JP3045933B2 - Apparatus and method for decontaminating radioactive metal waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for decontaminating radioactive metal waste for reducing metal waste such as pipes and plate materials generated during operation, periodic inspection and decommissioning of nuclear facilities. About.

[0002]

2. Description of the Related Art Methods for thoroughly decontaminating radioactive metal waste generated during the operation, periodic inspection and decommissioning of nuclear facilities are disclosed in JP-A-62-46297 and JP-A-60-186799. As described above, electrodischarge dyeing (contact type) using an acidic and neutral salt solution has been developed and put into practical use in Japan and overseas.

[0003] Electrolytic dyeing is effective for metal waste having a relatively simple shape such as a plate or a cylinder, and a metal waste is used as an anode, and a cathode is installed facing the surface to be decontaminated. Apply a DC voltage between the waste and the cathode to polish the base material of the decontamination surface,
It removes radioactivity from metal waste.

[0004]

However, the above-described electrodischarge dyeing has the following problems. Since the connection portion between the metal waste and the anode does not dissolve, contamination remains, and it is necessary to perform recontamination by regripping and the decontamination work is complicated. When decontaminating a large device, the current value increases in proportion to the surface area, so the connection between the device and the anode requires an anode jig in consideration of the contact area. Therefore, it is necessary to frequently exchange the anode jig according to the shape of the device. When processing a large amount of equipment, it is necessary to replace the electrode and replace the anode jig, so that the worker's exposure increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and does not require the re-gripping of electrodes and the attachment / detachment work of electrodes before and after decontamination. Provided is a radioactive metal waste decontamination apparatus and a decontamination method capable of reducing the level.

[0006] The method for decontaminating metal wastes using a non-contact electrolytic reaction of the present invention, JP-open flat 5-297192, JP-Open Rights
6-242295 and No. has been filed as Japanese Open flat No. 7-218694,
The present invention seeks to further improve the functions and performance of the prior application method.

[0007]

SUMMARY OF THE INVENTION The present invention utilizes a bipolar phenomenon in an electrolytic solution to electrolyze radioactively contaminated metal waste in a non-contact manner to dissolve the base material of the metal waste. In the apparatus for removing radioactivity, a cylindrical metal waste is installed in a cylindrical anode, a rod-shaped cathode is installed in the cylindrical metal waste, and the cylindrical anode and the rod-shaped cathode are connected to a DC power supply. It is characterized by applying a DC voltage from a DC power supply connected between the cylindrical anode and the rod-shaped cathode, the cylindrical metal waste outer surface to the negative electrode, the inner surface to the positive electrode to charge the inner surface Wherein the metal base material is dissolved.

[0008] An apparatus for removing radioactivity by dissolving a base material of the metal waste by non-contact electrolysis of a metal waste contaminated with a radioactive material by utilizing a bipolar phenomenon in an electrolyte,
A cylindrical anode is installed on the inner wall of the cylindrical insulating shield, a cylindrical cathode is installed on the outer wall of the cylindrical insulating shield, and a cylindrical metal waste is installed in the cylindrical anode. The cylindrical cathode is connected to a DC power supply, and an insulating disk having openings above and below the cylindrical insulating shield is provided.

Further, a DC voltage is applied from a DC power supply connected between the cylindrical anode and the cylindrical cathode to charge the outer surface of the cylindrical metal waste to the negative electrode and the inner surface to the positive electrode to charge the inner surface to the inner surface. When the metal base material is dissolved and the cylindrical metal waste is contaminated on both the inner and outer surfaces, the polarity of the DC power source is reversed to convert the anode to a cathode, and convert the cathode to an anode to convert the cylindrical metal waste into a cylindrical metal. Dissolving the outer surface of the waste.

