JP2000155196A - Canister for disposal of radioactive waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent radioactive substances in wastes housed in canisters from migrating into underground water. SOLUTION: A cylindrical canister side wall plate 4, a canister bottom plate 5 and a lid 6 are produced by using a clad material made of tantalum 1 and carbon steel 3 where copper 2 is used for an insert material, they are TIG- welded to each other by using a tantalum strap plate 7 to completely cover with tantalum 1 an outer wall of a canister for disposal of radioactive wastes. This makes it possible to prevent radioactive substances in wastes 8 housed in canisters for disposal of radioactive wastes from migrating into underground water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive waste disposal container, and more particularly, to a radioactive waste disposal container suitable for geological disposal of radioactive waste generated with the development and use of nuclear power. .

[0002]

2. Description of the Related Art As a method for disposing of radioactive waste, geological disposal buried in a formation remote from a human sphere is considered to be the most rational and highly safe method, and a safety protection system artificially provided. The basic idea is to ensure safety by a multiple protection system (multi-barrier system) that combines an (artificial barrier) and a stratum (natural barrier).

[0003] Containers, which are one of the components of the artificial barrier, are expected to function to suppress contact between groundwater and waste for a long period of time and prevent radioactive substances in waste from migrating to groundwater.

[0004] Materials for the container include metal materials, non-metallic materials other than metal, and barbed materials. However, there are many unclear points regarding the barbed materials in terms of long-term chemical durability, heat resistance, radiation resistance, and the like, and no examples have been studied so far.

[0005] In the case of non-bundled materials, concrete containers are being studied for the purpose of disposal of miscellaneous solid wastes (for example, The Atomic Energy Society of Japan, 1997 Autumn Conference, I7, October 1997).

Various metallic materials have been studied for the purpose of disposing of high-level radioactive waste. The metallic materials studied so far are classified into a semi-corrosion resistant metal which corrodes at a certain rate but hardly causes local corrosion and a high corrosion resistant metal which hardly corrodes due to the formation of a passive film.

[0007] Carbon steel, copper and alloys thereof are listed as the semi-corrosion resistant metals, and titanium, nickel-based alloys (Hastelloy, Inconel), high nickel alloys (Incoloy), and stainless steel are listed as the high corrosion resistant metals.

Further, a composite material which is expected to have corrosion resistance for the material outside the container and pressure resistance and shielding properties for the material inside the container has been considered. An example of this is a combination of titanium or copper as the outer material and carbon steel as the inner material (for example, Combustion Technical Report No. 85, March 1993).

[0009]

The non-binder materials represented by concrete are heat-generating due to the decay heat of radionuclides due to the lack of sealing technology, brittle materials, and low thermal conductivity. If so, there remains a problem that the temperature rises.

[0010] On the other hand, it is generally considered that metal materials have few problems seen in barbed materials and non-barbed materials, and extensive studies are being made on high-level radioactive waste overpack materials and the like.

However, although the quasi-corrosion resistant metal is less likely to cause local corrosion, it is necessary to set an appropriate corrosion allowance based on an accurate grasp of the overall corrosion rate in order to ensure a long corrosion life of more than 1000 years. . Further, the high corrosion-resistant metal has a very small amount of overall corrosion, but must be used under conditions that can maintain the soundness of the passivation film in order to avoid local corrosion such as crevice corrosion. Therefore, it is considered that if a material capable of maintaining higher corrosion resistance for a long time is selected, the function of the container can be further enhanced.

By the way, for a while from the initial stage of burial, the nucleus is placed under the influence of decay heat or radiation of the nuclide stored in the disposal container. It also receives external forces such as head pressure based on the burial depth. Therefore, in order for the container to fulfill the function of confining nuclides, the following performance is also required.

Mechanical strength against external force Stability against decay heat and radiation of nuclides Further, in order to facilitate transport and avoid the influence of radiolysis of groundwater, shielding properties against radiation are also required. In addition, in order to manufacture containers with such performance, it is necessary to satisfy the viewpoints of ease of manufacturing, workability, and weldability of large containers.

An object of the present invention is to provide a radioactive waste disposal container that can prevent radioactive substances in waste stored in the container from migrating into groundwater.

[0015]

In order to achieve the above object, the radioactive waste disposal container according to the present invention is characterized in that the outer wall of the radioactive waste disposal container is made of tantalum,
The inner wall is made of carbon steel or low alloy steel.

Specifically, the present invention provides the following containers.

The present invention provides a radioactive waste disposal container used for geological disposal of radioactive waste, wherein the radioactive waste disposal container has an outer wall made of tantalum and an inner wall made of carbon steel or low alloy steel. A radioactive waste disposal container is provided.

Further, in the radioactive waste disposal container used for geological disposal of radioactive waste, the radioactive waste disposal container may be made of tantalum using copper, titanium or an alloy of copper and titanium as an insert material. A radioactive waste disposal container characterized in that the container is made of a clad material of carbon steel or low alloy steel, and the tantalum is configured to be an outer wall of the radioactive waste disposal container.

