Method for dismantling the lower core structure

Abstract

This invention provides a method for dismantling a lower reactor core structure that can improve the efficiency of dismantling the lower reactor core structure. [Solution] In the method for dismantling a lower core structure of the present disclosure, the lower core structure comprises a core vessel having a cylindrical shape extending vertically and having a tube support at its upper part that penetrates both the inside and outside; a heat shield covering the portion of the core vessel below the tube support from the outer periphery; and baffle plates and former plates provided on the inside of the core vessel at vertical positions where the heat shield is provided. The method for dismantling a lower core structure includes a division step of horizontally cutting the core vessel in a range below the tube support and above the heat shield.

Description

Technical Field

[0001] The present disclosure relates to a method for disassembling a lower 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 structures is started before the completion of the removal of the fuel from the fuel storage pool.

Prior Art Documents

Patent Documents

[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 structures which are internal structures. Therefore, when disassembling a nuclear reactor, due to handling members with a high dose, there are many restrictions on the working time and working place. Among the in-vessel structures, the lower core structure located at the lower part inside the reactor vessel has a thermal shield covering the outer surface of the core basin, a baffle plate, a former plate, etc. arranged inside the core basin, and the structure of the lower core structure is complicated. For this reason, it has been a problem that disassembling the lower core structure requires a lot of labor.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a method for disassembling a lower core structure that can improve the disassembling efficiency of the lower core structure.

Means for Solving the Problems

[0006] To solve the above problems, the method for dismantling a lower core structure according to the present disclosure is a method for dismantling a lower core structure, wherein the lower core structure comprises a core vessel having a cylindrical shape extending vertically and having a pipe support at its upper part that penetrates both the inside and outside; a heat shield covering the portion of the core vessel below the pipe support from the outer periphery; and baffle plates and former plates provided inside the core vessel at vertical positions where the heat shield is provided, and the method includes a division step of horizontally cutting the core vessel in a range below the pipe support and above the heat shield.

[0007] Furthermore, the method for dismantling a lower core structure according to the present disclosure is a method for dismantling a lower core structure, wherein the lower core structure comprises a core vessel that is cylindrical in shape and extends vertically, a heat shield that covers the core vessel from the outer periphery, and baffle plates and former plates provided inside the core vessel at vertical positions where the heat shield is provided, wherein the baffle plates extend vertically and are provided in a plurality in an annular shape along the inner circumferential surface of the core vessel, the former plates are formed in an annular shape so as to cover the plurality of baffle plates from the outer periphery and extend horizontally, and the lower core structure comprises connecting bolts that connect some of the adjacent baffle plates among the plurality of baffle plates, and each baffle plate is connected to the former The lower assembly comprises fixing bolts for fixing to a plate, and includes a lower dismantling step for dismantling the core vessel and the lower assembly which is an assembly of the heat shield, the baffle plate and the former plate, the lower dismantling step includes a step of vertically cutting the lower assembly with a cutting line that passes through at least one of the two baffle plates connected by the connecting bolts and avoids the connecting bolts and the fixing bolts, and a step of vertically cutting the lower assembly with a cutting line that passes through at least one of the two baffle plates which have contact ends that abut without passing through the connecting bolts, at a position opposite to the contact end with the fixing bolts in between, and avoids the connecting bolts and the fixing bolts. [Effects of the Invention]

[0008] The method for dismantling the lower core structure described herein can improve the efficiency of dismantling the lower core structure. [Brief explanation of the drawing]

[0009] [Figure 1] This is a longitudinal cross-sectional view showing a pressurized water reactor according to an embodiment of the present disclosure. [Figure 2] This is a front view showing the lower core structure according to the embodiment of the present disclosure. [Figure 3] This is a longitudinal cross-sectional view showing a lower core structure according to an embodiment of the present disclosure. [Figure 4] This is an enlarged view of the upper end of the lower core vessel according to the present disclosure. [Figure 5] This is a side view of a baffle plate and a former plate according to an embodiment of the present disclosure. [Figure 6] This is a top view of the baffle plate and former plate according to the embodiments of the present disclosure. [Figure 7] This figure shows the baffle plate connection structure and the fixing structure between the former plate and the baffle plate according to the embodiment of this disclosure. [Figure 8] This is a side view of an example of equipment for dismantling the lower core structure according to the embodiment of this disclosure. [Figure 9] This is a view from above of an example of equipment for dismantling the lower core structure according to the embodiment of this disclosure. [Figure 10] This flowchart shows an example of a method for dismantling a lower core structure according to the present disclosure. [Figure 11] This is a schematic diagram illustrating the upper horizontal cutting process according to the embodiment of this disclosure. [Figure 12] This is a schematic diagram illustrating the upper vertical cutting process according to the embodiment of this disclosure. [Figure 13] This is a schematic diagram of a lifting jig used in the lower dismantling process according to the embodiment of this disclosure. [Figure 14] This is a schematic diagram illustrating the lower horizontal cutting process according to the embodiment of this disclosure. [Figure 15] This is a schematic diagram illustrating the lower vertical cutting process according to the embodiment of this disclosure. [Modes for carrying out the invention]

[0010] Hereinafter, with reference to the accompanying drawings, a mode for implementing the method for disassembling the lower core structure 6 according to the present disclosure will be described. However, the present disclosure is not limited to only this embodiment.

[0011] <Embodiment> (Nuclear reactor) FIG. 1 is a longitudinal sectional view showing a pressurized water reactor 1 which is a nuclear reactor to be disassembled according to the embodiment. FIG. 1 schematically shows the schematic configuration of the pressurized water reactor 1. The pressurized water reactor 1 (PWR: Pressurized Water Reactor) uses light water as a reactor coolant and a neutron moderator, and is a high-temperature and high-pressure water that does not boil throughout the entire core 15. This high-temperature and high-pressure water is sent to a steam generator to generate steam by heat exchange, and this steam is sent to a turbine generator to generate electricity. The pressurized water reactor 1 is disposed within a reactor cavity 100. The reactor cavity 100 is a space capable of storing cooling water (water), and a lower cavity 101 in which the lower core structure 6 described later can be temporarily placed is formed. Hereinafter, in the following description of the embodiment, it is assumed that the vertical direction Dv coincides with the vertical direction.

[0012] As shown in FIG. 1, the pressurized water reactor 1 of the present embodiment includes a reactor vessel 2, an upper core structure 5, and a lower core structure 6.

