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 cylindrical core vessel extending vertically and a heat shield covering the core vessel from the outer periphery, and the method for dismantling a lower core structure includes the steps of cutting the heat shield horizontally and vertically and sequentially removing it as a plurality of cut pieces, and after the heat shield has been removed, cutting the core vessel horizontally.

Description

Technical Field

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[0001] The present disclosure relates to a method for disassembling a lower reactor 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. <_{0000010}>

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, a nuclear reactor has many members with a high radiation dose (dose), including the in-vessel structures that are internal structures. Therefore, when disassembling a nuclear reactor, handling members with a high dose results in many restrictions on the working time and working location. Among the in-vessel structures, a thermal shield that covers the outer surface of the reactor core vessel is provided in the lower reactor core structure located at the lower part inside the reactor vessel. This thermal shield is installed at an interval from the reactor core vessel. For this reason, it has been difficult to horizontally cut the reactor core vessel and the thermal shield integrally. Thus, there are circumstances where the disassembly work of the lower reactor core structure cannot be smoothly advanced, and further improvement in the efficiency of the disassembly work has been demanded.

[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 reactor core structure that can improve the disassembly efficiency of the lower reactor 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 cylindrical core vessel extending vertically and a heat shield covering the core vessel from the outer periphery, and includes the steps of cutting the heat shield horizontally and vertically and sequentially removing it as a plurality of cut pieces, and after the heat shield has been removed, cutting the core vessel horizontally. Furthermore, in the step of removing the heat shield, the heat shield is sequentially cut and removed from above, and the step of removing the heat shield includes the steps of horizontally cutting the heat shield while the heat shield is suspended by a jig, and after the step of horizontally cutting the heat shield, vertically cutting the heat shield which is suspended by the jig to cut out a plurality of the cut pieces, in the step of cutting out a plurality of the cut pieces, each of the cut pieces is cut by vertically cutting the heat shield along a cutting line that straddles one of the jigs. . [Effects of the Invention]

[0007] 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]

[0008] [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 an example of equipment for dismantling the lower core structure according to the embodiment of this disclosure. [Figure 6] 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 7] This flowchart shows an example of a method for dismantling a lower core structure according to the present disclosure. [Figure 8] This is a schematic diagram illustrating the process of cutting the upper core vessel according to the embodiment of this disclosure. [Figure 9] This is a schematic diagram illustrating the process of cutting and removing a heat shield according to an embodiment of the present disclosure. [Figure 10]This is a schematic diagram illustrating the process of cutting and removing a heat shield according to an embodiment of the present disclosure. [Figure 11] This is a schematic diagram illustrating the process of cutting the lower core vessel according to the embodiment of this disclosure. [Figure 12] This flowchart shows an example of a method for dismantling a lower core structure according to the first modified example of this disclosure. [Figure 13] This flowchart shows an example of a method for dismantling a lower core structure according to the second modification of this disclosure. [Figure 14] This flowchart shows an example of a method for dismantling a lower core structure according to the third modified example of this disclosure. [Modes for carrying out the invention]

[0009] The following describes an embodiment for implementing the method for dismantling the lower core structure 6 according to this disclosure, with reference to the attached drawings. However, this disclosure is not limited to this embodiment.

[0010] <Embodiment> (nuclear reactor) Figure 1 is a longitudinal cross-sectional view showing a pressurized water reactor 1, which is the reactor to be dismantled according to this embodiment. Figure 1 schematically illustrates the general configuration of the pressurized water reactor 1. It is a pressurized water reactor 1 (PWR) that uses light water as the reactor coolant and neutron moderator to create high-temperature, high-pressure water that does not boil throughout the entire core 15, 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. The pressurized water reactor 1 is located in a reactor cavity 100. The reactor cavity 100 is a space capable of storing cooling water (water), and a lower cavity 101 is formed therein where the lower core structure 6, which will be described later, can be temporarily placed. In the following description of the embodiment, the vertical direction Dv is assumed to coincide with the vertical direction.

[0011] 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.

[0012] (Reactor vessel) The reactor vessel 2 has a reactor vessel main body 20 and a reactor vessel head 21 so that an in-vessel structure can be inserted therein. The reactor vessel 2 is disposed inside an installation hole 103 formed 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 head 21) protrudes from the cavity floor surface 102 of the lower cavity 101.

