Effect of hydride orientation on tensile properties and crack formation in zirconium alloy cladding tubes

Hydride precipitation and reorientation are of great importance to evaluate considering their detrimental influence on mechanical properties of nuclear fuel claddings. In this work, a fully recrystallized Zr-Sn-Nb cladding tube was hydrided with 120 and 220 wppm concentration, followed by thermo-mechanical treatment to produce specimens with varying hydrogen contents and hydride orientations. Ring tensile test demonstrates that in contrast to circumferential ones, the radial hydrides lead to significant reductions in plastic elongation of cladding tubes. Scatter in values of mechanical properties are observed in the case of 220 wppm radial hydrides, which could be attributed to irregular distribution of interconnected radial hydrides. Microstructure characterization reveals that microvoids initiate at the junction boundaries of hydride platelets under the tension effect of surrounding α-matrix deformation. These microvoids are proposed to propagate along the interior of brittle hydrides, rather than the interface, eventually leading to premature fracture failure given the alignment of radial hydrides perpendicular to the external tensile stress. The presented results are expected to shed light on microcrack initiation and propagation with respect to hydride orientation in zirconium-based nuclear fuel claddings.