Evolution of Continuous Melting and Decontamination Technology for Dismantled Metal by an Induction Cold Crucible

An induction cold crucible melting is one of the most promising technologies for the reuse and decontamination of the radioactively contaminated metallic materials generated during the dismantling of nuclear facilities, because the crucible ensures a long life operation without generating secondary wastes. Fundamental equipment of the Melting and Recycling of Metals by Cold Crucible (MERC) process was developed in 1996 and 1997. In the MERC, surrogates of dismantled stainless steel, such as tubings, pipings, plates, bars, channels and mechanical parts, were continuously supplied together with flux for decontamination, followed by melting in the crucible. The melt was precisely withdrawn ensuring the melt dome was kept at a suitable level for the melting process. The maximum withdrawal velocity employed was 12mm/min. Round ingots of 140mm in maximum diameter and rectangular slabs of 50mmx170mm in maximum dimension were cut in 300mm lengths by a lubricant free mechanical saw, followed by slag delamination. They were automatically transported to the outlet of the equipment by a conveying system. The ingots proved to be suitable for manufacturing into shielding material and containers for highly active wastes. Concerning the tracer partitioning using the simulated radioactive nuclides, the following results were obtained. More than 90% of Co and 60% of Mn remained in the ingot. While, more than 85% of Sr, 80% of Hf and 80% of Ce were partitioned to the slag, more than 80% of Cs and 55% of Zn were partitioned to the dust. This work was done under the sponsorship of Science and Technology Agency of Japan.