The method of cleaning metal surfaces from radioactive contamination

 

The invention relates to nuclear technology, namely the decontamination of metal surfaces contaminated pricefixing radionuclides. The inventive method of cleaning metal surfaces contaminated with radionuclides, includes a step of forming on the surface being cleaned easily removable polymer film formed after applying the film-forming composition. The composition of the film-forming composition includes a water-soluble film former, a plasticizer, a surfactant and a mineral acid in an amount to provide a pH of the solution in the region of 0.5-2. The process of decontamination is performed during anodic polarization of the treated surface with a density of passing current of 0.2-7.5 a/DM2. The cured polymer film is removed along with fixed in it radionuclides. Advantages of the invention are that it allows for a deep cleaning of metal surfaces from radioactive contamination without the formation of liquid waste. 2 C.p. f-crystals, 5 PL.

The invention relates to nuclear technology, in particular to the decontamination of metal surfaces contaminated pricefixing is sustained fashion storage or final disposal, requirements to methods of decontamination, including metal surfaces, become more hard along with the fact that the method should be effective, radiation safe in its implementation, the number of generated waste which is subject to further processing should be minimal. The formed secondary waste should be efficient in terms of handling. In recent years more and more applications are "dry" methods of decontamination, the implementation of which do not form liquid waste. Effective dry cleaning metal surfaces from radioactive contamination are easily removable film with a special composition. Films are formed directly on the metal surface after applying a layer of the original film-forming composition.

The selection of the composition of the components of film-forming compositions of the films give the required properties.

Formulations recommended for implementation for dry decontamination of metal surfaces, various. Components included in almost all songs are foaming agent, plasticizer and surfactant (surfactant). In some cases magnavore component substances forming the film. The basis of the film-forming compositions used for cleaning metal surfaces, are natural or synthetic latexes; organic solvents; vodoemulsionnye or water-soluble polymeric materials.

Composition-based latexes are expensive and also require the introduction of the film-forming composition explosive and flammable organic solvents.

Toxicity and increased fire hazards is a significant drawback of compositions based on organic solvents.

The greatest distribution for the decontamination of metal surfaces with easily removable polymer films obtained compositions based on water-soluble polymeric film-forming agents.

In the composition based on water-soluble film-forming agents include (in addition to the last): plasticizer, surfactant, and can also be added complexing agents.

The method of cleaning metal surfaces contaminated with radionuclides, by forming them easily removable polymer film by applying to the surface of the film-forming composition based on water-soluble film-forming agent can get the t optimal adhesion - held on the surface and at the same time can be easily removed as needed, have sufficient strength and elasticity. The introduction of complexing agents, plasticizer, mineral acids within certain limits in the composition of the aqueous solution of the foaming agent does not lead to the destruction of the polymer base of the resulting coatings [1, 2]. However, when using this method completely removes only non-fixed and partly suboficiales radioactive contamination.

It is known that the desorption of radionuclides from the metal surface increases with increasing positive potential when current passes through them [1].

On the principle of anodic polarization based most described in the literature methods electrochemical decontamination. Contaminated surface serves as the anode, the cathode is a plate of metal, which is resistant to the electrolyte.

Good results on decontamination and to provide the desired surface finish of various metals obtained using electrolyte based on sulfuric, phosphoric and nitric acids.

Electrochemical methods allow for intensive, full decontamination of metal surfaces regardless of the composition of bhamy liquid radioactive waste electrochemical process make the method of radiation-dangerous and uneconomical, as the generated secondary waste require a considerable amount of further processing.

Object of the present invention is to provide a method of cleaning metal surfaces from radioactive contamination, for enhancing the effectiveness of decontamination by removal of radionuclides pricefixing in the structure of the surface layer on the surface. In addition, the object of the invention is to provide a method of decontamination of metal surfaces, which, along with deep decontamination would in the process of implementation of the minimum amount of secondary waste.

The problem is solved due to the fact that in the method of cleaning metal surfaces from radioactive contamination, including forming on the cleaned surfaces easily removable polymer films by applying a film-forming composition, which comprises water-soluble foaming agent, plasticizer, surfactant, and removing the formed polymer film fixed it radionuclides. The feature of the proposed method lies in the fact that in the process of cleaning metal surfaces from radioactive contamination are andno the shedding of the composition and the electrolyte. To enhance the electrochemical component of the process in the composition is injected mineral acid (H2SO4and/or H3RHO4and/or HNO3in a quantity sufficient to make the pH of the solution was 0.5-2. When the pH value of the solution is less than 0.5, the surface layer is discharged enough that reduces the effectiveness of decontamination, and when the pH value is greater than 2, it is possible the crosslinking of the polymer included in the film-forming composition that increases the adhesion of the film to the metal surface.

Applying a film-forming composition is carried out at polarization machined metal surfaces with a current density of from 0.2 to 7.5 A/DM2. At the current density of less 0.2 a/DM2decreases the speed of the process, and at the current density exceeding 7,5 A/DM2decreases its efficiency by side processes (e.g., gas evolution at the electrodes).

