The Prevalence of Radioactivity in a Number of Non-Nuclear Industries
Radiology, Nuclear Medicine and Medical Imaging
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AbstractFour different non-nuclear industries have been investigated regarding the presence of radioactive elements, with the focus on natural radioactivity. The aim of the studies was to investigate the flow of radionuclides in the processes and/or to estimate doses to exposed workers. The first industry investigated was phosphate processing in the manufacture of dicalcium phosphate (DCP), which is used as a feed supplement for domestic animals. The phosphate ore used at the plant had an average activity concentration of 837 Bq/kg of 238U in secular equilibrium with its daughters. Investigation of the flow of radioactivity in the manufacturing process showed several separation and concentration processes. The major part of the uranium was found in the DCP, while the major part of radium was found in the by-product calcium chloride. Estimated doses to workers at the plant from external radiation and dust inhalation were below 1 mSv per year. The second study concerned the removal of radioactivity at a waterworks treating mainly surface water. Apart from natural radioactive elements, also 137Cs, 90Sr and 239+240Pu, originating from fallout from atmospheric nuclear weapon tests and the Chernobyl accident, were included in the study. The method used for purification is a combination of coagulation/flocculation and filtration in sand beds. Two different coagulants are used, FeCl3 and Al2(SO4)3. The results for both coagulants showed high removal efficiencies for uranium, thorium, polonium and plutonium, while radium, strontium and caesium passed through the process and could therefore subsequently reach the municipal distribution network with almost unchanged activity concentrations. The third investigation is a study of exposure to thorium during TIG-welding with thoriated tungsten electrodes. Breathing zone samples were collected for welders at five different workshops. Breathing zone samples from electrode grinding were collected at the laboratory. Dose assessments were made based on both realistic and conservative assumptions showing that, in the realistic case, the annual committed effective doses were below 0.3 mSv for welding and 10 microSv for grinding. Based on conservative assumptions the annual committed effective doses were around 1 mSv or lower for welding and about 60 microSv for grinding. The fourth study concerned the use of zircon in the ceramics industry. Zircon is used as an ingredient (about 10% by weight) in glaze, and samples collected from three different plants contained 3,000 to 3,900 Bq/kg of the uranium series elements and 470 to 740 Bq/kg of thorium series elements. The estimated annual effective doses to exposed workers were low, below 90 microSv. One waste stream from the manufacturing process was identified: glaze spill to the waste water system, and another is suggested to be 210Po in the flue gases from the high-temperature furnaces.