Materials
The Core Materials of the Fusion Fuel Cycle
Every fusion power plant creates its own fuel inside the plasma — world reserves aren't enough to source it externally. Ordered by mass number, ascending.
MetricImperial (°F, oz/ft³)
1
Atomic Number · Z
1
Mass Number · A
H
¹H
Isotope Notation
Protium
Most common hydrogen isotope, a reference quantity in the fuel cycle
Density
0.09 kg/m³ (gas at room temperature, H₂)
Melting Point
−259.1 °C
Boiling Point
−252.9 °C
Flammability
Highly flammable, forms explosive mixtures with air/O₂.
Toxicity
Non-toxic, but poses an asphyxiation risk at high concentration in enclosed spaces.
▶
Challenge in Nuclear Fusion
- Not a fusion fuel itself — still must be cleanly separated from D/T streams
- A constant component of impurity/off-gas streams throughout the fuel cycle
- Isotope accountancy/analytics requires highly precise measurement equipment
Cluster 3 · Fusion Fuel Data Series
1
Atomic Number · Z
2
Mass Number · A
D
²H
Isotope Notation
Deuterium
The second fusion fuel
Density
0.18 kg/m³ (gas at room temperature, D₂)
Melting Point
−254.4 °C
Boiling Point
−249.7 °C
Flammability
Highly flammable like hydrogen, forms explosive mixtures with air/O₂.
Toxicity
Chemically non-toxic like protium; asphyxiation risk at high concentration.
▶
Challenge in Nuclear Fusion
- Extraction from seawater is energy-intensive (heavy-water electrolysis/distillation)
- The raw resource itself is practically unlimited — no supply shortage expected
Cluster 3 · Fusion Fuel Data Series
1
Atomic Number · Z
Radioactive
3
Mass Number · A
T
³H
Isotope Notation
Tritium
The actual fusion fuel
Half-Life
12.32 years → Decays to Helium-3 (β⁻, 18.6 keV)
Density (liquid, ~25 K)
≈ 0.257 g/cm³ · Gas at room temperature (T₂)
Melting Point
−254.54 °C (20.62 K)
Boiling Point
−248.11 °C (25.04 K)
Flammability
Highly flammable, forms explosive mixtures with air/O₂ (like H₂).
Toxicity
Chemically non-toxic · radiologically: hazard if inhaled/ingested.
▶
Challenge in Nuclear Fusion
- Doesn't occur naturally in usable quantities – must be bred in the reactor itself via lithium breeder blankets (breeding ratio > 1 required)
- Short half-life (12.3 yrs) prevents stockpiling – continuous re-production is required
- Extreme permeability through metals – leaks are hard to fully prevent
- Very limited world stock (~20–25 kg) and high price (~USD 35,000/g)
Cluster 3 · Fusion Fuel Data Series
2
Atomic Number · Z
3
Mass Number · A
He
³He
Isotope Notation
Helium-3
Rare isotope, candidate for aneutronic fusion
Density
0.135 kg/m³ (gas at room temperature)
Melting Point
solid only under pressure (no melting point at standard pressure)
Boiling Point
−269.9 °C
Flammability
Not flammable (noble gas).
Toxicity
Chemically inert and non-toxic; asphyxiation risk at high concentration.
▶
Challenge in Nuclear Fusion
- No economical source on Earth — an extremely rare isotope
- Potential lunar mining (regolith) is discussed, but technically and economically unproven
- Required for aneutronic D-³He fusion, which is still at the research stage
Cluster 3 · Fusion Fuel Data Series
3
Atomic Number · Z
6
Mass Number · A
Li
⁶Li
Isotope Notation
Lithium-6
The feedstock for tritium breeding
Density
0.534 g/cm³
Melting Point
180.5 °C
Boiling Point
1342 °C
Flammability
Highly flammable, reacts violently with water.
Toxicity
Corrosive on contact with moisture/skin; protective equipment required when handling.
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Challenge in Nuclear Fusion
- Only ~7.6% of natural lithium — extensive isotope separation required
- Traditional separation (mercury amalgam) is environmentally problematic; new methods in development, including at PSI
- The limiting factor for many tritium-breeding blanket concepts
Cluster 3 · Fusion Fuel Data Series
3
Atomic Number · Z
7
Mass Number · A
Li
⁷Li
Isotope Notation
Lithium-7
Carrier medium for FLiBe coolant loops
Density
0.534 g/cm³
Melting Point
180.5 °C
Boiling Point
1342 °C
Flammability
Highly flammable, reacts violently with water.
Toxicity
Corrosive on contact with moisture/skin; protective equipment required when handling.
▶
Challenge in Nuclear Fusion
- Contributes little to tritium breeding, but is central as a FLiBe coolant
- Available at industrial scale (~92% of natural lithium); processing into FLiBe is demanding
Cluster 3 · Fusion Fuel Data Series
4
Atomic Number · Z
9
Mass Number · A
Be
⁹Be
Isotope Notation
Beryllium
Neutron multiplier in the blanket
Density
1.85 g/cm³
Melting Point
1287 °C
Boiling Point
2469 °C
Flammability
Powder/dust is combustible, bulk material is not.
Toxicity
Highly toxic, carcinogenic (berylliosis risk from dust/vapor inhalation).
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Challenge in Nuclear Fusion
- Highly toxic – strict handling and occupational-safety regulations (berylliosis risk)
- Demanding to process, only a handful of specialized suppliers worldwide
- Central as a neutron multiplier in many blanket concepts
Cluster 3 · Fusion Fuel Data Series
74
Atomic Number · Z
184
Mass Number · A
W
¹⁸⁴W
Isotope Notation
Tungsten
Blanket shell material
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.
Toxicity
Low toxicity as bulk metal; fine dust may be harmful to health.
▶
Challenge in Nuclear Fusion
- Highest melting point of any metal – demanding to process and shape
- Direct plasma contact at the first wall requires the highest purity and precision
- Usually alloyed with vanadium for improved mechanical properties
Cluster 3 · Fusion Fuel Data Series