JPH0216497A - Electric melting furnace for solidifying radioactive waste utilizing magnetic field and melting method - Google Patents

Abstract

PURPOSE:To make a glass melting furnace small in size and light in weight, to increase glass melting sped and to prevent the sedimentation of a furnace bottom sediment by attaching plural electrodes for allowing an AC current to be applied to molten glass and plural magnetic poles for generating an alternating magnetic field to the glass melting furnace. CONSTITUTION:Electrodes 2, 3 are inserted into one pair of opposed side walls of a melting furnace, connected electrically to a secondary winding side of a transformer 4, and molten glass 8 is conducted electrically by an AC current and heated, also, magnetic poles 5, 6 are inserted into the other pair of side walls, and by a magnetic pole excitation winding 7 connected electrically to a primary winding side of the transformer 4, an alternating magnetic field for intersecting with a current for flowing in the molten glass 8 is generated. In such a way, by an interaction of these current and magnetic field, the molten glass is allowed to generate force of the same direction hourly, the heat transfer quantity to a raw material layer from the molten glass is increased and the melting capacity is improved, the melting furnace can be made small in size and light in weight, and also, the setting and sedimentation to the furnace bottom of a furnace bottom sediment can be suppressed and prevented.

Description

[Detailed Description of the Invention] <Prior Art> Vitrification is a solidified form for safer transportation, storage, and disposal of highly radioactive waste generated from radioactive material reprocessing plants. Highly radioactive waste and glass raw materials (
When the raw materials (hereinafter simply referred to as raw materials) are fed into the melting furnace, the raw materials cover the surface of the molten glass in the melting furnace, and heat transfer from the molten glass causes evaporation of water in the waste. Calcining and vitrification reactions occur continuously, and the glass mixes with the already existing molten glass to form a homogeneous glass. The energy necessary to maintain the molten glass at a high temperature is supplied by passing an electric current between at least a pair of electrodes placed oppositely in the molten glass and generating Joule heat in the '/B molten glass existing between them. Ru.

The molten glass is poured continuously or intermittently into a metal container called a canister, which is stored in a storage facility and eventually disposed of by burying it in deep underground or other methods. It is planned.

<Problem to be solved by the invention> This type of melting furnace is placed in a radiation-shielded space called a cell to reduce radiation exposure of operators, and is operated, maintained, and replaced by remote control. Therefore, there is a desire to make the melting furnace as small and lightweight as possible, and to reduce the amount of secondary waste as much as possible after the melting furnace reaches the end of its life. However, as mentioned above, the raw materials are heated and melted mainly by heat transfer from the molten glass surface.
In order to increase the processing capacity of a melting furnace, it is necessary to increase the area of the top surface of the molten glass (hereinafter referred to as the melting surface area). The amount of waste generated also increased.

In addition, Ru, Pd, Rh contained in highly radioactive waste
Since platinum group elements such as glass are poorly soluble in glass and have a high specific gravity, they settle and accumulate at the bottom of the melting furnace. Pd and Rh are reduced in glass and exist as metals that are good conductors of electricity.
Ru exists as a metal or RuO2 crystal, but RuO
Although 2 is an oxide, it is a good conductor of electricity, as it is used in conductive pastes for electronic parts. When such highly conductive substances are deposited at the bottom of the furnace in a high concentration, the high-temperature resistivity of the glass near the bottom becomes smaller than that of the glass at the top (glass near the bottom containing a high concentration of platinum group elements). (hereinafter referred to as furnace bottom deposits), the current flowing between the electrodes concentrates on the furnace bottom, causing the temperature at the furnace bottom to rise abnormally, and conversely, the melting temperature of the glass on the surface decreases, reducing the raw material melting ability. is what happened.

Yet again? 8. When making the bottom of the melting furnace almost horizontal,
The platinum group elements deposited at the bottom of the furnace did not flow after the glass was poured into the canister, and accumulated further at the bottom of the furnace, eventually making operation impossible. To eliminate this inconvenience, place 3 at the bottom of the hearth.
By providing an inclination of 0° to 70°, glass can be extracted continuously or intermittently from the glass outlet attached to the furnace bottom along with the furnace bottom deposits, and the distance between the furnace bottom and the electrodes can be adjusted to the distance between the pair of electrodes. It was necessary to set the distance to about 1/2 or more, but this made the melting furnace deep and caused a drop in the temperature of the glass near the bottom of the furnace.

The object of the present invention is to solve the problems of reducing the size and weight of a glass melting furnace, increasing the glass melting rate, and preventing the accumulation of deposits on the bottom of the furnace.

