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Layered Armour Limiters Developed for UKAEA

Mon, 04 September, 2023

TWI, working alongside Frazer-Nash Consultancy, has developed and manufactured layered armour limiters for the United Kingdom Atomic Energy Authority (UKAEA).

This work was delivered under the STEP (Spherical Tokamak for Energy Production) Manufacturing Support Services Framework, established to support design and construction of the UK’s prototype fusion energy plant in Nottinghamshire that will generate electricity for the National Grid.

The limiters have been created for use specifically in tokamaks, and are in-vessel components designed to protect the first wall from the extremely high heat loads that occur during transient plasma events.

In some extreme and off-normal scenarios, the limiters are required to absorb thermal loads that are greater than any material would be expected to withstand without melting and would need to be replaced after such an event.

The design for the prototype limiters consisted of four off pure tungsten monoblocks that are joined to a single copper chromium zirconium tube with a copper insert (see image below).

Figure 1. Schematic of prototype limiter, courtesy of UKAEA
Figure 1. Schematic of prototype limiter, courtesy of UKAEA

The development of the limiters included assessing the suitability of manufacturing the monoblock assemblies. This was done through a machining process to create a lower conductivity layer situated within the pure tungsten monoblock.

Several designs were created for the monoblocks, allowing UKAEA to assess the thermal conductivity properties of the differing designs

Radial diffusion bonding was used for the manufacture of these assemblies, bonding the components together to create a total of four layered armoured limiter demonstrators. You can see an image of a layered armour limiter assembly, below:

Figure 2. Image of an assembled layered armour limiter demonstrator
Figure 2. Image of an assembled layered armour limiter demonstrator

UKAEA has tested the most porous design at their HIVE facility (Heating by Induction to Verify Extremes), with results showing that the sample performed well after undergoing 500 cycles at a front face temperature of 1100°C. The limiter showed no signs of thermal performance degradation or ligament cracking, and UKAEA tests showed a drop in effective conductivity through the machined featured layer of around 60%, whilst also exhibiting no signs of debonding at the pipe interface.

You can see an image taken during the testing, below:

Figure 3. Image of an assembled layered armour limiter demonstrator during testing, courtesy of UKAEA
Figure 3. Image of an assembled layered armour limiter demonstrator during testing, courtesy of UKAEA

UKAEA’s technical lead for the contract, James Roberts, is now due to present a poster detailing the work and testing at the upcoming, ‘International Symposium on Fusion Nuclear Technology (ISFNT 15),’ which is taking place from 10-15 September 2023 in Gran Canaria, Spain.

At TWI we continue to support the fusion industry using our expertise in design, testing and prototyping, and if you have an engineering challenge that you would like to discuss, please feel free to contact us using the email address:

About UK Atomic Energy Authority

United Kingdom Atomic Energy Authority (UKAEA) is the UK’s national organisation responsible for the research and delivery of sustainable fusion energy. It is an executive non-departmental public body, sponsored by the Department for Energy Security and Net Zero.

Fusion energy has great potential to deliver safe, sustainable, low carbon energy for generations to come. It is based on the same processes that power the Sun and stars, and would form part of the world’s future energy mix. Achieving this is a major technical challenge that involves working at the forefront of science, engineering, and technology.

UKAEA’s programmes include the MAST-Upgrade (Mega Amp Spherical Tokamak) fusion experiment and the JET (Joint European Torus) fusion research facility. JET is operated by UKAEA at its Culham Campus near Oxford, on behalf of EUROfusion scientists and engineers.

STEP (Spherical Tokamak for Energy Production) is UKAEA’s ambitious programme to accelerate the delivery of fusion energy, with plans to deliver a prototype powerplant producing net electricity in the 2040s in Nottinghamshire.

In 2021, UKAEA opened its Fusion Technology Facility near Rotherham in South Yorkshire, to develop and test materials and components for future fusion powerplants. UKAEA also undertakes cutting edge work with academia, other research organisations and the industrial supply chain in a wide spectrum of areas, including robotics and materials.

More information: Social Media: @UKAEAofficial

For more information, please email:

For more information please email: