JP5936121B2 - Radioactive material decontamination method - Google Patents

Description

The present invention relates to a decontamination method of radioactive materials containing radioactive cesium and / or radioactive strontium.

  The Fukushima Daiichi nuclear power plant accident occurred due to the Great East Japan Earthquake on March 11, 2011, and the diffusion and contamination of radioactive materials accompanying these accidents have caused serious situations. In the long term, the radioactive material in question is radioactive cesium and / or radioactive strontium. Radioactive materials that are diffused and contaminated over a wide area need to be decontaminated and returned to a normal environment. For this reason, an effective decontamination agent is also needed with the radioactive substance decontamination method.

  As a conventional decontaminating agent, what is confirmed in the examples of Patent Document 1 is to use a composition of nitric acid, phosphoric acid, silica gel, and a surfactant, and to decontaminate by drying and solidifying. Yes. Patent Document 2 proposes a base, a polyethoxylated aliphatic alcohol, a copolymer of ethylene oxide and propylene oxyto, and a decontaminating agent that becomes water. However, the decontamination efficiency of these decontaminants and decontamination methods is not so high, and further improvement has been demanded.

Special table 2009-511653 gazette JP 2002-522594 A

The present invention provides a method for decontaminating radioactive materials with high decontamination efficiency in order to solve the above-mentioned conventional problems.

The decontamination method for radioactive substances of the present invention is a decontamination method for radioactive pollutants containing radioactive cesium and / or radioactive strontium, and comprises phosphoric acid, hydrogen chloride, sulfuric acid, silica, wetting agent, water A radioactive substance decontamination agent having a pH of 2 or less, and applying the decontamination agent to the target object to which the contaminants are adhered, and neutralizing with a neutralizing agent before drying and solidifying. It is characterized by washing with water or ice blasting after summing and foaming to deposit a radioactive substance on the surface.

  The present invention is a composition containing phosphoric acid, hydrogen chloride, sulfuric acid, silica, a wetting agent, and water. By using a strongly acidic decontaminating agent having a pH of 2 or less, various kinds in nature are used. The radioactive substance containing radioactive cesium and / or radioactive strontium existing as a salt of can be efficiently decontaminated.

FIG. 1 is a schematic perspective view showing a plate-like flake ice piece in one embodiment of the present invention. FIG. 2 is a schematic explanatory view of an ice making machine in one embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a nozzle in one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a nozzle according to another embodiment of the present invention.

  Radioactive cesium (Cs) is an alkali metal, and radioactive strontium (Sr) is an alkaline earth metal, which are considered to be various salts in nature. In particular, it is known that it is easily adsorbed by certain types of clays, for example, clays forming 2: 1 type layered silicates. Since clay is generally difficult to clean and remove, the present invention uses radioactive acid cesium and / or radioactive strontium that exist as various kinds of salts in nature by chemical reaction by using a strongly acidic decontamination agent. Detach and decontaminate.

  In the present invention, phosphoric acid, hydrogen chloride and sulfuric acid are used to maintain strong acidity. Silica is used to adsorb radioactive substances desorbed from clay and the like. Silica is also used to keep the decontaminant on the surface of contaminants for a time of, for example, about 5 to 30 minutes, utilizing the thickening effect.

  The radioactive substance decontamination agent is phosphoric acid 30 to 40% by mass, hydrogen chloride 1 to 5% by mass, sulfuric acid 1 to 5% by mass, radioactive substance adsorbing silica (particle size 10 to 100 nm), thickening effect silica (particles) (Diameter 300 to 1000 nm), silica total 10 to 20% by mass, wetting agent 10 to 20% by mass, and the balance is preferably water. If it is the said range, it can decontaminate more efficiently. The mixing ratio of the silica for radioactive substance adsorption and the silica for thickening effect is in the range of 50 to 100% by mass of silica for radioactive substance adsorption and 0 to 50% by mass of silica for thickening effect when the total silica is 100% by mass. .

