JP2000131495A - Method for high-frequency melting treatment of radioactive waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for high-frequency melting treatment of radioactive wastes that can duct a melting treatment at a lower temperature than conventional methods and prolonge the life of a melting furnace. SOLUTION: In a method for the high-frequency melting treatment of radioactive wastes where metallic wastes and non-metallic wastes under the influence of radioactivity are heated and melted by high frequency, the wastes are melted in a conductive ceramic melter 3 filled or doped with graphite 10 and a conductive ceramic canister.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency melting method for radioactive waste, which can be melted at a lower temperature than conventional ones and can extend the life of a melting furnace.

[0002]

2. Description of the Related Art Conventionally, a high-frequency induction melting method using high-frequency heating has been known as a method for melting and solidifying radioactive metallic waste and nonmetallic waste. This is a method in which the waste is melted and solidified in a conductive ceramic canister, and has an advantage that both a conductive metal and a nonconductive nonmetal can be melted. There is a problem that it is difficult to obtain a certain conductive ceramic and the cost is high. Also, since the canister is disposable or discarded after being used several times, the cost becomes high and the canister itself becomes waste. There was also a problem that it could not be done. For this reason, there is a difficulty in applying this conductive ceramic to a crucible (ceramic melter) of a so-called ceramic melter method that can dissolve a large amount without being disposable.

On the other hand, in the high-frequency induction melting method, lining of an electrically insulating refractory or melting by high-frequency induction using a non-conductive crucible is performed, but metal waste is easily melted. Although it can be performed, nonmetallic wastes can be added and melted only in a small amount, and there is a drawback that it is difficult to cope with fluctuations in the waste composition. In order to make up for this drawback, auxiliary heating with a plasma burner or the like has been proposed. However, there has been a problem that the melting furnace becomes structurally complicated and the cost becomes high.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and can melt radioactive metallic and non-metallic wastes at a lower temperature than before. Therefore, it is possible to easily obtain conductive ceramics, reduce energy costs, greatly extend the life of the melting furnace, and efficiently melt a large amount of waste. It has been completed for the purpose of providing a high-frequency melting treatment method for radioactive waste.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a radioactive metallic waste and a nonmetallic waste in a conductive ceramic melter filled with graphite. And high-frequency melting of the radioactive waste, wherein the molten metal is discharged into a mold and then solidified and then treated for waste treatment. The radioactive metallic waste and the non-metallic waste are melted together with the graphite in a conductive ceramic canister to be added, and then the molten metal is cooled and solidified together with the canister for waste treatment. A high-frequency melting treatment method for radioactive waste characterized by the following features.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a case where high-frequency melting is performed using a ceramic melter type furnace, in which 1 is a cover of the high-frequency melting furnace, 2 is an induction coil,
Reference numeral 3 denotes a ceramic melter, 4 denotes a tap hole, 5 denotes a mold such as a crucible or a molding die made of iron, ceramic, or the like. The radioactive waste put in the ceramic melter 3 is heated and melted by high frequency, and thereafter, the molten metal is formed. It is basically the same as the conventional ceramic melter-type high-frequency melting method in that it is taken out, cooled and solidified, and the obtained solidified product is packed in a drum or the like and discarded.

The present invention has a characteristic configuration in that the waste is melted in a conductive ceramic melter 3 filled with block-shaped graphite 10. That is,
By the heat generated by the high frequency and the heating by the graphite 10 having excellent thermal conductivity, the entire inside of the ceramic melter 3 is uniformly and efficiently melted at a relatively low temperature while preventing radiation cooling from the surface. More specifically, a slag phase is formed on the upper part of the ceramic melter 3 during the melting process,
Since this slag has a low thermal conductivity, the temperature decreases due to radiant cooling from the surface and the viscosity increases, making it difficult to flow at the time of tapping. 3 has a problem that the life is shortened and the energy cost is increased. On the other hand, in the present invention, by inserting the block-shaped graphite 10 having excellent thermal conductivity, the slag can be satisfactorily heated and melted at a relatively low temperature without lowering the viscosity of the slag. Thus, the life of the ceramic melter 3 can be extended. Further, the graphite block generates heat by high-frequency induction, so that it can be more efficiently melted. The conductive ceramic melter 3 is obtained by mixing fine powder of a conductive substance such as carbon black or graphite into a ceramic composition forming the ceramic melter.
It can be obtained by firing.

