How to dismantle a suppression chamber

Abstract

This invention provides a method for dismantling suppression chambers that reduces the time required for dismantling suppression chambers by minimizing tasks such as assembling, dismantling, and transporting temporary scaffolding during the dismantling process. [Solution] A movable scaffold, which can move inside the shell, is used to dismantle and remove items inside the shell while moving it within the shell.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for dismantling a suppression chamber. BACKGROUND ART

[0002] A suppression chamber, which is a facility of a nuclear power plant, is located at the lower part of a reactor containment vessel, and has a function of reducing the pressure inside the reactor containment vessel by introducing steam into the suppression chamber and cooling it with water when the pressure inside the reactor containment vessel rises due to steam or the like. The suppression chamber has a shell composed of an annular steel pipe, and stores water inside the shell.

[0003] Such a suppression chamber is required to be properly dismantled with safety considerations when the decommissioning of the reactor is decided, but dismantling a huge suppression chamber requires time and cost.

[0004] Patent Document 1 discloses a method for dismantling a suppression chamber. In this dismantling method, first, an opening is made in the upper part of the torus chamber that accommodates the suppression chamber, an assembly-type internal scaffold is carried into the torus chamber through the opening and assembled, and a part of the suppression chamber is dismantled using the internal scaffold and carried out through the opening. Next, into the space created by removing a part of the suppression chamber, parts of an assembly-type dismantling stand and a lifting frame that can move freely inside the torus chamber are carried in through the opening and assembled, and the operation of dismantling the suppression chamber part by part using these and carrying the parts out through the opening is repeated. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0005] PATENT DOCUMENT 1 Japanese Patent No. 6369791 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] Furthermore, as shown in Figure 1, another method for dismantling the suppression chamber 10 inside the torus chamber T, which consists of walls W, ceiling C, and floor F, involves assembling a flattening scaffold 21 to level the bottom of the shell 11, as well as temporary scaffolds 25 and 26 inside the shell 11. These are then used to dismantle and remove the vent headers 12 and downcomers 13 inside the shell 11, or to cut and remove other materials, before dismantling the shell 11.

[0007] However, when moving the temporary scaffolding 25 and 26 within the shell 11 in accordance with the progress of the dismantling work, there is a problem in that there are no horizontal surfaces within the shell 11 except for the areas where the flattened scaffolding 21 is installed, and that it is time-consuming to repeat the work of assembling, dismantling, and transporting the temporary scaffolding 25 and 26 each time they are moved.

[0008] Therefore, the object of this invention is to provide a method for dismantling a suppression chamber that can reduce the time required for dismantling a suppression chamber by reducing the work involved in assembling, dismantling, and transporting temporary scaffolding when dismantling a suppression chamber. [Means for solving the problem]

[0009] One aspect of the present invention is a method for dismantling a suppression chamber, comprising: a mobile scaffolding placement step of arranging a mobile scaffolding that is movable inside the shell of the suppression chamber, which is made of an annular tube, in a first region within the shell; a first work step of performing work to dismantle an object in the first region using the mobile scaffolding arranged in the first region; a moving step of moving the mobile scaffolding from the first region to a second region within the shell; and a second work step of performing work to dismantle an object in the second region using the mobile scaffolding arranged in the second region. [Effects of the Invention]

[0010] According to one aspect of this invention, by using a mobile scaffolding in the first area to dismantle objects in the first area, and then moving the mobile scaffolding to the second area and using the mobile scaffolding to dismantle objects in the second area, the work of assembling, dismantling, and transporting fixed temporary scaffolding that cannot be moved can be reduced, thereby reducing the time and cost required for dismantling the suppression chamber. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows a conventional example of temporary scaffolding 25 and 26 installed inside shell 11. [Figure 2] This is a schematic diagram showing an example of a boiling water reactor N according to this embodiment. [Figure 3] This is a schematic plan view showing a part of the shell 11 of the suppression chamber 10 according to this embodiment. [Figure 4] This flowchart shows an example of a method for dismantling the suppression chamber 10 according to this embodiment. [Figure 5] This is a schematic cross-sectional view of the shell 11 according to this embodiment. [Figure 6] This is a schematic cross-sectional view of the shell 11 according to this embodiment. [Figure 7] This is a schematic cross-sectional view of the shell 11 according to this embodiment. [Figure 8] This is a schematic cross-sectional view of the shell 11 according to this embodiment. [Figure 9] This is a schematic cross-sectional view of the shell 11 according to this embodiment. [Figure 10] This is a schematic side view of the shell 11 according to this embodiment. [Figure 11] This is a schematic perspective view of the bridge crane 40 according to this embodiment. [Figure 12] This is a schematic cross-sectional view of the shell 11 according to this embodiment. [Figure 13] This is a schematic side view of the shell 11 according to this embodiment. [Figure 14] This is a schematic side view of the shell 11 according to this embodiment. [Figure 15] It is a schematic side view of the shell 11 according to the present embodiment. [Figure 16] It is a schematic side view of the shell 11 according to the present embodiment. [Figure 17] It is a schematic cross-sectional view of the shell 11 according to modified example 2. [Figure 18] It is a schematic cross-sectional view of the shell 11 according to modified example 2. [Figure 19] It is a flowchart showing an example of the disassembly method for the suppression chamber 10 according to modified example 2. [Figure 20] It is a schematic side view of the shell 11 according to modified example 2. [Figure 21] It is a schematic side view of the shell 11 according to modified example 2. [Figure 22] It is a schematic side view of the shell 11 according to modified example 2. [Figure 23] It is a schematic side view of the shell 11 according to modified example 2. [Figure 24] It is a schematic side view of the shell 11 according to modified example 2. [Mode for Carrying Out the Invention]

[0012] Embodiments of the present invention will be described with reference to the drawings.

