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Decontamination facilities against radiation pollution. 1. Introduction
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Decontamination facilities against radiation pollution 1. Introduction Contamination and energy loads on the environment increased greatly as a result of population growth and industrial development in the 20th century. The load is primarily connected with the increased contamination by naturally occurring and technology-related chemical agents, with different sources of radiation and its broad spectrum, with the increase of entropy of the Earth's atmosphere and crust (accumulation of energy and temperature growth concerned). The environment cannot treat all human wastes in the equilibrium conditions as it was before the 20th century. This problem represents a real threat to life conservancy in future. Radionuclides (RN) affect the biosphere due to the following factors: damage effect of the radioactivity, chemical and toxic effect of the radionuclides or their compounds, their incorporation into the organisms due to affinity for calcium and sodium, which are the important components of bone tissue/blood and lymph correspondingly. This refers to the radioactive isotopes of Sr and Cs. That is why the damage effect of the radionuclides on the biosphere is so strong. And that is why the measures for its protection and decontamination are so important.
2. Sources of radioactive contamination • Normally operating enterprises, as well as radiation accidents occurred on the enterprises are the sources of radioactive contamination. • Such sources include: • Ore mining and uranium raw material processing enterprises; • Machine-building plants, which produce fuel assemblies for the Atomic Power Stations (APS) and equipment using radionuclides; • Enterprises, which produce and use isotopes; • APS and combined heat and power plants (CHP), which use coal containing radionuclides; • Transport facilities, which carry out the transportation of the RN-containing materials or nuclear power units; • Testing and utilization of the nuclear weapons and nuclear military machines; • Research investigations, measurements and medical procedures, which are carried out with the help of radionuclides; • Autonomous nuclear power plants; • Radioactive waste treatment and decontamination activities, their volume reduction and conversion into the form suitable for long-term storage (Radon Group). • Nuclear terrorist attacks. • The system of safe handling with the RN-containing materials was tried and tested in the course of normal maintenance of the nuclear facilities and proper utilization of the radionuclides. The main problems are connected with the radiation accidents of the past and future periods, because such accidents cannot be formalized and are random and multifactorial in nature. In addition, the historical international experience has shown that such radiation accidents have the disastrous consequences. That is why it is very important to develop a RA prevention and recovery plan, as well as the facilities and qualified personnel to implement that plan.
Terrorist attacks should be considered separately. The terrorists often try either to defeat civil population, staff of force authorities, and staff of government authorities, or to create a non-viable environment including panic and terror situations. The simplest and the most efficient way of introduction of the radionuclides into the environment is to apply the radioactive aerosols especially in nanodispersed and water-soluble forms. An aerosol released into the air creates a stable slowly sinking cloud that can affect the large areas under the favorable atmospheric conditions. Estimates show that one kilogram of aerosol released into the air can cover up to 10 km2. The same is with the water supply facilities. Radionuclides are introduced into the water supply facilities in the chemical form. Standard water treatment technologies cannot detect such contaminations. Thus it is possible to contaminate the water supply facilities of the major population centers, medical institutions, and common areas. But while the water supply systems can be equipped with physical protection, monitoring and automatic control facilities, the air basin can be monitored only locally. The other variants of the terrorist attacks determined by the external and internal reasons are also possible. However their effect is limited. Therefore the most probable variant of nuclear terrorist attack is the introduction of the aerosols into the air. This scenario forms a list of measures and technologies for recovery. 3. Decontamination Decontamination is the process of radionuclides removal from mediums and surfaces to the extent allowed by the standards in place. Decontamination is performed with the help of facilities and/or equipment, which allow removing radionuclides from the treated mediums and minimizing the amount of generated LRW with subsequent waste volume reduction and waste disposal. The objects of decontamination include air, soil, ground, flora, water basins, infrastructure of the population centers, enterprises, etc. The type of decontamination that should be applied is determined depending on the physical form of the contaminated object.
3.1. Types of decontamination There are following types of mediums in the context of decontamination: air medium (gas), fluid medium (water-based solutions, non-water-based solutions), and solid medium (grounds, smooth and porous surfaces, particulates). In reality two or three mediums in different proportions could create the complex systems. For example a cloud of liquid and solid aerosols in the air, RN solutions, and/or their dispersions insoluble in water, concrete or soil, which pores are filled with the radioactive solutions. Such variety of mediums creates different types of decontamination, which provide the best decontamination results. Air (gas) decontamination includes the following types: filtration; electrostatic, gravitation, sonic precipitation; absorption (cleaning). Water and water-based solutions are decontaminated with the help of granular and film-type sorbents. Coagulation, filtration, flotation, electrochemical, foam methods. Solid mediums are decontaminated with the help of liquid, film, foam, plasma, electrochemicalmethods. Mechanical methods. Additionally localization method of decontamination that prevents RN transfer in the aerosol form, and isolation method of decontamination that protects an object from the radioactive contamination are used.
