Method for dismantling the upper core structure

Abstract

To efficiently dispose of in-reactor structures. [Solution] The method for dismantling the upper core structure is a method for dismantling the upper core structure stored in the reactor vessel, and includes the step of cutting at least a part of the upper core structure, which is to be cut, into a plurality of vertical cutting pieces, wherein in the cutting step, at least a part of the upper core structure is cut such that the height dimension of the cutting piece cut from the lowest part of the upper core structure is the smallest among the plurality of cutting pieces.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a technique for disassembling in-vessel structures in a reactor vessel in water stored in a working pool and carrying out the disassembled in-vessel structures from the working pool with respect to a method for disassembling a nuclear power plant.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a method for disassembling a nuclear power plant as described in Patent Document 1, in order to dispose of the disassembled in-vessel structures, it is necessary to appropriately process them according to the radioactivity level of the in-vessel structures. The in-vessel structures to be disposed of are stored in containers according to their respective radioactivity levels, but depending on the size of the in-vessel structures, it is necessary to cut the in-vessel structures before storing them in the containers. It is required to efficiently carry out such disposal processing of the in-vessel structures.

[0005] This disclosure has been made in view of the above circumstances, and an object thereof is to provide a method for disassembling an upper core structure capable of efficiently carrying out disposal processing of in-vessel structures.

Means for Solving the Problems

[0006] In order to solve the above problems, a method for disassembling an upper core structure according to this disclosure is a method for disassembling an upper core structure accommodated in a reactor vessel. The method for disassembling the upper core structure The process of removing and the process of disassembling, includes a step of cutting. In the removal process, the upper core structure is removed from the reactor vessel. In the dismantling process, the removed upper core structure is dismantled. The cutting step involves cutting at least a portion of the upper core structure, which is the target of the cutting, into multiple pieces vertically. Of the disassembled upper core structure, at least the vertically extending members are cut into a plurality of vertical pieces. In the cutting process, Of the plurality of cut pieces, the height dimension of the cut piece cut from the lowest part of the upper core structure is the smallest. Upper and lower extension member Cut it off. The upper and lower extending members include at least one of a guide tube and an upper core support column. [Effects of the Invention]

[0007] According to the method for dismantling the upper core structure of this disclosure, the disposal of the in-core structure can be carried out efficiently. [Brief explanation of the drawing]

[0008] [Figure 1] This is a longitudinal cross-sectional view showing a pressurized water reactor, which is the reactor to be dismantled according to this embodiment. [Figure 2] This is a schematic diagram showing a pressurized water reactor, with water stored inside according to the embodiment, with its reactor vessel lid removed, positioned within the reactor building pool. [Figure 3] This is a perspective view showing the upper core structure according to the embodiment. [Figure 4] This is a flowchart of the method for cutting the upper core structure in the first embodiment of this disclosure. [Figure 5] This is an elevation view showing an example of a cutting line of the upper core structure in the first embodiment of the present disclosure. [Figure 6] This is an elevation view showing an example of a cutting line of the upper core structure in a modified example of the first embodiment of the present disclosure. [Figure 7] This is a flowchart of the method for cutting the upper core structure in the second embodiment of the present disclosure. [Figure 8] This is an elevation view showing an example of a cutting line of the upper core structure in a second embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] <First Embodiment> Next, a method for dismantling the upper core structure according to the embodiment of this disclosure will be described with reference to the drawings. (nuclear reactor) Figure 1 is a longitudinal cross-sectional view showing a pressurized water reactor, which is the reactor to be dismantled according to this embodiment. The reactor is a pressurized water reactor (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 7, 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.

[0010] Figure 2 is a schematic diagram showing a pressurized water reactor, with water stored inside and the reactor vessel lid removed, positioned within the reactor building pool according to the embodiment. As shown in Figure 2, the pressurized water reactor 1 is located within the reactor building pool 100. Within the reactor building pool 100, a cavity is formed, which is a space capable of storing cooling water (water). In this embodiment, the reactor building pool 100 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 that workers can walk on. The second cavity 120 has a second floor surface 121 that is recessed from the first floor surface 111. That is, 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.

