Method for dismantling internal reactor structures

Abstract

This invention provides a method for dismantling in-furnace structures that can improve work efficiency during the dismantling of in-furnace structures. [Solution] A method for dismantling an in-core structure is a method for dismantling an in-core structure housed inside a reactor vessel, and includes the steps of: removing an existing temporary support frame for the in-core structure that is installed in an immovable state inside the cavity; lifting the in-core structure from the reactor vessel after removing the temporary support frame for the in-core structure; and dismantling the lifted in-core structure.

Description

Technical Field

[0001] This disclosure relates to a method for disassembling in-vessel structures.

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, after removing the fuel from the reactor vessel, the in-vessel structures inside the reactor vessel are taken out to a working pool located above the reactor vessel and storing water, and the in-vessel structures are disassembled in the water stored in the working pool.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Inside the cavity, for example, an existing in-vessel structure temporary pedestal used during periodic inspections is installed. However, the in-vessel structure temporary pedestal may interfere with the disassembly work of the in-vessel structures.

[0005] This disclosure has been made to solve the above problems, and an object thereof is to provide a method for disassembling in-vessel structures that can improve workability in the disassembly work of in-vessel structures.

Means for Solving the Problems

[0006] To solve the above problems, the method for dismantling an in-core structure according to this disclosure is a method for dismantling an in-core structure housed inside a reactor vessel, and includes the steps of: removing an existing temporary support frame for the in-core structure that is installed in an immovable state inside the cavity; lifting the in-core structure from the reactor vessel after the temporary support frame for the in-core structure has been removed; and dismantling the lifted in-core structure. [Effects of the Invention]

[0007] The method for dismantling in-furnace structures described herein can improve work efficiency. [Brief explanation of the drawing]

[0008] [Figure 1] This is a longitudinal cross-sectional view showing a nuclear reactor according to an embodiment of this disclosure. [Figure 2] This is a cross-sectional view showing a reactor and cavity according to an embodiment of this disclosure. [Figure 3] This is a perspective view showing a crane installed above the reactor vessel. [Figure 4] This is a process diagram showing the procedure for the dismantling method of a reactor vessel according to the embodiment. [Figure 5] This is a cross-sectional view showing the cavity. [Figure 6] This is a plan view showing the cavity. [Figure 7] This is a side view showing the existing temporary support structure and the upper in-core structure suspended above the temporary support structure. [Figure 8] This is a side view showing the existing temporary support structure and the upper in-core structure placed on the temporary support structure. [Figure 9] This is a side view showing the existing temporary support structure and the lower internal reactor structure suspended above the temporary support structure. [Figure 10] This is a side view showing the existing temporary support structure and the lower internal reactor structure placed on the temporary support structure. [Figure 11] This is a step diagram showing the procedure for a method of dismantling an in-furnace structure according to the present disclosure. [Modes for carrying out the invention]

[0009] The following describes a method for dismantling a reactor vessel according to the embodiment of this disclosure, with reference to the drawings. Before describing the method for dismantling a reactor vessel, the reactor will be described first.

[0010] <Reactor> Figure 1 is a longitudinal cross-sectional view showing a reactor 1 according to an embodiment of the present disclosure. Figure 2 is a cross-sectional view showing the reactor 1 and a cavity 100. The nuclear power plant comprises a reactor 1, a steam generator, and a steam turbine power generation system. The reactor 1 and the steam generator are located inside a reactor containment vessel. The reactor 1 is, for example, a pressurized water reactor (PWR).

[0011] <Reactor vessel> As shown in Figure 2, the reactor 1 is located inside the cavity 100. As shown in Figures 1 and 2, the reactor 1 comprises a reactor vessel 2. The reactor vessel 2 has a reactor vessel body 20 and a reactor vessel lid 21. The reactor vessel body 20 includes a cylindrical vessel body and a bottom head that closes the bottom of the vessel body. The reactor vessel lid 21 closes the opening at the top of the reactor vessel body 20. The reactor vessel lid 21 is fitted to the reactor vessel body 20 in a manner that allows it to be opened and closed.

