JPS59188600A - Device for melting and decontaminating metal contaminated with radioactivity - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is directed to an apparatus for decontaminating metal waste by melting metal waste contaminated with radioactive substances in the presence of a slag agent and transferring and extracting the radioactive substances to the slag. In particular, the present invention relates to an apparatus for melting and decontaminating radioactively contaminated metals using a slag remelting method.

[Background of the invention]

The following two types of melting furnaces for molten metal decontamination are considered. One method is to place metal waste and slag agent in a heat-resistant crucible in advance and melt the entire product using an external heating source. The other method uses an electric furnace such as an electroslag remelting furnace that uses non-consumable electrodes to supply metal one by one, and uses the electrical resistance heat of the molten slag to melt it while separating only the molten metal and cooling it to solidify it. It is.

The former method uses a heat-resistant crucible, but it is subject to severe wear and tear due to heat, and the crucible must be destroyed in order to separate and recover the metal and slag that have cooled and solidified inside the crucible. Therefore, since these crucible waste materials are also treated as pollutants, the amount of secondary waste will further increase. In addition, the cost is high because the crucible must be replaced each time. The latter electroslag remelting furnace (li: Ielectro 8
1agRemel ting = ES FLs or less E
The method using SR (abbreviated as SR) eliminates the drawbacks of the former, allows the crucible to be used repeatedly, and has good reactivity between the molten slag and the metal, so it is advantageous in terms of economy and decontamination effect.

Conventionally, radioactively contaminated metals were melted using an ESR furnace as shown in Figure 1.

In FIG. 1, the water-cooled tonal crucible 2 has a solidified metal retention section formed of a cylindrical space in the center of its bottom, and a wide-diameter molten slag bath 5 is formed above this solidified metal reservoir. ing. Scrap pieces 8 obtained by shredding radioactively contaminated metal are fed into the molten slag bath 5 of such a water-cooled tempering crucible 2 from a scrap feeding device 9 . The molten slag itself becomes a heating source due to the Joule heat generated by the steady current applied between the heat-resistant conductive electrode rod 1 such as a carbon rod, the molten metal layer 6, the solidified metal layer 7, and the crucible bottom plate 3. . The scrap melted by this heat moves to the central molten metal layer 6, and during the melting process, contaminants move to the slag layer 5 and are extracted. However, in this method, the unmelted metal pieces stay at a position away from the electrode rod and are thrown into the wall of the water-cooled crucible, so the thermal efficiency related to metal melting is low. For example, in order to melt iron with a melting point of 1535C and maintain the slag temperature in the iron piece retention area at 1550C or higher, it is necessary to further increase the temperature in the vicinity of the electrode rod by 150 to 200C. For this reason, it has become clear that the power supply will increase.

[Purpose of the invention]

The purpose of the present invention is to provide non-consumable electrode type electroslag melting (
E8R) In the melting decontamination equipment for radioactively contaminated metal using a furnace, it is possible to improve the thermal efficiency, reduce the power supply, eliminate the remaining unmelted metal, and obtain the desired melting decontamination equipment. An object of the present invention is to provide a metal melting decontamination device.

[Summary of the invention]

The present inventors focused on the fact that the heat generating part in the slag in an ESR furnace is distributed according to the voltage gradient along the current line extending from the electrode rod to the molten metal layer below, and discovered that Unmelted metal (scrap pieces) is retained at the bottom of the furnace, and radioactively contaminated metal is melted in the region below the non-consumable electrode, where the heat generation part is the largest.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 2 is a longitudinal cross-sectional view showing an embodiment of the present invention. In FIG. 2, a water-cooled crucible 13 made of copper or the like is made of a cylindrical body, and the crucible 13 has a cold water inlet 13A and a cold water outlet 13B.
is provided to cool the inside of the crucible 13 with water. Further, a crucible 14 is provided concentrically with the crucible 13, and this crucible 14 is also provided with an inlet/outlet for cold water, although not particularly shown, so that water cooling is performed from inside. The upper end surface of the crucible 14 has a planar shape, and a receptacle 14A is formed on this surface where unmolten metal remains. An annular copper bottom plate 15 is provided in the annular space formed by the crucible 13 and the crucible 14, and the copper bottom plate 15 has a mechanism to be raised and lowered by a bottom plate extraction device 16. The non-consumable electrode 17 is located above the receiving part 14A, and is arranged so that its lower end is immersed in the molten slag 18, and a plurality of electrodes are arranged in a cylindrical shape at predetermined intervals. . In the figure, reference numeral 19 indicates a scrap input device for inputting scrap pieces of radioactively contaminated metal, and reference numeral 20 indicates a slag agent supply device.

