JP2002341092A - Miscellaneous solid waste volume reduction method and high frequency induction furnace for miscellaneous solid waste fusion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-level radioactive miscellaneous solid waste volume reduction method capable of treating safely a large quantity of nonmetal solid waste by using a simpler constitution. SOLUTION: A lifting stand 2 for inserting a canister 10 into this induction furnace is equipped with a driving device 3 capable of stopping at an optional position and supporting the stand. At first, the low-level radioactive miscellaneous solid waste having much metal is stored in the canister 10, and an electromagnetic coil 1 is placed on the position of a metal layer 11 in the canister until the metal is fused, to thereby heat mainly the metal layer, and nonmetal is also fused by heat transfer. When a nonmetal layer 12 is formed, nonmetal waste is inputted, and the relative position of the electromagnetic coil 1 is moved up to the position especially facing to a conductive sleeve 4 in the nonmetal layer 12, to thereby heat mainly the nonmetal, and the output of the electromagnetic coil 1 is adjusted so that the temperature of the metal layer 11 is maintained at a lower value than a damage temperature of a furnace wall.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for melting solid waste containing a mixture of metals and nonmetals, especially low-level radioactive solid waste generated in a nuclear power plant, and a high-frequency induction furnace for melting.

[0002]

2. Description of the Related Art Among low-level radioactive wastes generated in nuclear power plants and facilities handling radioactive materials, miscellaneous solid wastes such as heat insulation materials and structural material waste materials are disposed of by disposal. At the time of disposal, the waste is packed in a 200-liter drum, and a waste body in which the mortar is filled in the gap is produced. In order to reduce disposal costs, it is desirable to reduce the volume of waste before packing it in drums.

[0003] One of the methods for reducing the volume of miscellaneous solid waste in which metal and nonmetal are mixed is a method of melting and solidifying the waste using a high-frequency induction heating furnace. It melts miscellaneous solid waste by induction heating in a canister installed in a high-frequency melting furnace and reduces its volume. is there. Conventionally, solid waste was melted by causing the canister itself to generate heat by electromagnetic induction.Thus, canisters made of expensive conductive ceramics had to be thrown away. Canisters using high general ceramics can now be used.

When melting miscellaneous solid waste by this method,
Non-metallic components cannot be directly induction heated. Therefore, the non-metal component is melted by heat conduction using the molten metal, which has been heated to a high temperature by induction heating the conductive metal, as a heat source. In order to allow the non-metal components to be melted together, the mixing ratio of the metal and the non-metal is limited, and the solid waste having a large non-metal component ratio cannot be melted stably. Therefore, the inventors of the present application have previously devised a method of arranging a sleeve made of a conductive material such as graphite in a non-metal melting region, and effectively melting the non-metal component using the heat generated. It is disclosed in Japanese Patent Application No. 2000-335169.

In this method, as shown in FIG. 4, a canister is provided between induction heating coils, a conductive sleeve is floated on a non-metal layer separated from a metal layer, and induction heating is performed. The non-metal is melted by applying heat and heat of the sleeve. Since the sleeve floats above the non-metal layer, heat generation near the surface is increased, which is advantageous. Here, when the required amount of heat of the non-metal layer increases, such as when additional non-metal waste is added, the high-frequency output of the coil is increased to increase the heat generated by the metal and the sleeve. However, since the heat generated in the metal layer also increases at this time, the temperature of the molten metal rises, and the canister wall particularly near the interface between the metal layer and the non-metal layer is easily eroded. The wall may melt and the molten metal inside may leak. As described above, in the above method disclosed by the inventors, the molten metal and the sleeve are heat sources, but the heat generation ratio of both is determined, and the mixing ratio of the metal component and the non-metal component in the solid waste is determined. It cannot be adjusted arbitrarily according to the operating conditions such as changes in the amount of water and additional throws, making driving difficult.