[0013] As shown in Figure 2, the nuclear reactor N includes a reactor pressure vessel 1, and a reactor containment vessel 2 installed so as to enclose the reactor pressure vessel 1.

[0014] In the reactor pressure vessel 1, heat generated by nuclear fuel through fission reaction generates steam from water circulating inside the vessel. The reactor pressure vessel 1 is made of thick steel plates to withstand the high-temperature and high-pressure environment generated by the fission reaction, and also functions as a first protective layer to prevent radioactive materials from leaking to the outside even when an accident occurs.

[0015] The reactor containment vessel 2 has a robust structure made of steel and reinforced concrete, and when high-temperature, high-pressure steam is generated in reactor N, it controls the pressure internally, preventing damage or explosion due to a sudden rise in pressure. In addition, the reactor containment vessel 2 shields against radiation, minimizing radiation exposure to reactor operators and the general public. Furthermore, in the event of an accident in reactor N and radioactive material is leaked, the reactor containment vessel 2 plays a role in containing the radioactive material and preventing its leakage to the outside.

[0016] The reactor containment vessel 2 is connected to the suppression chamber 10 via vent pipes 3. The suppression chamber 10 consists of steel pipes arranged in a ring shape around the lower part of the reactor containment vessel 2, and these steel pipes are called the shell 11. The shell 11 is installed in the torus chamber T so as to float above the floor F by shell support members 15 (see Figure 5). The suppression chamber 10 is also connected to the drywell (not shown) of the reactor containment vessel 2 via a plurality of vent pipes 3.

[0017] The suppression chamber 10 has a ring shape formed by alternating even-numbered bays 16B and odd-numbered bays 16A (sometimes referred to collectively as bay 16) as shown in Figure 3. In this embodiment, the suppression chamber 10 is composed of bays 1 through 16, with even-numbered bays 16B consisting of bays 2, 4, ..., 14, and 16, and odd-numbered bays 16A consisting of bays 1, 3, ..., 13, and 15.

[0018] The vent pipe 3 has a vent header 12 and several downcomers 13 within the suppression chamber 10. The vent header 12 is a steel pipe provided in an annular shape within the suppression chamber 10 and is positioned above the bottom of the shell 11 by a header support 14 (see Figure 5). The downcomers 13 branch off from the vent header 12 and extend downward, opening into the pool water stored in the suppression chamber 10. This prevents damage or explosion due to a sudden rise in pressure when the pressure inside the reactor containment vessel 2 increases, by discharging gas and steam into the suppression chamber 10 through the vent pipe 3, vent header 12, and downcomers 13. The annular vent header 12 is connected to the vent pipe 3 in the even-numbered bays 16B.

[0019] As shown in Figure 1, the bottom surface of the suppression chamber 10's shell 11 is curved downwards, making it difficult for workers to safely perform tasks in its current state. Therefore, a horizontal, flattened scaffolding 21 is sometimes installed to carry out the dismantling of the suppression chamber 10. In addition, temporary scaffolding 25 and 26 may be assembled for each bay 16 in order to dismantle and remove items inside the shell 11, such as the vent header 12 and downcomer 13.

[0020] However, the assembly, dismantling, and transportation of temporary scaffolding 25 and 26 must be repeated for each bay 16, which is inefficient. Therefore, the dismantling method of the suppression chamber 10 in this embodiment aims to reduce the time spent on the assembly, dismantling, and transportation of temporary scaffolding 25 and 26, thereby shortening the construction period and reducing the number of man-hours.

[0021] The method for disassembling the suppression chamber 10 will be explained using Figures 4 to 16. Figure 4 is a flowchart illustrating an example of the disassembly method for the suppression chamber 10 according to this embodiment. Furthermore, the following explanation will describe the case where the first bay 16 is bay 2, the second bay 16 is bay 3, and the last bay 16 is bay 1.

[0022] First, as shown in Figure 5, flattening scaffolding 21 is installed in the first bay 16 (Bay 2) and the adjacent (second) bay 16 (Bay 3) (Step S11). This eliminates the need for demolition workers to perform demolition work on the curved bottom of the shell 11, allowing them to perform demolition work on a horizontal surface.

