From Big Medical Encyclopedia

DEACTIVATION — removal of radioactive materials from a surface of various objects or Wednesdays. Is one of the main actions for antiradiation protection.

Radiocontamination of objects of the environment and the person can result from accidents on the nuclear installations and devices using radioactive sources during the transportation, removal and storage radioactive waste (see); owing to disturbances of the accident prevention during the work with radioactive materials (see), as a result of nuclear explosions and use of atomic and thermonuclear weapons.

At the enterprises and in institutions where the personnel have contact with radioactive materials, D. is a planned action. Detection of radiocontamination and its quantitative assessment are made by means of the dosimetric and radiometric equipment (see. Dosimetry of ionizing radiation , dosimeters; Radio isotope diagnostic units ).

Conditionally distinguish three types of radiocontamination: superficial, volume and structural (e.g., the induced radioactivity of the soil as a result of neutron emission of nuclear explosion). Superficial radiocontamination is characterized by availability of radioactive materials on a surface of various objects and the equipment, integuments etc. Understand homogeneous distribution of radioactive materials as volume pollution in liquid, gas or in firm environments.

The theory and practice

the Theory and the practician D. are based on knowledge of patterns of radiocontamination and physical. - the chemical processes which are its cornerstone. The nature of interaction and anchoring strength of radioactive materials with object of pollution are caused by processes of adhesion, absorption and adsorption, chemisorption, a complex formation and ion exchange. E.g., at hit of radioactive materials on the surface of skin there can be an adhesion bond of radioactive particles to a surface, adsorption of skin by their superficial structures, chemisorption, a complex formation and ion exchange to participation of active radicals of the water-in-oil film covering skin and biochemical, components of this body. The role of each of these processes is defined by aggregate state and physical. - chemical properties of radioactive materials and their carriers and features of an object of pollution. With other things being equal anchoring strength of radiocontamination at the expense of physical. it is less forces of adhesion, than owing to chemical interaction. Therefore removal of radiocontamination in a solid phase (e.g., in the form of dust) is reached easier, than D. of pollution by radioactive solutions. The radioactive materials which are in solutions, free of isotope carriers are stronger fixed on surfaces and more difficultly deactivated, than radioactive materials in the form of solutions with carriers and ballast salts.

Sorption of radioactive materials on surfaces depends on their chemical state in solutions and the ionic potential of an element. Anchoring strength of many elements increases at the pH values of the contaminating solution close to pH values of transition of radionuclide to colloidal state and with increase of its ionic potential. As a result of diffusion and other processes radioactive materials can partially get into depth of coverings from polymeric materials and into glass. On metallic surfaces it is promoted by corrosion and formation of an oxide film. D.'s efficiency decreases with increase in time of contact of radioactive materials with objects. Radioactive materials depending on their nature and physical. - chemical properties can be in surface waters in ionodispersny (molecular), pseudo-colloid (colloid) and coarse-dispersion (particles> of 0,1 microns) states. The chemical composition of water and availability in it of organic impurity in turn exerts impact on dominance of this or that form.

Methods of deactivation

apply To D. mechanical, physical. - chemical and biol, methods; most often use a combination of the first two. The arsenal of ways and D.'s means is very extensive. The mechanical method D. provides removal of a surface layer of radiocontamination by cutting, strippings, processings by means of sandblasters etc. Physical. - chemical methods are based on dilution, distillation (distillation), sedimentation, ion-exchange absorption of radioactive materials from solutions, on use of special filter mediums for purification of air, use of various deactivating solutions, etc. Biol, the method D. is based on sorption of radioactive materials by the soil, active silt, plankton and perifitony. For this purpose use bacteria beds (see), aerotanks. Biol, a method is applied generally to D. of drain waters (see. Bioscrubbling ). At pollution by short-lived radioactive materials in some cases use a passive method which comes down to endurance of an object of pollution (without any processing) during the certain period necessary for natural disintegration of radioactive material to safe level. Use this method for D. of a polluted air (standing him in special tanks — gas-holders), and also some types of the equipment, drain waters before dumping into the sewerage etc. The choice of methods D. depends on an object D. and the nature of pollution. At mitigation of consequences of accidents the organization, volume and priority of works on D., including the choice of methods D., are defined by scales of pollution and character of the developed situation.

