Radionuclide fluxes at a plant manufacturing dicalcium phosphate for domestic animals

The objectives of this study is to map out the fluxes of radionuclides from the 238U decay series as well as estimate doses to workers at a dicalcium phosphate plant. At the studied plant phosphate rock is used for the production of dicalcium phosphate, which is a source of calcium and phosphorous for domestic animals. A by-product in the manufacturing process is calcium chloride which is used in the oil industry, food industry and as road salt. In the phosphate rock, the radionuclides were found in secular radioactive equilibrium with an average activity concentration of 830 Bq·kg-1. Separation and concentration processes was observed. Most of the 226Ra was found in the calcium chloride while the major part of 238U was found in the dicalcium phosphate, about 950 Bq·kg-1. The annual occupational effective dose to workers was found to be below the 1 mSv limit. The study shows a good example of an important non-nuclear industry with a high input of natural radionuclides and several conceivable pathways to man. (author)