Microscale Electrochemical Corrosion of Uranium Oxide Particles

Abstract

Understanding the corrosion of spent nuclear fuel is important for the development of long-term storage solutions. However, the risk of radiation contamination presents challenges for experimental analysis. Adapted from the system for analysis at the liquid-vacuum interface (SALVI), we developed a miniaturized uranium oxide (UO₂)-attached working electrode (WE) to reduce contamination risk. To protect UO₂ particles in a miniatured electrochemical cell, a thin layer of Nafion was formed on the surface. Atomic force microscopy (AFM) shows a dense layer of UO₂ particles and indicates their participation in electrochemical reactions. Particles remain intact on the electrode surface with slight redistribution. X-ray photoelectron spectroscopy (XPS) reveals a difference in the distribution of U(IV), U(V), and U(VI) between pristine and corroded UO₂ electrodes. The presence of U(V)/U(VI) on the corroded electrode surface demonstrates that electrochemically driven UO₂ oxidation can be studied using these cells. Our observations of U(V) in the micro-electrode due to the selective semi-permeability of Nafion suggest that interfacial water plays a key role, potentially simulating a water-lean scenario in fuel storage conditions. This novel approach offers analytical reproducibility, design flexibility, a small footprint, and a low irradiation dose, while separating the α-effect. This approach provides a valuable microscale electrochemical platform for spent fuel corrosion studies with minimal radiological materials and the potential for diverse configurations.

Keywords: Nafion membrane; microscale electrochemical cell; multimodal characterization; particle-attached electrode; system for analysis at the liquid–vacuum interface (SALVI); uranium oxide (UO2).

Figure 1

(a) The schematic showing the step-by-step fabrication process of particle deposition (i–iii), Nafion film formation (iv–vi); (b) the assembled electrochemical device and the setup to perform an electrochemical analysis of UO₂-containing SALVI E-cells.

Figure 2

CV results of (a) UO₂ WE (Device A) and (b) Nafion control WE with a 100 mV/s scan rate in 0.1 M of NaClO₄ electrolyte.

Figure 3

(a) The CV sweeping profile of the UO₂ device B with different scanning rates (i.e., 40, 60, 80, 100 mV/s). Identified peaks are (i) −0.4 V, (ii) 0.13 V, (iii) 0.81 V, and (iv) −0.24 V; (b) AFM topography 3D image of the corroded UO₂ WE surface; (c) CV scan profiles of the Nafion control device with a scan rate of 60 mV/s. Identified peaks are (1) −0.5 V, (2) 0.08 V, (3) 0.65 V, (4) 0.862 V, (5) 0.23 V, and (6) −0.53 V, and (d) AFM topography 3D image of the pristine UO₂ WE surface.

Figure 4

XPS spectra for as-synthesized exfoliated UO₂ with (a) narrow-scan U(4f) and (b) wide-scan survey. The XPS spectra shown for the CV-scanned exfoliated UO₂ with (c) narrow-scan U(4f) and (d) wide-scan survey. The narrow-scan U(4f) shows peak binding energies for the U(4f_7/2), since the corresponding doublets in the U(4f_5/2) region are fixed at a spacing of 10.9 eV and peak area ratio of 3:4 (U(4f_5/2):U(4f(_7/2)).

Figure 5

Schematics showing the UO₂ oxidation process of (a) the UO₂ electrode with a Nafion layer which allows for limited H₂O exposure to the UO₂ particle layer and (b) its corresponding reaction route diagram using microscale cells compared to (c) the fully H₂O-exposed UO₂ electrode from previous works [24], and (d) its corresponding reaction route diagram.