Immobilizing nuclear waste the focus of WSU research

By Will Ferguson, College of Arts & Sciences

WallRICHLAND, Wash. – New research at Washington State University could help in the design of long-term nuclear waste storage facilities and make it easier to clean already contaminated areas.

GribatNathalie Wall, assistant professor of chemistry, and Larissa Gribat, chemistry doctoral candidate, are investigating ways to contain technetium (Tc), a radioactive element produced during the burnup of uranium fuel.

“Tc remains radioactive and an environmental concern for thousands of years,” Wall said. “If we put Tc in a repository we want to keep it there indefinitely. This work will help make this possible.”

Wall and Gribat’s findings will be helpful toward remediating contamination in areas like the Hanford nuclear site in southeastern Washington and other U.S. Department of Energy (DOE) facilities.

Getting waste to stay put

A toxic stew of nuclear waste sits in underground storage tanks at Hanford, the relic of four decades of plutonium production – from the Manhattan Project, during World War II, to 1987, when Hanford’s last reactor powered down.

The effort to clean up Hanford’s radioactive waste is one of the most expensive and challenging remediation projects in U.S. history, already costing upwards of $30 billion. The DOE projects remaining cleanup will cost $112 billion over the next 50 years.

An especially critical challenge at Hanford and other nuclear-contaminated sites is preventing waste from leaking into soil and groundwater. Radioactive elements, which can cause serious health problems for people and animals, take thousands or even millions of years to naturally decay. They can spread via groundwater to vitally important fresh water resources – in the case of Hanford, to Washington’s Columbia River.

Wall and Gribat are investigating how technetium interacts with naturally occurring iron minerals and microbes in the soil. Their goal is to figure out the precise combination of these materials that causes Tc to switch between a form that moves readily through the environment and one that stays put.

Similar but not the same

Tc has several different forms, called oxidation states, that determine how readily it spreads through the environment. Previous lab research shows that, when exposed to iron, the element can switch between Tc(VII), a very water-soluble oxidation state that spreads easily through the subsurface, to Tc(IV), a more water-insoluble and immobile oxidation state.

“Iron was supposed to be the barrier Tc couldn’t get around,” Wall said. “However, we now know iron by itself does not completely stop the spread of Tc in the environment.

“We are trying to figure out the specific combination of iron minerals and their environment that causes Tc to switch from a form that spreads easily to one that is containable. If we can do this, it will help engineers design better repositories and remediation tools.”

Wall and Gribat received funding from the DOE and U.S. Department of Defense to gather this much-needed data through a combination of radiochemistry, electrochemistry and inorganic chemistry. They are conducting their research at the Pacific Northwest National Laboratory’s Environmental Molecular Sciences Laboratory in Richland, Wash.

Safety training to handle materials

Gribat has worked with Tc throughout her Ph.D. work in the WSU radiochemistry program. She received training in the safe use of radioactive materials at the Radiation Safety Office at WSU Pullman and said her experiments involve the smallest amount of radioactivity possible to get research results for publication.

“After a while the safety procedures become second nature,” she said. “However, no matter what work a chemist is doing, it is essential to stay focused and pay attention to what is happening right then.

“There are scientists who work with dangerous and contagious viruses,” she said. “For me, this work seems very safe in comparison. It is all in the eye of the beholder.”