[0011] 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.

[0012] The reactor vessel 2 has a reactor vessel main body 21, a reactor vessel head 22 (upper vessel head), and a housing 25 so that the in-vessel structures can be inserted therein. The reactor vessel 2 is disposed inside a hole formed to be recessed with respect to the first floor surface 111. The reactor vessel 2 is disposed in a state where a part thereof (specifically, the reactor vessel head 22) protrudes from the first floor surface 111.

[0013] The upper part of the reactor vessel main body 21 can be opened by removing the reactor vessel head 22. The lower part of the reactor vessel main body 21 has a cylindrical shape closed by a lower vessel head having a hemispherical shape. At the upper part of the reactor vessel main 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 the light water are formed. Further, the reactor vessel main body 21 has a water injection nozzle (water injection plenum; not shown) formed separately from the inlet nozzle 23 and the outlet nozzle 24.

[0014] The reactor vessel head 22 is attached to the upper part of the reactor vessel main body 21. The reactor vessel head 22 is fixedly attached to the reactor vessel main body 21 so as to be openable and closable by a plurality of stud bolts and nuts (not shown). The housing 25 is integrally attached to the upper part of the reactor vessel head 22.

[0015] The control rod drive mechanism 3 is configured to move the control rod cluster 4 in the vertical direction Dv. The control rod cluster 4 is a structure in which the upper ends of a plurality of control rods 41 are gathered together. The control rod 41 is a rod-shaped or plate-shaped object for controlling the output of the reactor. The control rod drive mechanism 3 is housed in the housing 25 above the reactor vessel head 22 in the vertical direction Dv.

[0016] FIG. 3 is a perspective view showing an upper core structure according to the embodiment. The upper core structure 5 is disposed inside the reactor vessel 2. The upper core structure 5 can be withdrawn from the reactor vessel main body 21 by being moved upward in the vertical direction Dv with respect to the reactor vessel main body 21. As shown in FIG. 3, the upper core structure 5 of the present embodiment at least includes an upper core plate 51, an upper core support plate 52, upper core support columns 53, guide tubes 55, a water level gauge support pipe 57, and a flow column (not shown). Note that the upper core structure 5 is not limited to having only the above structure. For example, the upper core structure 5 may have other components (all not shown) such as a mixer and a thermocouple lead-out pipe.

[0017] The upper core plate 51 is disposed apart downward in the vertical direction Dv with respect to the upper core support plate 52. The upper core plate 51 has a disk shape with a number of through holes. A control rod cluster drive shaft 45 (see FIG. 1) capable of gripping the control rod cluster 4 is inserted through a part of the plurality of through holes of the upper core plate 51.

[0018] The upper core support plate 52 is disposed apart upward in the vertical direction Dv with respect to the upper core plate 51. As shown in FIGS. 1 and 2, the upper core support plate 52 is fixed to the reactor vessel main body 21 above the inlet nozzle 23 and the outlet nozzle 24 in the vertical direction Dv inside the reactor vessel main body 21.

[0019] As shown in FIG. 3, the upper core support plate 52 exemplified in the present embodiment is formed in a disk shape larger than the upper core plate 51. A plurality of through holes (not shown) are formed in the upper core support plate 52 at the same positions as a part of the through holes formed in the upper core plate 51 when viewed in the vertical direction Dv. The guide tubes 55 and the water level gauge support pipe 57 are inserted through the through holes of the upper core support plate 52. Also, as shown in FIG. 2, the upper surface of the upper core support plate 52 of the present embodiment is disposed at the same height as the first floor surface 111 in the vertical direction Dv when the upper core structure 5 is disposed inside the reactor vessel 2.