In order to shorten the processing time by accelerating the melting of the metal, the heat generation of the metal in the initial stage is promoted. In order to reduce the heat generation rate of the metal and increase the heat generation rate of the sleeve when melting the components, it is preferable that the heat generation rate of the metal layer and the non-metal layer can be adjusted. The inventors of the present application have filed an invention to solve this problem with Japanese Patent Application No.
278065.

The disclosed invention provides a compensating heat source that moves up and down outside the canister, and when non-metal waste is added, causes the compensating heat source to follow the movement of the boundary between the metal layer and the non-metal layer, and from the vicinity of the boundary. Heating the outer canister wall at the top promotes the melting of the non-metallic solid waste. According to the method of the present invention, the safety of the canister can be ensured by controlling the temperature of the molten metal so as not to rise extremely.

However, in this method, since a movable compensation heat source is provided in the high-frequency melting and heating furnace, the equipment cost increases, and it becomes difficult to suppress the cost of disposal. Furthermore, the melting point of ceramics such as alumina is not significantly higher than the melting point of nonmetals in miscellaneous waste,
When the non-metal in the canister is melted by heating from the outside of the canister, the outer wall of the canister may be melted, and a high degree of temperature control is required for safe operation.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a low-level radioactive miscellaneous solid waste capable of safely treating a large amount of nonmetallic solid waste using a simpler configuration. An object of the present invention is to provide a volume reduction method and a high-frequency induction furnace for melting solid waste used in the method.

[0010]

In order to solve the above-mentioned problems, a method for reducing the volume of miscellaneous solid waste according to the present invention is provided by storing low-level radioactive miscellaneous solid waste containing a mixture of metal and nonmetal in a canister. It is placed in the furnace and the miscellaneous solid waste stored is melted in the canister by high-frequency induction heating to reduce the volume.The canister is placed at a position facing the electromagnetic coil in the high-frequency induction furnace, and the metal is melted. Until the electromagnetic coil is placed at the position of the metal layer in the canister, the metal layer is mainly heated, the non-metal is also melted by the heat, and the conductive sleeve is poured into the non-metal layer on the generated metal layer When the non-metal waste is introduced, the relative position of the electromagnetic coil is moved to a position facing the non-metal layer to mainly heat the non-metal, and the output of the electromagnetic coil is reduced by the temperature of the metal layer. Predetermined And adjusting so as to maintain a lower degree value.

In the method for reducing the volume of miscellaneous solid waste according to the present invention, first, waste mainly composed of metal is loaded in a canister and melted by high-frequency heating to produce a molten metal. Next, miscellaneous solid waste containing non-metals is sequentially charged and heating is continued to melt the waste. Since metal has a higher specific gravity than nonmetal, the molten metal is separated into a lower metal layer and an upper nonmetal layer. Even when the canister is made of non-conductive ceramics, if the conductive sleeve is put in and induction-heated together, the heat generation of the sleeve is added to the induction heat of the metal, so that the melting of the non-metal can be promoted. When the conductive sleeve is configured to have a specific gravity smaller than that of the nonmetal layer, the conductive sleeve always floats on the surface of the nonmetal layer, so that the nonmetallic solid can be more easily melted.

In the conventional method for reducing volume of miscellaneous solid waste, the position where the canister is placed in the internal space of the electromagnetic coil is fixed. Therefore, when the ratio of nonmetallic waste increases, power is supplied to the high-frequency coil in order to melt them. When the amount is increased, the temperature in the metal layer is increased, and there is a possibility that melting of the furnace material may occur.

