More plutonium studies urged

Monday, Jan. 31, 2000 | 11:27 a.m.

A nuclear engineer is calling for more research on chemical changes in stored plutonium that may allow the radioactive material to dissolve and perhaps travel in water -- a recent finding that could have a serious impact on both the future of aging nuclear weapons and the burial of high-level nuclear waste at Yucca Mountain.

Gary Cerefice of UNLV's Harry Reid Center for Environmental Research said the subtle changes to the toxic metal plutonium, found in nuclear weapons, nuclear reactors and irradiated reactor wastes, are not well understood.

Scientists recently discovered in a laboratory that a change occurs in plutonium that resembles rust forming on a car's bumper, Cerefice said.

This potentially unstable form of plutonium discovered by Energy Department scientists and others was important because no one had observed such changes in the radioactive element in 60 years, Cerefice said on Friday.

"This may provide a new path for plutonium to dissolve," Cerefice said during a health physics seminar at UNLV.

Scientific concern about changes in the plutonium is focusing on what happens to the element's cores at the heart of nuclear weapons, he said. Experts are asking how fast the changes occur. Water, liquid or vapor are needed to change the plutonium's form and color, and it may take time.

But the change may occur fast, and that's what has scientists worried.

They are now looking at whether aging, stockpiled weapons would explode as designed if the plutonium changes, Cerefice said. If changes to the plutonium occur faster than expected, weapons would have to be remade and it will cost the Defense Department much more money, he said.

On the other hand, nuclear waste experts are wondering what happens as plutonium changes if it is buried 90 miles northwest of Las Vegas inside Yucca Mountain for thousands of years. The mountain is the only site singled out by Congress for study as the world's first high-level nuclear waste repository.

"From a scientific view, I'd love to know what's going on," said Cerefice, who studied what to do with plutonium cores removed from nuclear weapons as a graduate student at the Massachusetts Institute of Technology.

The DOE estimates that only a few to no plutonium particles will flow through ground water at Yucca Mountain, Cerefice said, but with the latest discovery about the element's shape-shifting, more studies are necessary.

The new research could explain, however, how plutonium particles from a 1960s-era underground nuclear explosion at the Nevada Test Site traveled a mile from the site in 30 years.

Yucca scientists are well aware of the potential problem with plutonium, and heightened research is continuing at Los Alamos National Laboratory in New Mexico.

"Of course, we will stay tuned to the ongoing work and its results, but we see no impact on the repository from what has been done so far," DOE technical coordinator Abe van Luik of Nevada's Yucca Mountain Project Office said.

The form of plutonium mentioned in the recent Science article is not coming to Yucca as it is planned, van Luik said. And the DOE's computer models for Yucca have already taken into account changes in plutonium over time, he said.

Plutonium metal is one the the most studied elements, UNLV chemist Vernon Hodge said. Hodge has studied plutonium particles riding tiny bits of matter called colloids since 1969.

The potential for microscopic plutonium particles to escape a corroded container buried in a repository at Yucca is under study by the DOE, nuclear consultant David Stahl said.

The DOE wants to know if particles from plutonium in commercial reactor wastes could escape corroded containers buried in the repository and travel in ground water, Stahl said.

To bury plutonium, the DOE will first turn the pure metal into nuclear reactor fuel or into a stable form that looks like a ceramic hockey puck. Then five to 10 of them will be sealed inside a can stacked like tennis balls.

The cans will be placed inside four or five ceramic containers that hang like ornaments on a Christmas tree inside a larger package. The package is then expected to be filled with molten glass at DOE's Savannah River plant before being shipped to a repository.