[0012] An inlet nozzle 22 and an outlet nozzle 23 are formed in the cylindrical side wall of the reactor vessel body 20. Light water, which serves as the primary coolant, is supplied to the inside of the reactor vessel body 20 through the inlet nozzle 22. The light water inside the reactor vessel body 20 is discharged to the outside of the reactor vessel body 20 through the outlet nozzle 23.

[0013] <Furnace internal structure> Inside the reactor vessel 2, a reactor internal structure (CI) is arranged. The reactor internal structure has an upper reactor internal structure 5 and a lower reactor internal structure 6. The reactor internal structure includes the upper reactor internal structure 5 and the lower reactor internal structure 6. When not distinguishing between the upper reactor internal structure 5 and the lower reactor internal structure 6, it may be described as "reactor internal structure". The reactor internal structure includes at least one of the upper reactor internal structure 5 and the lower reactor internal structure 6.

[0014] <Upper reactor internal structure> The upper reactor internal structure 5 has an upper core plate 30, an upper core support plate 31, a plurality of upper core support columns 32, a plurality of guide tubes 33, and a water level gauge support tube 34. The upper core plate 30 and the upper core support plate 31 are arranged facing each other in the vertical direction Dv. The upper core support plate 31 is arranged near the opening at the upper end of the reactor vessel main body 20.

[0015] 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.

[0016] <Lower reactor internal structure> As shown in FIGS. 1 and 4, the lower reactor internal structure 6 has a core barrel 40, a thermal shield 50, a lower core plate 8, a lower core support plate 9, lower core support columns 10, lower instrumentation guide tubes 12, and a connecting plate 13.

[0017] <Core barrel> The core barrel 40 has a cylindrical shape. As shown in FIG. 1, the core barrel 40 has an upper core barrel 41 and a lower core barrel 42. The upper core barrel 41 is the upper part of the core barrel 40, and the lower core barrel 42 is the lower part of the core barrel 40. Inside the upper core barrel 41, the upper reactor internal structure 5 is accommodated. The upper core barrel 41 has a cylindrical body. An opening is formed in the side wall of the cylindrical body.

[0018] The lower core vessel 42 is located below the upper core vessel 41. The lower core vessel 42 has a cylindrical shape. The core 15 is formed inside the lower core vessel 42.

[0019] <Heat shielding material> The thermal shield 50 is cylindrical in shape and covers the lower core vessel 42 from the radially outer side. The thermal shield 50 is formed to cover the entire circumference of the lower core vessel 42.

[0020] <Irradiation test specimen guide tube> The irradiation test specimen guide tube 7 is provided on the outer surface of the heat shield 50. The irradiation test specimen guide tube 7 extends in the vertical direction Dv.

[0021] <Lower core plate> The lower core plate 8 is located at the bottom of the lower core tank 42. The lower core plate 8 is disc-shaped, and its thickness direction is aligned with the vertical direction Dv. The lower core plate 8 is located inside the lower core tank 42. The lower core plate 8 is joined to the lower core tank 42. The core 15 is formed by the core tank 40, the upper core plate 30, and the lower core plate 8.

[0022] <Lower core support plate> The lower core support plate 9 is positioned below the lower core plate 8 at a distance Dv in the vertical direction. The lower core support plate 9 is located outside the lower core vessel 42 in the vertical direction Dv. The lower core support plate 9 is disc-shaped, and its thickness direction is aligned with the vertical direction Dv. Multiple lower core support columns 10 are provided at positions Dv in the vertical direction 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 lower instrumentation guide tube 12 is held by the lower core support plate 9 and extends below the lower core support plate 9.

[0023] <Connecting plate> The connecting plate 13 is positioned below the lower core support plate 9 in the vertical direction Dv. The connecting plate 13 is located outside the lower core vessel 42 in the vertical direction Dv. The connecting plate 13 is disc-shaped, and its thickness direction is aligned with the vertical direction Dv. The outer diameter of the connecting plate 13 is smaller than the outer diameter of the lower core support plate 9. The connecting plate 13 is located, for example, inside the bottom head of the reactor vessel body 20.