However, in the method of the present invention, while the metal component is molten, the electromagnetic coil is placed at a position corresponding to the metal layer and heated until the temperature of the molten metal becomes sufficiently high, and the non-metal waste is transferred by the heat transfer from the metal layer. Melt the material. Then, miscellaneous solid waste containing a large amount of non-metallic components is introduced and treated. Further, if the input waste is melted and reduced in volume, new waste is added to store as much waste as possible.
When the applied power has to be increased because the amount of non-metal waste has been increased in this way, the position of the electromagnetic coil is moved toward the non-metal layer to distribute the applied power to the non-metal waste side. Then, the power is adjusted while monitoring the temperature so that the molten metal does not overheat, and the non-metallic waste is melted mainly by induction heating of the sleeve.

As described above, in the method of the present invention, the supply energy is appropriately distributed by adjusting the position of the electromagnetic coil in accordance with the amount of nonmetallic waste, so that the molten metal does not damage the wall of the canister. It can be operated at such a temperature. Therefore, the canister storing the reduced volume of miscellaneous solid waste can sturdily endure long-term storage. Adjustment of the position of the canister can be performed by raising and lowering the base on which the canister is mounted.
Further, before carrying the canister into the high-frequency induction furnace, miscellaneous solid waste may be charged in advance. In particular, there is no problem even if the metal-rich waste and conductive sleeve required in the early stage of the melting process are in the canister from the beginning,
In addition, if the metal content of the miscellaneous solid waste to be treated is sufficiently large, the melting treatment can be performed without having to separately charge the waste during treatment.

Further, the high frequency induction furnace for melting miscellaneous solid waste of the present invention comprises: an electromagnetic coil surrounding the canister and supplying high frequency energy to the contents of the canister; a high frequency power supply for supplying power to the electromagnetic coil; An elevator is provided for mounting the canister and elevating the electromagnetic coil. In the high-frequency induction furnace according to the present invention, the lifting table includes a height deflection mechanism and a molten metal temperature measuring device, so that the canister can be changed to an appropriate height during the induction heating process, and the supply power is adjusted based on the molten metal temperature. It is characterized by being constituted so that it can be done.

By using the high frequency induction furnace for melting solid wastes of the present invention, the position of the electromagnetic coil is changed to the position of the metal layer and the non-metal layer as required, so that the temperature of the molten metal does not exceed a predetermined temperature. And adjust the power supply while monitoring
The miscellaneous solid waste volume reduction method of the present invention can be appropriately performed. Further, the high-frequency induction furnace for melting miscellaneous solid waste of the present invention has a great feature in that the lifting platform that takes the canister into the position of the electromagnetic coil can be held at an intermediate height, and the conventional It is enough to make a small improvement to the high-frequency induction furnace, or it can be constructed by modifying an existing high-frequency induction furnace.

The high-frequency induction furnace for melting miscellaneous solid waste according to the present invention further includes a miscellaneous solid supply device for supplying miscellaneous waste to the canister, and the miscellaneous solid waste is appropriately stored in the canister during the induction heating step. Is preferably added. It is preferable that the canister used for the induction furnace for melting miscellaneous solid wastes is formed of non-conductive ceramics and can store a conductive sleeve therein.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments with reference to the drawings. FIG. 1 shows one embodiment of the present invention.
It is a lineblock diagram of the high frequency induction furnace for miscellaneous solid waste melting in an example. FIG. 2 and FIG. 3 are diagrams for explaining a method of operating the high-frequency induction furnace of the present embodiment.

As shown in FIG. 1, a driving device 3 in which a lift 2 is installed under an electromagnetic coil 1 and a distance can be set.
Driven in the vertical direction. A high-frequency current whose output has been adjusted is supplied to the electromagnetic coil 1 from a high-frequency power supply 5. Above the high-frequency induction furnace, a miscellaneous solids supply device 6 is provided so that miscellaneous solid waste can be appropriately charged into the canister 10. Further, the conductive sleeve 4 is put into the canister 10.

The lift 2 is provided with a temperature detecting end 7 such as a thermocouple. The temperature at the bottom of the canister 10 is measured and displayed on a thermometer 8. From this temperature, the temperature of the molten metal can be estimated. Although not shown in the figure, it goes without saying that the periphery of the induction furnace is surrounded by a heat insulating material to prevent useless heat radiation. Further, a conveyor for carrying the canister 10 under the high-frequency induction furnace and a conveyor for carrying out the canister 10 are provided.

