The "canyons" at Savannah River Site have a name that conjures images of a narrow valley in nature, often with a stream of crystalline water flowing through the divide.
But the word has an altogether different meaning at the site - one that involves gargantuan steel tanks, plutonium and a very involved chemical separation process.
Two of the most prominent facilities on the site's landscape are the two canyons, named F and H. Inside the canyons, nuclear materials are chemically separated, and usable materials are isolated from waste that is treated and buried, sent to steel tanks or discarded in other ways.
Thick concrete walls contain the canyons' operations. Long, wide troughs run through the center of each facility, creating the shape of a "canyon" if imagined without roofs.
In the 1950s, the canyons were built to separate plutonium and uranium from waste products, with design principles used at Hanford Engineer Works, an older production site in Washington state, similar to SRS.
The logic was to have a remote, concrete-shielded operation that could contain the highly radioactive solutions and protect workers against exposure to radiation.
Work is scheduled to continue through 2002 in one canyon and through 2006 in the other.
"There are studies around the Energy Department complex to ensure that no other materials are left to process, and the government will make a decision on that, and it hasn't been made just yet," said Judy Spencer, a spokeswoman for Westinghouse Savannah River Co. Westinghouse operates SRS under contract with the Energy Department.
The canyons have always isolated plutonium and other materials, but the missions for which that plutonium is used have varied over the years.
"Previously, the canyon was a major source of plutonium for the weapons stockpile," Ms. Spencer said. "But since the Cold War ended, we are cleaning up legacy material. And we are storing it for future disposition. It's going to be determined with the government what that will be."
In the early 1990s, SRS supplied plutonium for NASA's Cassini mission, an unmanned expedition to Saturn, traveling 1 billion kilometers from Earth.
The canyons provided the 72 pounds of plutonium needed to power the spacecraft's generators for the seven-year mission.
Such projects historically have fueled protests from many who oppose the use of plutonium as an energy source and weapon-building material.
Those who staged protests against NASA's Cassini mission said that if there were an accident after takeoff, the plutonium could be released into Earth's atmosphere and poison millions.
"I wasn't opposed to the mission. I thought that an enormous amount of plutonium was put aboard the mission without proper exploration of alternate power sources," said Arjun Makhijani, president of the Institute for Energy and Environmental Research. "And there was haste to put that much plutonium out into space in the way that they did.
"The amount of plutonium on Cassini was somewhat greater than the total amount of all nuclear weapons testing ... on that one flight."
Dr. Makhijani said the material used in weapons is plutonium-239 and the material in batteries aboard the NASA flight was plutonium-238 - a substance that is much more radioactive.
NASA and those who supported the use of the plutonium for the mission argued that the risk was small.
Maintaining equipment in the canyons has proved to be a challenge, and hazardous for some employees. For example, cranes used in the canyons are exposed to contamination during the process. Hands-on maintenance and repair is required for the cranes, and during that work some of the employees have had the highest exposure to radiation.
The cranes have been waterproofed and made corrosion-resistant to reduce radiation exposure.
Reach Clarissa J. Walker at (706) 828-3851.