Fuel And Sustainability Glossary

Definitions of the key fuel-cycle and sustainability terms used across these pages, stated plainly and honestly.

Fuel and isotope terms

• Deuterium — stable heavy hydrogen isotope (one proton, one neutron); the primary fusion fuel, separated from water.
• Tritium — radioactive hydrogen isotope (one proton, two neutrons); half-life about 12.3 years; bred in the lithium blanket.
• Helium-3 — stable, scarce helium isotope; produced when tritium decays; fuels the burner and serves refrigeration, detection, and imaging.
• Lithium — abundant element used in the breeding blanket; captures neutrons to make tritium.

Cycle terms

• Tritium breeding ratio (TBR) — tritium atoms produced per tritium atom consumed; studied at 1.1, 1.5, and 1.8.
• Neutron economy — how fusion neutrons are allocated among breeding, multiplication, absorption, and leakage.
• Closed fuel cycle — a cycle that regenerates its fuel internally, needing only abundant external inputs.
• Local vs net breeding — breeding measured before losses versus the fuel actually delivered after recovery losses.

Machines and canon

• Breeder (Hyperion) — deuterium-tritium spherical tokamak; design Q 3.424, 88.7 MW, 9.86 MA, 16.84 T peak.
• Burner (Aegis / MetroVolt) — deuterium-helium-3 tandem mirror; 26.49 T plug, 17 T throat, 5.44% neutron fraction.
• Design and simulation study — computed targets, not measurements; construction begins Q2 2027, first tritium ~2030.

Honest note

All quantitative figures on these pages are computed design targets, not measured results, and none is economic. See a sustainable fuel cycle and sustainability metrics.

How to read these terms together

These terms interlock: deuterium and lithium enter, neutrons breed tritium, tritium sustains the plant and decays to helium-3, and the loop closes. Read as a sequence rather than isolated definitions, they describe a single self-sustaining fuel cycle. Every quantity attached to them on these pages is a computed design target for machines still in simulation, never a measurement or an economic figure.