4. Air decontamination. • 4.1. Aerosol decontamination • The practice shows that aerosol contamination of the environment possesses the greatest destructive ability. To reduce the adverse factor of aerosols it is necessary to provide their quick deposition in a place of their release and on the adjacent areas. Contaminated area can be limited by the place of aerosol release and the hazard area can be reduced by several times. • The sources of aerosol contamination are the following: • Accidents, or fire on the objects, on which the radionuclides are used • Terrorist attacks • Operations with the open radionuclides • Primary and secondary transfer of aerosols containing radionuclides • Radon gas that creates a group of radionuclides (in the form of aerosol) as a result of radioactive decay. • This task can be solved with the help of infrastructural and technological preventive measures. Air treatment allows to prevent environment pollution, to fix the aerosols on the limited surface, and thus to prepare to complete decontamination. The main method of air treatment is the coagulation of aerosols with their subsequent deposition. For these purposes sonic, electrostatic, condensation, gravitation, turbulence, etc. methods are used. Condensation and gravitation methods are the most universal. They are implemented in the form of spraying of decontamination solutions under the pressure in the place of aerosol release and dissemination. Aerosol decontamination agent is a complex substance dissolved in water or any other suitable solvent.
5. Decontamination of solid surfaces and materials • According to the literature and common practice the decontamination is often divided into electrochemical, plasma, abrasive, liquid, film, etc. However the last two types decontamination are the most popular ones. That is why we will speak about these two methods below. • Liquid decontamination can be performed with help of solutions and with the help of foams, where foam decontamination method is a variant of liquid decontamination, as a foam is a solution in the disperse state, in which effective surface to volume ratio is sufficiently shifted toward effective surface. The foams among other things provide adsorption, colloid and cavitation processes, improving mass transfer of pollutants from a surface into a liquid. • Film decontamination implies the application of isolation, localization, and decontamination types of agents developed on the basis of polymer bindings. These decontamination agents represent the polymer solutions on the stage of their application. Thus this method can be considered as the method of liquid decontamination. The main processes of mass transfer of the radionuclides from a surface into a solution and their binding with the components of a compound occur in the liquid phase. • Thus liquid decontamination can be presented by such types of decontamination as: • Decontamination with the help of inorganic and organic solutions (decontamination solutions) • Decontamination with the help of foams prepared due to introduction of surface active agents into the compound (foam decontamination). • Decontamination with the help of polymer solutions prepared due to introduction of filming agents (polymer decontamination).
There are a number of decontamination agents including those produced by our Company under Raddez-1 trademark, which passed the tests and were utilized by Rosatom, the Ministry of Civil Defense and Emergency Response, the Ministry of the Internal Affairs, the Ministry of Defense, and during the recovery from an accident on Chernobyl Nuclear Power Plant. However improved ecological requirements to the modern nuclear power industry have forced us to seek for the new solutions. As a result of our investigations we have developed new generation decontamination agents. These decontamination agents were developed on the basis of the following criteria: • High efficiency – decontamination agent should allow to remove a broad spectrum of radionuclides • Environmental compatibility – decontamination agent should not create the environmental disruption • Cost effectiveness – decontamination agent should allow to minimize the costs associated with decontamination of a unit surface area • Technological effectiveness – decrease of labor intensity and operation time for the purpose of radiation burden reduction • Fire safety • Minimization or complete avoidance of LRW in different chemical forms. • The developed agents are produced under Raddez-1 trademark and represent the organosilicon composition modified in such a way as to provide binding of core radioactive elements, which are used or produced in the nuclear industry.
