Experimental Characterization and Modeling of I-SCC of Zirconium Alloy in an Iodine Vapor Environment

The I-SCC behaviour of cold-worked stress-relieved (CWSR) zircaloy-4 was investigated with internal pressure tests in inert and vapor iodine environments. I-SCC susceptibility was established from tests on un-irradiated and neutron-irradiated cladding tubes. I-SCC crack propagation rates were evaluated from tests on pre-cracked tubes. The internal pressure tests conducted on un-irradiated CWSR zircaloy-4 cladding tubes in a gaseous iodine environment were used to investigate the influence of test temperature (320°C, 350°C, or 380°C) on the I-SCC process. The experimental results exhibited 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 both the initiation and the propagation of the I-SCC crack. The coupling was implemented in the CAST3M finite element code using either massive elements or Cohesive Elements. (author)