Outside the Box Thinking for Unusual Nuclear Wastes
A diverse, collaborative group at the CHWM Energy Frontier Research Center provides answers about what it takes to store a highly radioactive subset of defense-related nuclear waste.
Newswise — In 1943 on an isolated expanse of desert dotted with green-gray sagebrush, construction crews started building a top secret chemical facility known as T-Plant. It housed the first industrial process to pluck plutonium for the nation's nuclear arsenal from irradiated fuel rods.
Operating T-Plant and similar facilities created radioactive wastes in Washington State, Idaho, and South Carolina. The Cold War waste—approximately 90 million gallons—is in 100-plus interim storage tanks. The best approach to permanently store the waste, and keep it away from soil and groundwater, is to turn it into a solid material.
"There won't be just one material that solves our nation's nuclear waste problem," said Kristen Pace, a doctoral student at the Center for Hierarchical Waste Form Materials (CHWM).
At CHWM, Pace and her colleagues learn what it takes to store a highly radioactive subset of defense-related waste. These small batches contain troublemakers, such as cesium-packed liquids that'll evaporate into the air during the conventional storage process. An alternative is needed to trap the troublemakers to protect our air, water, and soil. The CHWM team's foundational studies focus on questions about materials that could contain the problematic subset.
Putting elements away. The conventional storage process turns liquid nuclear waste into a solid that won't leak like a liquid could. That solid is radiation-resistant glass. To make glass, engineers prepare the waste from the tanks at a massive industrial plant. They remove plutonium and other troublemakers, creating small batches of waste that are held back. The engineers mix the bulk of the waste with glass-making materials and feed it into ultra-hot melters. They pour the resulting molten glass into special drums. In the drums, the glass cools into a form that'll last for thousands of years.
Some components of the waste, such as cesium, technetium, and iodine, need a different storage option. Glass won't do. The ideal option would pack in several troublemakers, reducing the volume that's stored. To create such materials, we need science-based recipes.
"I'm hopeful that in several more years, we'll be able to come up with a nice material for some of the radionuclides we want to sequester that will last as long as the time it takes for the last radionuclide to decay," said Hans-Conrad zur Loye, CHWM's Director and University of South Carolina professor. "We're doing great science for a good reason."
The CHWM team delves into what they call hierarchical materials. Imagine a tower of cream puffs, with row upon row of pastry stuffed with creamy fillings. Similarly, scientists make a porous structure (like empty pastry shells), incorporating a troublemaking radioactive element. Inside the pores, they add another material (like a filling) with a different troublemaker whipped in. How is that a hierarchy? A small structure (filling) rests inside a larger structure (pastry).
While scientists have made great strides with hierarchical materials, there isn't a cookbook for making materials for these small-batch wastes. The team answers the tough questions needed to write that book.
"The goal is not to have an answer in hand," said zur Loye, "but to understand the underlying science."
Never talked to one before. To get at that science, zur Loye took an outside-the-box approach. He set his sights on a diverse team, including three types of chemists who rarely worked together. His goal was a close-knit team that could make radioactive materials, measure their properties, and model the results.
Making materials means working with highly radioactive elements. That's not easy. Few labs are set up for it. He brought in experts from DOE's Savannah River National Lab (SRNL) and other places capable of making highly radioactive materials. He added experimental chemists who measure different features, such as pore size, and computational chemists who simulate how the materials behave using complex mathematics.
They leveraged their talents through projects and short-term fellowships. Working with three classes of hierarchical materials, including tiny particles, they design custom structures, create them, run tests, and use the results to build simulations that, in turn, refine future designs and tests.
Students are a key ingredient. Several work at other labs for a few months or longer, reminiscent of foreign student exchange programs. For example, Pace spends four days a week at SRNL, about an hour or so down the road from the University of South Carolina where she studies. At SRNL, she makes special salt crystals to hold plutonium.
"It's fun to work with everyone," said zur Loye. "We had a lot to learn from each other."
But it wasn't always easy. Pace typically works with experimental chemists. "I'd never talked to modelers or computational scientists before," she said. "When I first started working with them, I had no idea how hard it would be to convey the problem."
A world of difference. Their inclusive team roster gives CHWM a soup to nuts view of hierarchical materials. It may lead to new ways to address troublemakers from Cold War wastes. "None of this happens quickly," said zur Loye. "But I'd like to think that what we're doing will help us get there in my lifetime."
The University of South Carolina leads the center, established in 2016. CHWM members are from Alfred University, Brookhaven National Laboratory, Clemson University, Commissariat à l'Energie in France, Pacific Northwest National Laboratory, Savannah River National Laboratory, and the University of Florida.
This article is part of a series that explores how scientific teams come together in the Department of Energy's Energy Frontier Research Centers to solve intractable problems.
The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit https://science.energy.gov.
Kristin Manke is a Communications Specialist on detail with the Office of Science.