JP2954212B1 - Radioactive waste melting equipment - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To prevent corrosion and damage of a melting furnace vessel, to have high safety and reliability, to reduce installation space, and to facilitate operation and maintenance. SOLUTION: An apparatus for melting and processing radioactive waste by a high-temperature melting furnace of a method of melting while maintaining a state in which a molten melting vessel container 22 to be cooled and a melt 28 to be heated therein are not in direct contact with each other. is there. Many heat pipes 30
To form a melting furnace vessel by arranging those evaporator sides,
Install in the cell. The respective heat pipes are extended, their condensing portions are drawn out of the cell, and a cooling means (water cooling pipe 34) is attached to the condensing portions of each heat pipe. While forming a solidified layer between the melting furnace vessel and the molten material, for example, induction heating is performed by a high-frequency induction coil 34. The heat pipe preferably has a structure in which sodium is sealed in an enclosure as a working fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for melting and processing radioactive waste, and more particularly, to a method for safely heating a melt without directly contacting a melting furnace vessel and in a radioactive material management section. The present invention relates to a melt processing apparatus that can perform processing. The present apparatus is particularly suitable for collectively reducing and solidifying various types of radioactive solid waste such as combustibles, metals, glass, and other flame retardants.

[0002]

2. Description of the Related Art Radioactive miscellaneous solid waste generated from nuclear facilities and the like is generated in a large amount and contains various types of substances such as combustibles, metals, glass, and other flame retardants. The radioactive miscellaneous solid wastes cannot be unconditionally compared because the radioactivity levels and the mixing ratio vary depending on the generating facility. However, for example, in high-level solid waste in a reprocessing facility, metal, wood, waste, and the like are in a mixed state, and the ratio is not uniform according to the work content, but roughly 90% is made of metal, The remainder is considered to be glass materials, combustibles (such as rags), and flame retardants (such as vinyl sheets).

[0003] For this reason, there is a technique for simply and simply treating (volume reduction / solidification) radioactive miscellaneous solid wastes in which the waste components are not clearly separated and whose mixing ratio is various. Development was desired. In view of this, from the viewpoint of reducing the processing cost or environmental load, a cold crucible induction melting technique for collectively incinerating and melting these radioactive miscellaneous solid wastes at a high temperature has been proposed (JP-A-7-63895).
Gazette). This is to cool the melting furnace vessel and keep the temperature of the melting furnace vessel low while realizing melting at high temperature.
This is a technique for forming a thin layer (skull layer) of solidified material inside the melting furnace container to prevent the molten material from directly contacting the melting furnace container, thereby preventing corrosion and damage of the melting furnace container.

FIG. 8 shows an example of a conventional cold crucible induction melting system, and FIG. 9 shows an example of the melting furnace. The cold crucible induction melting apparatus 10 has a configuration in which a water-cooled copper melting furnace vessel 12 divided by slits is installed in a water-cooled high-frequency induction coil 14. Cooling water passages 16 are provided at the bottom and side walls of the melting furnace 12 so that the cooling water flows in from a cooling water inlet 16a and flows out of a cooling water outlet 16b, thereby cooling the water. The radioactive miscellaneous solid waste is charged into the melting furnace 12. Then, the cooling water is circulated to cool the melting furnace container 12, and a high-frequency current is supplied from the high-frequency power supply to the high-frequency induction coil 14.

[0005] Among the radioactive miscellaneous solid waste put into the melting furnace container 12, the metallic substance contained therein is conductive. Electricity flows through the conductive material and induction heating is performed. This heat generation indirectly heats the surrounding inflammables such as combustibles and glass. That is, the metal is the starting source of the melting heating. The mixed combustibles are burned to reduce the volume, and the non-combustibles are melted. The glass material becomes conductive when it is in a molten state, so that a current flows in response to a high-frequency current of the high-frequency induction coil 14 and is directly heated. In this way, the melting area gradually expands, and eventually the whole reaches a molten state. The melt is designated by reference numeral 18.

