The international process for immobilization of high-activity waste from aqueous fuel reprocessing is vitrification. In the United States joule-heated melter technology has been implemented at West Valley and the Savannah River Site, but improved melter concepts are sought to bring down the costs of processing. The cold-crucible induction melter (CCIM) design is being evaluated for many applications, including radioactive wastes because it eliminates many materials and operating constraints inherent in the baseline technology. The cold-crucible design is also smaller, less expensive, and generates much less waste for ultimate disposal. In addition, it should allow a much more flexible operating envelope, which will be crucial if the heterogeneous wastes at the U.S. Department of Energy (DOE) reprocessing sites are to be vitrified.
A joule-heated melter operates by passing current between water-cooled electrodes through a molten pool in a refractory-lined chamber. This design is inherently limited by susceptibility of materials to corrosion and melting. In addition, redox conditions and free metal content have exacerbated materials problems or lead to electrical short-circuiting causing failures in developmental DOE melters. In contrast, the CCIM design is based on inductive coupling of a water-cooled high-frequency electrical coil with the glass, causing eddy currents that produce heat and mixing.
While significant marketing claims have been made by technology suppliers and developers, little data is available for engineering and economic evaluation of the technology, and no facilities are available in the United States to support testing. In addition to verifying the capabilities of the technology, further development can exploit opportunities for optimization through better understanding of the electromagnetic thermal phenomena intrinsic to the cold-crucible melter. Induction frequency, applied power, and coil and crucible configuration are all related but independent variables that can be explored to optimize throughput while designing a system for maximum reliability in a remote environment. This paper is an introduction to the technology as it applies to vitrification of materials not electrically conductive at ambient temperatures, the potential for research improvements, and the new system being built at the Idaho National Engineering and Environmental Laboratory.