Occupational exposures in the phosphate fertilizer industry located at Huelva (south-western Spain)

摘要

The Spanish Government implanted the 96/29/EURATOM directive in 2001, where it was regulated the sanitary protection against ionizing radiations. Some applications of these regulatory rules might affect to the industries that are devoted to the phosphoric acid production. This possibility is founded on the presence of high uranium concentrations (about 100-150 μg/g of U) and other radioactive elements in the commercial sedimentary phosphate ore, which is used as raw material by acid phosphoric factories. A major fraction (about 80 %) of uranium present in the phosphate rock is dissolved with sulphuric acid and remains associated to the acid phosphoric and fertilizers. A ~(238)U-daughter, ~(226)Ra, is also present in the phosphate rock. This radionuclide, which is important from a radiological viewpoint, is conveyed, associated to the phosphogypsum (PG), to air opened piles around the factories. The PG is a by-product coming from phosphoric acid production that presents high amounts of natural radionuclides such as ~(226)Ra and ~(210)Po. Although the origin and distribution of those radionuclides has been well studied, there is a lack of information on the radiation exposure levels in workers of phosphoric acid factories. This paper presents our preliminary results on radioactive doses received (external and inhalation pathways) by workers involved in a phosphoric plant of an industrial complex in Huelva, South-West of Spain. This research must be extended in the frame of a wide research project, where two industrial complexes are studied. Four different plants form the phosphoric acid factory studied. Several sections are considered in every plant according to the chemical process most representative. The external dose rate was measured in every section. The dose rate is expressed as an increment over the natural background level of the surrounding area, being the obtained values generally from 0 to 12 mSv/y. To know the exposition received by workers, of course, previous dose rates have to be corrected by the corresponding occupation factors. In these cases, the occupational factor was around cero, and therefore their dose contributions to workers must be considered negligible. According to our results, the application of the 96/29/EURATOM directive to phosphoric acid industry can affect to occupational factor in some working locations inside the factories. Thus, some specific areas should be considered as controlled zones, e.g. the sections where the filtration processes are developed. However, the outdoor areas around the plant present natural background levels. Then, the own facilities act as a shielding for this radiation sources.