An experimental study on decontamination by surface condition

Surface decontamination is one of the very important problem to be completely solved in the isotope laboratory where there is always the possibility of radioactive contamination, i.e., on the floors, walls, working tables and benches etc., Isotope laboratories require surface covering of material which can be easily and effectively decontaminated. These experiment were done to find an effective decontamination procedure for kind of surfaces which usually are found in radioisotope laboratories and the best type of surface material, that is, one which is easily decontaminated from the point of view of radiation health and safely. This study is presented to guide radioisotope laboratories in Korea which may need to renovate existing unsafe facilities. In some contaminated facilities entirely new installations may be required. Twelve types of surface material are used for study in this experiment. These include 10 cm square of stainless steel, aluminum, ceramic and mosaic tiles, glass, acrylic, formica board, asphalt tile and coated wood with 4 kinds of paints. Stepwise decontamination was performed with various decontamination procedures following a spill of I131 on the center of the surface material being tested. Twelve different decontamination procedures were tested. These included wet wiping with water and detergent, or dry wiping, or removing with gummed paper. Additional chemical procedures used 10% solution of hydrochloric acid, or surface acid, or ammonium citrate, or potassium iodide, or acetone or carbon tetrachloride. The final testing method was abrasion of the test surfaces. Brief analysis of experimental results on the decontaminability on the tested surface showed: 1. Metallic surfaces such as stainless steel or aluminum, or glass, or a piece of ceramic tile or acrylic are recommended as the surface materials for isotope laboratories because these are easily decontaminated by wet wiping only. 2. Formica board, asphalt tile and wood are not easily decontaminated and only effective decontamination method is abrasion. However, decontamination procedures with the following chemicals are more effective than wet wiping; use hydrochloric acid on the surface of asphalt tile and formica board; acetone on the surface of asphalt tile, varnished and lacquered wood. 3. Whenever a surface is contaminated with liquid radioactive material, day wiping is the first step to prevent spreading and flowing but is incomplete. Dry wiping does not decontaminate the area to a permissible or safe level. The second necessary step in decontamination is a thorough wet wiping. Thirdly the area must be checked for residual contamination and chemical or physical decontamination used if still contaminated. 4. Laboratory floors and tables must present a smooth, continuous surface without scratches or cracks to prevent contamination which can not be decontaminated. 5. A protective coating is recommended for porous covering surface such as wood, asphalt tile or formica board. These can not be easily decontaminated