Numerical Implementation of an Anisotropic Viscoplastic Model to Describe the Behavior of Zircaloy-4 Tubes under Irradiation

Abstract

To ensure the structural integrity of nuclear fuel cladding tubes during their service life, it is necessary to perform precise calculations of stress and strain levels in the materials under operating conditions. In this context, the present work focuses on the implementation of a specific anisotropic viscoplastic constitutive law for Zircaloy-4 alloys that captures behavior under irradiation. Key aspects of the formulation and numerical resolution are detailed: the radial return algorithm, the integration of the equations according to the Newton-Raphson method, and the solution within a material system. The developed material model is implemented as a user routine in the finite element code Code Aster. Finally, comparisons are made between the obtained results and those reported in the literature, aiming to validate and improve the understanding of models used in predicting the behavior of materials in nuclear applications.