Modeling of the non-monotonous viscoplastic behavior of uranium dioxide

Abstract In order to evaluate the stress level during pellet cladding mechanical interaction (PCMI), Electricite de France is involved in a large program of investigation of the mechanical properties of both fuel pellets and claddings. In this paper, we focus on the mechanical behavior of uranium dioxide. These pellets exhibit a yield point during strain hardening tests and sigmoidal creep curves, that is inflection points characteristic of a non-monotonous viscoplastic flow in the first stages of the tests. Inspired by Alexander and Haasen’s work upon single crystal silicon, we develop a dislocation-based model that is able to describe the viscoplasticity of uranium dioxide in the range of temperature and stress of the PCMI. After developing this model, we introduce it into the Pilvin’s polycrystalline approach. The self-consistency of the polycrystalline approach in the case of a non-monotonous viscoplastic flow is demonstrated in an independent article.