separately from the inlet nozzle 23 and the outlet nozzle 24.

[0015] The reactor vessel head 22 is attached to the upper part of the reactor vessel body 21. The reactor vessel head 22 is fixed to the reactor vessel body 21 so as to be openable and closable by a plurality of stud bolts and nuts (not shown).

[0016] The upper core structure 5 is disposed inside the reactor vessel 2. The upper core structure 5 can be withdrawn from the reactor vessel body 21 by being moved upward in the vertical direction Dv with respect to the reactor vessel body 21. As shown in FIGS. 3 and 4, the upper core structure 5 of the present embodiment includes an upper core plate 51, an upper core support plate 52, upper core support columns 53, guide tubes 55, and a connecting portion 59.

[0017] Note that the upper core structure 5 does not have only the structure described above. The upper core structure 5 has other configurations such as a mixer and a thermocouple lead-out tube, etc. as a configuration not shown.

[0018] The upper core plate 51 is disposed below the upper core support plate 52 and separated therefrom in the vertical direction Dv. In the upper core plate 51, a large number of through holes are formed in a disk shape. The guide tubes 55 are inserted through the through holes of the upper core plate 51.

[0019] The upper core support plate 52 is positioned above the upper core plate 51 in the vertical direction Dv. As shown in Figures 1 and 2, the upper core support plate 52 is fixed to the reactor vessel body 21 internally, above the inlet nozzle 23 and outlet nozzle 24 in the vertical direction Dv. As shown in Figures 3 and 4, the upper core support plate 52 is formed in a larger disc shape than the upper core plate 51. The upper core support plate 52 has numerous through holes at the same positions as the upper core plate 51 when viewed from the vertical direction Dv. Guide tubes 55 are inserted through the through holes of the upper core support plate 52. Also, as shown in Figure 2, the upper surface of the upper core support plate 52 in this embodiment is positioned at the same height as the first floor surface 111 in the vertical direction Dv when the upper core structure 5 is positioned inside the reactor vessel 2. As shown in Figure 4, the upper core support plate 52 in this embodiment has a support plate body 521 and reinforcing beams 522.

[0020] The support plate body 521 is formed in a disc shape. The reinforcing beam 522 is formed to increase the rigidity of the support plate body 521. Specifically, the reinforcing beam 522 is positioned below the support plate body 521 in the vertical direction Dv. The reinforcing beam 522 is fixed to the support plate body 521 by fastening members such as bolts so as to be an integral part of it. The reinforcing beam 522 is formed to have a greater thickness in the vertical direction Dv than the support plate body 521. The reinforcing beam 522 is shaped so as not to interfere with the guide tube 55.

[0021] As shown in Figures 3 and 4, the multiple upper core support columns 53 are connected to the upper core support plate 52 and the upper core plate 51. The multiple upper core support columns 53 extend linearly in the vertical direction Dv. The upper ends of the upper core support columns 53 are fixed to the upper core support plate 52. The lower ends of the upper core support columns 53 are fixed to the upper core plate 51. When viewed from the vertical direction Dv, the multiple upper core support columns 53 are offset from the guide tube 55 so as not to overlap. As shown in Figures 4 and 5, the upper core structure 5 of this embodiment has multiple first upper core support columns 53A and multiple second upper core support columns 53B as upper core support columns 53.

[0022] The first upper core support column 53A is connected to the support plate body 521 and the upper core plate 51. The first upper core support column 53A is formed in a cylindrical shape extending in the vertical direction Dv. The first upper core support column 53A is positioned so as not to overlap with the reinforcing beam 522. In other words, the first upper core support column 53A does not come into contact with the reinforcing beam 522, but only with the support plate body 521. The upper end of the first upper core support column 53A is in contact with and fixed to the lower surface of the support plate body 521. The lower end of the first upper core support column 53A is in contact with and fixed to the upper surface of the upper core plate 51.

