JPH0664188B2 - Radionuclide electrodeposition removal device - Google Patents

Description

Detailed Description of the Invention

 Purpose of the invention

[Industrial applications]

The present invention provides a liquid containing a radionuclide in an ionic form,
The present invention relates to improvement of a device for removing this radionuclide by electrodeposition.

[Prior art]

Waste liquids containing various radionuclides are generated in nuclear power plants and research facilities that use radioisotopes. As a typical method for removing radionuclides from this waste liquid, adsorption treatment with an ion exchange resin is performed.
When the radionuclide in the waste liquid is a heavy metal ion such as ⁵⁴ Mn or ⁶⁰ Co, a chelate ion exchange resin (hereinafter,
Adsorption by "chelate resin" is effective. Since the chelate resin having adsorbed the radionuclide removes 99% or more of the adsorbed radionuclide with an eluent such as H ₂ SO ₄ or HC, the chelate resin after regeneration can be advantageously reused. This eluent enriched with radionuclide needs to be reduced in volume and finally solidified. In the treatment of radionuclide-containing liquids typified by the eluents described above, as a means for achieving the highest volume reduction, the applicants have electrolyzed the radionuclide together with the heavy metal by electrolysis in the presence of non-radioactive heavy metal ions. We have invented a method of depositing and removing it and have already proposed it (Japanese Patent Application No. 59-85860). The eluent of the chelate resin contains radioactive nuclides such as ⁵⁴ Mn, ⁶⁰ Co, ⁶⁵ Zn, and ¹¹⁰ mAg, so Cu, Ni, Co, Mn,
Non-radioactive heavy metal ions such as Zn, preferably 100 mg
When the electrolysis is carried out by adding an amount necessary to obtain a concentration of / or higher, the radionuclide is electrodeposited along with the electrodeposition of the heavy metal. One typical embodiment is the presence of Ni ions as heavy metal ions, electrolysis is carried out at a pH of the liquid of 3 to 7, and a current density of 0.7 A / dm.
It is carried out under ^two or more conditions (Japanese Patent Application No. 60-162669).
issue). Another is that when Cu ions exist as heavy metal ions from the beginning, Ni ions are allowed to exist and electrolysis is performed first.
It is carried out under the condition that Cu ions are electrodeposited and then Ni ions are electrodeposited (Japanese Patent Application No. 60-162670). Electrodeposition of Cu ions is carried out at pH 4 or less and current density of 0.3 A / dm ² or less, and electrodeposition of Ni ions is carried out at pH 3 to 7 and current density of 0.7 A / dm ² or more. These methods pose particular problems in terms of dose
Electrodeposition of ⁶⁰ Co is performed well. Regardless of which method is adopted, when performing the electrodeposition removal of the radionuclide, the electrodeposition on the cathode surface must be performed uniformly, and the formation of hydroxide and the peeling of the electrodeposit should be prevented. I have to. Therefore, an electrodeposition removing device satisfying such conditions is required. It is needless to say that the structure of the apparatus is desired to be as simple as possible and easy to manufacture and operate, since the electrodeposited material is concentrated with radioactive substances.

[Problems to be Solved by the Invention]

SUMMARY OF THE INVENTION An object of the present invention is to meet the above demand for an apparatus for electrodeposition removing radionuclides, and to provide an apparatus having a simple structure in which electrodeposition of radionuclides is uniformly and favorably performed. Structure of the invention

[Means for Solving the Problems]

