JP6338835B2 - Acid gel for decontamination of radioactive material and decontamination method - Google Patents

Description

  The present invention relates to an acidic gel that can be used to decontaminate a solid surface having a radioactive substance on the surface, and a decontamination method using the acidic gel. The decontamination may be, for example, radioactive decontamination.

  Acid gels can be used on the surface of all types of solids to be treated, such as metals, plastics, ceramics, porous (eg concrete).

  In general, decontamination including radioactive decontamination is a large-scale treatment with a high removal rate, a small amount of chemical solution used for decontamination, and a low work load, that is, a short time for decontamination work. Matters such as no need for facilities are regarded as important.

  As an example of decontamination, Patent Document 1 proposes a composition having high detergency containing malonic acid and hydrazine as active ingredients. However, since the decontamination object must be immersed in the chemical solution, new equipment and equipment are required. Moreover, since it is necessary to immerse the decontamination target in a solution at 80 ° C. to 100 ° C., human burdens such as management of chemicals during work and continuous work for a long time are great.

  Patent Document 2 includes one or more of nitric hydrofluoric acid, nitric hydrofluoric acid and oxalic acid, nitric hydrofluoric acid and permanganic acid, nitric hydrofluoric acid and potassium permanganate, nitric hydrofluoric acid and citric acid, and A composition containing a gelling agent and a solvent, which is applied to the surface to be decontaminated and held on the surface, has been proposed. However, the dose after the decontamination process is 1/2 or less before the decontamination and the removal rate is low. Patent Documents 3 and 4 propose colloidal solutions containing an inorganic acid, an oxidizing agent, a gelling agent, and the like that can be easily removed by brushing, suction, or the like after being applied to the surface to be decontaminated. However, since the chemical after application is finally dried, it takes time. Depending on the surrounding environment, there is a possibility that the dried chemical may be detached from the surface to be decontaminated during the decontamination process.

Japanese Patent Laid-Open No. Sho 62-127483 JP2012-185097 Special table 2004-535510 Special table 2009-511653

  Conventional chemical decontamination methods have problems in that if the object to be decontaminated is large, a new decontamination treatment facility is installed, the size is increased, a large amount of chemicals are required, and the cost of waste liquid treatment after work increases. . Moreover, even if the amount of the chemical used is small, it is not sufficient in terms of decontamination and safety.

  An object of the present invention is to provide a decontamination material and a decontamination method that do not require new equipment and facilities and that can be stably decontaminated with a small amount of chemical solution.

The present invention provides the following acidic gel and decontamination method.
Item 1.
(i) an acidic gel containing at least one acid selected from the group consisting of inorganic acids and organic acids (ii) an organic polymer thickener and (iii) a water-soluble aprotic solvent, i) An acidic gel having an acid ratio of 5 to 80% by weight.
Item 2.
(I) The acidic gel according to item 1, wherein the acid comprises at least one selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid and hydrofluoric acid.
Item 3.
(Ii) The acidic gel according to any one of Items 1 and 2, wherein the organic polymer thickener is polyethylene glycol having a viscosity average molecular weight of 1.7 million or more.
Item 4.
(Ii) The acidic gel according to any one of Items 1 to 3, wherein the organic polymer thickener is xanthan gum.
Item 5.
(Iii) The acidic gel according to any one of Items 1 to 4, wherein the water-soluble aprotic solvent is one or two selected from dimethylformamide and dimethyl sulfoxide.
Item 6.
Item 6. The acidic gel according to any one of Items 1 to 5, comprising 3 to 20% by weight of an organic polymer thickener with respect to 100 parts by weight of the acidic gel.
Item 7.
Item 7. A solid decontamination method, wherein the acidic gel according to any one of Items 1 to 6 is brought into contact with the surface of a solid to be decontaminated having a radioactive substance on the surface.
Item 8.
Item 8. The method according to Item 7, wherein the solid surface to be decontaminated is a metal surface.
Item 9.
Item 9. The method according to Item 7 or 8, wherein the solid surface to be decontaminated is a stainless steel surface.

  Since the acidic gel of the present invention has little decrease in viscosity over time, the chemical after the decrease in viscosity is retained without being removed from the surface to be decontaminated, and stable decontamination is possible. The acidic gel of the present invention is a gel using an organic polymer thickener, and can reduce the amount of radioactive waste. In addition, since it can be applied only by coating, no new equipment or equipment is required.

