Method for dismantling the upper core structure

Abstract

Even materials with different radiation levels can be processed by simplifying the work process. [Solution] A method for dismantling an upper core structure comprises an upper core plate, an upper core support plate positioned vertically above the upper core plate, and a guide tube having a lower tube and an upper tube and extending vertically from the upper core plate to the upper core support plate, the method comprising: removing fixing bolts that fix the lower tube to the upper core support plate; pulling the upper tube upward in the vertical direction to release the engagement of the lower tube, which is connected to the upper tube via connecting bolts, with the upper core plate; removing the connecting bolts; pulling up and removing the upper tube; and pulling up and removing the lower tube.

Description

Technical Field

[0001] The present disclosure relates to a method for disassembling an upper 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 structure 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 structure which is an internal structure. Therefore, when disassembling a nuclear reactor, it often touches members with a high dose, and the working time and the restrictions on the working place increase. Among the in-vessel structures, the upper core structure located at the upper part inside the reactor vessel is also composed of members with various levels of dose. Specifically, one end of the guide tube of the upper core structure is arranged near the core, while the other end is arranged near the lid of the reactor vessel. Therefore, the guide tube is a member with various levels of dose depending on the part. Thus, it is desired to simplify the work and disassemble the upper core structure even for members with different doses.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a method for disassembling an upper core structure that can simplify the work and process members with different doses. [Means for solving the problem]

[0006] To solve the above problems, the method for dismantling an upper core structure according to the present disclosure comprises an upper core plate, an upper core support plate positioned vertically above the upper core plate, and a guide tube having a lower tube and an upper tube and extending vertically from the upper core plate to the upper core support plate, the method for dismantling an upper core structure comprising the steps of: removing fixing bolts that fix the lower tube to the upper core support plate; pulling the upper tube upward in the vertical direction to release the engagement of the lower tube, which is connected to the upper tube via connecting bolts, with the upper core plate; removing the connecting bolts; pulling up and removing the upper tube; and pulling up and removing the lower tube. [Effects of the Invention]

[0007] According to the method for dismantling the upper core structure of this disclosure, even components with different radiation levels can be processed with simplified work procedures. [Brief explanation of the drawing]

[0008] [Figure 1] This is a longitudinal cross-sectional view showing a pressurized water reactor according to the embodiment. [Figure 2] This is a schematic diagram showing a pressurized water reactor, with water stored inside and its reactor vessel lid removed, positioned inside a pool within the reactor building according to the embodiment. [Figure 3] This is a perspective view showing the upper core structure according to the embodiment. [Figure 4] This is a longitudinal cross-sectional view showing the upper core structure according to the embodiment. [Figure 5] This figure shows the positional relationship of the guide tubes with respect to the upper core support plate according to the embodiment. [Figure 6] This is a flowchart illustrating a method for dismantling the upper core structure according to the embodiment. [Figure 7]This diagram shows the relationship between the upper core support plate and the guide tubes being fixed to the upper core plate according to this embodiment. [Figure 8] This figure shows an example of how to remove the fixing bolt according to the embodiment. [Figure 9] This figure shows an example of how the upper and lower tubes according to the embodiment are pulled up and removed. [Figure 10] This figure shows an example of the configuration of a device for lifting the upper tube according to the embodiment. [Figure 11] This figure shows an example of the configuration of a device for lifting the lower tube of the embodiment. [Modes for carrying out the invention]

[0009] The following describes embodiments for implementing the method of dismantling the upper core structure according to this disclosure, with reference to the attached drawings. However, this disclosure is not limited to these embodiments.

[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. The reactor is a pressurized water reactor 1 (PWR) that uses light water as a reactor coolant and neutron moderator to create high-temperature, high-pressure water that does not boil throughout the entire core 7, sends this high-temperature, high-pressure water to a steam generator to generate steam through heat exchange, and sends this steam to a turbine generator to generate electricity.

[0011] As shown in FIG. 2, the pressurized water reactor 1 is disposed within the pool 100 in the reactor building. A space capable of storing cooling water (water) is formed within the pool 100 in the reactor building. The pool 100 in the reactor building of the present embodiment has, as a space, a first cavity 110 in which the pressurized water reactor 1 is disposed, and a second cavity 120 disposed adjacent to the first cavity 110. The first cavity 110 has a first floor surface 111 on which an operator can walk. The second cavity 120 has a second floor surface 121 that is recessed from the first floor surface 111. That is, the second floor surface 121 is located below the first floor surface 111 in the vertical direction Dv. Thereby, the second cavity 120 is formed as a space that is recessed below the first cavity 110 in the vertical direction Dv.

[0012] As shown in FIGS. 1 and 2, the pressurized water reactor 1 of the present embodiment includes a reactor vessel 2, a control rod drive device 3, an upper core structure 5, and a lower core structure 6.

[0013] [[ID= (8]]The reactor vessel 2 has a reactor vessel main body 21 and a reactor vessel head 22 (upper nozzle) so that in-vessel structures can be inserted therein. The reactor vessel 2 is disposed inside a hole formed so as to be recessed with respect to the first floor surface 111. The reactor vessel 2 is disposed in a state where a part thereof (specifically, the reactor vessel head 22) protrudes from the first floor surface 111.

[0014] The upper part of the reactor vessel main body 21 can be opened by removing the reactor vessel head 22. The lower part of the reactor vessel main body 21 has a cylindrical shape closed by a lower nozzle having a hemispherical shape. An inlet nozzle 23 (inlet plenum) for supplying light water (coolant) as primary cooling water (water) and an outlet nozzle 24 (outlet plenum) for discharging the light water are formed in the upper part of the reactor vessel main body 21. Further, the reactor vessel main body 21 has a water injection nozzle (water injection plenum), not shown, formed separately from the inlet nozzle 23 and the outlet nozzle 24.

[0015] The reactor vessel head 22 is mounted on the upper part of the reactor vessel body 21. The reactor vessel head 22 is fixedly attached to the reactor vessel body 21 by a plurality of stud bolts and nuts (not shown) so as to be openable and closable.