[0013] (Reactor vessel) The reactor vessel 2 has a reactor vessel main body 20 and a reactor vessel lid 21 so that in-vessel structures can be inserted therein. The reactor vessel 2 is disposed inside an installation hole 103 formed so as to be recessed with respect to the cavity floor surface 102 of the lower cavity 101. The reactor vessel 2 is disposed in a state where a part thereof (specifically, the reactor vessel lid 21) protrudes from the cavity floor surface 102 of the lower cavity 101.

[0014] The reactor vessel main body 20 can be opened at the top by removing the reactor vessel head 21. The lower part of the reactor vessel main body 20 has a cylindrical shape closed by a hemispherical bottom mirror. At the upper part of the reactor vessel main body 20, an inlet nozzle 22 for supplying light water (coolant) as primary cooling water (water) and an outlet nozzle 23 for discharging light water are formed. Further, the reactor vessel main body 20 has a water injection nozzle (not shown) separately from the inlet nozzle 22 and the outlet nozzle 23.

[0015] The reactor vessel head 21 is mounted on the upper part of the reactor vessel main body 20. The reactor vessel head 21 is fixed to the reactor vessel main body 20 so as to be openable and closable by a plurality of stud bolts and nuts (not shown).

[0016] (Upper core structure) 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 20 by being moved upward in the vertical direction Dv with respect to the reactor vessel main body 20. The upper core structure 5 of the present embodiment has an upper core plate 30, an upper core support plate 31, a plurality of upper core support columns 32, and a plurality of guide tubes 33. The upper core plate 30 and the upper core support plate 31 are disposed facing each other in the vertical direction Dv. The upper core support plate 31 is disposed in the vicinity of the opening at the upper end of the reactor vessel main body 20 and is located above the upper core plate 30. The plurality of upper core support columns 32 extend in the vertical direction Dv and connect the upper core support plate 31 and the upper core plate 30. The plurality of guide tubes 33 are inserted into the upper core support plate 31 and the upper core plate 30 from above. 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 water level gauge support pipe, a mixer, a thermocouple lead-out pipe, and a reinforcing beam as configurations (not shown).

[0017] (Lower core structure) 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 20 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 20. As shown in Figures 2 and 3, the lower core structure 6 of this embodiment includes a core tank 40, a heat shield 50, a baffle plate 60, a former plate 61, an irradiation test specimen guide tube 7, a lower core plate 8, a lower core support plate 9, a lower core support column 10, a rectifier plate 11, a lower instrumentation guide tube 12, and a connecting plate 13. Note that the lower core structure 6 does not have only the structure described above.

[0018] (Core tank) The core vessel 40 is formed in a cylindrical shape so as to extend downward in the vertical direction Dv from the upper end of the reactor vessel body 20. As shown in Figure 1, the core vessel 40 is positioned with a predetermined gap between it and the inner wall surface of the reactor vessel body 20. The core vessel 40 is suspended and supported from the upper end of the reactor vessel body 20.

[0019] As shown in Figure 2, the reactor core vessel 40 is cylindrical in shape, extending vertically. More specifically, the reactor core vessel 40 is formed in a cylindrical shape extending in the vertical direction Dv. That is, the central axis of the reactor core vessel 40 extends in the vertical direction Dv. Hereinafter, the central axis of the reactor core vessel 40 will be simply referred to as "axis O", the radial direction with respect to this axis O will be simply referred to as "radial direction", and the circumferential direction with respect to this axis O will be simply referred to as "circumferential direction". The reactor core vessel 40 has an upper reactor core vessel 41 and a lower reactor core vessel 42.

[0020] The upper core vessel 41 constitutes the upper part of the core vessel 40. The upper core structure 5 is housed inside the upper core vessel 41 (see Figure 1). The upper core vessel 41 has an upper core vessel body 43 and a tube support 44. The upper core vessel body 43 is formed in a cylindrical shape extending in the vertical direction Dv. The tube support 44 is provided in the upper core vessel 41. That is, the tube support 44 is provided in the upper part of the core vessel 40. The tube support 44 penetrates radially through the inside and outside of the upper core vessel 41. In the illustrated example, there are two tube supports 44 spaced apart in the circumferential direction. The two tube supports 44 are formed to be of similar size and are provided in approximately the same position in the vertical direction Dv. That is, the lower ends of the two tube supports 44 are both located in approximately the same position in the vertical direction Dv.

[0021] The lower core vessel 42 constitutes the lower portion of the core vessel 40. That is, the lower core vessel 42 is located below the upper core vessel 41. The lower core vessel 42 is formed integrally with the upper core vessel 41. The lower core vessel 42 has a lower core vessel body 45 and a vessel-side backing plate 46 (see Figure 4). The lower core vessel body 45 is formed in a cylindrical shape extending in the vertical direction Dv. As shown in Figure 4, the vessel-side backing plate 46 is provided at the upper end of the lower core vessel 42. Multiple vessel-side backing plates 46 are provided in the circumferential direction. The vessel-side backing plates 46 protrude radially outward from the outer circumferential surface of the lower core vessel body 45.

[0022] The boundary between the upper core vessel 41 and the lower core vessel 42 is formed with thin walls. That is, the lower end portion of the upper core vessel 41 and the upper end portion of the lower core vessel 42 are formed with thin walls. Hereinafter, the portion of the core vessel 40 that is formed with thinner walls than other parts will be referred to as the thin-walled portion 47. Specifically, this thin-walled portion 47 is formed with thinner walls than the portion of the core vessel 40 where the tube supports 44 are provided. Furthermore, this thin-walled portion 47 is formed in the core vessel 40 at least below the tube supports 44 and above the heat shield 50 and the irradiation test specimen guide tube 7, which will be described later.

[0023] (Thermal shield) As shown in Figures 2 and 3, the heat shield 50 covers the portion of the core vessel 40 below the tube supports 44 from the outer periphery. In this embodiment, more specifically, the heat shield 50 is provided on the outer periphery of the lower core vessel 42 of the core vessel 40. Furthermore, the heat shield 50 is provided around the entire circumference of the core vessel 40. The heat shield 50 comprises a heat shield body 51 and a heat shield side backing plate 52 (see Figure 4).

[0024] The thermal shield body 51 is formed in a cylindrical shape extending in the vertical direction Dv. The thermal shield body is provided with a radial gap between it and the outer surface of the lower core vessel 42 over its entire circumference. The thermal shield body 51 is provided to cover substantially the entire vertical direction Dv of the lower core vessel 42. The upper end of the thermal shield body 51 is located slightly below the upper end of the lower core vessel 42, and the lower end of the thermal shield body 51 is located slightly above the lower end of the lower core vessel 42.

