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Release Date: October 21, 1994
Media Contact: Media & External Communications, (509) 375-3776
NEW LAB LOOKS TO MOLECULES FOR WASTE SOLUTION
RICHLAND, WA -- Winning World War II and the Cold War meant meeting some extraordinary scientific challenges, but cleaning the mess left behind from those battles will require the same sort of scientific innovation.
While it played a major role in defeating Japan in 1945 and staring down the Soviet Union afterward, the Hanford Site in southeast Washington also generated hundreds of millions of gallons of highly radioactive waste during its 50-year history of producing nuclear materials. Today, nearly 60 million gallons of the most toxic materials are stored in 177 aging underground storage tanks at Hanford. The tanks include large amounts of liquid, salted with smaller amounts of cesium, strontium and other radioactive isotopes.
Currently, cost-effective technology does not exist to safely empty and store the tanks' contents. But computer scientists and chemists at a new U.S. Department of Energy laboratory in Richland, Washington, are investigating a possible solution.
Researchers at the new Environmental Molecular Sciences Laboratory, which is operated for DOE by its Pacific Northwest Laboratory, are looking at the possibility of using molecules known as crown ethers to bind to highly radioactive pollutants such as cesium and strontium. Scientists believe that once the crown ethers attach themselves to the radioactive isotopes, the molecules could be used to separate the highly radioactive contaminants from the large volume of liquid waste.
The small amounts of cesium and strontium then could be disposed in a long-term repository for high-level waste while the remaining water, now considered low-level waste, could be treated and disposed in a more economical fashion. According to the EMSL researchers, such a method would significantly decrease the cost and time of environmental cleanup activities at Hanford and at several other contaminated sites in the United States.
"It's a very complicated problem," explains Dr. Mark Thompson, a chemist at the EMSL. "To be effective in waste treatment, a crown ether must have affinity, selectivity and reversibility. It must have high affinity to bind with a target radionuclide, the selectivity to seek out the radionuclide in an environment that includes other molecules competing for its attention and it should be able to be reused."
One crown ether, called 18-crown-6, has been widely studied and is known to have a preference to bind to potassium in water. "It's quite possible that a derivative of this or some other crown ether might have an affinity for cesium or strontium," says Dr. David Feller, another chemist at the EMSL. "In fact, one 18-crown-6 derivative, called dicyclohexano-18-crown-6, has been found to be effective in separating strontium from acid waste streams but it's not as efficient as what would be necessary for treating tank wastes."
In the past, organic chemists in the laboratory would have to use trial and error to locate an effective crown ether derivative -- a process that could take years or even decades. Instead, EMSL chemists will be using computer modeling techniques to narrow the field of possibilities from several thousand to a handful of likely candidates.
The research team is using both quantum mechanical and classical mechanical methods to model the behavior of 18-crown-6, the most well-known crown ether.
"First, we have to understand how water and solvents interact with a known crown ether before we have enough knowledge to suggest possible crown ether derivatives that might bind to radioactive isotopes," explains Dr. Eric Glendening, a post-doctorate researcher at the EMSL. "To date, we have been successful in reproducing in a computer what we observe in the laboratory -- that 18-crown-6 has a preference to bind to potassium in small amounts of water. This has helped us calibrate our methods."
But before researchers can look for possible derivatives to tackle radioactive isotopes or even examine how 18-crown-6 binds to potassium in large amounts of water, they'll have to have access to the next generation of supercomputers -- massively parallel computers capable of performing advanced modeling of molecular processes.
"Our model calculations for 18-crown-6 and potassium are at the very edge of what is feasible using a combination of the fastest Cray supercomputers and high-speed workstations," explains Feller. "Today's computers can't do the calculations fast enough. One calculation can take as long as a month. We're going to need the next generation of machines."
This next generation will be arriving soon at the EMSL, and software engineers at the laboratory are already at work designing software that may reduce the month-long calculation to a day. "These machines will allow us to make calculations of this magnitude routine," says Feller.
Two papers on the group's work to date will be published in the Journal of the American Chemical Society and the Journal of Physical Chemistry this fall.
The $230-million EMSL is currently under construction in Richland. Researchers are using interim facilities at PNL until it is complete in 1997. When finished, the 200,000-square-foot EMSL will house up to 270 permanent staff, visiting scientists and students who will work to develop the science and technology needed to clean up environmental problems at government and industrial sites across the country. Research conducted at the national user facility also is expected to lead to advances in energy, new materials, health and medicine, and agriculture.
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