Method for dismantling internal reactor structures

Abstract

To provide a method of dismantling core internals, which improves workability of dismantling work of core internals.SOLUTION: A method of dismantling core internals for dismantling a reactor vessel representing a reactor internal consisting of former plates fixed to an inner circumferential wall of a cylindrical reactor vessel body and baffle plates fixed to inner sides of the former plates, the method involving cutting the reactor vessel while the reactor vessel body, former plates, and baffle plates are assembled together.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a method for dismantling an in-vessel structure that cuts the in-vessel structure disposed inside a reactor vessel.

Background Art

[0002] In a nuclear power plant, a reactor containment vessel is erected on solid ground such as bedrock, and a nuclear reactor is disposed inside thereof. The nuclear reactor is configured by arranging in-vessel structures such as fuel inside a reactor vessel. When decommissioning the nuclear reactor, the in-vessel structures are taken out from the inside of the reactor vessel and cut into a predetermined size. As a technique for cutting in-vessel structures, for example, there is one described in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A core tank serving as an in-vessel structure is configured such that a former plate is fixed to the inner peripheral wall portion of a cylindrical core tank body, and a baffle plate is fixed to the inner side of the former plate. The former plate is fixed to the inner peripheral wall portion of the core tank body by a plurality of bolts, and the baffle plate is fixed to the former plate by a plurality of bolts. Therefore, when dismantling the core tank, after loosening the bolts relative to the former plate to remove the baffle plate and loosening the bolts relative to the core tank body to remove the former plate, the core tank body is cut into a predetermined size. This leads to the problem that the dismantling work of the core tank takes a long time.

[0005] The present disclosure solves the above-described problem, and an object thereof is to provide a method for dismantling an in-vessel structure that improves the workability of the dismantling work of the in-vessel structure.

Means for Solving the Problems

[0006] To achieve the above objective, the present disclosure is a method for dismantling an in-core structure, in which a core vessel, as an in-core structure, is constructed by fixing a former plate to the inner circumferential wall of a cylindrical core vessel body and fixing a baffle plate to the inside of the former plate, and the method for dismantling an in-core structure is to cut the core vessel body, the former plate and the baffle plate while they are assembled as a single unit. [Effects of the Invention]

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

[0008] [Figure 1] Figure 1 is a longitudinal cross-sectional view of a pressurized water reactor. [Figure 2] Figure 2 is a schematic plan view representing the reactor core vessel as an internal structure of the reactor. [Figure 3] Figure 3 is a schematic plan view showing the main parts of the reactor core. [Figure 4] Figure 4 is a schematic longitudinal cross-sectional view representing the reactor core. [Figure 5] Figure 5 is a schematic perspective view showing the interconnected structure of the reactor core vessel. [Figure 6] Figure 6 is a schematic cross-sectional view showing the core vessel in a cross-section. [Modes for carrying out the invention]

[0009] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure, and where there are multiple embodiments, they may be combinations of these embodiments. Furthermore, the components in the embodiments include those readily conceivable by those skilled in the art, those that are substantially identical, and those that are equivalent.

[0010] <Pressurized Water Reactor> Figure 1 is a longitudinal cross-sectional view of a pressurized water reactor.

[0011] The nuclear power plant, although not shown in the figures, comprises a reactor and steam generator located within a reactor containment vessel, and a steam turbine power generation system. The reactor in this embodiment is a pressurized water reactor (PWR). However, the reactor may be any type of reactor, such as a boiling water reactor (BWR) or a fast breeder reactor (FBR).

[0012] As shown in Figure 1, in a pressurized water reactor 10, the reactor vessel 11 is composed of a reactor vessel body 12 and a reactor vessel lid 13 attached to the top of the reactor vessel, so that internal reactor structures can be inserted inside. The reactor vessel lid 13 is fixed to the reactor vessel body 12 so as to be openable and closable by a plurality of stud bolts 14 and nuts 15.

[0013] The reactor vessel body 12 has a cylindrical shape with an open top and a closed, hemispherical bottom. An inlet nozzle 16 for supplying light water as the primary coolant and an outlet nozzle 17 for discharging light water are formed at the top. The reactor vessel body 12 houses a core tank 18, and its upper part is supported by the inner wall surface of the reactor vessel body 12. The upper core support plate 19 is located inside the reactor vessel body 12, and its upper part is supported above the core tank 18. The upper core plate 20 is suspended and supported from the upper core support plate 19 by a plurality of core support rods 21.