[0024] <Cavity> Next, with reference to Figures 5 and 6, the cavity 100 in which the reactor 1 is located will be described. Figure 5 is a cross-sectional view showing the cavity 100. Figure 6 is a plan view showing the cavity 100. The cavity 100 is a recess formed inside the containment vessel. The cavity 100 is made of concrete. Inside the cavity 100, water is filled to form a pool.

[0025] The cavity 100 has side walls 101 and a floor surface 102. The side walls 101 extend in the vertical direction Dv. The side walls 101 are formed from the floor surface 102 to the operation floor. The side walls 101 are formed to surround the cavity 100 in a plan view.

[0026] As shown in Figure 6, the cavity 100 has a predetermined length in the X-axis direction and a predetermined width in the Y-axis direction. A canal 104 is connected to the cavity 100. The canal 104 extends in the X-axis direction. The width of the canal 104 along the Y-axis direction is narrower than the width of the cavity 100.

[0027] Floor surface 102 includes multiple floor surfaces 102a, 102b, and 102c. Floor surfaces 102a, 102b, and 103c are aligned in the X-axis direction. Floor surface 102a is the area where the upper in-core structure 5 is located, for example, during periodic inspections. Floor surface 102b is the floor surface formed around the opening where the reactor vessel 2 is located. Floor surface 102c is the area where the lower in-core structure 6 is located, for example, during periodic inspections. Floor surface 102c is located closer to the canal 104 than floor surfaces 102a and 102b. The canal 104 is a passage that communicates with the spent fuel pit where spent fuel is stored.

[0028] As shown in Figure 5, floor surfaces 102a and 102b are formed at the same depth. Floor surfaces 102a and 102b are in the same position as the flange surface of the reactor vessel body 20. Floor surface 102c is formed at a deeper position than floor surfaces 102a and 102b. Floor surface 102c is the space for arranging the lower in-core structure 6 and corresponds to the length along the vertical direction Dv of the lower in-core structure 6.

[0029] <Existing temporary support frame> Next, the existing temporary support frames 110 and 120 will be described. As shown in Figure 5, temporary support frames 110 and 120 are provided on the floor surfaces 102a and 102c of the cavity 100.

[0030] <Temporary support frame for upper in-core structure> Figure 7 is a side view showing the existing temporary support frame 110 and the upper in-furnace structure 5 suspended above the temporary support frame 110. Figure 8 is a side view showing the existing temporary support frame 110 and the upper in-furnace structure 5 placed on the temporary support frame 110.

[0031] As shown in Figures 5, 7, and 8, the temporary support frame 110 is a temporary support frame 110 for temporarily storing the upper in-core structure 5. For example, during periodic inspections, the upper in-core structure 5, which has been lifted from the reactor vessel body 20, is placed on the temporary support frame 110. The temporary support frame 110 is designed to support the upper in-core structure 5 without damaging it.

[0032] The temporary support frame 110 is positioned on the floor surface 102a. The temporary support frame 110 is fixed to the floor surface 102a in an immovable manner. The temporary support frame 110 has a plurality of legs 111, a support ring 112, and guide pins 113. The plurality of legs 111 extend upward from the floor surface 102a. The plurality of legs 111 support the support ring 112. The support ring 112 is a ring-shaped member that receives the upper in-core structure 5. The support ring 112 receives the upper core support plate 31 of the upper in-core structure 5.

[0033] The guide pin 113 is a guide member for guiding the upper in-core structure 5 when it is placed on the temporary support frame 110. The guide pin 113 is fixed to the support ring 112. The guide pin 113 extends upward from the support ring 112.

[0034] The suspension device 130 for suspending the upper in-furnace structure 5 has a guide hole formed therein for inserting a guide pin 113. The upper in-furnace structure 5 is positioned and supported with respect to the suspension device 130. By lowering the upper in-furnace structure 5 with the guide pin 113 inserted through the guide hole in the suspension device 130, the upper in-furnace structure 5 is guided toward the temporary support frame 110.