The radionuclide electrodeposition removing apparatus of the present invention is an apparatus for electrolyzing a liquid containing a radionuclide in the presence of a non-radioactive heavy metal to remove the radionuclide by electrodeposition together with the heavy metal,
As shown in FIG. 1, two anode plates 2 are provided in an electrolytic cell 1 so as to face each other, and a plurality of anode plates 2 (6 in the illustrated example are provided between them).
Are arranged in parallel to the anodes, and the surfaces of the cathode plates 31, 36 at both ends of this cathode array facing the anodes are insulated. It is considered that the larger the number of cathodes, the larger the cathode area and the better the electrodeposit can be obtained. If there is a significant difference and the electrodeposition is not good, and therefore it is rather disadvantageous, and if the cathode surface facing the anode is not insulated, the electrodeposit will adhere preferentially only to this surface. However, the present inventors have found that the electrodeposited state is also unfavorable. Normally, 4 or more and 6 or less are suitable. If the distance between the electrode plates is reduced so as to reduce the distance between both ends of the cathode array, it becomes difficult for the current to pass through and the flow of the electrolytic solution is hindered. A range of 10 to 40 mm, usually about 15 to 25 mm is suitable.
The same applies to the distance between the anode and the cathode. Platinum-plated titanium plate is suitable for the material of the anode, and stainless steel plate is suitable for the material of the cathode. In order to insulate the surface of the cathode facing the anode, for example, as shown in the figure, the surfaces of the cathode plates 31 and 36 are electrically non-conductive and electrolytic through a suitable packing 4 for complete insulation. An insulating plate 5 made of a material that withstands the liquid, such as polyvinyl chloride, acrylic resin, polyethylene, or rubber, may be fixed using a suitable clamp 6 or the like, and the surface may be covered.
Of course, other means such as painting can be used. Regarding the overall configuration of the electrodeposition removing device, the example shown in FIG. 2 is the unit of FIG. 1, that is, four cathode plates arranged in parallel with the anode are grouped into one electrolytic cell. It is arranged.

[Action]

When electrolysis is performed under the above electrode configuration, the surfaces of the cathodes at both ends facing the anodes are insulated, so that all the current flowing from the anodes reaches the cathodes by wrapping around the cathodes at both ends. As a result, there is no great difference in the length of the flow path of the electrolytic current to each cathode, and there is no great difference in the amount of electrodeposition to each cathode. The same is true between the parts on the individual cathodes. In this way, by performing a substantially uniform electrodeposition,
The electrodeposit is dense and grows in close contact with the electrodes. At the same time, radionuclides such as ⁶⁰ Co and ⁵⁴ Mn are also electrodeposited.

Example 1 The experimental apparatus shown in FIG. 3 was assembled by using the electrolytic cell having the structure shown in FIG. 1 and having the number of cathodes changed. The anode is of Pt-Ti plating type, and the cathode is composed of 6 SUS304 stainless steels. In FIG. 3, 7 is a tank for a liquid to be electrolyzed, and 8 is a chemical tank. V is the power supply,
P is a pump and pHIC is a pH indicator and controller. A solution containing Na ₂ CO ₄ 3 wt% Ni 2 ⁺ 50ppm ⁶⁰ Co 5 × 10 ⁻⁴ μCi / m as a simulated waste liquid is supplied from the tank to the electrolytic cell and circulated so as to return to the tank due to overflow. Electrolyzing while letting. Ni was electrodeposited at a current density of about 0.5 A / dm ² until the Ni ²⁺ concentration decreased to about 2 ppm. The amount of electrodeposition on the six cathodes is shown as a ratio in FIG. 4 with 1 being the maximum. Almost uniform electrodeposition was obtained, and the deposition state was also good. ⁶⁰
The electrodeposition of Co also showed the same level of uniformity as that of Ni.

Comparative Example 1 Electrolysis was performed without insulating the cathodes at both ends shown in FIG. The amount of electrodeposition of each cathode was as shown in FIG. 5, and it concentrated on the cathodes at both ends, and the cathodes in the central part decreased and became non-uniform. Further, on the cathode surface facing the anode where a large amount of electrodeposition occurred, formation of hydroxide and partial peeling of the electrodeposit occurred.

Example 2 Example 1 was repeated, changing the number of cathodes to 4 or 7. In the case of four sheets, generally good results close to Example 1 were obtained. In the case of 7 sheets, the amount of electrodeposition of the cathode in the central portion tended to be low.