[0023] Next, in the first bay 16 (bay 2), a mobile scaffolding 50 is constructed on top of the flattened scaffolding 21 (step S12). The mobile scaffolding 50 consists of multiple levels and is equipped with stairs (not shown) for demolition workers to move between levels. The mobile scaffolding 50 is also equipped with wheels or sliding plates (not shown) at its lower end, allowing it to travel on the flattened scaffolding 21 and move between adjacent bays 16. During demolition work, if the mobile scaffolding 50 is insufficient, a fixed temporary scaffolding will be constructed or the scaffolding will be extended using the mobile scaffolding 50 as a foothold. The mobile scaffolding 50 does not prevent the construction of fixed temporary scaffolding, but it is preferable not to construct the fixed temporary scaffolding in the path of the mobile scaffolding 50 (because it will need to be moved aside or removed when the mobile scaffolding 50 is moved).

[0024] Next, in the first bay 16 (bay 2), the vent header 12 is temporarily suspended from the ceiling C and the header support 14 is removed (step S13). Temporary suspension means connecting the wires or chains of the lifting device to the object to be temporarily suspended (slinging), and supporting the load of the object to be temporarily suspended with another object (for example, the ceiling C or the ceiling of the shell 11) via the lifting device. In step S13, the upper hook of the chain block 31 (an example of a "lifting device") is connected to a suspension fitting (not shown) installed on the ceiling C, and the lower hook of the chain block 31 is connected to a suspension fitting (not shown) installed on the vent header 12 (an example of an "object to be temporarily suspended"), thereby supporting the load of the vent header 12 and the downcomer 13 with the ceiling C.

[0025] Next, in the first bay 16 (bay 2), the vent pipe 3 is temporarily suspended from the ceiling (or ceiling C) of the shell 11 and cut along the cutting line 32 (step S14). This separates the vent header 12 from the vent pipe 3. Note that in Figure 5, the chain block 31 for temporarily suspending the vent pipe 3 is omitted, but it is temporarily suspended in the same way as in step S13.

[0026] Next, as shown in Figure 6, the mobile scaffolding 50 located in the first bay 16 (Bay 2) is moved to the adjacent (second) bay 16 (Bay 3) (Step S15). At this time, it is assumed that the temporary suspension of the header and the header support 14 in the adjacent bay (Bay 3) are removed.

[0027] Next, in the first bay 16 (bay 2), the vent header 12, the upper half of the shell 11, and the vent pipe 3 are dismantled and removed (step S16). Specifically, as shown in Figure 7, the vent header 12, the downcomer 13, and the tip 3a of the vent pipe 3 are lowered using a chain block 31. At this time, the lower end of the downcomer 13 touches the flattening scaffolding 21 before the vent header 12, so each time the lower end of the downcomer 13 touches, the downcomer 13 is dismantled by repeatedly cutting along cutting lines 34A and 34B, cutting lines 35A and 35B, and cutting lines 36A and 36B, and finally the remaining part 13a of the downcomer 13 and the vent header 12 are seated on the flattening scaffolding 21 (see Figure 8). Next, the vent header 12 is dismantled and removed on the flattening scaffolding 21. The upper half of the shell 11 is also cut and removed. Furthermore, as shown in Figure 8, the vent pipe 3 is also cut along the cutting line 37 and removed.

[0028] Next, the flattening scaffolding 21 in the first bay 16 (bay 2) is moved to the bay next to the next one (the third bay) 16 (bay 4) (step S17). Specifically, the flattening scaffolding 21 in the first bay 16 (bay 2) is dismantled, and the flattening scaffolding 21 is reassembled inside the shell 11 of the bay next to the next one (the third bay) 16 (bay 4).

[0029] Next, as shown in Figures 9 and 10, a bridge crane 40 is installed in bay 2 (step S18). As shown in Figure 11, the bridge crane 40 has a girder 41, legs 42 provided at both ends of the girder 41, and a running section 43 provided at the bottom of the legs 42, and moves on a track 44. A trolley 45 is installed on the girder 41 and is movable along the longitudinal direction of the girder 41. The trolley 45 lifts (raises) and lowers (lowers) objects via a wire 46. The bridge crane 40 is used to support and transport loads such as the vent header 12, shell 11, and objects inside the shell 11. Note that the shell support members 15 are not shown in Figures 10, 13, and 20.

[0030] Next, the lower half of the shell 11 of the first bay (bay 2) is dismantled and removed (step S19). The dismantled portion of the suppression chamber 10 is then removed, for example, through an upper opening (not shown) in the ceiling C.

[0031] Next, as shown in Figures 12 and 13, in bay 16 (bay 3 in the example of Figures 12 and 13) where the mobile scaffolding 50 is located, the vent header 12 is temporarily suspended from the ceiling C and the header support 14 is removed (step S20). Specifically, the upper hook of the chain block 31 is connected to a suspension fitting (not shown) provided on the ceiling C, and the lower hook of the chain block 31 is connected to a suspension fitting (not shown) provided on the vent header 12 using the mobile scaffolding 50, thereby supporting the load of the vent header 12 and downcomer 13 on the ceiling C.

[0032] Next, as shown in Figure 13, the mobile scaffolding 50 is moved to the adjacent bay 16 (the bay 16 with the next higher number; however, if it is bay 16, it is bay 1; in the example of Figure 13, it is bay 4) (step S21). However, if the destination shell 11 has already been dismantled (i.e., the destination bay 16 is bay 2), the mobile scaffolding 50 is dismantled and removed.

