UK Fusion Energy Ltd, the UKAEA company delivering the UK’s first prototype fusion energy plant, has published two European patent applications, marking an important milestone for the STEP (Spherical Tokamak for Energy Production) programme.
The applications describe a modular vacuum vessel architecture and associated sealing technology that together support a new approach to fusion reactor assembly and maintenance.
The technologies explore new approaches to vacuum vessel’s construction, maintenance and lifecycle management, helping address key engineering challenges associated with future fusion power plants.
The applications are:
- EP4742271A1 – Modular Vessel Assembly’
- EP4742272A1 – Fluid Sealing Device for a Modular Vessel Assembly’
Together, they describe a vacuum vessel concept in which the tokamak is divided into a series of stacked annular modules, rather than being constructed as a single welded structure.
This approach has been developed to simplify maintenance and component replacement and to improve access to internal systems, supporting more efficient lifecycle management of key reactor components.
Vacuum vessel architecture
Vacuum vessels are among the most complex systems in a fusion power plant. They must maintain a vacuum while operating in an environment exposed to high temperatures, electromagnetic forces and neutron loads. Most fusion vacuum vessels are built as large welded structures. While effective, these designs can make maintenance and component replacement challenging.
The STEP patent applications describe a different approach: a vacuum vessel made up of stacked ring modules. Each module combines the vacuum vessel with associated in-vessel systems, allowing sections to be assembled, removed and maintained individually.
By dividing the tokamak in this way, the design aims to reduce the number of connections that need to be made and broken during maintenance activities and improve access to internal systems. Individual vessel sections can be removed, serviced and reinstalled independently, creating a more maintainable architecture than conventional monolithic vacuum vessel designs.
The sealing challenge
A modular vessel design depends on being able to maintain a reliable vacuum seal between each section.
The second patent application focuses on the sealing system located between adjacent modules. The design is intended to maintain vacuum integrity while accommodating the manufacturing tolerances and deformation that can occur in large fabricated structures. This is a key challenge for any modular vacuum vessel concept, where reliable sealing performance must be maintained across multiple vessel interfaces.
The vessel architecture and sealing technology form a single engineering solution, enabling a modular vacuum vessel while maintaining the conditions needed for plasma confinement.
