An ion bombardment simulation technique for neutron irradiation was applied to “thick” materials to study the effect of radiation damage on the ductility change in Zircaloy-2 in an iodine environment. Specimens were prepared from actual cladding tubes and, prior to the irradiation, they were heat-treated in vacuo at 450, 580, and 700°C for 2 h. Irradiation was performed by 52-MeV alpha particles up to the 0.32 displacements per atom (dpa) at 340°C. The ion beam for this energy penetrates through the specimen, leaving only the radiation damage within the target materials. In some cases, 100-MPa axial stress was applied during irradiation to examine the stress effect on plastic strain behavior after irradiation. The uniaxial tension test for postirradiation examination was carried out in a 4-torr iodine partial pressure at 6 × 10⁻⁴/min strain rate and at 350°C temperature. Similar tests were also conducted in argon gas environment, as a reference. Ductility loss begins to appear after 0.03 dpa irradiation, both in iodine and argon gas environments. The iodine presence resulted in ductility reduction, compared with the argon result in all irradiation dose ranges examined. The ductility change in the iodine environment depended on preirradiation annealing temperature up to 0.16 dpa, with 580°C specimens showing the largest plastic strain. At higher dose range, however, the ductility approached a saturation value and the difference in preirradiation annealing seemed to diminish. The stress applied during irradiation caused ductility loss to commence at lower dosage than in the case of stress-free irradiation. These results are discussed in relation to the existing stress corrosion cracking models.