[0023] The second upper core support column 53B is connected to the support plate body 521 and the upper core plate 51. The second upper core support column 53B is positioned to overlap with the reinforcing beam 522. In other words, the first upper core support column 53A is in contact with the support plate body 521. The upper end of the second upper core support column 53B is fixed to the support plate body 521. The lower end of the second upper core support column 53B is in contact with and fixed to the upper surface of the upper core plate 51. The second upper core support column 53B in this embodiment has a support column base portion 531B and a support column tip portion 532B. The support column base is formed in a cylindrical shape extending in the vertical direction Dv. The support column base portion 531B is formed to have the same cross-sectional shape as, for example, the first upper core support column 53A. The upper end of the support column base portion 531B is in contact with the lower surface of the reinforcing beam 522. The lower end of the base portion 531B of the support column is in contact with and fixed to the upper surface of the upper core plate 51. The tip portion 532B of the support column is formed in a cylindrical shape that extends upward in the vertical direction Dv from the base portion 531B. The tip portion 532B of the support column has a smaller outer diameter (thinner) than the base portion of the support column. The tip portion 532B of the support column is positioned to penetrate the reinforcing beam 522. The upper end of the tip portion 532B of the support column protrudes upward in the vertical direction Dv relative to the support plate body 521. The lower end of the tip portion 532B of the support column is connected to the upper end of the base portion 531B of the support column.

[0024] As shown in Figures 3 and 4, the guide tube 55 is fixed to the upper core support plate 52 by being inserted through a through-hole in the upper core support plate 52. The guide tube 55 guides the vertical movement Dv of the control rod cluster 4. The guide tube 55 is designed so that the control cluster can be inserted into it. The guide tube 55 is made of, for example, stainless steel. The guide tube 55 is inserted from above in the vertical direction Dv into the through-hole in the upper core support plate 52 and the through-hole in the upper core plate 51. In other words, the guide tube 55 is movable above the vertical direction Dv relative to the upper core support plate 52 and the upper core plate 51 by releasing its fixation. Specifically, the lower end of the guide tube 55 is connected to the upper core plate 51. The upper end of the guide tube 55 is positioned above the vertical direction Dv relative to the upper core support plate 52.

[0025] As shown in Figures 4 and 5, the connecting portion 59 connects the upper core support column 53 to the upper core support plate 52. One connecting portion 59 is provided for each upper core support column 53. The connecting portion 59 directly fixes the upper core support plate 52 and the upper core support column 53. Specifically, the connecting portion 59 fixes the upper core support column 53 to the upper core support plate 52 from above in the vertical direction Dv. Furthermore, the connecting portion 59 is provided with a rotation-preventing mechanism to prevent rotation of the upper core support plate 52 and the upper core support column 53. The connecting portion 59 in this embodiment has a first connecting portion 591 and a second connecting portion 592.

[0026] The first connecting portion 591 connects the first upper core support column 53A to the upper core support plate 52. The first connecting portion 591 is a bolt fixed from above in the vertical direction Dv. Multiple first connecting portions 591 are arranged for each first upper core support column 53A. The first connecting portion 591 is fastened to the upper end of the first upper core support column 53A and the upper core support plate 52, sandwiching the upper core support plate 52, thereby fixing the first upper core support column 53A to the upper core support plate 52. The first connecting portion 591 is fixed to the upper core support plate 52 by welding. This prevents the first connecting portion 591 from rotating relative to the upper core support plate 52 and the first upper core support column 53A.

[0027] The second connecting portion 592 connects the second upper core support column 53B to the upper core support plate 52. The second connecting portion 592 is a nut that is fixed from above in the vertical direction Dv. Only one second connecting portion 592 is provided for each second upper core support column 53B. The second connecting portion 592 is fastened to the upper end of the support column tip 532B so as to sandwich the upper core support plate 52, thereby fixing the support column tip 532B to the upper core support plate 52. The second connecting portion 592 is fixed to the upper core support plate 52 by welding. In this way, the second connecting portion 592 is prevented from rotating relative to the upper core support plate 52 and the second upper core support column 53B.

[0028] As shown in Figures 1 and 2, the lower core structure 6 is located inside the reactor vessel 2. Many of the components of the lower core structure 6 are positioned vertically Dv below the upper core structure 5. The lower core structure 6 can be removed from the reactor vessel body 21 by moving it vertically Dv above the reactor vessel body 21. The lower core structure 6 is separable from the upper core structure 5 inside the reactor vessel body 21.

[0029] (Method for dismantling the upper core structure) The following describes a method for dismantling the upper core structure 5 according to the embodiment of this disclosure. Figure 6 is a flowchart showing the method for dismantling the upper core structure 5 according to the embodiment of this disclosure.