[0020] As shown in Figure 3, the multiple upper core support columns 53 connect the upper core support plate 52 and the upper core plate 51. The multiple upper core support columns 53 extend in the vertical direction Dv and also in a straight line. 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 spaced apart at positions that are not overlapping (not separated from) the through-holes in the upper core plate 51 and the upper core support plate 52. In other words, the multiple upper core support columns 53 are offset from the guide tubes 55 and the water level gauge support tubes 57 so as not to overlap.

[0021] The guide tube 55 is fixed to the upper core support plate 52 by being inserted through a through hole (not shown) in the upper core support plate 52. The guide tube 55 guides the vertical movement Dv of the control rod cluster drive shaft 45 (see Figure 1) for driving the control rod cluster 4. The control rod cluster drive shaft 45 is inserted through the inside of the guide tube 55. 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. The lower end of the guide tube 55 is connected to the upper core plate 51. Also, as shown in Figure 1, the upper end of the guide tube 55 extends to a position above the upper core support plate 52 in the vertical direction Dv and below the control rod drive unit 3.

[0022] Here, the upper core support columns 53, guide tubes 55, water level gauge support pipes 57, and flow columns (not shown) of the upper core structure 5 that extend in the vertical direction Dv (up and down direction) are referred to as the vertically extending members 5e.

[0023] 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 below the upper core structure 5 in the vertical direction Dv. The lower core structure 6 can be removed from the reactor vessel body 21 by moving it above the upper core structure 5 in the vertical direction Dv. The lower core structure 6 is separable from the upper core structure 5 inside the reactor vessel body 21. The lower core structure 6 in this embodiment includes a core tank 61, a lower core plate 62, and a lower core support plate 63. However, the lower core structure 6 does not have only the structure described above. The lower core structure 6 may have other components such as a thermal shield (not shown), a baffle plate (not shown), and a lower instrumentation guide tube (not shown).

[0024] The core vessel 61 is formed in a cylindrical shape so as to extend downward in the vertical direction Dv from the upper core support plate 52. The core vessel 61 is positioned with a predetermined gap between it and the inner wall surface of the reactor vessel body 21. The core vessel 61 is suspended and supported by the upper core support plate 52 and is also connected to the upper core plate 51.

[0025] The lower core plate 62 is connected to the lower part of the core tank 61. The lower core plate 62 has a disc shape and numerous through-holes. Lower instrumentation guide tubes (not shown) are inserted through the through-holes in the lower core plate 62. The core 7 is formed by the upper core plate 51, the core tank 61, and the lower core plate 62.

[0026] The reactor core 7 contains numerous fuel assemblies 71. Each fuel assembly 71 is composed of numerous fuel rods bundled together in a grid pattern by a support grid. Furthermore, numerous control rods 41 can be positioned inside the reactor core 7. These control rods 41 form a control rod cluster 4 and can be inserted into the fuel assemblies 71 by a control rod drive unit 3.

[0027] The lower core support plate 63 is positioned below the lower core plate 62 in the vertical direction Dv. The lower core support plate 63 is located near the lower mirror and is fixed to the reactor vessel body 21. The lower core support plate 63 is disc-shaped and has numerous through holes.

[0028] (Method for dismantling the upper core structure) Figure 4 is a flowchart of the method for dismantling the upper core structure in the first embodiment of this disclosure. As shown in Figure 4, the method S10 for dismantling the upper core structure in this first embodiment includes a step S11 for removing the upper core structure, a step S12 for cutting it, and a step S13 for storing it in a waste container.

[0029] In step S11, the process of removing the upper core structure, the upper core structure 5 is removed from the reactor vessel 2. Various work methods can be applied to remove the upper core structure 5 from the reactor vessel 2.

[0030] Figure 5 is an elevation view showing an example of a cutting line of the upper core structure in the first embodiment of the present disclosure. In cutting step S12, as shown in Figure 5, the upper core structure 5, which is the target of cutting, is cut into multiple vertical pieces 200. In cutting step S12, the vertically extending members 5e of the upper core structure 5, namely the upper core support column 53, guide tube 55, water level gauge support pipe 57, and flow column (not shown), are cut into multiple vertical pieces.