[0016] The upper core structure 5 is disposed inside the reactor vessel 2. The upper core structure 5 can be withdrawn from the reactor vessel body 21 by being moved upward in the vertical direction Dv with respect to the reactor vessel body 21. As shown in FIGS. 3 and 4, the upper core structure 5 of the present embodiment includes an upper core plate 51, an upper core support plate 52, upper core support columns 53, guide tubes 55, fixing bolts 58 (see FIG. 6), connecting bolts 59 (see FIG. 6), and a water level gauge support pipe (not shown).

[0017] Note that the upper core structure 5 does not have only the structure described above. As a configuration not shown, the upper core structure 5 has other configurations such as, for example, a mixer, a thermocouple lead-out pipe, and a reinforcing beam.

[0018] The upper core plate 51 is disposed apart downward in the vertical direction Dv from the upper core support plate 52. In the upper core plate 51, a large number of through holes are formed in a disk shape. The guide tubes 55 and the water level gauge support pipe are inserted through the through holes of the upper core plate 51.

[0019] The upper core support plate 52 is positioned above the upper core plate 51 in the vertical direction Dv. As shown in Figures 1 and 2, the upper core support plate 52 is fixed to the reactor vessel body 21 internally, above the inlet nozzle 23 and outlet nozzle 24 in the vertical direction Dv. As shown in Figures 3 and 4, the upper core support plate 52 is formed in a larger disc shape than the upper core plate 51. The upper core support plate 52 has numerous through-holes at the same positions as the upper core plate 51 when viewed from the vertical direction Dv. Guide tubes 55 and water level gauge support pipes are inserted through the through-holes of the upper core support plate 52. Among the multiple through-holes, those that do not have guide tubes 55 or water level gauge support pipes inserted are closed by removable covers (dotted lines in Figure 5). Furthermore, as shown in Figure 2, the upper surface of the upper core support plate 52 in this embodiment is positioned at the same height as the first floor surface 111 in the vertical direction Dv when the upper core structure 5 is placed inside the reactor vessel 2.

[0020] As shown in Figures 3 and 4, the multiple upper core support columns 53 are connected to the upper core support plate 52 and the upper core plate 51. The multiple upper core support columns 53 extend in a straight line in the vertical direction Dv. The upper ends of the upper core support columns 53 are fixed to the upper core support plate 52. The lower ends of the upper core support columns 53 are fixed to the upper core plate 51. When viewed from the vertical direction Dv, the multiple upper core support columns 53 are offset from the guide tubes 55 and water level gauge support tubes so as not to overlap.

[0021] The guide tube 55 is fixed to the upper core support plate 52 by being inserted through a through-hole in the upper core support plate 52. The guide tube 55 guides the vertical movement Dv of the control rod cluster. The guide tube 55 is designed to allow the control cluster to be inserted inside. The guide tube 55 is made of, for example, stainless steel. The guide tube 55 is inserted from above in the vertical direction Dv into the through-hole in the upper core support plate 52 and the through-hole in the upper core plate 51. In other words, the guide tube 55 is movable upward in the vertical direction Dv relative to the upper core support plate 52 and the upper core plate 51 by releasing its fixation. Specifically, the lower end of the guide tube 55 is connected to the upper core plate 51. In other words, the upper end of the guide tube 55 is positioned above in the vertical direction Dv relative to the upper core support plate 52. As shown in Figure 6, the guide tube 55 of this embodiment includes an upper tube 551, a lower tube 555, a fixing bolt 58, and a connecting bolt 59.

[0022] The upper tube 551 extends linearly in the vertical direction Dv. The upper tube 551 is positioned above the upper core support plate 52 in the vertical direction Dv. The lower end of the upper tube 551 is fixed to the lower tube 555. In this embodiment, the upper tube 551 has an upper tube body 553 and an upper flange 554.

[0023] The upper tube body 553 is a tubular member extending in the vertical direction Dv. The upper tube body 553 is designed so that a control rod cluster can be inserted through it. The upper flange 554 is formed at the lower end of the upper tube body 553. The upper flange 554 extends from the upper tube body 553 in the horizontal direction Dh, which is perpendicular to the vertical direction Dv.

[0024] The lower tube 555 is positioned below the upper tube 551 in the vertical direction Dv. The lower tube 555 extends in the vertical direction Dv while being inserted through a through-hole in the upper core support plate 52. The upper end of the lower tube 555 is fixed to the upper core support plate 52. The upper end of the lower tube 555 is also fixed to the lower end of the upper tube 551 at a position different from that of the upper core support plate 52. The lower tube 555 in this embodiment has a lower tube body 557 and a lower flange 558.

[0025] The lower tube body 557 is a tubular member extending in the vertical direction Dv. The control rod cluster can be inserted through the lower tube body 557. The lower flange 558 is formed at the upper end of the lower tube body 557. The lower flange 558 extends horizontally Dh from the lower tube body 557. The lower flange 558 is positioned in contact with the upper flange 554. Specifically, the upper surface of the lower flange 558 (the surface facing upward in the vertical direction Dv) is in contact with the lower surface of the upper flange 554 (the surface facing downward in the vertical direction Dv). The lower surface of the lower flange 558 (the surface facing downward in the vertical direction Dv) is in contact with the upper surface of the upper core support plate 52.

[0026] Furthermore, the lower tube 555 is constructed by connecting an intermediate lower tube 561, which constitutes the middle section, and a bottom tube 562, which constitutes the bottom section. The intermediate lower tube 561 has a part of the lower tube body 557 and a lower flange 558. The lower tube body 557 of the intermediate lower tube 561 is formed, for example, in a rectangular tubular shape. The bottom tube 562 has a part of the lower tube body 557 and a lower connecting pin 50b. The lower tube body 557 of the bottom tube 562 is formed, for example, in a cylindrical shape.