[0030] The dismantling method for the upper core structure 5 involves dismantling the upper core support columns 53. As shown in Figure 2, the dismantling method for the upper core structure 5 is carried out in a state where it is possible to contact the internal components of the reactor vessel body 21 installed in the pool 100 inside the reactor building. In other words, the dismantling method for the upper core structure 5 is carried out with the reactor vessel lid 22 removed from the reactor vessel body 21. Furthermore, the dismantling method for the upper core structure 5 is carried out with water stored inside the reactor vessel body 21. Specifically, water is stored inside the reactor vessel body 21 up to the position where the upper core support plate 52 is located. In other words, the upper surface of the upper core support plate 52 is located above the liquid surface of the cooling water in the vertical direction Dv. The lower surface of the upper core support plate 52 may be in contact with the cooling water. In addition, the dismantling method for the upper core structure 5 is carried out with the control rod cluster removed from inside the guide tube 55.

[0031] In this embodiment, the dismantling method for the upper core structure 5 shown in Figure 6 first involves removing the anti-rotation device for the connecting portion 59 (step S1). The anti-rotation device for the connecting portion 59 is removed while the upper core structure 5 is positioned inside the reactor vessel body 21. In other words, the upper core structure 5 is positioned inside the reactor vessel 2, which contains water. Therefore, the lower parts of the upper core plate 51 and the upper core support columns 53 are submerged in water. The upper core support columns 53 may be entirely submerged, or their lower parts may be submerged while their tops are in the air.

[0032] In this state, the anti-rotation device for the welded or other connecting portion 59 is removed from above in the vertical direction Dv. At this time, in order to release the anti-rotation device, the welded portion or a part of the connecting portion 59 may be cut off with a cutter or grinder. Preferably, the connecting portion 59 is loosened to a state in which it is easily removed by a worker after the fixing or other fastening is released. Even when the anti-rotation device for the connecting portion 59 is released, the fixing of the upper core support plate 52 and the upper core support column 53 by the connecting portion 59 is not released. In other words, the connection of the upper core support column 53 to the upper core support plate 52 is maintained.

[0033] As shown in Figure 6, after the anti-rotation device of the connecting portion 59 is removed, a step (step S2) is performed in which the connection between a portion of the upper core support columns 53 and the upper core support plate 52 is released. Specifically, after the anti-rotation device is removed and before the upper core structure 5 is moved, a portion of the connecting portion 59 is removed. For example, in this embodiment, a portion of the first connecting portion 591 and all of the second connecting portion 592 are removed. The first connecting portion 591 is removed, leaving only a portion (for example, four evenly spaced) that is spaced apart circumferentially from the upper core support plate 52.

[0034] Furthermore, the configuration is not limited to one in which a part of the first connecting portion 591 and all of the second connecting portion 592 are removed. For example, the configuration may be one in which all of the first connecting portion 591 and a part of the second connecting portion 592 are removed.

[0035] Step S3 is performed in which the upper core structure 5 is moved to a workspace outside the reactor vessel 2 after the rotation stopper of the connecting portion 59 is removed. Specifically, after the rotation stopper of the connecting portion 59 is removed, and then a part of the connecting portion 59 is removed, the upper core structure 5 is moved. By lifting the upper core support plate 52, the upper core structure 5 is moved together with the upper core support column 53, which is connected to the upper core support plate 52 via the connecting portion 59, and the upper core plate 51, which is connected to the upper core support column 53. The upper core structure 5 is moved from inside the reactor vessel body 21 to the workspace of the second cavity 120. The workspace of the second cavity 120 may contain scaffolding for disassembling the upper core structure 5 and cutting equipment used for cutting components.

[0036] As the upper core structure 5 is moved, as shown in Figure 7, the first cavity 110 and the second cavity 120 are filled with water to a depth that overlaps with the movement path of the upper core structure 5. Therefore, the cavities are filled with water to a position above the first floor surface 111 in the vertical direction Dv, where the upper core structure 5 does not come out of the water while it is moving. Subsequently, the upper core structure 5 is pulled out of the reactor vessel body 21 by being lifted upward in the vertical direction Dv by the overhead crane 150 or the like while underwater. The upper core structure 5, which has been pulled out of the reactor vessel body 21, is moved to the working space of the second cavity 120 by the overhead crane 150 moving horizontally in the direction Dh.

[0037] Furthermore, the configuration in which the upper core structure 5 is moved from inside the reactor vessel body 21 to the working space of the second cavity 120 is not limited to this configuration. The upper core structure 5 may also be moved from inside the reactor vessel body 21 to the working space of the first cavity 110.

