LONG-TERM EXPERIMENTS

The columns are left in the lysimeters for 10 or 11 years before being pulled out and analyzed using advanced electron microscopy, medical imaging techniques and three-dimensional X-rays to view changes. Computer modeling will help predict how those 10-year changes might happen over tens of thousands of years and even longer.

Long-term modeling is critical. The neptunium Peruski is studying has a half-life — the time it takes for half of the material to undergo radioactive decay — exceeding 2 million years. While environmental contamination from neptunium is highly unlikely now, scientists must have plans to safely handle nuclear waste well into the future, Peruski says.

“You don’t want to wait until this is a problem to solve it,” she adds.

Through her research, Peruski hopes to better understand what causes neptunium to move in the environment so engineers can design effective storage methods. She will analyze several neptunium samples exposed to environmental variables and document their changes over time.

These long-term experiments coupled with laboratory experiments and computer modeling will lead to a better understanding of the physical, chemical and biological processes that govern the mobility of radionuclides in natural and engineered systems. The work is important to evaluate the risk posed by subsurface contamination, to design remediation strategies for contaminated sites and to facilitate the use of safe disposal practices.

“For radioactive waste disposal, we’re putting the radioisotopes into very specific chemical and physical forms, and then we bury them in the ground,” Powell says. “So understanding what type of transformations happen to them while they’re buried is very important. Has it decomposed? Has it degraded in any way that would release radioisotopes?”

Powell and Kaplan also can test the effectiveness of burying waste in metal containers or embedding waste in glass, ceramic or concrete.

“Part of it is materials testing and part of it is risk analysis to understand how fast particular radioisotopes will move once they are released from an engineered waste disposal facility,” Powell says.

ONE OF A KIND

The lysimeters give Kaplan and Powell a method to put laboratory results from small-scale experiments through longer, more extensive experiments in natural environments.

“They really are one of a kind,” Kaplan says. “There are no other facilities in the world that study radionuclides under controlled experimental conditions in the field.”

Designing the lysimeters to be safe while exposing waste to environmental pressure and maintaining experimental control has been a challenge. Some scientists have been suspicious, Powell acknowledges, but in September, Powell and Kaplan were invited to speak at an international conference in Japan to share details of their engineered lysimeter test beds.

“Other scientists are becoming increasingly interested as they see some of the data that Dan and I have published from these newer experiments,” Powell says. “Lysimeters allow us to bridge the gap from the laboratory to larger field-scale experiments and ultimately to a large, full-scale, engineered waste disposal facility.”

Kaplan adds: “The plutonium that Brian studied as a graduate student, after 11 years in the field, its movement was barely detectable. These are very slow processes that are very hard to study. The more time you have, the better prediction you have about how [the material] will behave. Once we get this information, we can model and calculate how far it moves, how fast it may move and how much risk there may be that it moves into the human food chain.”