The dissolution of the metal base material on the inner surface of the cylindrical metal waste and the reduction and destruction of the oxide film formed on the inner surface of the cylindrical metal waste are repeated by alternately reversing the polarity of the DC power supply. And

An apparatus for removing radioactivity by dissolving a base material of the metal waste by non-contact electrolysis of a metal waste contaminated with a radioactive substance by utilizing a bipolar phenomenon in an electrolyte,
An insulating shielding container having an opening at the top is installed in the electrolytic cell, a cathode is provided at the bottom of the electrolytic cell, an anode is provided at the bottom of the insulating shielding container, and the metal waste is provided with an opening at the top. The supporting container has a side surface made of an insulating material, a bottom portion of the supporting container made of metal, and a side surface of the supporting container having a mesh-like shape for flowing an electrolytic solution. Characterized by being installed in an insulating shielding container having an opening at the top.

Further, a DC voltage is applied between the anode and the cathode to charge the metal material at the bottom of the support container facing the anode to the negative electrode and the upper surface of the metal waste held by the support container to the positive electrode. And melting the metal base material.

[0013]

According to the present invention, in a device and a decontamination method for decontaminating metal waste by non-contact electrolysis of metal waste, the decontamination performance and shape adaptability of metal waste are further improved. Can be planned.

That is, according to the present invention, a cylindrical metal waste such as a pipe is installed in a cylindrical anode, a rod-shaped cathode is inserted into the cylindrical metal waste, and a direct current connected between the anode and the cathode is inserted. A DC voltage is applied from a power supply to charge the inner surface of the cylindrical metal waste to a positive electrode to dissolve the metal base material on the inner surface. Therefore, there is no need to connect the anode and the metal waste unlike the conventional contact-type electro-discharge dyeing, so that the radiation exposure of the workers involved in the connection work is reduced.

A cylindrical anode is installed on the inner wall of the cylindrical insulating shield, a cylindrical cathode is installed on the outer wall of the cylindrical insulating shield, and a cylindrical metal waste is installed in the cylindrical anode. A DC voltage is applied from a DC power supply connected between the anode and the cathode to charge the inner surface of the cylindrical metal waste to the positive electrode and dissolve the metal base material on the inner surface.

Further, by disposing an insulating disc having openings above and below the cylindrical insulating shield, electrolysis between the anode and the cathode is suppressed, and the metal base material of the cylindrical metal waste is efficiently produced. Can be dissolved.

Accordingly, the decontamination surface of the inner surface of the cylinder is efficiently charged to the positive electrode and dissolved without the necessity of inserting the cathode into the cylindrical metal waste as in the conventional contact-type electro-discharge dyeing. The radioactive oxide film adhering to the inner surface of the waste, or the radioactivity penetrating the base material is removed as the metal base material dissolves.

When the inner and outer surfaces of the cylindrical metal waste are also contaminated, the outer surface can be charged to the positive electrode by reversing the polarity of the DC power supply, so that the metal base material can be easily dissolved. In addition, radioactivity can be removed from metal waste.

For cylindrical metal waste such as carbon steel, which has a thick oxide film, adheres firmly, and is difficult to remove radioactivity, the polarity of the DC voltage is alternately reversed to obtain the metal base. By repeating dissolution of the material and reduction / destruction of the oxide film on the surface of the metal base material, radioactivity can be removed with a small amount of dissolution, and the amount of secondary waste generated due to decontamination can be reduced. .

Further, in the case of decontaminating curved plate-shaped metal waste or a cut piece after cutting the metal waste, a tool, or other foreign matter, an insulating shielding container having an opening at an upper portion in an electrolytic cell. Is installed, a cathode is provided at the bottom of the electrolytic cell, an anode is provided at the bottom of the insulating shielding container, and a curved plate-shaped metal waste or miscellaneous material is placed in a supporting container having an opening at the top, and the supporting container is provided. Is made of an insulating material, and the bottom of the supporting container is made of an insoluble metal.

Further, the side surface of the supporting container is provided in an insulating shielding container having a large number of mesh-like holes for flowing an electrolytic solution and having an opening at an upper portion, and a DC voltage is applied between the anode and the cathode. To charge the insoluble metal at the bottom of the support container facing the anode to the negative electrode, and charge the upper surface (contaminated surface) of the curved plate-like metal waste or miscellaneous material placed in the support container to the positive electrode. To dissolve the metal matrix. By configuring the bottom of the support container with an insoluble metal, it is possible to uniformly dissolve the contaminated surface of the curved plate-shaped metal waste or miscellaneous material.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of an apparatus for decontaminating radioactive metal waste according to the present invention will be described with reference to FIGS.
FIG. 1 is a vertical sectional view of an electrolytic cell showing an example of an apparatus for explaining the first embodiment. In the figure, reference numeral 1 denotes an electrolytic cell, and the electrolytic cell 1 is filled with an electrolytic solution 2. ing. Electrolyte solution 2
A cylindrical anode 3, a cylindrical metal 4 of radioactive metal waste to be decontaminated in the cylindrical anode 3, and a rod-shaped cathode 5 installed in the cylindrical metal 4.