Means for Solving the Problems> The electric melting furnace for solidifying radioactive waste using a magnetic field of the present invention includes a glass melting furnace, a plurality of electrodes for passing an alternating current to the molten glass in the glass melting furnace, and an alternating magnetic field. The above object is achieved by attaching a plurality of Fj & poles that generate , and generating forces in the same direction over time on the molten glass through the interaction of these currents and magnetic fields.

The magnetic pole can penetrate the furnace wall of the melting furnace and come into contact with the molten glass, or it can be installed inside the furnace wall and not come into contact with the molten glass, and the magnetic pole has an excitation winding for generating an alternating magnetic field. The magnetic poles may be used under superconducting conditions using materials that exhibit normal conductivity or materials that exhibit superconductivity. In a melting furnace having a sloped furnace bottom, it is installed near a flat furnace bottom, and an auxiliary electrode is installed near the sloped furnace bottom.

Further, the method of the present invention involves passing an alternating current through the molten glass between a plurality of electrodes provided in a glass melting furnace, and generating an alternating magnetic field between a plurality of 81 poles, and by the interaction between these currents and the magnetic field. A force in the same direction over time is generated in the molten glass to cause the molten glass to flow, thereby promoting heat transfer from the molten glass to the unmelted raw material present on the molten surface, or to the bottom of the melting furnace. It becomes possible to suppress and prevent sedimentation and accumulation of substances that tend to settle to the bottom of the furnace.

Effect> The interaction between the direct current for heating and the magnetic field creates a force that promotes the flow of molten glass in the melting furnace according to Fleming's left hand rule.

This force makes it possible to increase the amount of heat transferred from the molten glass to the raw material layer on the molten surface, improve the melting ability, and suppress and prevent sedimentation and accumulation of furnace bottom deposits.

<Example> FIG. 1 shows the basic structure when a magnetic field is applied to the tank of an electric melting furnace 1. Electrodes 2.3 are inserted into a pair of opposing side walls of the melting furnace 1, and the electrodes 2.3 are electrically connected to the secondary winding side of the transformer 4, so that the molten glass 8 (- An alternating current is applied to the molten glass (the dotted chain line indicates the position of the molten glass liquid level), and the molten glass 8 is caused to generate heat by this current. In addition, the other 1#fl facing the melting furnace 1
A magnetic pole 5.6 is inserted into the side wall of the molten glass 8, and the magnetic pole 6 intersects the current flowing through the molten glass 8 by the auxiliary magnetic winding 7, which is electrically connected to the primary winding side of the transformer 4. Generates an alternating magnetic field. When the magnetic flux density of the magnetic field is B and the current density in the fluid is J, the electromagnetic force F generated per unit volume of the fluid can be expressed by the following equation using Fleming's left-hand rule.

F=JxB However, F, J, and B are vector quantities.

Although the magnitude and direction of the current flowing and the magnetic field change over time, the generated force F does not change by -N. Therefore, a force in one direction is generated in the molten glass 8 and is forced into the melting furnace 1. Convection is caused.

The present invention is based on the basic concept of placing the molten glass 8 through which an electric current is passed in a magnetic field, and generating a convection driving force in the molten glass 8 in the melting furnace 1 by the force generated in the molten glass 8 itself. It is something.

In addition to being made of a normal conductive material, the magnetic pole excitation winding 7 may be made of a superconducting material and used under conditions that exhibit superconductivity.

When the molten glass 8 in the melting furnace 1 is being heated by the current passed between the electrodes 2.3, natural convection occurs as shown by the arrows in FIG. The heat generated in the molten glass 8 is
The glass raw material 9a and radioactive waste 9b that are transferred from the molten glass 8 to the raw material layer 9 existing on the melting surface by convection heat transfer and radiation, and are mainly supplied to the melting furnace 1 by this ripening ff1Q are melted. As already stated. In general, the refractories constituting the melting furnace 1 usually have a multilayer structure, but are not shown in the figure.

The magnetic pole 5.6 may be inserted into the tank so as to penetrate the side wall of the melting furnace 1 and come into contact with the molten glass 8, as shown in FIG. As shown, the melting furnace 1 can be made of a refractory having sufficient magnetic permeability in an oval shape, and the magnet 1if15.6 can be installed inside the refractory so that it does not come into contact with the molten glass 8.

