Development of a damaged viscoplasticity model with preliminary application in Zircaloy cladding material

Structural integrity of nuclear fuel cladding is the most important factor limiting the life and the safety of nuclear fuels. However, a rigorous evaluation of the damage and fracture behavior of the cladding is hindered by the absence of a constitutive model which can reasonably describe the complex mechanical behavior of the metallic cladding material. In this paper, a damaged viscoplasticity model is proposed by combing the damaged plasticity model, i.e., the classical Gurson-Tvergaard-Needleman (GTN) model, and a general viscoplasticity model. After instantiating the general viscoplasticity model by the thermal creep, the irradiation creep and the irradiation growth models, the damaged viscoplasticity model can thus describe the damaged viscoplastic behavior of Zircaloy cladding material. In addition, the model can describe the hydrogen embrittlement by correlating the damage parameters with the hydride content. A stress updating algorithm is proposed to implement the model within the general finite element software, i.e., ABAQUS. Then the model is evaluated by parametric studies. The typical failure behavior of the Zircaloy cladding is also investigated by using the developed constitutive model.