JPH0749182A - Method for melting solidification and cooling crucible therefor - Google Patents

Abstract

PURPOSE:To simplify the disposal of waste produced during operation, and if necessary, effect phase separation when molten material solidifies by improving the safety and heat efficiency of a cooling crucible when the material is cooled and solidifies after being melted by using the cooling crucible. CONSTITUTION:An electric coil 2 is arranged around a crucible composed of an electrically conductive cooling wall constructed by an assembly of segments insulated from one another by means of slits 15. Material to be melted in the crucible is melted by using electromagnetic action and then solidifies. A protection wall 17 made of electrically conductive material is provided on the inner wall face of the crucible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of using a cooling crucible for heating a material, particularly a material contaminated by radioactive substances, to a temperature higher than its melting temperature and then cooling and solidifying the material. The present invention relates to a method for increasing efficiency, simplifying the treatment of waste generated during operation, and, if necessary, performing phase separation in solidifying a molten material, and a cooling crucible used in the method.

[0002]

2. Description of the Related Art A technique for melting a melted material in a cooled crucible made of a material having a melting point lower than that of the melted material without being contaminated by the crucible material has already been disclosed in German Patent No. 518499 of 1931. Are known. According to this technique, the melting vessel is made of a conductive material such as quartz glass, copper, or silver, and preferably the high-frequency current is used to heat the melting material while cooling the vessel, whereby tantalum, It dissolves refractory metals such as tungsten and thorium. When the melting vessel is made of a conductive material, it is made up of metal segments electrically insulated from each other. It has also been suggested to provide a thin oxide layer between the melting material and the crucible material for thermal insulation.

Since then, a number of patents relating to cooling crucibles have been filed. For example, in Japanese Patent Laid-Open No. 63-192543 (corresponding French Patent Publication No. 87-00814), a solidified material is continuously treated. A crucible shape has been proposed, as well as the provision of an insulating layer between the segments of crucible material.

In such a cooling crucible, since a low temperature cooling wall and a high temperature melt are present adjacent to each other, there are some problems. The first is the problem of electrical shorts. As described above, in the conductive cooling crucible, it is indispensable to provide an electrically insulating layer, for example, a slit in the present invention, or a mica layer in the above-mentioned German patent invention, between the segments forming the cooling crucible.
Even if an electromagnetic coil is provided around the conductive cooling crucible having no slit, the magnetic field is attenuated in the crucible and it is impossible to dissolve the melted material in the crucible. Therefore, it is necessary to provide a crucible composed of a large number of segments with slits penetrating the interior of the crucible in the direction orthogonal to the winding direction of the coil. And each segment is water cooled independently,
The segments are integrated at the bottom of the crucible. When molten metal enters (is inserted into) such a slit, an electrical short circuit occurs, and a phenomenon similar to the case where the number of slits is substantially reduced, that is, a decrease in heating effect occurs. Also,
The molten metal solidifies to significantly increase the pull-out resistance of the solidified volume reducing body, and in some cases, the cooling crucible may be deformed due to the pull-out resistance.

The second problem is steam explosion. In the case of the conventional method that does not use a protective wall, an extremely large temperature gradient is generated between the cooling crucible and the molten metal. In many cases, there will be no problem while the crucible is sufficiently cooled. However, if the temperature of a specific portion of the crucible is raised for some reason, the crucible is destroyed and the cooling body (often water) of the crucible leaks to the outside and comes into contact with the hot melt. At this time, the cooling body undergoes a rapid volume expansion, and as a result, there is a risk of causing the furnace to explode.

The third problem is a decrease in heating efficiency. When the melting material is excellent in thermal conductivity like metal, the Joule heat generated in the melting material is heat-conducted, and as a result, the heat loss through the wall of the cooling crucible becomes remarkable and the heating efficiency is reduced. It is also an object of the present invention that the dissolved material is composed of two or more kinds of substances having different physical properties, particularly electrical conductivity, and that these substances are not mixed homogeneously, and the obtained solidification is in a phase-separated form. In that case, it is difficult to heat uniformly. This is because in this case, the frequency suitable for induction heating differs depending on each substance.

For the first and second problems, there are already 19
Inductoslag Ingot Melting method was introduced in the 70's Bureau of
Proposed by Mines (PGClites and RABeall
(assigned to US Department of the Interior): Indu
ction-Melting of Metals in Cold.Self-lined Crucible
s, US Pat. 3775091.Nov. 27, 1973), in continuous casting using Ti scrap as a raw material, CaF ₂ was added in order to prevent electrical short circuit and expect thermal insulation effect.

The second problem is that some measure is required when the target of dissolution is highly toxic. This is the case when dealing with radioactive materials, and it has been proposed to apply Inductoslag Inogot Melting to the dissolution of radioactive waste scraps (RG Elson, MP Schlienger and E. von.
Tiesenhausen: Selection of a Melting-Furnace for Con
solidation of Nuclear Fuel Hulls. Battelle Memoria
l Insti., Pacific Northwest Lab., BNWL-1968, UC-70, De
c, 1976,41..available from National Technical Infor
mation Center, Springfiled.Va.).

However, the thickness of the protective wall of the slag is several mm or less, and it is necessary to form it extremely uniformly, which is generally extremely difficult. The reason is as follows. Generally, slag is not induction-heated by itself, but is melted by conduction heat transfer from a metal. Therefore, when the slag layer is thick, it becomes difficult to melt the slag particularly near the cooling wall, and the slag is mixed in the metal, or the unmelted slag cannot cover the inlet to supply the material. On the other hand, when the slag layer is thin, the molten metal and the cooling wall come into direct contact with each other, increasing the risk of steam explosion.

When the frequency band in which the slag itself is induction-heated is selected, it is possible to melt the slag by providing a layer of the solidified slag near the cooling wall, but the penetration depth of the magnetic field in the conductor is increased. However, the effect of electromagnetic stirring is small and the target metal material cannot be inductively melted.

[0011]

SUMMARY OF THE INVENTION A first object of the present invention is to reduce the risk of a refrigerant in the cooling crucible flowing out of the crucible in a cooling crucible for melting and solidifying a metal to cause an accident due to vapor explosion of the refrigerant. The point is to significantly reduce it.

