A unified model to describe the anisotropic viscoplastic behaviour of zircaloy-4 cladding tubes between 320 °C and 400 °C from an unirradiated state to high fluence and under fast neutron flux

Abstract
This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of Zircaloy-4 claddings in a stress relieved state over the fluence range 0-85.10 ²⁴ nm ^-2 ( MeV). The model, identified from uni and biaxial tests conducted at 350 and 4000°C, is validated from tests made at 320, 380 and 420°C. This model is able to simulate strain hardening under an internal pressure followed by a stress relaxation period, since the loading produces an interaction between the pellet and the cladding (thermal creep). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).