The cylindrical metal 4 is fixed on a gantry 6, and the cylindrical anode 3 and the bar-shaped cathode 5 are connected to a DC power source 7, respectively. A handling mechanism 8 for taking the cylindrical metal 4 in and out of the electrolytic cell 1 is provided above the electrolytic cell 1.

Next, the positional relationship among the cylindrical anode 3, the cylindrical metal 4, and the bar-shaped cathode 5 will be described in detail with reference to FIGS. 2 (a) and 2 (b). 2A is a plan view of the device, and FIG. 2B is a longitudinal sectional view of FIG. At the center of the cylindrical anode 3 is a cylindrical metal 4
However, a bar-shaped cathode 5 is installed at the center of the cylindrical metal 4, and a DC power supply 7 is connected to the cylindrical anode 3 and the bar-shaped cathode 5, respectively.

In this state, the DC power source 7 supplies the cylindrical anode 3
When a DC voltage having a predetermined current density is applied between the cylindrical cathode 3 and the rod-shaped cathode 5, the reaction shown in FIG. 3 occurs on the surface of the cylindrical anode 3 and the inner and outer surfaces of the rod-shaped cathode 5 and the cylindrical metal 4. These reactions are as shown below. (Cylindrical anode) H ₂ O → 2H ⁺ + 1 / 2O ₂ ↑ + 2e ⁻ (1) (Bar-shaped cathode) H ⁺ + 2e ⁻ 2H ₂ ↑ (2) (Cylindrical metal outer ^{surface) H + + 2e - → H} 2 ↑ ........................ (3) ( a cylindrical metal inner ^{surface) M → M n + + ne} - ........................ (4)

Since the outer surface of the cylindrical metal 4 faces the cylindrical anode 3, it is charged to the negative electrode by dielectric action, and the inner surface of the cylindrical metal 4 is polarized and charged to the positive electrode because it faces the rod-shaped cathode 5. Then, the metal base material on the inner surface dissolves.

As a result, the radioactivity fixed on the inner surface of the cylindrical metal 4 or penetrating into the base material is removed from the cylindrical metal 4 by dissolving the base material and transferred to the electrolytic solution 2, and is transferred to the electrolytic solution 2. Radioactivity can be removed or the radioactivity level can be reduced.

A second embodiment of the apparatus for decontaminating radioactive metal waste according to the present invention will be described with reference to FIGS. FIG. 4 is a vertical sectional view of an electrolytic cell showing an example of an apparatus for explaining the second embodiment. In the drawing, reference numeral 1 denotes an electrolytic cell, and the electrolytic cell 1 is filled with an electrolytic solution 2. .

A cylindrical electrode jig 9 and a cylindrical metal 4 to be decontaminated are set in the electrolytic solution 2, and the cylindrical metal 4 is fixed on a gantry 6. The cylindrical electrode jig 9 is connected to the DC power supply 7. A handling mechanism 8 for taking the cylindrical metal 4 in and out of the electrolytic cell 1 is provided above the electrolytic cell 1.

Next, details of the cylindrical electrode jig 9 are shown in FIG.
This will be described with reference to (a) and (b). (A) is a plan view and (b) is a longitudinal sectional view. The cylindrical electrode jig 9 has a cylindrical anode 3 on the inner wall of a cylindrical insulating shield 10 and a cylindrical cathode 11 on the outer wall of the cylindrical insulating shield 10. The DC power supply 7 is connected to the cylindrical anode 3 and the cylindrical cathode 11, respectively.