[0038] After the upper core structure 5 is moved to the work area, the water level is lowered as shown in Figure 8. At this time, the water level is adjusted to a depth where the first floor surface 111 is exposed and at least a portion of the upper core structure 5 above the work area of ​​the second cavity 120 is covered. Specifically, the water level is lowered to the same height as the first floor surface 111. As a result, in the upper core structure 5 located in the work area of ​​the second cavity 120, only the lower parts of the upper core plate 51 and the upper core support columns 53 are submerged in water. Before and after the movement of the upper core structure 5, the inside of the reactor vessel body 21 remains filled with water. After the movement of the upper core structure 5, a temporary cover 200 is placed to close the opening at the upper end of the reactor vessel body 21. The temporary cover 200 is placed at the same height as the first floor surface 111 in the vertical direction Dv. The temporary cover 200 is formed in a shape that covers the entire opening of the reactor vessel body 21 so that it can suppress the diffusion of radiation from inside the reactor vessel body 21 to the outside.

[0039] As shown in Figure 6, after the upper core structure 5 is moved to the work space, a process (step S4) is carried out in the work space in which the connecting parts 59 are removed. Specifically, after the upper core structure 5 is moved and the water level is lowered, all connecting parts 59 are removed. This releases the connection between the upper core support plate 52 and the upper core support columns 53 by the connecting parts 59. In other words, the upper core support columns 53 are no longer connected to the upper core support plate 52, and the upper core support plate 52 is made movable upward in the vertical direction Dv.

[0040] After the connecting portion 59 is removed, a process (step S5) is carried out in which the upper core support plate 52 is separated from the upper core support column 53 and transported. By lifting the upper core support plate 52, it is separated from the upper core support column 53, and only the upper core support plate 52 is moved. The upper core support plate 52 is moved from the work space of the second cavity 120 to the work space of the first cavity 110. Scaffolding for disassembling the upper core support plate 52 may be provided in the work space of the first cavity 110. In the upper core plate 51 moved to the work space of the first cavity 110, the support plate body 521 and the reinforcing beam 522 are separated.

[0041] Furthermore, if the upper core support plate 52 is located in the workspace of the first cavity 110, it will be moved to the workspace of the second cavity 120. Moreover, the upper core support plate 52 is not limited to being moved between the first cavity 110 and the second cavity 120, but may also be moved to an external workspace.

[0042] After the upper core support plate 52 is separated from the upper core support column 53, a process (step S5) is carried out in which the upper core support column 53 is lifted and removed from the upper core plate 51. In the working space of the second cavity 120, the upper core support column 53 is lifted, and only the upper core support column 53 is pulled out from the upper core plate 51. Before lifting the upper core support column 53, fastening members such as bolts that fix the upper core plate 51 and the upper core support column 53 are removed underwater via jigs or the like.

[0043] Specifically, the overhead crane 150 is attached to the upper core support column 53. As shown in Figure 9, a lifting jig 300 is attached to the overhead crane 150. The lifting jig 300 is used when the overhead crane 150 lifts the upper core support column 53. The lifting jig 300 in this embodiment includes a protective cover 310, a load cell 320, an electric hoist 330, and a lifting member 240.

[0044] The protective cover 310 is suspended from the overhead crane 150. The protective cover 310 is capable of accommodating the upper core support column 53 inside. The protective cover 310 is formed in a closed-bottom cylindrical shape with the top closed and the bottom open. In other words, the protective cover 310 is capable of inserting the upper core support column 53 from the lower end in the vertical direction Dv. The protective cover 310 is formed to a size that can accommodate the entire upper core support column 53. The protective cover 310 is formed of a material and size that can suppress the diffusion of radiation from the upper core support column 53 housed inside to the outside. A load cell 320 is installed inside the protective cover 310. The load cell 320 is capable of measuring the load generated on the electric hoist 330. The electric hoist 330 is capable of raising and lowering heavy objects by using electricity to move a motor with a wire attached. The electric hoist 330 is connected to the load cell 320 inside the protective cover 310. The electric hoist 330 is positioned below the load cell 320 in the vertical direction Dv. The lifting member 240 is attached to the tip of the electric hoist 330. The lifting member 240 is detachably attached to the upper end of the upper core support column 53.

