JP3042030B2 - How to seal containers for geological disposal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sealing a container for geological disposal.

[0002]

2. Description of the Related Art The handling of high-level radioactive waste (waste liquid and the like) generated in facilities related to a nuclear power plant can be improved, for example, by vitrification.

[0003] The solidified package (canister) containing the vitrified material in a container is placed in an artificially constructed radioactive waste storage facility in order to prevent radiation contamination until the emission of radiation is significantly reduced. In addition to long-term storage and storage, there are plans to store and dispose of it in the deep underground and isolate it from the living area.

[0004] In this underground disposal plan, the movement and diffusion of radionuclides can be suppressed by utilizing the properties of natural rocks, but it is important to note that the state of rocks in the underground formation cannot be completely grasped. Based on this, it is considered practical to control the leakage of radionuclides using artificial structures. The plan also states that using borosilicate glass as a solidified body and using a stainless steel alloy as a storage container to form a solidified package (canister) are effective.

Further, in a solidified package in which radioactive waste is confined, a bedrock (parent rock) is excavated to form a disposal hole, and an appropriate amount of buffer material made of bentonite is spread on the bottom of the disposal hole, and is placed thereon. The canister is placed in a sealed state with an overpack (container) made of an appropriate metal material such as carbon steel, and a buffer material is filled around the overpack to form a buffer layer. Disposal covering is carried out.

When such a disposal is performed, when the inundation phenomenon occurs from the bedrock, a part of the buffer material swells and the internal pressure of the buffer layer increases, thereby preventing the intrusion of water and ensuring the sealing performance. In addition, radioactive waste is overpacked,
By being multiply covered with a canister and a glass layer, the safety at the time of geological disposal can be improved.

FIG. 4 shows a conventional example of a container for geological disposal. In FIG. 4, reference numeral 1 denotes a container body, 2 denotes a round hole-shaped opening, 3 denotes a disk-shaped closing lid, 4 denotes a welded portion, and P denotes a canister (solidified package in which a vitrified material is stored in a container). is there.

In such a container for geological disposal, a canister P is loaded into the container body 1 through an opening 2 of the container body 1 and a closing lid 3 is provided.
Is welded between the inner surface of the opening 2 and the edge of the closing lid 3 to form a welded portion 4. The thickness of the container body 1 and the closing lid 3 is, for example, 250 mm.
By setting such a degree, good sealing performance against corrosion or the like is obtained.

[0009]

However, the width of the groove above the welding groove is increased in the welded portion 4 based on the fact that the welding operation is performed in a thick wall and in a radioactive atmosphere. It is necessary to enhance workability, and therefore the amount of weld metal increases, and the weld 4 and the metallographic structure in the vicinity of the weld 4 appear in FIG.
As shown in (1), a large tensile residual stress σ is easily applied. In this case, since the container body 1 and the closing lid 3 are thick-walled structures, it is also difficult to perform preheating or post-heat treatment during welding work to reduce the residual stress. Further, when the welded portion 4 is formed, the heat at the time of forming the weld bead is quickly transmitted and easily cooled due to the large heat capacity of the container body 1 and the closing lid 3, and the rapid cooling facilitates the welding. It is necessary to take into account hydrogen embrittlement and hydrogen cracking due to hydrogen embrittlement due to the hydrogen occlusion phenomenon.

The present invention has been made in view of such circumstances, and aims to reduce residual stress in a welded portion, improve workability in a welded portion, cause a hydrogen occlusion phenomenon, and a hydrogen embrittlement phenomenon caused by the phenomenon. The purpose is to prevent such problems.

[0011]

In order to achieve the above object, in the method of sealing a container for geological disposal according to the present invention, a thin plate is inserted into an opening of a container body, and the inner surface of the opening is thinned. The step of welding between the edges of the sheet material is repeated, and the opening is sealed with the thinned sheet material and the welded portion.

[0012]

When a process of welding a thin plate to an opening is performed in a plurality of times, tensile stress is applied to the weld and the thin plate as the weld is formed. By performing plastic deformation by the stress generated at the time of welding, the residual stress is reduced in the welded portion and its vicinity. And when welding a thin plate material, the space above it is opened based on the thinness of the thin plate material, and the welding workability is improved.

[0013]

FIG. 1 shows a geological disposal container sealed by a method for sealing a geological disposal container according to the present invention,
FIG. 2 shows a state in the middle of the sealing operation process.

1 and 2, reference numeral 11 denotes a thin plate material, 12 denotes a weld bead, and 13 denotes an inward flange. The opening 2, the thin plate 11 and the inward flange 13
Is set to a circular shape or the like in accordance with the cross-sectional shape of the canister P.