Figure 3fa) and Figure 3(b) also show the magnetic flux B and current J
FIG. 4 shows a longitudinal section thereof. In this example, magnetic flux B and current J
When determining the direction of
The force F generated on the molten glass 8 by the interaction with the molten glass 8 is directed downward. FIG. 5 schematically shows the accelerated convection of the molten glass in this case. By promoting convection, the amount of heat transferred from the molten glass 8 to the raw material layer increases,
The overall heat transfer amount Q' is larger than the heat transfer JiQ when no magnetic field is applied for the same heat transfer area. In other words, when comparing at the same melting surface area, the former has a higher melting speed of the raw material than the latter, and when comparing at the same melting speed, the melting surface area is smaller. Therefore, by directly applying a magnetic field to the energized melting furnace, This makes it possible to make the melting furnace smaller and lighter.

The above has been described mainly from the viewpoint of increasing the melting rate by promoting the convection of the molten glass 8, but next, it will be explained from the viewpoint of suppressing sedimentation of the furnace bottom deposit \lA10.

FIG. 6 shows how the furnace bottom H1 stack 10 is deposited on the flat furnace bottom. As mentioned above, the furnace bottom deposits 10 have a lower resistivity than the molten glass 8, so when electricity is passed between the electric currents 5 and 6, the current flows through the tank more than when the furnace bottom deposits 10 are not deposited. It shows a tendency to concentrate at the bottom.

The concave arrow 11 signifies this and is a typical current line flowing through the bottom sediment 10.

In FIGS. 7 and 8, the melting furnace 1 has a flat bottom structure, and the magnetic poles 5.6 are arranged so that the magnetic flux is almost orthogonal to the current and the magnetic flux density B is highest at a depth near the bottom of the furnace. The directions of current density J and magnetic flux density B are combined so that electromagnetic force F is directed upward. FIG. 9 shows that the furnace bottom deposit 10 is moved upward by the above-mentioned upward force, and at that time, the molten glass 8 is also exerted with an upward force and tends to move upward, so that the upward movement of the deposit 10 is This means that movement will become easier. In this way, the interaction between the current and the magnetic flux suppresses or prevents the settling and accumulation of the furnace bottom deposits 10 on the furnace bottom, and even if the furnace bottom deposits 10 are included in the molten glass 8, It is possible to suppress or prevent the deposits 10 from accumulating on the furnace bottom, and to smoothly operate the melting furnace 1 without causing current concentration on the furnace bottom deposits 10. Making the furnace bottom flat not only makes the structure of the melting furnace 1 simpler than a structure in which the furnace bottom is sloped, but also makes the depth of the furnace shallower, making the melting furnace 1 smaller and lighter. Needless to say, it can be done.

The embodiments shown in FIGS. 10 and 11 show embodiments in which the furnace bottom is sloped toward the glass outlet in the furnace bottom. As the melting furnace becomes deeper, the temperature of the molten glass 8 near the bottom of the furnace tends to drop, so a pair of auxiliary supports Z @ 2 a, 3 a are provided near the bottom of the furnace to heat the molten glass 8 near the bottom of the furnace. ing. Furthermore, the magnetic poles 5.6 are arranged so as to obtain a magnetic flux that is substantially perpendicular to the current flowing between the auxiliary electrodes 2a, 3a. The directions of the current and magnetic flux are determined so that an upward force acts on the molten glass 8 and the furnace bottom deposits 10 near the furnace bottom. If there were no magnetic field, the furnace bottom deposits 10 would accumulate until the molten glass 8 was periodically withdrawn by a freeze valve (not shown) at the glass outlet 12.
gradually accumulates at the bottom of the furnace and reduces the resistance between the auxiliary electrodes 2a and 38, so it is necessary to flow more current through the electrodes 2 and 3 to raise the temperature of the molten glass 8 near the bottom of the furnace. In order to suppress the erosion of the electrode 2.3 and to reduce the current Th electrode surface density to a certain value or less, the electrode 2.3 must be enlarged to secure the necessary surface area. However, by applying a magnetic field, the bottom deposits can be made to flow upwards, and the decrease in resistance between the auxiliary electrodes 2a and 3a can be suppressed, and as a result, it is possible to avoid increasing the size of the electrodes 2.3. .

In addition, in this embodiment in which the magnetic pole 5.6 is arranged on the sloped bottom of the furnace, the magnetic pole 5.6 can be smaller than in the case where the bottom of the melting furnace 1 is flat, and the required magnetic flux is also reduced. You'll end up needing less.

<Effects of the Invention> According to the present invention, a force that promotes flow is generated in the molten glass in the melting furnace by the interaction between the direct heating Th current and the magnetic field. The amount of heat transferred to the upper raw material layer increases, which can improve the melting capacity, and with the same melting capacity, the melting furnace can be made smaller and lighter, reducing the amount of secondary waste when the melting furnace reaches the end of its life. I can do it. In addition, by promoting the flow in the tank described above, the bottom of the melting furnace is made of a flat 1rI4 structure, and the bottom of the furnace is
r! It becomes possible to suppress and prevent materials from settling and accumulating on the bottom of the furnace.

