Effect of zirconium oxide on the stress-corrosion susceptibility of irradiated Zircaloy cladding

Cladding specimens were obtained from two fuel rods irradiated in the Big Rock Point Reactor to a burnup of approximately 8 gigawatt days per ton. Both claddings had a uniform, thick (approximately 4/mu/m) zirconium oxide layer on the inner surface. The significant difference between the two rods was the degree of fission-gas release (0.2 versus 14.3 percent). The cladding specimens, with the fuel removed, were subjected to stress-rupture tests to evaluate their stress corrosion cracking (SCC) susceptibility at an initial iodine concentration of 0.6 mg/cm/sup 2/ and a temperature of 325 degree C. Specimens from the high-gas-release rod exhibited significantly increased susceptibility to iodine SCC. The results suggest that the inner-surface oxide provides a barrier to iodine penetration. 10 refs