Occupational exposure to natural radioactivity in the zirconium mineral manufacturing industries

The spanish 'Real Decatur 783/2001', published as result of the adaptation of the European Council directive 96/29/EURATOM (B.S.S. directive), regulates in Spain the use of natural radioactive substances. This decree establishes the need to study and control those activities in which significant increases of the exposure of workers or members of the public could take place. One of these natural radioactive substances are zirconium minerals. They are widely employed in some industrial activities, such as the production of zirconia and zirconium chemicals, glazed ceramic products manufacture, refractories, foundry sands (including investment casting) and zirconium mineral manufacturing. Its major end uses are fine ceramics where it acts as an opacifier in glazes and enamels and also as an additive in special glass (i.e. TV glass). This paper provides a description of a measurement campaign carried out to estimate the risk of occupational exposure to natural radioactivity in the zirconium mineral manufacturing industries. Zirconium raw sands have generally a granular size of 100 to 200 μm, which may be reduced to around 2 μm for use in ceramics and paint applications by milling to flour. These sands contain varying concentrations of natural radionuclides: 232Th,235U, and mostly 238U, together with their progenies. The first part of the study is to identify situations and areas where worker s are exposed to radiation. Five pathways of exposure were found: inhalation of dust, ingestion of dust, inhalation of radon, skin contamination and external irradiation. Samples from raw materials and from the environment at the work areas are performed; both where the zircon sands are unloaded and stored and at the milling area. Secondly, collected samples are analysed to evaluate activities on those natural radionuclides. Gamma spectrometry analysis is performed for the whole of the samples. For this purpose, a Ge-HP detector (high purity Ge detectors) is used. Dust samples from environment are analysed for measurement of 210Pb and 210Po as well. 210Pb is quantified by a beta measurement in a low background proportional counter, while a Si-surface-barrier alpha detector is used for Po- 210 spectrometry. Finally, an estimation of the radiation dose received by workers is performed, based on the previous measurements. External exposure is caused prevalently by gamma radiation from radionuclides in the 238U and 232Th series. Internal exposure is linked to radionuclides intake, mainly thought inhalation of 222Rn, its short-lived decay products, 210Pb and 210Po. (authors)