[0045] The overhead crane 150 approaches one of the upper core support columns 53 from above in the vertical direction Dv and attaches the lifting member 240 to the upper end of the upper core support column 53. The upper core support column 53 with the lifting member 240 attached is then lifted above in the vertical direction Dv by the electric hoist 330 moving above in the vertical direction Dv. The lifted upper core support column 53 is gradually housed inside the protective cover 310. Subsequently, the overhead crane 150 moves further above in the vertical direction Dv, housing the entire upper core support column 53 inside the protective cover 310. The upper core support column 53 housed inside the protective cover 310 is then removed from the upper core plate 51 along with the protective cover 310 by the overhead crane 150 moving in the horizontal direction Dh. Subsequently, the upper core support column 53 and protective cover 310 are positioned so as to be submerged in a horizontal position within the second cavity 120, which is filled with water up to the level of the first floor surface 111. After that, the upper core support column 53 and protective cover 310 may be moved directly to the cutting device.

[0046] As shown in Figure 6, after the upper core support column 53 is removed, a process (step S7) is carried out in which the upper core support column 53 is cut into multiple pieces. Specifically, the upper core support column 53 that has been lifted and removed is cut by a cutting device (not shown) so as to be divided in the vertical direction Dv. The upper core support plate 52 and the upper core plate 51 are also cut.

[0047] (Effects and Benefits) In the dismantling method for the upper core structure 5 according to this embodiment, the anti-rotation device for the connecting portion 59 is removed while the upper core structure 5 is positioned inside the reactor vessel body 21. The upper core structure 5 positioned inside the reactor vessel body 21 is more likely to maintain a stable position compared to the upper core structure 5 positioned in the working space of the second cavity 120. Furthermore, the presence of water inside the reactor vessel body 21 suppresses the diffusion of radiation. In addition, removing the anti-rotation device for the connecting portion 59, which is firmly fixed by welding or the like, involves complex work such as removing the welded parts. Such complex work can be performed on the upper core structure 5, which maintains a stable position in an environment where the diffusion of radiation is suppressed. As a result, the effects of radiation can be reduced, and the work efficiency of the workers can be improved.

[0048] Furthermore, after the anti-rotation mechanism of the connecting portion 59 is removed, the connection between a portion of the multiple upper core support columns 53 and the upper core support plate 52 is released. In particular, in this embodiment, a portion of the first connecting portion 591 and all of the second connecting portion 592 are removed. As a result, when lifting the upper core support plate 52 and moving the upper core structure 5, the connection between the upper core support columns 53 and the upper core support plate 52 is maintained by only the minimum necessary number of connecting portions 59. In other words, many of the connecting portions 59 that are unnecessary when supporting the load required to lift the upper core support plate 52 and move the upper core structure 5 can be removed before moving the upper core structure 5. Therefore, the work of removing a large number of connecting portions 59 can be performed on the upper core structure 5, which maintains a stable posture in an environment where the diffusion of radiation is suppressed. As a result, the effects of radiation can be suppressed and the work efficiency of workers can be improved.

[0049] Furthermore, when the upper core structure 5 is moved, the first cavity 110 and the second cavity 120 are filled with water to a depth that overlaps with the movement path of the upper core structure 5. Therefore, during the process of being withdrawn from the reactor vessel body 21 and moved to the working space of the second cavity 120, the upper core structure 5 is always moved while submerged in water. Thus, when moving the upper core structure 5, which includes the upper core plate 51 with a high radiation dose, the diffusion of radiation can be suppressed.

[0050] Furthermore, after the upper core structure 5 is moved to the work area, the water level is lowered to the same height as the first floor surface 111. As a result, within the upper core structure 5 located in the work area of ​​the second cavity 120, the area around the upper core plate 51, which has a high radiation dose, remains submerged in water. Therefore, when dismantling the upper core structure 5, including the upper core plate 51, in the work area of ​​the second cavity 120, the diffusion of radiation can be suppressed. In addition, since there is no water above the first floor surface 111, a wider work area for workers can be secured, improving work efficiency. Therefore, sufficient working time can be secured when workers dismantle the upper core structure 5 in the work area of ​​the second cavity 120, improving work efficiency.

[0051] Furthermore, when the upper core support column 53 is lifted and removed, it is housed inside the protective cover 310 and lifted up. Because it is in contact with the upper core plate 51, which has a relatively high radiation dose among the upper core structures 5, the radiation dose in the lower region of the upper core support column 53 is also high. When moving such an upper core support column 53, the protective cover 310 can suppress the diffusion of radiation from the upper core support column 53 during movement. Therefore, workers can secure sufficient time to move the upper core support column 53, improving work efficiency.

