JPS6020720B2 - Decontamination method for metal materials contaminated with radioactivity - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for removing beams from iron-based metal materials contaminated with radioactivity, and particularly relates to a method for removing beams from metal materials contaminated with radioactivity, which can reduce the amount of radioactive metal material waste. .

Nuclear power plants generate large amounts of radioactively contaminated ferrous metal waste when replacing equipment and piping.

These are cut into appropriate sizes and stored in drums. In the future, as the number of nuclear power plants increases and the number of years of operation increases, such waste will tend to increase, and therefore, it is desired to develop a method to reduce it. A typical method is the beam removal method, which involves electrolytic polishing in a concentrated acid solution.

In this method, most radioactive metal waste is contaminated only on the surface, and since the contamination is mainly attached as metal oxides, electrolytic polishing is used to remove the metal from the surface layer of the mother village. This method involves dissolving a portion of the oxide, peeling the remainder off the surface, and disposing of it as non-radioactive metal waste. This method is an excellent method in terms of removing radioactive debris, but since the surface layer of the contaminated home village dissolves in the electrolyte, the electrolyte is consumed and radiation is emitted into the electrolyte. Noh's metal ions are coming down. Therefore, it is necessary to renew the electrolytic solution one after another, and the problem is that the amount of waste liquid increases. The present invention has been made in view of the current situation, and its purpose is to provide a method for removing beams from radioactively contaminated iron-based metal materials that can reduce the amount of radioactive liquid waste.

Z To summarize the present invention, the method for beam removal of radioactively contaminated metal materials (first invention) of the present invention is to remove radioactively contaminated iron-based metal materials in an aqueous alkali metal chloride solution. The method of removing beams of a metal material contaminated with radioactivity according to the present invention is characterized in that radioactive contaminants on the surface Z of the metal material are separated and removed by melting a part of the metal material through anode electrolysis. The method (second invention) involves anodic electrolysis of a radioactively contaminated iron-based metal material in an aqueous alkali metal chloride solution to dissolve a part of the metal base, thereby removing the surface of the metal material. It is characterized by separating and removing radioactive contaminants, then removing sludge from the aqueous solution, and removing heavy metal ions from the aqueous solution using an adsorbent that selectively adsorbs heavy metal ions. . 2 In the conventional electrolytic polishing method, concentrated phosphoric acid or sulfuric acid, etc. are used, so Co
Since not only the surface oxide layer containing the large amount of radioactive material consisting of Co-60 but also the base material is dissolved at the same time, the electrolyte is consumed and radioactive materials such as Co-60 accumulate in the electrolyte.
It's coming. Since it is difficult to remove the metal ions dissolved in such a strong acid and regenerate the acid, the electrolytic waste liquid must be treated as radioactive liquid waste. In the present invention, in order to solve the above problems, 3. an aqueous solution of an alkali metal chloride such as sodium chloride made neutral or weakly alkaline (usually at a concentration of about 3% by weight or more);
Inside, contaminated iron-based metal materials are subjected to anode electrolysis.

In this way, when electrolyzing the material to be treated as an anode in a solution containing neutral or slightly alkaline chlorine 4 ions, the oxide on the surface does not dissolve, and the iron-based metal base of the oxide becomes [1}M→Mn++ne
By dissolving by m, the surface oxide falls off.

On the other hand, at the cathode, which is the opposite pole, the following formula ■Misaki 20 books Ichiu 2
Hydroxyl ions are generated by the reaction of 10 H- [21], and the hydroxide ions combine with the metal ions generated at the anode to form a metal oxide and precipitate.

Therefore, substantially no metal ions are dissolved in the electrolyte, and there is no consumption of the electrolyte. Therefore, the metal material after anode electrolysis is washed with water, and the sludge consisting of the oxide of the contaminant and the metal hydroxide based on the metal material is removed using known means such as a filter or a centrifuge. The liquid can be recycled and used repeatedly. For this purpose, the electrolyte needs to be neutral or slightly alkaline, but alkali metal chlorides were specifically chosen because the electrolyte contains corrosive ions such as chlorine ions. This is because it is necessary.