The canister 10 is formed of an inexpensive and non-conductive material having a relatively high melting point, such as alumina or silicon oxide, and the conductive sleeve 4 is formed of a conductive material having a small specific gravity, such as graphite. Since the average specific gravity of the non-metallic molten metal is about 3.0 and the specific gravity of the graphite-based material is, for example, about 1.8, the conductive sleeve 4 can sufficiently obtain buoyancy with respect to the non-metallic molten layer 12. .

In the melting treatment of miscellaneous solid waste using induction heating, the metal component is first melted, and then the temperature of the molten metal is raised to melt the non-metal component by heat transfer. For this reason, first, the miscellaneous solid waste having a large proportion of the metal component is charged into the canister, and as shown in FIG.
And induction heating by supplying high frequency power.

Before starting the processing steps, the lifting platform 2 is lowered to the upper surface of the conveyor, and the canister 10 carried in by the conveyor is received on the platform. The lift 2 on which the canister 10 is mounted is lifted into the electromagnetic coil 2 by the driving device 3, and the bottom of the canister 10 stops at a position corresponding to the electromagnetic coil 1. By the miscellaneous solid supply device 6, miscellaneous solid waste having a high metal component ratio is charged into the canister 10. Next, the conductive sleeve 4 is mounted on the miscellaneous solid waste. The initial contents may be charged in the canister 10 before being carried into the induction furnace.

When a high-frequency current is supplied from the high-frequency power supply 5 to the electromagnetic coil 1 surrounding the canister 10, the metal component is induced to generate heat, melts, sews down the space of the miscellaneous solid waste, and drops down at the bottom to form a molten metal layer. 11 is formed. Since the non-metallic component is a non-conductive substance, there is no induction heat generated by the electromagnetic coil 1, but the molten metal rises to a temperature equal to or higher than the melting point of the non-metallic component due to the induced heat and melts the non-metallic component by heat transfer. The layer 12 is formed. Since the non-metal component covers the metal layer and has a heat retaining effect, the temperature rise of the molten metal is easy.

The conductive sleeve 4 is floating on the non-metallic melt layer 12 formed in the canister 10. The conductive sleeve 4 has a cylindrical shape, and is naturally located at the center of the canister 1 due to a magnetic field generated when a high-frequency current flows through the electromagnetic coil 2. The heating of the non-metallic component
The induction heat generated in the conductive sleeve 4 floating on the surface also contributes, but in the initial state, the electromagnetic coil 1 is located below the canister 10 and is separated from the conductive sleeve 4 and only a small amount of energy is distributed. The contribution of the conductive sleeve 4 is limited.

The non-metal component in the miscellaneous solid is a heat insulating material, concrete, or the like. In order to efficiently melt the miscellaneous solid added in the middle, the temperature of the non-metal component is set to about 1400 ° to 1500 ° C. Preferably, the treatment is performed at a temperature considerably higher than the melting point. On the other hand, when the canister 10 is formed of an alumina-based material, the heat-resistant temperature of the canister 10 is about 1700 ° C. to 1800 ° C., so that the temperature of the molten metal in the canister 10 is suppressed to about 1500 ° C. to 1600 ° C.

When the melting of the nonmetallic component has progressed, the nonmetallic waste is charged from the miscellaneous solid supply device 6 into the canister 10. In the conventional method, the supply power is increased in order to melt the newly supplied non-metal component, so that the temperature of the molten metal layer rises and may damage the furnace wall. In this embodiment, as shown in FIG. 2B, the elevator 2 is lowered to move the electromagnetic coil 4 to a position corresponding to the conductive sleeve 4 floating on the non-metallic molten layer 12 and guide the electromagnetic coil 4 to the electromagnetic sleeve 4. The proportion of generated heat is increased so that sufficient heat is conducted to the non-metallic waste. At this time, since the ratio of the energy allocated to the molten metal layer 11 decreases, the output of the high-frequency power supply 5 is adjusted so that the temperature of the molten metal layer 11 becomes a temperature that does not damage the furnace wall.