[0052] Furthermore, the upper core support column 53 is lifted and removed, and then cut into multiple pieces. This makes the long upper core support column 53 smaller. Therefore, the upper core support column 53 can be processed into pieces that fit into a predetermined size waste container corresponding to the dose level, which is an indicator of the amount of radioactive material contained in the waste. As a result, the upper core support column 53 can be easily disposed of.

[0053] Furthermore, a temporary lid 200 is placed to cover the opening at the top of the reactor vessel body 21. This prevents foreign matter (metal shavings) from entering the inside of the reactor vessel body 21. As a result, contamination of the entire plant system by foreign matter via the inside of the reactor vessel body 21 can be suppressed. Moreover, since the opening at the top of the reactor vessel body 21 is covered by the lid 200 during the work, the space for dismantling work using remote equipment can be expanded. Consequently, the workability of remote equipment can be improved.

[0054] Furthermore, the upper core structure 5 is a large and very tall piece of equipment (for example, the height from the upper core support plate 52 to the upper core plate 51 can be about 3m). In this embodiment, most of the dismantling work is carried out with this upper core structure 5 housed in the reactor vessel body 21. Therefore, workers can access the upper surface of the upper core support plate 52, which is the target of the work, by walking across the first floor surface 111. As a result, the need for additional scaffolding and other work to be carried out on the upper surface of the upper core support plate 52 can be suppressed.

[0055] Furthermore, in-core structures such as the upper core structure 5 are located near the fuel and are high-radiation target equipment due to material activation and adhesion of radioactive products caused by neutron irradiation during operation. For this reason, these devices are usually handled underwater, relying on the shielding effect of water. However, underwater work requires waterproof remote work equipment, which is inefficient and raises significant operational concerns such as equipment failure. Nevertheless, according to the dismantling method for the upper core structure 5 of this embodiment, the work can be simplified and processed as described above.

[0056] Furthermore, considering the differences in radioactivity levels (distribution) of the upper core structure 5, which is normally handled in a submerged state due to high radiation levels, applying a partial submersion method allows access by workers, eliminates the need for complex equipment control, and enables the selection of a more reliable dismantling method than remote underwater dismantling.

[0057] Furthermore, the upper core support plate 52, which has a low radiation level, can be used as a shielding material. Therefore, the upper core support plate 52 can suppress the diffusion of radiation. Consequently, it is possible to secure working time for workers and improve work efficiency.

[0058] (Other embodiments) Although embodiments of this disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes and the like that do not depart from the gist of this disclosure.

[0059] Furthermore, the reactor having the upper core support columns 53 to be dismantled is not limited to pressurized water reactors 1, but may have an upper core structure 5. For example, the reactor may be a boiling water reactor.

[0060] Furthermore, the step of disconnecting some of the upper core support columns 53 from the upper core support plate 52 does not need to be performed. In other words, after removing the anti-rotation device from the connecting portion 59, the upper core structure 5 may be moved without removing the connecting portion 59 at all.

[0061] Furthermore, it is not necessary to adjust the water level in the cavity when the upper core structure 5 is moved. For example, the upper core structure 5 may be moved while a certain amount of water is continuously stored in the cavity. Also, after the upper core structure 5 is moved, it is not necessary to fill it with water as shown in Figure 7, and then readjust the water level as shown in Figure 8 after the upper core structure 5 has been moved from inside the reactor to outside the reactor and installed.

[0062] Furthermore, the configuration in which the upper core support column 53 is housed in a protective cover 310 and moved is not limited to this configuration. For example, as shown in Figure 7, in an environment where the first cavity 110 and the second cavity 120 are filled with water to a depth that overlaps with the movement path of the upper core structure 5, even if the upper core support column 53 has a high radiation dose at its lower end, sufficient shielding effect can be obtained with water alone. In such cases, the upper core support column 53 may be moved without using the protective cover 310.

[0063] <Note> The method for dismantling the upper core structure 5 described in each embodiment can be understood, for example, as follows.