[0006] Among the radioactive miscellaneous solid wastes, the metal does not directly contact the inner wall of the melting furnace because a floating force acts on the metal itself by the action of an electromagnetic field when certain conditions are satisfied. In the case of a glass material, the contact surface with the inner wall of the melting furnace becomes a solid layer (skull layer) 19 by cooling, and the melt 18 does not directly contact the furnace material (melting furnace vessel wall).
2 can prevent high temperature erosion. Further, since the melting furnace itself is water-cooled, it is not limited to its heat-resistant temperature. Therefore, it is possible to melt and process radioactive miscellaneous solid waste at an arbitrary temperature by supplying necessary power, which is an extremely effective treatment technique.

[0007]

However, in the above-mentioned prior art, since water is used for cooling the melting furnace container, the cooling water leaks from the melting furnace container and may come into contact with the high-temperature molten material. This may cause a steam explosion. Therefore, inspection and maintenance must be performed frequently so that such a situation does not occur, and careful driving is required. Furthermore, measures such as strengthening of protective walls are also necessary in case of emergency.

Further, since radioactive waste is incinerated and melted, it is necessary to install this type of melting furnace in a radioactive material management section such as a cell or a glove box in order to confine radioactive nuclides. If the conventional cold crucible induction melting furnace is applied as it is, a large amount of water will be brought into the radioactive material management section for cooling the melting furnace vessel. Therefore, if the cooling water piping is damaged, the cooling water leaked in the radioactive material management section must be treated as secondary waste, and the treatment is difficult.

In addition, it is necessary to periodically remove the scale adhering to the inside of the cooling water pipe in maintenance, which is troublesome. Alternatively, even if pure water is used as the cooling water for the purpose of suppressing scale adhesion, water quality control is required, and a purification facility for that purpose is required. Further, since the cooling system piping becomes long and the handling becomes complicated, the pressure loss of the cooling water increases, the required pump power increases, and a large space is required for installing the equipment.

[0010] It is an object of the present invention to provide a radioactive waste that can prevent corrosion and damage of a melting furnace vessel, has extremely high safety and reliability, requires only a small installation space for equipment, and can be easily operated and maintained. An object of the present invention is to provide an apparatus for melting and processing an object.

[0011]

SUMMARY OF THE INVENTION The present invention provides a method for melting a molten furnace while maintaining a state in which a molten furnace vessel to be cooled is not in direct contact with a melt heated in the molten furnace vessel. It presupposes an apparatus that melts radioactive waste with a high-temperature melting furnace. In the present invention, a melting furnace container is constituted by arranging a large number of heat pipes, the evaporating portions of which are densely juxtaposed with an insulating material therebetween. It is installed in a section, each heat pipe is extended, their condensing section side is drawn out of the radioactive material management section, and cooling means is attached to the condensing section side of each heat pipe.

When the melting furnace vessel body is used separately, the melting furnace vessel is constituted by arranging a plurality of heat pipes side by side on the outside of the melting furnace vessel body. In that case, the heat pipes may be densely arranged side by side or may be arranged at intervals.

As the heat pipe, for example, a heat pipe having a structure in which sodium is used as a working fluid and sealed in a sealed container is preferable. Further, as a cooling means provided on the condensing portion side of each heat pipe, there is a method of providing water cooling by providing a water cooling pipe, but also a method of providing a cooler and cooling with a cooling medium, or a method of providing fins and air cooling. Good.

The radioactive waste put in the melting furnace vessel is heated and melted. The evaporation part of the heat pipe is located on the melting furnace vessel itself or outside the melting furnace vessel body, and the cooling means is provided on the condensation part side, so the heat pipe transports the heat of the melting furnace vessel to the cooling means. Then, cooling is performed there, so that the melting furnace vessel is efficiently cooled. At this time, since the molten material is kept in a state where it does not directly contact the furnace material (melting furnace vessel wall), high-temperature erosion of the melting furnace can be prevented. Further, since the melting furnace itself is cooled as described above, it is not limited to its heat-resistant temperature. Therefore, by supplying the necessary power, it is possible to melt the radioactive miscellaneous solid waste at an arbitrary temperature.

