A molten salt mixture of lithium fluoride and beryllium fluoride being considered as a combined coolant, neutron multiplier, and tritium breeder for advanced fusion blankets.
ReviewedLast reviewed: 9 Aug 2026·Category: Fuels & Materials
Composition
FLiBe is a eutectic mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2), with a melting point of approximately 459°C. It combines two essential fusion blanket functions in a single liquid: lithium for tritium breeding and beryllium for neutron multiplication.[1]
Triple function: FLiBe simultaneously serves as (1) a tritium breeding medium (lithium captures neutrons to produce tritium), (2) a neutron multiplier (beryllium undergoes (n,2n) reactions), and (3) a heat transfer fluid (carrying thermal energy to the power conversion system). This integration simplifies blanket design.
Applications
FLiBe has been proposed for use in several fusion reactor concepts, including the ARC/SPARC design from CFS and various stellarator power plant studies. It was extensively studied in the Molten Salt Reactor Experiment (MSRE) at Oak Ridge in the 1960s, providing a substantial engineering database.[2]
Challenges
Key challenges include: tritium permeation through heat exchanger walls (tritium dissolved in FLiBe can diffuse through metal surfaces); beryllium toxicity; corrosion of structural materials at high temperature; and the management of transmutation products (including tritium fluoride).[3]
Sources
Sawan, M.E. and Abdou, M.A. "Physics and technology conditions for attaining tritium self-sufficiency for the DT fuel cycle." Fusion Engineering and Design, 81, 1131–1144, 2006.
Haubenreich, P.N. and Engel, J.R. "Experience with the Molten-Salt Reactor Experiment." Nuclear Applications and Technology, 8, 118–136, 1970.
Meier, W.R. et al. "Fusion technology aspects of laser inertial fusion energy." Fusion Engineering and Design, 89, 2489–2492, 2014.