When the corrosivity is weak, such as an aqueous solution of sulfate or nitrate, the base material does not dissolve, as shown in equation '1) above, and oxygen is only generated from the surface of the material to be treated. On the other hand, the metal hydroxides precipitated in the electrolytic solution also have solubility, albeit slightly.

However, cobalt ions, which only exist in small amounts, are difficult to precipitate, and are therefore the main cause of radioactive contamination. Co-60 accumulates little by little in alkalinity. Therefore, it is necessary to remove this by some method. For this purpose, it is possible to use an ion exchange resin, but this would also remove the sodium chloride in the electrolyte, making it impossible to regenerate the electrolyte, and requiring a large amount of ion exchange resin. shall be. For this reason, in the present invention, heavy metal ions can be removed using an adsorbent that selectively adsorbs heavy metal ions, and the resulting solution can be reused by feeding it into an electrolytic cell.

As such an adsorbent, activated carbon impregnated with about 10% oxine is specifically suitable. Oxine has the following molecular structure, and although it does not adsorb alkali metal ions such as sodium ions, it adsorbs heavy metal ions by releasing hydrogen ions.

According to the present invention, with the above-described structure and operation, an iron-based metal material contaminated in a neutral or weakly alkaline alkali metal chloride aqueous solution is anodically electrolyzed, and the ferrous metal material generated in the electrolyte is After separating and removing the sludge, the heavy metal ions are further adsorbed and removed using an adsorbent that selectively adsorbs heavy metal ions, such as activated carbon impregnated with oxine, and this liquid is returned to the electrolytic cell and reused as required. By using this method, it is possible to obtain a decontamination effect equivalent to that of the conventional electrolytic polishing method, and to significantly reduce the amount of radioactive waste generated by beam removal. Incidentally, a calculation example comparing the method of the present invention and the conventional method in terms of the amount of radioactive waste is shown in Table 1 below.

As is clear from Table 1, according to the present invention, the amount of radioactive waste can be significantly reduced.

Next, the regeneration of the electrolyte in the present invention can be carried out in a batch manner, that is, a method in which the electrolyte is regenerated each time a certain amount of the material to be treated is electrolyzed, or alternatively, while electrolyzing, a part of the electrolyte can be regenerated. It is also possible to withdraw the liquid and continuously regenerate and circulate the liquid.

The drawing shows a continuous circulation type float sheet showing a specific example of the present invention, in which 1 is an electrolytic cell, 2 is a material to be treated, 3 is a counter electrode, 4 is an electrolytic solution, 5 is a DC power source, 6 is a pump, and 7 8 is a filtration machine, 8 is a slang, 9 is a pump, and 10 is an adsorption tower. Referring to the drawings, an electrolytic cell 1 is filled with an electrolytic solution 4 such as an aqueous sodium chloride solution, a material to be treated 2 and a counter electrode 3 are immersed, and a current is applied by a DC power source 5 using the material to be treated 2 as an anode.
A part of the electrolytic solution 4 is continuously drawn out by a pump 6, and a slang 8 is separated by a furnace 7. Pump 9 to pump the furnace liquid.
The liquid is sent to an adsorption tower 10 filled with an adsorbent such as oxine-impregnated activated carbon, where heavy metal ions are adsorbed and removed, and then returned to the electrolytic cell 1 for reuse. Next, the present invention will be explained with reference to Examples, but the present invention is not limited to these in any way.

Example 1 Test pieces of 2 other x 2 enemies were taken from a carbon steel enemy back in a nuclear power plant, and the test pieces were anode-coated in sodium chloride solutions of various concentrations and IJ acid solution of 80% concentration for comparison. Electrolysis was performed.

Table 2 below shows the results of measuring the radioactivity of the test piece, slange, and furnace liquid under various conditions and electrolysis, and after washing with water. As is clear from Table 2, radioactive contaminants can be sufficiently removed not only by phosphoric acid but also by sodium chloride.