[0027] Furthermore, the lower tube 555 and the upper core plate 51 have a fitting portion 50 that is released when they are separated in the vertical direction Dv. When the fitting portion 50 is in a fitted state, it restricts the horizontal movement Dh of the lower tube 555 relative to the upper core plate 51. The fitting portion 50 is released when the lower tube 555 and the upper core plate 51 are separated in the vertical direction Dv. Specifically, the fitting portion 50 in this embodiment is composed of a fitting hole 50a (hole) formed in the upper core plate 51 and a lower connecting pin 50b (pin) formed in the lower tube 555.

[0028] The fitting holes 50a are recessed from the upper surface of the upper core plate 51 (the surface facing upward in the vertical direction Dv). In this embodiment, the fitting holes 50a are formed as through holes that penetrate the upper core plate 51. One lower connecting pin 50b can be inserted into one fitting hole 50a. Multiple fitting holes 50a are formed for each through hole so as to surround the through hole in the upper core plate 51. The lower connecting pins 50b extend in an elongated rod shape in the vertical direction Dv from the lower end of the lower tube body 557. Multiple lower connecting pins 50b are formed for each lower tube 555. The number of lower connecting pins 50b formed in one lower tube 555 is the same as the number of fitting holes 50a formed around one through hole. When the lower connecting pins 50b are inserted into the fitting holes 50a, their movement in the horizontal direction Dh is restricted.

[0029] As shown in Figure 6, the fixing bolts 58 secure the guide tube 55 to the upper core support plate 52. Multiple fixing bolts (for example, four) are arranged for each guide tube 55. The fixing bolts 58 directly secure the lower tube 555 to the upper core support plate 52. Specifically, the fixing bolts 58 secure the lower flange 558 to the upper core support plate 52 from above in the vertical direction Dv. Furthermore, the fixing bolts 58 are secured to the lower flange 558 and the upper core support plate 52 in a non-rotatable manner. In addition, the fixing bolts 58 do not directly secure the upper tube 551 to the upper core support plate 52.

[0030] The connecting bolts 59 secure the upper tube 551 and the lower tube 555. Multiple connecting bolts 59 are arranged for each guide tube 55. The connecting bolts 59 directly secure the upper tube 551 and the lower tube 555. Specifically, the connecting bolts 59 secure the upper flange 554 to the lower flange 558 from above in the vertical direction Dv. Furthermore, the connecting bolts 59 are secured to the upper flange 554 and the lower flange 558 in a non-rotatable manner. In addition, when viewed from above in the vertical direction Dv, the connecting bolts 59 are positioned away from (not overlapping with) the fixing bolts 58. Each connecting bolt 59 is positioned so that it can be accessed simultaneously by a worker from the upper core support plate 52 without having to move, relative to the nearest fixing bolt 58. In other words, the connecting bolts 59 are positioned very close to the fixing bolts 58.

[0031] As shown in Figures 1 and 2, the lower core structure 6 is located inside the reactor vessel 2. Many of the components of the lower core structure 6 are positioned vertically Dv below the upper core structure 5. The lower core structure 6 can be removed from the reactor vessel body 21 by moving it vertically Dv above the reactor vessel body 21. The lower core structure 6 is separable from the upper core structure 5 inside the reactor vessel body 21.

[0032] (Method for dismantling the upper core structure) The following describes a method for dismantling the upper core structure 5 according to the embodiment of this disclosure. Figure 7 is a flowchart showing the method for dismantling the upper core structure 5 according to the embodiment of this disclosure.

[0033] The dismantling method for the upper core structure 5 involves dismantling the guide tubes 55. The dismantling method for the upper core structure 5 is carried out in a state where it is possible to contact the internal components of the reactor vessel body 21, which is installed in the pool 100 inside the reactor building. In other words, the dismantling method for the upper core structure 5 is carried out with the reactor vessel lid 22 removed from the reactor vessel body 21. Furthermore, the dismantling method for the upper core structure 5 is carried out with water stored inside the reactor vessel body 21. Specifically, water is stored inside the reactor vessel body 21 up to the position where the upper core support plate 52 is located. In other words, the upper surface of the upper core support plate 52 is located above the liquid surface of the cooling water in the vertical direction Dv. The lower surface of the upper core support plate 52 may be in contact with the cooling water. In addition, the dismantling method for the upper core structure 5 is carried out with the control rod cluster removed from inside the guide tubes 55.

[0034] In the dismantling method for the upper core structure 5 shown in Figure 7, the first step is to remove the fixing bolts 58 (step S1). The fixing bolts 58 are removed while the upper core structure 5 is located inside the reactor vessel body 21. In other words, the upper core structure 5 is located inside the reactor vessel 2, which contains water. Therefore, the upper core plate 51 and the lower tube 555 are located in water. At this time, the step of removing the fixing bolts 58 is performed on the upper core support plate 52, which is located in an airy environment above the water.

[0035] In this state, the fixing bolts 58 that secure the lower tube 555 to the upper core support plate 52 are removed. More specifically, firstly, the anti-rotation mechanism of the fixing bolts 58 is removed from above in the vertical direction Dv. At this time, in order to release the anti-rotation mechanism, the welded portion or the head of the fixing bolt 58 may be cut off with a cutter or grinder. After that, the fixing bolts 58 are removed from the lower tube 555 and the upper core support plate 52 by pulling them out in the vertical direction Dv. As a result, the guide tube 55 is released from its fixation to the upper core support plate 52 and becomes movable in the vertical direction Dv upward relative to the upper core support plate 52 (and upper core plate 51). Also, the worker makes contact with the fixing bolts 58 from the first floor surface 111. When viewed from above in the vertical direction Dv, the worker makes contact with and removes the fixing bolts 58 that are located near the outer circumference of the upper core support plate 52. Furthermore, when workers perform work on fixing bolts 58 located near the center of the upper core support plate 52 when viewed from above in the vertical direction Dv, a work platform 140 equipped with a movable device such as casters is used, as shown in Figure 8. At that time, the work platform 140 is moved above the upper core support plate 52 and the guide tube 55 in the vertical direction Dv. Workers perform work on the fixing bolts 58 from the work platform 140. Also, when workers make contact with the fixing bolts 58 from the work platform 140, they make contact with the fixing bolts 58 via a jig.

