September 10, 2025
Lithium-lead (Li-Pb) alloy is a leading candidate material for tritium breeding in fusion blanket concepts. Historically, research and development efforts have primarily focused on lithium in its natural isotopic composition.
However, the isotope lithium-6 (Li-6) is of particular importance for tritium production due to its significantly higher neutron absorption cross-section. Naturally occurring lithium consists of only 7.8% Li-6, with the remainder being lithium-7 (Li-7). To achieve the desired tritium breeding ratio (TBR) in fusion breeder materials, it is anticipated that a higher content of Li-6 will be necessary. Nevertheless, Li-6 is currently scarce for commercial applications, primarily due to the absence of an environmentally sustainable large-scale production process. Fortunately, a U.S. stockpile of Li-6 is accessible for civilian research purposes through the Idaho National Laboratory (INL).
This project investigates the behavior of a range of isotopic compositions of Li-6-enriched samples of liquid lithium-lead (Li-Pb), after irradiation with thermal neutrons. This 12-month study will demonstrate advanced techniques to characterize the Li-6/Li-7 isotopic ratio in post-irradiation conditions, accurately quantify tritium generated in irradiated Li-Pb samples (even at very low concentrations) using the best available techniques (BAT), and transfer expertise in post-irradiation examination (PIE) and handling of irradiated Li-Pb samples, constituting the first such study on breeder materials relevant to fusion power plant (FPP) applications. This project will continue existing collaboration, and lay the groundwork for future development work, between Kyoto Fusioneering and INL, which may include irradiation of these materials with fast neutrons, more in-depth characterization of Li-isotope-ratio measurement, investigation of benchmarks between different techniques for tritium quantification at low concentrations, and potentially to apply the lessons learned to other Li- based breeder materials, such as liquid lithium and FLiBe (lithium- beryllium-fluoride) molten salts.