The Core Materials of the Fusion Fuel Cycle

Most common hydrogen isotope, a reference quantity in the fuel cycle

Globally available quantities

practically unlimited — Most abundant element in the universe

Radioactive

No

Density

0.09 kg/m³ (H₂ gas, standard conditions)

Melting point

−259.1 °C

Boiling point

−252.9 °C

Flammability

Highly flammable.

Not a fusion fuel itself, but must be cleanly separated from D/T.

The second fusion fuel

Globally available quantities

practically unlimited — ~33 mg/l in seawater

Radioactive

No

Density

0.18 kg/m³ (D₂ gas, standard conditions)

Melting point

−254.4 °C

Boiling point

−249.7 °C

Flammability

Highly flammable like hydrogen.

Can be extracted from seawater relatively easily (heavy-water electrolysis).

The actual fusion fuel

Globally available quantities

~20 kg — Estimated world reserve

Radioactive

Yes — β⁻ emitter (very low energy, no external radiation hazard)

Half-life

12.32 years

Density

0.27 kg/m³ (T₂ gas, standard conditions)

Melting point

−252.5 °C

Boiling point

−248.1 °C

Flammability

Flammable like hydrogen, and radioactive.

Not procurable externally in reactor quantities — must be bred on-site in the plant.

Rare isotope, candidate for aneutronic fusion

Globally available quantities

extremely rare — No economical source on Earth

Radioactive

No

Density

0.135 kg/m³ (gas, standard conditions)

Melting point

solid only under pressure (no melting point at standard pressure)

Boiling point

−269.9 °C

Flammability

Not flammable (noble gas).

Believed present in lunar regolith — a starting point for space-resource debates.

The feedstock for tritium breeding

Globally available quantities

limited — Li-6 world reserve (isotopically pure)

Radioactive

No

Density

0.534 g/cm³

Melting point

180.5 °C

Boiling point

1342 °C

Flammability

Highly flammable, reacts violently with water.

The limiting factor for many blanket concepts.

Carrier medium for FLiBe coolant loops

Globally available quantities

~28 million t — Total world lithium reserves (~92% as Li-7)

Radioactive

No

Density

0.534 g/cm³

Melting point

180.5 °C

Boiling point

1342 °C

Flammability

Highly flammable, reacts violently with water.

Contributes little to tritium breeding, but central to FLiBe.

Neutron multiplier in the blanket

Globally available quantities

~480 t — Global annual production

Radioactive

No

Density

1.85 g/cm³

Melting point

1287 °C

Boiling point

2469 °C

Flammability

Powder/dust is combustible, bulk material is not. Highly toxic (berylliosis risk).

One of the lightest structural metals; strict handling regulations apply.

Blanket shell material

Globally available quantities

~100,000 t — Global annual production

Radioactive

No

Density

19.25 g/cm³

Melting point

3422 °C (highest of all metals)

Boiling point

5555 °C

Flammability

Not flammable as bulk metal; fine dust is combustible.

Hardest unalloyed metal, often alloyed with vanadium.