First-Principles Study of the Hydrogen Resistance Mechanism of PuO(2)

[Image: see text] The in-depth investigation of hydrogen behaviors in Pu-oxide overlayers (mainly PuO(2) and α-Pu(2)O(3)) is critical for modeling the complex induction period of Pu hydriding. Within density functional theory (DFT) + U + D3 schemes, our systematic first-principles calculations and ab initio thermodynamic evaluations reveal that the hydrogen incorporation, dissolution behaviors, and diffusion mechanism in PuO(2) are quite different from those in α-Pu(2)O(3), among which the highly endothermic incorporation and dissolution of hydrogen are the primary hydrogen resistance mechanism of PuO(2). Since its difficult recombination, atomic H is the preferred existence state in PuO(2), but H will recombine spontaneously in α-Pu(2)O(3). In PuO(2), H diffusion is always clinging to O anions, whereas in α-Pu(2)O(3), H(2) prefers to migrate along O vacancies with higher barriers. H dissolution in intact PuO(2) is very difficult, which can only be driven by extremely high pressure P(H(2)) and temperature. Based on a series of theoretical studies, we conclude that the main interactions between hydrogen and Pu-oxide overlayers are not involved with chemical reactions, and intact PuO(2) can effectively inhibit hydrogen permeation.