Oxygen sensors and electrochemical oxygen pumps for lead alloy cooled nuclear systems

MYRRHA, a Multi-purpose hYbrid Research Reactor for High-tech Applications is currently under development at the Belgian nuclear research center SCK•CEN. It is the first prototype of a nuclear reactor driven by a particle accelerator in the world. LeadBismuth Eutectic (LBE) has been selected as spallation neutron source and as primary reactor coolant. Oxygen control strategy has been defined to mitigate undesirable liquid metal corrosion occurring between the steel surface of the main components of MYRRHA and the LBE itself. The development of a reliable oxygen sensor and control device beyond the state-of-the-art for operation in the conditions foreseen in MYRRHA are therefore crucial. A potentiometric oxygen sensor based on the use of yttria partially stabilized zirconia as solid electrolyte combined respectively with air/perovskite oxides, Cu/Cu2O, In/In2O3 or LBE/PbO reference electrode has been developed and operated succesfully between 200 and 450 °C in oxygen saturated LBE overcoming the operating temperature limit of previously used Bi/Bi2O3 and air/Pt reference electrode oxygen sensors being of 280 °C and 300 °C approximately. An electrochemical oxygen pump based on the use of yttria partially stabilized zirconia as solid electrolyte and air/Lanthanum Strontium Manganite electrode has been tested both to add and extract oxygen from LBE. The oxygen addition might be limited by the oxygen reduction kinetics at the air/LSM side while, the oxygen extraction is limited at high oxygen potential by the diffusion of oxygen ions through the solid electrolyte and at low oxygen potential by the oxygen diffusion in the liquid LBE.