[0031] In this first embodiment, the entire upper core structure 5, which has been removed, is divided into multiple upper and lower cut pieces 200 without disassembling the upper core plate 51, upper core support plate 52, upper core support column 53, guide tube 55, water level gauge support pipe 57, and flow column (not shown). In the cutting process S12, the upper and lower extended members 5e are cut along a horizontally extending cutting line 80 using a cutting machine such as a handsaw or a plasma cutter. In this first embodiment, the upper core structure 5 is cut into, for example, three upper and lower cut pieces 200A to 200C. Note that the number of upper and lower cuts of the upper core structure 5 is not limited to three; it may be two, four or more.

[0032] In the cutting process S12, the upper core structure 5 is cut such that, among the multiple cutting pieces 200, the height dimension h1 of the cutting piece 200C cut from the lowest part of the upper core structure 5 is the smallest. In the cutting process S12, a cutting line 80 is set on the upper core structure 5 that passes through multiple vertical extension members 5e and extends horizontally. Here, the cutting line 80 is a straight line that indicates the position on which the cutting blade (not shown) of the cutting machine passes when cutting the vertical extension members 5e. In this first embodiment, two types of cutting lines 80 are set: a first cutting line 81 and a second cutting line 82. In this first embodiment, the first cutting line 81 is set so that the height dimension of the cutting piece 200C cut from the lowest part of the upper core structure 5 is h1. The second cutting line 82 is set such that the cutting pieces 200A and 200B, which are cut from the upper part (upper part) of the upper core structure 5, are greater than the height dimension h1, with respect to the height dimension h2, which is greater than the height dimension h1.

[0033] The height dimension h1 of cut piece 200C and the height dimensions h2 of cut pieces 200A and 200B are set according to the respective radioactivity levels of cut piece 200 (200A to 200C). Here, the radioactivity level of cut piece 200 may be the radioactivity level measured by a measuring instrument, or it may be the radioactivity level obtained by simulation or calculation. Here, the cut pieces 200 are stored in a waste container in step S13. The cut pieces 200 are stored in a waste container appropriate to the radioactivity level of the cut pieces 200. The waste container (not shown) tends to have a smaller internal storage space as the thickness of the container wall increases with the radioactivity level of the waste being stored. In other words, the upper limit of the height dimension of the cut pieces 200 that can be stored in the container is determined by the radioactivity level of the cut pieces 200.

[0034] The upper and lower extension members 5e of the upper core structure 5 (upper core support columns 53, guide tubes 55, water level gauge support pipes, and flow columns) have increasing radioactivity levels from the top to the bottom in the vertical direction Dv. The height dimension h1 of the cut piece 200C, which is cut from the lowest part of the upper core structure 5 where the radioactivity level is highest, is set so that it can be stored in a waste container corresponding to the radioactivity level of the cut piece 200C. The cut pieces 200A and 200B, which are cut from the upper core structure 5 above the lowest part in the vertical direction Dv, have lower radioactivity levels than cut piece 200C. Therefore, the height dimension h2 of the cut pieces 200A and 200B is set so that they can be stored in a waste container that stores waste with a lower radioactivity level than the waste container in which cut piece 200C is stored.

[0035] In cutting step S12, the upper and lower extended members 5e are cut into multiple pieces 200C vertically, and then the upper and lower extended members 5e are removed from the upper core plate 51 and the upper core support plate 52.

[0036] In step S13, the process of storing the waste in a waste container, the multiple cut pieces 200 cut in step S12 are stored in a waste container. In step S13, within the reactor building pool 100, the multiple cut pieces 200 are stored in different waste containers according to the radioactivity level of the cut pieces 200. In this first embodiment, the cut piece 200C cut from the bottom is stored in a waste container that stores waste with a higher radioactivity level than the waste container in which the cut pieces 200A and 200B cut from the upper part of the upper core structure 5 are stored. The cut pieces 200 stored in the waste containers are then transported outside the reactor building pool 100.

