Testing and Modelling Iodine-induced Stress Corrosion Cracking (I-SCC) in Zircaloy alloys
Résumé
The I-SCC behavior of cold-worked stress-relieved (CWSR) Zircaloy-4 was investigated by means of internal pressure tests in both inert and gaseous iodine environments. I-SCC susceptibility was derived from tests on both un-irradiated and neutron-irradiated claddings tubes. Crack propagation rates were obtained from tests on pre-cracked tubes. The internal pressure tests conducted on un-irradiated cold-worked stress-relieved Zircaloy-4 cladding tubes in an iodine vapor environment were used to investigate the influence of loading mode (either constant pressure tests, constant circumferential strain rate tests, or constant circumferential strain tests) and test temperature (320DC to 488DC) on the I-SCC process. The experimental results obtained with different loading modes indicated that there is an apparent threshold hoop stress, below which I-SCC does not occur.The tests were simulated by finite element models using a specific viscoplastic constitutive equation. The I-SCC initiation and time-to-failure predictions were modelled by a Kachanov's damage law written with a hoop stress threshold. In the simulations, the Kachanov's law can be used in post-treatment of calculations or coupled with the viscoplastic constitutive equation for the cladding in order to simulate the initiation and the propagation of the I-SCC crack. The coupling was implemented in the finite-element code CAST3M.
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