  The gel of the present invention comprises (i) at least one acid selected from the group consisting of inorganic acids and organic acids (ii) an organic polymer thickener and (iii) a water-soluble aprotic solvent. It is a gel comprising (i) an acidic gel having an acid ratio of 15 to 60% by weight.

(i) At least one acid selected from the group consisting of inorganic acids and organic acids Organic acids include formic acid, acetic acid, glycolic acid, lactic acid, malic acid, tartaric acid, hydroxyacrylic acid, oxybutyric acid, glyceric acid, gluconic acid , Citric acid, hydroxypivalic acid, glyceric acid, tartronic acid, mandelic acid, β-hydroxypropionic acid, β-hydroxybutanoic acid, β-hydroxypentanoic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, Azelaic acid, diglycolic acid, maleic acid, fumaric acid, 1,2,3-propanetricarboxylic acid, 1,2,3,4-butanetetracarboxylic acid, methanesulfonic acid, ethanesulfonic acid, toluenesulfonic acid, etc. It is done. Examples of inorganic acids include hydrofluoric acid, nitric acid, hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, boric acid, and perchloric acid. These acids can be selected according to the material to be removed, but are preferably inorganic acids, and more preferably sulfuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid. These acids can be used alone or in combination of two or more.

  The acid is 5 to 80% by weight, preferably 10 to 70% by weight, more preferably 15 to 60% by weight, based on the total amount of the acidic gel.

(Ii) Organic polymer thickener Organic polymer thickeners include, for example, polyalkylene glycol, carboxyvinyl polymer, polyacrylic acid and neutralized products thereof, polyvinyl alcohol, polyvinyl pyrrolidone, polyether, etc. Representative polymer compounds, such as hydroxyethylcellulose, xanthan gum, diyutan gum, gellan gum, tamarind gum, guar gum, sodium alginate, carrageenan, pectin, and other polysaccharide derivatives, dextrin fatty acid esters, inulin fatty acid esters, etc. Examples include an oil gelling agent, a silicone-based thickening gelling agent represented by lysine-modified silicone at both ends, a crosslinked dimethylsilicone, a polyamide resin, an amino acid-based gelling agent, aluminum distearate, gelatin, and the like. , Preferably polyethylene glycol, xanthan gum. It is preferable not to contain an inorganic thickener.

  As for the molecular weight of polyethylene glycol, the viscosity average molecular weight is 1 million or more, preferably 1.3 million or more, and more preferably 1.7 million or more. The viscosity average molecular weight can be calculated from the retention time at the peak top of the molecular weight distribution using a differential refractometer as a detector of the GPC apparatus.

  The organic polymer thickener is 1 to 40% by weight, preferably 2 to 30% by weight, more preferably 3 to 20% by weight, based on the total amount of the acidic gel. In the present invention, since a highly viscous gel can be obtained even with a small amount of thickener, it is possible to arbitrarily adjust the thickener concentration when it is desired to increase the acid concentration.

(Iii) Water-soluble aprotic solvents include, for example, nitriles represented by acetonitrile, propionitrile, amides represented by dimethylformamide, formamide, dimethylacetamide, acetamide, diethylene glycol dimethyl ether, diethylene glycol diethyl ether , Ethers typified by ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, dioxane, etc., nitrogen-containing organic compounds typified by N-methylpyrrolidone, sulfur-containing organic compounds typified by dimethyl sulfoxide, etc. Preferably, it is one or both selected from dimethylformamide and dimethylsulfoxide. These solvents disperse organic polymer thickeners such as xanthan gum and polyethylene glycol to facilitate gel production.

  The water-soluble aprotic solvent is preferably 5 to 30% by weight, more preferably 10 to 20% by weight, based on the total amount of the acidic gel.

  In addition to the above (i), (ii), and (iii), the present invention, if necessary, water, oxidation / reduction agent, rust / corrosion inhibitor, emulsifier, dispersant, antiseptic, antifoaming agent, penetrant, Additives such as colorants, fragrances and the like can be added.

  In the present invention, the order of addition of each component is not particularly limited, but the desired order of addition is to first mix (ii) an organic polymer thickener and (iii) an aprotic solvent, where (i ) Add acid and optionally water.

