Multimodal Analysis of UO₂ Corrosion enabled by a Microfluidic Electrochemical Cell

Understanding the corrosion kinetics and mechanisms of spent nuclear fuel (SNF) is crucial for accessing the long term risks associated with the geologic storage of SNF.¹ Traditional experimental approaches have posed serious challenges, given the need for substantial resources and access to shielded hot cell facilities to protect researchers from the intense radiation field. One response is to work with depleted UO₂, a close but ultimately unsatisfactory analogue to SNF. An alternative would be to downsize the amount of SNF required such that the need for shielded hot cell facilities would be diminished.<br/><br/>Indeed, an innovative solution has emerged—the Particle-attached Microfluidic Electrochemical Cell (PAMEC)--which has the proven potential to work with microgram quantities of material. Central to the PAMEC is the electrochemical method, which is widely employed for studying corrosion processes. With respect to UO₂ corrosion, the PAMEC electrode is a composite of microgram quantities of UO₂ powder, polyvinylidene fluoride (PVDF), and carbon black.² ³ The PAMEC has already proven effective in studying UO₂ redox behavior, providing consistent results with those from traditional bulk electrochemical studies.⁴<br/><br/>In more detail, the PAMEC is a vacuum-compatible microfluidic platform that provides precise control over experimental conditions (e.g., flow rates, dissolved volatile concentrations such as H₂), minimal resource utilization, and the ability to observe redox reactions in real-time and in situ. PAMEC’s in situ and real time analytic and imaging capabilities, made possible by an ultra-thin 50 nm detection window, include scanning electron microscopy (SEM) combined with Energy-dispersive X-ray spectroscopy (EDS). The same set up allows for operando high-resolution X-ray absorption near-edge structure (HR-XANES) spectroscopy, which we used to track U oxidation states during multiple cyclic voltammetry scans of UO₂. The compact nature of the PAMEC simplified shipping the loaded device to the Karlsruhe Institute of Technology (KIT) synchrotron facility CAT-ACT beamline in Karlsruhe, Germany for operando HR-XANES analysis.<br/><br/>Our research has showcased the ability of the PAMEC using UO₂ corrosion as an example. We envision this approach can greatly reduce the risk associated with studying the corrosion of SNF under conditions that resemble repository environments, as well as allow for multimodal analyses for acquiring complementary characterization and more in-depth understanding of the corrosion process.<br/><br/><br/>(1) Ewing, R. C. Long-term storage of spent nuclear fuel. <i>Nature Materials </i><b>2015</b>, <i>14</i> (3), 252-257. DOI: 10.1038/nmat4226.<br/>(2) Yao, J.; Lahiri, N.; Tripathi, S.; Riechers, S. L.; Ilton, E. S.; Chatterjee, S.; Buck, E. C. A microfluidic electrochemical cell for studying the corrosion of uranium dioxide (UO2). <i>RSC Advances </i><b>2022</b>, <i>12</i> (30), 19350-19358, 10.1039/D2RA02501A. DOI: 10.1039/D2RA02501A.<br/>(3) Yao, J.; Tripathi, S.; McNamara, B. K.; Lahiri, N.; Riechers, S. L.; Chatterjee, S.; Reilly, D. D.; Ilton, E. S.; Buck, E. C. Advancing radioactive material research method: the development of a novel in situ particle-attached microfluidic electrochemical cell. <i>Frontiers in Nuclear Engineering </i><b>2023</b>, <i>2</i>, Original Research. DOI: 10.3389/fnuen.2023.1206110.<br/>(4) Sunder, S.; Strandlund, L. K.; Shoesmith, D. W. <i>Anodic dissolution of UO2 in slightly alkaline sodium perchlorate solutions</i>; AECL--11440; Canada, 1996. http://inis.iaea.org/search/search.aspx?orig_q=RN:28006012.