[0037] (Effects and Benefits) In the dismantling method S10 of the upper core structure 5 of the first embodiment described above, the upper core structure 5 is cut such that the height dimension h1 of the cutting piece 200C, which is cut from the lowest part of the upper core structure 5, is the smallest among the multiple cutting pieces 200. This allows for the efficient removal of high-radiation portions of the upper core structure 5. Consequently, the removed pieces 200C can be efficiently stored in waste containers with limited storage space, which are designed for storing high-radiation waste. As a result, the disposal of the upper core structure 5, which is an internal reactor structure, can be carried out efficiently.

[0038] Furthermore, in the first embodiment described above, the upper core structure 5 is removed from the reactor vessel 2, and the entire removed upper core structure 5 is cut into multiple vertical sections. This makes it easy to perform the cutting operation to cut the entire upper core structure 5. Therefore, it becomes possible to efficiently cut the upper core structure 5 into pieces 200A, 200B, and 200C according to the radioactivity level.

[0039] Furthermore, in the first embodiment described above, the upper and lower extending member 5e includes a guide tube 55 and an upper core support column 53. In this way, the guide tubes 55 and upper core support columns 53 that make up the upper core structure 5 can be cut according to the radioactivity level, so the guide tubes 55 and upper core support columns 53 can be disposed of efficiently.

[0040] Furthermore, in the first embodiment described above, multiple pieces 200, which are cut so that the height dimension h1 of the piece 200C cut from the lowest part of the upper core structure 5 is the smallest, are stored in different waste containers according to the radioactivity level of the piece 200. This allows the 200 pieces to be efficiently stored in waste containers appropriate for their radioactivity levels. Therefore, the number of waste containers used for storing high-radioactivity waste can be reduced.

[0041] Furthermore, in the first embodiment described above, the cut piece 200C, which is cut from the very bottom, is stored in a waste container that stores waste with a higher radioactivity level than the waste container that stores the cut pieces 200A and 200B, which are cut from the upper part of the upper core structure 5. This allows only the piece 200C with the highest radioactivity level among multiple pieces 200 to be stored in the waste container for high-radioactivity waste. Therefore, the number of waste containers used for storing high-radioactivity waste can be further reduced.

[0042] (Modification of the first embodiment) Figure 6 is an elevation view showing an example of a cutting line of the upper core structure in a modified example of the first embodiment of the present disclosure. In the first embodiment described above, the cut pieces 200A and 200B, which are cut from the upper core structure 5 above the lowest part in the vertical direction Dv, are cut to the same height dimension h2, but the embodiment is not limited to this. For example, as shown in the modified version of the first embodiment in Figure 6, in the cutting step S12, the upper core structure 5 may be cut such that the height dimensions of the multiple cut pieces 200 progressively decrease from the top to the bottom of the upper core structure 5. In this modified version, the height dimension h3 of the cut piece 200B cut from the upper part of the upper core structure 5 above the vertical direction Dv is greater than the height dimension h1 of the cut piece 200C cut from the bottommost part of the upper core structure 5, and the height dimension h4 of the cut piece 200A cut from the upper part of the vertical direction Dv of the cut piece 200B is greater than the height dimension h3. The second cutting line 82B is set in such a way that the height dimension h3 of the cut piece 200B above the vertical direction Dv is greater than the height dimension h3.

[0043] In the modified version of the first embodiment described above, at least a portion of the upper core structure 5 is cut such that the height dimensions h4, h3, and h1 of the multiple cut pieces 200A to 200C gradually decrease from the top to the bottom of the upper core structure 5. As a result, the height dimensions h4, h3, and h1 of the multiple cut pieces 200A to 200C will differ according to the radioactivity level. Therefore, for example, when preparing multiple types of waste containers according to the radioactivity level, the multiple cut pieces 200 can be made to a size suitable for storage in waste containers of a size appropriate to each radioactivity level.

[0044] <Second Embodiment> Next, a second embodiment of the method for dismantling the upper core structure according to this disclosure will be described. In the second embodiment described below, only the configuration of the method for dismantling the upper core structure differs from the first embodiment, so the same reference numerals are used for the same parts as in the first embodiment, and redundant explanations are omitted.

