The United Kingdom's national fusion research organization, operating the MAST Upgrade spherical tokamak and leading the design of STEP — the UK's planned prototype fusion power plant.
The UK Atomic Energy Authority (UKAEA) is the United Kingdom's national organization for fusion energy research and development. Based at the Culham Centre for Fusion Energy in Oxfordshire, UKAEA has been at the forefront of magnetic confinement fusion research for more than six decades, hosting the Joint European Torus (JET) from 1983 until its final operations in December 2023, and now leading the UK's ambitious plans to build a prototype fusion power plant.1
UKAEA was established in 1954 to oversee the United Kingdom's civil nuclear energy program, including both fission and fusion research. While its fission responsibilities were transferred to other bodies over the decades, UKAEA retained its fusion mandate and became increasingly focused on magnetic confinement research at Culham. The organization operated JET on behalf of the European fusion community under contract to EUROfusion and its predecessors, managing what was for many years the world's most capable tokamak and the only device in the world to have operated with deuterium-tritium fuel mixtures on a sustained experimental basis.2
The Mega Amp Spherical Tokamak Upgrade (MAST-U) began operations in 2021 and serves as UKAEA's primary experimental facility. The device is designed to test innovative exhaust handling concepts — particularly the Super-X divertor, which spreads the intense heat flux leaving the plasma over a larger area, potentially solving one of the most critical engineering challenges facing any future fusion power plant. Early results from MAST-U have demonstrated significant reductions in target heat flux using the Super-X configuration, validating the concept for further development.
The most ambitious element of UKAEA's current program is STEP — the Spherical Tokamak for Energy Production. Announced by the UK government in 2019 with initial funding of 220 million pounds, STEP aims to design, build, and operate a prototype fusion power plant that will put net electricity on the grid. The plant will be sited at West Burton in Nottinghamshire, a former coal power station, and is targeted for completion in the 2040s. STEP's compact spherical tokamak design draws directly on physics results from MAST-U and represents a departure from the larger conventional tokamak geometry pursued by ITER and EU-DEMO.4
Beyond its experimental and design programs, UKAEA has developed world-leading capabilities in fusion-relevant robotics and remote maintenance, materials science for extreme environments, tritium handling and processing, and advanced computing for plasma simulation. The organization operates dedicated facilities including the Materials Research Facility for testing irradiated materials and the RACE (Remote Applications in Challenging Environments) center for developing robotic maintenance systems that will be essential inside any future fusion power plant.5
Following the United Kingdom's departure from the European Union, UKAEA's relationship with EUROfusion entered a transitional phase, though the UK subsequently re-associated with the Euratom Research and Training Programme, preserving scientific collaboration while UKAEA pursues its independent STEP program. The organization employs over 2,000 staff and continues to expand, positioning the UK as one of the leading nations in the international race to deliver fusion electricity.