In such an apparatus for melting and decontaminating radioactively contaminated metal, the position of the interface is controlled so that the solidified metal (ingot) 22 is sequentially pulled out so as to form molten slag in the upper part of the melting crucible 13.

The unmelted metal (scrap pieces) 23 is melted by the heat generated by the slag, and during the melting process, the radioactive material is transferred to the slag layer.
After only the decontaminated metal flows into the molten slag layer 18, it solidifies in the cooling crucible.

Here, the thermal efficiency, etc. of the conventional system shown in FIG. 1 and the present embodiment shown in FIG. 2 will be compared.

Of the heat actually generated in the slag layer, the heat Q3 retained in the slag layer as a heat source for metal melting is the residual heat obtained by subtracting the amount dissipated to the gas phase, crucible, ingot, and electrode from the total calorific value, and the ratio is 30 ~35%. The utilization efficiency η of using this heat for metal melting is approximately 0.25 in the peripheral injection method as in the conventional method (FIG. 1), and approximately 0.3 in the method according to this embodiment. Finally, the thermal efficiency used for metal melting with respect to the total calorific value is the product of η·Qs, which is 7 to 8% in the conventional method and 9 to 10% in this embodiment.

Next, the actual calorific value will be compared. The required power supply is determined primarily by the total amount of slag. The thickness of the electrode rod must be selected to match the diameter or cross-sectional area of the crucible, and is expressed in fill ratio (electrode rod diameter/crucible inner diameter ratio).
It is normal to take 0.3 or more. In the case of the conventional example, the electrode rod 1 was arranged as shown in Fig. 3, and the inner diameter of the crucible was 20 cm.
If the diameter of the electrode rod is 7z, the space in the gap of the scrap input section will be 6 crn. On the other hand, according to this embodiment, as shown in FIG. 4, the diameter of the scrap inlet is 6 mm, and the outer diameter is 9 mm if the cylindrical electrode rod has the same cross-sectional area as the conventional example.
．． The inner diameter of the crucible should be 15 cm in height. If the inner diameter of the crucible is reduced from 20(7) to 15 crn, the amount of slag can be reduced to about half, and the amount of power supplied will also be reduced. -Furthermore, by introducing the scrap pieces into the central area of the crucible where the amount of heat generated is large, there is no need to excessively raise the temperature of the slag. For example, when melting copper, the temperature near the electrode rod must be 1750 t:' or higher in the conventional example, but it may be about 1700 r in this embodiment. As a result, the calorific value required to raise the molten silicic acid-calcia (Show 20aO) slag by 500% is 2.5 kal/m
OL can be saved. This corresponds to a heat saving of approximately 5%.

FIG. 5 shows another embodiment of the present invention, which differs from the embodiment shown in FIG. 2 in the arrangement of the non-consumable electrode scrap charging device and the slag agent charging device.

That is, one non-consumable electrode 24 is arranged on the central axis of the crucible as in FIG. A supply port 26A is provided. Therefore, in FIG. 5, other components are designated by the same reference numerals as in FIG. 2.

(9) Even in such a decontamination device for radioactively contaminated metal, scrap pieces of radioactively contaminated metal remain on the receiving part 14A and are efficiently dissolved, so that the same effect as in the embodiment shown in FIG. 2 can be obtained. There is.

FIG. 6 is a partial vertical sectional view showing another embodiment of the present invention, in which one non-consumable electrode 24 is arranged on the central axis of the crucible, and a cylindrical member 2γ is placed concentrically with this non-consumable electrode 24. A scrap input device 25 is provided in this cylindrical member 27.
Radioactively contaminated scrap pieces are input from the slag agent supply device 26, and slag agent is supplied from the slag agent supply device 26.