[0033] Next, as shown in Figure 14, in bay 16 (bay 3 in the example of Figure 14) where the mobile scaffolding 50 was located until it was moved in step S21, the vent header 12 is cut along the cutting line 38 (see Figure 13), and then the vent header 12 is lowered and seated on the flattened scaffolding 21 (step S22). Specifically, as explained in step S16, the vent header 12 and downcomer 13 are lowered using the chain block 31. At this time, the lower end of the downcomer 13 touches the flattened scaffolding 21 before the vent header 12, so the cutting operation is repeated each time the lower end of the downcomer 13 touches the ground to dismantle the downcomer 13, and finally, the remaining part 13a of the downcomer 13 and the vent header 12 are seated on the flattened scaffolding 21. The downcomer 13 that has been disassembled by the cutting operation is temporarily placed on the flattened scaffolding 21.

[0034] Next, as shown in Figure 15, in bay 16 (Bay 3 in the example of Figure 15) where the vent header 12 was seated on the flattening scaffolding 21 in step S22, a portion 11x of the upper half of the shell 11 is cut along cutting lines 39x and 39y, and moved by bridge crane 40 (step S23). The destination is, for example, near the exit of the torus room T (the same applies hereafter).

[0035] Next, the disassembled downcomers 13 that were temporarily placed on the flattened scaffolding 21 in step S22 are moved by the bridge crane 40 (step S24).

[0036] Next, as shown in Figure 15, in bay 16 (bay 3 in the example of Figure 15) where the vent header 12 was seated on the flattening scaffolding 21 in step S22, a portion of the vent header 12 seated on the flattening scaffolding 21 is cut along the cutting line 39 and moved by the bridge crane 40 (step S25). In this embodiment, as shown in Figure 15, when the shell 11 is viewed from the side, the extension of the cutting line 39 of the vent header 12 is cut so that it coincides with the end of the upper half of the shell 11 that remained after being cut in step S23.

[0037] Next, it is determined whether the upper half of the shell 11 and the entire vent header 12 have been moved (step S26). Specifically, it is determined whether the upper half of the shell 11 and the entire vent header 12 in bay 16, where the vent header 12 was seated on the flattening scaffolding 21 in step S22, have been moved from bay 16 by the bridge crane 40. For example, in the example in Figure 15, the upper half of the shell 11 and the vent header 12 are still remaining in bay 3, so it is determined to be "NO", and if they have all been moved, it is determined to be "YES". In other words, the upper half of the shell 11 and the vent header 12 are dismantled and removed by repeating the work of cutting and moving parts of each (steps S23 and S25). Then, when all parts of the upper half of the shell 11 and the vent header 12 have been moved, that is, when the dismantling and removal of the upper half of the shell 11 and the vent header 12 is complete, the process moves to step S27.

[0038] For example, if the result is "NO" in the situation shown in Figure 15, then, as shown in Figure 16, in bay 16 (bay 3 in the example of Figure 16) where the vent header 12 was seated on the flattening scaffolding 21 in step S22, a portion 11x of the upper half of the shell 11 is cut along the cutting line 39 and moved by the bridge crane 40 (step S23), and then a portion of the vent header 12 is cut and moved by the bridge crane 40 (step S25).

[0039] Then, if "YES" is determined in step S26, the flattened scaffolding 21, which was seated on the vent header 12 in step S22 in bay 16 (bay 3 in the example of Figure 16), is moved to the bay 16 two bays away (bay 16 with a number two higher; bay 5 in the example of Figure 16) (step S27). The method of moving the flattened scaffolding 21 is the same as in step S17. However, if the shell 11 at the destination has already been dismantled, the flattened scaffolding 21 is dismantled and removed.

[0040] Next, the lower half 11a of the shell 11 of the bay 16 immediately preceding the bay 16 in step S22 (the bay 16 with a lower number; in the example of Figure 16, bay 2) is dismantled and moved by the bridge crane 40 (step S28).

[0041] Next, it is determined whether or not the dismantling and removal of the vent headers 12 has been completed for all bays 16 (step S29). If it is determined that the dismantling and removal of the vent headers 12 has not been completed for all bays 16 (step S29: NO), the process proceeds to step S20, and steps S20 to S28 are repeated until the dismantling and removal of the vent headers 12 has been completed for all bays 16.

[0042] However, when repeating steps S20 to S28, for even-numbered bays 16B where the vent pipe 3 is connected to the vent header 12, the dismantling work proceeds as follows from steps S23 to S26. First, as shown in Figure 8, with the vent header 12 and the tip 3a of the vent pipe 3 seated on the flattened scaffolding 21, the upper half of the shell 11 and the vent header 12 are cut one by one. Once the part to which the tip 3a of the vent pipe 3 is connected is passed, the vent pipe 3 with the cut tip 3a is cut and removed (see Figure 8), and then the remaining upper half of the shell 11 and the vent header 12 are cut one by one again.