Since the cooling means is provided outside the radioactive material management section, even if it is a water-cooled type, even if it leaks, it does not cause a steam explosion and the amount of waste does not increase. .

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view showing an embodiment of a radioactive waste melting apparatus according to the present invention, and FIG. 2 is an explanatory view of a melting furnace portion thereof. This melt processing equipment
The radioactive waste is induction-heated in the melting furnace container 22 by the melting furnace container 22 to be cooled and the high-frequency induction coil 24 wound around the melting furnace container 22.
This is a method in which the melt 28 is melt-processed while maintaining a state in which the melt 28 does not directly contact. In the present invention, a large number of heat pipes 30 are used as heat transport means, and their evaporating units are located on the side of the melting furnace container 22. The melting furnace container 22 is installed in a cell which is a radioactive material management section, the heat pipe 30 penetrates the cell wall 32 and is drawn out of the cell, and a cooling means (here, a water cooling pipe 34) is provided on the condensing portion side of each heat pipe 30. ) Is attached so as to perform forced cooling.

By supplying a high-frequency current to the high-frequency induction coil 24, an induction current is generated and melted in the metallic substance of the radioactive miscellaneous solid waste in the melting furnace container 22. The heat burns combustibles and melts the glass material. Since the molten glass material exhibits conductivity, an induced current is generated and further melts. Since the melting furnace container 22 is cooled by the heat pipe 30, a thin layer (skull layer) 29 of the solidified material is formed between the melt 28 and the melting furnace container 22. Therefore, the high-temperature melt does not come into direct contact with the melting furnace vessel, so that corrosion and damage of the melting furnace vessel can be prevented.
This is especially true for systems that deal with radioactive waste that is difficult to access directly, such as those installed inside cells, etc., which makes it possible to maintain the melting furnace free of charge and greatly reduce operating costs. Is very advantageous.

As described above, in the present invention, a heat pipe is incorporated as a heat transport means, and a device for cooling the melting furnace container is devised. The heat from the melt is released to the outside in the following cycle using the latent heat of vaporization of the working fluid sealed in the heat pipe. Heat pipe wall heating → Evaporation of working fluid (evaporator side) → Transfer of steam → Condensation (condensation) at condenser side →
Reflux of the working fluid The condensing part side passes through the melt and several types of boundaries,
Even if the cooling water leaks, there is no fear of causing a steam explosion. Further, cooling water does not enter the cell. The heat pipe itself is a static device and does not have any moving parts, so that it becomes a highly reliable cooling mechanism.

In the above embodiment, forced water cooling is performed using a water-cooled pipe as a cooling means. However, depending on conditions, a fin 36 may be provided and air-cooled as shown in FIG. 3 or shown in FIG. As described above, a cooler 38 may be provided for cooling with a cooling medium. In both FIGS. 3 and 4, the configuration of the melting furnace in the cell may be the same as that in FIG. 1 described above, and the corresponding members are denoted by the same reference numerals and description thereof will be omitted.

The melting furnace container is, for example, as shown in FIG.
A large number of heat pipes 40 may be configured by closely arranging their evaporating sections on the side of an electric insulating material (such as mica) 42 closely. The heat pipes 40 are kept in a container shape using an electrically insulating binding band 44. That is, in this case, the heat pipe 40 itself constitutes a melting furnace container. Therefore, by adjusting the number of heat pipes, it becomes possible to manufacture a melting furnace container having an arbitrary size (diameter). When the band is used for binding the heat pipes, the furnace container can be easily manufactured.

When a large number of heat pipes are densely arranged, it is possible to join the heat pipes together by welding or the like without using a binding band.
In this case, the joining (welding) portion is a portion that does not contribute to induction heating (a position vertically deviated from a portion around which the high-frequency induction coil is wound).