A second object of the present invention is to improve the heating efficiency in the operation of the cooling crucible. For this purpose, the molten material is inserted into the slit of the cooling crucible to prevent electrical short circuit, to prevent heat loss through the wall of the cooling crucible, and when there are two or more materials with different electrical conductivity in the crucible. In addition, for example, the heating efficiency of both the metal and the slag is increased.

A third object of the present invention is to reduce the volume and separation of secondary waste that is inevitably generated when the crucible of the present invention is used for melting and solidifying a metal contaminated with radioactivity. The point is to provide a way to do.

A fourth object of the present invention is to realize phase separation of a mixture of metal and oxide generated in the cooling crucible.

[0015]

The present inventors first of all,
In order to safely melt the melted material using electromagnetic induction in a cooled conductive container having a slit with an energizing coil that circulates to the outside, the melted material existing between the cooling crucible wall and the melted material It has been found that the layer of slag added together is not sufficient and the protective wall needs to be placed on the inner wall of the cooling crucible. By thus providing the protective wall along the inner wall of the cooling crucible, the molten metal cannot be inserted into the slit of the cooling crucible, and the above problem does not occur. Further, when the protective wall having the slit is used, even if the molten metal is inserted into the slit of the protective wall, this does not reach the slit of the cooling crucible.

When the protective wall is present, the cooling crucible and the molten metal do not come into direct contact with each other. Generally, the electrical conductivity of the protective wall is smaller than that of the crucible material or the metal to be melted, and therefore the heat of Joule formation is small. Moreover, the temperature on the cooling crucible side of the protective wall is low due to heat removal. Therefore, in the case of the present invention, a gentle temperature gradient can be realized near the cooling wall,
Even if the crucible is not sufficiently cooled, there is no danger of an immediate steam explosion.

Secondly, in such a protective wall, especially when a large amount of non-metals other than metal is added, including the case where the added non-metal is 100%, the electric conductivity of the protective wall is that of the cooling crucible. It has been found that it needs to be smaller, preferably between the melted material and the added slag. When such a protective wall is used, especially when the electrical conductivity of the protective wall is smaller than that of the crucible material or the metal to be melted, the metal can be heated by induction heating, and the oxide can be heated between the metal heated by induction heating and the protection wall. Both can be heated by conduction heat to achieve melting.

Third, in particular, the protective wall in contact with the melted material or the added slag reacts with the melted material or the slag and is worn away, so that it is necessary to replace it in the course of operating the crucible.
At this time, the protective wall becomes a waste, but it was found that it is necessary to select a flammable protective wall in order to facilitate this treatment.

Fourthly, it was found that the heating efficiency of the molten material or the slag is remarkably improved when the protective wall has a structure having slits.

Fifth, when the object to be melted is a mixture of a conductor and a non-conductor, the conductor is gathered in the center of the crucible by using an electromagnetic force, and the non-conductor is held around the center of the crucible. As 2
It has been found that the phases can be separated.

Sixth, when the object to be melted is a mixture of a conductor and a non-conductor, if the power source is cut off after the melting, both can be separated by specific gravity. At this time, generally, a non-conductor having a low density is accumulated on the upper part of the crucible. In this way, even after the molten material is once solidified, the conductive material for starting melting (referred to as the base material) can be supplied by simply supplying power again without newly charging in the crucible. It was found that a mixture of non-conductor and conductor can be melted.

Seventh, particularly when performing continuous treatment, such a protective wall moves in the pulling direction under the condition that the relative speed between the crucible and the protective wall is finite and the relative speed between the melted / solidified body and the crucible is zero. This is effective in extending the life of the protective wall.

Eighth, by stacking protective walls of finite length satisfying the seventh condition in the course of operation,
It has been found that it is possible to increase the amount of dissolved material that can be continuously processed.

The present invention was made by appropriately combining the above findings. The configuration of the present invention as the means for solving the above problems is as follows. 1. A current-carrying coil is arranged around a crucible made of a conductive cooling wall composed of a group of segments electrically insulated from each other by a slit, and the material to be melted in the crucible is melted by utilizing electromagnetic action, A melting and solidifying method of subsequently solidifying, characterized in that a protective wall of a conductive material is provided on an inner wall surface of the crucible.

2. A current-carrying coil is arranged around a crucible made of a conductive cooling wall composed of a group of segments electrically insulated from each other by a slit, and the material to be melted in the crucible is melted by utilizing electromagnetic action, A crucible for subsequent solidification, characterized in that a protective wall of a conductive material is provided on an inner wall surface of the crucible.

3. 3. The protective wall according to 1 or 2 above, which is used in an exchangeable state for an inner wall of a crucible that melts a material to be melted and then solidifies.

4. In the above 1, 2 or 3, the electrical conductivity of the protective wall is smaller than the electrical conductivity of the cooling wall.

5. In the above 1, 2 or 3, the protective wall is made of a flammable material.

6. In the above 1, 2 or 3, the protective wall is composed of an assembly of segments electrically insulated from each other by a slit.

7. In the above 1, 2 or 3, the value of the electric current supplied to the coil during operation is maintained at an appropriate value or appropriately changed to perform phase separation of materials having different electric conductivities arranged in the cooling crucible. And

8. 2. The melting and solidifying method according to the above 1, characterized in that the material melted and solidified along the inner wall of the crucible is pulled out together with the protective wall in the drawing direction of the material melted and solidified.

9. 9. The melting and solidifying method according to the above 8, wherein a protective wall having a constant length is supplied in correspondence with the pulling out of the melted and solidified material.

[0033]

[Operation] Hereinafter, the structure of the present invention, together with its operation, will be described with reference to the drawings. FIG. 1 is a schematic half-cut perspective view showing an example of a melting container used when a material is batch-processed by the method of the present invention. The melting vessel is made of a conductive metal, and the vessel wall has a water cooling structure and is electrically insulated from each other by a slit 15. Hereinafter, this melting container is referred to as a cooling crucible 1.

Around the cooling crucible 1, a water-cooled energizing coil 2 spirally wrapping around its outer periphery and a plug 4 are arranged. Further, inside the cooling crucible 1, a protective wall 17 made of graphite and having a wall thickness of about 3 mm is arranged in a state of being almost in contact with the inner wall of the crucible. The energizing coil 2 is connected to the high frequency oscillator 3. The induced current flowing through the crucible wall surface caused by the high-frequency current is guided to the crucible inner wall because the slit 15 having the insulating function is present in the crucible.

