JP2006010339A - Disposal container and disposal method for high-level radioactive waste and transuranium waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a disposal container and disposal method for high level radioactive waste and TRU waste which can assure safety for a long period by preventing degradation of the disposal container due to corrosion when the high level radioactive waste and TRU waste are disposed of, and can reduce the energy and resource required in manufacturing the disposal container. <P>SOLUTION: The disposal container is constituted of a complex materials obtained by forming the container body by spreading mixture of organic polymer material to be a precursor of ceramic fiber and fine powder of one or more kinds of carbon, silicon-carbide, boron-nitride, or boro-silicon carbonitride on the ceramic fiber or cloth consisting of carbon fiber or the silicon-carbide fiber, and sintering the container shape. The high level radioactive waste or TRU waste are contained in the disposal container, which is disposed of in stratum in a state placing clay material in which one or more kinds of carbon, silicon carbide or boron nitride are added are placed around the container. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a disposal container for containing high-level radioactive waste and TRU (super uranium element) waste in a sealed state, and a disposal method using the same.

  As is well known, the disposal method of radioactive waste varies depending on the strength of radioactivity, the half-life of the radionuclide, the form of waste, and the like. In particular, disposal of TRU waste containing high-level radioactive waste (primary waste liquid and its solidified product) discharged from spent fuel reprocessing, and artificial radionuclides with atomic numbers higher than uranium, such as neptunium and plutonium Therefore, it is necessary to ensure safety against high levels of radioactivity and long-term radioactivity, and it is required to dispose of them appropriately under strict management.

  In general, in the case of high-level radioactive waste, after being mixed with a glass raw material and melted, the melt is poured into a stainless canister and solidified. The vitrified body is cooled and stored for 30 to 50 years in a sealed canister, then stored in a thick overpack made of steel, etc., and stored in a deep layer several hundred meters deep underground. Is done. At that time, a clay material (bentonite or the like) mixed with silica sand or the like is installed around the overpack. The canister and the overpack are sealed by closing the opening of the container body with a lid and welding the lid.

  On the other hand, in the case of TRU waste, it is usually placed in a container such as a drum can made of iron, stainless steel, etc. and solidified with cement, etc., and then stored in a box-like container as a container. Etc. are buried and solidified in the basement. Also in this case, like high-level radioactive waste, a clay material such as bentonite is installed so as to cover the box-shaped container.

  However, in the above conventional disposal method, when installing an overpack or a box-shaped container containing solidified high-level radioactive waste or TRU waste in an underground disposal environment, The clay material produced in 1 was installed in an atmospheric oxidation environment, so that the clay material accelerated the corrosion of the metal disposal container. And when disposal containers, such as an overpack and a canister, progress corrosion, there existed a possibility of affecting the safety ensuring for a long term.

  In addition, high-grade high-grade materials such as stainless steel, iron, copper, and titanium are used for metal disposal containers such as overpacks. To consume a lot of energy. For this reason, the use of a large amount of the above-mentioned high-grade material for disposal of radioactive waste is nothing but a waste of energy and resources, and there is a strong demand for suppressing its consumption.

  The present invention has been made in view of such circumstances, and when disposing of high-level radioactive waste and TRU waste, it is possible to prevent deterioration of the disposal container due to corrosion and ensure safety over a long period of time. An object of the present invention is to provide a high-level radioactive waste and TRU waste disposal container and disposal method capable of reducing the energy and resources required for manufacturing the disposal container.

  As a result of intensive studies to solve the above problems, the inventors have made ceramic fiber or cloth made of carbon fiber or silicon carbide fiber, an organic polymer substance serving as a precursor thereof, and a microscopic material such as carbon or silicon carbide. A composite material obtained by applying a mixture with powder to form a container shape and firing the container shape body is used as a structural material of a disposal container for high-level radioactive waste or TRU waste. It is possible to prevent deterioration of such metal disposal containers due to corrosion, and to significantly reduce the energy and resources required for manufacturing the above disposal containers compared to conventional ones, and around the disposal containers such as carbon and silicon carbide By disposing the geological layer with clay material added with fine powder (reducing material) installed, the migration of radionuclides into the geological layer can be greatly delayed. Heading the Rukoto, in which has led to the completion of the present invention.