[0013] The upper part of the reactor vessel main body 20 can be opened by removing the reactor vessel head 21. The lower part of the reactor vessel main body 20 has a cylindrical shape closed by a lower mirror having a hemispherical shape. An inlet nozzle 22 for supplying light water (coolant) as primary cooling water (water) and an outlet nozzle 23 for discharging the light water are formed in the upper part of the reactor vessel main body 20. Further, a water injection nozzle (not shown) is formed in the reactor vessel main body 20 separately from the inlet nozzle 22 and the outlet nozzle 23.

[0014] The reactor vessel head 21 is attached to the upper part of the reactor vessel main body 20. The reactor vessel head 21 is fixedly attached to the reactor vessel main body 20 so as to be openable and closable by a plurality of stud bolts and nuts (not shown).

[0015] (Upper core structure) The upper core structure 5 is located inside the reactor vessel 2. The upper core structure 5 can be removed from the reactor vessel body 20 by moving it upward in the vertical direction Dv relative to the reactor vessel body 20. The upper core structure 5 in this 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 arranged opposite each other in the vertical direction Dv. The upper core support plate 31 is located near the opening at the upper end of the reactor vessel body 20 and is positioned 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. Furthermore, the upper core structure 5 does not consist solely of the structure described above. The upper core structure 5 also has other components, not shown in the diagram, such as water level gauge support tubes, mixers, thermocouple lead-out tubes, and reinforcing beams.

[0016] (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.

[0017] (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.

[0018] 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.

[0019] The upper core vessel 41 constitutes the upper portion of the core vessel 40. The upper core structure 5 is housed within the upper core vessel 41 (see Figure 1). The upper core vessel 41 comprises the 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. The tube support 44 penetrates radially through the inside and outside of the upper core vessel 41. In the illustrated example, two tube supports 44 are provided spaced apart in the circumferential direction.

[0020] 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.

[0021] (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).

[0022] The thermal shield body 51 is formed in a cylindrical shape extending in the vertical direction Dv. The thermal shield body 51 is provided with a radial gap between it and the outer surface of the lower core vessel 42 over its entire circumference in the circumferential direction. The thermal shield body 51 is provided so as 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.

[0023] 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. That is, the heat shield side backing plates 52 are placed on the core tank 40. The load of the heat shield 50 is supported by the heat shield side backing plates 52 on the core tank 40. Bolts 53 are inserted through the heat shield side backing plates 52 from the radially outer side of the heat shield 50. The thermal shield 50 is fixed to the reactor core 40 at the portion of the thermal shield side backing plate 52 by these bolts 53. The lower end of the thermal shield 50 is connected to a flexible metal 54 that extends radially outward from the reactor core 40. Multiple flexible metals 54 are provided in the circumferential direction. A structure such as a bracing rod may also be provided between the lower end of the thermal shield 50 and the reactor core 40.

[0024] (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. 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.

[0025] (Forma board) The former plate 61 is installed inside the lower core vessel 42 at a vertical position Dv where the heat shield 50 is provided. The former plate 61 is formed in an annular shape so as to cover 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. The former plate 61 is fixed to the inner surface of the core vessel 40 by bolts (not shown). In addition, the baffle plates 60 are fixed to the inner edge of the former plate 61 by bolts (not shown).

[0026] (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.

[0027] (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.

[0028] 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.

[0029] (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 core vessel 40 and the heat shield 50 of the lower core structure 6 will be described.

[0030] The dismantling of this lower core structure 6 is carried out, for example, inside the reactor cavity 100 shown in Figures 5 and 6. Inside the reactor cavity 100, there are a turntable 110, a cutting device 111, a waste storage container 114, and the like.

[0031] 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.

[0032] The cutting device 111 is capable of cutting the lower core structure 6 in the horizontal direction Dh and the vertical direction Dv. The cutting device 111 is installed near the turntable 110. An example of the cutting device 111 is a tower-type cutting device. The cutting device 111 has a base 111a, a tower 111b, a first disc saw 111c, and a second disc saw 111d. The base 111a is placed on the cavity floor surface 102. In the illustrated example, the turntable 110 is placed on the base 111a. The tower 111b extends upward from the base 111a.