5.1. Decontamination with the help of solutions Different solution compositions are represented in DEZ product line (from mild solutions like DEZ-1 and DEZ-2 to more strong like DEZ-5). These solutions are intended for removal of firmly chemically bounded contaminants from the metal surfaces. Decontamination with the help of solutions has some disadvantages including low technological effectiveness and large amounts of LRW, problems with treatment of porous materials and particulates. Solutions for decontamination developed and produced by Chimmed * - tests were performed in accordance with GOST R 50773-95
5.2. Foam decontamination • Foam decontamination is a form of liquid decontamination. While maintaining all positive features of decontamination with the help of solutions, this method of treatment possesses a number of own advantages, such as: • Reduction of LRW amounts while preservation of decontamination efficiency; • Increased energy of RN particles desorbed from the treated surfaces due to cavitation effect; • Increased volumes with respect to RN particles due to large liquid-air interface; • Large coefficient of RN particles diffusion from the pores of a material to its surface due to intensive processes of mass transfer occurring in foam volume; - Better technological effectiveness during the treatment of vertical surfaces, ceilings, hard-to-reach areas; • Possibility to apply decontaminant to the surfaces with complex geometric configuration, possibility to carry out works in pipelines, air conduits, ventilation systems. • Foam decontamination is applied during the treatment of: • skin and hair cover of people and animals; • buildings and constructions; • equipment and transport facilities; • porous and fiber materials; • soil and plants; • large sized components of building and equipment.
Agents used for foam decontamination developed and produced by Chimmed Decontamination of buildings and constructions, equipment and transport facilities. Localized surfaces of the objects mentioned above could be treated with the help of Raddez – D-1. The same treatment techniques are used during skin treatment. The agent can be used to perform the treatment of working areaы, living areas, amenity premises, tools and appliances.
Macro surfaces are treated with Raddez+Foam-1, Raddez-Foam-1 (for negative temperature). Foam surfacing is carried out with the help of generator that allows to produce the foam with different extension ratio: from high to low extension. Extension adjustment in the low range is effective when it comes to heavily contaminated surfaces. Raddez Foam-1 solution is the extension of Raddez - D~< solution. While the foam has a lot of advantages it should be removed. • In case of localized surfaces the procedure of foam surfacing can be carried out with the help of auxiliary materials, while in case of Raddez Foam-1 application vacuum pumping, steam and air blowout procedures should be implemented. This task can be carried out in two steps: foam application and its collection or removal. Non-robotic treatment implies the minimization of time of entry into the radiation area. For these purposes both steps should be carried out simultaneously. Besides the practice shows that the foams are effective against the particles, which are bounded with the surfaces due to physical adsorption forces. That is why in order to increase the decontamination factor for chemically and physically bounded radionuclides the following combined methods should be applied additionally to foam decontamination: • Ultrasonic • Steam • Brush • To remove the staff involved in the process of decontamination from the treated surfaces for the purpose of radiation burden decrease foam machine is equipped with telescopic tube, feeding hose and drainage hose for spent solution. Robotic remotely controlled unit designed for example on the basis of Brok 40 robot can be used in the high radiation areas.
5.3. Film decontamination Polymer film decontamination agents are used to recover the territories, to decontaminate the buildings, constructions, and infrastructure of the population centers, as well as in cases of radiological terrorism. The main task of the polymer film decontamination agents is to localize the radionuclides on the surface preventing their emission into the air. The decontamination agents are applied to the treated surface like J1KM. The film will safely protect any surface from the erosion during one year after it will dry out. In the process of drying out the film will accumulate the radionuclides in the form of solid aerosols and chemical compounds due to physical and chemical bindings occurring between the film structure and radionuclides. As polymer film decontamination agents are characterized by poor adhesive ability with regard to construction materials, they can be easily removed from a surface manually or mechanically. In case a surface has the complex geometric shape, the film is reinforced with fabric, gauze, or micromesh to ease its removal in future. 5.3.1. Containment of radionuclides Polymer film decontamination agents are called localizing agents, if they do not possess decontamination ability. Such agents do not contain components, which provide radionuclide binding. They are much chipper and more eco-friendly. The main task of such agents is to avoid the emission of radionuclides till the moment the problem with radioactive contamination removal will be solved.