  The silica is preferably at least one silica selected from fumed silica and colloidal silica. This is because radioactive materials can be adsorbed efficiently and later processing is easy. For the vertical coating, it is preferable to use a mixture of colloidal silica for adsorbing radioactive material and fumed silica (amorphous silica) for thickening effect. For flat coating, it is preferable to use only acidic colloidal silica having a small particle size and easily diffusing into an acidic liquid.

  Any wetting agent can be used as long as it wets the surface of the contaminant for a predetermined period of time and can easily penetrate the decontamination agent, such as ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, copolymers thereof, and glycerin. At least one compound selected is preferred.

  The decontamination method of the present invention is a method using the above-mentioned radioactive substance decontamination agent, which is applied to a target object to which a contaminant is attached, washed with water or ice blasted before being dried and solidified. To do. Clay substances having a diameter of 100 μm or less become difficult to remove when dried and solidified, and therefore, they are washed with water or ice blasted while wet.

The ice blasting preferably uses plate flake ice pieces. FIG. 1 is a schematic perspective view showing a plate-like flake ice piece 1 in one embodiment of the present invention. The plate-like flake ice piece 1 has a main surface 2 and a side surface portion 3. Since the plate-like flake ice pieces 1 are oriented in a direction not receiving fluid resistance when riding on the air flow, they easily collide with the target object from the side surface portion 3. For this reason, the kinetic energy of the plate-like flake ice pieces 1 is concentrated on the side surface portion 3. Kinetic energy can be expressed by the following formula .
Kinetic energy E = (1/2) mv ²
Where m is mass and v is velocity.

The plate-like flake ice piece 1 is preferably an indefinite shape having a thickness t of 3 mm or less and a surface area of one principal surface of the thickness t ² or more. More preferably, it is an indefinite shape having a thickness of 0.5 to 2 mm and a main surface of 2 to 3 mm square. If it is this range, it will be efficient to fly from an ice making machine to a nozzle, and to inject from a nozzle tip and to remove contaminants.

  The specific gravity of the plate-like flake ice pieces is preferably 0.92 or less, more preferably 0.5 or less. If it is the said range, it is efficient to fly from an ice making machine to a nozzle, and to inject from a nozzle tip and to remove contaminants. To reduce the specific gravity, bubbles (air) are involved during ice making. When the specific gravity is heavy, it is suitable for short-distance transportation (for example, horizontal distance of 10 m or less), and when the specific gravity is lightened, short distance is possible, but it is suitable for long-distance transportation (for example, horizontal distance of about 10 to 70 m).

  The speed of the plate-like flake ice pieces ejected from the nozzle tip is preferably 15 m / second or more. If it is this speed, it can act on washing etc. efficiently.

  The ice making machine in the ice blasting apparatus of one Example of this invention is demonstrated using FIG. The ice making machine 10 supplies liquid water 7 to the tank 6 to form a liquid water supply unit. Liquid water 7 is supplied from a water supply pipe 4 through a regulating valve 5. Reference numeral 8 denotes a protective cover. An aluminum cooling drum 9 partially immersed in the liquid water 7 is rotated in the direction of the arrow, and ice is made on the cooling drum 9 to obtain plate ice 12. The cooling drum 9 is supplied with refrigerant from the shaft core portion 11, and the surface of the cooling drum 9 is cooled to −21 ° C. as an example. The plate ice 12 is then scraped off by a scraper 13. The flake-shaped ice pieces 14 scraped off are dropped into an ice piece storage portion 15 connected to the pipe 17. The temperature of the flaky ice pieces in the ice piece storage unit 15 is −9 ° C. as an example. The plate-like flake ice pieces dropped in the ice piece storage unit 15 are sucked from the nozzles that generate suction force and move to the pipe 17. As an example, the inner diameter of the pipe is 22 mm.

