Decontamination of radioactive materials
The removal of radioactive contamination which is deposited on surfaces or spread throughout a work area.
Decontamination methods are mechanical or chemical. Commonly used mechanical methods are vacuum cleaning, sand blasting, blasting with solid carbon dioxide, flame cleaning, scraping, ultrasonic cleaning, vibratory finishing, and using lasers to vaporize contaminants.
Chemical methods are used primarily to decontaminate components and tools that are immersed in a tank, either by means of a chemical solvent to dissolve the contaminant, or by using electropolishing techniques to remove the surface layer, including contaminants, from metals. Chemical decontamination methods are also used to remove radioactive deposits from the interior surfaces of piping, pumps, heat exchangers, and boilers. For these applications, the solvent is pumped or flushed through the system, dissolving the radioactive deposits. The solution itself is then radioactive, and the contaminants are typically removed using filters or ion-exchange resins. The use of this approach to clean the coolant systems of nuclear reactors has become common. Dilute chemical reagents, including organic acids, are used to decontaminate the primary coolant systems of operating nuclear power plants to minimize radiation exposure of the workers.
Personnel decontamination methods differ from those used for materials primarily because of the possibilities of injury to the subject. Soap and water (sequestrants and detergents) normally remove more than 99% of the contaminants. If it is necessary to remove the remainder, chemical methods which remove the outer layers of skin can be used. These chemicals, such as citric acid, potassium permanganate, and sodium bisulfite, should be used with caution and preferably under medical supervision because of the risk of injury to the skin surface. It is very difficult to remove radioactive material once it is fixed inside the body, and the safest and most reliable way to prevent radiation exposure from contamination is the application of health physics procedures to prevent entry of radioactive material into the body.