[0025] As shown in Figure 4, the heat shield side backing plates 52 are provided at the upper end of the heat shield body 51. Multiple heat shield side backing plates 52 are provided in the circumferential direction. The number of heat shield side backing plates 52 is the same as the number of tank side backing plates 46. The heat shield side backing plates 52 protrude radially inward from the inner circumferential surface of the heat shield body 51. The heat shield side backing plates 52 abut against the corresponding tank side backing plates 46 from above. The heat shield 50 is supported by the load of the reactor core vessel 40 by the heat shield side backing plates 52. Bolts 53 are inserted through the heat shield side backing plates 52 from the radially outer side of the heat shield 50. The heat shield 50 is fixed to the reactor core vessel 40 at the portion of the heat shield side backing plates 52 by these bolts 53. Furthermore, the lower end of the heat shield 50 is connected to a flexible metal 54 that extends radially outward from the core vessel 40. Additionally, a support structure, such as a bracing rod, may be provided between the lower end of the heat shield 50 and the core vessel 40.

[0026] (Baffle board) As shown in Figure 3, the baffle plates 60 are installed inside the lower core vessel 42 at a vertical position Dv where the heat shield 50 is located. As shown in Figures 5 and 6, multiple baffle plates 60 are provided in an annular shape along the inner circumferential surface of the lower core vessel 42. Each baffle plate 60 is formed in a rectangular plate shape extending in the vertical direction Dv. The ends of two adjacent baffle plates 60 in the circumferential direction are in contact with each other when viewed from the vertical direction Dv. Furthermore, two adjacent baffle plates 60 in the circumferential direction are arranged in orientations perpendicular to each other when viewed from the vertical direction Dv. Also, as shown in Figure 7, some adjacent baffle plates 60 are connected by connecting bolts 62. The connecting bolts 62 are provided so as to penetrate the ends of the two baffle plates 60 that are to be connected that are in contact with each other.

[0027] (Forma board) As shown in Figure 3, the former plate 61 is installed inside the lower core vessel 42 at a vertical position Dv where the heat shield 50 is provided. As shown in Figures 5 and 6, the former plate 61 is formed in an annular shape so as to cover the multiple baffle plates 60 from the outer circumference. The former plate 61 is formed in a flat plate shape that extends in the horizontal direction Dh. Multiple former plates 61 are provided at intervals in the vertical direction Dv. As shown in Figure 7, each baffle plate 60 is fixed to the former plate 61 by fixing bolts 63. The fixing bolts 63 are provided around the entire circumference of the inner edge of the former plate 61. Each fixing bolt 63 is positioned to avoid the connecting bolts 62 between the baffle plates 60. The fixing bolts 63 are inserted from the inner circumference of the baffle plate 60. In addition, the outer edge of the former plate 61 is fixed to the core vessel 40 by second fixing bolts 64. The second fixing bolt 64 is provided around the entire circumference of the outer edge of the former plate 61. The second fixing bolt 64 is inserted from the outer periphery side of the core vessel 40.

[0028] (Irradiation test specimen guide tube) As shown in Figure 2, the irradiation test specimen guide tube 7 is provided on the outer circumference of the reactor core vessel 40. In this embodiment, the irradiation test specimen guide tube 7 is provided on the outer circumference of the heat shield 50. The irradiation test specimen guide tube 7 extends in the vertical direction Dv and is provided in multiple locations in the circumferential direction. The upper end of the irradiation test specimen guide tube 7 protrudes above the heat shield 50. The irradiation test specimen guide tube 7 is used to insert and remove test specimens at specific locations within the reactor when performing irradiation tests in the reactor.

[0029] (Lower core plate) As shown in Figure 3, the lower core plate 8 is connected to the lower part of the core tank 40. The lower core plate 8 is located at the lower end of the baffle plate 60. The lower core plate 8 has numerous through-holes formed in a disc shape. These through-holes allow water to pass through the lower core plate 8. The reactor core 15 is formed by the upper core plate 30, the lower core plate 8, and the core tank 40.

[0030] The lower core support plate 9 is positioned below the lower core plate 8 at a vertical distance Dv. Multiple lower core support columns 10 are provided at a vertical distance Dv between the lower core plate 8 and the lower core support plate 9. The multiple lower core support columns 10 connect the lower core plate 8 and the lower core support plate 9 vertically. The baffle plate 11 is provided between the lower core plate 8 and the lower core support plate 9. The lower instrumentation guide tube 12 is held by the lower core support plate 9 and extends below the lower core support plate 9. The connecting plate 13 is located below the lower core support plate 9.

[0031] (Method for dismantling the lower core structure) The following describes the dismantling of the lower core structure 6 according to the embodiment of this disclosure. Here, the procedure for dismantling the portion of the lower core structure 6 above the lower core support plate 9 will be described.

[0032] The dismantling of this lower core structure 6 is carried out, for example, inside the reactor cavity 100 shown in Figures 8 and 9. As shown in Figures 8 and 9, the reactor cavity 100 is equipped with a turntable 110, a first cutting device 111, a second cutting device 112, a waste storage container 114, and the like.

[0033] The lower core structure 6 is placed on the turntable 110. The turntable 110 is rotatable around a central axis that passes through the center of the turntable 110 and extends in the vertical direction Dv. As the turntable 110 rotates around this central axis, the lower core structure 6 placed on the turntable 110 rotates. The first cutting device 111 is installed so as to be movable within the reactor cavity 100.

[0034] The first cutting device 111 is capable of cutting the lower core structure 6 in the horizontal direction Dh. The first cutting device 111 is movable in the horizontal direction Dh (for example, left-right direction in Figure 9). An example of the first cutting device 111 is a rail-type cutting device. A rail-type first cutting device 111 has, for example, a rail 111a that is movable in the horizontal direction Dh and a wire saw 111b that extends in the horizontal direction Dh and perpendicular to the direction of movement of the rail 111a. The wire saw 111b cuts the lower core structure 6 horizontally. Horizontal cutting means cutting the object to be cut in the horizontal direction Dh. The wire saw 111b is movable in the vertical direction Dv. At this time, by moving the first cutting device 111 while rotating the lower core structure 6 with a turret, the lower core structure 6 can be cut efficiently while reducing the amount of horizontal movement Dh of the first cutting device 111. Furthermore, the first cutting device 111 may also be equipped with a disc saw (not shown) capable of horizontally cutting the lower core structure 6, in addition to the wire saw 111b.

[0035] The second cutting device 112 is capable of cutting the lower core structure 6 in the vertical direction Dv. The second cutting device 112 includes, for example, a disc saw (not shown) capable of vertically cutting the lower core structure 6. Vertical cutting means cutting the object to be cut in the vertical direction Dv (vertical direction).

