Zirconium alloy cladding tubes used in nuclear fuel rods are susceptible to delayed hydride cracking, which is a time-dependent crack growth process resulting from the stress-assisted diffusion of hydrogen to the crack tip, followed by the formation of radial hydrides and the subsequent fracture of the hydrides in the crack-tip region. Delayed hydride cracking in zirconium alloys could be a potential issue for disposal or reactor operation of high burnup fuel rods because transient stresses

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... ciated with pellet-cladding mechanical interaction during in-reactor power ramps may be sufficiently high to cause substantial hydride reorientation, formation of hydride rims and blisters, as well as radial hydrides that can make the cladding tubes susceptible to hydride fractures followed by radial-hydride-assisted delayed hydride cracking. This article reviews the current understanding of the delayed hydride cracking behavior of zirconium alloy cladding tubes for fuel rods, focusing on the degradation mechanisms in high burnup fuel rods and loading scenarios, which could potentially lead to substantial changes in the hydride microstructure and cladding failure by delayed hydride cracking during the disposal of spent nuclear fuel rods in a waste repository. A brief summary of the general characteristics of delayed hydride cracking in zirconium + Work supported by the U.S. Nuclear Regulatory Commission (Contract No. NRC-02-07-006) and Southwest Research Institute ® (Focused Internal Research and Development Program). alloy cladding is presented first. Relevant information on the cladding stresses under various usage conditions are then compiled and categorized into several characteristic stress transients that can be anticipated during reactor operation. Delayed hydride cracking in cladding tubes under stress transients is then examined under various temperatures, cooling rates, burnup levels, and loading conditions.