[0045] Figure 7 is a flowchart of the method for cutting the upper core structure in the second embodiment of the present disclosure. As shown in Figure 7, the method S20 for dismantling the upper core structure of this second embodiment includes a step S21 for removing the upper core structure, a step S22 for dismantling the upper core structure, a step S23 for cutting, and a step S24 for storing in a waste container.

[0046] In step S21, the process of removing the upper core structure, the upper core structure 5 is removed from the reactor vessel 2. Various work methods can be applied to remove the upper core structure 5 from the reactor vessel 2.

[0047] In step S22, which involves disassembling the upper core structure 5, the removed upper core structure 5 is disassembled. Specifically, the upper core structure 5 consists of vertically extending members 5e, namely the upper core support column 53, guide tube 55, water level gauge support pipe 57, and flow column (not shown), which are removed from the upper core plate 51 and the upper core support plate 52.

[0048] Figure 8 is an elevation view showing an example of a cutting line of the upper core structure in a second embodiment of the present disclosure. In cutting step S23, at least a portion of the upper core structure 5, which is the target of cutting, is cut into multiple pieces vertically. In this second embodiment, in cutting step S23, as shown in Figure 8, the upper and lower extension members 5e, which consist of the upper core support column 53, guide tube 55, water level gauge support pipe 57, and flow column (not shown), are cut into multiple vertical pieces 300. In cutting step S23, the upper and lower extension members 5e are cut along a horizontally extending cutting line 80C using a cutting machine such as a handsaw or plasma cutting machine. In this second embodiment, the upper and lower extension members 5e are cut into, for example, three vertical pieces 300A to 300C.

[0049] In the cutting process S23, the upper and lower extension members 5e are cut such that the height dimension h11 of the cut piece 300C cut from the lowest section of the upper and lower extension members 5e is the smallest among the multiple cut pieces 300 cut from the upper and lower extension members 5e. In this second embodiment, two types of cutting lines 80C are set: a first cutting line 81C and a second cutting line 82C. In this second embodiment, the first cutting line 81C is set so that the cut piece 300C cut from the lowest part of the upper core structure 5 has a height dimension h11. The second cutting line 82C is set so that the cut pieces 300A and 300B cut from the upper part of the upper core structure 5 above the vertical direction Dv relative to the lowest part have a height dimension h12 which is greater than the height dimension h11.

[0050] In step S24, the process of storing the waste in a waste container, the multiple cut pieces 300 cut in step S23 are stored in a waste container. In step S24, within the reactor building pool 100, the multiple cut pieces 300 are stored in different waste containers according to the radioactivity level of the cut pieces 300. In this second embodiment, the cut piece 300C cut from the bottom is stored in a waste container that stores waste with a higher radioactivity level than the waste container in which the cut pieces 300A and 300B cut from the upper part of the upper core structure 5 are stored. The cut pieces 300 stored in the waste containers are then transported outside the reactor building pool 100.

[0051] (Effects and Benefits) In the dismantling method S20 for the upper core structure 5 of the second embodiment described above, similar to the dismantling method S10 for the upper core structure 5 of the first embodiment described above, the height dimension h11 of the cutting piece 300 cut from the lowest part of the upper core structure 5 is reduced, so that the disposal of the upper core structure 5, which is an in-reactor structure, can be carried out efficiently.

[0052] Furthermore, in the second embodiment described above, after removing the upper core structure 5 from the reactor vessel 2, the removed upper core structure 5 is disassembled, and at least the vertically extending upper and lower extension members 5e of the disassembled upper core structure 5 are cut into multiple vertical pieces 300. Therefore, since it is only necessary to cut the disassembled upper and lower extension members 5e into multiple vertical pieces 300, the cutting work on the upper and lower extension members 5e is made easier.

