Radioactivity Assessment in Phosphate Industry Facilities: The OCP Group's Experience

Phosphorus (usually expressed as P2O5) is one of the main elements used in fertilizer manufacture. Twenty five percent of the fertilizer consumed in the world uses P2O5. Phosphate ore is a vital raw material for the production of fertilizers. It contains, in addition to P2O5, a multitude of other elements, some of which are radioactive. The radionuclide decay chains are approximately in equilibrium. During fertilizer production, the chemical transformation causes a new distribution of radionuclides among the different phases: phosphoric acid, phosphogypsum, fertilizers and deposits (scales); this depends on the chemical behaviour of each element in phosphoric acid. Studies have shown that the radioactivity content of deposits inside tubular and other process equipment (including pipes carrying phosphoric acid) is mainly due to the presence of radium and its decay products (226Ra, 214Pb and 214Bi). Hence, radiation doses increase in the vicinity of this equipment. In order to control exposure, regular measurement campaigns have been undertaken across the entire facility. This has allowed a detailed map of dose distributions to be established. A washing solution has been developed that effectively dissolves radioactive scales, thus substantially reducing radiation doses down to low levels. This paper describes the approach followed and the results achieved. (author)