Graphite Electrode DC Arc Furnace at the Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID

Site Name:

Idaho National Engineering and Environmental Laboratory

Location:

Idaho Falls, ID

Period of
Operation:

1997-1998

Cleanup
Type:

Bench-scale studies and engineering-scale furnace (ESF) tests

Technology:
Graphite Electrode DC Arc Furnace
- ESF system included the furnace, power control systems, feed systems, off-gas system, and control system
- ESF - 3.5 ft diameter by 4 ft high stainless steel vessel enclosing the furnace hearth; graphite crucible was lined with Monofrax K-3 refractory; four graphite rods threaded into the crucible; layers of porous graphite, firebrick, and refractory material surround crucible; nitrogen used to prevent oxygen from attacking the graphite crucible
- ESF included penetrations for glass overflow discharge, furnace offgas, and pyrometer access; overflow section heated to temperatures as high as 1,500C to keep glass molten for pouring
- Outer walls of furnace equipped with air cooling jacket and two cooling coils - to prevent glass migration throughout refractories and insulation
- Bottom drain - inductively heated/freeze-valve bottom drain for removing metals and/or slag from the bottom of the furnace
- Bench-scale testing included 43 nonradioactive waste tests and 5 radioactive waste tests
- Two ESF tests conducted in FY 1997 - one using feed spiked with heavy metals and with plutonium surrogates; one using nonradioactive debris
- First test feed rate was about 5 kg/hr and about 320 kg of feed material was processed over an 86-hour period; operational problems caused furnace to be shut down during second test
- One ESF test conducted in FY 1998 on Pantex neutron generators - process 150 neutron generators over a 21-hour period at a rate of 27 lbs/hr

Cleanup Authority:
RCRA and NRC

Principal Investigator:
Ronald Goles
Battelle, Pacific Northwest
National Laboratory
P.O. Box 999, MS K6-24
Richland, WA 99352
Telephone: 509-376-2030
Fax: 509-376-3108
E-mail: rwgoles@pnl.gov
MWFA Product Line Manager:
Whitney St. Michael
Mixed Waste Focus Area
Lockheed Martin
Idaho Technologies Company
Idaho National Engineering
and Environmental Laboratory
2525 N. Freemont
Idaho Falls, ID 83415
Telephone: 208-526-3206
Fax: 208-526-1061
E-mail: whitney@inel.gov

Contaminants:
Metals, Radionulcides
- Plutonium-238 and heavy metals including lead

Waste Source:
Waste streams and surrogates from various DOE facilities

Type/Quantity of Media Treated:
- INEEL wastes including soils, high metal wastes, organics/oils/solvents, and debris
- Slag from Rocky Flats
- Plutonium-238 waste from SRS
- Neutron generators (tritium and lead) - about 150

Purpose/Significance of Application:
Determine potential applicability of DC arc plasma furnace to treat a variety of wastes from DOE facilities

Regulatory Requirements/Cleanup Goals:
RCRA Land Disposal Restriction criteria for metals and NRC disposal criteria

Results:
- The first 1997 test performed as planned with minor problems such as failure of the overflow heater, which was corrected; produced a uniform, homogeneous vitrified product with a low leach rate for TCLP metals; the behavior of Plutonium-238 was identical to that of Plutonium-239, with the majority of the plutonium partitioning in the glass phase
- During the second 1997 test, the furnace failed as a result of current firing through a fracture in the sidewall; the system was shut down and repaired
- 1998 test results showed that the ESF was capable of processing neutron generators, with the resulting glass form passing the TCLP test for metals; however, approximately 75% of the available lead partitioned to the offgas system (attributed to the glass collection problem) and 85% of the available tritium was released through the process stack
- Operational problems with the 1998 test included the inability to operate the bottom drain of the melter and the need to operate in a continuous overflow mode, causing problems with glass collection
- In general, high water content in sludges (30wt%) increased electrode corrosion, caused problems with feeding via the solids auger and caused water to collect in the off-gas system

Cost Factors:
- Projected cost for full-scale - $50 to $80 million capital cost; operating costs of $12 to $18 million through the startup period and $48 to $62 million for a five year operating period
- Projected treatment and disposal costs - $7,400 to $10,800 per cubic meter, based on 17,000 cubic meters of waste
- Total life cycle costs estimated to be $124 to $184 million

Description:
A series of bench-scale tests using radioactive and nonradioactive wastes were conducted at INEEL to determine the potential for using a DC Arc Furnace for waste treatment. Several types of wastes were tested including Rocky Flats Pondcrete (slag); INEEL soils, high metals wastes, organics/oils/solvents; and debris; and an SRS 238Pu contaminated debris waste. A DC Arc ESF system, including the furnace, power control systems, feed systems, off-gas system, and control system, was used for two sets of tests of radioactive and nonradioactive wastes in 1997, and to test the ability to process neutron generators in 1998.

The results of the first 1997 test showed that the DC Arc Furnace could produce a solid, homogenous glass form that met the TCLP criteria for metals. The system was then shutdown during the second test when the furnace failed. Following repairs, the system was shown to be capable of processing neutron generators, with the glass form meeting the TCLP limits for metals. However, several operational difficulties led to the partitioning of a majority of the primary contaminants (tritium and lead) to the off-gas. Since these demonstrations, several design improvements have been made to the prototype system, including a second generation melter and improvements in the feed system and off-gas treatment systems.