Means and ways of deactivation

of various surfaces and the equipment, individual protection equipment and integuments apply liquid processing To D. more often. Its main objective — destruction of communication of radioactive ions (or carriers) with a surface and prevention of repeated sorption of radioactive materials. Distinguish the simple and difficult deactivating means.

Simple consist of one ingredient (diluted to - you, kompleksoobrazovatel, oxidizers, some soaps, surfactants, etc.); difficult means — multi-component mixtures or specially picked up compoundings which mechanism of action has complex character and it consists of features of action of each component. Carry synthetic to number of such means detergents (see) which in turn combine with complexing agents, firm fillers etc.

In some cases apply the anhydrous (dry) ways D. based on binding of radioactive materials by quickly hardening structures (films). It yields satisfactory results at dry aerosol pollution of surfaces. As film-forming structures use water-soluble latex in combination with detergents (see), a polyvinyl acetate emulsion, etc. Such structures apply on a surface of various objects and the equipment before repair work and after their termination. Then both layers of coverings are removed and sent to places of burial of radioactive waste.

Owing to high speed of penetration of the radioactive materials into depth of skin which are especially in organic solvents D. of integuments shall be carried out in perhaps earlier terms after pollution. The smooth elastic skin covered with a water-in-oil film is cleared easier, than the rough, covered with hair skin with cracks. Microtraumas of skin sharply (in tens, hundreds of times) increase absorption of radioactive materials. D.'s means of skin shall be highly effective, not strengthen a percutaneous resorption of substances and not exert an adverse effect on an organism at prolonged use.

An easy and profitable way of cleaning of skin of radiocontamination is washing by warm water and soap by means of a brush. However at the high densities of pollution this procedure does not provide appropriate. The deactivating means which compounding includes the surfactants (S), kompleksoobrazovatel, adsorbents and other firm fillers meet fullestly specified requirements. Molecules and ions surfactant, being adsorbed on limit of the section, lower surface intention of solution, promoting dispersion and stabilization of pollution in solution. Kompleksoobrazovateli is connected by radioactive ions in the strong water-soluble and hardly dissociated connections. Special firm fillers, performing functions of a mechanical factor of washing, promote also adsorption or ion-exchange absorption of radioactive materials from solution.

In the USSR the highly effective deactivating means are created and implemented in practice. They are applied to D. by skin from pollution by cleavage products of uranium, plutonium, transuranic elements and some other nuclides. For D. of skin from polonium, radioisotopes of mercury and bismuth 1 — 3% solutions salt and lemon to - t, kompleksoobrazovately, and also 5% solutions of Unithiolum or oxathiol can be used. However use of these agents shall be limited because of their irritant action on skin at the long use and ability to strengthen a percutaneous resorption. For this reason it is not recommended to apply organic solvents. Processing of integuments shall continue no more than 10 — 12 min.; further cleaning does not influence removal of strongly fixed radiocontamination. At the use of the highly effective deactivating means in most cases the specified time is enough for full removal of radioactive materials.

Of pneumosuits, overalls, dressing gowns, footwear it is etc. made in specially equipped mechanized laundries. The choice of the modes D. is defined by character and extent of pollution, and also a type of material, from to-rogo they are made. Individual protection equipment from polymeric materials processes the oxalate solutions containing sodium salts sulfofat to - t or sulphanole. Of cotton clothes apply the solutions containing complexing connections to D. They are applied either together with soap, or with synthetic detergents. In some cases at high levels of pollution for D. use acid solutions <(pH2) and solutions containing oxidizers. Footwear is difficult cleared of radiocontamination. The method of ultrasonic processing is most perspective in this respect.

