Modelling actinide redistribution in mixed oxide fuel for sodium fast reactors

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. (c) 2013 Elsevier Ltd. All rights reserved.