[0035] As shown in Figure 8, for example, during periodic inspections, the upper in-core structure 5 is placed on a temporary support frame 110. With the upper in-core structure 5 supported on the temporary support frame 110, the upper core support columns 32 and the upper core plate 30 are positioned below the support ring 112. In this state, the upper core plate 30 is positioned above the floor surface 102a.

[0036] <Temporary support frame for lower in-core structure> Figure 9 is a side view showing the existing temporary support frame 120 and the lower in-furnace structure 6 suspended above the temporary support frame 120. Figure 10 is a side view showing the existing temporary support frame 120 and the lower in-furnace structure 6 placed on the temporary support frame 120.

[0037] As shown in Figures 5, 9, and 10, the temporary support frame 120 is a temporary support frame 120 for temporarily storing the lower in-core structure 6. For example, during periodic inspections, the lower in-core structure 6, which has been lifted from the reactor vessel body 20, is placed on the temporary support frame 120. The temporary support frame 120 is designed to support the lower in-core structure 6 without damaging it.

[0038] The temporary support frame 120 is positioned on the floor surface 102c. The temporary support frame 120 is fixed to the floor surface 102c in an immovable manner. The temporary support frame 120 has a plurality of legs 121, a connecting ring 122, and a receiving portion 123. The plurality of legs 121 extend upward from the floor surface 102c. The connecting ring 122 connects the plurality of legs 121 in the circumferential direction of the connecting ring 122. The plurality of legs 121 protrude upward from the connecting ring 122. The receiving portion 123 is provided at the upper end of the plurality of legs 121. The receiving portion 123 is the part that receives the lower internal furnace structure 6.

[0039] Guide pins 125 are provided on the side wall of the cavity 100. The guide pins 125 are guide members for guiding the lower in-furnace structure 6 when it is placed on the temporary support frame 120. The guide pins 125 are fixed to the side wall and extend in the vertical direction.

[0040] The suspension device 140 for suspending the lower in-furnace structure 6 has a guide hole formed therein for inserting a guide pin 125. The lower in-furnace structure 6 is positioned and supported with respect to the suspension device 140. By lowering the lower in-furnace structure 6 with the guide pin 125 inserted through the guide hole in the suspension device 140, the lower in-furnace structure 6 is guided toward the temporary support frame 120.

[0041] As shown in Figure 10, for example, during periodic inspections, the lower in-core structure 6 is placed on a temporary support frame 120. With the lower in-core structure 6 supported on the temporary support frame 120, the lower core support plate 9 is supported by the receiving portion 123. In this state, the lower instrumentation guide tube 12 and connecting plate 13 are located below the receiving portion 123 and above the floor surface 102c.

[0042] <Method for dismantling the reactor vessel> Next, a method for dismantling the in-core structure will be described. Figure 11 is a process diagram showing the steps of a method for dismantling an in-core structure according to an embodiment of this disclosure. The method for dismantling an in-core structure includes the steps of: S11 of removing the existing temporary support frames 110 and 120; S12 of installing support frames; S13 of lifting the in-core structure from the reactor vessel 2; and S14 of dismantling the in-core structure.

[0043] <Process of removing the existing temporary support structure> In step S11, which involves removing the existing temporary support frames 110 and 120, for example, the legs 111 and 121 of the temporary support frames 110 and 120 are cut. If the radiation dose of the temporary support frames 110 and 120 themselves is at an acceptable level, it is preferable to remove them in the air. After cutting, the temporary support frames 110 and 120 are removed from the floor surfaces 102a and 102c. The cladding on the floor surfaces 102a and 102c from which the temporary support frames 110 and 120 have been removed is repaired as appropriate. In the subsequent steps S12 and S13, if there is no interference with other objects, a portion of the legs 111 and 121 may remain on the floor surfaces 102a and 102c. Other objects include, for example, the upper in-core structure 5, the lower in-core structure 6, and the cutting equipment for dismantling.

