Oxidative Corrosion of the UO2 (001) Surface by Nonclassical Diffusion
Joanne E Stubbs, Craig A Biwer, Anne M Chaka1
1Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|November 1, 2017
Summary
Oxygen interstitials diffuse into uranium oxide surfaces, altering lattice structure and oxidation states. This study reveals the subsurface oxygen diffusion profile beneath the (001) surface, crucial for nuclear fuel stability.
Area of Science:
- Materials Science
- Nuclear Engineering
- Surface Chemistry
Background:
- Uranium oxide (UO2) stability is critical for the nuclear fuel cycle.
- Interstitial oxygen concentration and uranium oxidation state influence UO2 properties.
- Previous work showed oxygen interstitial superlattice formation on UO2 (111) surfaces.
Purpose of the Study:
- To investigate the oxygen diffusion profile beneath the UO2 (001) surface.
- To understand the structural changes and oxidation front penetration.
- To correlate surface structure with bulk material properties.
Main Methods:
- Surface X-ray scattering ( ৬-ray diffraction) to probe subsurface structure.
- X-ray photoelectron spectroscopy (XPS) to determine uranium oxidation states.
- Controlled exposure of UO2 (001) to dry O2 gas at ambient conditions.
Main Results:
- Observed oscillations in lattice parameters in the top layers, indicating preferential interstitial occupation.
- Identified a contraction in deeper layers, with an oxidation front penetration of ~52 Å.
- Detected uranium oxidation states ranging from U(IV) to U(VI) via XPS.
Conclusions:
- The oxygen diffusion profile beneath the UO2 (001) surface is characterized by preferential interstitial occupation and significant oxidation front penetration.
- These findings provide insights into the corrosion mechanisms and long-term stability of nuclear fuel.
- The results are consistent with previously observed interstitial networks in oxidized UO2 surfaces.
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