[0014] The core vessel 18 is supported below by a lower core support plate 22, the lower core support plate 22 being positioned and supported on the inner wall surface of the reactor vessel body 12 by a positioning member 23 on its outer circumference. The core vessel 18 is supported below by a lower core plate 24. The core 25 is composed of numerous fuel assemblies 26, with numerous control rods 27 arranged inside, and the control rods 27 are insertable into the fuel assemblies 26. The upper core support plate 19 has numerous control rod cluster guide tubes 28 fixed to it, through which control rods 27 can be inserted. The reactor vessel lid 13 is hemispherical in shape, and a control rod drive device 29 is located there, with multiple control rod cluster drive shafts 30 inserted into the control rod cluster guide tubes 28, and control rods 27 connected to their lower ends. The control rod drive device 29 controls the reactor output by inserting and removing each control rod 27 from the core 25.

[0015] Furthermore, a detector guide device 31 is positioned inside the reactor vessel 11. The detector guide device 31 guides a neutron flux detector (not shown) from the instrumentation tube holder 32 of the reactor vessel lid 13 through a guide member 33 to the reactor core 25 (fuel assembly 26). The neutron flux detector can measure neutron levels and distribution (neutron flux). Specifically, the detector guide device 31 guides the neutron flux detector (not shown) from the instrumentation tube holder 32 of the reactor vessel lid 13 through a guide member 33 and a guide thimble (not shown) fixed to the lower end of the guide member 33 to the reactor core 25 (fuel assembly 26).

[0016] <Core tank> Figure 2 is a schematic plan view representing the core vessel as an internal structure of the reactor, Figure 3 is a schematic plan view representing the main part of the core vessel, Figure 4 is a schematic longitudinal section view representing the core vessel, and Figure 5 is a schematic perspective view representing the connecting structure of the core vessel.

[0017] As shown in Figures 2 to 5, the core vessel 18, as an internal structure of the reactor, comprises a core vessel body 51, a former plate 52, and a baffle plate 53.

[0018] The reactor core tank main body 51 has a cylindrical shape. A plurality of former plates 52 are provided, each having a ring shape. The former plate 52 has an outer peripheral surface that is substantially perfectly circular, and an inner peripheral surface that has a jagged shape. That is, the inner peripheral surface of the former plate 52 is formed by two surfaces 52a and 52b that are orthogonal to the horizontal plane and orthogonal to each other. The former plate 52 is provided with an outer diameter that is the same as or slightly smaller than the inner diameter of the reactor core tank main body 51. A plurality of baffle plates 53 are provided, each having a rectangular plate shape.

[0019] The former plate 52 is disposed on the inner side of the reactor core tank main body 51. A plurality of the former plates 52 are arranged at intervals in the axial direction of the reactor core tank main body 51. The former plate 52 is fixed by a plurality of first bolts 61 in a state where the outer peripheral surface is in contact with the inner peripheral surface of the reactor core tank main body 51. The plurality of first bolts 61 penetrate the reactor core tank main body 51 from the outer peripheral surface side of the reactor core tank main body 51 and are screwed into the former plate 52. The plurality of first bolts 61 are arranged at intervals in the circumferential direction of the reactor core tank main body 51 and the former plate 52.

[0020] The plurality of baffle plates 53 are arranged on the inner side of the former plates 52. The plurality of baffle plates 53 are arranged along the axial direction, and are fixed by a plurality of second bolts 62 in a state of being in contact with the surfaces 52a and 52b of the former plates 52.

[0021] The reactor core tank main body 51 and the former plate 52 are connected by the first bolts 61, and the former plate 52 and the baffle plate 53 are connected by the second bolts 62. A plurality of fuel assemblies 26 are arranged inside the reactor core tank 18. The fuel assemblies 26 are arranged adjacent to the baffle plate 53. The flow of coolant leading to the fuel assemblies 26 is divided by the baffle plate 53.

[0022] <Method for dismantling reactor internal structures> FIG. 6 is a schematic cross-sectional view showing a cutting state of the reactor core tank.

[0023] As shown in FIG. 1, the reactor vessel lid 13 is removed from the reactor vessel main body 12, and reactor internal structures such as the reactor core 25 are carried out from the inside. The reactor internal structures include the reactor core tank 18.

[0024] The reactor core 18 is connected to the reactor core body 51 and the former plate 52 by first bolts 61, and to the former plate 52 and the baffle plate 53 by second bolts 62. In this embodiment, the dismantling method for the in-reactor structure is as shown in Figures 3 and 4, in which the reactor core body 51, former plate 52, and baffle plate 53 are cut while they are assembled as a single unit.