  The ice piece storage part 15 is preferably provided with a discharge port 16 for discharging the flaky ice pieces to the outside. In this way, when the injection of flaky ice pieces is not necessary, the flaky ice pieces can be discharged to the outside, and troubles such as pipe clogging can be avoided.

Next, the nozzle will be described. Although any nozzle can be used, the nozzles shown in FIGS. 3 to 4 can be used as an example. The nozzle (injection gun) 20 of FIG. 3 introduces air from a tapered air introduction tube 21 and injects it from the tip toward the injection port 22, thereby causing the ejector portion E to have a negative pressure and flake-shaped ice pieces to become the pipe 17. Is sucked from. Thereafter, the air is mixed with the air from the air introduction pipe 21 in the ejector part E, and is ejected from the ejection port 22 toward the tip. As an example, the air introduced from the air introduction pipe 21 is 7 atm and 11 m ³ / min. As a result, the pipe 17 can be operated at 70 m, a blast injection distance of 30 cm, and an initial injection speed of 15 m / sec or more.

  FIG. 4 shows another nozzle (injection gun) 30. When air is introduced from the air introduction pipe 23 and injected toward the injection port 24, the ejector portion E becomes negative pressure, and the flaky ice pieces become pipe 17. Is sucked from. Thereafter, it is mixed with air from the air introduction pipe 23 in the ejector part E, and is ejected from the ejection port 24 toward the tip. Other exemplary conditions are the same as those in FIG.

  Alkaline or acidic water may be added to the flaky ice pieces used in the present invention in order to enhance detergency. For example, sodium bicarbonate water, alkaline electrolyte, citric acid, acidic electrolyte, cleaning agent and the like can be added. If the amount is small, a surfactant may be added.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to the following Example.

<Decontamination agent 1: Low viscosity type (for flat coating)>
35% by mass of phosphoric acid
Hydrogen chloride 3% by mass
3% by mass of sulfuric acid
Silica (Nissan Colloidal Silica, D50: 10 nm) 15% by mass
Ethylene glycol 15% by mass
Water residue <Decontamination agent 2: High viscosity type (for elevation coating)>
35% by mass of phosphoric acid
Hydrogen chloride 3% by mass
3% by mass of sulfuric acid
Silica (made by Nippon Aerosil Co., Ltd., trade name “Aerosil”, D50: 100 nm) 15% by mass
Ethylene glycol 15% by mass
Water residue <Measurement of radiation dose>
The radiation dose was measured using a model RDS-100 Survey Meter manufactured by ANLOR.

Example 1
Using the low-viscosity type decontamination agent, the asphalt road surface contaminated with radionuclides was applied to two areas of length × width: about 10 cm × 10 cm on the surface of the asphalt road. Immediately after application, it was observed that the clay-like substance separated from the surface of the asphalt road and floated up. Then, while wet, a neutralizing agent was applied and rinsed off. This decontamination work was 3 minutes. Table 1 shows the radiation dose and the decontamination rate before and after decontamination. The radiation dose in the test environment was 0.40-0.61 μSV / h.

  From Table 1, it can be confirmed that the decontamination reagent of this example can efficiently remove the radionuclide from the pollutant of the fine clay containing the radionuclide (presumed to contain 2: 1 silicate). It was.

(Example 2)
Using the high-viscosity type decontamination agent, it was applied to a concrete block (40 cm long, 20 cm wide, 10 cm high) contaminated with radionuclides. Immediately after application, it was observed that the clay-like substance separated from the surface of the concrete block like a bubble and floated. After coating, it was allowed to stand for 5 minutes, and then sucked with vacuum while wet. Table 2 shows the radiation dose and decontamination rate before and after decontamination. The radiation dose in the test environment was 0.11 to 0.14 μSV / h.

  From Table 2, it can be confirmed that the decontamination agent of this example can efficiently remove the radionuclide from the pollutant of the fine clay containing the radionuclide (presumed to contain 2: 1 silicate). It was.

