Impact of liquid sodium corrosion on microstructure and electrical properties of yttrium-doped thoria prepared by co-precipitation

Within the development of SFR nuclear reactors, yttrium-doped thoria has been suggested by previous researchers as an electrolyte in sensors monitoring oxygen in liquid sodium. In this paper, Th1-xYxO2-x/2 electrical properties were assessed by impedance spectroscopy before their chemical durability was evaluated in liquid sodium. Pellets always kept their mechanical integrity although sodium penetration was evidenced through the modification of the cleavage surfaces. Post-immersion impedance spectroscopy showed a decrease of grain boundary contribution, even if the global conductivity was not significantly affected. These good performances could be strongly affected by the presence of impurities since silicon-doping increased the sodium penetration.