Distribution of Cobalt between MgO-Saturated FeO_x-MgO-CaO-SiO₂ Slag and Fe-Cu-Co Molten Alloy

抄録

During the decommissioning phase of a nuclear reactor, most of the steel-reinforced concrete shielding around a pressure vessel is considered as low-level radioactive waste. It is highly desirable to reduce the radioactivity level of this waste to below the clearance level. Normally, the radioactivity of steel after irradiation is found to be proportional to the cobalt content. In this study, for the production of low-activation steel in steelmaking process, cobalt distribution between MgO-saturated FeO_x-MgO-CaO-SiO₂ slag and Fe-Cu-Co molten alloy was investigated. The results are summarized as follows: (1) the distribution ratio increases with decreasing temperature and (2) the activity coefficient of CoO decreases with increasing temperature and decreasing slag basicity. Although low temperature and low basicity are suitable conditions for refining, it is extremely difficult to decrease the Co content by an oxidation reaction, because of a very small distribution ratio of cobalt.