[0064] (1) A method for dismantling an upper core structure 5 according to the first embodiment, comprising an upper core plate 51, an upper core support plate 52 positioned vertically above the upper core plate 51 in a direction Dv, and a plurality of upper core support columns 53 connecting the upper core plate 51 and the upper core support plate 52, wherein the upper core structure 5 is positioned inside a reactor vessel 2 in which water is stored, and a rotation stopper is provided for the connecting portion 59 that connects the upper core support column 53 to the upper core support plate 52. The process includes the steps of removing the connector, lifting the upper core support plate 52 so that the upper core structure 5, together with the upper core support column 53 connected to the upper core support plate 52 via the connecting portion 59 and the upper core plate 51 connected to the upper core support column 53, is moved to a work space outside the reactor vessel 2, the connecting portion 59 is removed in the work space, and the upper core support plate 52 is separated from the upper core support column 53 and transported.

[0065] With this configuration, the upper core structure 5, positioned inside the reactor vessel 2, is more likely to maintain a stable posture compared to an upper core structure 5 positioned in a workspace. Furthermore, the presence of water inside the reactor vessel 2 helps to suppress the diffusion of radiation. Additionally, removing the anti-rotation devices from the firmly fixed connecting parts 59 involves complex work. This complex work can be performed on the upper core structure 5, which maintains a stable posture in an environment where radiation diffusion is suppressed. As a result, the effects of radiation can be reduced, and the work efficiency of the workers can be improved.

[0066] (2) A method for dismantling the upper core structure 5 according to the second embodiment is the method for dismantling the upper core structure 5 according to (1), further comprising the step of removing a part of the connecting part 59 after removing the anti-rotation device and before moving the upper core structure 5, thereby releasing the connection between a part of the plurality of upper core support columns 53 and the upper core support plate 52.

[0067] With this configuration, when lifting the upper core support plate 52 and moving the upper core structure 5, the connection between the upper core support column 53 and the upper core support plate 52 is maintained by a small number of connecting parts 59. In other words, when supporting the load required to lift the upper core support plate 52 and move the upper core structure 5, many of the unnecessary connecting parts 59 can be removed before moving the upper core structure 5. Therefore, the work of removing a large number of connecting parts 59 can be carried out on the upper core structure 5, which maintains a stable posture in an environment where the diffusion of radiation is suppressed. As a result, the effects of radiation can be suppressed and the work efficiency of workers can be improved.

[0068] (3) A method for dismantling the upper core structure 5 according to the third embodiment is the method for dismantling the upper core structure 5 according to (1) or (2), wherein the reactor vessel 2 is placed in a reactor building pool 100 having a space inside which water can be stored, and the reactor building pool 100 has a first cavity 110 in which the reactor vessel 2 is placed as the space, and a second cavity 120 adjacent to the first cavity 110 and recessed below the first cavity 110 in the vertical direction Dv, the work space is placed in the second cavity 120, and when the upper core structure 5 is moved, the first cavity 110 and the second cavity 120 are filled with water to a depth that overlaps with the movement path of the upper core structure 5.

[0069] With this configuration, the upper core structure 5 is always submerged in water during the process of being withdrawn from the reactor vessel 2 and moved to the work area. Therefore, when moving the upper core structure 5, which includes the upper core plate 51 with a high radiation dose, the diffusion of radiation can be suppressed.

[0070] (4) A method for dismantling the upper core structure 5 according to a fourth embodiment is the method for dismantling the upper core structure 5 according to (3), wherein the first cavity 110 has a first floor surface 111 in which a recess is formed in which the reactor vessel 2 is housed, and the second cavity 120 has a second floor surface 121 located below the first floor surface 111 in the vertical direction Dv and on which the work space is arranged, and after the upper core structure 5 is moved to the work space, the first floor surface 111 is exposed and the water level is adjusted to a depth that covers at least a part of the upper core structure 5 on the work space.

[0071] With this configuration, within the upper core structure 5 located in the workspace of the second cavity 120, the area around the upper core plate 51, which has a high radiation dose, remains submerged in water. Therefore, when dismantling the upper core structure 5, including the upper core plate 51, in the workspace of the second cavity 120, the diffusion of radiation can be suppressed. In addition, since there is no water above the first floor surface 111, a wider work area for workers can be secured, improving work efficiency. Therefore, sufficient working time can be secured for workers dismantling the upper core structure 5 in the workspace of the second cavity 120, improving work efficiency.

