A Mixed Waste Focus Area technology, developed through funding from DOE's Office of Science and Technology, is generating some heat at several DOE sites: the Graphite Electrode DC Arc Furnace is a high-temperature technology that can treat a wide range of mixed wastes without prior segregation. Adapted from a simple industrial process, the DC Arc Furnace can treat soils, sludges, debris, containers of buried and stored waste, and weapons components. The furnace uses direct current and graphite electrodes to create a high-temperature plasma arc for heating waste to a molten state that cools into a stable glassy or crystalline waste form. Hazardous organics are destroyed in the fire, and the majority of hazardous metals and radioactive components are incorporated into the molten phase. The system's air pollution control system removes particulates from the off-gas.

In connection with the Massachusetts Institute of Technology and Electropyrolysis, Inc., Pacific Northwest National Laboratory demonstrated the large-scale, state-of-the-art arc technology on simulated nuclear wastes. Researchers then modified the design to accommodate the semiremote operation necessary for radioactive processing and constructed a system in radioactive facilities in Hanford. The entire program was conducted over a six-year period. Bill Bonner, a principal investigator on the technology with PNNL, states, “We've worked with the DOE sites to design the system and tested it on an engineering scale to produce data that is useful in solving some of DOE's most difficult waste management problems.”

A series of nonradioactive and radioactive bench-scale tests were completed at PNNL on Idaho National Engineering and Environmental Laboratory radioactive mixed wastes to determine the potential for using the DC Arc Furnace for that waste treatment application. A second waste stream composed of simulated ²³⁸Pu-contaminated job control waste from the Savannah River Site was also successfully tested. These tests helped evaluate the processability of a wide range of feeds and operating conditions before committing to engineering-scale tests.

The technology testing was completed in April 1998, and there are plans to apply the technology to mixed waste from Hanford. Notes Dr. Bonner, “We've been able to integrate our knowledge and experience of radioactive waste treatment with state-of-the-art commercial technology to produce a system for successfully treating DOE wastes. In fact, the program has spawned a thriving small business that is now providing this technology commercially.”

For further information, contact Bill Bonner, PNNL, (509) 372-6263.