Scholars join forces at WastePD
High-level radioactive waste in the United States stems generally from two sources: spent fuel from nuclear reactors, and the legacy of the manufacture of nuclear bombs during the Cold War, so-called defense waste. Issues associated with the transformation and disposal of defense waste prompted the Department of Energy last year to initiate four new Energy Frontier Research Centers (EFRCs), one of which is based in The Ohio State University's Department of Materials Science and Engineering.
The Center for Performance and Design of Nuclear Waste Forms and Containers (WastePD) is the first EFRC based at Ohio State, and also within the state of Ohio. WastePD is being led by Gerald Frankel, PhD. Other participating materials science faculty include Wolfgang Windl, Jenifer Locke, and Christopher Taylor. In all there are 13 principal investigators from nine institutions, including Pacific Northwest National Laboratory (PNNL), the French Center for Atomic Energy (CEA), and QuesTek Innovations, a small company in Evanston, Ill.
Most defense waste is currently in underground tanks in Hanford, Wash., and Savannah River, S.C. This tank waste is mixed with complex borosilicate glass, a process that has been underway at Savannah River for 20 years but has not yet begun at Hanford. Some dangerous radionuclides cannot be processed through glass melting and must be isolated in other materials, likely crystalline ceramics. And the containers for all of this waste will be metallic. Eventually, all of the U.S.’s high-level waste will be placed in a permanent mined repository, and the current administration is looking to restart the Yucca Mountain Project, which was defunded by the Obama administration.
The most important performance parameter of any nuclear waste form is its ability to withstand degradation during long-term exposure to the repository environment, which will be ground water. WastePD is therefore studying the aqueous corrosion of glasses, ceramics, and metals, which is aligned with the expertise in Ohio State’s Fontana Corrosion Center. Glass and ceramics are generally considered to be extremely resistant to corrosion in natural waters, but in fact they do corrode and can do so at a high rate. Generally, the rate of glass corrosion slows with time, but it can increase again to very high rates for reasons that are not fundamentally understood. As a result, the models of repository behavior do not consider waste form corrosion.
The premise of WastePD is that bringing together the communities studying glass, ceramic, and metal corrosion will result in synergies and advances that would not otherwise have been possible. For example, team members at PNNL have, for the first time ever, imaged details of the gel that forms on corroded glass using flash freezing, cryogenic sample preparation and atom-probe tomography. The gel consists of interpenetrating 2-3 nanometer scaled silica and water phases. This approach will soon be used to study pits in metals and corroded ceramics.
Ohio State’s materials science and engineering faculty are primarily active on the Metals Team, along with colleagues from QuesTek and the University of Virginia. The Metals Team is focused on developing an approach for the design of corrosion-resistant alloys (CRAs) using Integrated Computational Materials Engineering (ICME) principles. CRAs are now designed using intuition, experience, and empiricism. Such approaches are not useful when investigating a hot new class of alloys called high entropy alloys (HEAs), which have near equi-atomic concentrations of many different elements. WastePD will use calculable parameters to predict corrosion behavior, and eventually multiscale models of each of the critical steps in the corrosion process.