Fracture of zircaloy cladding under simulated power ramp conditions

The behaviour of Zircaloy cladding under stresses imposed by fuel dimensional changes is discussed, and results are presented which suggest that correct choice of cladding properties, in particular cold-work level and texture, is important if the probability of low-ductility failures in fuel pins is to be reduced. Evidence is presented, based on laboratory tests and post-irradiation examination of cladding, which leads to the conclusion that failure of Zircaloy can occur by stress-corrosion cracking in the presence of fission product iodine, and it is further demonstrated that the process is strongly stress-dependent. Consideration is also given to the influence of irradiation exposure, strain rate, and adverse stress systems, for instance at pellet ridges or cracks, on the cracking susceptibility of cladding. (author)