Furthermore, in the case of a melting furnace with a slope at the bottom,
By suppressing and preventing sedimentation and accumulation of the furnace bottom deposits, it is possible to reduce the size of the auxiliary electrode that directly heats the molten glass in the vicinity of the furnace bottom.

In addition, if a superconducting material is used in the excitation winding and current is passed under conditions that exhibit superconductivity, the magnetic flux density generated in the magnetic poles can be increased, and the flow generated in the molten glass can be further promoted. By installing magnetic poles inside, the molten glass 8
By avoiding contact with the molten glass 8, corrosion of the magnetic pole 5.6 due to contact with the molten glass 8 can be reduced.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the basic structure of the electric melting furnace for solidifying radioactive waste using a magnetic field according to the present invention, and Figure 2 shows the main flow when heated by the current passed between the electrodes. Explanatory diagrams schematically showing the situation, Figures 3(a) and 3(b)
) is F! Figure 4 is an explanatory diagram showing how the i-poles are arranged and the relationship between the magnetic flux density B of the magnetic field, the current density J in the fluid, and the electromagnetic force F generated per unit volume of the fluid. 11 is a sectional view, and FIG. 5 is an explanatory diagram schematically showing the convection of molten glass in the case of FIG. 4. FIG. Figures 7 and 8 are explanatory diagrams showing typical flowing current lines, and show the magnetic flux density B of the magnetic field when moving the bottom deposits upward, the current density J in the fluid, and the power generated per unit volume of fluid. An explanatory diagram showing the relationship with the generated electromagnetic force F, Figure 9 is an explanatory diagram showing the state in which the furnace bottom deposits are moved upward in the case of Figure 8, and Figures 10 and 11 are FIG. 4 is a v1 cross-sectional view and a line cross-sectional view of an embodiment in which the furnace bottom is not sloped toward the glass outlet. 1... Glass 7g melting furnace, 2.3... Electrode, 2a, 3
a... Auxiliary electrode, 4... Transformer, 5.6... Magnetic pole, 7... Magnetic pole excitation winding, 8... Molten glass, 9...
- Raw material layer, 9a... Highly radioactive waste, 9b... Glass raw material, 10... Furnace bottom deposit, 11... Typical current line flowing through the furnace bottom deposit, 12... Glass Outlet.

Claims (1)

[Scope of Claims] 1. A glass melting furnace is equipped with a plurality of electrodes for passing an alternating current through the molten glass in the glass melting furnace and a plurality of magnetic poles for generating an alternating magnetic field, and the interaction between these currents and the magnetic field is An electric melting furnace for solidifying radioactive waste using a magnetic field, characterized in that a force is generated in the same direction over time on the molten glass. 2. Electric melting for solidifying radioactive waste using a magnetic field according to claim 1, wherein the magnetic pole penetrates the wall of the melting furnace and comes into contact with the molten glass, or is installed inside the furnace wall so as not to come into contact with the molten glass. Furnace. 3. The excitation winding for generating an alternating magnetic field at the magnetic poles uses a material exhibiting normal conductivity or a material exhibiting superconductivity and is used under conditions exhibiting superconductivity.Using the magnetic field of claim 1 Electric melting furnace for solidifying radioactive waste. 4. The electric melting furnace for solidifying radioactive waste using a magnetic field according to claim 1, wherein the melting furnace has a flat furnace bottom, and the magnetic pole is disposed near the flat furnace bottom. 5. Electric melting for solidifying radioactive waste using a magnetic field according to claim 1, wherein the melting furnace has a sloped furnace bottom, and the magnetic pole is arranged together with an auxiliary electrode near the sloped furnace bottom. Furnace. 6. An alternating current is passed through the molten glass between the multiple electrodes installed in the glass melting furnace, and an alternating magnetic field is generated between the multiple magnetic poles, and the interaction between these currents and the magnetic field causes the molten glass to change over time. An electric melting method for solidifying radioactive waste using a magnetic field characterized by generating a directional force to flow the molten glass and promoting heat transfer from the molten glass to unmelted raw materials present on the molten surface. . 7. An alternating current is passed through the molten glass between the multiple electrodes installed in the glass melting furnace, and an alternating magnetic field is generated between the multiple magnetic poles, and the interaction between these currents and the magnetic field causes the molten glass to change over time. Electric melting for radioactive waste solidification using a magnetic field, which generates a force in the direction to cause the molten glass to flow, thereby suppressing and preventing the sedimentation and accumulation of substances that tend to settle at the bottom of the melting furnace. Method.