In this state, the DC power source 7 supplies the cylindrical anode 3
When a DC voltage having a predetermined current density is applied between the cylindrical anode 3 and the cylindrical cathode 11, the reaction shown in FIG. 6 occurs on the surface of the cylindrical anode 3, the surface of the cylindrical cathode 11, and the inner and outer surfaces of the cylindrical metal 4. These reactions are as shown in equations (1) to (4). Here, the rod-shaped cathode shown in the expression (2) is replaced with a cylindrical cathode.

Since the outer surface of the cylindrical metal 4 faces the cylindrical anode 3, the negative electrode is charged by the dielectric action, and the inner surface of the cylindrical metal 4 is polarized and charged to the positive electrode, and the metal base material on the inner surface is melted. .

As a result, the radioactivity fixed on the inner surface of the cylindrical metal 4 or penetrating into the base metal is removed from the cylindrical metal 4 by dissolving the base metal and transferred to the electrolytic solution 2, and is transferred to the electrolytic solution 2. Radioactivity can be removed or the radioactivity level can be reduced.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 7 shows the result of melting the inner surface of the stainless steel cylindrical metal 4 by the conventional contact electrolysis (interpolated cathode) and the result of melting by the interpolated cathode of the first embodiment of the present invention. The result of dissolution by the cylindrical cathode 11 of Example 2 is shown as a dissolution rate ratio (experimental value / theoretical value). The theoretical value is a value that can be obtained by Faraday's law.

In the third embodiment, phosphoric acid was selected as the electrolyte, the concentration of the phosphoric acid was 40%, the temperature of the electrolyte was 60 ° C., and a direct current voltage was applied between the anode and the cathode, which were coated with platinum on titanium. Electrolysis was performed at a density of 0.6 / cm ² .

As can be seen from the figure, although the dissolution rate is lower than that of the conventional contact electrolysis, even the electrolysis method of the present invention can dissolve the inner surface of the cylindrical metal, so that the radioactivity of the metal waste is removed or the radioactivity level is lowered. Can be done.

As described above, since the inner surface can be melted without connecting the anode to the cylindrical metal as shown in the first embodiment of the present invention, the workability of decontamination is improved, and Exposure can be reduced. Further, as shown in the second embodiment, since the inner surface can be melted without inserting the cathode into the cylindrical metal, the metal can be easily taken in and out of the electrolytic cell 1, and an apparatus using a handling mechanism or the like can be used. This makes it easier to automate the operation, and further reduces the exposure of workers.

Next, a fourth embodiment according to the present invention will be described with reference to FIG. FIG. 8 shows the result of melting the inner and outer surfaces of the cylindrical metal 4 made of stainless steel by reversing the polarity of the DC power supply in the second embodiment, showing the dissolution rate ratio (experimental value / theoretical value). In the embodiment, the phosphoric acid concentration is 40% and the electrolyte temperature is
At 60 ° C., a DC voltage was applied between the anode and the cathode in which titanium was coated with platinum, and electrolysis was performed at a current density of 0.6 A / cm ² .

As can be seen from this embodiment, by reversing the polarity of the DC power supply, the inner and outer surfaces of the cylindrical metal can be melted at almost the same melting rate. As described above, since the inner and outer surfaces of the cylindrical metal can be melted only by reversing the polarity of the DC power supply, the radioactivity of the cylindrical metal can be removed or the radioactivity level can be reduced.

Next, a fifth embodiment according to the present invention will be described. When the cylindrical metal 4 is carbon steel, an oxide film, rust and the like are thickly and firmly formed on the surface of the base material, and this oxide film is difficult to be removed simply by anodic electrolysis. Since most of the radioactivity is contained in the oxide film, it took a long time to remove the radioactivity from the cylindrical metal 4.

