  Hydrogen embrittlement of uranium, which arises due to the formation of a
structurally weak pyrophoric hydride, poses a major safety risk in material
applications. Previous experiments have shown that hydriding begins on top or
near the surface (i.e., subsurface) of a-uranium. However, the fundamental
molecular-level mechanism of this process remains unknown. In this work,
starting from pristine {\alpha}-U bulk and surfaces, we present a systematic
investigation of possible mechanisms for formation of the metal hydride.
Specifically, we address this problem by examining the individual steps of
hydrogen embrittlement, including surface adsorption, subsurface absorption,
and the inter-layer diffusion of atomic hydrogen. Furthermore, by examining
these processes across different facets, we highlight the importance of both
(1) hydrogen monolayer coverage and (2) applied tensile strain on hydriding
kinetics. Taken together, by studying previously overlooked phenomena, this
study provides foundational insights into the initial steps of this overall
complex process. We anticipate that this work will guide near-term future
development of multiscale kinetic models for uranium hydriding and
subsequently, identify potential strategies to mitigate this undesired process.