  That is, the disposal container for high-level radioactive waste and TRU waste according to the present invention according to claim 1 is made of organic fiber that becomes a precursor of these ceramic fibers on ceramic fibers or cloth made of carbon fibers or silicon carbide fibers. It is composed of a composite material obtained by applying a mixture of a molecular substance and carbon, silicon carbide, boron nitride or one or more fine powders of borosilicon carbonitride to form a container shape and firing the container shape. It is characterized by this.

  The disposal method for high-level radioactive waste and TRU waste according to the present invention as set forth in claim 2, the high-level radioactive waste or TRU waste is accommodated in the disposal container according to claim 1, and carbon is disposed around the container. Further, the present invention is characterized in that the geological disposal is performed in a state where a clay material to which one kind or two or more kinds of fine powders of silicon carbide or boron nitride is added is installed.

According to the disposal container for high-level radioactive waste and TRU waste according to the present invention, when disposing of high-level radioactive waste and TRU waste, the deterioration due to corrosion of a conventional metal container is prevented. , Safety can be ensured for a long time.
Since the disposal container is manufactured using ceramic fibers or cloth made of carbon fiber or silicon carbide fiber instead of the conventional stainless steel or steel container, the energy required for manufacturing the disposal container Resources can be significantly reduced compared to the conventional case, and disposal costs can be reduced. Further, since the material is lighter than stainless steel or iron, the weight of the disposal container itself can be reduced, and thereby the handling performance of the disposal container can be improved.

  Further, according to the disposal method for high-level radioactive waste and TRU waste according to the present invention, one or two of carbon, silicon carbide or boron nitride is added to the clay material such as bentonite installed around the disposal container at the time of geological disposal. Since more than seeds of fine powders are added, the disposal environment can be made nearly reducible from the initial stage of the disposal container installation to suppress the corrosion of the disposal container, and should be disposed of after a long period of time. Even if the radionuclide leaks from the container, the elution of the radionuclide can be prevented by adsorption or insolubilization. That is, a highly reliable radionuclide immobilization environment can be created around the disposal container, and the radionuclide migration delay effect can be further improved as compared with conventional clay materials. This is also clear from the fact that the uranium deposits that exist in nature are those in which the flowing uranium is immobilized by a reducing environment containing an organic substance mainly composed of carbon.

  1 to 3 show an embodiment of a disposal container according to the present invention. FIG. 1 is a disposal container 10 for enclosing high-level radioactive waste (glass solidified body), and FIG. 2 is a TRU waste (cement solidified body). ), FIG. 3 shows a disposal container (overpack) 12 that houses the disposal container 10 of FIG. 1 in a sealed state. As shown in FIGS. 1 to 3, each disposal container 10, 11, 12 is formed in a cylindrical shape or a box shape, and a container holding portion such as a constriction is formed on the outside of each disposal container in order to improve handling. ing.

  All of these disposal containers 10, 11, and 12 are made of a carbon fiber or silicon carbide fiber ceramic fiber or a cloth woven with ceramic fiber, an organic polymer substance that is a precursor of these ceramic fibers, carbon, silicon carbide, and nitridation. It is a container made of a composite material obtained by applying a mixture of one or two or more fine powders of boron or borosilicon carbonitride to form a container shape and firing this container shape body.