Preferably, the tantalum and the carbon steel or the low alloy steel are joined to each other by any one of diffusion welding, cold welding, and explosive pressure bonding.

Further, the present invention relates to a radioactive waste disposal container used for geological disposal of radioactive waste, wherein the radioactive waste disposal container is made of carbon steel or low carbon steel or copper alloy. It is made of a plate material in which tantalum is vapor-deposited on the surface of any one of the alloy steel and the clad material of copper, titanium or an alloy of the copper and titanium, and the tantalum is configured to be an outer wall of the radioactive waste disposal container. The present invention provides a radioactive waste disposal container characterized in that:

[0021] Preferably, the tantalum is deposited by chemical vapor deposition or physical vapor deposition of any of sputtering, vacuum deposition, and ion plating.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radioactive waste disposal container according to an embodiment of the present invention will be described below with reference to tables and drawings.

It is an object of the present invention to manufacture a radioactive waste disposal container from a material having an outer wall surface made of tantalum and an inner wall surface made of carbon steel or low alloy steel. This is intended to give tantalum a corrosion resistance function and to give carbon steel or low alloy steel a function of pressure resistance and radiation shielding.

The production of such a material is performed by any of the following methods.

The first method is to clad a tantalum plate on a carbon steel or low alloy steel plate. In this method, copper, titanium, or an alloy thereof is used as an insert material, and a tantalum plate and a plate of carbon steel or low alloy steel are joined by any one of cold press welding, diffusion welding, and explosive pressing.

The second method is a method in which tantalum is vapor-deposited on the surface of either copper, titanium or their alloy in a clad material of copper, titanium or any of their alloys and carbon steel or low alloy steel. is there. Tantalum is deposited by chemical vapor deposition or physical vapor deposition such as sputtering, vacuum deposition, or ion plating.

In the clad material of tantalum and carbon steel or low-alloy steel, tantalum only has corrosion resistance, so its thickness may be about 0.1 to 2.0 mm. Since the specific gravity of tantalum is more than twice that of carbon steel or low alloy steel,
Making the tantalum too thick increases the weight of the container, which is undesirable.

The thickness of the insert material such as copper, titanium or an alloy thereof may be about 1.0 to 10.0 mm. One of the functions of the insert material is to prevent the formation of an intermetallic compound when tantalum and carbon steel or low-alloy steel are directly joined to prevent the joining interface from becoming brittle.

Furthermore, when tantalum is mechanically locally damaged during transportation or embedding of a container, if the underlying carbon steel or low alloy steel is directly exposed, galvanic corrosion may cause corrosion of carbon steel or low alloy steel. The insert material is promoted and has a function of suppressing hydrogen generation on the tantalum surface when the buried environment is a reducing atmosphere, thereby suppressing hydrogen embrittlement of tantalum itself.

That is, in the corrosion potential series, tantalum is more noble than carbon steel or low alloy steel, and copper, titanium or their alloy is located between tantalum and carbon steel or low alloy steel.

Therefore, galvanic corrosion caused by a combination of tantalum and carbon steel or low alloy steel is mitigated by inserting an insert material.

The thickness of the carbon steel or low alloy steel varies depending on the required pressure resistance and radiation shielding properties, and these functions can be enhanced by increasing the thickness. If the weight of the contents is about several to ten tons, the strength may be about 3.0 to 10.0 mm. The maximum thickness is limited to about 300.0 mm from the viewpoint of welding between clad materials.

When tantalum is deposited on a clad material of copper, titanium or an alloy thereof and carbon steel or low alloy steel, the thickness of the tantalum layer is 0.001 to 0.1 mm.
Any degree is acceptable. The thickness of each material constituting the material may be the same as described above, and the function of each material is also the same.

The plate materials manufactured by any of the methods are joined into a predetermined container shape by TIG welding, resistance welding, or electron beam welding after cutting. In this case, it is important that only the tantalum forms the outer wall surface of the container and that no other metal is exposed.

The corrosion resistance of tantalum is comparable to that of gold and platinum, and the corrosive environment at 150 ° C. or lower is limited to fluorine, hydrofluoric acid, fuming sulfuric acid and a strong alkaline aqueous solution having a concentration of 10% or more.

The high corrosion resistance is shown in Table 1 (DLMacleary: Co
rrosion, 18, 67 (1962)), as shown in the comparison of the corrosion rates of various metals, they are extremely superior to high corrosion resistant metals such as titanium.

[0037]

[Table 1]

Further, an excellent point of tantalum is that there is no occurrence of local corrosion such as pitting, crevice corrosion, and stress corrosion cracking, which are common concerns in high corrosion resistant metals.

The geological disposal environment is considered to be different depending on the type of radioactive waste, but generally the environmental conditions shown in Table 2 are assumed.

[0040]

[Table 2]

In this environment, the total amount of corrosion of tantalum is 1 μm or less in 1000 years. In addition, pitting, crevice corrosion,
There is no local corrosion such as stress corrosion cracking.

