Residual Cobalt Ratio During Arc Plasma Melting Treatment of Low Level Radioactive Wastes Containing Nickel

The plasma melting treatment of low level radioactive waste is currently in practical use. This treatment is applied to typical radioactive wastes such as carbon steel and concrete to produce a solidified product. The scaling factor method is used to evaluate the concentrations of radio-nuclides in the product. Because cobalt (Co) plays a particularly important role, it is important to clarify the behavior of Co during the treatment. In this report, we investigated the residual Co ratio in the slag produced during the plasma melting treatment of a nickel alloy. We found that a residual Co ratio of less than 10% was achieved in the slag when a Ni concentration of less than 80 wt% and a Fe concentration of more than 20 wt% was kept in the molten metal. The effect of the reduction of Co oxides by Fe on the residual Co ratio was the most dominant among the Co oxidation/reduction reactions occurring in the molten melt.