Natural radioactivities in iron and nickel ores imported into Japan and the dose assessment for workers handling them

In Japan, Fe and Ni ores are imported from foreign countries to be used as industrial raw materials for manufacturing industrial products like stainless steel. A part of these ores might contain high radioactivity, and then workers handling these ores would be exposed to radiations without being aware of it. Activity concentrations in these ores should be measured to evaluate the radiation exposure of workers. In this study, Fe and Ni ores used as industrial raw materials were collected from iron and steel companies, and the activity concentrations of 238U series, 232Th series and 40K in these ores were determined using ICP-MS and gamma ray spectrometry. The activity concentrations of 238U series, 232Th series and 40K in these ores samples were lower than the IAEA values. The doses to workers handling these ores were estimated using methods for dose assessment given in a report by the European Commission. In each scenario, a maximum value of annual effective doses for them was estimated to be about 6.8  10-6 Sv, which was lower than intervention exemption levels (annual dose: 1.0  10-3 Sv) given in ICRP Publication 82