Surface adsorption and dissolution mechanisms of UO2 (110) and (111) in oxidizing environments: Insights for sustainable nuclear fuel recycling

Abstract

The interfacial reaction of uranium dioxide (UO₂) in humid environments is critical for nuclear safety and storage but remains poorly understood. This study employs first-principles DFT + U calculations to investigate O₂ and H₂O₂ adsorption on UO₂ (110) and (111) surfaces and their impact on surface dissolution behavior. The results reveal both physical and chemical adsorption of O₂, alongside dissociative adsorption of H₂O₂. The vibrational frequencies of O₂ with bond lengths of 1.235 Å–1.254 Å is 1451.0 cm⁻¹–1509.5 cm⁻¹, while O₂ with bond lengths of 1.334 Å–1.338 Å shows frequencies of 1133.6 cm⁻¹–1184.1 cm⁻¹, suggesting non-dissociative O₂ behaves as superoxide (O₂^–). To elucidate the atomistic evolution of oxidized surfaces in moist air or oxidizing solutions, we further explored interactions between H₂O molecules and the most stable O₂/H₂O₂ adsorption configurations. Results show that H₂O dissociates into OH groups and H atoms, forming U–O and H–O bonds. This work provides new insights into O₂/H₂O₂ adsorption morphologies on UO₂ surfaces and their interactions with water at oxide interfaces.