In Situ SEM study of iodine-induced stress corrosion cracking (ISCC) in Zircaloy-4

Stress corrosion cracking (SCC) of Zirconium alloys by an abundant fission product, iodine, has been extensively studied in order to understand the mechanism of failure of fuel cladding in nuclear reactors. This study was an attempt to observe the fracture mechanics of ISCC in Zircaloy-4 during in situ scanning electron microscope (SEM) tensile tests.A 200mm long section of a Zircaloy-4 cladding tube with an outer diameter of 9’55mm and a wall thickness of 0,55mm, was bisected and then cold rolled into flat strips 14mm wide and 0,5mm thick. The material was annealed at 680°C for 1 h at a time in an Argon atmosphere between successive cold working steps. Following the final cold roll the material was annealed at 1080°C for 4 h in an Argon atmosphere and air-quenched.Tensile test specimens with a gauge length of 12’5mm and a width of 3’12mm were cut from the sheet metal by spark erosion accordinq to scaled down ANSI/ASTM E8-79a specifications. The specimens had to be lapped and polished to a thickness of 0’16mm in order to obtain a maximum stress of 500MPa without exceeding the 250N limit of the apparatus.