Here, the carbon fiber as the ceramic fiber is produced by firing a precursor made of an organic polymer material such as polyacrylonitrile, cellulose, or pitch. Examples of commercially available carbon fibers or cloths thereof include trading card yarn, trading card cloth (trade name manufactured by Toray Industries, Inc.), pyrofil CF tow and cloth (trade name manufactured by Mitsubishi Rayon Co., Ltd.), and the like.
Silicon carbide fibers as ceramic fibers are produced by firing a precursor made of an organic polymer material such as polycarbosilane or polysilane. Examples of the commercially available products include hynicalon and nicaron fibers and woven products thereof (trade names manufactured by Nippon Carbon Co., Ltd.).
Further, carbon fiber or carbonized carbon fiber or carbonized carbon fiber is obtained by applying polyorganoborosilazane as a precursor made of an organic polymer substance and baking it to convert polyorganoborosilazane to borosilicon carbonitride. What formed the boro silicon carbon nitride on the circumference | surroundings of a silicon fiber can also be used as a ceramic fiber in this invention.
Organic polymer substances that are precursors of these ceramic fibers can also be obtained from the above-mentioned manufacturers.

As a method for producing the composite material using these ceramic fibers or cloth, for example, a method generally called a PIP (Polymer Infiltration and Pyrolysis) method can be adopted.
In this method, first, a ceramic fiber or cloth is coated with a mixture of an organic polymer substance serving as a precursor thereof and one or more fine powders of carbon, silicon carbide, boron nitride, or borosilicon carbonitride. The container shape is formed by a filament winding method or the like. When the ceramic fiber is a carbon fiber, a carbon fiber-based precursor (polyacrylonitrile-based, cellulose-based, pitch-based) is used as the precursor, and the ceramic fiber is a silicon carbide fiber. In general, silicon carbide fiber-based precursors (polycarbosilane-based, polysilane-based) are used as the precursor. Here, regardless of the type of ceramic fiber used, carbon fiber is used as the precursor. It is preferable to use a precursor of the system. By doing so, a dense matrix with few pores can be formed after firing. However, the precursor used for the second and subsequent coatings may be the same as or different from the precursor used for the first coating. Further, as described above, as the fine powder to be mixed with the precursor, any one kind or two or more kinds of fine powder can be freely selected from carbon, silicon carbide, boron nitride or borosilicon carbonitride. The size is preferably on the order of submicrons. By mixing this fine powder into the precursor, the proportion of the precursor remaining around the ceramic fiber during the infusibilization and firing processes described below can be increased, resulting in fewer voids formed in the matrix. can do.

  Examples of the winding pattern by the filament winding method include helical winding, label winding, and parallel winding, and it is possible to appropriately select a winding pattern suitable for the shape of the container. Also, the layer thickness can be appropriately set according to the strength and long-term durability required for the container. In addition, the mold used for winding the ceramic fiber may be pulled out or left as it is after the container shape is formed, either of which may be adopted. When the mold is left as it is and used as the inner shell (liner), for example, a metal material which is a material for a conventional disposal container can be used. On the other hand, in the case of removing the mold, there is a method in which the mold is made of aluminum and melted during high-temperature firing. Alternatively, it is also possible to use as a mold a material such as paper that has a certain degree of strength at the time of molding and burns away at high temperature firing.

  When the winding of the ceramic fiber is completed by the filament winding method, vacuum impregnation is performed, and then infusibilization is performed at 200 ° C. to 300 ° C. in the atmosphere, followed by high-temperature inert gas such as high-purity argon. Baking in an atmosphere (1000 ° C. or higher). The vacuum impregnation is a process for improving the adhesion between the ceramic fiber and the precursor, and the infusibilization is a process for preventing the precursor from melting and evaporating during high-temperature firing.

  Thereafter, a series of processes consisting of application of a precursor mixed with or without mixing fine powder, vacuum impregnation, infusibilization, and firing is repeated several times. Through the above treatment, the precursor, which was an organic polymer substance, is mineralized to form a matrix (constituting elements consisting of silicon, boron, carbon, nitrogen, and oxygen), and in this matrix, fine powder crystals are surrounded. Thus, a dense composite material having a structure in which ceramic fibers accompanied with the above are contained can be obtained.

