Deuterium: from seawater (abundant). Tritium: from lithium (moderately abundant).
Fuel is far more abundant than uranium — potential to power civilisation for millions of years.
Why Fusion Requires Extreme Conditions
THE COULOMB BARRIER:
Both nuclei are positively charged → they REPEL each other.
To fuse, nuclei must get close enough for the STRONG NUCLEAR FORCE to take over.
This requires overcoming the electrostatic repulsion — needs extremely high kinetic energy.
REQUIRED CONDITIONS:
TEMPERATURE: ~100 million °C (ten times hotter than the Sun's core for practical fusion reactors).
At this temperature, matter exists as PLASMA — fully ionised gas of electrons and nuclei.
High temperature → high kinetic energy → nuclei approach close enough to fuse.
CONFINEMENT:
No material can contain plasma at 100 million °C.
SOLUTIONS:
MAGNETIC CONFINEMENT: powerful magnetic fields (tokamak design) hold plasma away from walls — JET, ITER.
INERTIAL CONFINEMENT: powerful lasers compress a small pellet of fuel — NIF (USA).
PRESSURE:
In stars: enormous gravitational pressure provides confinement.
On Earth: must use magnetic or laser confinement instead.
Fusion as an Energy Source
ADVANTAGES OF FUSION:
VIRTUALLY UNLIMITED FUEL: deuterium from seawater; tritium from lithium.
NO CO₂ EMISSIONS during operation.
NO LONG-LIVED RADIOACTIVE WASTE: products (helium + neutrons) — neutron activation of reactor walls is manageable, much shorter half-lives than fission waste.
INHERENTLY SAFE: reaction stops immediately if conditions not maintained — cannot 'run away' like fission.
High energy density: small amount of fuel → huge energy.
CHALLENGES:
Extreme temperatures require plasma confinement — technically very difficult.
More energy currently required to initiate and maintain fusion than is produced — net energy gain not yet achieved consistently.
Materials: reactor walls damaged by high-energy neutrons over time.
JET (Joint European Torus): record fusion energy output 2022.
ITER: international reactor under construction in France — target: Q > 10 (10× more energy out than in).
First commercial fusion power: optimistically predicted 2040s–2050s.
FUSION vs FISSION:
Fusion: cleaner waste, more fuel, inherently safer, not yet achieved at scale.
Fission: already used commercially, radioactive waste problem, limited uranium.
⚠️ Common Mistake
Fusion releases energy because the product nucleus has LESS MASS than the sum of the reactants — the mass defect converts to energy (E=mc²). Same principle as fission but with different nuclei. Fusion requires EXTREMELY HIGH TEMPERATURE (not just high pressure) because nuclei must have enough kinetic energy to overcome electrostatic repulsion.
Fusion: two small nuclei join → larger nucleus + energy. Powers the Sun. D-T fusion: ²H + ³H → ⁴He + n. Requires ~100 million °C plasma. Confinement: magnetic (tokamak/ITER) or laser. Advantages: abundant fuel, clean waste, inherently safe. Challenge: net energy gain not yet achieved. Compare with fission: fusion cleaner but not yet practical.
🎯 Matching Activity — Fusion vs Fission
Match each property to fusion, fission, or both. — drag the symbols on the right to match the component names on the left.
Fusion only
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Fission only
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Both
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Fusion only
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Fission only
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Large nucleus absorbs neutron and splits — used in nuclear reactors today