Technology Could Whip WIPP Waste

Los Alamos National Laboratory
Kathy DeLucas, (505) 665-9201/[email protected]

NEW TECHNOLOGY COULD WHIP WIPP WASTE

LOS ALAMOS, N.M., April 23, 1997 -- Researchers at Los Alamos National Laboratory are developing techniques for using an ionized gas to remove uranium, plutonium and related radioactive isotopes from contaminated tools, gloveboxes, pipes and other materials.

Since the development of the atomic bomb began in the early 1940s, the U.S. weapons complex has accumulated approximately 256,000 cubic meters of transuranic waste, waste that cannot be disposed of in an ordinary landfill because of its radioactivity.

Transuranic waste refers to radioactive materials that are contaminated with isotopes of uranium and certain isotopes of plutonium, and nuclides with atomic number greater than uranium. It is produced primarily from the chemical processing of spent nuclear fuel and from use of plutonium in the fabrication of nuclear weapons.

The cost of treatment, storage and disposal of transuranic waste varies but can be as high as $71,000 per cubic meter and may involve the creation of significant secondary waste streams. Until now, the waste could not be decontaminated but awaited storage at a site such as the Waste Isolation Pilot Plant.

Los Alamos scientists Phil Chamberlin, Carter Munson, John Fitzpatrick and John Veilleux are using a plasma to etch away the contamination and hopefully leave many materials uncontaminated. The plasma
is created from energy that strips electrons from neutral molecules creating both free electrons and positively charged ions.

The research team uses a bench-top trifluoride gas plasma system to produce fluorine ions that remove up to 99.9 percent of uranium from metal surfaces. For the experiment, graduate student Veilleux places a known amount of uranyl nitrate in a crevice of an aluminum holder and measures the amount of radioactivity with an alpha counter. He then places the contaminated holder into the plasma chamber.

Radio frequency power causes the trifluoride to break apart producing fluorine ions. The ions travel to surfaces where they break uranium's existing chemical bonds and react with it. Once the uranium atom is fully bonded with six fluorine atoms, the now gaseous molecule can be pumped away. This process also applies to plutonium and its sister isotopes that will react with fluorine.

The radioactive metallic gas bound to the fluorine molecules is recovered in a liquid nitrogen-cooled trap. Veilleux introduces a small amount of water or nitric acid so the radioactive gas will react and form a solution or solid when the temperature rises.

In only 15 minutes in the plasma chamber, the metal sample is 66 percent clean. After nearly two hours in the plasma chamber, the metal is nearly completely clean, although the cleaning rates differ depending on certain conditions within the chamber.

Veilleux says the plasma system has many advantages over other treatments, such as acid washes, to remove the contamination. Plasma systems can be operated remotely and do not require direct human contact with the waste. The waste stream is fully recoverable; the uranium can be disassociated from the fluorine and may be used again, if necessary.

"Even if plasma decontamination can be used for only 10 percent of the transuranic waste, taxpayers would save more than $1 billion in disposal fees," Veilleux said.

Researchers hope to continue their study to see if contamination can be removed from the inside of pipes and if all surfaces become clean.

Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.

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