[0033] The first disc saw 111c is a disc saw capable of horizontally cutting the lower core structure 6. Horizontal cutting means cutting the object to be cut in the horizontal direction Dh. The first disc saw 111c is mounted on the tower 111b. The first disc saw 111c is designed to be movable vertically Dv along the tower 111b and rotatable horizontally Dh around the tower 111b. The second disc saw 111d is a disc saw capable of vertically cutting the lower core structure 6. Vertical cutting means cutting the object to be cut in the vertical direction Dv. The second disc saw 111d is mounted on the tower 111b. The second disc saw 111d is designed to be movable vertically Dv along the tower 111b and rotatable horizontally Dh around the tower 111b. By rotating the lower core structure 6 using the turntable 110 while operating the cutting device 111, the entire lower core structure 6 can be efficiently cut.

[0034] 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.

[0035] 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.

[0036] Next, referring to the flowchart in Figure 7, an example of the procedure for dismantling the lower core structure 6 will be described. It should be assumed that, in this case, all parts of the pressurized water reactor 1 other than the lower core structure 6 have been removed beforehand. That is, the upper core structure 5 and fuel assemblies have been removed from the core tank 40 beforehand.

[0037] First, the upper core vessel 41 is cut (step S11). In other words, step S11 is the process of cutting the upper part of the heat shield 50 in the core vessel 40. In step S11, the entire upper core vessel 41 does not have to be cut. Also, the upper end of the lower core vessel 42 may be cut along with the upper core vessel 41.

[0038] The process of cutting the upper core vessel 41 includes a step of horizontally cutting the upper core vessel 41 (step S11a) and a step of vertically cutting the upper core vessel 41 (step S11b). In step S11a, for example as shown in Figure 8, the upper core vessel 41 is cut horizontally in the direction Dh by a first disc saw 111c. Figure 8 shows an example of the cutting line L10 in step S11a. In step S11b, for example, the upper core vessel 41 is cut vertically by a second disc saw 111d. Figure 8 shows an example of the cutting line L11 in step S11b. The cut pieces of the upper core vessel 41 generated in the process of cutting the upper core vessel 41 are stored in a waste storage container 114. The order of the steps of horizontally cutting the upper core vessel 41 and vertically cutting the upper core vessel 41 can be changed as appropriate. Alternatively, in step S11, only the process of horizontally cutting the upper core vessel 41 may be performed.

[0039] Subsequently, the heat shield 50 is sequentially cut and removed from the top (step S12). In step S12, as shown in Figure 9, support members 115 are installed below the heat shield 50. Multiple support members 115 are installed circumferentially to surround the lower core structure 6. The multiple support members 115 are positioned circumferentially offset from the multiple bending members 54. Each support member 115 is in contact with the lower end of the heat shield 50. The multiple support members 115 support the load of the heat shield 50.

[0040] In this embodiment, the step of removing the heat shield 50 (step S12) includes the step of cutting the heat shield 50 horizontally (step S12a) and the step of cutting the heat shield 50 vertically (step S12b).

[0041] First, a step (step S12a) is performed to horizontally cut the heat shield 50. In this step, the upper end of the heat shield 50 is suspended by a plurality of jigs 113, and the upper end of the heat shield 50 is horizontally cut by the first disc saw 111c. Figure 9 shows the cutting line L20 of step S12a.

[0042] After step S12a, a step (step S12b) is performed to vertically cut the heat shield 50. In the step of vertically cutting the heat shield 50, as shown in Figure 10, the cutting pieces 120, which are lifted by a plurality of jigs 113, are vertically cut by the second disc saw 111d. Figures 9 and 10 illustrate the cutting line L21 in step S12b. For example, in step S12b, the heat shield 50 is vertically cut along the cutting line L21 that passes between the jigs 113. In this way, the heat shield 50 is sequentially removed from the core vessel 40 as a plurality of cutting pieces 121. The removed cutting pieces 121 of the heat shield 50 are stored in the waste storage container 114. In this embodiment, the heat shield 50 is removed all the way to the lower end in a single step S12. In this embodiment, each time a cutting piece 121 is cut out, an additional lifting jig 113 is installed on the part corresponding to the cutting piece 121, and the piece is vertically cut along a cutting line L21 that sandwiches the newly added jig 113.