FIG. 3 is a graph schematically illustrating a state change when miscellaneous solid waste is additionally charged. FIG.
3A shows a change in height of the electromagnetic coil 1 with respect to the canister 10, FIG. 3B shows an output of the high-frequency power supply 5, and FIG. FIG. 3D shows a change in the amount of induced heat supplied by electromagnetic induction, and FIG. 3D shows a change in the temperature of the metal melt layer 11 and the surface temperature of the non-metal melt layer 12.

The height of the electromagnetic coil 1 is set such that when a molten solid layer of metal and non-metal is formed by the induced heat generation of the metal waste in the initial stage, and a new miscellaneous solid waste is added, the conductive sleeve 4 Up to the position. The high-frequency output is increased so as to recover the temperature of the molten metal layer 11 lowered by the additional introduction of the miscellaneous solid waste. The amount of heat supplied to the molten metal layer and the non-metallic molten layer changes according to changes in the coil height and the high-frequency output, and their temperatures also change accordingly.

More specifically, the height of the electromagnetic coil 1 with respect to the canister 10 is fixed at a low position corresponding to the vicinity of the bottom of the canister 10 until the metal component is completely melted first, and the high frequency power supply 5 is also connected to the molten metal layer. 11
Is maintained at an appropriate temperature such that the temperature is lower than the dangerous temperature of the furnace wall. When new miscellaneous solid waste is put into the canister 10 in this state, the non-metallic molten layer 11
, The amount of heat transferred from the molten metal layer 11 increases, and the temperature of the molten metal layer 11 also slightly decreases.

Here, when the relative position of the electromagnetic coil 1 is moved to a position corresponding to the conductive sleeve 4, the calorific value of the molten metal layer 11 decreases, and the induced calorific value on the conductive sleeve 4 side increases. Then, the temperature of the non-metallic molten layer 12 slightly recovers. Further, the high-frequency power is increased until the temperature of the molten metal layer 11 becomes an appropriate temperature equal to or lower than the damage temperature of the furnace wall.
Then, the amount of heat supplied to the non-metallic miscellaneous solid waste via the conductive sleeve 4 increases, and the newly added waste quickly melts. The optimum high-frequency power increase may be calculated by observing the temperature change of the molten metal layer after adjusting the position of the electromagnetic coil 1 to adjust the high-frequency output. The optimum high-frequency power can be estimated based on the amount, and the high-frequency output can be adjusted simultaneously with the adjustment of the position of the electromagnetic coil.

When the waste is melted, the elevator 2 is lowered to the position of the conveyor, moved to the carry-out conveyor, moved to the cooling place, and cooled by natural cooling. The cooled canister 10 is put into a drum and the gap is closed with mortar to be a waste. The conductive sleeve 4 can be collected before cooling and used repeatedly.

[0033] In this way, by melting all the miscellaneous solid waste, the solid matter having a shape becomes fluid and fills the space, and the volume is remarkably reduced. Can also be economically processed. Further, since the temperature inside the canister is controlled to a temperature lower than the temperature at which the furnace wall is damaged, the canister is sufficiently strong and can safely store waste and store it for a long period without causing collapse or leakage of the furnace wall. In the above embodiment, in view of the facility improvement, the drive device 3 is capable of stopping the change of the relative height of the electromagnetic coil 1 at an intermediate position on the lift 2 on which the electromagnetic coil 1 is mounted. Although what is performed has been described, it goes without saying that the electromagnetic coil 1 may be moved in the vertical direction.