The inside of the crucible wall is water-cooled by flowing cooling water so that the water-cooling pipe (not shown) buried in the crucible wall passes through the inlet 7 to the outlet 8, and this water-cooling structure can withstand high temperatures. The crucible is housed in a chamber (not shown) whose atmosphere can be adjusted, and can be placed under pressure conditions such as pressurization or depressurization and an atmosphere such as Ar or He. Alternatively, the crucible can be provided with an upper lid (not shown) to seal the inside of the crucible.

In the melting and solidifying treatment of the metal, slag or the mixture of both using the cooling crucible 1, since the crucible itself is cooled, the crucible wall is not chemically damaged and it is safe. However, when the target of the melting treatment is a substance containing radioactive waste, the above-mentioned melting treatment process needs to be carried out under extremely safe conditions. In the present invention, a protective wall 17 exists between the cooling crucible 1 and the molten material 10. The protective wall literally prevents direct contact between the cooling crucible and the molten material and protects the cooling crucible.

When the object of melting is a mixture of a slag that is not a good conductor of electricity and a metal that is a good conductor, the electrical conductivity of the protective wall is smaller than that of the cooling crucible, preferably a material between the metal and the added slag. You have to choose. At this time, the induced current flowing through the cooling wall heats the protective wall, thus raising the temperature of the protective wall and partly penetrating the protective wall to heat the melted material, in particular the metal part. in this case,
The metal is melted by induction heating, and the slag is melted by conduction heat transfer from the protective wall and the molten metal. In this way, even if materials having different electric conductivities are arranged in the crucible, both can be heated to the same temperature and melted.

Even when the coil current and the frequency are the same, the temperature reached by the protective wall and the melting material changes depending on the physical values such as the electrical conductivity of the protective wall or the melting material and the thickness of the protective wall. Therefore, if the type of protective wall is selected according to the melting material, the temperature of the protective wall is generally set lower than the temperature of the melting material and higher than the temperature of the cooling crucible,
The temperature of the protective wall can be set higher than the temperature of the melting material.

The protective wall is worn out during the melting process of the material and must be replaced regularly. In particular, when the subject of dissolution treatment is a substance such as radioactive waste, it is necessary to devise a method for improving safety and easily treating secondary waste. In order to achieve this, the present invention has devised to place a substance made of a flammable material inside the container as well as having a lower electrical conductivity than that of the cooling container.

It is more preferable to provide the protective wall with slits in the same direction as the slits provided in the crucible in order to improve heating efficiency. This is because the induction current flowing near the skin of the protective wall can guide the induction current inside the protective wall by the same principle as the induction heating of the cooling crucible by the coil, and efficiently heats the molten material. Because you can.

When the object of melting and solidification is a mixture of a metal, which is a good conductor of electricity, and a poor conductor, such as an oxide, and the purpose is to obtain a solidified product in which the phases are separated from each other. In general, a phase-separated solidified body can be obtained by supplying electric power to such an extent that the metal and the oxide are melted to melt the metal and the oxide, and then stopping the supply of the electric power. In the conventional method without a protective wall, when the power supply is completely stopped for a long time, the oxide is incompletely separated so as to surround the metal, and conversely, when the stop time is short. The separation of the two is realized in a form close to incomplete specific gravity separation.

The reason for this is as follows. When the protective wall is not used, electromagnetic stirring is remarkable, so that mixing of the oxide and the metal in the melting process cannot be avoided. Of course, the frequency can be increased to weaken the strength of electromagnetic stirring. However, in this case, there is a problem that the magnetic field is attenuated in the oxide, and the induction heating and melting of the metal cannot be realized.

Further, if the protective wall is not used, it is difficult to take out the incompletely separated solidified body out of the cooling crucible.
This is because a slit exists in the cooling crucible, and the melt enters this slit.

In order to achieve more complete phase separation, a conductive protective wall may be installed inside the cooling crucible. At this time, the protective wall exerts both functions of damping the magnetic field and generating Joule heat, so that the metal and the oxide can be dissolved under the condition of weak electromagnetic stirring. The strength of stirring or the amount of Joule heat generation depends on the thickness of the protective wall together with the power and frequency. Further, the form of phase separation depends on the power cutoff method as described above. In particular, when the specific gravity separation is performed, the present invention using a protective wall is more complete than the conventional method using a cooling crucible. This is because the protective wall has a heat insulating effect and makes it possible to prolong the residence time from the time when the electric power is cut off to the time when it solidifies.

Further, in the method according to the present invention, it is relatively easy to take out the solidified body which has been phase-separated from the cooling crucible 1. Because the protection wall 17 is present, the slit 1
This is because the phenomenon that the melt penetrates into No. 5 does not occur.

In general, continuous processing is required to increase the processing speed including phase separation. For example, when the continuous processing type crucible shown in FIG. 3 is used, phase separation is more effectively realized. Since the electromagnetic force mainly acts on the metal 10, the metal 10 generally accumulates near the center of the crucible and the oxide 11 accumulates around the crucible. Particularly when the volume of the oxide 11 is larger than that of the metal 10, a large metal mass 1 is formed in the molten portion.
There may be a row of bead-shaped metal 10 having a substantially spherical shape on the central axis below 0. This is because the metal 10 in the melted portion was held under the equilibrium condition of electromagnetic force and gravity, the number of beads was excessive, and the metal out of equilibrium fell off and separated, and was formed into a substantially spherical shape by the surface tension. Such a bead sequence is not preferable from the viewpoint of phase separation because the weight of a mass of metal excluding the melted portion is small.

