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Many Zircaloy cladding failures and the results of out-of-pile iodine stress corrosion tests are so similar as to suggest that fission of uranium produces enough iodine to attack the cladding locally. This paper presents a study of the effects of iodine on the fracture of Zircaloy-2 sheet being stressed very locally. Discs produced from Zircaloy-2 sheet were bent biaxially by pressing an indentor into the center of the disc. The force necessary to penetrate the discs decreased when either the initial amount of iodine or the temperature was increased, for cold-worked as well as recrystallized Zircaloy-2. Uniaxial short-time creep tests and tests with stressed slotted rings, both performed in environments containing iodine, did not result in stress corrosion cracking.
Microprobe analysis of the regions adjacent to cracks revealed deposition of iodine compounds on the walls of narrow cracks or near the crack tips. The propagation of the cracks in cold-worked material is affected by the manufacturing process of the sheet. The main conclusion of this investigation is that a high degree of local deformation is needed before biaxially stressed Zircaloy-2 suffers from stress corrosion by gaseous iodine.
iodine, Zircaloy-2, stress, corrosion, fractures (materials), biaxial stresses, uniaxial creep, slotted rings, scanning electron microscopy, electron probes, microanalysis, irradiation, zirconium alloys
van der Schaaf, B
Physical metallurgist, Reactor Centrum Nederland, Petten/N.H.,