  Water can be added to adjust the concentration, but it may not be added when the acid is used at a high concentration.

  Examples of the material for the decontamination target surface of the present invention include metals, plastics, ceramics, and / or porous materials (for example, concrete), and these materials can be used on these surfaces. Preferred examples of the metal include stainless steel, steel, cast iron, and specific examples of the stainless steel include austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and duplex stainless steel. SUS304, SUS304L, SUS316, SUS316L, SUS317, SUS317L, SUS321, SUS310S, SUS347, ferritic stainless steel, SUS430, SUS444, SUS445J1, SUS443J3, L SUS420J2 is included in each site-based stainless steel. Examples of steel include ordinary steel, alloy steel, and tool steel. SS (general structural rolled steel), SPCC (cold rolled steel plate and steel strip) for ordinary steel, SC (carbon steel for mechanical structure), SCM (chromium molybdenum steel), tool steel for alloy steel SKH (high speed tool steel), SK (carbon tool steel), and cast iron include FC (gray cast iron) and FCD (spheroidal graphite cast iron), respectively.

  The decontamination may be, for example, radioactive decontamination. Preferred decontamination targets include nuclear power plant parts during periodic inspection or decommissioning.

  In the present invention, spray, brush, roller, or dipping can be used as the method for applying the acidic gel. The acidic gel can be easily applied to the surface to be decontaminated by making it a fine gel.

  The surface treatment time in the acidic gel of the present invention may be appropriately selected according to the treatment substrate and the deposit, but is usually 1 to 48 hours, preferably 2 to 24 hours.

  EXAMPLES The present invention will be described in detail below using examples, but the present invention is not limited to the following examples.

Examples 1-12 and Comparative Examples 1-2
The acidic gel was prepared with the composition shown in Tables 1 and 2, and dipped in a SUS316 or SS400 test piece (20 × 20 mm) and applied. It left still at 25 degreeC for 24 hours, and evaluated the fluidity | liquidity of the acidic gel visually. Moreover, after wash | cleaning acidic gel with water, the test piece was dried and the film thickness reduction | decrease amount was calculated | required from the mass change which deducted the mass after a process from the initial mass. It is said that the thickness of oxide film such as piping contaminated with radioactive material is 1 to 2 μm, and 2 μm etching is considered sufficient for decontamination purposes.

[Liquidity]
After 24 hours of application, the gel is highly viscous and does not flow ○
24 hours after application, the gel is highly viscous but flows.
24 hours after application, the gel drops to the same viscosity as water.
[Etching evaluation]
After 24 hours of coating, etching of the substrate surface is 2 μm or more ○
24 hours after coating, etching of the substrate surface is 1 to 2 μm.
24 hours after coating, etching of the substrate surface is 1 μm or less.

Claims (8)

(I) At least one acid selected from the group consisting of inorganic acids and organic acids (ii) Organic polymer thickeners and (iii) Acids for decontamination of radioactive materials containing water-soluble aprotic solvents (I) the ratio of the acid is 5 to 80% by weight, and (i) the acid contains at least one selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid and formic acid, ii) An acidic gel for decontamination of radioactive substances, wherein the organic polymer thickener contains polyethylene glycol having a viscosity average molecular weight of 1.7 million or more, or xanthan gum. (Ii) The radioactive gel decontamination acidic gel according to claim 1, wherein the organic polymer thickener is polyethylene glycol having a viscosity average molecular weight of 1.7 million or more. (Ii) The acidic gel for decontamination of radioactive substances according to claim 1, wherein the organic polymer thickener is xanthan gum. (Iii) The water-soluble aprotic solvent is one or two selected from dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone. Decontamination of a radioactive substance according to any one of claims 1 to 3 Acid gel. The acidic gel for decontamination of a radioactive substance according to any one of claims 1 to 4, comprising (ii) 3 to 20% by weight of an organic polymer thickener with respect to the acidic gel for decontamination of a radioactive substance. A solid decontamination method comprising contacting the acidic gel for decontamination of a radioactive substance according to any one of claims 1 to 5 with the surface of a solid to be decontaminated having a radioactive substance on the surface. The method according to claim 6, wherein the solid surface to be decontaminated is a metal surface. The method according to claim 7, wherein the solid surface to be decontaminated is a stainless steel surface.