ORNL Pit Number 1 is located in a burial ground containing seven pits and trenches used for ORNL's Graphite Reactor. All seven pits were used for waste disposal. The burial site is located a couple of miles from the main ORNL complex.
As electricity is applied to the electrodes, the current will heat a graphite and glass frit starter path that is on the ground between the electrodes and will begin melting the soil. When molten, the soil will become electrically conductive, spreading the melt zone down and out through the contaminated soil. The electrodes will move down into the soil, advancing at a rate of one to two inches each hour, to a depth required to heat 50 to 75 percent of the pit (a maximum of 20 feet).
Soil and waste in the pit will reach temperatures of 1,600 to 2,000 degrees Celsius during the melt. Contaminated wastes will be destroyed through pyrolysis, a process that decomposes organic contaminants without oxygen. Solid organic material will also be decomposed during soil melt processing. The inorganic portion of the soil will typically break down into major oxide groups, such as silica and aluminum. Radioactive material in the pit will be immobilized.
When the target volume has been melted, the current will be turned off and the electrodes cut off at the surface of the melt. Because the glass forms a cap at the surface, part of the electrodes will remain in the glass. Gases produced during the process will be collected through an off-gas hood, then piped to the off-gas treatment system. There, acidic gases and large particles will be removed. After the gas is cleaned and filtered, it will be released to the atmosphere.
It will take 150 to 200 hours or about two weeks for the mass in the pit to harden. During the process the volume of soil in the pit will be reduced from 25 to 45 percent.
The strength of the ISV obsidian-like material averages about ten times the strength of unreinforced concrete. Since it is similar to natural obsidian, scientists believe it has a mean life of 18 million years. Tests performed by the U.S. Environmental Protection Agency have shown that the material is unaffected by freezing and thawing or wet and dry weather exposure. EPA tests have also shown that the ISV obsidian is not toxic to plants and animals.
ISV was invented in 1980 by scientists at the Battelle Pacific Northwest Laboratory for the U.S. Department of Energy. The technology is patented in the U.S., Canada, the United Kingdom, Germany, France, Italy, and Japan. Geosafe Corporation in Richland, Washington, has been sublicensed to commercialize the technology.
Since its development, ISV has been tested more than 190 times at various scales, including bench, engineering, pilot, and full-scale. It has been used to treat a wide range of hazardous materials, including heavy metals, organics, and radioactive materials.
ORNL will work with scientists from Battelle Pacific Northwest Laboratory to immobilize 50 to 75 percent of the material in Pit Number 1. If successful, the project will be expanded to immobilize the entire pit.
More information on DOE's In-Situ Remediation Integrated Program can be found on the Internet at http://sc94.ameslab.gov/OTD/tech_summs/In_Situ_Rem/In_Situ_TOC.html .