Alternatively, as shown in FIG. 6, a plurality of heat pipes 52 on the side of the evaporator may be arranged outside the melting furnace vessel body 50 to constitute a melting furnace vessel. As shown in A, they may be juxtaposed in a substantially dense state, or may be juxtaposed at intervals as shown in B. In any case, a tying band 54 is provided on the outside thereof, and a heat pipe 52 is provided.
It is better not to come off. When the melting furnace container body is used separately from the heat pipe as described above, it is necessary to balance heat so that a skull layer can be formed inside the melting furnace container. Further, from the viewpoint of this heat balance, it is preferable that the melting furnace vessel main body is made of a non-conductive material.

In each of the above embodiments, the heat pipe has a circular cross section. However, the present invention is not limited to this. As shown in FIG. 7A, the heat pipe 60 may have a substantially square cross section. As described above, the non-circular shape can increase the contact area and improve the heat transfer performance.
Alternatively, as shown in FIG. 7B, the heat pipe 62 may have a substantially trapezoidal cross section. This not only improves the heat transfer performance, but also makes it easier to bind.
Also in these, the section other than the portion constituting the melting furnace container or the portion in contact with the melting furnace container body may have a circular cross section.

As the heat pipe, for example, a pipe in which sodium is used as a working fluid and sealed in a stainless steel pipe (sealed container) is preferable. This combination is mainly because sodium has excellent characteristics as a working fluid (indicated by a merit number). Stainless steel is a relatively inexpensive material that has a good track record in industrial use, and has good compatibility with sodium. Operating temperature 1000K (72
Above 7 ° C.), heat removal on a 10 MW / m ² scale is possible. This means that when a melting furnace having a diameter of 1 m or more is constituted by a heat pipe having an effective sectional area of 10 cm ² , it is possible to remove heat of about 3 MW, and a sufficient amount of heat can be secured. However, as long as cooling conditions can be satisfied, not only the above-mentioned heat pipe made of sodium-filled stainless steel but also a combination of various working fluids and materials of the sealed vessel may be used. When sodium is used as the working fluid, as a material having good compatibility with sodium, in addition to stainless steel,
Nickel, chromium, and niobium are known, and depending on the thermal, mechanical properties, and cost conditions, a sealed container manufactured using these materials can also be used. The merit number is a numerical value represented by the following equation, and it is considered that the larger this value is, the better the working fluid is. (Number of merit) = (density) x (surface tension) x (latent heat) /
(Viscosity)

When sodium is used as the working fluid, it is necessary to evaluate the effect of the induced current because sodium is a conductive liquid metal. During high-frequency induction heating, the induced current generated in the heat pipe concentrates on its surface and decreases exponentially as it goes inside (skin effect). As a result of calculation, the penetration depth of the induced current is 1
mm, and it is considered that the induced current acts only on the enclosure of the heat pipe. If the electromagnetic penetration depth increases for some reason and an induced current flows through the sodium condensate, there is some Joule heating, but the encapsulation container and sodium can be regarded as electrically integrated, so the encapsulation container wall Electromagnetic force does not act in the direction away from.

In an extreme case, if a sodium droplet or a liquid film is present away from the enclosure wall, an electromagnetic force acts in a direction away from the enclosure wall, so that sodium gathers at the center of the enclosure. However, a situation in which the heat does not contribute to heat transport from the wall surface is also assumed. However, in the heat pipe, since the wick is arranged on the inner surface of the wall, the electromagnetic force on the liquid sodium away from the wall acts in a complicated manner, and as a result, the flow of sodium is promoted, and the positive effect of improving heat transfer Can be expected. Electromagnetic force is also considered to microscopically act on steam and mist-like sodium generated in the evaporator.However, since the driving force in these condensers is the sodium pressure difference in the heat pipe axial direction, Even if mist-like sodium collects at the center of the heat pipe under the influence of the electromagnetic force, it does not hinder the movement of the sodium from the evaporator to the condenser. In conclusion,
Even if sodium is used, a situation where the function as a working fluid is not impaired does not occur.