[0044] <Steps to install the support stand> The process S12 of installing the support stands is performed after the process S11 of removing the existing temporary support stands 110 and 120. In the process S12 of installing the support stands, the support stand for the upper in-furnace structure 5 is installed on the floor surface 102a, and the support stand for the lower in-furnace structure 6 is installed on the floor surface 102c.

[0045] For example, the support base for the upper in-core structure 5 is installed at a position further from the side wall 101 compared to the position where the temporary support frame 110 was installed. The support base can support the upper in-core structure 5 and does not have any obstructing members when cutting the upper in-core structure 5. The support base supports the upper core plate 30 from below the position where the temporary support frame 110 supports it.

[0046] For example, the support base for the lower in-core structure 6 is installed at a position further from the side wall compared to the position where the temporary support frame 120 was installed. The support base can support the lower in-core structure 6 and does not have any obstructing members when cutting the lower in-core structure 6. The support base supports, for example, the lower core support plate 9 or connecting plate 13 from a position lower than where the temporary support frame 120 supports it.

[0047] <Process of lifting internal reactor structures from the reactor vessel> The process S13 of lifting the in-core structures from the reactor vessel 2 is performed after the process S12 of installing the support bases. In the process S13 of lifting the in-core structures, for example, an existing crane used for handling fuel can be used to lift the upper in-core structure 5 and the lower in-core structure 6 that are housed inside the reactor vessel body 20. The lifted upper in-core structure 5 and the lower in-core structure 6 are then placed on the support bases, respectively.

[0048] <Process of dismantling the internal structure of the furnace> The process S14 for dismantling the in-core structure is performed after the process S13 for lifting the in-core structure. In the process S13 for dismantling the in-core structure, the upper in-core structure 5 and the lower in-core structure 6 are cut, for example, using a cutting device. In the process S13 for dismantling the in-core structure, the upper in-core structure 5 and the lower in-core structure 6 are cut into multiple parts, for example, so that they can be transported.

[0049] <Challenges in the comparative example> Next, the problems in the comparative example will be explained. The comparative example is a method for dismantling the upper in-furnace structure 5 and the lower in-furnace structure 6 while the existing temporary support frames 110 and 120 are in place.

[0050] For example, since the existing temporary support frames 110 and 120 are equipped with guide members, the work of placing the upper in-furnace structure 5 and the lower in-furnace structure 6 on the temporary support frames 110 and 120 required high positional accuracy and was therefore a complex operation.

[0051] Furthermore, the existing temporary support frames 110 and 120 are equipped with guide members, which hinder the dismantling work of the upper and lower in-furnace structures 5 and 6. For example, the guide pin 113 of the temporary support frame 110 is located close to the upper in-furnace structure 5 and extends vertically in the direction Dv along the upper in-furnace structure 5, thus interfering with the cutting of the upper in-furnace structure 5.

[0052] Furthermore, the temporary support frames 110 and 120 were not designed with cutting operations in mind, and there was a risk that they could not withstand the reaction forces and vibrations that occur during cutting.

[0053] Furthermore, the temporary support frames 110 and 120 may be positioned close to the side walls of the cavity 100, which raises concerns about reduced work efficiency when cutting in confined spaces.

[0054] Furthermore, in the temporary support frame 110, multiple legs 111 are positioned adjacent to the upper core support column 32, so it was not possible to cut the upper core support column 32 while it was being supported by the temporary support frame 110.

[0055] <Effects and Effects> In the dismantling method for the in-core structures, the existing temporary support frames 110 and 120 are removed before the upper in-core structure 5 and the lower in-core structure 6 are dismantled. Therefore, the existing temporary support frames 110 and 120 do not get in the way when dismantling the upper in-core structure 5 and the lower in-core structure 6. As a result, the work efficiency in the dismantling of the in-core structures can be improved.

[0056] In this method of dismantling the in-furnace structure, the upper in-furnace structure 5 and the lower in-furnace structure 6, which are placed on a dismantling support, can be dismantled. Since the dismantling support does not have any members that would obstruct the cutting of the in-furnace structure, the work efficiency in the dismantling operation can be improved. In addition, the dismantling support is positioned away from the side wall of the cavity 100. Therefore, contact between the side wall and the cutting device can be suppressed during the cutting operation. Furthermore, in this method of dismantling the in-furnace structure, access to the upper in-furnace structure 5 and the lower in-furnace structure 6 by the cutting device can be made easier.