[0043] The order of the steps for horizontally cutting the heat shield 50 and vertically cutting the heat shield 50 can be changed as appropriate. Also, in step S12, the portion of the heat shield 50 including the heat shield side backing plate 52 may be cut after, for example, the fixing of the heat shield 50 by the bolts 53 is released, or it may be left in the core vessel 40 in step S12 and cut together with the core vessel 40 in a later step.

[0044] After the heat shield 50 is removed down to its lower end in step S12, a step of cutting the lower core vessel 42 is performed (step S13). In other words, step S13 is the process of cutting the portion of the core vessel 40 that has been exposed after the heat shield 50 has been removed. The lower core vessel 42 is cut sequentially from the top.

[0045] The process of cutting the lower core vessel 42 includes a step of horizontally cutting the lower core vessel 42 (step S13a) and a step of vertically cutting the lower core vessel 42 (step S13b). In step S13a, for example as shown in Figure 11, the lower core vessel 42 is cut horizontally in the direction Dh by a first disc saw 111c. Figure 11 shows an example of the cutting line L30 in step S13a. In step S13b, for example, the lower core vessel 42 is cut vertically by a second disc saw 111d. Figure 11 shows an example of the cutting line L31 in step S13b. The cut pieces of the lower core vessel 42 generated in the process of cutting the lower core vessel 42 are stored in a waste storage container 114. The order of the steps of horizontally cutting the lower core vessel 42 and vertically cutting the lower core vessel 42 can be changed as appropriate. Alternatively, in step S13, only the process of horizontally cutting the lower core vessel 42 may be performed.

[0046] Following the above procedure, the dismantling of the core vessel 40 and the thermal shield 50 of the lower core structure 6 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.

[0047] (Effects and Benefits) The method for dismantling the lower core structure 6 according to this embodiment includes the steps of cutting the heat shield 50 in the horizontal direction Dh and the vertical direction Dv and sequentially removing it as a plurality of cut pieces 121, and cutting the lower core tank 42 horizontally after the heat shield 50 has been removed.

[0048] With the above configuration, the lower core vessel 42 can be horizontally cut after the heat shield 50 has been removed. This allows the lower core vessel 42 to be horizontally cut without considering the effect of the heat shield 50. Therefore, the dismantling efficiency of the lower core structure 6 can be improved.

[0049] In this embodiment, in the step of removing the heat shield 50, the heat shield 50 is sequentially cut and removed from the top.

[0050] The above configuration makes it easy to lift the cut pieces 121 of the heat shield 50 upwards. Therefore, the cut pieces 121 can be smoothly moved to the waste storage container 114 immediately after being cut. Consequently, the efficiency of dismantling the lower core structure 6 can be further improved.

[0051] In this embodiment, after the heat shield 50 has been removed down to its lower end, the lower core vessel 42 is cut.

[0052] With the above configuration, cutting of the lower core vessel 42 can begin after the heat shield 50 has been cut and removed from its upper end to its lower end. In other words, cutting of the lower core vessel 42 can begin after the removal of the heat shield 50 is complete. Therefore, the number of times the cutting target needs to be switched can be reduced, making it possible to dismantle the lower core structure 6 even more efficiently.

[0053] (First variation) Next, a first modified example of the method for dismantling the lower core structure 6 will be described with reference to Figure 12. In this modified example, after the step of cutting the upper core vessel 41 (step S11), the step of cutting and removing the heat shield 50 from above (step S12) is performed. However, in step S12 of this modified example, only a portion of the heat shield 50 is partially removed. After that, the step of cutting the lower core vessel 42 is performed (step S13). In step S13 of this modified example, the portion of the lower core vessel 42 that is exposed after the heat shield 50 has been partially removed is cut. After that, the step of determining whether or not the removal of the heat shield 50 and the lower core vessel 42 has been completed (step S14) is performed. If the removal of the heat shield 50 and the lower core vessel 42 has not been completed (step S14; NO), steps S12 and S13 are performed again. In this way, the steps of removing the heat shield 50 and cutting the lower core vessel 42 are performed alternately. If the removal of the thermal shield 50 is complete (step S14; YES), the dismantling flow of the core vessel 40 and the thermal shield 50 of the lower core structure 6 is completed.