[0036] Furthermore, when removing the fixing bolt 58, the connecting bolt 59 that connects the upper tube 551 and the lower tube 555 is loosened while maintaining the connection between the upper tube 551 and the lower tube 555. Specifically, before releasing the fixing bolt 58, which maintains a stable fixed state for work, the anti-rotation mechanism of the connecting bolt 59 is removed from above in the vertical direction Dv. This work is performed by workers to contact and remove the connecting bolts 59 located near the outer circumference of the upper core support plate 52. For connecting bolts 59 that cannot be accessed from near the outer circumference of the upper core support plate 52, the work platform 140 is used. Furthermore, the connecting bolts 59 are loosened to a point where they cannot be completely removed. It is preferable that the connecting bolts 59 are loosened to a point where any sticking is released and they can be easily removed by workers. Also, even when the connecting bolts 59 are loosened, the fixing between the upper tube 551 and the lower tube 555 by the connecting bolts 59 is not released. In other words, the connecting bolt 59 can only be loosened, not removed.

[0037] After the fixing bolts 58 are removed, a step (step S2) is performed to release the lower tube 555 from its engagement with the upper core plate 51. Specifically, the upper tube 551 is pulled upward in the vertical direction Dv, thereby releasing the engagement of the lower tube 555, which is connected to the upper tube 551 via connecting bolts 59, with the upper core plate 51. At this time, as shown in Figure 9, a lifting device such as an overhead crane 150 installed in the containment vessel (not shown) where the reactor building pool 100 is located is attached to the upper tube 551. The overhead crane 150 is suspended from the ceiling of the containment vessel. The overhead crane 150 is movable in the horizontal direction Dh and the vertical direction Dv toward any position within the first cavity 110 and the second cavity 120. As shown in Figure 10, a first lifting jig 200 is attached to the overhead crane 150. The first lifting jig 200 is used when the overhead crane 150 lifts the upper tube 551. The first lifting jig 200 of this embodiment includes a chain block 210, a first load cell 220, a slide hammer 230, and a lifting member 240.

[0038] The chain hoist 210 is a tool used to lift and lower heavy objects using pulleys and ropes. The chain hoist 210 is suspended from an overhead crane 150. The first load cell 220 is attached to the chain hoist 210 and is capable of measuring the load applied to the chain hoist 210. The slide hammer 230 is attached to the chain hoist 210. The slide hammer 230 is positioned vertically below the first load cell 220 in a direction Dv. The slide hammer 230 is capable of applying a pulling force toward the tip of the chain hoist 210 by the impact generated when a weight is slid toward the tip and strikes a stopper. The lifting member 240 is attached to the tip of the chain hoist 210. The lifting member 240 has, for example, a trapezoidal tip and is made impossible to remove from the guide tube 55 by rotating 90 degrees after being inserted into the guide tube 55. The lifting member 240 can have any configuration as long as it is detachable from the guide tube 55.

[0039] The lifting member 240 is inserted into the upper tube 551 from above in the vertical direction Dv, and the lifting member 240 rotates, thereby attaching the lifting member 240 to the upper tube 551. The upper tube 551 with the lifting member 240 attached is lifted above the vertical direction Dv relative to the upper core support plate 52 as the overhead crane 150 moves above the vertical direction Dv. Since the upper tube 551 is connected to the lower tube 555 by connecting bolts 59, the entire guide tube 55 is lifted above the vertical direction Dv. In other words, the lower tube 555 is lifted above the upper core plate 51 in the vertical direction Dv together with the upper tube 551. As a result, the lower tube 555 moves above the vertical direction Dv relative to the upper core plate 51, and the lower connecting pin 50b is pulled out of the fitting hole 50a. This releases the fitting between the lower tube 555 and the upper core plate 51.

[0040] Furthermore, with the lower tube 555 disengaged from the upper core plate 51, the guide tube 55 is removed from the overhead crane 150. Specifically, the guide tube 55 is moved upward in the vertical direction Dv to a position where the engagement of the fitting portion 50 is disengaged, and then lowered in such a way that the fitting portion 50 is not engaged. Therefore, the guide tube 55 is lowered without being pulled out through the through-hole of the upper core support plate 52. As a result, the guide tube 55 is supported in a way that it leans against the upper core support plate 52 and the upper core plate 51, with the engagement with the upper core plate 51 disengaged.

[0041] As shown in Figure 7, after the engagement between the lower tube 555 and the upper core plate 51 is released, the process of removing the connecting bolts 59 (step S3) is performed. At this time, the process of removing the connecting bolts 59 is performed on the upper core support plate 52, which is located in the air environment above the water. The connecting bolts 59 that fix the upper tube 551 and the lower tube 555 are removed. The connecting bolts 59 are removed while the guide tube 55 is supported by the upper core support plate 52 and the upper core plate 51. Then, the connecting bolts 59 are removed from the upper tube 551 and the lower tube 555 by pulling them upward in the vertical direction Dv. As a result, the fixing of the upper tube 551 and the lower tube 555 is released, and the upper tube 551 becomes movable relative to the lower tube 555. Also, the worker makes contact with the connecting bolts 59 from the first floor surface 111. For multiple connecting bolts 59, the worker will contact and remove the connecting bolts 59 located near the outer circumference of the upper core support plate 52 when viewed from above in the vertical direction Dv. Also, when viewed from above in the vertical direction Dv,

[0042] As shown in Figure 7, after the connecting bolts 59 are removed, a step (step S4) is performed to lift and remove the upper tube 551. Specifically, the upper tube 551 is lifted upward in the vertical direction Dv and removed from the upper core support plate 52. Specifically, as shown in Figure 9, the overhead crane 150 is attached to the upper tube 551. With the lifting member 240 inserted into the upper tube 551 from above in the vertical direction Dv, the lifting member 240 rotates, thereby attaching the lifting member 240 to the upper tube 551. With the lifting member 240 attached, the upper tube 551 is lifted upward in the vertical direction Dv relative to the upper core support plate 52 as the overhead crane 150 moves upward in the vertical direction Dv. Then, the overhead crane 150 moves horizontally in the horizontal direction Dh, and the upper tube 551 is removed from the upper core support plate 52. Furthermore, the upper tube 551 may be transported directly by workers without the use of lifting equipment such as the overhead crane 150.