[0053] (Other embodiments) This disclosure is not limited to the configuration of the embodiments described above, and design modifications are possible without departing from the spirit thereof. In the embodiments described above, the upper and lower extension members 5e of the upper core structure 5 are cut into three vertical sections, but the embodiment is not limited to this. The number of sections into which the upper and lower extension members 5e of the upper core structure 5 are cut is not limited to three sections; it may be two sections, four sections or more. Furthermore, in each of the above embodiments, the cut pieces 200A and 200B, and 300A and 300B, which are cut from the upper part of the vertical direction Dv relative to the bottommost cut pieces 200C and 300C, are given the same height dimensions h2 and h12, respectively, but this is not limited to this. The upper part of the vertical direction Dv relative to the bottommost cut pieces 200C and 300C may be cut at a position that is easy to cut, for example, as long as it can be stored in a waste container corresponding to the radioactivity level of each cut piece 200 and 300.

[0054] <Note> The method for dismantling the upper core structure 5 described in the embodiment can be understood, for example, as follows.

[0055] (1) The first embodiment of the method for dismantling the upper core structure 5 is a method for dismantling the upper core structure 5 housed in the reactor vessel 2, and includes steps S12 and S23 of cutting at least a part of the upper core structure 5 to be cut into a plurality of vertical cutting pieces 200 and 300, wherein in the cutting steps S12 and S23, at least a part of the upper core structure 5 is cut such that the height dimensions h1 and h11 of the cutting piece 200C and 300C cut from the lowest part of the upper core structure 5 are the smallest among the plurality of cutting pieces 200 and 300.

[0056] Therefore, by reducing the height dimensions h1 and h11 of the cuttings 200C and 300C, which are cut from the lowest part of the upper core structure 5, the cuttings 200C and 300C, which are highly radioactive waste, can be efficiently stored in waste containers with small storage space. As a result, the disposal of the upper core structure 5, which is an internal structure of the reactor, can be carried out efficiently.

[0057] (2) The method S10 for dismantling the upper core structure 5 according to the second embodiment is the method S10 for dismantling the upper core structure 5 according to (1), wherein in the cutting step S12, at least a part of the upper core structure 5 is cut such that the height dimensions of the plurality of cut pieces 200, 300 become progressively smaller from the top to the bottom of the upper core structure 5.

[0058] This makes it easier to create multiple cut pieces (200, 300) with height dimensions suitable for storage in waste containers according to their radioactivity levels.

[0059] (3) A dismantling method S10 for the upper core structure 5 according to the third embodiment is the dismantling method S10 for the upper core structure 5 according to (1) or (2), further comprising a step S11 of removing the upper core structure 5 from the reactor vessel 2, wherein in the cutting step S12, the entire removed upper core structure 5 is cut into multiple vertical sections.

[0060] With this configuration, the upper core structure 5 is removed from the reactor vessel 2, and the entire removed upper core structure 5 is cut into multiple sections vertically. This makes it easy to cut the entire upper core structure 5. Therefore, the upper core structure 5 can be dismantled efficiently.

[0061] (4) A dismantling method S20 for the upper core structure 5 according to the fourth embodiment is a dismantling method S20 for the upper core structure 5 according to any one of (1) to (3), further comprising a step S21 of removing the upper core structure 5 from the reactor vessel 2 and a step S22 of dismantling the removed upper core structure 5, wherein in the cutting step S23, at least the vertically extending vertical extension members 5e of the dismantled upper core structure 5 are cut vertically into a plurality of cutting pieces 300.

[0062] With this configuration, after removing the upper core structure 5 from the reactor vessel 2, the removed upper core structure 5 is disassembled, and at least the vertically extending upper and lower extension members 5e of the disassembled upper core structure 5 are cut into multiple vertical pieces 300. Therefore, since it is only necessary to cut the disassembled upper and lower extension members 5e into multiple vertical pieces 300, the cutting work on the upper and lower extension members 5e is made easier.

[0063] (5) The method S20 for dismantling the upper core structure 5 according to the fifth embodiment is the method S20 for dismantling the upper core structure 5 according to (4), wherein the upper and lower extension member 5e includes at least one of the guide tube 55 and the upper core support column 53.