In order to solve this, the levitation metal in the melted portion is grown to a stage just before its equilibrium is broken, and then the supply of electric power is cut off so that the metal mass 10 in the melted portion is converted into oxide 11. Specific gravity separation may be performed by sedimentation to the solidus line.
At this time, the problem with the cooling crucible that does not use the protective wall 17 is reheating after the power is cut off. This is because, in the conventional method that does not use a protective wall, the oxide 11 is generally dissolved by the heat of induction heating of the metal 10, but after the specific gravity separation, there is no metal in the melted portion, so the induction melting cannot be performed. Is. However, in the method according to the present invention, since the conductive protective wall is present inside the cooling crucible, during remelting, the protective wall is first heated, and the heat initiates the dissolution of the oxide or metal, which eventually melts. Induction melting of metal is further promoted as the metal mass in the part grows. In this way, a solidified body in which the phases of the metal 10 and the oxide 11 are alternately formed along the extraction direction in the continuous processing is formed.

FIG. 7 is a schematic half-cut perspective view showing another example of a cooling crucible for continuously treating a material by the method of the present invention. This cooling crucible is similar to that of FIG.
7 is slightly different in that there is no mounting flange portion on the upper edge and the bottom 18 is on the protective wall. Providing this bottom 18 is not always necessary. Due to the absence of the above-mentioned flange portion, the protective wall 17 can be pulled out downward together with the solidified material by the pulling rod 5 provided below the cooling crucible 1 as in Examples 8 to 11 described later. At the top of the crucible is provided a supply of melted material (not shown) and a supply of cylindrical short protective wall segments into the cooling crucible. The protective wall segment supply device has a protective wall segment 17 ′ having a length commensurate with the length of the protective wall 17 pulled out in the process of melting the material, as in Example 11 described later. This is necessary when performing operations that intermittently add to the. Such continuous operation is required especially when the amount of material dissolved is large and the length of the protective wall is insufficient.

In FIG. 10, a protective wall segment 17 'for replenishment is prepared in a pipe line extending laterally from the upper part of the cooling crucible, and supplied from here to the upper edge of the protective wall 17 in the cooling crucible and placed. An example of the device for performing the above is shown.

Even in this continuous operation mode, since the protective wall as described above exists between the melted material and the cooling crucible, a molten substance having a particularly high electric conductivity is inserted into the slit of the cooling crucible and heated. There is no loss of efficiency. Further, since the solidified body of the melting material and the protective wall 17 are pulled out downward by the pulling rod 5 at a constant speed, the protective wall 17
A shearing force sufficient to break the protective wall 17 is unlikely to occur, and the mechanical breakage of the protective wall 17 can be kept to a minimum. In addition, when the material whose electrical conductivity is smaller than that of the cooling crucible and is in the middle of the melting material and the added slag is selected as the protective wall, the protective wall functions as a heat insulating material for the melting material. It is possible to improve efficiency.

[0051]

The present invention will be described in more detail based on the following examples. [Example 1] HUL in PWR (pressurized water reactor)
1 and 5 are a schematic half-cut perspective view of a cooling crucible used for high-temperature treatment of Zircaloy, which is a material for L (nuclear fuel cladding), and a schematic view of a melt flow state in the crucible, respectively. The composition of zircaloy is Sn: 1.2 to 1.7, Fe:
0.07-0.2, Cr: 0.05-0.15, Ni:
0.03-0.08, balance: Zr, melting temperature is 1
The temperature is 800 to 1850 ° C. and the density is 6.55 g / cm ³ .

The cooling crucible body 1 has an inner diameter of 45 mm and a height of 10
It is 0 mm and the material is copper. A protective wall 17 made of graphite and having a thickness of 3 mm is arranged in the crucible. After passing cooling water through the cooling crucible 1 and sealing the inside of the container with the upper lid 16 connected to the supply hopper 6 of the HULL, the gas supply port 13
The inside of the container 1 and the hopper 6 was maintained in an inert atmosphere by flowing Ar gas from the discharge port 14 to the inside. Then about 1
Simulated radioactive waste (atomic number 24, 26-28, 34, HULL before use, cut into a size of 0φ × 40 mm,
Simulated HULL containing 1 wt% of 37-40, 42-52, 55-60, 62-64, and 75 elemental oxides) was added to the vessel together with slag. In the following embodiments, this simulated HULL is simply called HULL. The HULL does not necessarily have to be cut, and the volume may be reduced as it is used in the nuclear reactor if an appropriate supply device is used. The addition amount of slag is 5w of HULL
t%, and its composition is 75 wt% CaF ₂ and MgF ₂
It is 25 wt%.

Under the above conditions, a high frequency current of 2000 A having a frequency of 30 kHz was supplied. During operation, Ar gas was constantly supplied at 101 / min. The HULL and the protection wall 17 were heated to red heat. Eventually, HULL melted, and HULL was accumulated in the center of the container to form a pool of molten Zircaloy 10. Further, the slag 11 was dispersed around the space inside the container.
Subsequently, HULL was further supplied from the hopper 6 into the container. In this way, the inside of the container was filled with the melted Zircaloy 10 and the molten slag 11. From the viewing window in the upper part of the crucible, it was observed that the molten Zircaloy 10 was held in non-contact with the protective wall 17. When the flow of the melt in the crucible was measured by a water-cooled Vive's sensor, as shown in FIG. 5, the zircaloy metal 10 in a vertical section passing through the central axis was measured.
Four circulating streams were observed in the.

Various filters were provided in the exhaust gas. Cs, Ca, F ₂ , MgF _2, etc. were recovered during the dissolution process.

After melting about 1 kg of HULL, the output of the high frequency power supply was lowered to naturally cool the melt. By inverting the container, the solidified body of Zircaloy and the slag could be easily taken out. Zr, Nb, M in the slag
Elements such as n, Sb, Te and C were mixed. In addition to the metal composition of HULL, Ru, Co
The element was mixed. Since the solidified body of metal did not contain a long-lived nuclide, it can be processed in the reactor site and reused as HULL.

Since the slag contained long-lived nuclides, it was vitrified and permanently disposed of.

The wear of the graphite protective wall 17 was observed at the stage where the HULL melting treatment as described above was repeated 10 times.
A part was broken and a place where the cooling crucible and the molten slag were in direct contact was also observed, but there was no hindrance to the melting of HULL. The average thickness of the protective wall was 1 mm.

On the other hand, when the protective wall 17 is not used, the molten zircaloy is inserted into the gap of the slit 15 of the cooling wall to cause an electrical short circuit and the heating efficiency is reduced by 20%, and a part of the cooling wall is melted due to the short circuit. Although it was damaged, no water leakage occurred.