[0043] In this embodiment, the steps of removing the connecting bolts 59 (step S3) and pulling up and removing the upper tube 551 (step S4) are repeatedly performed. Specifically, for multiple connecting bolts 59, when viewed from above in the vertical direction Dv, the worker makes contact with and removes the connecting bolts 59 that are located closer to the outer circumference of the upper core support plate 52. After that, the upper tube 551 from which the connecting bolts 59 have been removed is removed from the upper core support plate 52. In this way, the removal of the connecting bolts 59 and the upper tube 551 is carried out sequentially from a position closer to the outer circumference of the upper core support plate 52 towards a position closer to the center.

[0044] The step of lifting and removing the upper tube 551 (step S4) may be performed after removing all the connecting bolts 59.

[0045] As shown in Figure 7, after the upper tube 551 is removed, a step (step S5) is performed in which the lower tube 555 is lifted and removed. Specifically, the overhead crane 150 is attached to the lower tube 555. At that time, as shown in Figure 11, a second lifting jig 300 is attached to the overhead crane 150. The second lifting jig 300 is used when the overhead crane 150 lifts the lower tube 555. The second lifting jig 300 in this embodiment has a protective cover 310, a second load cell 320, an electric hoist 330, and a lifting member 240.

[0046] The protective cover 310 is suspended from the overhead crane 150. The protective cover 310 is capable of accommodating the lower tube 555 inside. The protective cover 310 is formed in a closed-bottom cylindrical shape with the top closed and the bottom open. In other words, the protective cover 310 is capable of inserting the lower tube 555 from the lower end in the vertical direction Dv. The protective cover 310 is formed to be large enough to accommodate the entire lower tube 555. The protective cover 310 is made of a material and size that can suppress the diffusion of radiation from the lower tube 555 housed inside to the outside. The second load cell 320 is mounted inside the protective cover 310. The second load cell 320 is capable of measuring the load generated on the electric hoist 330. The electric hoist 330 is capable of raising and lowering heavy objects by using electricity to move a motor with a wire attached. The electric hoist 330 is connected to the second load cell 320 inside the protective cover 310. The electric hoist 330 is positioned below the second load cell 320 in the vertical direction Dv. In the second lifting fixture 300, the lifting member 240 is attached to the tip of the electric hoist 330.

[0047] With the lifting member 240 inserted into the lower tube 555 from above in the vertical direction Dv, the lifting member 240 rotates, thereby attaching it to the lower tube 555. The lower tube 555, with the lifting member 240 attached, is lifted above the vertical direction Dv relative to the upper core plate 51 and the upper core support plate 52 as the overhead crane 150 moves above the vertical direction Dv. The portion of the lifted lower tube 555 located above the vertical direction Dv relative to the upper core support plate 52 is gradually housed inside the protective cover 310. Subsequently, the overhead crane 150 moves further above the vertical direction Dv, housing the entire lower tube 555 within the protective cover 310. The lower tube 555 housed within the protective cover 310 is removed from above the upper core support plate 52 along with the protective cover 310 as the overhead crane 150 moves horizontally in the direction Dh. At that time, the lower tube 555 and the protective cover 310 are positioned so that they are submerged in the second cavity 120, which is filled with water up to the level of the first floor surface 111.

[0048] As shown in Figure 7, after the lower tube 555 is removed, a step (step S6) is performed to cut the lower tube 555 into multiple pieces. Specifically, the lower tube 555 that has been lifted and removed is cut by a cutting device (not shown) so as to be divided in the vertical direction Dv. In addition to the lower tube 555, the upper tube 551 may also be cut.

[0049] The water level gauge support pipe may be dismantled using the same process and procedure as the guide tube 55 described above, or it may be dismantled using a different process and procedure.

[0050] (Effects and Benefits) In the dismantling method for the upper core structure 5 according to this embodiment, firstly, the fixing bolts 58 are removed, and the fixing between the lower tube 555 and the upper core support plate 52 is released. As a result, the guide tube 55 is made movable upward in the vertical direction Dv relative to the upper core support plate 52 and the upper core plate 51. In this state, the upper tube 551 is lifted upward in the vertical direction Dv by the overhead crane 150, and the entire guide tube 55 is moved upward in the vertical direction Dv relative to the upper core plate 51. As a result, the lower connecting pin 50b comes out of the fitting hole 50a, and the fitting of the lower tube 555 to the upper core plate 51 is released. Therefore, the lower connecting pin 50b and fitting hole 50a, which are fitted near the upper core plate 51 located at a position vertically Dv below the upper core support plate 52, can be released by gripping and moving the upper tube 551 from a position vertically Dv above the upper core support plate 52. In other words, the lower tube 555 can be released from its engagement with the upper core plate 51 without touching the space between the upper core support plate 52 and the upper core plate 51, which have high radiation levels, or the lower tube 555 itself.

[0051] Furthermore, the connecting bolts 59 are removed from the guide tube 55, which has been released from its engagement with the upper core plate 51. This makes the upper tube 551 and the lower tube 555 separable. In this state, the upper tube 551 is lifted and removed by the overhead crane 150. Therefore, the upper tube 551 can be removed first without removing the lower tube 555. As a result, the lifting stroke (amount of movement in the vertical direction Dv) is shorter compared to lifting and removing the entire long guide tube 55 at once. This avoids complicating the lifting operation.

[0052] Furthermore, after the upper tube 551 is removed, the lower tube 555 is lifted and removed by the overhead crane 150. Therefore, the upper tube 551 and the lower tube 555, which have different radiation levels, can be processed separately. In particular, by processing only the lower tube 555, which has a higher radiation level because it was located closer to the core 7 than the upper tube 551, the radiation level of the lower tube 555 can be controlled during processing. In this way, according to the dismantling method of the upper core structure 5, even components with different radiation levels can be processed with simplified work.

