RU2847785C1 - Method for deactivating the surfaces of protective equipment and operating rooms - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to a method of decontamination and can be used to decontaminate surfaces, for example, metal surfaces of protective equipment, including those used in "hot" radiochemical laboratories when working with radioactive and nuclear materials. Decontamination of surfaces contaminated with radionuclides is carried out by applying a film-forming gel-like composition containing polyvinyl alcohol, nitric or orthophosphoric acid, glycerin, trilon B and surfactants. The composition used ensures that radionuclides are captured in the protective removable film that forms within 24 hours of the gel being applied.

EFFECT: rapid cleaning of contaminated surfaces from alpha-emitting radionuclides by 40-350 times, from beta-emitting radionuclides by 100-150 times, with effective retention of radionuclides in the polymer composition.

1 cl, 2 tbl, 2 ex

Description

Characteristics of analogues of the invention

Currently, specialized acidic and alkaline solutions are used to decontaminate protective equipment at radiochemical facilities, industrial plants, and "hot" research laboratories. Solutions of various compositions are used for these purposes, including acids, alkalis, oxidizing agents, surfactants, organic acids, complexing agents, and other reagents, depending on the objects of decontamination and the level of contamination. The corrosive oxide film of metals is the main source of equipment contamination and, in fact, the main object of decontamination. Decontamination with acids and alkalis consists of removing radionuclides from the oxide film or removing the film itself using oxidation-reduction reagents. Surfactants wet the treated surface, and surfactant molecules form adsorption layers on the treated surface and on radioactive contaminants, which can reduce the adhesion between radioactive particles and the contaminated surface by 2-3 orders of magnitude. Moreover, adhesion weakens so much that some radioactive contaminants can spontaneously pass into the decontamination solution. In the second stage of the decontamination process, radioactive contaminants must be contained within the decontamination solution and retained therein. To effectively retain radionuclides, complexing agents are used, which bind the radionuclide present in the solution as ions. Despite the high efficiency of decontamination with solutions, the main drawback of routine solution washing of protective equipment surfaces and operator rooms is the large amount of liquid radioactive waste generated, which requires solidification. Injecting large volumes of liquid radioactive waste into deep geological formations is permitted only at certain nuclear power plant sites, and to a very limited extent. In accordance with paragraph 1 of Article 30 of Federal Law No. 190-FZ of July 11, 2011 “On the Management of Radioactive Waste and on Amendments to Certain Legislative Acts of the Russian Federation,” technical means and organizational measures related to the handling of liquid radioactive waste must ensure their conversion into a solidified form, bringing them into compliance with the acceptance criteria, and disposal.

Among the wide range of decontamination methods being developed, surface decontamination using polymer film compositions is recently being considered. Decontamination with removable polymer compositions is sufficiently effective to prevent the formation of secondary liquid radioactive waste, immobilize radionuclides in the film matrix, and eliminate the risks of radionuclide dispersal and migration in the environment, as well as dusting and gas emission associated with other decontamination methods.

The closest analogue, coinciding with the claimed invention by the greatest number of essential features, is a surface cleaning composition (RU Patent No. 2127290 C1, Surface cleaning composition. (Alekseev V.V., Zubarev V.A., Likhomanova A.I., Sorokin N.M.) As of 07/02/2021, the patent passed into the public domain. Published in BI on 03/10/1999, full text), which was selected as a prototype. The proposed composition can be applied to metal surfaces made of structural steel; surfaces painted with oil, alkyd, epoxy and other paints and varnishes, corrosion-resistant steel, aluminum alloys, vacuum rubber, plastic compound, plexiglass, glass. The composition is applied to vertical and horizontal surfaces and surfaces of complex configurations without preliminary preparation.

Preparation and application of the composition. A water-soluble polymer adhesive is added to an aqueous solution of polyvinyl alcohol, prepared in a water bath at a temperature of 60 to 80°C and cooled to 40°C, followed by stirring. The remaining components are then added sequentially according to the recipe. The prepared composition is filtered through a sieve and applied to the surface using all known painting methods. Before application, the initial radioactive contamination level of the surface is measured.