[0043] If it is determined in step S29 that the dismantling and removal of the vent headers 12 has been completed for all bays 16 (step S29: YES), then the lower half 11a of the shell 11 of the last bay (bay 1) is dismantled and moved by the bridge crane 40 (step S30).

[0044] Next, the bridge crane 40 is dismantled (step S31), completing the dismantling of the suppression chamber.

[0045] As described above, the method for dismantling the suppression chamber 10 of this embodiment includes: step S15 (an example of a "mobile scaffolding placement step"), which involves placing a movable scaffolding 50, which is movable inside the shell 11 consisting of an annular tube in the suppression chamber 10, in the third bay (an example of a "first area") within the shell 11; step S20 (an example of a "first work step"), which involves using the movable scaffolding 50 placed in the third bay to dismantle the vent header 12 and downcomer 13 (an example of an "object") located in the third bay; step S21 (an example of a "movement step"), which involves moving the movable scaffolding 50 from the third bay to the fourth bay (an example of a "second area") within the shell 11; and step S20 (an example of a "second work step"), which involves using the movable scaffolding 50 placed in the fourth bay to dismantle the vent header 12 and downcomer 13 (an example of an "object") located in the fourth bay.

[0046] Therefore, according to the dismantling method of the suppression chamber 10 of this embodiment, the work to dismantle the vent header 12 and downcomer 13 of bay 3 is performed using the mobile scaffolding 50 in bay 3, and then the mobile scaffolding 50 is moved to bay 4, and the work to dismantle the vent header 12 and downcomer 13 of bay 4 is performed using the mobile scaffolding 50. As a result, the work of assembling, dismantling, and transporting fixed temporary scaffolding that cannot be moved can be reduced, and the time required for dismantling the suppression chamber 10 can be reduced.

[0047] Furthermore, in this embodiment, for example, work to temporarily suspend the vent header 12 from the ceiling C using the mobile scaffolding 50 can be performed in bay 4, and once that work is completed, the mobile scaffolding 50 can be moved to the adjacent bay 5, and work to temporarily suspend the vent header 12 from the ceiling C using the mobile scaffolding 50 can be performed in bay 5, while simultaneously lowering and dismantling the temporarily suspended vent header 12 in bay 4, thus improving work efficiency.

[0048] Furthermore, the dismantling method for the suppression chamber 10 in this embodiment further includes steps S11, S17, and S27 (an example of a "horizontal work platform installation process"), in which a flattening platform 21 (an example of a "horizontal work platform") is installed on the bottom of the shell 11, and the mobile scaffolding 50 moves on top of the flattening platform 21. This makes it easier to move the mobile scaffolding 50, which would otherwise be difficult to move due to the downward curve of the bottom surface of the shell 11.

[0049] Next, a modified example of this embodiment will be described.

[0050] First, let's describe Modification 1. In this embodiment, a bridge crane 40 is used for dismantling and removing the shell 11 and the inside of the shell 11, but in Modification 1, an overhead crane, jib crane, cable crane, telpher, lifting device, temporary lifting equipment, etc. may be used instead or in addition to the above.

[0051] Next, a modified example 2 will be described using Figures 17 to 24. In the above embodiment, the mobile scaffolding 50 moves on the flattened scaffolding 21, but in modified example 2, instead of providing the flattened scaffolding 21, rails 61 are installed inside the shell 11 as shown in Figure 17, and the mobile scaffolding 51 moves on the rails 61. The mobile scaffolding 51 in modified example 2 differs from the mobile scaffolding 50 in this embodiment in that it is provided with wheels or sliding plates (not shown) that can move on the rails 61, whereas the mobile scaffolding 50 in this embodiment had wheels or sliding plates that could move on the flattened scaffolding 21, but otherwise it has the same configuration.

[0052] In the modified configuration 2, a trolley 60, shown in Figure 18, moves along the rails 61 separately from the mobile scaffolding 51. The trolley 60 has wheels or sliding plates (not shown) for moving along the rails 61, and a horizontal steel plate on which demolition workers and vent headers 12 can be mounted. The trolley 60 is positioned in a bay 16 one to two bays behind the mobile scaffolding 51, and moves between the bays 16 with the vent headers 12 loaded on it. In principle, the trolley 60 moves in the opposite direction to follow the mobile scaffolding 51, but it may also move in the opposite direction to dismantle the loaded vent headers 12.

[0053] Next, using the flowchart in Figure 19, we will explain the method for disassembling the suppression chamber 10 according to Modification 2. In the following explanation, we will describe the case where the first bay 16 is bay 2, the second bay 16 is bay 3, and the last bay 16 is bay 1.

[0054] First, install rails 61 in all bays 16 (step S111). At this time, the rails 61 in each bay 16 are connected so that they can circle. Note that the rails 61 exist to move the mobile scaffolding 51 and trolley 60, so rails 61 may not be installed in bays 16 where these will not be moved immediately, and may be installed until the time comes when they will be moved.