[0034]

As described above, according to the high-frequency induction furnace for melting miscellaneous solid waste of the present invention, the temperature of the molten metal is controlled so as not to damage the canister, and the miscellaneous solid containing non-metals is prevented. Melt volume reduction of waste can be performed. Further, the apparatus of the present invention can be made by only slightly improving the conventional high-frequency induction furnace, so that the apparatus is economical. Further, since the molten metal layer is not excessively heated, the operating cost is reduced. can do.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a high-frequency induction furnace for melting miscellaneous solid waste in one embodiment of the present invention.

FIG. 2 is a diagram showing a flow of heat in a high-frequency induction furnace for melting miscellaneous solid waste according to the present embodiment.

FIG. 3 is a graph showing a state change in an operation state of the embodiment.

FIG. 4 is a cross-sectional view of a conventional high-frequency induction furnace for melting miscellaneous solid waste.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electromagnetic coil 2 elevator 3 elevator driver 4 conductive sleeve 5 high-frequency power supply 6 miscellaneous solids supply device 7 temperature detector 8 thermometer 10 canister 11 molten metal layer 12 non-metal molten layer

Continued on the front page F term (reference) 3K059 AB03 AB08 AB14 AB16 AB19 AB20 AB27 AB28 AC33 AD03 AD34 4D004 AA16 AA31 AA33 AB09 CA29 CB33 CB41

Claims (6)

[Claims] 1. A low-level radioactive miscellaneous solid waste in which a metal and a non-metal are mixed is housed in a canister and placed in a high-frequency induction furnace, and the miscellaneous solid waste is melted in the canister by high-frequency induction heating. In the method for reducing the volume of low-level radioactive miscellaneous solid waste to reduce the volume, the canister is placed at a position facing the electromagnetic coil in the high-frequency induction furnace, and the miscellaneous solid waste having a large proportion of metal and a conductive sleeve are first placed on the canister Until the metal charged into the canister melts into the canister, the electromagnetic coil is placed at a position corresponding to the bottom in the canister and mainly heats the metal layer to melt the non-metal, thereby forming the metal layer. The conductive sleeve is floated on the top, and then the relative position of the electromagnetic coil corresponds to the conductive sleeve when a large amount of non-metal waste is thrown in. A method for reducing the volume of miscellaneous solid waste, characterized in that the heating of the non-metal is mainly performed by moving to a position, and the output of the electromagnetic coil is adjusted so that the temperature of the metal layer is maintained at a value lower than a predetermined temperature. 2. The method according to claim 1, wherein a relative position between the electromagnetic coil and the canister is adjusted by moving up and down a table on which the canister is mounted. 3. The method for reducing the volume of miscellaneous solid waste according to claim 1 or 2, instead of adding the content after placing the canister in a high-frequency induction furnace, adding the content to the canister in advance. A method for reducing the volume of miscellaneous solid waste, which comprises charging a material and a conductive sleeve. 4. An electromagnetic coil that surrounds the canister and supplies high-frequency energy to the contents of the canister, a high-frequency power supply that supplies electric power to the electromagnetic coil, and a canister mounted thereon and moved up and down in the electromagnetic coil. A high-frequency induction furnace including a lift table, wherein the lift table can be changed to an appropriate height during an induction heating step, and a measuring device for measuring a metal melt temperature in a canister is provided. A high-frequency induction furnace for melting solid wastes, characterized in that the power supplied to the electromagnetic coil can be adjusted based on the electric power. 5. A miscellaneous solid waste supply device for supplying miscellaneous waste to the canister is provided, so that miscellaneous solid waste can be appropriately added to the canister during the induction heating step. The high-frequency induction furnace for melting solid wastes according to claim 3. 6. A canister used for the induction furnace for melting solid wastes is formed of non-conductive ceramics,
The high-frequency induction furnace for melting solid wastes according to claim 3 or 4, wherein a conductive sleeve can be accommodated therein.