In order to verify the safety, an experiment was conducted on the assumption that the cooling water circulation pump of the crucible was stopped. If the high frequency power supply was stopped at the same time when the cooling water was stopped, there was no damage to the cooling crucible. However, if no protective wall is used,
Molten zircaloy and slag were mixed in due to electromagnetic stirring, and when both were in direct contact with the cooling crucible, the cooling water boiled and was about to cause a serious accident. Thus, it was found that the protective wall has a remarkable effect on enhancing safety.

Since the protective wall becomes secondary waste, the volume was reduced by burning in the controlled area for volume reduction. Elements such as Cs, Zr, Nb, Mn, Sb, and Te were collected in the exhaust gas filter. As described above, the volume reduction of the secondary waste can be realized very easily by the method according to the present invention.

[Embodiment 2] As a second embodiment, HUL
3 and 6 are a schematic half-cut perspective view of a cooling crucible and a schematic view of a molten and fluidized state in the crucible in a device for continuously reducing the melting of L, respectively. The inner diameter of the cooling crucible is 45m
m, height 200 mm, and the material is copper. Further, the material of the interior protective wall is graphite and its thickness is 3 mm.
First, a ferrous base material was charged into the crucible, cooling water was supplied to the crucible, and then the crucible was sealed. The material of the base material is not limited to iron, and for example, zircaloy may be used.

After the inside of the cooling crucible 1 was replaced with Ar gas, a high frequency current of 2000 A at a frequency of 30 kHz was applied to the coil 2.
Shed to. At this time, the pull-out rod 5 was operated to set the upper end of the base material at the position where the electromagnetic field was most effective. About 2
Since the upper end of the base material was completely melted by the energization for a minute, from the supply section 6 provided on the upper lid 16 of the crucible, HUL was made at a rate of 25 g / min
L and slag were supplied to the cooling crucible 1, and the extraction bar 5 having the upper plate 5a was pulled downward at a speed corresponding to this supply amount. At that time, the drawing speed was adjusted so that the meniscus, that is, the height of the free surface 12 of the molten metal was substantially constant.

Upon continuous withdrawal, a solidified body of zircaloy and slag was eventually obtained from the lower end of the cooling crucible. Since dust similar to that in Example 1 mixed with Ar gas came out from the gas outlet 14, it was collected as appropriate.

After about 20 minutes of continuous operation from the start of the extraction of the solidified body (total charging amount of about 5000 g), the energization of the high frequency current was stopped. As described above, the present invention is not limited to batch processing, but can be applied to other processing forms such as continuous processing.

On the other hand, when the protective wall is not used, the molten zircaloy is inserted into the gap of the slit of the cooling wall to cause an electrical short circuit, the heating efficiency is reduced by 20%, and a part of the cooling wall is melted due to the short circuit. Although I did, no water leaks occurred.

In order to verify the safety, an experiment was conducted on the assumption that the cooling water circulation pump of the crucible was stopped. When the protective wall was not present, the molten zircaloy and the slag were mixed due to electromagnetic stirring, and when both were in direct contact with the cooling crucible, the cooling water boiled and was on the verge of causing a serious accident.

As described above, it was found that the protective wall has a remarkable effect in enhancing safety. In this case, since the melting target is only the metal, the above-mentioned third problem regarding simultaneous heating of the oxide did not occur.

[Example 3] The present invention was applied to the solidification treatment of the high-level waste liquid (HLLW) after extracting and separating (reprocessing) uranium and plutonium from spent nuclear fuel. The simulated waste consisting of the stable isotope of HLLW after calcination, which exists in the form of oxide, is hereinafter simply referred to as waste. FIG. 2 shows a schematic diagram of a melt flow state in a crucible for treating waste in batches.

The cooling crucible body 1 has an inner diameter of 45 mm and a height of 1
The length is 00 mm and the material is copper. The thickness of the crucible is 3
A protective wall of graphite material of mm is arranged. First, a mixture of 90 g of glass powder and about 10 g of waste was charged from the supply section 6 provided on the upper lid 16 of the crucible. Cooling water was passed through the crucible to close the upper lid.

Subsequently, Ar gas was flown from the gas supply port 13 to the discharge port 14 to maintain the inside of the crucible in an inert atmosphere. After that, the coil current was increased to 2000A.
The waste partially melted from the side close to the base material, and eventually spread to the entire waste. The operating temperature was maintained at 1300 ° C.

At the same time, when the fluid flow in the crucible was measured by a water-cooled Vive's sensor, as shown in FIG. 2, four circulating flows were observed in the central portion 9 in the vertical cross section passing through the central axis. Energization was stopped 50 minutes after the start of operation, and after cooling and solidification, a vitrified body was obtained.

On the other hand, when the protective wall was not present, the metal could be melted, but the oxide having low electric conductivity could not be melted.

In order to verify the safety, an experiment was conducted on the assumption that the cooling water circulation pump of the crucible was stopped. Without the protective wall, the molten oxide was in direct contact with the cooling crucible, and the cooling water boiled, which was on the verge of causing a serious accident.

As described above, it was found that the protective wall has a remarkable effect in enhancing safety. In this case, the object to be melted was a mixture of a metal and an oxide, and in the presence of an electromagnetic field, the oxide was in contact with the cooling crucible, so that the above-mentioned first problem of electrical short circuit did not occur.

[Fourth Embodiment] As a fourth embodiment, FIG.
Fig. 1 shows a schematic diagram of the melt flow state in the crucible for continuously solidifying the waste. The inner diameter of the cooling crucible is 45 mm,
The height is 200 mm and the material is copper. The material of the interior protective wall is graphite and its thickness is 3 mm.

First, a base material made of stainless steel was inserted into the crucible from below. After supplying cooling water to the crucible, the crucible was sealed.
After replacing the inside of the cooling crucible with Ar gas, a high frequency current of 2000 A was passed through the coil. By operating the pull-out rod, the upper lid of the base material was set at the position where the electromagnetic field was most effective.

