CHARACTERISTICS OF MELTING FOR THE RADIOACTIVE ALUMINUM WASTES FROM THE DECOMMISSIONED NUCLEAR FACILITIES

摘要

The characteristics of an aluminum melting and the radionuclide distribution have been investigated in a muffle furnace and a lab-scale arc furnace as part of the fundamental research for a melting of the metallic wastes generated by dismantling research reactors. The melting of aluminum was carried out with the use of surrogate nuclides such as cobalt, cesium, and strontium and fluxes such as NaCl-KCl-Na_3AlF_6 (Flux A), NaCl-NaF-KF (Flux B), CaF_2 (Flux C), and LiF-KCl-BaCl_2 (Flux D). The effects of the melting temperature and the type of flux on the melting of the aluminum and the nuclide distribution in the ingot, slag, and dust phase were investigated in a muffle furnace. The addition of the flux increased the fluidity of the aluminum melt, which has a slight difference according to the type of fluxes, and the amounts of the slag generated during the melting with the Flux types B and C were larger than those with flux types A and D. The results of the XRD(X-Ray Diffracto -meter) analysis showed that the surrogate nuclides move into the slag, which can be easily separated from the melt, and then they combine with the aluminum oxide to form a more stable compound. The distribution ratio of the cobalt in the ingot phase was less than 20% according to the type of fluxes. A removal efficiency of more than 99.5% for cesium and strontium from the ingot phase could be achieved. Similar results for the slag formation and the distribution of the surrogate nuclides were obtained in a direct current graphite arc melting system. Therefore, it is expected that a greaterrnpart of the aluminum wastes generated from the retired research reactors can be recycled or their volume reduced to be disposed of by a melting.