Estimation of the efficiency of the dry method of decontamination of surface contamination of alpha-emitting-radionuclides

The article describes the evaluation of the efficiency of using the technology of dry method of decontamination of α-radionuclides from working surfaces of premises for different materials, equipment and building structures.

Materials and methods. Instruments for measuring of ambient dose equivalent rate (ADER) with a lower limit of 0.03 μSv/h. Specific activity of α-radionuclides in the samples was determined by radiometric, radiochemical and spectrometric methods using standard methods in the accredited laboratory. The measurements in situ were also carried out using the ISOCS «CANBERRA» mobile gamma-ray spectrometry system with high purity germanium detector and a collimator. Technological equipment included industrial vacuum cleaner with nozzles; high-pressure device; packing sets for RAW collection; HEPA filters; personal protective equipment.

Results. Maps of spatial distribution of surface α-contamination in the building was constructed. We performed cluster analysis of data for zoning of contaminated surfaces. The decontamination factor for porous (brick, concrete), smooth (wood, brown tiles, laminate) and sticky (bitumen, mastic) surfaces was determined.

Conclusion. The cluster analysis made it possible to identify 4 levels of surface α- and β- contamination, particles/cm² ∙ min: zone I - for α- above 50, for β- above 10,000; zone II - for α- 5-50, for β- 2,000-10,000; zone III - for α- no more than 5, for β- 2000; zone IV - corresponds to the background values of the workspace surfaces. The dry decontamination method revealed a high content of fine dust aerosol fraction deposited in the lungs. To increase the efficiency of dust suppression, water aerosol with droplet size of 100 - 400 microns and quartz sand with particle size of 100-200 microns were sprayed at the rate of 200-400 g per 1 m². The decontamination coefficient depends on the coating material and the level of surface contamination: concrete - 91 to 97.8%; brick - 85-86%, wood - 38.8-53%; brownstone tiles - up to 29%; mastic - 22-28%; bitumen - 15.9-20%. To protect the personnel, radiation-hygienic rationing of PM₁₀ and PM_2,5 content is necessary.