[0054] Thus, in this modified example, after the heat shield 50 is partially removed, the lower core vessel 42 is cut in the process of cutting the lower core vessel 42, in which the portion of the lower core vessel 42 exposed by the removal of the heat shield 50 is cut. The process of removing the heat shield 50 and the process of cutting the lower core vessel 42 are then performed alternately.

[0055] With the above configuration, the lower core structure 6 can be dismantled while progressively shortening its vertical dimension Dv. This makes it easier to handle the lower core structure 6 during dismantling. Therefore, the dismantling efficiency of the lower core structure 6 can be improved.

[0056] (Second variation) Next, a second modified example of the method for dismantling the lower core structure 6 will be described with reference to Figure 13. In this modified example, after the step of cutting the upper core vessel 41 (step S11), a step of cutting and removing the heat shield 50 from below (step S21) is performed. In step S21, the heat shield 50 is sequentially cut and removed from below. The heat shield 50 is supported by the core vessel 40 at the portion of the heat shield side backing plate 52. The step of removing the heat shield 50 (step S21) includes a step of horizontally cutting the heat shield 50 (step S21a) and a step of vertically cutting the heat shield 50 (step S21b). The step of removing the heat shield 50 (step S21) is performed in the same manner as the step of removing the heat shield 50 (step S12) in the embodiment described above.

[0057] Thus, in this modified example, in the step of removing the heat shield 50, the heat shield 50 is sequentially cut and removed from the bottom.

[0058] The heat shield 50 is supported on the reactor core vessel 40 by a heat shield side backing plate 52 provided at its upper end. Therefore, the load of the heat shield 50 is supported by the reactor core vessel 40 at its upper end. For this reason, the removal process of the heat shield 50 can be carried out by sequentially removing the heat shield 50 from below, without having to separately provide a support 115 to support the heat shield 50 below it.

[0059] (Third variation) Next, a third modified example of the method for dismantling the lower core structure 6 will be described with reference to Figure 14. In the embodiments described above and this modified example, the case in which the core vessel 40 is cut in two parts, an upper part located above the heat shield 50 and a lower part on which the heat shield 50 is provided, was described. However, in this modified example, the core vessel 40 is cut all at once after the heat shield 50 has been removed. In this modified example, first, the heat shield 50 is cut from above (step S12). After that, the core vessel 40 is cut (step S31). In this step, the core vessel 40 is cut all at once from the upper core vessel 41 to the lower core vessel 42. The step of cutting the core vessel 40 (step S31) includes the step of cutting the core vessel 40 horizontally (step S31a) and the step of cutting the core vessel 40 vertically (step S31b). The step of cutting the core vessel 40 (step S31) is performed in the same manner as the step of cutting the lower core vessel 42 (step S13) in the embodiment described above. In this modified example, the heat shield 50 may also be cut from below and removed.

[0060] (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.

[0061] In the above embodiment, the cutting device 111 is described as a tower-type cutting device, and the case in which the lower core structure 6 is cut in the horizontal direction Dh and the vertical direction Dv by a single cutting device 111 has been described, but it is not limited to this. For example, the cutting device 111 may be divided into a first rail-type cutting device equipped with a wire saw capable of cutting the lower core structure 6 in the horizontal direction Dh, and a second cutting device equipped with a disc saw capable of cutting the lower core structure 6 in the vertical direction Dv. Also, although a turntable 110 was given as an example of a mounting platform for the lower core structure 6, if a cutting device that can move in the horizontal direction is applied, a simple frame can also be used as a mounting platform for the lower core structure 6. Furthermore, although jig 113 was given as an example of a jig for lifting the lower core structure 6, other lifting jigs can also be applied.

[0062] In the above embodiment, the case in which the heat shield 50 is provided around the entire circumference of the core vessel 40 has been described, but it is not limited to this. For example, the heat shield 50 may be provided only partially on the outer surface of the core vessel 40. That is, multiple heat shields 50 may be provided on the outer surface of the core vessel 40 at intervals in the circumferential direction. Even in such a case, the method for dismantling the lower core structure 6 described above can be applied.

