An important aspect of materials phenomena during the service of structural Zr alloys for nuclear cladding components is associated with hydrogen picking, which leads to the formation of δ-hydrides ZrHx (x = 1.55 or 1.66), the structural evolution of which is essential to the mechanical stability of the cladding components. In this work, we report the formation of δ-hydrides due to accidental hydrogen pickup, using high-resolution transmission electron microscopy (HRTEM). The results showed that the habit plane for relatively large δ-hydrides was (0001)α, with the plate morphology. The morphology for regions with populous nano-sized hydrides is irregularly blocky, albeit being of the same orientation relationship between hydrides and matrix. Such remarkable morphological change is associated with multi-nucleation and twinning in the hydrides crystals in the nano-scale.