  According to the disposal containers 10, 11, and 12 made of the above composite material, it is possible to prevent deterioration of conventional metal containers due to corrosion, and contain high-level radioactive waste or TRU waste inside for a long period of time. You can keep it. That is, since the conventional metal disposal container uses a pure material that does not exist in nature, it acts to transition to a more stable state after corrosion. Since the disposal containers 10, 11, and 12 use materials that are present in nature such as carbon as a main element (that is, materials that are in a stable state from the beginning), alterations such as corrosion hardly occur. Further, since the composite material is mainly composed of a reducing material such as carbon, silicon carbide, boron nitride, etc., it is possible to obtain an effect of preventing the elution of the radionuclide by adsorption or insolubilization. Therefore, the migration of the radionuclide into the formation can be greatly delayed, and safety can be ensured for a long time.

  In addition, since the disposal containers 10, 11 and 12 are manufactured using ceramic fibers or cloth made of carbon fibers or silicon carbide fibers instead of the conventional stainless steel or steel containers, The energy and resources required for the production can be greatly reduced compared to the conventional case, and the disposal container can be produced at a low cost. Moreover, since the material is lighter than stainless steel or iron, the weight of the disposal container itself can be reduced, and thereby the handling performance of the disposal container can be improved.

  Next, an embodiment of a disposal method for high-level radioactive waste or TRU waste using the disposal container will be described. For example, when disposing of high-level radioactive waste, first, the high-level radioactive waste liquid is stored in a tank or the like for a certain period until it becomes suitable for solidification treatment, and then the waste liquid is solidified by vitrification or the like. For example, when the glass is solidified, the waste liquid is pretreated, mixed with the glass raw material and heated, and the melt is poured into the disposal container 10 of FIG. 1 manufactured by the above-described manufacturing method and solidified. Then, after vitrifying the vitrified body in the disposal container 10 for 30 to 50 years, the disposal container 10 is stored in the disposal container (overpack) 12 of FIG. 3 manufactured by the same manufacturing method. It is housed in a sealed state and buried in a rock body that is deeper than several hundred meters underground. At that time, as shown in FIG. 4, the geological disposal with the clay material 13 added with fine powder having one or more reducing properties of carbon, silicon carbide or boron nitride around the overpack 12 is installed. To do.

  According to such a disposal method, since the disposal environment becomes nearly reducible from the initial stage of installation of the disposal container, it is assumed that the radionuclide may leak from the disposal container 12 after a long period of time. It is also possible to adsorb radionuclides and prevent their elution. That is, a highly reliable radionuclide immobilization environment can be created around the disposal container 12, and the radionuclide migration delay effect can be further improved as compared with conventional clay materials. Further, even when a conventional metal disposal container is used as the disposal container, the corrosion of the metal material can be suppressed, and the durability of the disposal container can be improved.

  In the case of disposing of TRU waste, as in the case of disposing of high-level radioactive waste, one or two of carbon, silicon carbide, or boron nitride is disposed around the container containing the solidified TRU waste. By carrying out geological disposal in the state where the clay material 13 to which fine powder of seeds or more has been added is installed, a radionuclide migration delay effect can be obtained.

It is a side view which shows one Embodiment of the disposal container of the high level radioactive waste which concerns on this invention. It is a side view which shows one Embodiment of the disposal container of TRU waste which concerns on this invention. It is a side view of the overpack which accommodates the disposal container of FIG. It is a schematic diagram which shows the state by which the overpack of FIG. 3 is embed | buried under the ground.

Explanation of symbols

10 High-level radioactive waste disposal container 11 TRU waste disposal container 12 Overpack (disposal container)
13 Clay materials

Claims (2)

  A ceramic fiber or cloth made of carbon fiber or silicon carbide fiber, an organic polymer substance that is a precursor of these ceramic fibers, and one or more fine powders of carbon, silicon carbide, boron nitride, or borosilicon carbonitride. A high-level radioactive waste and TRU waste disposal container comprising a composite material obtained by applying a mixture to form a container shape and firing the container shape.   A high-level radioactive waste or TRU waste is accommodated in the disposal container of claim 1, and a clay material added with one or more fine powders of carbon, silicon carbide or boron nitride is installed around the container. A disposal method for high-level radioactive waste and TRU waste, characterized in that geological disposal is performed in a state.

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