By Scott Miller
Photography by Ashley Jones & Josh Wilson
Clemson researchers are pioneering ways to use medical imaging technology to study the movement of radionuclides through soil
Four years ago, scientists with Clemson University and Savannah River National Laboratory buried the radioisotope neptunium-237 in a 2-foot-long, soil-filled PVC column to analyze how it would react in the environment.
Last year, Kathryn Peruski dug it up. Using Clemson’s Electron Microscopy Facility, the Clemson Ph.D. candidate captured the first image of the miniscule fragmenting of particles off of the neptunium, a radioactive byproduct of nuclear power generation and nuclear weapons production that is stored underground.
“She really got extraordinarily interesting results. It has really changed our view of what is going on,” says Dan Kaplan, senior research fellow with the Savannah River National Laboratory (SRNL). “In particular she found that neptunium was moving in a form that had never been observed before.”
Her discovery is part of a long effort to better understand how disposed nuclear waste could move through soil and potentially enter water and food supplies. And now, the experiments go on. Peruski replaced the buried radioisotope with another that a future Clemson student will dig up years later, possibly in a decade or more.
OUTDOOR TEST BEDS
Peruski is working under the guidance of Brian A. Powell, Fjeld Professor in Nuclear Environmental Engineering and Science at Clemson. Powell holds a joint appointment with SRNL to advance research on environmental remediation and radioactive waste disposal. SRNL’s Joint Appointment program provides an opportunity for university faculty to explore collaborative research opportunities with SRNL researchers and strengthen the relationship between SRNL and the joint appointee’s home university.
Powell began working closely with Kaplan in 2001. At the time, Powell was a graduate student — he earned both his master’s degree and Ph.D. in environmental engineering and science from Clemson under the mentorship of Professor Robert Fjeld. Powell, Fjeld and Kaplan were testing a theory that the radioactive element
plutonium was more mobile than believed, that it could unexpectedly change its oxidation state and move rapidly underground. They found that it was indeed mobile but not at the alarming rate some scientists feared. In fact, plutonium, regardless of the chemical state it was buried in, would convert to a specific form that was largely immobile, they discovered.
“Those results may not be sexy, but having the field data to prove our theoretical understanding of plutonium geochemistry is critical for the Department of Energy to confirm that when they bury waste, they know it is going to be safe. The data is there to support that,” Powell says. “These lysimeter facilities are really supporting the risk analysis that the DOE has to do when disposing of waste.”
A lysimeter is a large bed of concrete with holes where scientists can insert the 2-foot-long, 4- to 6-inch-thick PVC columns filled with soil and some form of radioisotope. The lysimeters are placed outdoors, so the isotopes are then exposed to natural elements like rain and temperature. The testbeds are engineered with plumbing to capture the rainwater.
Powell and Kaplan have designed and built lysimeter test beds both at Savannah River National Lab and at Clemson’s innovation campus in Anderson County. Having multiple locations gives them opportunity to instrument the facilities differently and study different aspects of radionuclide disposal risk.
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