In order to remove the radioactivity from the carbon steel cylindrical metal 4 in a short time, it is effective to alternately reverse the polarity of the DC power supply 7 described above. By charging the inner surface (contaminated surface) of the cylindrical metal 4 made of carbon steel to the negative electrode, the following reaction occurs, and the oxide film, rust, etc. on the surface are reduced and destroyed. (Negative electrode charged surface) Reduction and destruction of oxide film, rust, etc. Fe ₃ O ₄ + 8H ⁺ + 2e → 3Fe ²⁺ + 4H ₂ O (5) Fe ₂ O ₃ + 6H ⁺ + 2e → 2Fe ²⁺ + 3H ₂ O… (6)

As described above, the oxide film or rust on the contaminated surface of the cylindrical metal 4 is reduced and destroyed, and the radioactivity in the oxide film is removed. Further, since the polarity of the DC power source 7 is alternately reversed, the contaminated surface is also charged to the positive electrode, and after the oxide film is removed, the exposed metal base material is dissolved, and the contamination permeating the metal base material is also removed. .

Therefore, the radioactivity adhered or penetrated into the base material together with the oxide film of the cylindrical metal 4 is removed from the cylindrical metal 4 with a small amount of dissolution by reducing and destroying the oxide film and dissolving the base material. Then, the solution is transferred to the electrolyte solution 2 to remove the radioactivity of the cylindrical metal 4 or to lower the radioactivity level, and to reduce the amount of secondary waste generated due to the decontamination.

Next, a sixth embodiment of the radioactive metal waste decontamination apparatus of the present invention will be described with reference to FIGS. 9 (a) and 9 (b). FIG. 9A is a plan view showing a state in which an insulating disk 12 having openings above and below a cylindrical insulating shield 10 is attached, and FIG. 9B is a longitudinal sectional view. Cylindrical insulating shield 10
The cylindrical anode 3 is attached to the inner wall of the cylinder, the cylindrical cathode 11 is attached to the outer wall of the cylindrical insulating shield 10, and the cylindrical metal 4 is installed in the cylindrical anode 3. Are connected to a DC power supply 7, respectively.

In this state, when a voltage having a predetermined current density is applied between the cylindrical anode 3 and the cylindrical cathode 11 from the DC power supply 7 by the same operation as in the second embodiment, the above-mentioned (1) to (5) are applied.
The reaction shown in the equation (4) occurs, the inner surface of the cylindrical metal 4 is charged to the positive electrode, and the metal base material on the inner surface is dissolved.

Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG. 10 shows a case where the cylindrical insulating shield 10 shown in the second embodiment is used, and an insulating disk having openings above and below the cylindrical insulating shield 10 of the fifth embodiment. The result of melting the inner surface of the stainless steel cylindrical metal 4 when 12 was attached was shown as a dissolution rate ratio (experimental value / theoretical value).

In the sixth embodiment, phosphoric acid was selected as the electrolytic solution 2, a phosphoric acid concentration of 40%, an electrolytic solution temperature of 60 ° C., and a direct current between the cylindrical anode 3 and the cylindrical cathode 11 coated with platinum on titanium. Electrolysis was performed at a current density of 0.6 A / cm ² by applying a voltage.

As can be seen from the figure, the cylindrical insulating shield 10
When the insulating disk 12 is attached above and below
Doubled. This is because, by attaching the insulating disks 12 above and below the cylindrical insulating shield 10, the current leaking to the anode 3 and the cathode 11 is shielded, and electrolysis between the electrodes is suppressed.

When the insulating disks 12 are attached above and below the cylindrical insulating shield 10 as described above, the melting speed of the metal is improved, and the radioactivity of the cylindrical metal 4 is removed in a short time or the radioactivity level is reduced. Can be reduced.

Next, a seventh embodiment according to the present invention will be described with reference to FIG. FIG. 11 shows a vertical cross-sectional view of the electrolytic cell 1 in the present embodiment. Reference numeral 13 denotes a supporting container having an opening at the top, and the supporting container 13 is provided by a handling mechanism 8 installed on the upper part of the electrolytic cell 1. 1 is suspended inside.

The side surface of the supporting container 13 is made of an insulating material having a large number of mesh-like holes for flowing the electrolytic solution, and the bottom portion is made of a metal material 18. Is stored.

The supporting container 13 is installed in an insulating shielding container 15 having an opening at the top, and a plate-like anode 16 is provided on the bottom of the shielding container 15 with the bottom of the shielding container 15 interposed therebetween. A plate-like cathode 17 is provided at the bottom.

