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V.P. Pimenov, E.A. Kuzmina Ltd. SRC “NEOHIM”
Report, Yaroslavl, 2005 Paintworks at building structures and equipment in the conditions of construction and assembly area or under the current production at nuclear power plants and other facilities, operated under the conditions of possible radiation contamination, by paints containing volatile flammable organic solvents, are major difficulties in the coating. These difficulties relate to the need for explosion and fire safety and reduce the toxicity of paint work, that is, the need for construction of temporary ventilation in explosion-proof, which is costly and, in particular, is technically and economically difficult under the current production conditions.
Operating conditions of coatings on objects of atomic industry are also characterized by the simultaneous effect of a number of aggressive factors: radiation pollution, radiation, high humidity and temperature, exposure to fumes, spills, hostile environment. Consequently, coverage, operating in conditions of radioactive contamination should not only be econtaminated to levels not exceeding the GOST 51102-97 “Polymer protective decontaminated coatings. General technical requirements", but to reliably protect metal and concrete from the corrosive effects of aggressive environment. In addition, the coatings are demanded to possess also high flame-proof properties.
When exposed to intense radiation, combined with the mechanical loads, when exposed to alkalis, acids, decontamination facilities and high temperatures, materials based on epoxy resin are most suitable. They have worked well in terms of radiation 1ґ109 rad and at temperatures up to 150 ° C .
Consequently, the solution to the problem of reducing the number of volatile flammable solvents in paint compositions was complicated by requirement to safeguard the above properties of the coating. It is known that for solvent-free compositions low-viscosity film-forming components are needed, characterized by a high concentration of polar functional groups that increase the tendency of coatings to sorption of radionuclides. As a result of the extensive research of influence of various components of the paint composition on the structure and properties of coatings based on them [1, 2], a solvent-free epoxy decontaminated enamel EP-1155D has been developed. The content of volatile substances in the enamel (a mixture of semi-finished enamel and hardening agent) does not exceed 5% at a viscosity with preserving the technologically acceptable viability of the enamel (at least 3 hours.).
Main technical characteristics of a two-layer coating (160-180 microns) on the basis of the enamel EP-1155D are the following:
Enamel can withstand prolonged exposure to temperature (70 ± 5) ° C and briefly at (150 ± 5) ° C with preservation of the physical and mechanical properties and the ability to deactivation.
The enamel is resistant to corrosive liquids at elevated temperatures (55 ± 5) ° C: 5% solution of nitric acid at least 10 hours, 5% solution of sodium hydroxide is not less than 100 hours. Resistance to decontaminating solution is not less than 14 hours and water resistance of at least 120 hours at elevated temperature (65 ± 5) ° C.
Radiation resistance is not less than 1 mGy for dose rate 104 Gy / h.
On the basis of tests executed by Federal State Unitary Enterprise "NIKIMT" was received opinion on compliance Enamel EP-1155D requirements to GOST 51102-97 and its use was recommended to protect building structures, premises and equipment of nuclear technology and reprocessing plants in the areas of controlled access.
Tests of fire proof properties of enamel EP-1155D and coatings based on it to GOST 12.1.044-89 were conducted, and it is determined:
flashpoint of enamel - (147 ± 8) ° C;
ignition temperature of enamel - 150 ° C;
self-ignition temperature of enamels - 445 ° C;
lower temperature limit of flame propagation - (139 ± 12) ° C.
It allowed to obtain an expert opinion of the Authority for certification of Fire Safety StroyPOZhTEST, that:
- Enamel EP-1155D is fire and explosion safe under normal conditions of use and storage;
- Enamel does not form explosive concentrations with air under actual conditions of application;
- It is allowed to carry out painting works with enamel EP-1155D in the premises of all categories in the explosion and fire hazard, subject to the general requirements of fire safety.
According to fire safety regulations NPB 244-97, establishing the range of fire danger rating of decorative and finishing materials applied to the non-inflammable base coating of the enamel EP-1155D has the following characteristics: flammability group - G1 (readily flammable), a group of flammability - B2 (moderatey flammable) in terms of toxicity - low risk, the coating does not spread flame.
It is allowed the use of enamel coatings based on EP-1155D in buildings of all degrees of fire resistance, all classes of structural and functional fire hazards, including the evacuation routes. Allowed the use of coatings in industrial and warehouse buildings, structures and premises in categories A, B, B1, which are manufactured, used or stored flammable liquids.
Full-scale tests were carried out at the Kalinin nuclear plant. After two years of operation in real conditions of the existing nuclear plant, coating based on the enamel EP-1155D preserved protective and decorative properties in all areas, regardless of the nature of operational impacts.
As a result, enamel EP-1155D was recommended by an industry standard OST 95 10590-2004 "Polymer protective coatings for nuclear power stations. Part 2. Decontaminated protective polymer coatings and polymer protective radiation-resistant coatings for special and Corrosion Protection" for painting the building structures and equipment areas of controlled access in nuclear plants.
References:
1. Pimenov V.P., Chalykh A.E., Nenakhov S.A., Rohan E.V. Decontaminating and structure of the coatings. LMC, 1993, № 3, pp. 19-21.
2. Roan A.E., Chaudet L.G., Pimenov V.P. et al Decontaminating and the surface properties of epoxy coatings and paints, 1999, № 6, pp. 10-12 |
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