(Example 3)
Contaminated soil containing radionuclides was decontaminated using a low viscosity type decontamination agent. 200 cc of 0.47 μSV / h contaminated soil was collected and placed in a beaker. 200 cc of the decontaminating agent was added from above the contaminated soil and stirred for 20 minutes. When the mixture was allowed to stand, it was divided into three layers of 250 cc of sand (soil), 100 cc of fine mud, and 50 cc of the decontaminant solution from the bottom. The radiation dose of these three layers was sand (soil) 0.31 μSV / h, fine mud 0.18 μSV / h, and decontamination solution 0.10 μSV / h. Thereafter, moisture was removed through a filter. The radiation dose of the mixture before moisture removal was 0.31 μSV / h, and the radiation dose of the mixture after moisture removal by the filter was 0.23 μSV / h. The decontamination rate was 51%, and it was confirmed that the radionuclide could be efficiently removed from the pollutant of fine clay containing the radionuclide (presumed to contain 2: 1 silicate). The radiation dose in the test environment was 0.11 to 0.14 μSV / h.

Example 4
The natural stone surface was decontaminated in the radiation-contaminated area. First, a low viscosity type decontamination agent was applied to the natural stone surface. The coating amount was 500 cc per 1 m ² . Then, while wet, it was cleaned using an ice blasting apparatus comprising an ice making machine shown in FIG. 2 and a nozzle shown in FIG. The contents of this ice blasting apparatus are as shown in Table 3 below.

  The thickness of the plate-like flake ice pieces obtained by the ice blasting apparatus shown in Table 3 was indeterminate with a thickness of 0.5 to 3 mm, a main surface of 2 to 3 mm square, and the specific gravity was 0.5. The specific gravity is light because air bubbles are involved. Table 4 shows the results of decontamination. The radiation dose in the test environment was 0.15 μSV / h. The decontamination effect was high.

  As is clear from the above examples, it can be seen that the decontamination rate of radiation pollutants by the decontamination agent is extremely high.

  The ice blasting method and ice blasting apparatus of the present invention are used to remove contaminants such as radiation-contaminated objects and industrial-contaminated objects, remove labels from glass bottles, deburr resin molded products, remove rust, remove painted materials, and clean semiconductor surfaces. It can be applied to various removal fields such as conversion.

DESCRIPTION OF SYMBOLS 1 Plate-like flake ice piece 2 Main surface 3 Side part 4 Water supply pipe 5 Regulating valve 6 Tank 7 Liquid water 8 Protective cover 9 Cooling drum 10 Ice making machine 11 Shaft core part 12 Sheet ice 13 Scraper 14 Flakes-like ice piece 15 Ice piece Reservoir 16 Discharge port 17 Pipe 20, 30 Nozzle (spray gun)
21 and 23 Air introduction pipes 22 and 24

Claims (5)

A decontamination method for radioactive pollutants containing radioactive cesium and / or radioactive strontium,
And phosphoric acid, using hydrogen chloride, sulfuric acid, and silica, and wetting agents, water only contains the radioactive substance decontaminant pH is 2 or less,
The decontaminant is applied to the target object to which the contaminants are attached, neutralized with a neutralizing agent before foaming and solidified, foamed to deposit radioactive substances on the surface, and then washed with water or ice blasted. A decontamination method for radioactive substances characterized by the above. The composition of the radioactive substance decontamination agent is:
Phosphoric acid 30-40% by mass
Hydrogen chloride 1-5% by mass
Sulfuric acid 1-5% by mass
Silica 10-20% by mass
Wetting agent 10-20% by mass
The method for decontaminating radioactive materials according to claim 1, wherein the residue is water residue. The radioactive substance decontamination method according to claim 1, wherein the silica is at least one silica selected from fumed silica and colloidal silica. The radioactive material according to any one of claims 1 to 3, wherein the wetting agent is at least one compound selected from ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, a copolymer thereof, and glycerin . Decontamination method . The said ice blast is a decontamination method of the radioactive substance in any one of Claims 1-4 which uses a plate-like flake ice piece.

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