When a DC voltage is applied between the plate anode 16 and the plate cathode 17 in this state, a potential difference is generated with the insulating shielding container 15 interposed therebetween.
The surface of the metal material 18 provided at the bottom of the is charged to the negative electrode. On the other hand, since the metal 14 is in contact with the metal material 18 at the bottom of the support container 13, the metal 14 is polarized, and the upper surface of the metal 14 is charged to the positive electrode to dissolve the base material of the metal 14.

Next, an eighth embodiment of the present invention will be described with reference to FIG. FIG. 12A shows a support container 13 according to the seventh embodiment.
And FIG. 12 (b) shows a case where the bottom is made of an inert metal obtained by applying a platinum coating to titanium (Example 2). FIG. 3 shows the dissolution rate distribution of the plate-shaped stainless steel in the case of the configuration (Example 1) in terms of a dissolution rate ratio (dissolution rate at each position / average dissolution rate).

In the eighth embodiment, phosphoric acid was selected as the acidic electrolyte, the concentration of the phosphoric acid was 40%, the temperature of the electrolyte was room temperature, and a direct current voltage was applied between the anode and the cathode of which platinum was coated on titanium. Electrolysis was performed at a current density of 0.6 A / cm ² .

As can be seen from FIG. 12 (b), when the bottom of the supporting container is made of a metal material, the surface of the stainless steel can be substantially uniformly dissolved. However, as shown in FIG. When it is made of an insulating material having the above holes, the end portions are not easily dissolved.

This is because when dissolving a metal by a non-contact electrolytic reaction, a potential higher than the equilibrium potential of the metal dissolution reaction must be applied to the metal surface, but due to the effect of current leaking between the anode and the cathode, Since the potential is high at the center of the metal surface and low at the end, it is difficult to dissolve.

As described above, the bottom of the support container 13 is made of a metal material.
If it is composed of 18, the metal surface can be uniformly dissolved, so that curved plate-shaped metal waste, scraps after cutting the metal waste, and miscellaneous materials such as tools can be uniformly decontaminated. The radioactivity of the metal waste can be removed or the radioactivity level can be reduced.

Further, by using an insulating support container having an opening at the top, the amount of metal waste decontamination treatment per batch can be increased, and the insulating support container has a drive mechanism. Since it can be easily taken in and out of the electrolytic cell when used, automation in the case of mass processing is facilitated.

In the embodiments described so far, phosphoric acid was used as the electrolytic solution. However, similar results were obtained by using sulfuric acid, nitric acid, sodium sulfate, sodium nitrate and the like.

In the decontamination method and apparatus of the present invention, when the structural material of the electrolytic cell is metal, electrolysis occurs on the wall surface of the electrolytic cell due to the dielectric action, so that the surface of the metal waste is efficiently charged to the positive electrode or the negative electrode. Can not do.

Accordingly, the structural material of the electrolytic cell, the insulating shield for cylindrical metal waste, the insulating disk, and the insulating shielding container for plate metal waste, such as fluororesin or FRP, are resistant. Either a single insulating material having excellent chemical properties and heat resistance or a metal lined with an insulating material is used.

The opening of the insulating disc only needs to have a hole through which the cylindrical metal passes, but the upper disc is easy to remove, so that the lower disc is fixed. The upper disk may be arbitrarily attached with a different opening diameter according to the outer diameter of the cylindrical metal.

The material of the electrode is, in addition to the titanium-coated platinum electrode used in the examples, a copper-lined titanium-lined platinum-coated electrode, a platinum-only electrode, and a metal other than titanium. Electrodes with a platinum coating, lead oxide electrodes and the like can also be used.

Further, the supporting container for storing metal waste is
It is preferable that the side surface of the supporting container be lined with an insulating material having excellent chemical resistance and heat resistance, such as a fluororesin or FRP.

[0066]

According to the method for removing radioactivity by dissolving a metal base material in a dielectric action by electrolyzing metal waste in an electrolytic solution in a non-contact manner, the decontamination performance and shape adaptability of the metal waste are improved. According to the present invention, the following effects can be obtained.