[0036] Here, the lower core structure 6 and the cut pieces of the lower core structure 6 can be freely transported within the reactor cavity 100 by a transport device (not shown), such as a crane.

[0037] The waste container 114 contains the dismantled lower core structure 6 pieces. The waste container 114 is placed in an empty space within the reactor cavity 100. The appropriate waste container 114 is selected according to the radiation level of the pieces to be contained. During the dismantling of the lower core structure 6, the reactor cavity 100 is filled with water so that the entire lower core structure 6 is submerged. However, some low-dose areas of the lower core structure 6 may be dismantled while exposed to the air.

[0038] Next, with reference to the flowchart in Figure 10, an example of the procedure for dismantling the lower core structure 6 will be described. Here, it is assumed that the parts of the pressurized water reactor 1 other than the lower core structure 6 have been removed in advance. That is, the upper core structure 5 and fuel assemblies have been removed from the core tank 40 in advance. In this embodiment, after the upper dismantling process (step S1) for dismantling the upper part of the lower core structure 6 is performed, the lower dismantling process (step S2) for dismantling the lower part of the lower core structure 6 is performed.

[0039] First, the upper dismantling process will be explained. In the upper dismantling process, the upper part of the lower core structure 6 is dismantled. More specifically, in the upper dismantling process, the upper core tank 41 is dismantled. In this embodiment, the upper core tank 41 is dismantled sequentially from the top. In the upper dismantling process, the upper horizontal cutting process (step S11) is performed. As shown in Figure 11, in the upper horizontal cutting process, the first cutting device 111 horizontally cuts the upper core tank 41. In Figure 11, the cutting line L10 from the upper horizontal cutting process and the cutting line L11 from the upper vertical cutting process, which will be described later, are shown by dashed lines. In the upper dismantling process, the upper core tank 41 is lifted upward by a lifting jig 113 while being horizontally cut.

[0040] Following the upper horizontal cutting process, an upper vertical cutting process (step S12) is performed. In the upper vertical cutting process, a portion of the upper core tank 41 that was horizontally cut in the upper horizontal cutting process is moved to the second cutting device 112. Then, as shown in Figure 12, the second cutting device 112 further vertically cuts a portion of the upper core tank 41. In Figure 12, the cutting line L11 from the upper vertical cutting process is shown as a dashed line. In this way, the upper core tank 41 is divided into multiple parts, forming small cut pieces 150. These cut pieces 150 of the upper core tank 41 are each stored in a waste storage container 114. In this embodiment, each time a cut piece 150 is cut, an additional lifting jig 113 is installed in the part corresponding to the cut piece 150, and the newly added jig 113 is sandwiched between the cut pieces along the cutting line L11.

[0041] After the upper vertical cutting process, it is determined whether or not the dismantling of the upper core tank 41 is complete (step S13). If the dismantling of the upper core tank 41 is not complete (step S13; NO), the process returns to the upper horizontal cutting process, and steps S11 to S12 described above are repeated. In this embodiment, while the upper vertical cutting process is being performed by the second cutting device 112, the upper horizontal cutting process is performed by the first cutting device 111. In the upper dismantling process, it is preferable to minimize the number of times the tube stalks 44 are horizontally cut as much as possible. In this embodiment, in order to reduce the vertical dimension Dv of the cut piece 150 and minimize the number of times the tube stalks 44 are horizontally cut, the tube stalks 44 are cut horizontally only once.

[0042] If the dismantling of the upper core tank 41 is complete (Step S13; YES), the process proceeds to the lower dismantling process (Step S2).

[0043] At this point, the upper horizontal cutting process, which occurs just before it is determined that the dismantling of the upper core vessel 41 is complete, is a division process (step S14) that divides the core vessel 40 into the part above the heat shield 50 and the part below where the heat shield 50 is installed.

[0044] In the division process, as shown in Figure 4, a horizontal cut is made in the core vessel 40 in the area below the tube support 44 and above the heat shield 50. In Figure 4, the cutting line L12 made in the division process is shown as a dashed line. Furthermore, in this embodiment, a horizontal cut is made in the core vessel 40 in the area below the tube support 44 and above the irradiation test specimen guide tube 7. Furthermore, in this embodiment, a portion of the core vessel 40 that is thinner than the portion where the tube support 44 is provided (thin-walled portion 47) is horizontally cut.

[0045] Next, the lower dismantling process will be described. In the lower dismantling process, the portion of the core vessel 40 located below the cutting line L12 made in the division process, and the lower assembly 155, which is an assembly of the heat shield 50, baffle plate 60, and former plate 61, are dismantled. The lower assembly 155 here refers to the assembly of the lower core structure 6 excluding the portion removed in the upper dismantling process. The lower assembly 155 mainly includes the lower core vessel 42, the heat shield 50, the baffle plate 60, and the former plate 61. In this embodiment, the lower assembly 155 also includes the lower end portion of the upper core vessel 41 that remained after the upper dismantling process. Note that the lower assembly 155 may include components other than those described above.

[0046] Furthermore, in the lower dismantling process, the lower assembly 155 described above is cut using, for example, the lifting jig 120 shown in Figure 13. This lifting jig 120 is capable of lifting the lower assembly 155. The lifting jig 120 has a first claw portion 121, a second claw portion 122, and an eye bolt 123. The first claw portion 121 extends in the vertical direction Dv. The first claw portion 121 is capable of being inserted from above between the core vessel 40 and the heat shield 50. Two second claw portions 122 are provided so as to sandwich the first claw portion 121 in the horizontal direction Dh. One of the two second claw portions 122 (the second claw portion 122 positioned radially inward relative to the first claw portion 121) and the first claw portion 121 are capable of sandwiching the core vessel 40 in the horizontal direction Dh. Furthermore, the other of the two second claw portions 122 (the second claw portion 122 positioned radially outward relative to the first claw portion 121) and the first claw portion 121 are designed to be able to clamp the heat shield 50 in the horizontal direction Dh.