[0063] <Note> The method for dismantling the lower core structure 6 described in each embodiment can be understood, for example, as follows.

[0064] (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 that is cylindrical in shape and extends vertically, and a heat shield 50 that covers the core vessel 40 from the outer periphery, and includes the steps of cutting the heat shield 50 in the horizontal direction Dh and the vertical direction Dv and sequentially removing a plurality of cut pieces 121, and cutting the core vessel 40 horizontally after the heat shield 50 has been removed.

[0065] With the above configuration, the reactor core 40 can be cut horizontally after the heat shield 50 has been removed. This allows the reactor core 40 to be cut horizontally without considering the effect of the heat shield 50.

[0066] (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 in the step of removing the heat shield 50, the heat shield 50 is sequentially cut and removed from the top.

[0067] With the above configuration, it becomes easy to lift the cut pieces 121 of the heat shield 50 upwards.

[0068] (3) The third embodiment of the method for dismantling the lower core structure 6 is the method for dismantling the lower core structure 6 of (2), wherein after the heat shield 50 has been removed down to its lower end, the core vessel 40 is cut.

[0069] With the above configuration, cutting of the reactor core vessel 40 can be started after the removal of the heat shield 50 is completed.

[0070] (4) The fourth embodiment of the method for dismantling the lower core structure 6 is the method for dismantling the lower core structure 6 of (2), wherein after the heat shield 50 is partially removed, the core vessel 40 is cut, and the portion of the core vessel 40 that is exposed after the heat shield 50 has been removed is cut, and the steps of removing the heat shield 50 and cutting the core vessel 40 are performed alternately.

[0071] With the above configuration, the dismantling of the lower core structure 6 can be carried out while sequentially shortening the vertical dimension Dv of the lower core structure 6.

[0072] (5) The fifth method for dismantling the lower core structure 6 is the method for dismantling the lower core structure 6 of (1), wherein the heat shield 50 has a heat shield side backing plate 52 at its upper end that protrudes inward and is placed on the core tank 40, and in the step of removing the heat shield 50, the heat shield 50 is sequentially cut and removed from the bottom.

[0073] In the above configuration, by sequentially removing the heat shield 50 from the bottom, the removal process of the heat shield 50 can be performed without separately providing a support 115 below the heat shield 50 to support the heat shield 50. [Explanation of Symbols]

[0074] 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 50 Heat shield 51 Heat shield body 52 Heat shield side backing plate 53 volts 54 Flexible metal 60 baffle board 61 Forma plate 100 reactor cavities 101 Lower Cavity 102 Cavity floor 103 Installation hole 110 Turntable 111 Cutting device 111a Pedestal 111b Tower 111c 1st Disc Saw 111d Second Disc Saw 113 Jig 114 Waste storage containers 115 Support 120 Cut piece 121 Cut piece Dv vertical direction Dh horizontal direction L10 cutting line L11 cutting line L20 cutting line L21 cutting line L30 cutting line L31 cutting line O axis

Claims

1. 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, It has, The process involves cutting the heat shield in the horizontal and vertical directions and sequentially removing it as a plurality of cut pieces. After the heat shield is removed, the process involves horizontally cutting the reactor core vessel, Includes, In the step of removing the heat shield, the heat shield is sequentially cut and removed from the top, The step of removing the heat shield is: The process involves horizontally cutting the heat shield while the heat shield is suspended by a jig, The process of horizontally cutting the heat shield, followed by vertically cutting the heat shield which has been lifted by the jig to cut out a plurality of the cut pieces, Includes, In the process of cutting out multiple pieces, each piece is cut out by vertically cutting the heat shield along a cutting line that encloses one of the jigs. Method for dismantling the lower core structure.

2. After the heat shield has been removed down to its lower end, the process of cutting the reactor core vessel is carried out. A method for dismantling a lower core structure according to claim 1.

3. After the heat shield is partially removed, in the step of cutting the reactor core, the portion of the reactor core that has been exposed due to the removal of the heat shield is cut. The process of removing the heat shield and the process of cutting the reactor core are performed alternately. A method for dismantling a lower core structure according to claim 1.

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