The corrosiveness of carbon steel or low alloy steel as the inner wall material depends on the type of radioactive waste to be stored. However, since it is a closed space, the oxygen concentration is extremely low, and cement or glass is used. No corrosion occurs due to solidification and alkaline environment.

The present material is stable against radiation, has no problem with the influence of decay heat, has excellent radiation shielding properties, and is extremely excellent in terms of strength and manufacturability.

The shape of the container is preferably any of a cylinder, a rectangular parallelepiped, and a hexagonal column in consideration of the handling at the time of transfer and installation.

Next, a specific embodiment of the radioactive waste disposal container according to the present invention will be described. Table 3 is a specification example of the radioactive waste disposal container according to one embodiment of the present invention. This radioactive waste disposal container is designed for cement solidified radioactive waste (weight: about 10t).

[0046]

[Table 3]

Production of the radioactive waste disposal container according to the specifications in Table 3 was performed in the following procedure.

First, the clad material used was produced by diffusion welding, and as shown in FIG.
And 7mm thick carbon steel sheet 3 and 2mm thick insert material
Of copper plate 2.

FIG. 2 is a perspective view of a radioactive waste disposal container.
FIG. 3 shows a longitudinal sectional view of the radioactive waste disposal container.

A clad material having a thickness of 10 mm is cut into a required shape.
After processing and forming, cylindrical container side wall plate by TIG welding
4 was made. At the time of welding, it is necessary to separately weld the base material and the composite material, and the tantalum plate 7 of the same material was used for joining the tantalum plates.

The disc-shaped container bottom plate 5 and the lid 6 have the same thickness of 10 mm.
side plate 4 and bottom plate 5
The container on the side for storing the waste 8 was prepared by TIG welding using a tantalum backing plate 7.

Next, after storing the waste 8, the lid 6 is
4 is joined and sealed by TIG welding using a tantalum backing plate 7. Thereby, the outer wall of the container is completely covered with tantalum, and the external leakage of the waste 8 can be suppressed for a long period of time due to the high corrosion resistance maintaining function of tantalum.

[0053]

According to the present invention, contact between groundwater and waste is suppressed for a long period of 1000 years or more after geological disposal, and radioactive materials in radioactive waste in a radioactive waste disposal container leak to groundwater. Migration can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a tantalum cladding material used for a radioactive waste disposal container according to one embodiment of the present invention.

FIG. 2 is a perspective view of a radioactive waste disposal container according to one embodiment of the present invention.

FIG. 3 is a vertical sectional view of the radioactive waste disposal container of FIG. 2;

[Explanation of symbols]

1 ... tantalum plate, 2 ... copper plate, 3 ... carbon steel plate, 4 ... side wall plate, 5
… Bottom plate, 6… Lid, 7… Tantalum plate, 8… Waste

 ──────────────────────────────────────────────────の Continuing from the front page (72) Moto Yamamoto 3-2-2, Sachimachi, Hitachi-shi, Ibaraki Prefecture Within Hitachi New Clear Engineering Co., Ltd. (72) Ichiro Watanabe 3-chome, Sachimachi, Hitachi-shi, Ibaraki No. 2 Hitachi New Clear Engineering Co., Ltd. (72) Inventor Sanji Ebine 3-2-2 Sachicho, Hitachi City, Ibaraki Prefecture Within Hitachi New Clear Engineering Co., Ltd. (72) Inventor Hiroyuki Tsuchiya Hitachi New Clear Engineering Co., Ltd. 3-2-2, Sachicho, Hitachi City, Ibaraki Prefecture

Claims (5)

[Claims] 1. A radioactive waste disposal container used for geological disposal of radioactive waste, wherein the radioactive waste disposal container has an outer wall made of tantalum and an inner wall made of carbon steel or low alloy steel. Radioactive waste disposal container. 2. A radioactive waste disposal container used for geological disposal of radioactive waste, wherein said radioactive waste disposal container is made of copper, titanium or said copper,
Tantalum using any of the alloys of titanium as an insert material, and manufactured from a clad material of carbon steel or low alloy steel, the tantalum is configured to be the outer wall of the radioactive waste disposal container. A radioactive waste disposal container. 3. The radioactive waste disposal according to claim 2, wherein said tantalum and said carbon steel or low alloy steel are joined to each other by any one of diffusion welding, cold welding and explosion pressure bonding. container. 4. A radioactive waste disposal container used for geological disposal of radioactive waste, wherein the radioactive waste disposal container comprises copper, titanium or an alloy of copper and titanium and carbon steel or low alloy steel. The clad material is made of a plate material in which tantalum is vapor-deposited on any surface of the copper, titanium or the alloy of the copper and titanium, and the tantalum is configured to be an outer wall of the radioactive waste disposal container. A radioactive waste disposal container. 5. The radioactive waste disposal container according to claim 4, wherein said tantalum is deposited by chemical vapor deposition or physical vapor deposition of sputtering, vacuum vapor deposition, or ion plating.