Garnet-type lithium sensors for the monitoring and control of Pb-Li alloys in tritium breeding modules

During the EU-DEMO conceptualization, eutectic Pb-Li was considered as the prime candidate liquid breeding material. Nonetheless, the conversion of lithium into tritium through the breeding reaction will result in a decrease in the lithium concentration within the alloy. Then, the monitoring of the lithium concentration in Pb-Li alloys is critical for the optimal Tritium Breeding Blanket (TBB) performance, as lithium affects dissolution of structural materials, tritium inventory and extraction rates. Garnet-like ceramics possess desirable properties for their use in lithium sensors, like high lithium-ion conductivity, good chemical stability, low thermal expansion coefficient, and great mechanical strength. For these reasons, electrochemical sensors based on garnet-type ceramics offer advantages for measuring lithium in molten Pb-Li alloys, such as high selectivity and fast response. This work presents the development of lithium sensors based on the garnet-type ceramic Li6BaLa2Ta2O12. The material was characterized by XRD and SEM, exhibiting good crystallinity and a homogeneous microstructure. The sensors were evaluated in a potentiometric configuration in molten Pb-Li alloys with lithium concentrations ranging from 3 to 35 at% Li. Potentiometric measurements were used to obtain correlations that allow the determination of the lithium activity in the lead–lithium alloys studied.