(1) A cylindrical metal waste can be inserted into a cylindrical anode, and a rod-shaped cathode can be inserted into the cylindrical metal waste to charge the inner surface to a positive electrode and dissolve the metal base material. The radioactivity can be removed or the radioactivity level can be reduced, and the connection work between the anode and the metal waste is unnecessary, so that the radiation exposure of the workers involved in the connection work is reduced.

(2) By installing a cylindrical anode on the inner wall of the cylindrical insulating shield and a cylindrical cathode on the outer wall, the inner surface can be inserted into the cylindrical metal waste without inserting the cathode. Can be charged to the positive electrode to dissolve the metal base material, so that the radioactivity of the metal waste can be removed or the radioactivity level can be reduced. The workability of installing the objects becomes easy, and the radiation exposure of the workers involved in the decontamination work can be reduced.

(3) By disposing the insulating disks above and below the cylindrical insulating shield, the current leaking between the anode and the cathode is shielded, and the metal base material on the inner surface of the cylindrical metal waste is dissolved. Since the speed is increased, the radioactivity of the metal waste can be removed or the radioactivity level can be reduced in a short time.

(4) When the inner and outer surfaces of the cylindrical metal waste are contaminated, the polarity of the DC power source can be reversed to melt the inner and outer surfaces of the cylindrical metal waste. No electrode jig dedicated to the outer surface is required like dyeing. Therefore, there is no need to replace and grip the electrodes, and it is possible to reduce the amount of radiation exposure of workers involved in the decontamination work.

(5) For a cylindrical metal waste, such as carbon steel, which has a thick oxide film, adheres firmly, and has difficulty in removing radioactivity, a reduction treatment is performed by alternately reversing the polarity of the DC voltage. In addition, the reduction and destruction of the oxide film and the dissolution of the metal base material occur due to the oxidation treatment, so that radioactivity can be removed with a small amount of dissolved metal base material, and secondary waste associated with decontamination is generated. The amount can be reduced.

(6) For metal wastes in the form of a plate, scraps obtained by cutting metal wastes, and miscellaneous materials such as tools, the side surface is made of an insulating material and the bottom is made of a metal material. Since the metal surface can be uniformly dissolved by carrying out decontamination by storing it in a supporting container having a part, the radioactivity of the metal waste is removed or the radioactivity is removed without leaving radioactivity locally. The level can be reduced.

(7) Since the decontamination apparatus using a handling mechanism or the like can be easily automated, a large amount of metal waste can be quickly decontaminated.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a decontamination apparatus for explaining a first embodiment of a decontamination apparatus and a decontamination method for radioactive metal waste according to the present invention.

2A is a cross-sectional view schematically showing a main part in the electrolytic cell in FIG. 1, and FIG. 2B is a schematic vertical cross-sectional view of FIG.

FIG. 3 is a schematic diagram for explaining an electrolytic reaction in FIG. 2 (b).

FIG. 4 is a configuration diagram schematically showing a decontamination apparatus for explaining a second embodiment according to the present invention.

5A is a cross-sectional view schematically showing the inside of the electrolytic cell in FIG. 4, and FIG. 5B is a schematic vertical cross-sectional view of FIG.

FIG. 6 is a schematic diagram for explaining an electrolytic reaction in FIG. 5 (b).

FIG. 7 is a bar chart showing a comparison between the dissolution rate ratios of the first and third embodiments according to the present invention and a conventional example.

FIG. 8 is a bar chart showing a comparison of the dissolution rate ratio between an inner surface and an outer surface in a fourth embodiment according to the present invention.

9A is a schematic cross-sectional view for explaining a fifth embodiment according to the present invention in detail, and FIG. 9B is a schematic vertical cross-sectional view of FIG.

FIG. 10 is a bar chart showing a comparison of dissolution rate ratios with and without a disc in a sixth embodiment according to the present invention.

FIG. 11 is a configuration diagram schematically showing a decontamination apparatus for explaining a seventh embodiment of the present invention.