[0057] Furthermore, the method for dismantling the in-furnace structure allows for the cutting of the upper in-furnace structure 5 and the lower in-furnace structure 6, which are placed on a support stand. For example, it is also possible to cut the in-furnace structure while it is suspended, but in this case, there is a risk that the cut portion will fall downwards. The method for dismantling the in-furnace structure allows for the cutting of the in-furnace structure while it is placed on a support stand, thus preventing the cut portion from falling. The support stand can support the portion that will be lower after cutting.

[0058] The support structure for the upper in-core structure 5 supports, for example, the upper core plate 30 from below. The support structure for the lower in-core structure 6 supports, for example, the lower core support plate 9 or the connecting plate 13 from below. Most of the in-core structures supported by the support structures are located above the support structure. In the method of dismantling the in-core structures, the degree of freedom in the order of cutting is improved.

[0059] The support structure is designed to account for reaction forces and vibrations during cutting. Therefore, the upper and lower internal furnace structures 5 and 6 can be cut while supported by the support structure. Safety has been improved in the dismantling method for the internal furnace structures.

[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] For example, the support base for the in-furnace structure may include a turntable that can rotate around an axis extending in the vertical direction Dv. For example, in step S14 of dismantling the in-furnace structure, the turntable can be used to change the orientation of the in-furnace structure and cut it. The support base may also include a lifting mechanism for raising and lowering the in-furnace structure. This allows the height of the in-furnace structure to be changed and the structure to be cut.

[0062] Furthermore, the method for dismantling the in-furnace structure may include a step of lowering the water level in the cavity 100. For example, the method for dismantling the in-furnace structure may include the step of lowering the water level before step S11, which involves removing the temporary support structure. The cutting of the temporary support structures 110 and 120 may be carried out underwater or in the air.

[0063] In the above embodiment, the case of dismantling the upper in-furnace structure 5 and the lower in-furnace structure 6 is illustrated, but in the method of dismantling the in-furnace structure, only the upper in-furnace structure 5 may be dismantled, or only the lower in-furnace structure 6 may be dismantled.

[0064] In the above embodiment, the example shows the removal of temporary support frames 110 and 120 in step S11, but in the method of dismantling the in-furnace structure, only temporary support frame 110 may be removed, or only temporary support frame 120 may be removed.

[0065] In step S11, which involves removing the temporary support frames, all of the temporary support frames 110 and 120 may be removed, or only a portion of them may be removed. In step S11, which involves removing the temporary support frames, for example, only the guide pins 113 of the temporary support frame 110 may be removed.

[0066] In the above embodiment, an example is given of a case where the step of installing a support stand S12 is performed after the step of removing the temporary support stand S11. However, in the dismantling method of the in-furnace structure, it is not necessary to install a support stand. For example, existing temporary support stands 110 and 120 may be modified to be used as dismantling stands to support the upper in-furnace structure 5 and the lower in-furnace structure 6. For example, the temporary support stands 110 and 120 may be reinforced to withstand reaction forces and vibrations during cutting. Alternatively, the temporary support stands 110 and 120 may be modified to change the position in which they support the upper in-furnace structure 5 and the lower in-furnace structure 6.

[0067] <Note> The dismantling method for the furnace structure described in each embodiment can be understood, for example, as follows:

[0068] (1) A method for dismantling an in-core structure according to the first embodiment is a method for dismantling an in-core structure housed inside the reactor vessel 2, and includes the steps of: removing existing temporary in-core structure supports 110, 120 that are installed in an immovable state inside the cavity 100; lifting the in-core structure from the reactor vessel 2 after the removal of the temporary in-core structure supports 110, 120; and dismantling the lifted in-core structure.

[0069] This prevents the temporary support frames 110 and 120 from getting in the way, improving work efficiency during the dismantling of the in-furnace structure.

