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A Noncollinear Relativistic Computational Study of the Actinide Dioxides and their Interaction with Hydrogen

Pegg, James T.; (2018) A Noncollinear Relativistic Computational Study of the Actinide Dioxides and their Interaction with Hydrogen. Doctoral thesis (Eng.D), UCL (University College London). Green open access

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Abstract

The radiolytic decomposition of water and organic compounds (caused by the decay of actinide nuclei) results in the formation of hydrogen gas. The corrosion and oxidation of actinide metals is known to be catalysed by hydrogen; this has resulted in thermal excursions and the failure of containment vessels. The chemistry of the actinide dioxides (AnO2, An = U, Np, Pu) is key to understanding corrosion mechanisms. To circumvent complex experimental issues, computational methods offer another mode of study. To investigate the complex electronic structure, one must consider: exchange-correlation influences, noncollinear magnetic behaviour, and relativistic contributions. The magnetic ground-state of the AnO2 (An = U, Np, Pu) has been investigated. The diamagnetic (DM), ferromagnetic (FM), and antiferromagnetic (AFM) states have been considered. To treat the on-site Coulomb repulsion of the actinide f-electrons, DFT+U and HSE06 calculations have been completed. A transverse 3k AFM state of UO2 and NpO2 coupled to Pa3 ̅ (No. 205) crystal symmetry has been calculated; whereas, a longitudinal 3k AFM state of PuO2 coupled to Fm3 ̅m (No. 225) crystal symmetry has been calculated. A noncollinear relativistic low-index AnO2 (An = U, Np, Pu) PBEsol+U surface study has been conducted. The importance of relativistic influences and magnetic reorientation is highlighted. The electrostatic potential isosurfaces and scanning electron microscopy (SEM) images are shown. An octahedral Wulff AnO2 crystal morphology has been identified. The interaction of hydrogen with low-index AnO2 (An = U, Np, Pu) surfaces has been investigated by PBEsol+U. The density of states and Bader charges are included. A reduced actinide ion and OH group are formed by interaction of atomic H on all surfaces. The dissociation of molecular H2 on the PuO2 (011) and AnO2 (001)α surfaces has been found, only.

Type: Thesis (Doctoral)
Qualification: Eng.D
Title: A Noncollinear Relativistic Computational Study of the Actinide Dioxides and their Interaction with Hydrogen
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10051742
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