Domain overview
The fuel cycle behind a fusion reactor
Original Fusenergy explanation, framed against public technical references. Educational, not engineering or investment advice.
Fuel choice defines both the opportunity and the difficulty of a fusion concept. Deuterium–tritium is the near-term reference because it reaches useful reactivity at the lowest temperature of any candidate, but roughly 80% of its energy leaves as 14.1 MeV neutrons and one of its fuels, tritium, is radioactive with a 12.3-year half-life and does not exist in usable natural quantities. Deuterium, by contrast, is abundant in seawater, so the deuterium supply is effectively unlimited — the fuel problem is almost entirely a tritium problem.
Because tritium must be bred, a D–T plant is only viable if its blanket produces slightly more tritium than the plasma consumes, and if that tritium is captured, accounted for, and re-injected with very low losses. This makes fuel accounting, isotope separation, and inventory tracking safety-critical as well as economic concerns: regulators and operators both care intensely about how much tritium is where. Fuelling technology — pellet injection and gas puffing — then has to deliver fuel to the plasma core efficiently rather than just to its edge.
Advanced fuels change the trade entirely. Deuterium–helium-3 and proton–boron-11 promise far fewer neutrons and charged products suited to direct conversion, but they demand much higher temperatures, and helium-3 is genuinely scarce. The ten topics — deuterium supply, tritium inventory, lithium breeding, isotope separation, fuel accounting, injection, pellet fuelling, helium-3 scarcity, boron handling, and advanced-fuel temperatures — let you weigh those tradeoffs across all six lenses.
Tritium self-sufficiency
A D–T plant must breed its own tritium in the blanket with a breeding ratio above one and lose very little in processing. This is the tightest closed loop in the whole plant.
Deuterium is easy, tritium is hard
Deuterium is extracted from water at scale; the fuel-cycle challenge is almost entirely tritium breeding, extraction, accounting, and safe inventory management.
Advanced fuels and their price
D–He₃ and p–B11 cut neutron output and enable direct conversion, but require much higher temperatures and, for helium-3, a fuel that is extremely scarce on Earth.