[0064] With this configuration, if the upper and lower extension members 5e include at least one of the guide tubes 55 and the upper core support columns 53, the disposal of these guide tubes 55 and upper core support columns 53 can be carried out efficiently.

[0065] (6) The sixth method for dismantling the upper core structure 5 S10, S20 is any one of the methods for dismantling the upper core structure 5 S10, S20 of (1) to (5), further comprising the steps S13, S24 of storing a plurality of the cut pieces 200, 300 in waste containers, wherein in the steps S13, S24 of storing in waste containers, the plurality of the cut pieces 200, 300 are stored in different waste containers according to the radioactivity level of the cut pieces 200, 300.

[0066] This allows for the efficient storage of the cut pieces 200 and 300 in waste containers appropriate to their radioactivity levels. The cut pieces 200 and 300, which are cut from the bottommost part of the upper core structure 5, are then cut so that their height dimensions h1 and h11 are minimized.

[0067] (7) The dismantling methods S10 and S20 for the upper core structure 5 according to the seventh embodiment are the dismantling methods S10 and S20 for the upper core structure 5 according to (6), wherein the cut pieces 200C and 300C cut from the lowest part are stored in a waste container that stores waste with a higher radioactivity level than the waste container that stores the cut pieces 200A, 200B, 300A, and 300B cut from the upper part of the upper core structure 5.

[0068] This allows multiple pieces 200, 300 to be properly stored in waste containers appropriate to the radioactivity level of each piece. [Explanation of Symbols]

[0069] 1… Pressurized water reactor 2…Reactor vessel 3…Control rod drive mechanism 4…Control rod cluster 5…Upper core structure 5e... Upper and lower extension member 6…Lower core structure 7…Core 21…Reactor vessel 22...Reactor vessel lid 23... Inlet nozzle 24…Outlet nozzle 25… Housing 41... Control rods 45...Control rod cluster drive shaft 51…Upper core plate 52…Upper core support plate 53… Upper core support column 55... Guide tube 57…Water level gauge support pipe 61…Core tank 62...Lower core plate 63...Lower core support plate 71…Fuel assembly 80,80C…cutting line 81,81C…First cutting line 82,82B,82C…Second cutting line 100... Reactor building pool 110... First Cavity 111...First floor 120...Second cavity 121…Second floor surface 200,200A~200C,300,300A~300C...cut piece

Claims

1. A method for dismantling the upper core structure housed in the reactor vessel, A step of removing the upper core structure from the reactor vessel, The process of dismantling the removed upper core structure, The process includes cutting at least a portion of the upper core structure, which is to be cut, into multiple vertical cutting pieces, In the aforementioned cutting process, Of the disassembled upper core structure, at least the vertically extending members are cut into a plurality of vertical pieces, and the vertically extending members are cut such that the height dimension of the piece cut from the lowest part of the upper core structure is the smallest. The upper and lower extending members include at least one of a guide tube and an upper core support column. Method for dismantling the upper core structure.

2. In the aforementioned cutting process, The upper and lower extension members are cut such that the height of the plurality of cut pieces decreases sequentially from the top to the bottom of the upper core structure. A method for dismantling an upper reactor core structure according to claim 1.

3. The process further includes the step of removing the upper core structure from the reactor vessel, In the cutting process, the entire upper core structure that has been removed is cut into multiple pieces vertically. A method for dismantling an upper reactor core structure according to claim 1 or 2.

4. The process further includes the step of storing the multiple cut pieces in a waste container, In the step of storing the waste in the aforementioned waste container, the multiple cut pieces are stored in different waste containers according to the radioactivity level of the cut pieces. A method for dismantling an upper reactor core structure according to claim 1 or 2.

5. The cut piece, which is cut from the lowest part, is stored in a waste container that stores waste with a higher radioactivity level than the waste container that stores the cut piece, which is cut from the upper part of the upper core structure. The method for dismantling the upper core structure according to claim 4.

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