Fracture behavior of irradiated Zircaloy-4 cladding under simulated LOCA conditions

Laboratory-scale experiments were performed with Zircaloy-4 fuel cladding, irradiated to 39 and 44 GWd/t at a PWR, for evaluating high burn-up fuel rod behavior in a loss-of-coolant accident. Short test rods, fabricated with the cladding were heated, isothermally oxidized at 1,303 to 1,451 K in steam flow, and quenched with water flooding. Two cladding specimens, oxidized to about 26 to 29% ECR, were fractured during the quench, while four cladding specimens, oxidized to about 16 to 22% ECR, survived the quench. Threshold of fracture is comparable with that of unirradiated cladding specimens which are hydrided to the same level. Accordingly, in the burnup level of the present study, differences were not significant between irradiated and unirradiated cladding specimens in terms of threshold of fracture during quenching, though the threshold is reduced as initial hydrogen concentration increases.