[0047] The second claw portion 122 located on the outside of the heat shield 50, together with the first claw portion 121, clamps the heat shield 50, and the second claw portion 122 located on the inside of the reactor core vessel 40, together with the first claw portion 121, clamps the reactor core vessel 40. The second claw portion 122 has a second claw portion body 124 extending downward from the first claw portion 121, and a retaining screw 125 inserted through the second claw portion body 124. The second claw portion body 124 has a first portion 124a extending horizontally Dh from the first claw portion 121, and a second portion 124b extending downward from the end of the first portion 124a on the opposite side of the first claw portion 121 in the horizontal direction Dh. The retaining screw 125 is inserted horizontally Dh through the second portion 124b of the second claw portion body 124. The retaining screw 125 is positioned to extend from the second portion 124b toward the first claw portion 121. The retaining screw 125 is designed so that the distance between the end (tip) of the retaining screw 125 on the side of the first claw portion 121 and the first claw portion 121 in the horizontal direction Dh can be adjusted. Either the reactor core vessel 40 or the heat shield 50 is clamped between the tip of the retaining screw 125 and the first claw portion 121. The eyebolt 123 is provided at the upper end of the first claw portion 121. By attaching a hook or wire to the eyebolt 123, the lifting jig 120 itself is lifted upward.

[0048] In the lower dismantling process, the lower part of the lower core structure 6 is dismantled. More specifically, in the upper dismantling process, the lower assembly 155 is dismantled. In this embodiment, the lower assembly 155 is dismantled from the top down. In the lower dismantling process, the lower horizontal cutting process (step S21) is performed. As shown in Figure 14, in the upper horizontal cutting process, the first cutting device 111 horizontally cuts the lower assembly 155. In Figure 14, the cutting line L20 from the lower horizontal cutting process and the cutting line L21 from the lower vertical cutting process, which will be described later, are shown by dashed lines. In the lower dismantling process, the lower assembly 155 is lifted upward by the lifting jig 120 shown in Figure 13 and horizontally cut. In the lower horizontal cutting process, the lower assembly 155 is horizontally cut at a vertical position Dv different from that of the former plate 61.

[0049] Following the lower horizontal cutting process, a lower vertical cutting process (step S22) is performed. In the lower vertical cutting process, a portion of the lower assembly 155 that was horizontally cut in the lower horizontal cutting process is moved to the second cutting device 112. At this time, the lower assembly 155 that was horizontally cut is moved while being lifted by the lifting jig 120, which holds the core vessel 40 and the heat shield 50. Then, as shown in Figure 15, the lower assembly 155 is further vertically cut by the second cutting device 112. In Figure 15, the cutting line L21 from the lower vertical cutting process is shown as a dashed line. In the lower vertical cutting process, a portion of the lower assembly 155 that is lifted by multiple lifting jigs 120 is vertically cut between the multiple lifting jigs 120.

[0050] Furthermore, the lower vertical cutting process consists of a first lower vertical cutting process and a second lower vertical cutting process. In Figure 7, the cutting line L21 (first cutting line L22) from the first lower vertical cutting process is shown as a dashed line, and the cutting line L21 (second cutting line L23) from the second lower vertical cutting process is shown as a dashed line. As shown in Figure 7, in the first lower vertical cutting process, the lower assembly 155 is vertically cut by a cutting line L21 (first cutting line L22) that passes through at least one of the two baffle plates 60 connected by connecting bolts 62, while avoiding the connecting bolts 62 and the fixing bolts 63. In this embodiment, the first cutting line L22 is set to avoid the second fixing bolt 64.

[0051] In the second lower vertical cutting step, the lower assembly 155 is vertically cut by a cutting line L21 (second cutting line L23) that passes over at least one of the two baffle plates 60, each having a contact end 60a that abuts against it without the connecting bolt 62, on the opposite side of the fixing bolt 63 from the contact end 60a, while avoiding the connecting bolt 62 and the fixing bolt 63. In this embodiment, the second cutting line L23 is set to avoid the second fixing bolt 64.

[0052] In this way, the lower assembly 155 is divided into multiple parts, forming small cut pieces 156. These cut pieces 156 of the lower assembly 155 are each stored in a waste storage container 114. In this embodiment, each time a cut piece 156 is cut out, an additional lifting jig 120 is installed in the part corresponding to the cut piece 156, and the piece is vertically cut along a cutting line L21 that encloses the newly added jig 120.

[0053] After the lower vertical cutting process, it is determined whether or not the dismantling of the lower assembly 155 is complete (step S23). If the dismantling of the lower assembly 155 is not complete (step S23; NO), the process returns to the upper horizontal cutting process, and steps S21 to S22 described above are repeated. In this embodiment, while the lower vertical cutting process is being performed in the second cutting device 112, the lower horizontal cutting process is being performed in the first cutting device 111.

[0054] If the dismantling of the lower assembly 155 is complete (step S23; YES), the flow ends.

[0055] After following the above steps, the dismantling of the portion of the lower core structure 6 above the lower core support plate 9 is completed. Note that the dismantling procedure described above is merely an example. Therefore, the procedure for dismantling the lower core structure 6 can be modified as appropriate.

[0056] (Effects and Benefits) The method for dismantling the lower core structure 6 according to this embodiment includes a division step of horizontally cutting the core vessel 40 in a range below the pipe supports 44 and above the heat shield 50.

[0057] With the above configuration, the baffle plates 60, former plates 61, and heat shields 50 are installed in the core vessel 40, and the parts of the core vessel 40 that have a complex structure can be separated. This makes it possible to dismantle the upper part of the core vessel 40, which has a simple structure, and the lower part of the core vessel 40, which has a complex structure, using methods appropriate to each. Thus, the dismantling efficiency of the lower core structure 6 can be improved.

[0058] In this embodiment, during the splitting process, the reactor core 40 is horizontally cut in a range below the tube holder 44 and above the irradiation test specimen guide tube 7.

[0059] With the above configuration, the reactor core vessel 40 can be horizontally cut without cutting the irradiation test specimen guide tube 7 during the splitting process. This makes it easier to cut the reactor core vessel 40 during the splitting process. As a result, the efficiency of dismantling the lower reactor core structure 6 can be further improved.

[0060] In this embodiment, during the splitting process, the portion of the core vessel 40 that is formed to be thinner than the portion where the tube supports 44 are provided is horizontally cut.

[0061] The above configuration facilitates the cutting of the core vessel 40 during the dismantling process. This makes the dismantling process easier, and thus further improves the efficiency of dismantling the lower core structure 6.

[0062] The method for dismantling the lower core structure 6 according to this embodiment includes a lower dismantling step for dismantling the lower assembly 155. The lower dismantling step includes a step of vertically cutting the lower assembly 155 with a cutting line L21 that passes through at least one of the two baffle plates 60 connected by connecting bolts 62, while avoiding the connecting bolts 62 and the fixing bolts 63. The lower dismantling step includes a step of vertically cutting the lower assembly 155 with a cutting line L21 that passes through at least one of the two baffle plates 60 having contact ends 60a that abut without the connecting bolts 62, at a position opposite to the contact end 60a with the fixing bolts 63 in between, while avoiding the connecting bolts 62 and the fixing bolts 63.