FIG. 12A shows Example 1 in an eighth embodiment of the present invention.
(B) is the same as in Example 2. FIG.
FIG. 3 is a dissolution distribution characteristic diagram for explaining the following.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electrolysis tank, 2 ... Electrolyte solution, 3 ... Cylindrical anode, 4 ... Cylindrical metal, 5 ... Bar-shaped cathode, 6 ... Stand, 7 ... DC power supply, 8 ... Handling mechanism, 9 ... Cylindrical electrode jig, 10 ... cylindrical insulating shield, 11 ... cylindrical cathode, 12 ... insulating disk, 13 ... support container, 14 ... plate metal, 15 ... shielding container, 16 ... plate anode, 17
... plate cathode, 18 ... metal material.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-249600 (JP, A) JP-A-5-297192 (JP, A) JP-A-6-242295 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G21F 9/28

Claims (9)

(57) [Claims] 1. An electrolytic cell, a cylindrical anode disposed in an electrolytic solution in the electrolytic cell, a cylindrical metal waste disposed in the cylindrical anode, and a cylindrical metal waste disposed in the cylindrical metal waste. An apparatus for decontaminating radioactive metal waste, comprising: a rod-shaped cathode; and a DC power supply connected to the cylindrical anode and the rod-shaped cathode. 2. The method according to claim 1, wherein the cylindrical anode provided in the electrolytic solution and the rod-shaped cathode provided in the cylindrical anode are arranged in a circle.
A cylindrical metal waste is placed between a cylindrical anode and the rod-shaped cathode, and a DC voltage is applied from a DC power supply connected between the cylindrical anode and the rod-shaped cathode to form an outer surface of the cylindrical metal waste. A method for decontaminating radioactive metal waste, comprising: charging a negative electrode and an inner surface to a positive electrode to dissolve an inner base material of the metal waste. 3. An electrolytic cell, a cylindrical insulating shield provided in an electrolytic solution in the electrolytic cell, a cylindrical anode provided on an inner wall of the cylindrical insulating shield, and the cylindrical insulating member. A cylindrical cathode installed on the outer wall of the shield, a cylindrical metal waste installed in the cylindrical anode, and a DC power supply connecting the cylindrical anode and the cylindrical cathode are provided. Decontamination equipment for radioactive metal waste. 4. The apparatus for decontaminating radioactive metal waste according to claim 3, wherein an insulating disk having openings at both upper and lower ends of the cylindrical insulating shield is provided. To 5. A cylindrical anode and cylindrical cathode provided on the inner and outer walls of the cylindrical insulating shield body provided in the electrolytic solution, a cylindrical metal waste placed in the cylindrical inner anode A DC power supply is connected between the cylindrical anode and the cylindrical cathode, and a DC voltage is applied from the DC power supply to charge the outer surface of the cylindrical metal waste to a negative electrode and the inner surface to a positive electrode to charge the metal. A method for decontaminating radioactive metal waste, comprising dissolving an inner base material of the waste. 6. When the cylindrical metal waste is contaminated both inside and outside, the cathode of the DC power supply is reversed to convert the anode into a cathode and the cathode into an anode to convert the cylindrical metal waste into a cathode. 6. The method for decontaminating radioactive metal waste according to claim 2, wherein the outer surface of the radioactive metal is dissolved. 7. A method in which the melting of the metal base material on the inner surface of the cylindrical metal waste and the reduction and destruction of the oxide film formed on the inner surface of the cylindrical metal waste are repeated by alternately reversing the polarity of the DC power supply. The method for decontaminating radioactive metal waste according to claim 2 or 5, characterized in that: 8. An electrolytic cell, an insulative shielding container having an opening at the top provided in the electrolytic cell, a cathode disposed at the bottom of the electrolytic cell, and an anode disposed at the bottom of the insulative shielding container. And a supporting container having an opening at an upper portion for holding metal waste disposed in the insulating shielding container,
The side surface of the supporting container is made of an insulating material and the bottom portion is made of a metal material, and the side surface of the supporting container has a large number of mesh-like holes for the flow of an electrolyte. Decontamination equipment. 9. A DC voltage is applied between the anode and the cathode to charge a metal material at the bottom of the support container facing the anode to a negative electrode and charge the upper surface of the metal waste held by the support container to a positive electrode. 9. The apparatus for decontaminating radioactive metal waste according to claim 8, wherein an electric circuit is configured to perform the operation.