When the object to be treated is radioactive miscellaneous solid waste, the melt is melted while forming a solidified layer between the melting furnace vessel and the melt as described above. When only radioactive waste is treated with metallic materials, the molten metal is lifted up by the action of electromagnetic force by melting, and it is possible to hold and melt in the air without contacting the melting furnace vessel. . The present invention is applicable not only to the induction heating type melting furnace as described above but also to a plasma heating type melting furnace.

[0028]

The present invention is a radioactive waste melting apparatus configured to cool a melting furnace container by removing heat with a heat pipe. Therefore, a direct water-cooled melting furnace as in the prior art is dangerous. In the unlikely event that a steam explosion occurs, the safety and reliability can be significantly improved. As a result, there is no need for a protective wall or a pressure release device in the event of a steam explosion, so that the installation area of the equipment can be reduced, power for primary cooling is not required, and equipment costs can be reduced.
Also, maintenance of the equipment is easy.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of a melt processing apparatus according to the present invention.

FIG. 2 is an explanatory view showing an example of the melting furnace.

FIG. 3 is a conceptual diagram showing another embodiment of the melt processing apparatus according to the present invention.

FIG. 4 is a conceptual diagram showing still another embodiment of the melt processing apparatus according to the present invention.

FIG. 5 is an explanatory view showing a configuration example of a melting furnace container.

FIG. 6 is an explanatory view showing another configuration example of the melting furnace container.

FIG. 7 is an explanatory diagram showing an example of a cross-sectional shape of a heat pipe.

FIG. 8 is a conceptual diagram showing an example of a conventional radioactive miscellaneous solid waste melting apparatus.

FIG. 9 is an explanatory view showing an example of the melting furnace.

[Explanation of symbols]

 22 Melting furnace container 24 High frequency induction coil 28 Melt 30 Heat pipe 32 Cell wall 34 Water cooling pipe

────────────────────────────────────────────────── ─── of the front page continued (72) inventor Ichiro Kawaguchi Ibaraki Prefecture Naka-gun, Tokai-mura, Oaza Muramatsu address 4 33 nuclear cycle development Institute Tokai plant, Kawasaki Heavy Industries, Ltd. belongs to (58) investigated the field (Int.Cl. ⁶ , DB name) G21F 9/30

Claims (4)

(57) [Claims] 1. A radioactive waste produced by a high-temperature melting furnace in which a melting furnace vessel to be cooled and a melt heated in the melting furnace vessel are not in direct contact with each other while the melt is melt-processed. In the apparatus for melting processing, a number of heat pipes, their evaporating parts side are densely arranged side by side via an insulating material to constitute a melting furnace container, and the melting furnace container is installed in the radioactive material management section A heat treatment apparatus for radioactive waste, characterized in that each heat pipe is extended, its condensing part side is drawn out of the radioactive material management section, and cooling means is provided on the condensing part side of each heat pipe. 2. A radioactive waste produced by a high-temperature melting furnace of a type in which a melting furnace to be cooled and a melt to be heated in the melting furnace are not in direct contact with each other while the melt is melt-processed. In the apparatus for melting processing, outside the melting furnace container body, the evaporation part side of a number of heat pipes are arranged side by side to form a melting furnace container, and the melting furnace container is installed in the radioactive material management section, An apparatus for melting radioactive waste, characterized in that the heat pipes are extended, their condensing sections are drawn out of the radioactive substance management section, and cooling means is provided on the condensing sections of each heat pipe. 3. A high-temperature melting furnace, wherein a high-frequency induction coil located outside the melting furnace container heats the melt in the melting furnace container by induction heating, and at that time, solidifies between the melting furnace container and the melt. 3. The apparatus for melting radioactive waste according to claim 1 or 2, wherein the apparatus is configured to melt-process the melt while forming a layer of the material. 4. The radioactive waste melting treatment apparatus according to claim 1, wherein the heat pipe is a heat pipe having a structure in which sodium is sealed in an enclosure as a working fluid.