[0063] With the above configuration, the lower assembly 155 can be cut vertically while avoiding the connecting bolts 62 and fixing bolts 63. Therefore, it is possible to avoid the generation of fragments of the connecting bolts 62 and fixing bolts 63 during vertical cutting and the falling of these fragments. In addition, for the two baffle plates 60 that come into contact without the connecting bolts 62, it is possible to avoid the generation of fragments of their contact ends 60a and the falling of these fragments. Thus, it is possible to reduce the amount of falling debris generated when dismantling the lower core structure 6.

[0064] In this embodiment, the lower dismantling step includes the step of horizontally cutting the lower assembly 155 at a vertical Dv position different from that of the former plate 61.

[0065] With the above configuration, the lower assembly 155 can be cut horizontally while avoiding the former plate 61. This makes horizontal cutting of the lower assembly 155 easier. Therefore, the dismantling efficiency of the lower core structure 6 can be further improved.

[0066] The method for dismantling the lower core structure 6 according to this embodiment involves cutting the lower assembly 155 using a lifting jig 120 capable of lifting the lower assembly 155. The lifting jig 120 has a first claw portion 121 and two second claw portions 122. The first claw portion 121 extends in the vertical direction Dv and is insertable between the core vessel 40 and the heat shield 50. The two second claw portions 122 are provided to sandwich the first claw portion 121 in the horizontal direction Dh. One of the two second claw portions 122 and the first claw portion 121 are capable of sandwiching the core vessel 40 in the horizontal direction Dh. The other of the two second claw portions 122 and the first claw portion 121 are capable of sandwiching the heat shield 50 in the horizontal direction Dh. The lower dismantling process includes the step of lifting the horizontally cut lower assembly 155 while holding the core vessel 40 and the heat shield 50 with a lifting jig 120.

[0067] With the above configuration, even if the fixing between the core vessel 40 and the heat shield 50 is released during the dismantling of the lower core structure 6, the suspension jig 113 can hold the core vessel 40 and the heat shield 50 together. Therefore, the lower assembly 155 can be easily cut. In addition, the transport of the lower assembly 155 becomes easier. Therefore, the dismantling efficiency of the lower core structure 6 can be further improved.

[0068] In this embodiment, the lower dismantling step includes the step of vertically cutting the lower assembly 155, which is lifted by a plurality of lifting jigs 120, along a cutting line L21 that straddles one of the lifting jigs 120.

[0069] With the above configuration, the cut pieces 150 and 156 of the lower assembly 155, which are generated by vertical cutting, can be securely held by either one of the suspension jigs 113. Therefore, the falling of the cut pieces 150 and 156 can be prevented. In other words, the amount of falling material generated during the dismantling of the lower core structure 6 can be reduced. Therefore, the dismantling efficiency of the lower core structure 6 can be further improved.

[0070] (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.

[0071] In the above embodiment, the heat shield 50 is provided around the entire circumference of the core vessel 40, but this is not the only possible configuration. For example, multiple heat shields 50 may be provided partially around the core vessel 40. In this case, for example, the upper end of the irradiation test specimen guide tube 7 does not protrude above the heat shield 50, but even in such a case, the method for dismantling the lower core structure 6 of this embodiment is applicable. For example, in the division process, the core vessel 40 is horizontally cut along a cutting line L12 that is below the tube holder 44, above the heat shield 50, and passes through the thin-walled portion 47 of the core vessel 40.

[0072] In the above embodiment, the case in which the first cutting device 111 cuts the lower core structure 6 in the horizontal direction Dh and the second cutting device 112 cuts the lower core structure 6 in the vertical direction was described, but the invention is not limited to this. A single cutting device in which the first cutting device 111 and the second cutting device 112 are integrated may be capable of cutting the lower core structure 6 in the horizontal direction Dh and the vertical direction Dv.

[0073] In the above embodiment, the case in which the first cutting device 111 is a rail-type cutting device using a wire saw 111b and the second cutting device 112 is a gantry-type cutting device was described, but the invention is not limited to this. The first cutting device 111 and the second cutting device 112 can be changed as appropriate. Furthermore, although a turntable 110 was given as an example of a mounting platform for the lower core structure 6, it is also possible to use a simple frame as a mounting platform for the lower core structure 6 by applying a cutting device that can move in the horizontal direction. In addition, although jig 113 and lifting jig 120 were given as examples of jigs for lifting the lower core structure 6, other lifting jigs can also be applied.

[0074] In the above embodiment, the case in which the lower dismantling process is performed after the upper dismantling process has been described, but the embodiment is not limited to this. For example, first, the lower core structure 6 may be divided vertically Dv by a division process, and then the upper dismantling process and the lower dismantling process may be performed simultaneously. Alternatively, the upper dismantling process may be performed after the lower dismantling process.

[0075] In the upper dismantling process, the upper horizontal cutting process was described in which an annular member is cut out from the upper core vessel 41, and then the upper vertical cutting process further cuts the annular member cut out from the upper core vessel 41 in the vertical direction Dv to form the cut pieces 150. However, the process is not limited to this. The upper horizontal cutting process and the lower horizontal cutting process may be performed almost simultaneously, and the cut pieces 150 may be cut out one by one. Alternatively, the upper horizontal cutting process may be performed after the upper vertical cutting process.

[0076] In the lower dismantling process, the case described above involves cutting out an annular member from the lower assembly 155 in the lower horizontal cutting process, and then further cutting the annular member cut out from the lower assembly 155 in the vertical direction Dv in the lower vertical cutting process to form a cut piece 156. However, the process is not limited to this. The lower horizontal cutting process and the lower vertical cutting process may be performed almost simultaneously, and the cut pieces 156 may be cut out one by one. Alternatively, the lower horizontal cutting process may be performed after the lower vertical cutting process.

[0077] <Note> The method for dismantling the lower core structure 6 described in each embodiment can be understood, for example, as follows.

[0078] (1) A method for dismantling a lower core structure 6 according to the first embodiment is a method for dismantling a lower core structure 6, wherein the lower core structure 6 comprises a core vessel 40 having a cylindrical shape extending vertically and having a pipe support 44 that penetrates the inside and outside at its upper part, a heat shield 50 covering the portion of the core vessel 40 below the pipe support 44 from the outer circumference, and a baffle plate 60 and a former plate 61 provided inside the core vessel 40 at a vertical position Dv where the heat shield 50 is provided, and includes a division step of horizontally cutting the core vessel 40 in the range below the pipe support 44 and above the heat shield 50.

