Bench-scale arc melter for R&D in thermal treatment of mixed wastes

Abstract

A small dc arc melter was designed and constructed to run bench-scale investigations on various aspects of development for high-temperature (1,500-1,800°C) proccssing of simulatcd transuranic-contaminatcd waste and soil located at the Radioactive Waste Management Complex (RWMC). Several recent system design and treatment studies have shown that high-tempcrature melting is the preferred treatment. The small arc melter is needed to establish techniques and procedures (with surrogates) prior to using a similar melter with the transuranic-contaminatcd wastes in appropriate facilities at the site. This report documents the dcsign and construction, starting and heating procedures, and tests evaluating the mclter's ability to process several waste types stored at the RWMC. lt is found that a thin graphite strip provides reliable starting with initial high current capability for partially melting the soil/waste mixture. The heating procedure includes (1) the initial high current-low voltage mode, (2) a low current-high voltage mode that " commences after some slag has tbrmed and arcing dominates ovcr the receding graphite conduction path, and (3) a predominantly Joule heating mode during which thc currcnt can bc increased within the limits to maintain relatively quiescent operation. Scvcral experiments involving the melting of simulated wastes arc discussed. Energy balancc, slag tcmpcraturc, and electrode wear mcasurements are presented. Recommendations for further refinements to enhance its processing capabilities are identified. Future studies anticipated with the arc melter include waste form processing development; dissolution, retention, volatilization, and collection for transuranic and low-levcl radionuclides, as well as high vapor prcssure metals; clcctrode material development to minimize corrosion and erosion; refractory corrosion and/or skull formation effects; crucible or melter geometry; metal oxidation; and desirable melt reduction/oxidation (redox) conditions.

Group IVB oxide enhancement of the iron‐enriched basalt waste form

“…Heats between 8 and 10kg can be produced routinely in about an hour; details of the design and operation of the arc furnace are covered in another report [11]. The soil/waste combinations used for this study were melted in a water-cooled, stainless steel vessel.…”

Improving iron-enriched basalt with additions of ZrO{sub 2} and TiO{sub 2}

“…Details of the design and operation of the arc furnace are covered in another report. 26 The furnace uses carbon electrodes, and the combination of both the heat of the arc .…”