Nuclear fusion
The joining of light nuclei, such as deuterium and tritium, into a heavier nucleus, releasing energy; the process that powers the Sun and an experimental route to electricity.
The most accessible fusion reaction is deuterium-tritium (D-T):
It requires plasma temperatures of around 100–150 million °C. The Lawson triple product (density × temperature × confinement time) must exceed about 3 × 1021 keV·s/m3 for ignition. Two main approaches exist:
- Magnetic confinement: tokamaks (ITER, JET, JT-60SA, SPARC) and stellarators (Wendelstein 7-X).
- Inertial confinement: lasers compress fuel pellets. The US National Ignition Facility achieved target gain above 1 in December 2022 (3.15 MJ out from 2.05 MJ of laser energy) and later exceeded 5 MJ, although wall-plug laser energy is around 300 MJ.
Key metrics are Qplasma (fusion power over heating power) and Qengineering (net electricity). ITER in France aims for Q = 10 with 500 MW of fusion power; its revised baseline delays D-T operation to the late 2030s. Private companies such as Commonwealth Fusion Systems, Helion and TAE target pilot plants in the 2030s.
Outstanding challenges include tritium breeding from lithium blankets (tritium is scarce, about 20 kg globally), materials that withstand 14 MeV neutron damage, and economic power density. Fusion produces no long-lived high-level waste, but activated structures require management. Unlike fission, there is no chain reaction to run away.
Related terms
All terms →- Nuclear fission
The splitting of a heavy atomic nucleus such as uranium-235 or plutonium-239 into lighter nuclei after absorbing a neutron, releasing about 200 MeV of energy and further neutrons.
- Thorium fuel cycle
A nuclear fuel cycle that uses fertile thorium-232, which absorbs a neutron and decays to fissile uranium-233, as an alternative to uranium-plutonium fuel.
- Sievert (radiation dose)
The SI unit of effective dose, weighting absorbed radiation energy by radiation type and tissue sensitivity to estimate stochastic health risk; 1 Sv = 1 J/kg.
- SMR (Small Modular Reactor)
A nuclear reactor of up to about 300 MWe per module, designed for factory fabrication and modular deployment to cut construction time and financing risk.