[0055] Next, in the first bay 16 (bay 2), a mobile scaffolding 51 is constructed on the rail 61 (step S112). During the dismantling work, if the mobile scaffolding 51 is insufficient, a fixed temporary scaffolding will be constructed or the scaffolding will be extended using the mobile scaffolding 51 as a foothold. The mobile scaffolding 51 does not prevent the construction of fixed temporary scaffolding, but it is preferable not to construct the fixed temporary scaffolding in the path of the mobile scaffolding 51 (because it will need to be moved aside or removed when the mobile scaffolding 51 is moved).

[0056] Next, steps S113 and S114 are performed, but since these are the same as steps S13 and S14 in Figure 4, their explanation will be omitted.

[0057] Next, the mobile scaffolding 51 located in the first bay 16 (bay 2) is moved to the adjacent (second) bay 16 (bay 3) (step S115). At this time, it is assumed that the temporary suspension of the header and the header support 14 in the adjacent bay (bay 3) are removed.

[0058] Next, in the first bay 16 (bay 2), construct the trolley 60 on the rail 61 (step S116).

[0059] Next, step S117 is performed. Step S117 differs from step S16 in Figure 4 in that it uses a trolley 60 instead of a flattening scaffold 21, but other than that, it is almost the same as step S16 in Figure 4, so the explanation is omitted.

[0060] Next, we perform step S118, but since this is the same as step S18 in Figure 4, we will omit the explanation.

[0061] Next, step S119 is performed. Step S119 differs from step S20 in Figure 4 in that it uses mobile scaffolding 51 instead of mobile scaffolding 50, but other than that, it is almost the same as step S20 in Figure 4, so the explanation is omitted.

[0062] Next, as shown in Figure 20, the mobile scaffolding 51 and the trolley 60 are moved to the adjacent bay 16 (the bay with the next higher number; however, if the current bay is bay 16, then move to bay 1) (step S120). However, if the shell 11 at the destination for the mobile scaffolding 51 has already been dismantled, the mobile scaffolding 51 is dismantled and removed.

[0063] Next, as shown in Figure 21, in bay 16 where the trolley 60 is located (bay 3 in the example of Figure 21), the vent header 12 is lowered and seated on the trolley 60 (step S121). Step S121 differs from step S22 in Figure 4 in that the trolley 60 is used instead of the flattening scaffolding 21, but other than that, it is almost the same as step S22 in Figure 4, so a detailed explanation is omitted. However, the downcomer 13 that has been disassembled by the cutting work is temporarily placed on the trolley 60.

[0064] Next, as shown in Figure 22, the trolley 60 on which the vent header 12 is seated and the disassembled downcomer 13 (not shown) is temporarily placed is moved to the previous bay 16 (the bay with the number one less; however, if the current bay is bay 1, then it is bay 16; in the example of Figure 22, it is bay 2). The vent header 12 and the disassembled downcomer 13 are then dismantled using the bridge crane 40 and moved by the bridge crane 40 (step S122).

[0065] Next, as shown in Figure 23, the trolley 60 is moved to the adjacent bay (bay 16, which has a higher number; however, if the current bay is bay 16, then bay 1; in the example in Figure 23, bay 3), the ceiling portion 11y of the shell 11 is cut along the cutting lines 71 and 72, and the shell is lowered and seated on the trolley 60 (step S123). In this embodiment, however, in step S123, the ceiling portion 11y may not be cut into small pieces, but only a preliminary cutting line 73 may be made, and the edges may be cut along the preliminary cutting line 73 in step S124.

[0066] Next, as shown in Figure 24, the trolley 60 on which the ceiling section 11y of the shell 11 is seated is moved to the previous bay 16 (the bay 16 with the number one less; however, if the current bay is bay 1, it will be bay 16. In the example of Figure 24, it is bay 2), the ceiling section 11y is dismantled, and moved by the bridge crane 40 (step S124).

[0067] Next, the trolley 60 is moved to the adjacent bay 16 (the bay with the next higher number; however, if the current bay is bay 16, then bay 1 is used), the remaining upper half 11z of the shell 11 is cut off and loaded onto the trolley 60 (step S125).

[0068] Next, the trolley 60 is moved to the previous bay 16 (the bay 16 with the number one less; however, if the current bay is bay 1, then it is moved to bay 16), and the remaining upper half 11z of the shell 11 is dismantled using the bridge crane 40 and moved by the bridge crane 40 (step S126).

[0069] Next, the trolley 60 is moved to the adjacent bay 16 (the bay 16 with the next higher number; however, if it is currently in bay 16, it is moved to bay 1). In the bay 16 that the trolley 60 has left, the lower half 11a of the shell 11 and the rails 61 are dismantled and moved by the bridge crane 40 (step S127).

[0070] Next, it is determined whether or not the dismantling and removal of the vent headers 12 has been completed for all bays 16 (step S128). If it is determined that the dismantling and removal of the vent headers 12 has not been completed for all bays 16 (step S128: NO), the process proceeds to step S119, and steps S119 to S127 are repeated until the dismantling and removal of the vent headers 12 has been completed for all bays 16.

