Nuclear fusion is the joining of two light atomic nuclei to form a heavier one, releasing energy. Most power plant designs aim to fuse deuterium and tritium, two forms of hydrogen, at temperatures above 100 million degrees Celsius. It is the opposite of fission, used in today’s nuclear power stations, which splits heavy atoms such as uranium. Fusion produces no long-lived high-level waste and cannot run away like a fission chain reaction, but no fusion device has yet produced more electricity than it consumes.
Key UK and international projects
| Project | Where | Status |
|---|---|---|
| JET | Culham, Oxfordshire | Operated 1983–2023; now being decommissioned |
| STEP | West Burton, Nottinghamshire | Prototype plant; first operations targeted for 2040 |
| ITER | Southern France | International experiment; research operations planned from 2034 |
JET (Joint European Torus) was one of the world’s largest tokamaks, devices that hold plasma in a ring-shaped magnetic field. In its final experiments in 2023 it released a record 69 megajoules of fusion energy in a single pulse, as reported by the UK Atomic Energy Authority (UKAEA). That was still less energy than was used to heat the plasma.
STEP (Spherical Tokamak for Energy Production) will be built on the site of the former West Burton A coal power station. The government announced £2.5 billion of fusion funding in June 2025. The project is run by UK Industrial Fusion Solutions, part of UKAEA.
ITER, backed by the EU, China, India, Japan, Korea, Russia and the US, revised its schedule in 2024. Research operations are planned from 2034 and deuterium-tritium operation from 2039, about a decade later than earlier plans.
A realistic view of timing
Fusion is a long-term research effort, not a near-term source of power. STEP aims only to begin operating in 2040, and commercial fleets would follow later. Fusion will make no contribution to the UK’s 2030 clean power goals, and its role in reaching net zero by 2050 is uncertain.
Read more: The pros and cons of nuclear energy.