Melting Decontamination of Radioactive Scrap Metal by Graphite Arc Melter

Abstract

The partitioning phenomena of radioisotope cobalt-60 (60Co) and cesium-137 (137Cs) from a molten ingot, slag, and dust have been investigated for the effect of the slag type, slag concentration and basicity in a plasma arc melting process. A direct current plasma arc furnace was used to melt contaminated stainless steel, and mild steel with an acid, neutral, and basic slag (SiO2, CaO, Al2O3, Fe2O3, MgO) containing radioactive 60Co and 137Cs, to measure the partitioning phenomena. Calcium oxide and ferric oxide were added to provide an increase in the slag fluidity and oxidative potential, respectively. Most of the 60Co remained in the ingot phase and was barely present in the slag. 60Co decontamination factor was not highly dependent on the slag composition. The distribution ratio of 60Co the ingot and the slag phase showed that about 90% to 95% was recovered in the ingots. 137Cs was completely eliminated from the melt of the stainless steel as well as the carbon steel, and was distributed to the slag and dust phase. The partition remaining in the slag depended on whether the slag was basic or acidic and had a high oxidative flux (Fe2O3). A maximum of 52% of the 137Cs remained in the slag phase with an acid slag.