August 8, 2024
Lithium-lead (Li-Pb) is one of the leading candidate breeder materials for fusion blanket concepts. To date, most research and development on these materials has been with lithium in its natural isotopic state. Lithium-6 (Li-6) is the isotope of significance for tritium production thanks to its higher neutron absorption cross-section, but the abundance of Li-6 in natural lithium is only 7.8%, with lithium-7 (Li-7) comprising the remainder. To achieve a desirable tritium-breeding ratio (TBR) in candidate breeder materials, it is envisioned that higher Li-6 content is needed. However, Li-6 is presently unavailable or at least very limited for commercial purposes, due to the lack of an environmentally acceptable process to make it. Opportunely, there is a U.S. stockpile to which Idaho National Laboratory (INL) can gain access for civilian research endeavors.
This project investigates the behavior of various isotopic compositions of Li-6-enriched liquid lithium-lead (Li-Pb) samples. Over 12 months, we will demonstrate comprehensive techniques to characterize the Li-6/Li-7 isotope ratio in samples in a composition and form to be ready for irradiation. We will assess methods to measure bred tritium, focusing on detecting very low tritium concentrations in LiPb samples using the best available techniques. The resulting samples from this project will mark the first preparation of a relevant breeder composition—with varying ratios of enriched lithium—for a fusion power plant (FPP). This project will also lay the groundwork for future collaboration between Kyoto Fusioneering and INL, which includes irradiation of these samples, but also 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.