In the solution film-forming composition according to one of the private options, add a complexing agent, such as oxalic acid, which binds the products of electrochemical reactions, and prevents the crosslinking of the polymer, thereby reducing the adhesion of the formed polymer plait is allcauses in enhancing the effectiveness of decontamination by that electrochemical processing of the cleaned surface initiates the transition pricefixing impurities in the solution film-forming composition. The formation of the same in the final stage of the polymer film, which is fixed radionuclides, allows to avoid the formation of liquid waste.

Evaluation of the effectiveness of the film-forming composition as the electrolyte and the film-forming was conducted under laboratory conditions. As the water-soluble film-forming agent used polyvinyl alcohol (PVA), the plasticizer is glycerin. The composition of film-forming solutions, electrical parameters of electrochemical processes and the results of processing stainless steel are presented in table 1. This shows that all the studied compositions provide metal removal necessary for a thorough decontamination of stainless steel. The experiments also showed that the optimal parameters of the anodic treatment are: current density (0,2 -7,5 A/DM2); voltage (5-20); processing time, which in this electric mode is about 5 minutes

The viscosity of the film-forming compositions selected to evaluate the efficiency of the method was determined using viscosimetry>1 sec, while 40oWith - (381 sec). This viscosity allows the application of the original composition as the bulk, and more economical spray. At the rate of film-forming compositions of 0.25-0.5 kg/m2the thickness of the resulting coating is 90-110 μm, which provides a relatively easy removal of the spent coating to the metal surface.

At the specified flow film-forming composition during the formation of the coating is 4-8 hours under normal conditions. Determination of the adhesion of the formed films was carried out according to the method described by A. A. to Berlin and C. E. Basionym in the book "fundamentals of adhesion of polymers", Moscow, "Chemistry", 1969.

When the above parameters, flow, temperature, air humidity, the amount of adhesion of the formed film on the surface of the inactive stainless steel is 0.5-1.0 kg/m2.

To assess the effectiveness of decontamination using the proposed method used the following songs: 1) 10 wt.% PVA + 15 wt.% H3RHO4+ 3 wt.% glycerol + 0.1 wt.% Surfactant; 2) 10 wt.% PVA + 5 wt.% H2SO4+ 3 wt.% glycerol + 0.1 wt.% Surfactant; 3) 10 wt.% PVA + 15 wt.% H3RHO4+ 5 wt.% H2SO4+ 0.1 wt.% Surfactants; 4) 1 wt.% H2SO4

Decontamination was carried out as follows. Samples of stainless steel 12X18H10T (plate size 20 x 20 mm) before pollution was degreased in an aqueous surfactant solution, washed with distilled water, dried in air and wiping with a swab soaked in ethyl alcohol.

The prepared samples were activated droplet applying nitrate solution radionuclides239Ri,137Cs90Sr to the level of 1,103-9,103 Bq/cm2. An aliquot of the solution was applied on the sample surface and dried at room temperature for 1 month in a desiccator. Suboficiales contamination was removed wet swab, after which the samples were again dried.

Decontamination of these compounds were carried out in normal conditions during anodic polarization. Modes of electrochemical treatment corresponded to the modes that were identified as optimal in assessing the effectiveness of film-forming compositions (see above).

The cathode used plate stainless steel size 20 x 20 mm

The resulting polymer film was removed from samples with little effort. Measurement of the levels of radioactive contamination of the samples before and after decontamination was carried out with the help of theRef/AKonwhere aRefand aKonthe activity of the samples before and after decontamination.

The results of the decontamination samples of stainless steel, contaminated Cs, Sr and Pu, with the application of the proposed method are presented in tables 2-5.

Thus, the method can significantly improve the cleaning efficiency of metal surfaces in comparison with the methods of film decontamination by removing pricefixing radionuclides. Compared with the methods of electrochemical decontamination of the proposed method allows to reduce the environmental risk of the technological process by preventing the formation of liquid waste, and reduce the economic cost of recycling waste generated in the process.

The method is intended for use when cleaning equipment, pressure vessels, facilities, reprocessing plants, and equipment of industrial enterprises, contaminated as a result of emergency situations. The method can be carried out using equipment used in the electrochemical production.

Sources of information 1. Swedes Century. P. and others "Nuclear technology". Moscow, Atomizdat, 1979, pages 316-317, 323-326 is possible

1. The method of cleaning metal surfaces from radioactive contamination, including the formation of easily removable polymer coating on the cleaned surfaces by application of film-forming composition, which comprises water-soluble film former, a plasticizer and a surfactant, and removing the formed polymer film fixed it radionuclides, characterized in that the composition is administered mineral acid in an amount to provide a pH of the solution in the region of 0.5 to 2, and the process of cleaning metal surfaces carried out by anodic polarization of the surface current density of 0.2-7.5 a/DM2.

2. The method according to p. 1, wherein the film-forming composition applied to the surface to be cleaned under anodic potential.

3. The method according to p. 1, characterized in that the film-forming composition is injected complexing agent, such as oxalic acid.

 

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