JP2018031172A - Dismantling method for contaminated water storage tank - Google Patents

Abstract

An object of the present invention is to provide a more convenient means for cutting a bolt required for dismantling a contaminated water storage tank. A method for disassembling a contaminated water storage tank that has stored contaminated water containing a radioactive substance, wherein a bolt joint for integrating the constituent members of the tank is embedded with concrete. To form an injection hole communicating with the bolt, and to inject liquid nitrogen from the injection hole. The structural member is disassembled by breaking the bolt and breaking the bolt by applying an impact to the brittle bolt. [Selection] Figure 5

Description

  The present invention relates to a method for dismantling a contaminated water storage tank that is a steel structure.

Steel structures such as storage tanks may be integrated by joining the structural members of the steel structure with high-strength bolts. Therefore, when disassembling the steel structure, each component can be separated by loosening the high-strength bolt.
However, if a problem such as thread wear or crush occurs on the bolt, the bolt cannot be loosened and removed.
As a countermeasure to this problem, a method of cutting the bolt itself is known.
As a method for cutting the bolt, there are a method using a device having a specially shaped blade as shown in Patent Document 1, a method using fire such as gas cutting, plasma cutting, and lance cutting.

JP-A-11-262814

However, the conventional cutting method has the problems described below.
(1) The special-shaped cutting device shown in Patent Document 1 is a dedicated product, and the range of use is limited.
(2) Devices that use fire for cutting cannot be used in places where fire is strictly prohibited, such as places where flammables are nearby or factory sites that handle hazardous materials.

  Therefore, this invention makes it one of the objectives to provide a more convenient means in the cutting | disconnection of the bolt required at the time of the disassembly of a contaminated water storage tank.

The first invention of the present application to solve the above problem is a method for disassembling a contaminated water storage tank that has stored contaminated water containing a radioactive substance, and is a bolt for integrating the constituent members of the tank. Drilling the surface layer part formed by embedding the joint part with concrete, exposing the gap between the constituent members of the tank, drilling so as to expand the gap, forming an injection hole communicating with the bolt, The component member is disassembled by injecting liquid nitrogen from the injection hole to embrittle the bolt, impacting the embrittled bolt and breaking the bolt.
The second invention of the present application is characterized in that in the first invention, liquid nitrogen is injected after a bolt is drilled from the injection hole.

The present invention has the effects described below.
(1) The bolt can be easily cut only by applying an impact after embrittlement of the bolt with liquid nitrogen, and there is no need to prepare a special dedicated product.
(2) Since no fire is used, it can be carried out even in places where fire is strictly prohibited.
(3) Bolt embrittlement can be efficiently performed by injecting liquid nitrogen after drilling a part of the bolt.

The schematic front view which shows the initial state of a bolt coupling | bond part. The schematic front view which shows the state which is drilling the surface layer part. The schematic front view which shows the state which drilled the flange. The schematic front view which shows the state which drilled the volt | bolt. The schematic front view which shows the state which inject | poured liquid nitrogen. The schematic front view which shows the state which has given the impact force to the volt | bolt. The schematic plan view which shows the shape of a chisel tip. The schematic front view which shows the state which peeling has occurred in the surface layer part. The schematic front view which shows the state which the volt | bolt fractured | ruptured.

  Embodiments of the present invention will be described below with reference to the drawings.

The procedure of the method for disassembling a contaminated water storage tank according to the present invention will be described.
In addition, the procedure shown below is an example and each process can be abbreviate | omitted or a different process can be added according to site conditions. In addition, each step may be appropriately replaced within a consistent range.

<1> Bolt joint structure (Fig. 1)
First, the bottom plate structure of the tank before dismantling will be described.
The plurality of divided bottom plates 10 constituting the bottom plate of the tank are joined and integrated with bolts 20 in a state where the flanges 11 extending upward from the bottom surface are in contact with each other, and sealed with a sealing material 30. Yes.
And this bolt coupling | bond part is embed | buried with mortar, concrete, etc., and the state which formed the surface layer part 40 is exhibited.
From this state, the cutting operation of the bolt 20 proceeds.

<2> Black ink and surface drilling (Figure 2)
First, the position of the bolt 20 is specified and inking is performed. When the position of the bolt 20 is not visible, a detection device such as an electromagnetic wave radar can be used.
Then, as shown in FIG. 2, drilling of the surface layer portion 40 at the marked position is performed. This is because the bolt 20 is embedded by the surface layer portion 40, so that the surface layer portion 40 is drilled to secure a passage 41 to the bolt 20.
A known drilling machine such as the breaker 50 can be used for drilling the surface layer portion 40. In this embodiment, the hole diameter of the breaker 50 is about 30 mm.
At this time, if a suction type hole drilling machine is used, it is possible to prevent the diffusion of dust generated during the hole drilling operation of the surface layer portion 40.