[0053] In-reactor structures such as the upper core structure 5 are located near the fuel and are high-radiation target equipment due to material activation and adhesion of radioactive products caused by neutron irradiation during operation. For this reason, they are usually handled underwater, hoping for the shielding effect of water. However, underwater work requires waterproof remote work equipment, which is inefficient and raises significant operational concerns such as equipment failure. However, according to the dismantling method for the upper core structure 5 of this embodiment, the work can be simplified and processed as described above.

[0054] Furthermore, the guide tube 55 is fixed to the upper core plate 51 at its lower end by a pin fitting using a fitting portion 50. If such a guide tube 55 were to be cut and dismantled on-site, the fixing would be weak, and it might be difficult to cut it properly. However, by applying a method to pull the guide tube 55 out from the upper core plate 51 and the upper core support plate 52 in advance, it becomes unnecessary to select work that would make cutting difficult, thereby improving work efficiency.

[0055] Furthermore, considering the differences in radioactivity levels (distribution) of the upper core structure 5, which is normally handled in a submerged state due to high radiation levels, applying a partial submersion method allows access by workers, eliminates the need for complex equipment control, and enables the selection of a more reliable dismantling method than remote underwater dismantling.

[0056] Furthermore, when removing the guide tube 55, the upper core support plate 52, which has a low radiation level, can be used as a shielding material. Therefore, the upper core support plate 52 can suppress the diffusion of radiation. Consequently, workers can secure sufficient time to move the guide tube 55, improving work efficiency.

[0057] Furthermore, when removing the fixing bolt 58, the connecting bolt 59 is loosened while maintaining the connection between the upper tube 551 and the lower tube 555. Because the connection between the upper tube 551 and the lower tube 555 is maintained by the connecting bolt 59, the lower tube 555 can be lifted simultaneously by simply lifting the upper tube 551. Therefore, the lower tube 555 can be released from its engagement with the upper core plate 51 by using the upper tube 551. In addition, the connecting bolt 59 is located close to the fixing bolt 58. Therefore, the work of loosening the connecting bolt 59, which may be stuck and unable to be removed, can be performed at the same time as the work on the fixing bolt 58. Therefore, when removing the connecting bolt 59, it is not necessary to remove any sticking of the connecting bolt 59. Therefore, the work can be reduced to simply releasing the fixing of the loosened connecting bolt 59, making the removal of the connecting bolt 59 easier.

[0058] Furthermore, the lower tube 555 and the upper core plate 51 are released from their engagement by being separated in the vertical direction Dv. Therefore, the engagement between the lower tube 555 and the upper core plate 51 can be easily released simply by pulling the lower tube 555 upward in the vertical direction Dv relative to the upper core plate 51 together with the upper tube 551. In particular, since the engagement portion 50 is formed by the lower connecting pin 50b and the engagement hole 50a, the engagement between the lower connecting pin 50b and the engagement hole 50a can be easily released with only a slight upward movement in the vertical direction Dv.

[0059] Furthermore, when the fixing bolts 58 are removed, the upper core structure 5 is positioned inside the reactor vessel body 21, where the cooling water remains, with the upper core plate 51 and lower tubes 555 submerged in water. As a result, the diffusion of radiation from the upper core plate 51 and lower tubes 555, which have relatively high radiation levels, is suppressed by the cooling water. Consequently, workers can secure sufficient working time when working on the upper core support plate 52, thereby improving work efficiency.

[0060] Furthermore, the upper core structure 5 is positioned inside the reactor vessel body 21, where cooling water is still stored, with the upper core plate 51 and lower tubes 555 submerged in water. On the other hand, the removal of the fixing bolts 58 and connecting bolts 59 is carried out on the upper core support plate 52, which is in an airy environment above the water, rather than in water. The upper core support plate 52 has a relatively low degree of activation among the components of the internal structure. Moreover, the upper core support plate 52 is a thick plate with a high shielding effect, and the radiation level above the upper core support plate 52 is significantly lower than below it. Thus, the upper core support plate 52, which is a component with a low radioactivity level and a high shielding effect, is located between the fuel area below the upper core support plate 52, which is the dominant radiation source, and the workers. Therefore, even in the upper core structure 5, the dismantling work of the low-radiation fixing bolts 58 and connecting bolts 59 can be carried out in the airy environment above the upper core support plate 52, which has a relatively low radiation dose. Therefore, the time available for workers to dismantle the fixing bolts 58 and connecting bolts 59 can be secured while minimizing the effects of radiation, thereby improving work efficiency.

[0061] Furthermore, when the lower tube 555 is lifted and removed, it is housed inside the protective cover 310 as it is lifted. Therefore, the protective cover 310 can suppress the diffusion of radiation when moving the lower tube 555, which has a relatively high radiation dose among the upper core structures 5. Consequently, workers can have sufficient time to move the lower tube 555, improving work efficiency.

[0062] Furthermore, the lower tube 555 is lifted and removed, and then cut into multiple pieces. This makes the long lower tube 555 smaller. Therefore, the lower tube 555 can be processed into pieces that fit into a predetermined size waste container corresponding to the dose level, which is an indicator of the amount of radioactive material contained in the waste. As a result, the lower tube 555 can be easily disposed of.

[0063] (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.

[0064] Furthermore, the reactor having the guide tube 55 to be dismantled is not limited to pressurized water reactors 1, but may have an upper core structure 5. For example, the reactor may be a boiling water reactor.

[0065] Furthermore, the configuration of the fitting portion 50 is not limited to the configuration of the above embodiment, as long as it is a structure in which the horizontal movement Dh of the lower tube 555 relative to the upper core plate 51 is restricted when the fitting state is achieved, and the fitting is released when the tube is separated in the vertical direction Dv. For example, a pin may be formed in the upper core plate 51, and a hole into which the pin can be inserted may be formed in the lower tube 555. In other words, the fitting portion 50 may have a pin formed in one of the lower tube 555 and the upper core plate 51, and a hole into which the pin can be inserted may be formed in the other of the lower tube 555 and the upper core plate 51.

