The lighter isotope of lithium that reacts with thermal neutrons to breed tritium — the primary pathway for fusion fuel self-sufficiency, with natural abundance of 7.6%.
ReviewedLast reviewed: 9 Aug 2026·Category: Fuels & Materials
Role in Fusion
Lithium-6 (6Li) is the isotope of lithium used for tritium breeding in D–T fusion reactors. When a thermal neutron is captured by 6Li, the reaction produces tritium and helium-4 with a net energy release of 4.8 MeV: 6Li + n → T + 4He + 4.8 MeV.[1]
Natural abundance:6Li constitutes only 7.6% of natural lithium (the rest is 7Li). Many blanket designs require enrichment to 30–90% 6Li to achieve a tritium breeding ratio above 1.0. Lithium enrichment is a mature technology, originally developed for nuclear weapons programs.
Comparison with Lithium-7
7Li also breeds tritium but only with fast neutrons (energy > 2.5 MeV), and the reaction is endothermic: 7Li + n → T + 4He + n′ − 2.5 MeV. The secondary neutron produced helps maintain the neutron economy but the energy cost must be accounted for.[2]
Supply
Global lithium production exceeds 100,000 tonnes per year (driven by battery demand). A fusion power plant would consume only 10–30 kg of lithium per year, so lithium availability is not a constraint on fusion deployment. However, the enrichment infrastructure for 6Li would need to be scaled up.[3]
Sources
Abdou, M. et al. "Blanket/first wall challenges and required R&D on the pathway to DEMO." Fusion Engineering and Design, 100, 2–43, 2015.
Freidberg, J.P. Plasma Physics and Fusion Energy. Cambridge University Press, 2007.
Bradshaw, A.M. et al. "Is nuclear fusion a sustainable energy form?" Fusion Engineering and Design, 86, 2770–2773, 2011.