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Engineers Fight Corrosion in Nuclear Storage

Wednesday, February 3, 2021

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The University of Virginia was recently awarded a $718,000, three-year grant from the Nuclear Energy University Program to use corrosion science to help identify potential at-risk canisters used to store spent nuclear fuel.

According to the United States Energy Information Administration, nuclear energy produces more carbon-free electricity in the nation than all other power sources combined. In wake of more cities, states and even countries joining forces to achieve a net-zero carbon future, nuclear energy could be a solution should it be publicly accepted and conduct regulatory action.

Two major concerns, however, are how nuclear waste is stored and contained, in addition to preserving materials in generation-IV reactors’ anticipated extreme environments.

Leading the study with hopes to recertify private- and public-sector sites for interim storage are UVA’s Robert G. Kelly, AT&T Professor of Engineering and professor of materials science and engineering, and James T. Burns, associate professor of materials science and engineering.

Combined Efforts, Other Awards

To develop solutions to these issues, materials scientists and engineers focusing on corrosion science from the University of Virginia have joined multi-institutional teams involving universities, national labs and their private sector partners to better understand and mitigate corrosion that occurs in storage containment, and to guide the selection of anticorrosive materials for novel reactor designs.

The combined research efforts advance U.S. Department of Energy initiatives, including two Nuclear Energy University Program grants and two Energy Frontier Research Centers funded by the Office of Basic Energy Sciences.

4X-image / Getty Images

The University of Virginia was recently awarded a $718,000, three-year grant from the Nuclear Energy University Program to use corrosion science to help identify potential at-risk canisters used to store spent nuclear fuel.

In 2016, The Center for Performance and Design of Nuclear Waste Forms and Containers, also known as WastePD, at Ohio State University was established to generate a fundamental understanding of waste forms’ degradation mechanisms and specifically, nuclear waste forms’ ability to withstand corrosion in a repository over very long periods of time.

Since its founding, Gerald Frankel, professor of materials science and engineering, and director of the Fontana Corrosion Center at Ohio State University has served as WastePD’s director. The WastePD has considered glasses, ceramics, and metal in its research.

UVA Charles Henderson Chaired Professor of Materials Science and Engineering, John R. Scully, has also been awarded a multi-million-dollar, six-year award, in where he is leading metals research at WastePD and is focusing heavily on extremely corrosion-resistant alloys.

In their combined studies, the team identified a nickel-rich high-entropy alloy predicted to form a protective oxide thin-film and exhibit exceedingly high corrosion resistance, and was subsequently demonstrated in electrochemical testing.

In 2017, Scully was awarded a grant for just under $1 million from the Nuclear Energy University Program to investigate why a number of carbon-steel alloy canisters corroded in the early 2000s. During his investigation, Scully called on Sean Agnew, a UVA professor of materials science and engineering and an expert in materials’ mechanical properties and time-dependent phenomena, and Bi-Cheng Zhou, a UVA assistant professor of materials science and engineering and, Kang Wang, a post-doctoral fellow in his computational thermodynamics and kinetics research group, to identify and assign probabilities to reactions between fission gas decay products such as rubidium and corrosion-inhibiting oxides on a steel surface.

Through these experiments, the modeling was reported to suggest that rubidium-bearing products do react with chromium oxide to form a new oxide, possibly rendering the stainless steel vulnerable to accelerated corrosion. However, further research is underway.

By 2018, the Los Alamos National Laboratory and the University of California, Berkeley, announced the launch of Fundamental Understanding of Transport Under Reactor Extremes (FUTURE). Co-led by scientists at the university, the same year, Scully earned a $600,000 grant to explore how these extreme conditions affect transport and reactions that control corrosion of high-performance materials at the solid/liquid interface.

Waste Sites and Container Corrosion

According to UVA, the nuclear industry and its regulators have been envisioning safe interim storage of nuclear fuel since for nearly two decades. While numerous issues have delayed an approval for storage within the Yucca Mountain, the volume of waste has only continued to increase.

Currently, there are about 80,000 metric tons of spent nuclear fuel in the U.S., which has been housed in 3,000 canisters in 70 different sites. Although most of these canisters are principally owned and managed by power producers, the Nuclear Regulatory Commission anticipates up to 20 of the sites will require relicensing within the next 10 years.

To house spent fuel rods, first the thermally and reactively hot rods are actively cooled by being submerged in pools and are then placed inside a stainless steel canister measuring seven to eight feet in diameter and 25 feet long. The canister is then welded shut and encased in a concrete tube or cask with holes drilled at each end in order to further promote passive cooling.

However, the holes make the stainless-steel canisters vulnerable to localized corrosion and environmental cracking. If exposed to salt aerosols in higher temperatures, the canisters become at risk for forming a saturated chloride solution which can weaken the welds and potentially leak inconsequential amounts of radiation.

In using the recently awarded grant from the Nuclear Regulatory Commission, UVA hopes to identify which of the 3,000 canisters are most and least likely to undergo corrosion. To do so, engineers are developing a modeling tool that assesses risk by location, possible exposure to aerosols and other contaminants, and 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,” Kelly said.

The model is also designed to focus on the formation and growth of pits in the stainless steel caused by salt deposits and other corrosives. Kelly reports that the study is leveraging research conducted by Liat Bell, a Ph.D. student, and post-doc Danyil Kovalov, while Burns will use the pitting as a starting point for the growth of a stress-corrosion crack, considering the physics of passive cooling within the cask and the material properties of the canisters themselves. Burns is aided by Ph.D. advisee Sarah Blust and post-doc Zach Harris in his research.

Researchers at the Sandia National Laboratories, including UVA Engineering alumna Rebecca Schaller and Ph.D. student Ryan Katona, also plan to apply the model in ongoing storage work in order to validate or refine the model with a real canister.

Nashville-based technology business, Vextec, will lead the probability modeling, and has been tasked with running multiple simulations to identify variables that are most important in determining canister life.

The Department of Energy grants are slated to build on UVA’s research strength in corrosion and electrochemistry and are credited by Scully in that they sustain a virtuous cycle that inspires new talent.

“Students are offered unique opportunities to do great work,” he said. “Some may go on to join the national laboratories and become thought leaders in materials science and engineering. The support provided by national laboratories and the Department of Energy makes it possible for the next generation of researchers to do the same.

“It is an honor to join these efforts. Our partnership with the national laboratories contributes to new discoveries and knowledge in corrosion science and electrochemistry that would be otherwise unobtainable.”

   

Tagged categories: Colleges and Universities; Corrosion; Corrosion engineering; Corrosion protection; Corrosion resistance; NA; North America; Nuclear Power Plants; Quality Control; Research and development

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