[0070] (2) The method for dismantling an in-furnace structure according to the second embodiment is the method for dismantling an in-furnace structure described in (1) above, wherein the temporary in-furnace structure frames 110, 120 include an upper temporary in-furnace structure frame 110 for temporarily placing the upper in-furnace structure 5 and a lower temporary in-furnace structure frame 120 for temporarily placing the lower in-furnace structure 6, and in the step of removing the temporary in-furnace structure frames, at least one of the upper temporary in-furnace structure frame 110 and the lower temporary in-furnace structure frame 120 is dismantled.

[0071] This prevents the temporary support frames 110 and 120 from getting in the way, improving work efficiency during the dismantling of the in-furnace structure.

[0072] (3) The method for dismantling an in-furnace structure according to the third embodiment is the method for dismantling an in-furnace structure according to (1) or (2) above, which includes the step of removing the existing temporary support frame for the in-furnace structure and then installing a support base for receiving the in-furnace structure, and in the step of dismantling the in-furnace structure, the in-furnace structure is dismantled while the in-furnace structure is placed on the support base.

[0073] This allows the internal furnace structure to be stably supported using a support stand.

[0074] (4) The fourth embodiment of the method for dismantling an in-furnace structure is the method for dismantling an in-furnace structure described in (3) above, wherein the support base includes a turntable that is rotatable about an axis extending in the vertical direction Dv, and in the step of dismantling the in-furnace structure, the in-furnace structure is rotated to change the orientation of the in-furnace structure and dismantle the in-furnace structure.

[0075] This allows the orientation of the internal reactor structure to be changed, enabling the cutting of the internal reactor structure without moving the cutting device. [Explanation of Symbols]

[0076] 1 nuclear reactor 2 Reactor vessel 5 Upper reactor internals (furnace internals) 6 Lower reactor internals (furnace internals) 8 Lower core plate 9. Lower core support plate 10 Lower core support column 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 34 Water level gauge support pipe 40 reactor core tank 41 Upper reactor core tank 42 Lower core tank 43 Upper core vessel body 44 pipe stand 50 Heat shield 60 Cranes (Fuel Handling Cranes) 61 Main unit 63 rails 100 Cavity 101 Side wall 102, 102a, 102b, 102c Floor surface 103 holes 104 Canal 110 Temporary Stand 111 legs 112 Support ring 113 Guide pins 120 Temporary Stand 121 legs 122 Connecting rings 123 receiving part 125 Guide pins 130 Lifting equipment 140 Lifting equipment Dv vertical direction XX axis direction YY axis direction

Claims

1. A method for dismantling internal reactor structures housed inside the reactor vessel, The process involves removing the temporary support structure for existing in-core structures that is immovably installed inside the cavity, After removing the temporary support structure for the in-core structure, the process involves lifting the in-core structure from the reactor vessel. A method for dismantling an in-furnace structure, comprising the step of dismantling the in-furnace structure that has been lifted out.

2. The temporary support frame for the in-furnace structure is, A temporary support frame for the upper in-core structure, for temporarily storing the upper in-core structure, It includes a temporary support frame for lower in-furnace structures for temporarily storing lower in-furnace structures, The method for dismantling an in-furnace structure according to claim 1, wherein in the step of removing the temporary support frame for the in-furnace structure, at least one of the upper temporary support frame for the in-furnace structure and the lower temporary support frame for the in-furnace structure is dismantled.

3. The process includes removing the existing temporary support frame for the in-furnace structure and then installing a support frame to receive the in-furnace structure, The method for dismantling an in-furnace structure according to claim 1 or 2, wherein in the step of dismantling the in-furnace structure, the in-furnace structure is dismantled while it is placed on the support stand.

4. The support base includes a turntable that is rotatable about an axis extending vertically, The method for dismantling an in-furnace structure according to claim 3, wherein in the step of dismantling the in-furnace structure, the in-furnace structure is rotated to change the orientation of the in-furnace structure and the in-furnace structure is dismantled.

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