Materials scientists and engineers at the University of Virginia (UVA) (Charlottesville, Virginia, USA), in collaboration with other universities, national labs, and private-sector partners, are working to understand and mitigate corrosion that occurs when storing and containing nuclear waste. To that end, the Nuclear Regulatory Commission recently awarded the UVA-led team a three-year, $718,000 grant to develop a modeling tool that helps determine which of its 3,000 cannisters containing spent fuel rods are most prone to corrosion.
Two decades ago, the nuclear industry and its regulators saw interim storage of spent fuel as a safe, flexible, and cost-effective approach that would enable nuclear plants to remain operational until a permanent repository could be found. However, approval on such a repository has been delayed while the volume of waste has expanded to 80,000 metric tons housed in 3,000 cannisters in various sites across the country. Thus, an effort is currently underway to help the Nuclear Regulatory Commission recertify private- and public-sector sites for the interim storage of spent nuclear fuel.
In a project is led by UVA’s Robert G. Kelly, a professor of materials science and engineering, and James T. Burns, an associate professor of materials science and engineering, researchers are investigating several technical issues, including the encasements for spent fuel rods. The rods are first placed in a stainless-steel cannister, which is then encased in a concrete tube known as a cask. Holes are drilled into each end of the cask allow for passive cooling, but this also makes it vulnerable to localized corrosion and environmental cracking. What concerns the UVA team most are the salt aerosols, which can travel 100 miles inland, as well as the potential for the top sheets of weakened cannisters to slide off and expose the rods.
By developing a modeling tool that assesses risk by location, researchers can account for exposure to aerosols and other contaminants, as well as temperature dynamics within the concrete cask. “If we can show that, for a given site, it is not feasible for a crack to form in the container to a critical size, then the NRC can narrow the list of sites that require a physical inspection,” says Kelly.
Through research conducted by UVA graduate students Liat Bell and Danyil Kovalov, the team can generally predict the formation and growth of pits in the stainless-steel cannisters caused by salt deposits and other corrosives. From there, Bell uses the it as a starting point for the growth of a stress-corrosion crack. Probability monitoring into cannister life is conducted by Vextec, a small, Nashville, Tennessee-based technology business, while others apply this modeling research to real-life conditions.
This research advances U.S. Department of Energy (DOE) initiatives, including two Nuclear Energy University Program grants and two Energy Frontier Research Centers funded by the Office of Basic Energy Sciences. The DOE grants build on UVA’s research strength in corrosion and electrochemistry.
Source: UVA Engineering, https://engineering.virginia.edu.