Since the base material was completely melted in about 5 minutes of energization, 25 g / min from the supply section 6 provided on the upper lid 16 of the crucible.
The mixture of the waste and the glass powder was added to the cooling crucible at a rate of, and the extraction rod was pulled downward at a rate corresponding to this addition amount. At that time, the drawing speed was adjusted so that the meniscus, that is, the height of the interface between the molten liquid surface and the Ar gas gas was substantially constant. At this time, the mixing ratio of the waste and the glass powder was the same as in Example 3. Along with the drawing, the molten portion started solidification from below to form a solidification interface 12, and a vitrified body was obtained.

After continuous operation for about 20 minutes from the start of the extraction of the solidified body (total charging amount of about 500 g), energization of the high frequency current was stopped. When the liquid flow in the melting part in the crucible during the treatment was measured by a method similar to that of Example 1, a circulation flow similar to that of Example 2 was observed as shown in FIG.

As described above, the method according to the present invention enables vitrification not only in batch processing but also in continuous processing.

On the other hand, when the protective wall was not present, the metal could be dissolved, but the oxide having a low electric conductivity could not be dissolved.

In order to confirm the safety, an experiment was conducted on the assumption that the cooling water circulation pump of the crucible was stopped. Without the protective wall, the molten oxide was in direct contact with the cooling crucible, and the cooling water boiled, which was on the verge of causing a serious accident.

As described above, it was found that the protective wall has a remarkable effect in enhancing safety. In this case, the object to be melted was a mixture of a metal and an oxide, and the oxide was in contact with the cooling crucible in the presence of an electromagnetic field, so that the first problem relating to an electrical short circuit did not occur.

[Embodiment 5] A solidification treatment of waste was carried out in a manner substantially similar to that of Embodiment 4 except that a crucible made of a graphite material having slits was provided inside the cooling crucible. At this time, the pitch of the slits provided in the graphite was about 10 mm. Also,
The thickness of graphite was 3 mm.

First, a base material made of stainless steel was inserted into the crucible from below. After supplying cooling water to the crucible, the crucible was sealed.
After replacing the inside of the cooling crucible with Ar gas, a high frequency current of 1500 A was passed through the coil. By operating the pull-out rod, the upper end of the base material was set at the position where the electromagnetic field was most effective.

Since the base material was completely melted in about 5 minutes of energization, 25 g / min from the supply section 6 provided on the upper lid 16 of the crucible.
The mixture of the waste and the glass powder was added to the cooling crucible at a rate of, and the extraction rod was pulled downward at a rate corresponding to this addition amount. At this time, the drawing speed was adjusted so that the meniscus, that is, the height of the interface between the molten liquid surface and the Ar gas gas was substantially constant. At this time, the mixing ratio of the waste and the glass powder was the same as in Example 3.

Although the coil current value was smaller than that of Example 4, a vitrified body substantially similar to that of Example 4 was obtained. The reason for this is that since the graphite has slits, an induced current can flow on the inner surface of the graphite, and the efficiency of inductively heating the glass is improved.

After continuous operation for about 20 minutes from the start of the extraction of the solidified body (total charging amount of about 500 g), the energization of the high frequency current was stopped. After cooling, about 450 g of a solidified product could be recovered.

On the other hand, when the protective wall was not present, the metal could be dissolved, but the oxide having a low electric conductivity could not be dissolved.

In order to confirm the safety, an experiment was conducted on the assumption that the cooling water circulation pump of the crucible was stopped. Without the protective wall, the molten oxide was in direct contact with the cooling crucible, and the cooling water boiled, which was on the verge of causing a serious accident.

As described above, it was found that the protective wall has a remarkable effect in enhancing safety. In this case, the object to be melted was a mixture of a metal and an oxide, and the oxide was in contact with the cooling crucible in the presence of an electromagnetic field, so that the first problem relating to an electrical short circuit did not occur.

Example 6 About 1000 g of HULL was dissolved in substantially the same manner as in Example 2 except that the amount of slag added was the same as that of HULL. About 4
After 0 minutes of continuous operation, the supply of power, the supply of HULL and slag, and the extraction of the solidified product were stopped. After solidification by cooling
The solidified body covered with the slag was taken out. When the solidified body was divided by mechanical destruction, there was slag around and zircaloy inside. Zircaloy formed beads on the central axis in the first stage of the dissolution treatment, but rod-shaped zircaloys with a series of beads were obtained after the treatment.

As described above, it was found that even when a large amount of slag is contained, the solidified body after cooling can be phase-separated from the part containing a large amount of zircaloy and the slag.

On the other hand, when there is no protective wall, it is HULL.
Although it was possible to dissolve slag, it was not possible to dissolve slag with low electrical conductivity.

In order to confirm the safety, an experiment was conducted on the assumption that the cooling water circulation pump of the crucible was stopped. Without the protective wall, the molten oxide was in direct contact with the cooling crucible, and the cooling water boiled, which was on the verge of causing a serious accident.

As described above, it was found that the protective wall has a remarkable effect in enhancing safety. In this case, the object to be melted was a mixture of a metal and an oxide, and the oxide was in contact with the cooling crucible in the presence of an electromagnetic field, so that the first problem relating to an electrical short circuit did not occur.

Example 7 About 200 g of HULL was first dissolved by the same method as described in Example 2 except that the amount of slag added was the same as that of HULL. After that, the supply of electric power, the supply of HULL and slag, and the extraction of the solidified body were suddenly stopped. Within 5 seconds of stopping, the metal (density 6.55 g /
cm ³ ) settled, and conversely, the slag (density 4.0 g / cm ³ ) existing around the crucible floated up and covered the entire surface of the crucible. In this way, the specific gravity separation proceeded. After 5 minutes, the surface temperature of the slag fell to about 500 ° C.
After that, the value of the coil current was increased again to the conditions described in Example 2, and at the same time, the supply of HULL and slag and the extraction of the solidified body were restarted. The above operation was repeated 5 times to treat about 1000 g of HULL.

In the solidified body after cooling, phase separation in a form in which a portion containing a large amount of zircaloy and slag were alternately layered was recognized. In the process of phase separation, the beads of Zircaloy as found in Example 6 did not exist, and it was found that the method was superior to that of Example 6. Both could be easily separated by mechanical destruction.