[0079] With the above configuration, the baffle plates 60, former plates 61, and heat shields 50 are installed in the core vessel 40, and the parts of the core vessel 40 that have a complex structure can be separated. This makes it possible to dismantle the upper part of the core vessel 40, which has a simple structure, and the lower part of the core vessel 40, which has a complex structure, using methods appropriate for each.

[0080] (2) The method for dismantling the lower core structure 6 according to the second embodiment is the method for dismantling the lower core structure 6 according to (1), wherein the lower core structure 6 has an irradiation test piece guide tube 7 provided on the outer circumference of the core vessel 40, the upper end of the irradiation test piece guide tube 7 protrudes above the heat shield 50, and in the division step, the core vessel 40 is horizontally cut in the range below the tube stand 44 in the core vessel 40 and above the irradiation test piece guide tube 7.

[0081] With the above configuration, the reactor core vessel 40 can be horizontally cut without cutting the irradiation test specimen guide tube 7 during the splitting process. This makes it easier to cut the reactor core vessel 40 during the splitting process.

[0082] (3) The third embodiment of the method for dismantling the lower core structure 6 is the method for dismantling the lower core structure 6 according to (1) or (2), wherein in the division step, the portion of the core vessel 40 that is formed to be thinner than the portion where the pipe supports 44 are provided is horizontally cut.

[0083] The above configuration facilitates the cutting of the core vessel 40 during the splitting process. Therefore, the splitting process can be carried out simply.

[0084] (4) A fourth embodiment of the method for dismantling the lower core structure 6 is any of the methods for dismantling the lower core structure 6 described in (1) to (3), wherein the baffle plates 60 extend in the vertical direction Dv and are provided in a plurality in an annular shape along the inner circumferential surface of the core vessel 40, the former plate 61 is formed in an annular shape so as to cover the plurality of baffle plates 60 from the outer circumferential side and extends in the horizontal direction Dh, the lower core structure 6 has connecting bolts 62 that connect some of the adjacent baffle plates 60 among the plurality of baffle plates 60 and fixing bolts 63 that fix each baffle plate 60 to the former plate 61, and the portion of the core vessel 40 located below the cutting line L12 by the division process, and the heat shield 50 The process includes a lower dismantling step of dismantling a lower assembly 155 which is an assembly of the baffle plate 60 and the former plate 61, the lower dismantling step of vertically cutting the lower assembly 155 with a cutting line L21 that passes through at least one of the two baffle plates 60 connected by the connecting bolt 62 and avoids the connecting bolt 62 and the fixing bolt 63, and the lower assembly vertically cutting with a cutting line L21 that passes through at least one of the two baffle plates 60 which have contact ends 60a that abut without the connecting bolt 62, at a position opposite to the contact end 60a with the fixing bolt 63 in between, and avoids the connecting bolt 62 and the fixing bolt 63.

[0085] With the above configuration, the lower assembly 155 can be cut vertically while avoiding the connecting bolts 62 and fixing bolts 63. Therefore, it is possible to avoid the generation of fragments of the connecting bolts 62 and fixing bolts 63 during vertical cutting and the falling of these fragments. In addition, for the two baffle plates 60 that come into contact without the connecting bolts 62, it is possible to avoid the generation of fragments of their contact ends 60a and the falling of these fragments.

[0086] (5) The method for dismantling the lower core structure 6 according to the fifth embodiment is the method for dismantling the lower core structure 6 according to (4), wherein the lower dismantling step includes a step of horizontally cutting the lower assembly 155 at a vertical Dv position different from that of the former plate 61.

[0087] With the above configuration, the lower assembly 155 can be cut horizontally while avoiding the former plate 61.

[0088] (6) A sixth method for dismantling the lower core structure 6 is the method for dismantling the lower core structure 6 of (5), wherein the lower assembly 155 is cut using a lifting jig 120 capable of lifting the lower assembly 155, the lifting jig 120 having a first claw portion 121 that extends in the vertical direction Dv and can be inserted between the core tank 40 and the heat shield 50, and two portions provided to sandwich the first claw portion 121 in the horizontal direction Dh The first claw portion 121 has two second claw portions 122, and one of the two second claw portions 122 and the first claw portion 121 are capable of gripping the reactor core 40 in the horizontal direction Dh, and the other of the two second claw portions 122 and the first claw portion 121 are capable of gripping the heat shield 50 in the horizontal direction Dh, and the lower dismantling process includes the step of lifting the horizontally cut lower assembly 155 with the lifting jig 120 while holding the reactor core 40 and the heat shield 50.

[0089] With the above configuration, even if the core vessel 40 and the heat shield 50 are released from their fixed position during the dismantling of the lower core structure 6, the suspension jig 113 can hold the core vessel 40 and the heat shield 50 together. Therefore, the lower assembly 155 can be easily cut.

[0090] (7) A method for dismantling the lower core structure 6 according to the seventh embodiment is the method for dismantling the lower core structure 6 according to (6), wherein the lower dismantling step includes a step of vertically cutting the lower assembly 155, which is lifted by a plurality of lifting jigs 120, with a cutting line L21 that sandwiches one of the lifting jigs 120.

[0091] With the above configuration, the cut pieces 156 of the lower assembly 155, which are produced by vertical cutting, can be securely held by any one of the suspension jigs 120. Therefore, the cut pieces 120 can be prevented from falling.

[0092] (8) The eighth embodiment of the method for dismantling the lower core structure 6 is a method for dismantling the lower core structure 6, wherein the lower core structure 6 comprises a cylindrical core vessel 40 extending vertically, a heat shield 50 covering the core vessel 40 from the outer circumferential side, and baffle plates 60 and former plates 61 provided inside the core vessel 40 at a vertical position Dv where the heat shield 50 is provided, wherein the baffle plates 60 extend in the vertical direction Dv and are provided in multiple rings along the inner circumferential surface of the core vessel 40, the former plates 61 are formed in a ring shape so as to cover the multiple baffle plates 60 from the outer circumferential side and extend in the horizontal direction Dh, and the lower core structure 6 comprises connecting bolts 62 that connect some of the adjacent baffle plates 60 among the multiple baffle plates 60 and fixing each baffle plate 60 to the former plate 61 The lower assembly 155, which is an assembly of the core vessel 40, the heat shield 50, the baffle plate 60, and the former plate 61, includes a lower dismantling step of dismantling the lower assembly 155, which has fixing bolts 63, and includes a step of vertically cutting the lower assembly 155 with a cutting line L21 that passes through at least one of the two baffle plates 60 connected by the connecting bolts 62 and avoids the connecting bolts 62 and the fixing bolts 63, and a step of vertically cutting the lower assembly 155 with a cutting line L21 that passes through at least one of the two baffle plates 60 which have contact ends 60a that abut without the connecting bolts 62, on the opposite side of the fixing bolts 63 from the contact ends 60a, and avoids the connecting bolts 62 and the fixing bolts 63. [Explanation of symbols]