However, if the concentration of sodium chloride is as low as 0.5% by weight, the base material will not be melted uniformly and sufficient removal will not be possible. On the other hand, in the case of a sodium chloride solution, most of the radioactivity in the electrolyte is in the slang, and only a small amount remains in the electrolyte after the slang is separated and removed. However, in the case of a phosphoric acid solution, a considerable amount of radioactive material is dissolved in the electrolyte. Therefore, in order to regenerate the electrolytic solution after removing the metal material, in the case of a sodium chloride solution, the slang is separated and the radioactive nuclides slightly dissolved in the solution are removed by the adsorption treatment. However, in the case of a phosphoric acid solution, a large amount of radioactive material is dissolved, so it is virtually impossible to regenerate the solution. Furnace solution 5 of the electrolyte solution with a sodium chloride concentration of 10% by weight obtained in this way
Activated carbon impregnated with 10% oxine (24~
46 mesh) was passed through an adsorption column filled with 20'.

The amount of radioactivity in the solution after passing through was hardly measured. Further, the NaCI concentration in the liquid after passing was 10% by weight, with no change observed. Therefore, it is clear that this solution can be satisfactorily used as an electrolyte. When anode electrolysis was repeated using this solution as an electrolyte, substantially the same results were obtained. Example 2 Co-60 of 1 Ci as cobalt chloride was added to a sodium chloride solution with a concentration of 1% by weight and, for comparison, a phosphoric acid solution with a concentration of 8% by weight.
0% impregnated activated carbon (24-46 mesh) 20 [
was passed through an adsorption cylinder filled with

The amount of radioactivity in the solution after passing was 2 x 10-3 French Ci in the case of sodium chloride solution, but 0.95 μm Ci in the case of phosphoric acid solution, which could not be completely removed. . In addition, the NaCI concentration in the solution after passing through the adsorption cylinder remained unchanged at 10% by weight, and this solution was sufficiently usable as an electrolyte.When anode electrolysis was repeated using this solution as an electrolyte, approximately the same The results were obtained. In this way, heavy metal ions can be easily removed using activated carbon impregnated with oxine from neutral or weakly alkaline liquids such as sodium chloride solution, but heavy metal ions cannot be removed from highly concentrated acidic liquids such as phosphoric acid. It is difficult to remove. In particular, since the amount of heavy metal ions dissolved in a neutral or weakly alkaline liquid is extremely small, only a small amount of oxine-impregnated activated carbon is consumed. As explained above, according to the present invention, it is possible to obtain the same contamination effect on iron-based metal materials as the conventional electrolytic polishing method using a concentrated acid solution, and at the same time reduce the amount of radioactive waste generated during decontamination. It is possible to significantly reduce the amount.

[Brief explanation of drawings]

The drawing shows a continuous circulation type float sheet showing a specific example of the present invention. 1... Electrolytic cell, 2... Material to be treated, 3.
...opposite, 4. ... Electrolyte, 5...
・DC power supply, 6, 9...Pump, 8...
・Slange, 10... Adsorption tower.

Claims (1)

[Scope of Claims] 1 Radioactive contaminants on the surface of a radioactively contaminated iron-based metal material are removed by dissolving a part of the metal base by anodic electrolysis in an aqueous alkali metal chloride solution. A decontamination method for metal materials contaminated with radioactivity, characterized by separating and removing. 2 Radioactive contaminants on the surface of the metal material are separated and removed by dissolving a part of the metal base material by anode electrolysis of the iron-based metal material contaminated with radioactivity in an aqueous alkali metal chloride solution. , then removing the slang from the aqueous solution,
A method for decontaminating metal materials contaminated with radioactivity, characterized in that heavy metal ions in the aqueous solution are removed using an adsorbent that selectively adsorbs heavy metal ions. 3. The method for decontaminating metal materials contaminated with radioactivity according to claim 2, wherein the adsorbent is activated carbon impregnated with oxine.