5.3.2. Isolation of surfaces from radionuclide contamination • The third type offilm decontamination agents is the isolation coatings. They are used to protect important objects from possible deposition of aerosols. • The examples of those objects are listed below: • state administration and defense bodies • public facilities • fabrics, porous plastic • food • agricultural plants. • The experiments and practical work show that the application of these agents allows to improve the decontamination factor and to reduce costs in comparison with the other methods. These agents are especially useful when applied to the highly-porous materials, such as concrete, asphalt, slate, etc. However it is rather difficult to imagine that such isolation coatings could be applied to the major population centers, or industrial enterprise. • All decontamination agents should be ecologically friendly. They should not do damage to the environment. This problem is solved due to application of water-soluble and bio-degradable vinyl polymers, as will as due to application of additives authorized for use in every day life and on the enterprises. • From the ecological point of view polymer film decontamination agents, like foam agents can be used during the cleanup activities. For example in case of coverage of damage area with isolation coating, it can prevent the penetration of volatile matters into the atmosphere. It is possible to detoxify contaminants by introduction of active components into the solutions. Film decontamination facilities are ineffective against large volumes of pollutants. In such cases foam technologies are applied. Film decontamination agents are ineffective against aggressive and corrosion-active substances, because polymer film will be destroyed by such substances (acids, oxidizers, etc). The problem can be solved by application of inorganic fluorinated polymers. • The solutions with neutralizing agents, in particular Raddez-bio-1 solution developed by our company, possess additional germicidal effect. The film produced by Raddez-bio-1 gent is breathable and pervious, but destroys pathogenic bacteria. Such agent can be utilized at different disposal sites both in summer and in winter. • Film decontamination agents can be also utilized to carry out soil reinforcement works. Polymer film can withstand wind forces and precipitations during a long period of time, which is enough for natural soil reinforcement due to soil packing. To accelerate this process we add grass seeds and fertilizers into the solution (Raddez-agro~<).
Table 5 Film decontamination facilities designed and produced by Chimmed Surface application is carried out with the help of airless spraying units, by spraying, with the help of brush and roller. Method of application: the solution should be applied to the surface (coat thickness is up to 300). Then it should be dried out and removed during the decontamination. Alternatively it can perform its functions up to one year.
Multipurpose decontamination unit (MDU) The main task of decontamination is to achieve maximum decontamination factor and minimum LRW generation. The most handy and cost efficient method of decontamination is the combination of three surface treatment techniques: mechanical (brush application) + foam + vacuum. Such combined method can be applied to almost all types of surfaces (plain, porous, with complex geometry), to contaminations of high thickness physically bounded with the surfaces, etc. The multipurpose decontamination unit that we have designed and produced is based on the methods mentioned above.
MDU is intended for decontamination, degassing and disinfection of: • premises with painted surfaces, coated with ceramic tiles, with concrete, wooden structural elements including walls, windows, doors, floors, ceilings; • metal and plastic equipment; • external surfaces including localized segments of roofs, roads, grounds; • transport facilities (motor vehicles, airplanes, rolling stocks, sea crafts, etc.) • places without special-purpose canalization. • It is a single-operator unit. • MDU is equipped with the following main elements: • liquid-foam-vacuum unit; • two LRW collectors with the capacity equal to 100l each with removable lids and air filter; • hand held brushes; • pneumatic tools with the steel cord brushes for different surfaces; • spraying nozzle for polymer coating; • tank for preparation and filling of solution with the capacity up to 100l; • connection hoses with quick-release couplings, nozzles for application and removal of foam and solutions. • MDU input power is up to 3.5 kW.
Requirements for the MDUs • radioactive waste volumes minimization • elimination of liquid radioactive waste generation, if necessary • portability and low weight • simplicity and efficiency of the decontamination technologies for the purpose of radiation burden reduction • possibility of physically and chemically immobilized pollutants removal • elimination of the possibility of radionuclides penetration into the environment • equipment protection from external contamination.
MDU core technologies As a result of analysis of different sources of information, own investigations and tests, the following core decontamination technologies were chosen: • - Aerosol (radioactive aerosol deposition in the working area) • - Foam (removal of low and medium fixed contaminations with minimum amount of LRW) • - Film (removal of low and medium fixed contaminations with minimum amount of LRW) • - Liquid (removal of contaminations with the wide range of fixation with the generation of significant amounts of LRW) • - Mechanical (removal of firmly bounded contaminations) • - Vacuum (removal of fine poor fixed contaminations, LRW) • - Electrotechnological electrochemistry (removal of firmly bounded contaminations)/ultrasonic, plasma.
Combined technologies • Foam-vacuum. Foam-mechanical-vacuum • Film-mechanical. Film-mechanical-vacuum • Liquid-mechanical. Liquid-mechanical-vacuum • Electrochemical-vacuum.
MDU accessories • Synthetic and steel cord brushes operated manually or with the help of pneumatic drive • Air chipper • Air cutoff tool • Electric brush for simultaneous foam application, mechanical treatment and scumming • Hand held electrode for electrochemical decontamination
Electric brush for simultaneous foam application, mechanical treatment and scumming
Vacuum evaporator (ВВА-100) • intended for the evaporation of liquid radioactive wastes (LRW). • Vacuum evaporator BBA-100 is equipped with the following components: • Unit; • Vacuum pump; • Control panel; • Air filter; • Hoses with quick-release couplings.
