Modelling actinide redistribution in mixed oxide fuel for sodium fast reactors

• The actinide redistribution in MOX fuel for fast nuclear reactors was modelled.
• The effects of thermal diffusion and vapour transport on Pu and Am migration were examined.
• The model is implemented in the TRANSURANUS fuel performance code.
• Integral tests show a good agreement of the model with experiments.
• A sensitivity study confirms that thermal diffusion is the relevant mechanism for long-term operations.

In this paper, a model for the actinide redistribution mechanism in mixed oxide fuel for a sodium fast reactor is presented and compared with measured data collected from post irradiation examination on fuel from the JOYO experimental reactor. The model considers that solid-state thermal diffusion and vapour transport can simultaneously contribute to the plutonium and americium radial profiles. The effect of fuel non-stoichiometry on actinide transport as well as on pore velocity is taken into account. The model is embedded into the TRANSURANUS fuel rod performance code and calculates the evolution of the Am and Pu concentrations as a function of the radial temperature profile. The calculated actinide distribution is in good agreement with the experimental data. The results confirm that under normal operation conditions with a decreasing fuel power during its life-time, redistribution via pore migration is extremely important only during the central hole formation at the beginning of life, whereas thermal diffusion represents the dominant effect for long-term irradiation.