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Washington State University
CAS Connect February 2015

Promising breakthrough in radioactive waste cleanup

A toxic stew of nuclear waste sits in underground storage tanks at the Hanford Nuclear site in southeastern Washington. It is the relic of four decades of plutonium production that started when the Manhattan Project produced the first atomic weapon, in the middle of World War II, to 1987, when Hanford’s last nuclear reactor powered down.

Radioactive waste from Hanford's 209-E Criticality Facility awaits disposal.
Radioactive waste from Hanford’s 209-E Criticality Facility awaits disposal.

The effort to clean up Hanford’s radioactive waste is one of the most expensive and challenging remediation projects in U.S. history. To date, the project has cost upwards of $30 billion. The U.S. Department of Energy estimates the remaining cleanup work at Hanford will cost $112 billion over the next 50 years.

An especially critical challenge at Hanford and other nuclear-contaminated sites is preventing nuclear waste from leaking into the 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 and can spread via groundwater to vitally important fresh water resources, such as Washington’s Columbia River.

Nathalie Wall
Nathalie Wall

New research by Nathalie Wall, assistant professor of chemistry, and Larissa Gribat, chemistry doctoral candidate, could help in the design of new long-term nuclear waste storage facilities and make it easier to clean already contaminated areas. The two researchers are investigating how technetium (Tc), a radioactive element produced during the burnup of uranium fuel, interacts with naturally occurring iron minerals and microbes in the soil. Their goal is to figure out the precise combination of these naturally occurring materials that causes technetium to switch between a form that moves readily through the environment and one that stays put.

Similar but not the same

Technetium has several different forms, called oxidation states that determine how readily it spreads through the environment. Previous lab research shows 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, when exposed to iron.

“Iron was supposed to be the barrier technetium couldn’t get around,” Wall said. “However, we now know iron by itself does not completely stop the spread of technetium in the environment. We are trying to figure out the specific combination of iron minerals and their environment that cause technetium 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.”

Larissa Gribat
Larissa Gribat

Wall and Gribat received funding from the U.S. Department of Energy 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.

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

“After a while the safety procedures become second nature, however no matter what work a chemist is doing, it is essential to stay focused and pay attention to what is happening right then,” she said. “There are scientists who work with dangerous and contagious viruses. For me, this work seems very safe in comparison—it is all in the eye of the beholder.”

Wall and Gribat’s findings will be helpful toward remediating subsurface systems contaminated with technetium, including the Hanford site and other DOE facilities.

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