[0066] Furthermore, when workers are working on the upper core support plate 52, additional shielding material may be installed within the worker's movement range. Specifically, a shielding plate made of lead may be placed on the upper core support plate 52. By installing such a shielding plate, the diffusion of radiation can be further suppressed. Therefore, the workability of workers when working on the upper core support plate 52 can be improved.

[0067] Furthermore, the anti-rotation device for the connecting bolt 59 is not limited to being removed before releasing the fixing bolt 58. The anti-rotation device for the connecting bolt 59 may also be removed when the connecting bolt 59 is completely removed.

[0068] <Note> The method for dismantling the upper core structure 5 described in each embodiment can be understood, for example, as follows.

[0069] (1) A method for dismantling an upper core structure 5 according to the first embodiment, comprising an upper core plate 51, an upper core support plate 52 positioned above the upper core plate 51 in a vertical direction Dv, and a guide tube 55 having a lower tube 555 and an upper tube 551, extending in the vertical direction Dv so as to penetrate from the upper core plate 51 to the upper core support plate 52, the method comprising: removing fixing bolts 58 that fix the lower tube 555 to the upper core support plate 52; pulling the upper tube 551 upward in the vertical direction Dv to release the engagement of the lower tube 555, which is connected to the upper tube 551 via connecting bolts 59, with respect to the upper core plate 51; removing the connecting bolts 59; pulling up and removing the upper tube 551; and pulling up and removing the lower tube 555.

[0070] With this configuration, the fixing bolt 58 is removed, and the fixing between the lower tube 555 and the upper core support plate 52 is released. This allows the guide tube 55 to move upward in the vertical direction Dv relative to the upper core support plate 52 and the upper core plate 51. In this state, the upper tube 551 is pulled up in the vertical direction Dv, and the entire guide tube 55 is moved upward in the vertical direction Dv relative to the upper core plate 51. As a result, the engagement of the lower tube 555 with the upper core plate 51 is released. Therefore, the engagement can be released by grasping and moving the upper tube 551 from a position vertically Dv above the upper core support plate 52. In other words, the engagement of the lower tube 555 with the upper core plate 51 can be released without touching the space between the upper core support plate 52 and the upper core plate 51, which have high radiation levels, or the lower tube 555 itself. Furthermore, the connecting bolt 59 is removed from the guide tube 55, which has been released from its engagement with the upper core plate 51. This makes the upper tube 551 and the lower tube 555 separable. In this state, the upper tube 551 is lifted and removed. Therefore, the upper tube 551 can be removed first without removing the lower tube 555. As a result, the lifting stroke is shorter compared to when the entire long guide tube 55 is lifted and removed at once. This avoids complicating the lifting operation. Furthermore, after the upper tube 551 is removed, the lower tube 555 is lifted and removed. Therefore, the upper tube 551 and the lower tube 555, which have different radiation levels, can be processed separately. In this way, according to the method for dismantling the upper core structure 5, even components with different radiation levels can be processed with simplified work.

[0071] (2) The method for dismantling the upper core structure 5 according to the second embodiment is the method for dismantling the upper core structure 5 according to (1), wherein in the step of removing the fixing bolts 58, the connecting bolts 59 that connect the upper tube 551 and the lower tube 555 are loosened while maintaining the connection between the upper tube 551 and the lower tube 555.

[0072] With this configuration, the connection between the upper tube 551 and the lower tube 555 is maintained by the connecting bolt 59, so that the lower tube 555 can be simultaneously lifted by simply lifting the upper tube 551. Therefore, the lower tube 555 can be released from its engagement with the upper core plate 51 by using the upper tube 551. In addition, the connecting bolt 59 is positioned close to the fixing bolt 58. Therefore, the work of loosening the connecting bolt 59, which may be stuck and unable to be removed, can be performed at the same time as the work on the fixing bolt 58. Therefore, when removing the connecting bolt 59, it is not necessary to remove any sticking of the connecting bolt 59. Therefore, the work of releasing the fixing of the loosened connecting bolt 59 can be reduced to just releasing the fixing, making the work of removing the connecting bolt 59 easier.

[0073] (3) A method for dismantling the upper core structure 5 according to the third embodiment is the method for dismantling the upper core structure 5 according to (1) or (2), wherein the lower tube 555 and the upper core plate 51 have a fitting portion 50 that is released when separated in the vertical direction Dv, and in the step of releasing the fitting, the lower tube 555 together with the upper tube 551 is pulled up in the vertical direction Dv above the upper core plate 51, thereby releasing the fitting.

[0074] With this configuration, the lower tube 555 and the upper core plate 51 can be easily disengaged simply by pulling the lower tube 555 upward in the vertical direction Dv relative to the upper core plate 51, along with the upper tube 551.

[0075] (4) A method for dismantling the upper core structure 5 according to the fourth embodiment is the method for dismantling the upper core structure 5 according to (3), wherein the fitting portion 50 has a pin extending in the vertical direction Dv formed in one of the lower tube 555 and the upper core plate 51, and a hole formed in the other of the lower tube 555 and the upper core plate 51 into which the pin can be inserted.

[0076] With this configuration, the engagement between the lower connecting pin 50b and the fitting hole 50a can be easily released by only a slight upward movement in the vertical direction Dv.

[0077] (5) The method for dismantling the upper core structure 5 according to the fifth embodiment is any one of the methods for dismantling the upper core structure 5 described in (1) to (4), wherein in the step of removing the fixing bolts 58, the upper core structure 5 is placed inside the reactor vessel 2 in which water is stored, and the upper core plate 51 and the lower tube 555 are placed in water.

[0078] With this configuration, the diffusion of radiation from the upper core plate 51 and lower tube 555, which have relatively high radiation levels in the upper core structure 5, is suppressed by the cooling water. Therefore, it is possible to secure working time for workers when they are working on the upper core support plate 52, and work efficiency can be improved.

[0079] (6) The method for dismantling the upper core structure 5 according to the sixth embodiment is the method for dismantling the upper core structure 5 according to (5), wherein at least one of the steps of removing the fixing bolts 58 and removing the connecting bolts 59 is carried out in an air environment on the water.