In this embodiment, the other components are substantially the same as the embodiment shown in FIG.

FIG. 7 is a partial longitudinal sectional view showing another embodiment of the present invention, in which the upper part 28 of the crucible has a smaller inner diameter than the central part, and the outer diameter of the holder is approximately the same as the outer diameter of the part 14A. It has become. One non-consumable electrode 24 is arranged on the central axis of the crucible, and scrap pieces and slag agent are introduced into the internal space of the upper part 28 of the crucible. In this example, the scrap pieces accumulate on the 14A surface of the receiving part (10), so they are efficiently melted, and the upper opening of the crucible is small so that heat dissipation can be reduced, so the thermal efficiency is high. Become.

In the embodiment shown in FIG. 2, a plurality of non-consumable electrodes are arranged in a cylindrical shape, but they may be arranged in a rectangular tube shape. Further, the single non-consumable electrode may be a cylinder or a rectangular cylinder.

〔Effect of the invention〕

As described above, according to the present invention, the dissolution rate of metal contaminated with radioactive substances in slag can be increased, and decontamination treatment can be performed efficiently.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of a conventional melting decontamination device for radioactively contaminated metal, Fig. 2 is a longitudinal sectional view showing an embodiment of the melting decontamination device of the present invention, and Figs. 3 and 4 are respectively FIG. 5 is a cross-sectional view showing the position of the slag layer when the electrode rod is inserted in the conventional example and the embodiment shown in FIG. 2; FIGS. 6 and 7 are partial vertical sectional views showing embodiments of the pond of the present invention, respectively. (11) 1.17.24...Non-consumable electrode (rod), 2,13゜14...Water-cooled copper crucible, a, 15...Copper bottom plate, 4
゜16... Bottom plate pulling device, 5.18... Molten slag, 6゜21... Molten metal, 7.22... Solidified metal,
8.23...Radioactive contaminated scrap piece, 9,19.2
5... Scrap input device, 10.20.26...
Slag agent supply device, 11... Electric power supply, 12...
・Cooling water inlet/outlet, 14A...Reception part. Agent Patent Attorney Tatsuyuki Unuma (12) No. 3 (3rd Ward, 4th Ward)

Claims (1)

[Claims] 1. Melting and removal of radioactively contaminated metals, which is equipped with a melting furnace that melts metals contaminated with radioactive substances by heat generated by a section that loads the molten slag and extracts the contaminants into the slag. In the dyeing apparatus, an unmolten metal retention area is provided at the center of the bottom of the melting furnace and is formed higher than the furnace bottom at the periphery thereof, and a non-consumable electrode is provided above the unmolten metal retention area. 1. An apparatus for melting and decontaminating radioactively contaminated metal, characterized in that a supply device is provided for introducing radioactively contaminated metal onto the surface of the unmolten metal retention part from above the slag. 2. Claim 1, wherein the non-consumable electrode is formed in a cylindrical body, and the radioactively contaminated metal supply port of the supply device is located above the internal space of the cylindrical body. Melting and decontamination equipment for radioactively contaminated metals. 3. In claim 1, the non-consumable electrode is arranged in a cylindrical shape with a plurality of electrodes spaced apart, and a radioactively contaminated metal supply port of the supply device is provided above the inner space of the cylindrical part. An apparatus for melting and decontaminating radioactively contaminated metals, characterized in that: 4. In claim 1, the non-consumable electrode is a single electrode located above the central part of the unmolten metal retention section, and the supply device is located above the slag in the vicinity of this electrode. 1. A melting and decontamination device for radioactively contaminated metal, characterized in that a radioactively contaminated metal supply port is provided. 5. The apparatus for melting and decontaminating radioactively contaminated metal according to claim 2, characterized in that the cylindrical body is a cylindrical body. 6. The apparatus for melting and decontaminating radioactively contaminated metal according to claim 3, wherein the tubular shape is cylindrical.