[0025] At this time, the core vessel 18 is cut from the upper side at locations other than the positions of the multiple first bolts and multiple second bolts. The cutting method is mechanical cutting, but gas cutting or laser cutting may also be used.

[0026] To explain in more detail, first, with the core vessel body 51, former plate 52, and baffle plate 53 assembled as a single unit, the core vessel 18 is cut into a ring shape at the horizontal cutting position L1. As shown in Figure 6, the cut piece 18a of the core vessel 18 is ring-shaped, and the respective cut pieces 51A, 52A, and 53A of the core vessel body 51, former plate 52, and baffle plate 53 are connected by the first bolt 61 and the second bolt 62.

[0027] Next, as shown in Figures 3 and 6, the cut piece 18a of the core layer 18 is cut along the axial direction at vertical cutting positions L2. Multiple vertical cutting positions L2 are provided at intervals in the circumferential direction. At this time, the cut is made at a position other than the positions of the multiple first bolts and multiple second bolts.

[0028] In the above explanation, the reactor core vessel 18 was cut into a ring shape and then cut along the axial direction. However, the reactor core vessel 18 may also be cut along the axial direction and then cut along the horizontal direction.

[0029] [Effects of this embodiment] The first embodiment of the method for dismantling an in-core structure involves dismantling a core vessel 18, which is an in-core structure in which a former plate 52 is fixed to the inner circumferential wall of a cylindrical core vessel body 51, and a baffle plate 53 is fixed to the inside of the former plate 52. In this method, the core vessel body 51, the former plate 52, and the baffle plate 53 are cut while they are assembled as a single unit.

[0030] According to the first embodiment of the method for dismantling the in-reactor structure, it is no longer necessary to dismantle the core tank body 51, the former plate 52, and the baffle plate 53 in advance, thereby improving the workability of the dismantling work of the core layer 18 as an in-reactor structure.

[0031] The second embodiment of the method for dismantling an in-furnace structure is the same as the first embodiment of the method for dismantling an in-furnace structure, further comprising fixing a former plate 52 to the inner circumferential wall of the core vessel body 51 with a plurality of first bolts 61, fixing a baffle plate 53 to the inside of the former plate 52 with a plurality of second bolts 62, and cutting at positions other than the positions of the first bolts 61 and the second bolts 62. This eliminates the need to cut the first bolts 61 and the second bolts 62, thereby suppressing the generation of fine waste.

[0032] The third embodiment of the method for dismantling an in-core structure is the method for dismantling an in-core structure according to the first or second embodiment, further comprising cutting the core vessel body 51 into a ring shape. This allows the core layer 18 to be dismantled efficiently.

[0033] The fourth embodiment of the method for dismantling an in-core structure is a method for dismantling an in-core structure according to any one of the first to third embodiments, further comprising cutting the core vessel body 51 along the axial direction. This allows for efficient dismantling of the core layer 18.

[0034] The fifth embodiment of the method for dismantling an in-core structure is a method for dismantling an in-core structure according to any one of the first to fourth embodiments, further comprising cutting the core vessel body 51 into a ring shape and then cutting it along the axial direction. This allows the core layer 18 to be dismantled efficiently.

[0035] In the embodiments described above, the core vessel 18 was described as being cut along the horizontal or axial direction, but it may also be cut at an angle. [Explanation of symbols]

[0036] 10 Pressurized water reactor 11 Reactor vessel 12. Reactor vessel body 13 Reactor vessel lid 18 Core tank (core internal structure) 19 Upper core support plate 20 Upper core plate 21 Core support rods 25 Core 26 Fuel assembly 51 Core vessel body 52 Forma Plate 53 Baffle Plate 61 Bolt 1 62 Second bolt

Claims

1. In a method for dismantling a reactor core, which is an in-reactor structure in which a plurality of former plates are fixed to the inner circumferential wall of a cylindrical core vessel body at axial intervals with first bolts, and a plurality of baffle plates are fixed to the inside of the former plates at axial intervals with second bolts, With the core vessel body, the former plate, and the baffle plate assembled as a single unit, the core vessel body is cut radially into a ring shape between a plurality of first bolts arranged in the axial direction and between a plurality of second bolts arranged in the axial direction. Methods for dismantling internal reactor structures.

2. The reactor core body is cut along the axial direction. A method for dismantling an in-furnace structure according to claim 1.

3. After cutting the core vessel body into a ring shape, it is cut along the axial direction. A method for dismantling an in-furnace structure according to claim 1.

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