[0071] However, when repeating steps S119 to S127, for even-numbered bays 16B where the vent pipe 3 is connected to the vent header 12, between steps S122 and S123, the vent pipe 3 is temporarily suspended in the same manner as the vent header 12, cut, lowered, and seated on the trolley 60. Then, the trolley 60 is moved to the previous bay 16 (the bay with the number one less; however, if the current bay is bay 1, then bay 16), the vent pipe 3 is dismantled, and the trolley 60 is moved using the bridge crane 40.

[0072] If it is determined in step S128 that the dismantling and removal of the vent headers 12 has been completed for all bays 16 (step S128: YES), then the trolley 60 and the lower half 11a of the shell 11 of the last bay (bay 1) are dismantled and moved by the bridge crane 40 (step S129).

[0073] Next, the bridge crane 40 is dismantled (step S130), completing the dismantling of the suppression chamber.

[0074] Furthermore, regarding steps S122 to S126, which were explained using Figures 22 to 24, the construction period can be shortened by performing the work in parallel in bay 2 (an example of an even-numbered bay 16B) and bay 3 (an example of an odd-numbered bay 16A). A detailed explanation follows below.

[0075] As shown in Figure 22, while the vent header 12 and downcomer 13 are being dismantled and removed in bay 2 using the bridge crane 40, in parallel, in bay 3, preliminary cutting lines (cuts) 73 are being made in the ceiling portion 11y of the shell 11 (preparatory work for cutting the ceiling portion 11y). Then, once the dismantling and removal of the vent header 12 and downcomer 13 in bay 2 is complete, as shown in Figure 23, the trolley 60 is moved to bay 3, the ceiling portion 11y cut along the cutting lines 71 and 72 (see Figure 22) is lowered and placed on the trolley 60, and the trolley 60 is moved to bay 2. Next, as shown in Figure 24, while the ceiling section 11y is being dismantled and removed in bay 2 by cutting it along the preliminary cutting line 73 using the bridge crane 40, in parallel, work is being done in bay 3 to make preliminary cutting lines (cuts) 76 into the remaining upper half 11z of the shell 11 (preparation work for cutting the remaining 11z). Once the dismantling and removal of the ceiling section 11y in bay 2 is complete, the trolley 60 is moved to bay 3, the remaining 11z cut along the cutting lines 74 and 75 is lowered and placed on the trolley 60, and the trolley 60 is moved to bay 2. In this way, the process of dismantling and removing the shell in bay 2 and the preparation process of making preliminary cutting lines (cuts) on a portion of the upper half of the shell 11 in bay 3 are carried out in parallel. Once the dismantling and removal in bay 2 is complete, the trolley 60 is moved from bay 2 to bay 3, the portion cut out from the upper half of the shell 11 is lowered and placed on the trolley 60, and then moved back to bay 2. This cycle is repeated, thereby dismantling and removing the upper half of the shell 11.

[0076] In this embodiment, since the trolley 60 can move between adjacent bays 16, the dismantling process, in which the preliminary cutting line (notch) is cut and removed in bay 2, can be performed in parallel with the preparation process, in which preparation work for making the preliminary cutting line (notch) is carried out in bay 3, thereby shortening the construction period. In this example, the preliminary cutting line (notch) is made in bay 3, and then the trolley is moved to bay 2 before the preliminary cutting line (notch) is cut. However, it is also possible to cut the ceiling portion 11y or the remaining portion 11z of the shell 11 along the line indicated by the preliminary cutting line in bay 3, cut it into small pieces, then place each piece on the trolley 60, move it to bay 2, and then remove it.

[0077] The method for dismantling the suppression chamber in the modified example 2 described above includes step S115 (an example of a "mobile scaffolding placement step"), which involves placing a movable scaffolding 51, which is movable inside the shell 11 consisting of an annular tube in the suppression chamber 10, in the third bay (an example of a "first area") inside the shell 11, and step S119 (an example of a "first work step"), which involves using the movable scaffolding 51 placed in the third bay to dismantle the vent header 12 and downcomer 13 (an example of "objects") located in the third bay. The process includes steps S120 (an example of a "movement process") to move the mobile scaffolding 51 from bay 3 to bay 4 inside shell 11 (an example of a "second area"), step S119 (an example of a "second work process") to use the mobile scaffolding 51 positioned in bay 4 to dismantle the vent header 12 and downcomer 13 (an example of an "object") located in bay 4, and step S111 (an example of a "rail installation process") to install rails 61 inside shell 11, wherein the mobile scaffolding 51 moves along the rails 61.

[0078] Therefore, according to the dismantling method of the suppression chamber 10 in Modification 2, the work to dismantle the vent header 12 and downcomer 13 in bay 3 is performed using the mobile scaffolding 51 in bay 3, and then the mobile scaffolding 51 is moved to bay 4 and the work to dismantle the vent header 12 and downcomer 13 in bay 4 is performed using the mobile scaffolding 51. This reduces the work of assembling, dismantling, and transporting fixed temporary scaffolding that cannot be moved, and thus reduces the time required for dismantling the suppression chamber 10.

[0079] Furthermore, the method for dismantling the suppression chamber 10 in the modified example 2 further includes step S116 (an example of a "cart placement step") in which a trolley 60 that can move on the rails 61 is placed on the rails 61. This allows the trolley 60 that can move on the rails 61 to be used as a substitute for the flattening scaffolding 21 or for transporting the vent header 12, etc.