Carrying out decontamination, isolation, and containment work. The prepared composition with working viscosity is applied to the contaminated surface using a pneumatic spray, or, if necessary, a brush or roller. The resulting film is removed for decontamination work. During containment, the film is removed as needed based on operational requirements. When isolating clean surfaces, the film's service life is 6 months.

The deactivation coefficient for alpha emitters ranged from 150-340 for various formulations, while for beta emitters, it ranged from 400-850. Thus, surface cleaning compound No. 2127290 C1 possesses good deactivation properties. However, all formulations require the use of glyoxal, a liquid that solidifies at 15°C and boils at 51°C, requiring special storage and transportation conditions. In Russia, there is only one monopoly manufacturer of this reagent. Furthermore, the mixing and heating sequence of the reagents must be followed when preparing the surface cleaning compound.

In addition, a composition for normalizing the radiation environment (RU Patent No. 2306622 C1, (Federal State Unitary Enterprise "Investment and Construction Concern "Rosatomstroy", status - as of 07/02/2021 - not valid, full text), including an aqueous solution of polyvinyl alcohol and water-soluble salts, characterized in that it contains calcium salts and/or magnesium, and/or barium, and/or cadmium, and/or zinc, and/or nickel (II), and/or lead (II), and/or manganese (II), and/or sodium thiocyanates and/or ammonium as water-soluble salts, while the composition may additionally contain glycerin in an amount of 1.0-6.0 wt. %, necessary to increase the decontaminating ability of the composition, reduce hardness and improve the quality of removal of the coating from the surface, and Also, 0.1-0.3% sulfonol and nitric acid, respectively, were added to improve the composition's wetting of dusty and oily surfaces and to increase its decontamination capacity. The decontamination coefficient of the film compositions for alpha emitters ranged from 1000-1400 for various compositions, and from 400-600 for beta emitters. The inventors experimentally confirmed the optimal chemical composition of the film compositions for achieving maximum decontamination coefficients and mechanical properties of the film compositions. A disadvantage of the composition is its complex chemical composition, which can significantly impact its cost.

A close analogue should also be attributed to the method of cleaning metal surfaces from radioactive contamination (RU Patent No. 2210123, (Federal State Unitary Enterprise "All-Russian Research Institute of Inorganic Materials named after Academician A.A. Bochvar), as of October 26, 2021 the patent is not valid, the patent has passed into the public domain, full text) by applying polymer film compositions including 10 wt. % PVA, 5-15 wt. % H ₃ PO ₄ , 3 wt. % glycerin, 0.1 wt. % surfactants, individual compositions contained 5 wt. % H ₂ SO ₄ or 1 wt. % H ₂ C ₂ O _4. For more effective decontamination, anodic polarization of the surface with controlled current parameters is necessary, which complicates the process of decontamination of surfaces by the need to use a current source with the necessary parameters.

The essence of the proposed technical solution is to improve radiation conditions and quickly clean contaminated surfaces in operator areas where personnel are permanently or periodically present in factories, hot laboratories, and radiochemical complexes by simplifying the composition of removable polymer coatings. This ensures high levels of cleaning of contaminated surfaces from alpha- and beta-emitting radionuclides. Furthermore, the polymer composition achieves exceptional decontamination and radionuclide retention efficiency through the use of a film-based formulation for alpha emitters, as well as the addition of a complexing agent (Trilon B), which chemically binds radionuclides and requires no special storage conditions. It is less toxic than glyoxal.

Example of specific implementation

Specially prepared stainless steel substrate surfaces were contaminated with radionuclides by applying a highly diluted radioactive solution to the target. This solution was obtained by dissolving spent nuclear fuel in nitric acid, followed by spontaneous evaporation of the applied aliquots of the solution on the substrate at room temperature for three days. The resulting solution contained both alpha- and beta-emitting radionuclides.

