The Glass Sealing

It's a slow-motion horror movie: Nuclear waste leaks from underground storage shafts and seeps toward a river, where it contaminates drinking water used by millions of people. That's exactly the scenario unfolding at the Hanford Nuclear Reservation in rural Washington State.

The solution, too, sounds like a page ripped from a Hollywood screenplay: Insert two industrial-strength electrodes deep into the ground, and melt the soil-along with everything around it-into solid glass, trapping the toxic waste for thousands of years.

The U.S. Department of Energy is now testing the melting process-known as subsurface planar vitrification, or SPV-at Hanford on waste that threatens to leach into the Columbia River. The problem stems from
144 leaky disposal shafts, which were used
in the 1950s and ´60s to store paint-can-size barrels of nuclear waste.

Although SPV was invented in the 1990s, a British company, AMEC, recently pioneered the most efficient and commercially viable approach. With a $4-million contract from the DOE, AMEC plans to melt the first Hanford shaft by late this summer. For seven to 10 days, the graphite electrodes will heat the ground to temperatures of 1,700C, melting, or vitrifying, the waste and surrounding soil into a viscous mass. When cooled, the mixture will harden into black glass. Eventually this material will be dug up, packaged, and sent to a government waste site near Carlsbad, New Mexico, for permanent storage. AMEC says the glass is extremely stable and a million times as resistant to leaching as cement. If the project works, AMEC could end up melting the other 143 plutonium-contaminated tunnels on the site.

"The process either destroys the contaminants or locks them into the glass,†says AMEC's Leo Thompson, who is the project´s division manager. They can't go anywhere, so they can't hurt anybody.â€


HOW THE MELTING PROCESS WORKS

1.Two solid-graphite
electrodes, each about 30 feet long, are inserted into
the ground. These devices deliver up to four megawatts of electricity, depending on how much melting is needed.

2.Engineers pressure-inject a four-foot-tall sheet of graphite flake between the electrodes. The superheated flake melts the waste and its surroundings.

3.Situated above the waste-filled shaft, a containment hood keeps the electrodes from moving once the melt begins, and channels radioactive fumes into a filtering system, which removes toxic elements.

4.After seven to 10 days of 1,700?C heat, the area around the shaft becomes a molten mass. Once the electricity is turned off, this gel-like goo cools into solid glass, encasing any remaining waste for tens of thousands of years.