[0080] Furthermore, the method for dismantling the suppression chamber 10 in modified example 2 involves moving the mobile scaffolding 51 from bay 3 to bay 4, then moving the trolley 60 to bay 3, and loading the ceiling portion 11y of the shell 11 in bay 3 (an example of "part of the suppression chamber") onto the trolley 60 in step S123 (an example of "trolley loading process"), and after step S123, moving the trolley 60 to bay 2 (an example of "third area") inside the shell 11 in step S124 ("trolley loading process"). The process includes an example of a "movement process," a step S124 (an example of a "dismantling process") in which the ceiling section 11y loaded onto the trolley 60 in bay 2 is dismantled, and a preparation process (an example of a "preparation work") in which a preliminary cutting line (notch) 76 is made for cutting the remaining upper half 11z of the shell 11, which is different from the ceiling section 11y (an example of a "part of another suppression chamber"), in bay 3 after the trolley 60 has moved away. Step S124 and the preparation process are performed in parallel. This allows multiple processes to be performed in parallel, shortening the construction period. Examples of "part of a suppression chamber" and "part of another suppression chamber" include a part of the shell 11, a vent header 12 inside the shell 11, or other objects or parts thereof.

[0081] Furthermore, according to the suppression chamber dismantling method of Modification 2, the flattening scaffolding 21 is unnecessary, thus eliminating the need for repeated assembly and dismantling of the flattening scaffolding 21. Also, when lowering the vent header 12 as a whole, it is supported by the trolley 60, and after moving the vent header 12 and the trolley 60 to the previous bay 16, the dismantling work of the vent header 12 can proceed on the trolley 60, while the dismantling work of the upper half of the shell 11 can proceed in parallel in the bay 16 where the trolley 60 was originally located. Thus, the construction period can be shortened. [Explanation of Symbols]

[0082] 1: Reactor pressure vessel 2: Reactor containment vessel 3: Bent pipe 3a: Tip of the bent pipe 10: Suppression Chamber 11: Shell 11a: Lower half of the shell 11x: Part of the shell 11y: Shell ceiling 11z: Part of the shell 12: Vent Header 13: Downcomer 13: Downcomer 13a: Remaining part of the downcomer 14: Header support 15: Shell support member 16: Bay 16A: Odd number of bays 16B: Even-numbered bays 21: Flattened scaffolding 25: Temporary scaffolding 26: Temporary scaffolding 30: Bottom 31: Chain Block 32: Cutting line 33: Cutting line 34A: Cutting line 34B: Cutting line 35A: Cutting line 35B: Cutting line 36A: Cutting line 36B: Cutting line 37: Cutting line 38: Cutting line 39: Cutting line 39x: Cutting line 39y: Cutting line 40: Bridge-type crane 41: Garder 42: Legs 43: Running gear 44: Orbit 45: Trolley 46: Wire 50: Mobile scaffolding 51: Mobile scaffolding 60: Dolly 61: Rail 71: Cutting line 72: Cutting line 73: Pre-cut line 74: Cutting line 75: Cutting line 76: Pre-cut line C:Ceiling F:Floor N: Nuclear reactor T: Torus Room W: Wall

Claims

1. This is a method for dismantling a suppression chamber. A mobile scaffolding placement step involves arranging a mobile scaffolding that is movable inside the shell, which consists of an annular tube, in a first region within the shell of the suppression chamber. A first work step involves performing work to dismantle an object in the first area using the mobile scaffolding positioned in the first area, A movement step of moving the mobile scaffolding from the first region to the second region within the shell, A second work step involves using the mobile scaffolding positioned in the second area to perform work to dismantle an object in the second area, A method for dismantling a suppression chamber, characterized by including [a certain element].

2. A method for dismantling a suppression chamber according to claim 1, The process further includes a step of installing a horizontal work platform on the bottom of the shell, A method for dismantling a suppression chamber, characterized in that the mobile scaffolding moves on the horizontal work scaffolding.

3. A method for dismantling a suppression chamber according to claim 1, The process further includes a rail installation step in which rails are installed inside the shell, A method for dismantling a suppression chamber, characterized in that the mobile scaffolding moves along the rails.

4. A method for dismantling a suppression chamber according to claim 3, A method for dismantling a suppression chamber, further comprising the step of arranging a trolley that can move on the rails, on the rails.

5. A method for dismantling a suppression chamber according to claim 4, After the mobile scaffolding has moved from the first area, the trolley is moved to the first area, and a portion of the suppression chamber in the first area is loaded onto the trolley in a trolley loading process, After the trolley loading process, a trolley moving process is performed to move the trolley to a third area within the shell, A dismantling step of dismantling a portion of the shell loaded on the trolley in the third region, A preparatory step of performing preparatory work for cutting a part of the suppression chamber that is different from the part of the suppression chamber in the first area where the trolley has moved away, Includes, A method for dismantling a suppression chamber, characterized in that the dismantling process and the preparation process are carried out in parallel.

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