US start-up Commonwealth Fusion Systems (CFS) is the first international company to join the UK Atomic Energy Authority’s (UKAEA’s) Lithium Breeding Tritium Innovation programme (LIBRTI). The collaboration focuses on solving tritium fuel breeding, which is one of the largest remaining technical hurdles facing commercial nuclear fusion.
CFS, a private company based in Devens, Massachusetts, spun out of the Massachusetts Institute of Technology (MIT) in 2018. The company has raised more than $3bn in private capital, making it the best-funded fusion energy company globally. CFS is currently building its SPARC fusion demonstration machine and expects to generate electricity from its first ARC fusion power plant in Virginia in the early 2030s.
LIBRTI, a £220m ($291m) UK government initiative that aims to demonstrate net tritium production, is creating a first-of-a-kind technology facility at UKAEA’s Culham Campus following the recent acquisition of a high-flux neutron source. Tritium production is a vital capability for commercialising fusion energy.
Tritium (T) serves as the primary fuel source for first-generation commercial fusion reactors. It is a heavy, radioactive isotope of hydrogen containing one proton and two neutrons in its nucleus. To achieve controlled nuclear fusion, reactors must fuse tritium with deuterium (D), another hydrogen isotope containing one proton and one neutron. A single gram of D-T fusion fuel can produce as much thermal energy as 2,400 gallons of oil or 10 tonnes of coal.
However, tritium presents a massive supply-chain challenge for commercial energy deployment. The global annual production of civilian, commercially available tritium is only approximately 2 kilograms a year. This is a byproduct of heavy-water nuclear fission reactors. The total global inventory of non-military tritium sits between 20 and 30 kilograms. This will peak before 2030 and rapidly decline. Natural cosmic rays striking the atmosphere create about 400 grams of tritium globally each year, but it is too diffuse to collect.
Because tritium has a rapid 12.3-year half-life, the existing inventory is constantly decaying away. If commercial fusion plants are not built before the current heavy-water reactors retire, the world may lack the “matchstick” fuel required to ignite the first generation of commercial reactors. Because of its extreme rarity, tritium costs approximately $30,000 per gram. Clearly fusion plants cannot rely on external shipping. They must breed their own fuel on-site in real time.
The 2 kg annual global production rate totally inadequate in view of what upcoming fusion projects actually require. The international ITER tokamak project will require roughly 12 to 16 kilograms over its multi-year test campaign, which will consume a massive portion of the existing global supply. Compact reactors from companies such as CFS or First Light Fusion will need hundreds of grams to several kilograms just to fill their cores for initial startup operations.
Once operational, a single standard 1 GWe commercial fusion plant will consume roughly 50 to 55 kilograms of tritium a year. If fusion eventually scales up to supply just 10% of global electricity demand, the industry will consume an estimated 600 to 760 tonnes of tritium annually. This is why mastering the technology behind on-site tritium breeding blankets via programmes such as UKAEA’s LIBRTI is a non-negotiable requirement for the fusion industry.
In a fusion power plant, a blanket is the region where neutrons from the fusion process strike lithium atoms that then turn into tritium. The production technique is called breeding, and the new LIBRTI facility will enable industry partners to develop and verify their blanket technologies in fusion environments representative of full-scale machines.
CFS and UKAEA will work together, designing the experimental setup, developing testing protocols, and conducting experiments at the LIBRTI facility. CFS will build the test articles to be used in the first investigations.
CFS bases its technology on the tokamak design, using a breakthrough magnet technology to achieve a radically smaller, faster, and cheaper path to commercial fusion energy. This centres on the concept that stronger magnetic fields allow a fusion reactor to be significantly downsized while maintaining high power output.
The CFS magnets generate a steady magnetic field of 20 Tesla, which is twice the strength of conventional low-temperature superconductors. This will enable CFS to build reactors that are 40 times smaller in volume than the international ITER tokamak project while targeting similar power outputs.
CFS is executing a rapid commercialisation timeline using two successive reactor models. SPARC (Test Device) currently under construction in Devens, is intended to demonstrate net energy, It is targeting first plasma by 2030. The 200 MWe ARC (Commercial Plant) is intended to deliver electricity to the grid. It is in the conceptual design phase with deployment planned for the early 2030s.
The partnership with the UKAEA directly supports ARC’s unique FLiBe liquid immersion blanket. Instead of solid shielding, the ARC reactor core will be submerged in a tank of molten fluorine, lithium, and beryllium salt (FLiBe). The circulating molten salt absorbs the high-energy neutrons produced by the D-T fusion reaction, heating up to carry thermal energy out to drive electricity-producing turbines.
As neutrons hit the lithium atoms inside the FLiBe salt, they split to produce tritium. This tritium is extracted continuously to refuel the reactor, solving the global tritium scarcity issue. The liquid blanket also eliminates the mechanical stress and structural degradation that solid blankets suffer from neutron bombardment, allowing for easier maintenance access to the core.
Amanda Quadling, Senior Responsible Officer, LIBRTI, said: “Welcoming CFS is a defining moment for LIBRTI. Their participation adds momentum to our own efforts and accelerates the global pathway to demonstrated fusion power plant scale technology.
Brandon Sorbom, Co-founder and Chief Science Officer at CFS, said: “LIBRTI’s specialised testing capabilities will allow us to demonstrate net tritium production and increase confidence in our ARC blanket system design. Through this collaboration, CFS will gain hands-on experience engineering and building blanket systems directly representative of our commercial fusion power plant.”
Heena Mutha, Director of Fuel Cycle and Blanket Technology at CFS, commented: “It’s an incredible moment for the fusion industry that we’re building the capability to investigate the performance of blankets in a fusion-relevant environment. We look forward to this collaboration with the UKAEA and LIBRTI.”