[Embodiment 8] FIG. 8 shows a schematic view of an apparatus for continuously performing high-temperature volume reduction treatment on Zircaloy, which is a material of HULL (nuclear fuel cladding) in a PWR (pressurized water reactor). The composition of Zircaloy is Sn: 1.2-
1.7, Fe: 0.07 to 0.2, Cr: 0.05 to
0.15, Ni: 0.03 to 0.08, balance: Zr, melting temperature 1800 to 1850 ° C., density 6.55.
It is g / cm ³ . The inner diameter of the cooling crucible body 1 is 45 mm,
The height is 200 mm and the material is copper. In addition, a cylindrical protective wall having a bottom made of a graphite material and having a thickness of 3 mm is arranged in the crucible. The protective wall is arranged on the extraction rod. When the shearing force generated between the protective wall and the cooling crucible is larger than the self-weight of the protective wall itself, it is necessary to increase the bonding force between the protective wall and the pulling rod.

First, a base material made of iron was charged into the crucible, and cooling water was supplied to the crucible and then sealed. The material of the base material is not limited to iron, and may be any good electrical conductor,
For example, zircaloy may be used. By flowing Ar gas from the gas supply port 13 to the discharge port 14, the inside of the container and the hopper was maintained in an inert atmosphere. Then, the pulling rod was operated to set the upper end of the base material at the position where the electromagnetic field was most effective.

Under these conditions, a high frequency current having a frequency of 30 kHz was supplied up to 2000A. Ar during operation
Gas was supplied at 10 l / min. The iron base material and the protective wall became red hot and the temperature rose. After the energization for about 2 minutes, the upper end of the base material was completely melted, and the radiation thermometer indicated a value of 2100 ° C. Then, about 10 times from the processing material supply port 6 provided above the crucible.
Simulated radioactive waste (atomic number 24, 26-28, 34, 3
7-40, 42-52, 55-60, 62-64, and 75 elements in an amount of 1 wt. % Simulated HULL was added to the vessel along with the slag. In the following embodiments, this simulated HULL is simply called HULL. The amount of slag added is 5 wt. %, And the composition is CaF ₂ 7
5 wt. %, MgF ₂ 25 wt. %. HULL does not necessarily have to be cut, and the volume may be reduced as it is used in the nuclear reactor if an appropriate supply device is used.

The molten alloy of iron and zircaloy was collected in the center of the container. Moreover, the slag was distributed in a ring shape between the periphery of the molten alloy and the protective wall. HUL at a speed of 25g per minute
L and slag were supplied to the cooling crucible, and the extraction rod was pulled downward at a speed corresponding to this supply amount.

Thereafter, the drawing speed was adjusted so that the meniscus, that is, the height of the free surface of the molten metal was constant. In this way, the molten iron in the container was eventually pulled downward, and the molten portion was gradually replaced with zircaloy and molten slag. From the viewing window on the top of the crucible, it was observed that the molten zircaloy was held in non-contact with the protective wall.

When continuously withdrawn, a solidified body of zircaloy and slag covered with a protective wall from the lower end of the cooling crucible was eventually obtained. At this time, Ca, C, CaF ₂ , MgF _2, etc. were collected by various filters provided in the exhaust gas duct.

After continuous operation for about 20 minutes from the start of drawing out the solidified body (total charging amount of about 500 g), energization of the high frequency current was stopped and the solidified body was naturally cooled.

Zr, Nb, Mn, Sb and T are contained in the slag.
Elements such as e and C were mixed. In addition to the metal composition of HULL, Ru and Co elements were mixed in the metal. Since the solidified body of metal did not contain long-lived nuclides, it was processed in the reactor site and HULL
Can be reused as. In addition, since slag contained long-lived nuclides, it was vitrified and permanently disposed of.

In the treatment method according to the present invention, the protective wall was pulled downward together with the solidified body, so that the protective wall was not destroyed by the shearing force acting on the protective wall.

In order to verify the safety, an experiment was conducted on the assumption that the cooling water circulation pump of the crucible was stopped. If the high frequency power supply was stopped at the same time when the cooling water was stopped, there was no damage to the cooling crucible. However, if no protective wall is used,
Molten zircaloy and slag were mixed due to electromagnetic stirring, and when both were in direct contact with the cooling crucible, the cooling water boiled and was about to cause a serious accident. Thus, it was found that the protective wall has a remarkable effect on enhancing safety.

Since the protective wall becomes secondary waste, the volume was disposed of by incineration in the controlled area. C for exhaust gas filter
Elements such as s, Zr, Nb, Mn, Sb, and Te were recovered. As described above, the volume reduction of the secondary waste can be realized very easily by the method according to the present invention.

[Embodiment 9] In this embodiment, FIG. 9 shows a schematic view of an apparatus for continuously solidifying high-level simulated radioactive waste. The cooling crucible has an inner diameter of 45 mm, a height of 200 mm, and a material of copper. The material of the interior protective wall is graphite and its thickness is 3 mm.

First, a base material made of stainless steel was inserted into the crucible from below. After supplying cooling water to the crucible, the crucible was sealed.
After replacing the inside of the cooling crucible with Ar gas, a high frequency current of 2000 A was passed through the coil. By operating the pull-out rod, the upper end of the base material was set at the position where the electromagnetic field was most effective.

Since the base material was completely melted in about 5 minutes of energization, the mixture of waste and glass powder was added to the cooling crucible at a rate of 25 g / min from the supply section provided above the crucible, and The extraction rod was pulled downward at a speed corresponding to the amount added. The mixing ratio of glass powder and waste is 9: 1 by weight. At that time, the drawing speed was adjusted so that the meniscus, that is, the height of the interface between the molten liquid surface and the Ar gas gas was substantially constant. Along with the drawing, the molten portion started solidification from below to form a solidification interface 12, and a vitrified body was obtained.

After continuous operation for about 20 minutes from the start of the extraction of the solidified body (total charging amount of about 500 g), the application of high frequency current was stopped to obtain a solidified body of vitrified simulated radioactive waste.

[Embodiment 10] A solidification treatment of waste was carried out in a manner substantially similar to that of Embodiment 9 except that a crucible made of a graphite material having slits was provided inside the cooling crucible. At this time, the pitch of the slits provided in the graphite was about 10 mm. The thickness of graphite was 3 mm.