[0080] With this configuration, the dismantling of the low-radiation fixing bolts 58 and connecting bolts 59 can be carried out in the airy environment on the upper core support plate 52 of the upper core structure 5, where the radiation dose is relatively low. Therefore, the working time for workers dismantling the fixing bolts 58 and connecting bolts 59 can be secured while minimizing the effects of radiation, thereby improving work efficiency.

[0081] (7) A method for dismantling the upper core structure 5 according to the seventh embodiment is a method for dismantling the upper core structure 5 according to any one of (1) to (6), wherein in the step of lifting up and removing the lower tube 555, a protective cover 310 capable of housing the lower tube 555 is placed above the upper core support plate 52 in the vertical direction Dv, and the lower tube 555 is lifted up so that the lower tube 555 is housed inside the protective cover 310.

[0082] With this configuration, when moving the lower tube 555, which has a relatively high radiation dose within the upper core structure 5, the protective cover 310 can suppress the diffusion of radiation. Therefore, workers can have sufficient time to move the lower tube 555, improving work efficiency.

[0083] (8) A method for dismantling the upper core structure 5 according to the eighth aspect is a method for dismantling the upper core structure 5 according to any one of (1) to (7), further comprising the step of cutting the lower tube 555 that has been lifted and removed into a plurality of pieces.

[0084] With this configuration, the lower tube 555 can be processed into cut pieces that fit into a predetermined size waste container according to the dose level. Therefore, the lower tube 555 can be easily disposed of.

[0085] (9) A method for dismantling an upper core structure 5 according to the ninth embodiment, comprising an upper core plate 51, an upper core support plate 52 positioned vertically Dv above the upper core plate 51, and a guide tube 55 having a lower tube 555 and an upper tube 551, extending vertically Dv from the upper core plate 51 to the upper core support plate 52, wherein the upper core structure 5 is positioned inside a reactor vessel 2 in which water is stored, the upper core plate 51 and the lower tube 555 are positioned in water, and at least one of the fixing bolts 58 that fix the lower tube 555 to the upper core support plate 52 and the connecting bolts 59 that fix the upper tube 551 and the lower tube 555 is removed in an air environment above the water. [Explanation of symbols]

[0086] 1 Pressurized water reactor 2 Reactor vessel 21. Reactor vessel body 22 Reactor vessel lid 23 Inlet nozzle 24 Outlet nozzles 3. Control rod drive mechanism 5. Upper core structure 51 Upper core plate 52 Upper core support plate 53 Upper core support column 55 Guide tube 551 Upper tube 553 Upper tube body 554 Upper flange 555 Lower tube 557 Lower tube body 558 Lower flange 561 Intermediate lower tube 562 Bottom tube 50 Fitting part 50a Fitting hole 50b Lower connecting pin 58 Fixing bolts 59 Connecting bolts 6. Lower core structure 100 Reactor building indoor pool 110 First Cavity 111 First floor 120 Second Cavity 121 Second floor 140 Work platform 150 Overhead Cranes 200 First Lifting Jig 210 Chain Block 220 First Load Cell 230 Slide Hammer 240 Lifting Members 300 Second lifting jig 310 Protective Cover 320 Second load cell 330 Electric Hoist Dv Vertical direction Dh horizontal direction

Claims

1. A method for dismantling an upper core structure comprising an upper core plate, an upper core support plate positioned vertically above the upper core plate, and a guide tube having a lower tube and an upper tube, extending vertically from the upper core plate to the upper core support plate, wherein The steps include removing the fixing bolts that secure the lower tube to the upper core support plate, The process involves pulling the upper tube upward in the vertical direction to release the engagement of the lower tube, which is connected to the upper tube via a connecting bolt, with respect to the upper core plate. The process of removing the aforementioned connecting bolt, The process of lifting and removing the upper tube, The process of lifting up and removing the lower tube, A method for dismantling the upper core structure, including the core structure.

2. The method for dismantling an upper reactor core structure according to claim 1, wherein in the step of removing the fixing bolts, the connecting bolts connecting the upper tube and the lower tube are loosened while maintaining the connection between the upper tube and the lower tube.

3. The lower tube and the upper core plate have a fitting portion which is released when separated in the vertical direction. The method for dismantling an upper reactor core structure according to claim 1 or 2, wherein in the step of releasing the fitting, the lower tube is pulled up vertically upward with respect to the upper reactor core plate together with the upper tube, thereby releasing the fitting.

4. The method for dismantling an upper core structure according to claim 3, wherein the fitting portion comprises a vertically extending pin formed in one of the lower tube and the upper core plate, and a hole formed in the other of the lower tube and the upper core plate into which the pin can be inserted.

5. In the step of removing the fixing bolts, the upper core structure is placed inside a reactor vessel in which water is stored, and the upper core plate and the lower tube are placed in water, as described in claim 1 or 2, for the method of dismantling an upper core structure.

6. The method for dismantling an upper reactor core structure according to claim 5, wherein at least one of the steps of removing the fixing bolts and removing the connecting bolts is performed in an air environment on the water.

7. The method for dismantling an upper reactor core structure according to claim 1 or 2, wherein in the step of lifting up and removing the lower tube, a protective cover capable of housing the lower tube is positioned vertically above the upper reactor core support plate, and the lower tube is lifted up so that it is housed inside the protective cover.

8. A method for dismantling an upper reactor core structure according to claim 1 or 2, further comprising the step of cutting the lower tube, which has been lifted and removed, into a plurality of pieces.

9. A method for dismantling an upper core structure comprising an upper core plate, an upper core support plate positioned vertically above the upper core plate, and a guide tube having a lower tube and an upper tube, extending vertically from the upper core plate to the upper core support plate, wherein The upper core structure is located inside a reactor vessel in which water is stored, and the upper core plate and the lower tube are located in water. A method for dismantling an upper reactor core structure in which at least one of the fixing bolts that secure the lower tube to the upper core support plate, and the connecting bolts that secure the upper tube and the lower tube, is removed in an airborne environment above water.

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