[0093] 1 Pressurized water reactor 2 Reactor vessel 5. Upper core structure 6. Lower core structure 7. Irradiation test specimen guide tube 8 Lower core plate 9. Lower core support plate 10 Lower core support column 11 Current plate 12 Lower instrumentation guide tube 13 Connecting plate 15. Core 20 Reactor vessel body 21 Reactor vessel lid 22 Inlet nozzle 23 Outlet nozzle 30 Upper core plate 31 Upper core support plate 32 Upper core support columns 33 Guide Tubes 40 reactor core tank 41 Upper reactor core tank 42 Lower core tank 43 Upper core vessel body 44 pipe stand 45 Lower core tank body 46 Tank side backing plate 47 Thin-walled section 50 Heat shield 51 Heat shield body 52 Heat shield side backing plate 53 volts 54 Flexible metal 60 baffle board 60a Contact end 61 Forma plate 62 Connecting bolts 63 Fixing bolts 64 Second fixing bolt 100 reactor cavities 101 Lower Cavity 102 Cavity floor 103 Installation hole 110 Turntable 111 1st cutting device 111a Rail 111b Wire saw 112 Second cutting device 113 Jig 114 Waste storage containers 120 Lifting jig 121 1st claw part 122 2nd claw part 123 Eyebolt 124 Second claw body 124a Part 1 124b Part 2 125 Set screw 150 Cut piece 155 Lower aggregate 156 Cut piece Dv vertical direction Dh horizontal direction L10 cutting line L11 cutting line L12 cutting line L20 cutting line L21 cutting line L22 1st cutting line L23 2nd cutting line O axis

Claims

1. A method for dismantling the lower core structure, The aforementioned lower core structure is A core vessel with a cylindrical tube extending vertically and penetrating the inside and outside, located at the top, A heat shield covering the portion of the core vessel below the tube support from the outer periphery, A baffle plate and a former plate are provided on the inside of the reactor core vessel at a vertical position where the heat shield is provided, It has, This includes a division step of horizontally cutting the core vessel in a range below the tube holder and above the heat shield, Method for dismantling the lower core structure.

2. The aforementioned lower core structure is The reactor core vessel has an irradiation test specimen guide tube provided on its outer circumference, The upper end of the irradiation test specimen guide tube protrudes above the heat shield, In the division step, the reactor core is horizontally cut in a range below the tube holder and above the irradiation test specimen guide tube. A method for dismantling a lower core structure according to claim 1.

3. In the division process, the portion of the reactor core vessel that is formed to be thinner than the portion where the tube support is provided is horizontally cut. A method for dismantling a lower core structure according to claim 1 or 2.

4. The baffle plates extend in the vertical direction and are arranged in a ring shape along the inner circumferential surface of the reactor core vessel. The former plate is formed in an annular shape so as to cover the plurality of baffle plates from the outer periphery and extends in the horizontal direction. The aforementioned lower core structure is A connecting bolt that connects some of the adjacent baffle plates among the multiple baffle plates, Each of the baffle plates is fixed to the former plate by a fixing bolt, It has, The lower dismantling process includes dismantling the portion of the reactor core vessel located below the cutting line made by the division process, and the lower assembly which is an assembly of the heat shield, the baffle plate, and the former plate. The aforementioned lower dismantling process is, A step of vertically cutting the lower assembly with a cutting line that passes through at least one of the two baffle plates connected by the connecting bolts, and avoids the connecting bolts and the fixing bolts, A step of vertically cutting the lower assembly with a cutting line that avoids the connecting bolt and the fixing bolt, passing through at least one of the two baffle plates, which have contact ends that abut against each other without the connecting bolt, on the opposite side of the fixing bolt from the contact end, including, A method for dismantling a lower core structure according to claim 1 or 2.

5. The aforementioned lower dismantling process is, The process includes horizontally cutting the lower assembly at a vertical position different from that of the former plate, The method for dismantling the lower core structure according to claim 4.

6. A method for dismantling a lower core structure, comprising cutting the lower assembly using a lifting jig capable of lifting the lower assembly, The aforementioned lifting jig is, A first claw portion extends in the vertical direction and is insertable between the reactor core vessel and the heat shield, Two second claw portions are provided to sandwich the first claw portion in the horizontal direction, It has, One of the two second claw portions and the first claw portion are configured to grip the reactor core vessel horizontally. The other of the two second claws and the first claw are configured to horizontally clamp the heat shield, The lower dismantling process includes the step of lifting the horizontally cut lower assembly while holding the core vessel and the heat shield with the lifting jig. The method for dismantling the lower core structure according to claim 5.

7. The aforementioned lower dismantling process is, The process includes vertically cutting the lower assembly, which is lifted by multiple lifting jigs, along a cutting line that straddles one of the lifting jigs. The method for dismantling the lower core structure according to claim 6.

8. A method for dismantling the lower core structure, The aforementioned lower core structure is A cylindrical core vessel extending vertically, A heat shield covering the reactor core vessel from the outer periphery, A baffle plate and a former plate are provided on the inside of the reactor core vessel at a vertical position where the heat shield is provided, It has, The baffle plates extend in the vertical direction and are arranged in a ring shape along the inner circumferential surface of the reactor core vessel. The former plate is formed in an annular shape so as to cover the plurality of baffle plates from the outer periphery and extends in the horizontal direction. The aforementioned lower core structure is A connecting bolt that connects some of the adjacent baffle plates among the multiple baffle plates, Each of the baffle plates is fixed to the former plate by a fixing bolt, It has, This includes a lower dismantling step of dismantling the core vessel and the lower assembly which is an assembly of the heat shield, the baffle plate and the former plate, The aforementioned lower dismantling process is, A step of vertically cutting the lower assembly with a cutting line that passes through at least one of the two baffle plates connected by the connecting bolts, and avoids the connecting bolts and the fixing bolts, A step of vertically cutting the lower assembly with a cutting line that avoids the connecting bolt and the fixing bolt, passing through at least one of the two baffle plates, which have contact ends that abut against each other without the connecting bolt, on the opposite side of the fixing bolt from the contact end, including, Method for dismantling the lower core structure.

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