When the canister P is loaded into the container main body 1 through the opening 2, the opening 2 of the container main body 1 is opened.
The thin plate 11 is inserted into the opening 11, and the weight of the thin plate 11 is supported by the inward flange 13.
The first welding bead 12 is formed by the welding groove formed between the first welding bead (see FIG. 2). In this case, when the container body 1 is made of carbon steel or low alloy steel, a material equivalent thereto or soft iron having a small mechanical strength is used as the thin plate material 11. The thickness of the thin sheet material 11 is approximately equal to the thickness of one weld bead 12 (for example, approximately 3 mm).
Is set to When the weld bead 12 is formed, a tensile stress is applied to the weld bead 12 and the sheet material 11 and the like due to the contraction action of the portion of the weld bead 12, but the mechanical strength of the sheet material 11 is less than that of the container body 1. Since the sheet material 11 is relatively small, the stress generated by the plastic deformation of the sheet material 11 as a whole can be reduced. The formation of the first welding bead 12 results in the state shown in FIG.

Next, a second thin plate 11 slightly larger in diameter than the first thin plate 11 is prepared, and the second thin plate 11 is placed on the first thin plate 11 as shown by an arrow in FIG. The welding is performed between the inner surface of the opening 2 and the edge of the sheet material 11.

Subsequently, the process of welding between the inner surface of the opening 2 and the edge of the thin sheet material 11 that is successively piled up is repeated, and the welding portion 4 is formed by stacking a plurality of thin sheet materials 11 and welding beads 12. Thus, the opening 2 is completely sealed, and the upper surface of the container body 1 is flattened. As described above, when the sheet material 11 is sequentially welded in a plurality of times, since one sheet material 11 is thin, the space above the sheet material 11 is released as shown in FIG. In addition, since the welding instrument can be easily inserted into the space, welding workability is improved.

Further, the amount of weld metal per one welding when the thin sheet material 11 is welded is determined by the gap between the inner surface of the opening 2 and the edge of the thin sheet material 11 and the welding bead 12 shown in FIG.
And the thickness of the thin sheet material 11, so that the amount of heat of each welding becomes substantially equal, and the residual stress generated during one welding operation is reduced.

Since the heat of the weld bead 12 is transmitted to the container body 1 and the sheet material 11 and is radiated, the cooling of the sheet material 11 is delayed as compared with the example of FIG. No. 4 is less likely to cause a hydrogen occlusion phenomenon, which suppresses the reduction in brittleness and the generation of hydrogen cracks based on this.

The thin plates 11 used to close the opening 2 may be, for example, stacked in the same size. In this case, the inner peripheral surface of the opening 2 has a cylindrical shape instead of a tapered shape. Shape (straight shape) or the like.

[0021]

As described above, according to the method for sealing a container for geological disposal according to the present invention, a thin plate is inserted into the opening of the container body, and the inner surface of the opening and the edge of the thin plate are connected to each other. Since the welding operation is repeatedly performed during this time, and the opening is sealed with the thin plate material and the welded portion, the following effects are obtained. (1) When forming a welded portion, the range and the amount of weld metal are set by the gap between the opening of the container body and the edge of the sheet material, the thickness of the sheet material, and the like, thereby improving the reliability of welding work. it can. (2) Since the portion of the thin plate material is easily deformed, the residual stress in the welded portion and its vicinity can be reduced without being concentrated on a part. (3) When welding a thin plate material, the space above it is released, and welding workability can be improved. (4) By welding the thin plate material, the heat transfer speed at the time of welding can be reduced, and the occurrence of a hydrogen storage phenomenon and a hydrogen embrittlement phenomenon due to the phenomenon can be prevented.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing an example of a geological disposal container sealed by a method for sealing a geological disposal container according to the present invention.

FIG. 2 is a front sectional view showing a state in the middle of a sealing operation process according to the method for sealing a geological disposal container according to the present invention.

FIG. 3 is a distribution diagram of residual stress generated in a sealed portion by a method for sealing a geological disposal container according to the present invention.

FIG. 4 is a front sectional view showing an example of a geological disposal container sealed by a conventional method.

FIG. 5 is a distribution diagram of residual stress generated in a sealed portion in the example of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container main body 2 Opening 3 Closure lid 4 Welding part 11 Thin plate material 12 Weld bead 13 Inward flange P Canister (solidified package)

Claims (1)

(57) [Claims] 1. A step of inserting a thin plate into an opening of a container body and repeating welding between an inner surface of the opening and an edge of the thin plate, the opening being formed by the stacked thin plate and a welded portion. A method for sealing a container for geological disposal, characterized in that the container is sealed.