[0072] (5) A method for dismantling the upper core structure 5 according to the fifth embodiment is a method for dismantling the upper core structure 5 according to any one of (1) to (4), further comprising the step of lifting and removing the upper core support column 53 from the upper core plate 51 after the upper core support plate 52 has been separated from the upper core support column 53, wherein when lifting the upper core support column 53, a protective cover 310 capable of housing the upper core support column 53 is placed above the upper core support column 53 in the vertical direction Dv, and the upper core support column 53 is lifted so as to house the upper core support column 53 inside the protective cover 310.

[0073] With this configuration, when the upper core support column 53 is moved, the protective cover 310 can suppress the diffusion of radiation from the upper core support column 53 while it is being moved. Therefore, workers can have sufficient time to move the upper core support column 53, and work efficiency can be improved.

[0074] (6) A method for dismantling the upper core structure 5 according to the sixth embodiment is a method for dismantling the upper core structure 5 according to any one of (1) to (5), further comprising the step of cutting the upper core support column 53 that has been lifted and removed into a plurality of cut pieces.

[0075] With this configuration, the upper core support column 53 can be processed into cut pieces that fit into a predetermined size waste container according to the dose level. Therefore, the upper core support column 53 can be easily disposed of. [Explanation of Symbols]

[0076] 1 Pressurized water reactor 2 Reactor vessel 21. Reactor vessel body 22 Reactor vessel lid 23 Inlet nozzle 24 Outlet nozzles 3. Control rod drive mechanism 5. Upper core structure 51 Upper core plate 52 Upper core support plate 521 Support plate body 522 Reinforcement beam 53 Upper core support column 53A First Upper Core Support Column 53B Second Upper Core Support Column 531B Support column base 532B Support column tip 55 Guide tube 59 Connecting part 591 First connection part 592 Second connection part 6. Lower core structure 100 Reactor building indoor pool 110 First Cavity 111 First floor 120 Second Cavity 121 Second floor 150 Overhead Cranes 200 lids 300 Lifting fixtures 310 Protective Cover 320 load cell 330 Electric Hoist 340 Suspension component Dv Vertical direction Dh horizontal direction

Claims

1. A method for dismantling an upper core structure comprising an upper core plate, an upper core support plate positioned vertically above the upper core plate, and a plurality of upper core support columns connecting the upper core plate and the upper core support plate, With the upper core structure positioned inside the reactor vessel containing water, the process involves removing the anti-rotation mechanism from the connecting portion that connects the upper core support column to the upper core support plate, The process involves lifting the upper core support plate, thereby moving the upper core structure, together with the upper core support column connected to the upper core support plate via the connecting portion, and the upper core plate connected to the upper core support column, to a working space outside the reactor vessel. The process involves removing the connecting portion in the aforementioned workspace, The process involves separating the upper core support plate from the upper core support column and transporting it, A method for dismantling the upper core structure, including the core structure.

2. The method for dismantling an upper reactor core structure according to claim 1, further comprising the step of removing a part of the connecting portion after removing the rotation stopper and before moving the upper reactor core structure, thereby releasing the connection between a part of the plurality of upper reactor core support columns and the upper reactor core support plate.

3. The reactor vessel is placed in a pool inside the reactor building, which has a space formed inside that can store water. The reactor building pool comprises, as the space, a first cavity in which the reactor vessel is arranged, and a second cavity adjacent to the first cavity, formed as a recess below the first cavity in the vertical direction. The aforementioned workspace is located in the second cavity, The method for dismantling an upper reactor core structure according to claim 1 or 2, wherein when the upper reactor core structure is moved, the water is filled into the first cavity and the second cavity to a depth that overlaps with the movement path of the upper reactor core structure.

4. The first cavity has a first floor surface in which a recess is formed that accommodates the reactor vessel, The second cavity is located below the first floor surface in the vertical direction and has a second floor surface on which the workspace is located. The method for dismantling an upper reactor core structure according to claim 3, wherein, after the upper reactor core structure is moved to the work space, the water level is adjusted to a depth that exposes the first floor surface and covers at least a portion of the upper reactor core structure on the work space.

5. The process further includes the step of lifting and removing the upper core support column from the upper core plate after the upper core support plate has been separated from the upper core support column, A method for dismantling an upper core structure according to claim 1 or 2, wherein when raising the upper core support column, a protective cover capable of housing the upper core support column is positioned vertically above the upper core support column, and the upper core support column is raised so that the upper core support column is housed inside the protective cover.

6. The method for dismantling an upper reactor core structure according to claim 1 or 2, further comprising the step of cutting the upper reactor core support column, which has been lifted and removed, into a plurality of cut pieces.

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