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Vol. 6 (2019)

Coupled Modelling of ZrO2/α-Zr(O) Layers Growth under Thermal and Mechanical Gradients

October 31, 2019


The oxidation process of a nuclear reactor fuel rod clad made of zirconium is simulated. It is assumed that the oxygen is transported by anionic diffusion in the zirconia layer (ZrO2). Part of this oxygen reacts at the interface between the zirconia layer and the metal, while the rest diffuses in the oxygen-enriched metal volume (a-Zr(O)) to the core of the metal by an interstitial mechanism. The model is based on the thermodynamics of irreversible processes and takes into account the influence of driving forces on the oxygen migration in the metal such as the oxygen concentration gradient, the temperature gradient [1] and the mechanical stress gradient [2]. The growth of both ZrO2 and a-Zr(O) layers are simulated using the finite element software CAST3M. This model has been applied on an axisymmetric geometry by imposing a heat flow on the fuel side and a constant temperature on the waterside of the clad. The differences obtained in the inner and outer sides of the nuclear clad concerning the oxidation kinetics and oxygen distribution are related to some coupling parameters. Several values of those parameters are used in the simulations to highlight their influence on the oxidation behavior. Thus, we show that negative values for the heat of transport, which relates the gradient of ocncentration and the gradient of temperature, give coherent results with experimental observations on oxidation kinetics for both sides of the clad.


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