Materials of coverings from polyamides are worse purified, than coverings from polyvinylchloride. This material is in turn deactivated slightly more difficultly, than polyethylene. Treat easily deactivated materials of coverings polymethyl methacrylate, vinidur, styrene copolymers and viniplast. For D. of the protective coatings contaminated by radioactive materials of unknown structure or mix of substances 1% solution of contact of Petrov is recommended (see. Petrova contact ) with addition of 0,5% of solution oxalic to - you. Surfaces from stainless steel process 10% solution lemon to - you with afterpurification of 0,5% solution nitric to - you. Colored surfaces process previously organic solvents. Of a laboratory glassware is reached by processing by solutions inorganic to - t or cleaning mixture.

Widely applied in practice cleanings of natural waters ways of water treatment (volume coagulation by salts of iron and aluminum and filtering) are almost inefficient for removal from water of soluble forms of radionuclides (I, Sr, Ba, Cs, Mo, etc.), but more than 90% of the radioactive materials associated by a solid phase, and radioisotopes of easily hydrolyzed elements provide extraction (Zr, Nb, Ce, Pr, La, Pu, etc.). These ways cannot be used for effective water treatment from radiocontamination in an extraordinary situation and the more so in peace time. Therefore in practice of D. of water volume coagulation and filtering are preliminary ways of processing of water, and act as the main — sorption and ion-exchange absorption. Flow diagrams in the installations intended for D. of water are based on such sequence of refining processes. As highly effective sorbents some brands of active coals, in particular karboferrogel, natural ionites (vermiculite, bentonite, zeolites, montmorillonite clays, etc.) and synthetic ion-exchange sorbents are used.

Purification of air from radioactive dust and aerosols it is made on filters absorbers of various type. As filter mediums the greatest distribution was gained by the fabrics developed by I. V. Petryanov (see. Respirators ).

Deactivation in field conditions

In field conditions decontamination works are carried out with the help of simple receptions and available means.

Removal of radioactive materials from the surface of skin and visible mucous membranes of people is carried out with the help cleansing (see). In field conditions is carried out concerning regimentals and equipment, military equipment and weapon, constructions, and also water, food and fodder. Sanitary cleaning and D. can be partial and full. Holding actions for sanitary cleaning and D. shall not interfere with performance of fighting tasks. At partial D. radioactive materials delete from those parts and details of weapon or the equipment, to the Crimea the staff is forced to touch in the course of fighting activity, and also from the upper regimentals and means of antichemical protection which are put on people. At the same time objects D. wipe with dry rags, wash, and regimentals and means of protection shake out and clear. Partial D. of the surfaces covered with lubricant is made the rags moistened with solvent (kerosene, gasoline, diesel fuel, etc.).

At full D. radioactive materials delete from all surfaces of weapon, military equipment, regimentals and means of protection.

Of regimentals, equipment and footwear on first-aid posts or in to lay down. institutions make on the special platform, edges it is developed near the platform of sanitary cleaning. Work on this platform is regulated by special instructions.

Of water make only when it is not possible to organize water supply of staff not infected water. For D. waters use the appropriate engineering means.

Of food and fodder make in various ways depending on a type of food and the nature of packaging, namely: washing of a container water or the deactivating solution with simultaneous wiping by brushes or rags; a rearrangement of products from the infected container in pure; careful washing of some types of products water jet; removal of the infected layer of a product. After D. of food stuffs radiation control is carried out.

See also Protection against means of war of defeat .

Bibliography: Gorodinsky S. M. and Goldstein D. S. Deactivation of polymeric materials, M., 1975, bibliogr.; Ilyin L. A. and d river. Radioactive materials and skin, M., 1972; Kuznetsov Yu. V., Shebetkovskiyv. N and T r at with about in A. G. Bases of water treatment from radiocontaminations, M., 1974, bibliogr.

L. A. Ilyin.