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 PM2,5 content is necessary. © 2019 Izdatel'stvo Meditsina. All rights reserved

Assessment of the volume activity of α-radioactive wastes on surface and specific contamination by portable γ-spectrometry method

The aim of the study is to evaluate the volume activity of radioactive waste (RW) by surface and specific alpha contamination using portable gamma-spectrometry. Materials and methods. Methods of rapid assessment of the content of α-emitting radionuclides in solid waste of various morphologies using gamma-spectrometers based on germanium detectors are considered. Computational methods for determining the effectiveness of radionuclide registration are presented. Results. The possibility of using portable gamma-ray spectrometry to assess the surface and specific activity of various materials contaminated with α-emitters (232Th,235U,238U,237Np,239Pu,240Pu and241Am) is shown. The calculated values of the registration efficiency of low-energy gamma-emitters obtained by modeling the spatial-energy parameters of the detector are given. To simplify the solution of this problem, the calculation program used 20 standard templates of various geometries (rectangular, cylindrical, conical, spherical, etc.). The main sources of error in the survey of contaminated surfaces, largesized equipment and building structures were investigated. Conclusions. The possibilities of portable γ-spectrometry for estimating the volume of RW based on the surface density of contamination of materials with radionuclides of uranium and transuranic elements are investigated. When using γ-spectrometer with a high-purity germanium detector with a range of γ-quanta extended in the low-energy region, radionuclides such as232Th,235U,238U, 237 Np,241Am were determined by their own radiation or by the radiation of their daughter products. The “problem” element is plutonium, for rapid evaluation of which it is proposed, in accordance with the radionuclide vector methodology, to use241Am, which accumulates during the β-decay of241Pu. According to calculations, the most likely value of the activity ratio239Pu/241Am for the object where the work was performed (scaling factor) varies in the range from 5.0 to 9.0. Based on the results of calculations and experimental studies, the parameters of the efficiency of registration of various α-emitting radionuclides by portable γ-spectrometers. It has been found that for germanium detectors with an absolute efficiency of registering a point source of 7÷15%, it is n×10–5 ÷ n×10–4%. © 2020, Institut meditsiny truda RAMN. All rights reserved