In the proposed method of decontaminating surfaces with polymer film compositions pre-contaminated with radionuclides, gel-like compositions obtained from suspension solutions of the following composition were applied to the surface of disks made of 12X18H10T stainless steel

Composition 1 - polyvinyl alcohol - 12 wt.%, HNO ₃ - 2.5 wt.%, glycerin - 3.5 wt.%, trilon B - 0.5 wt.%, surfactant - 0.1 wt.%, or

Composition 2: polyvinyl alcohol - 12 wt.%, H ₃ PO ₄ - 6 wt.%, glycerin - 3.5 wt.%, trilon B - 0.5 wt.%, surfactant - 0.1 wt.%,

The applied gel-like compositions were brushed onto contaminated surfaces until a gel layer formed, completely covering the contaminated surface. After the gel spontaneously polymerized and a polymer film formed, they were removed with tweezers. The resulting polymer film was easily removed in one piece or in large fragments. Surface contamination before and after application of the polymer film composition was measured using a UIM-MD dosimetric instrument. A BDZA-2-01 detector was used to measure the alpha radiation count rate, and a BABDB-0-02I2 detector was used to measure the beta radiation count rate. The measurement error for contamination levels was 10-15%.

Example 1. Results of decontamination of stainless steel surfaces contaminated with alpha and beta emitters using composition 1 (single application)

The results of decontamination of contaminated surfaces using polymer film composition 1 are shown in Table 1.

Table 1 - Level of contamination of the surfaces of stainless steel samples before and after application of the polymer film composition 1

Substrate number Pollution levels,
α-emitting radionuclides, particles/min cm ² Decontamination coefficient Pollution levels,
β-emitting radionuclides, particles/min cm ² Decontamination coefficient original final original final 1 5700 198 29 25794 531 49 2 7200 126 57 30354 136 223 3 5700 180 32 31874 182 175 4 6600 114 58 34914 243 144 5 6600 120 55 31874 182 175 6 6300 150 42 36434 227 160 7 6300 162 39 34914 364 96 8 7500 252 30 31874 227 140 9 6600 156 42 39474 653 60 10 6900 210 33 36434 471 77 To _Wed - - 42 - - 130

Example 2. Results of decontamination of stainless steel surfaces contaminated with alpha and beta emitters using composition 2 (single application)

The results of decontamination of contaminated surfaces using polymer film composition 2 are shown in Table 2.

Table 2 - Level of contamination of the surfaces of stainless steel samples before and after application of the polymer film composition 2

Substrate number Pollution levels,
α-emitting radionuclides, particles/min cm ² Decontamination coefficient Pollution levels,
β-emitting radionuclides, particles/min cm ² Decontamination coefficient original final original final 1 3300 63 52 25794 2082 12 2 7200 14 500 36434 136 268 3 6600 7 917 39474 106 373 4 6900 75 92 33394 623 54 5 6300 12 525 31874 91 352 6 6000 21 286 28834 212 136 7 5700 16 352 28074 91 310 8 6300 360 18 33394 2538 13 9 6300 14 457 27314 136 201 10 5400 18 300 31874 288 111 To _Wed - - 350 - - 183

Claims (1)

A decontamination method comprising applying a prepared gel-like suspension of reagents to radionuclide-contaminated stainless steel surfaces with spontaneous polymerization of the gel and subsequent formation of a protective removable film, characterized in that the following composition of initial components is used as a film-forming composition for preparing the suspension, containing: polyvinyl alcohol - 11-13 wt.%, and HNO ₃ - 2-3 wt.% (or 5-7 wt.% H ₃ PO ₄ ), and glycerin - 3-4 wt.%, and Trilon B - 0.4-0.6 wt.%, and surfactant (or washing powder) - 0.05-0.15 wt.%, the rest is water; the suspension is prepared by mixing the initial components in specified proportions with water, followed by heating to 85-90 °C and stirring until a transparent gel is formed; The formed gel is applied with a brush or sprayer to surfaces contaminated with radionuclides in an even layer; the formation of a protective removable film occurs within 24 hours from the moment the gel is applied.