Example 3 For a simulated solution having the following composition, Na ₂ SO ₄ 3 wt% boric acid 0.1 wt% Cu ²⁺ , Ni ²⁺ 50-60 ppm ⁶⁰ Co 5.4 × 10 ⁻⁴ μCi / m ⁵⁴ Mn 6.1 × 10 ⁻⁴ μCi / m The following two-step electrodeposition was performed. (Cu electrodeposition) Under conditions of pH 4 and current density of 0.1 A / dm ² , until the residual amount of Cu ions is 1 ppm or less. (Ni electrodeposition) The current density was increased to 0.5 A / dm ² with the pH kept at 4. Concentrations of heavy metal ions and radionuclides (unit: μCi / m
) Changes are as follows. The percentage in parentheses indicates the residual rate. After Cu electrodeposition Ni After electrodeposition Cu ²⁺ 0.4ppm − (0.8%) − Ni ²⁺ 61ppm 1.9ppm (100%) (3.0%) ⁶⁰ Co 5.4 × 10 ⁻⁷ 9.1 × 10 ⁻⁷ (98%) (0.12% ) ⁵⁴ Mn 5.9 × 10 ^-4 3.2 × 10 ^-5 (97%) (5.2%) From these results, it can be seen that ⁶⁰ Co was almost completely removed and most of ⁵⁴ Mn was also electrodeposited. EFFECTS OF THE INVENTION By using the device of the present invention, the electrodeposition removal of the radionuclide in the radioactive liquid waste can be carried out in a favorable electrodeposition deposition state. Since the electrodeposit is closely packed and adheres well to the cathode, it can be processed without the risk of peeling off during handling. This electrodeposition removing device has a simple structure and is easy to manufacture and use, and can be easily designed to have an appropriate scale according to the amount of waste liquid to be treated.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a typical example of the structure of the electrodes of the electrodeposition removing apparatus of the present invention. FIG. 2 is a plan view showing an example of the configuration of the electrodeposition removing apparatus of the present invention. FIG. 3 is a conceptual diagram showing the configuration of the experimental apparatus of the embodiment of the present invention. FIGS. 4 and 5 are for explaining the effect of the present invention. FIG. 4 is an example and FIG. 5 is a comparative example, and the relative value of the electrodeposition deposition amount on each cathode is shown. It is a bar graph showing. 1 ... Electrolytic tank, 2 ... Anode plate 3 (31, 32, ... 36) ... Cathode plate 4 ... Packing, 5 ... Insulating plate 6 ... Clamp 7 ... Electrolyte liquid tank, 8 ... … Chemical solution tank V… Power supply, P… Pump pHIC… pH indication and control device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 999999999 Hokuriku Electric Power Co., Inc. 3-1, Sakurabashi, Toyama City, Toyama Prefecture (71) Applicant 999999999 Japan Nuclear Power Co., Ltd. 1-16-1 Otemachi, Chiyoda-ku, Tokyo ( 71) Applicant 999999999 JGC Co., Ltd. 2-2-1 Otemachi, Chiyoda-ku, Tokyo (71) Applicant 999999999 Unitika Co., Ltd. 1-50 Higashihonmachi, Amagasaki-shi, Hyogo (72) Inventor Ichiro Inomata Uchiyuki-cho, Chiyoda-ku, Tokyo 1-3 chome Tokyu Denryoku Co., Ltd. (72) Inventor Tadashi Ishibe 1 Higashishinmachi, Higashi-ku, Nagoya, Aichi Prefecture Chubu Denki Co., Ltd. (72) Masaaki Matsunaga 3-1-1 Sakurabashi-dori, Toyama, Toyama Hokuriku Electric Power Co., Inc. (72) Inventor Ryoichi Onuki 1-6-1, Otemachi, Chiyoda-ku, Tokyo Nihon Nuclear Power Co., Ltd. In-house (72) Inventor Kazunori Suzuki 2205 Narita-cho, Oarai-cho, Higashi-Ibaraki-gun, Ibaraki JGC Stock Company Inside Oarai Nuclear Technology Development Center (72) Inventor Minoru 2205 Narita-cho, Oarai-cho, Higashi-Ibaraki-gun, Ibaraki Company Oarai Nuclear Technology Development Center (72) Inventor Shozo Tomoshige 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Central Corporation Research Institute (72) Inventor Kozo Kondo 23 Uji Kozakura, Uji City Kyoto Prefecture Unitika Stock Company Central Research In-house (56) References JP 61-253394 (JP, A) JP 62-274098 (JP, A)

Claims (4)

[Claims] 1. An apparatus for electrolyzing a liquid containing a radionuclide in the presence of a non-radioactive heavy metal to electrodeposit and remove the radionuclide together with the heavy metal, and two anode plates are provided opposite each other in an electrolytic cell. An electrodeposition removing apparatus, characterized in that a plurality of cathode plates are arranged in parallel with the anodes between them, and the surfaces of the cathode rows opposite to the anodes are insulated. 2. The electrodeposition removing apparatus according to claim 1, wherein the number of cathodes is selected from the range of 4 to 6. 3. A plurality of cathode plates arranged in parallel with the anode as a unit, and multiple units are installed in the electrolytic cell.
Or the electrodeposition removing device of 2. 4. The electrodeposition removing apparatus according to claim 1, wherein a platinum-plated titanium plate is used as an anode and a stainless steel plate is used as a cathode.