First, cooling water was supplied to a crucible in which a base material made of stainless steel was inserted from below into the crucible and then sealed. After replacing the inside of the cooling crucible with Ar gas, a high frequency current of 1500 A was passed through the coil. By operating the pull-out rod, the upper end of the base material was set at the position where the electromagnetic field was most effective.

Since the base material was completely melted in about 5 minutes of energization, a mixture of waste and glass powder was added to the cooling crucible at a rate of 25 g / min from the supply section above the crucible, and
The extraction rod was pulled downward at a speed corresponding to this addition amount. At this time, the drawing speed was adjusted so that the meniscus, that is, the height of the interface between the molten liquid surface and the Ar gas gas was substantially constant. At this time, the mixing ratio of the waste and the glass powder was the same as in Example 9.

Although the coil current value was smaller than that in Example 9, a vitrified body substantially similar to that in Example 9 was obtained. The reason for this is that since there is a slit in graphite, it is possible for an induced current to flow inside the graphite,
It can be mentioned that the efficiency of inductively heating the glass is improved.

After about 20 minutes of continuous operation from the start of the extraction of the solidified body (total charging amount of about 500 g), the application of high frequency current was stopped to obtain a solidified body of the vitrified simulated radioactive waste.

Example 11 The melting volume of zircaloy was reduced by the same method as in Example 8 except that the protective wall segment 17 'was provided with a feeder. The outline of the apparatus is shown in FIG.

The cooling crucible body 1 has an inner diameter of 45 mm, a height of 200 mm, and is made of copper. At the upper end of the cooling crucible, a supply device 6 for supplying a treatment material, an inlet 13 for an inert gas, an outlet 14 and a protective wall segment 17 'are attached.

Further, in the crucible, a cylindrical protective wall having a thickness of 3 mm and having a bottom made of a graphite material is arranged. The protective wall is arranged on the extraction rod. When the shearing force generated between the protective wall and the cooling crucible is larger than the weight of the protective wall itself, it is necessary to increase the bonding force between the protective wall and the pulling rod.

First, the iron base material was melted in the same manner as in Example 8, and then HULL was supplied. H at a speed of 25g per minute
The ULL and the slag are supplied to the cooling crucible 1, and the extraction rod 5 is drawn downward at a speed corresponding to this supply amount to pull down the solidified body of zircaloy, the solidified body of slag and the protection wall 17. It was

After the operation for about 20 minutes, the meniscus 12 of molten zircaloy reached the upper edge of the protective wall 17, so that the withdrawal was once stopped and the protective wall segment 17 'was removed by using the feeder for the protective wall segment 17'. It was placed on the upper edge of the protective wall inside the crucible. After doing this, the operation was restarted.

By repeatedly supplying the protective wall segment 17 'five times, the volume reduction treatment of 2000 g of Zircaloy could be continuously performed.

As described above, in Example 11, it was possible to dramatically increase the amount of zircaloy that can be continuously treated, as compared with Example 8.

[0125]

The following effects were observed in the dissolution, reduction and solidification of the material according to the present invention. 1) The safety of the process of melting and solidifying a material by using a cooling crucible can be improved. 2) Enables volume reduction and separation of secondary waste generated when applied to the volume reduction of radioactively contaminated metals. 3) It becomes possible to improve heating efficiency. 4) Phase separation of the melted / solidified body can be realized.

[Brief description of drawings]

FIG. 1 is a schematic half-cut perspective view of a batch-processing type cooling crucible embodying the present invention.

FIG. 2 is a schematic view showing a flow state of a molten material inside a batch-processing type cooling crucible for carrying out the present invention.

FIG. 3 is a schematic half-cut perspective view of a continuous process cooling crucible embodying the present invention.

FIG. 4 is a schematic diagram showing a flow state of a molten material inside a continuous processing type cooling crucible for carrying out the present invention.

FIG. 5 is a schematic view showing a flow state of a molten material inside a batch processing type cooling crucible for carrying out the present invention.

FIG. 6 is a schematic view showing a flow state of a molten material inside a continuous treatment type cooling crucible for carrying out the present invention.

FIG. 7 is a schematic half-cut perspective view of another continuous process cooling crucible embodying the present invention.

FIG. 8 is a schematic diagram of a nuclear fuel processing apparatus embodying the present invention.

FIG. 9 is a schematic diagram of a high-temperature volume reduction treatment apparatus for high-level radioactive waste embodying the present invention.

FIG. 10 is a schematic diagram of another nuclear fuel cladding high-temperature volume reducing apparatus embodying the present invention, which is equipped with a protective wall segment supply device.

[Explanation of symbols]

 1 Cooling Crucible 2 Energizing Coil 3 High Frequency Oscillator 4 Stopper 5 Extractor Rod 5a Extractor Rod Top Plate 6 Treatment Material Supply Port 7 Cooling Water Inlet 8 Cooling Water Outlet 9 Glass Containing Waste 10 Molten Metal 11 Slag 12 Solidification Interface 13 Not Active gas inlet 14 Inert gas outlet 15 Slit 16 Crucible top cover 17 Protective wall 17 'Protective wall segment 18 Bottom

Claims (5)

[Claims] 1. A current-carrying coil is arranged around a crucible made of a conductive cooling wall composed of an assembly of segments electrically insulated from each other by a slit, and a melting target inside the crucible is utilized by utilizing electromagnetic action. A melting and solidifying method in which a material is melted and subsequently solidified, wherein a protective wall of a conductive material is provided on an inner wall surface of the crucible. 2. An energizing coil is arranged around a crucible made of a conductive cooling wall composed of an assembly of segments electrically insulated from each other by a slit, and the melting target in the crucible is utilized by utilizing electromagnetic action. A crucible for melting and subsequently solidifying a material, wherein a protective wall made of a conductive material is provided on an inner wall surface of the crucible. 3. The protective wall according to claim 1, wherein the material to be melted is used in an exchangeable state for the inner wall of the crucible that is solidified after being melted. 4. The melting and solidifying method according to claim 1, wherein the material solidified by melting along the inner wall of the crucible is drawn out together with the protective wall in the drawing direction of the material solidified by melting. 5. The method of melting and solidifying according to claim 4, wherein a protective wall segment having a constant length is supplied to the upper edge of the protective wall in response to the withdrawal of the molten and solidified material.