<3> Formation of injection hole (FIG. 3)
Next, a drill 60 a is inserted into the passage 41 provided in the surface layer portion 40, and a hole is drilled so as to expand the gap between the flanges 11 that are in contact with each other, thereby forming the injection hole 111.
The drilling diameter of the drill 60a can be set to be approximately the same as the drilling diameter of the surface layer portion 40 described above.
As the drilling by the drill 60a proceeds, the periphery of the shaft 20 of the bolt 20 being fastened and the outside communicate with each other from the injection hole 111.

<4> Bolt drilling (Figure 4)
In addition, after formation of the injection hole 111, the perforation part 21 can also be formed in the volt | bolt 20 as needed.
As shown in FIG. 4, when the bolt 20 is a high-strength bolt, since it takes time to drill, the drilled portion 21 is formed using a drill 60b having a smaller diameter instead of the drill 60a. In addition, the drilling by the drill 60a used for drilling the flange 11 may be advanced as it is.
The perforated part 21 can be formed in the form of a recess formed by partially drilling the bolt 20 or a through hole formed through the bolt 20.
If it is the aspect which penetrates the volt | bolt 20, the cooling effect of the volt | bolt 20 mentioned later can be exhibited more efficiently.

<5> Liquid nitrogen injection (FIG. 5)
When the shaft portion of the bolt 20 being fastened is visible, liquid nitrogen 70 is injected into the bolt 20 to cool or freeze the bolt 20.
As a method for injecting the liquid nitrogen 70, there are a method in which the liquid nitrogen 70 is poured into the passage 41, a method in which an injection nozzle is inserted into the passage 41, and the liquid nitrogen 70 is directly injected in the vicinity of the bolt 20.
As described above, when the perforated part 21 is formed in the bolt 20, if the liquid nitrogen 70 flows into the perforated part 21, a higher cooling effect can be obtained.
The bolt 20 that has been cooled or frozen by the liquid nitrogen 70 becomes brittle, that is, the bolt does not stretch and is easily broken.

<6> Introduction of impact force (Figs. 6 and 7)
Next, an impact force is applied to the embrittled bolt 20 to brittlely break the bolt.
As a method for applying the impact force, a known method can be adopted.
In FIG. 6, a chisel 80 made of forged steel is installed on an air hammer, and an impact force is applied in such a manner that the chisel 80 is repeatedly collided with the bolt 20.
As shown in FIG. 7, it is preferable that the chisel tip 81 has a rhombus shape having a major axis in a direction orthogonal to the axial direction of the bolt 20 in a plan view because the bolt 20 can be easily cut.

<7> Bolt breaking action (FIGS. 6 and 8)
As shown in FIG. 6, when an impact force is introduced into the bolt 20, a split tensile force T acts in a direction opposite to the axial force P caused by tightening the bolt 20.
When the split tensile force T becomes larger than the axial force P, the force of (TP) is transmitted from the bolt 20 to the surface layer portion 40, and shear failure occurs in the surface layer portion 40.
Then, as shown in FIG. 8, when the upper part (peeling part 42) of the surface layer part 40 that has undergone shearing is displaced upward, the force that restrains the flange 11 is lost, and the flanges 11 are separated from each other. It is displaced in the plane direction.
Since the bolt 20 is brittle, the shaft portion is easily broken by the displacement of the flange 11.

<8> Separation of components (FIG. 9)
After the rupture of the bolt 20, the divisional bottom plates 10 are unintegrated and can be separated and disassembled.
At this time, even if the surface layer portion (remaining portion 43) remaining on the divided bottom plate 10 is present, the remaining portion 43 is transported as it is without peeling off from the divided bottom plate 10 so that generation of extra dust can be avoided.

<9> Summary As described above, according to the method of the present example, the bolt can be easily cut by brittle fracture by giving an impact after embrittlement of the bolt with liquid nitrogen. It can be implemented in places where it cannot be used.
Also, when disassembling a contaminated water storage tank that has stored contaminated water containing radioactive substances, if the bolted joint is buried by a surface layer such as mortar, the surface layer has conventionally been manually swept. In contrast to the bolts that had to be removed, according to the present embodiment, drilling work on the surface layer portion can be suppressed to a minimum, so there is a risk of worker exposure due to dust suction and the like. It can also be reduced.

10 Split bottom plate 11 Flange 111 Injection hole 20 Bolt 21 Perforated part 30 Sealing material 40 Surface layer part 41 Path 42 Peeling part 43 Remaining part 50 Breaker 60 Drill 70 Liquid nitrogen 80 Chisel 81 Chisel tip

Claims (2)

A method for disassembling a contaminated water storage tank that has stored contaminated water containing radioactive substances,
Drilling a surface layer portion formed by embedding bolt connecting portions for integrating the structural members of the tank with concrete, exposing a gap between the structural members of the tank,
Drilling to expand the gap, forming an injection hole communicating with the bolt,
Injecting liquid nitrogen from the injection hole to embrittle the bolt,
The structural member is disassembled by impacting the embrittled bolt and breaking the bolt,
Dismantling method for contaminated water storage tanks.   The method for disassembling a contaminated water storage tank according to claim 1, wherein liquid nitrogen is injected after a bolt is drilled from the injection hole.

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