Surface decontamination, power

Radioactive contamination occurs in every area involved in the use of radioactive materials. Systematic and efficient maintenance is an essential condition for the safe operation of nuclear power plants, however maintenance and supervision works are dangereous because of radiation hazard of personnel. Radiation doses can be reduced by decontamination of the primary circuit. On metallic surfaces decontamination can only be achieved by the removal of the upper layer of the surface containing the contaminants. 

The installation comprises laser emitter, laser power-supply unit, water-air cooling system and guiding computer. Total weight of the installation is 40 kg consumed power is 3 kW from power network 220 V. The installation capacity reaches to 2 m per hour the distance from emitter to surface to be decontaminated can attain 1.5 m. Laser emitter is installed at a remotely operated rotator. 

Nanosized TiO (anatase) is nontoxic, chemically inert and inexpensive material. It is actively studied and widely used in the eleetronies, photonics [7] and especially in the photoeatalysis [S], In leeent years TiO has been studied beeause it is also known as a photoeatalyst [9], which accelerates the formation of the hydroxyl radieals under light. Hydroxyl radieals are powerful oxidizing agents that can disinfect and deodorize air, water, and surfaces in environmental-decontamination applications [10-... 

Some pressurised water reactor containments are equipped with fan coolers. These coolers would appear to offer the possibility of particle deposition by thermophoresis or even by difiusiophoresis. Analyses of the potential decontamination that could be achieved with such fan coolers have not been reported. They may not provide a long-term aerosol removal capability. Accumulation of insulating deposits of aerosol on their surfaces may limit effectiveness. Fan coolers do require power to operate and the necessary power may not be available under accident conditions. 

Typical mechanisms for aerosol removal from gas streams by filters are diffusion to surfaces, interception and impaction. Very large particles can be removed by gravitational settling. These mechanisms are quite dependent on the particle size and it is usually found that conventional filters have a minimum in filter efficiency for particles in a narrow size range less than 1 im. When the gas is hot relative to the filter, thermophoresis can enhance particle removal. When the aerosol laden gas stream contains elevated concentrations of steam that condenses within the filter, difflisiophoresis will enhance particle removal. These phoretic enhancements of filtration are attractive because filtration efficiencies by these mechanisms are not especially dependent on the aerosol particle size. Washed Venturi scmbbers involve the injection of water droplets into the aerosol laden gas and these water droplets act much like spray water droplets to remove aerosol particles. Electrostatic precipitation is, in principle, a very attractive decontamination process, but it is difficult to assure that the necessary power will be available to operate the precipitators under accident conditions. 

Kaneka Corp., a Japanese chemical company has established an efficient radioactive decontamination strategy by using their biosurfactant, called Kaneka Surfactin, which is composed of surfactin. They successfully carried out decontamination of areas affected by the Fukushima No. 1 nuclear power plant disaster. Efficient surface and detergent activity of surfactin make it eliminates radioactive cesium and other contaminants from the polluted area. Strategy adopted by Kaneka Corp. for radioactive decontamination of roads using surfactin solution is shown in Figure 14.8. 

In order to meet this fundamental requirement the procedures to be applied in the decontamination of a nuclear power plant have to satisfy a number of conditions. The most important ones will be summarized in the following it must be kept in mind, however, that in a given situation one or two of them may have greater importance than the others. Further, the following sections will concentrate on the removal of the tightly-adherent contamination layers present in the primary system, whereas removal of loosely-adhering contamination in cold systems or from the building walls and surfaces will not be treated. 

Besides the metallic structures of the circuits and components, nuclear power plants contain huge masses of concrete, a small fraction of which is activated and/ or contaminated. In order to keep the resulting waste volumes as small as possible, the fraction which contains radionuclides has to be separated during dismantling from the non-radioactive bulk of the material the techniques used for this will not be discussed in what follows. Likewise, decontamination of building walls and surfaces will not be treated here. 

Riess, R. German experience including chemical, electropolishing and decontamination for decommissioning. Paper ANS Executive Conf. E>econtamination of Power Reactors The Costs, Benefits and Consequences. Springfield, Ma., 1984 Sasaki, T, Kobayashi, T, Wada, K. Method and apparatus for regenerating an acid electrolyte that has been used in the decontamination of components with radioactively contaminated surfaces. European Patent Specification 0 141 590 B. 1 (30.1.1991)... 

The most commonly employed chelating agents are probably the ethylenediamine tetraacetic acid (EDTA) and related compounds. Among other applications, they are of special interest in corrosion, such as in chemical decontamination of water-cooled nuclear power plants. These compounds are especially reactive in contact with metal oxides or other solid metal compounds, because of their ability to form strong surface complexes between the adsorbate and the adsorbent. 

Noteworthy in particular were German formulations of viscous mustard that were intended to confer long-term persistence on surfaces and to thwart efforts of decontamination. Like mustard formulations for winter use, some of the Zahlost types have arsenicals as major components. Thickening materials that were available up to 1945 (e. g. chlorinated rubber, waxes and polystyrene), added for powerful enhancement of viscosity, incidentally made the chemical agent formulations completely insoluble in the usual technically available solvents. 

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