Abstract
The distribution of cerium (Ce) and uranium (U) in the ingot, slag and dust phases has been investigated for the effects 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 real wastes from the uranium conversion plant in KAERI. The slag former used to remove the contaminants mainly consists of silica (SiO_2), calcium oxide (CaO) and aluminum oxide (Al_2O_3). Calcium fluoride (CaF_2), nickel oxide (NiO), and ferric oxide (Fe_2O_3) were added to provide an increase in the slag fluidity and oxidative potential respectively. The cerium was used as the surrogate of the uranium because the thermochemical and physical properties of the cerium were greatly similar to those of the uranium. The cerium was removed from ingot phase to slag phase by up to 99%. The removal ratio of the cerium was increased with an increase of the amount of the slag former. And maximum removal of the cerium occurred when the slag basicity was 0.82. The natural uranium (UO_2) was partitioned from the ingot phase to the slag phase by up to 95%. The distribution of the natural uranium was considerably dependent on the basicity of the slag former and the composition of slag former. The optimum condition for the removal of the uranium was about 1.5 in basicity and 15wt% of slag former. According to the increase of the amount of the slag former, the distribution of uranium oxide linearly increased due to the increase of the capacity to capture uranium oxide within the slag. Through experiments with the various slag former, we verified that the slag formers containing calcium fluoride (CaF_2) and high silica were more effective for the melting decontamination of stainless steel wastes contaminated with uranium. In the melting tests with stainless steel wastes from the uranium conversion plant in KAERI, we found that the results of the uranium decontamination were mostly similar to those of the uranium oxide.