In addition, the block-shaped graphite 10 reacts with a metallic waste made of carbon steel or stainless steel to increase C in iron, thereby lowering the melting point. That is, it becomes possible to melt iron at a relatively low temperature like cast iron. Conventionally, heating was performed at about 1500 ° C. (at this time, the temperature of the iron in the ceramic melter was 1550 ° C. or more, and the temperature of the slag layer was 1400 to 14 ° C.)
In contrast, the present invention can melt at 1450 ° C. or lower, usually 1300 to 1400 ° C. (at this time, the iron temperature in the ceramic melter is 1350 to 1450 ° C., but the melting point is 1250 ° ° C and good fluidity because the temperature of the slag layer is small and the fluidity is good. And the service life of the ceramic melter 3 can be extended.

Since the graphite 10 is gradually oxidized and gradually consumed, it is preferable to add a carburizing agent such as kryptor for preventing the graphite from being consumed in the ceramic melter 3. A used silicon carbide ceramic filter may be used. It is also preferable that a powdery heat insulating material such as graphite powder or straw for maintaining the melting temperature is put on the molten metal surface of the ceramic melter 3. Further, it is needless to say that a slight fluidizing agent may be added as needed for the purpose of adjusting the melting point and viscosity of the slag.

FIG. 2 shows a case where the present invention is applied to an in-can melting method using a ceramic canister. In the figure, reference numeral 6 denotes a conductive ceramic canister, and graphite is added to the ceramic canister 6. . Conventionally, heating was performed at about 1500 ° C. (at this time, the temperature of the iron in the canister is 1550 ° C. or more, and the temperature of the slag layer is about 1400 to 1450 ° C.). (At this time, the temperature of the iron in the canister is 1350 to 1450 ° C., but the melting point is about 1250 ° C. due to casting, so that the fluidity is good. ), The voids when the viscosity is high are extremely small, and the degree of freedom in selecting the ceramic constituting the canister increases, and the energy cost is significantly reduced and the low cost canister (for example, Thin canisters, low-temperature firing canisters, canisters using low-grade raw materials, etc.) can be used. The conductive canister 6
Can be obtained by mixing and firing a fine powder of a conductive substance such as carbon black or graphite in a ceramic composition forming the canister. In the case of the high-frequency induction melting method, as the graphite, it is preferable to use powdery or granular cryptol or silicon carbide (including used silicon carbide-based filters) in order to prevent bulkiness in the canister, and Needless to say, a powdered heat insulating material or a fluidizing agent may be added. Immediately before the completion of melting, it is also effective to provide a melt holding time to make the molten metal composition uniform and to consume it by oxidation.

As described above, according to the present invention, since radioactive metallic waste and nonmetallic waste are treated as a molten and solidified product, they have excellent nuclide confinement and volume reduction effects, and are safe and reliable. To meet the needs of waste disposal. In addition, since melting can be performed at a lower temperature and in a larger amount than in the past, melting energy can be reduced, the life of the ceramic melter can be extended, and a low-cost ceramic canister can be employed.

[0012]

As is apparent from the above description, the present invention can melt a radioactive metallic waste or a nonmetallic waste at a lower temperature than before and obtain a conductive ceramic. Can be performed easily, the energy cost can be reduced, the life of the melting furnace can be greatly extended, and a large amount of waste can be efficiently melted. Therefore, the present invention greatly contributes to industrial development as a high-frequency melting treatment method for radioactive waste that has eliminated the conventional problems.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

[Explanation of symbols]

1: Cover of high-frequency melting furnace, 3: Ceramic melter,
5: mold, 6: ceramic canister, 10: graphite.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takeshi Hasebe 2-56, Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Japan F Co., Ltd. F-term (reference) 3K059 AA08 AB04 AB07 AB15 AB27 AB28 AD00 AD03 AD35 CD44 CD72

Claims (4)

[Claims] In a conductive ceramic melter filled with graphite, radioactive metallic waste and nonmetallic waste are melted by high frequency together with the graphite, and then the molten metal is poured into a mold and solidified. A high-frequency melting treatment method for radioactive waste, characterized in that the radioactive waste is treated by waste. 2. A radioactive metallic waste and a nonmetallic waste are melted together with the graphite in a conductive ceramic canister to which graphite is added by radio frequency melting, and then the molten metal is cooled and solidified together with the canister and disposed. A radio frequency melting treatment method for radioactive waste, characterized in that the material is treated. 3. The high-frequency melting method for radioactive waste according to claim 1, wherein a carburizing agent for preventing the consumption of graphite during the high-frequency melting is added. 4. A powder heat insulating material for maintaining a melting temperature at a molten metal surface during high frequency melting.
3. The high-frequency melting treatment method for radioactive waste according to claim 1.