Materials Technology Laboratory

Fusion material challenges

JET interiorHarnessing fusion energy is a demanding process and requires materials that can cope in extreme environments. Some of the challenges faced by fusion materials are:

  • Materials used in the fusion reactor are expected to be low-activity, meaning that when reactors are shut down, they can be dismantled and disposed of relatively rapidly, without the risk of radioactive contamination. This limits the elements that we can use in fusion reactor blanket materials, necessitating new materials to be utilised.
  • The new materials required for fusion reactors generally need to establish supply chains and are not nuclear qualified. Developing the qualification, regulation and industrial supply chain for these materials represents a key challenge to commercial fusion power.
  • The engineering challenges of fusion often necessitate complex component cooling, use of multi-material interfaces and complex shaping. Materials utilised must accommodate these advanced design requirements.
  • Material facing the plasma generated during fusion operations may require prolonged operation at temperatures in excess of 1000°C.
  • Materials inside the toroidal magnets of a fusion reactor may experience high magnetic fields (>10T) and must be tested to validate operation under these conditions.
  • Neutrons generated during the fusion reaction cause the structure of materials to change. In some cases, atoms are rearranged hundreds of times because of neutron bombardment during the lifetime of the reactor.
  • Materials coming into contact with plasma causes material erosion.
  • Liquid lithium will be contained within fusion blanket materials to allow for tritium generation – a fuel required for the fusion reaction. Exposure of metals to liquid lithium often negatively affects their properties.

 

It is clear that a specialised range of materials will be required to meet these challenges. The Material Technology Laboratory is always looking for future materials which may offer superior properties, but a selection of leading candidate materials we already use and study are:

  • Reduced Activation Ferritic Martensitic (RAFM) Steels – RAFM steels such as EUROFER97 are considered the primary candidate for most fusion breeding blanket designs and internal piping for DEMO fusion reactors. These are reduced activation 9%Cr steels, akin to P91 grade steels with elemental substitution.
  • Nano-strengthened steels – MTL are also looking into oxide dispersion strengthened (ODS) variants of EUROFER97, 14%Cr ODS steels and cast nano-precipitate strengthened steels. These materials offer superior high temperature performance compared to conventional RAFM steels, but with a less mature supply chain.
  • Tungsten – with a melting point in excess of 3400°C, tungsten is well-suited to a plasma-facing role in the first wall blanket. It is also less susceptible to plasma erosion than other candidate materials. However, at temperatures below 400°C, tungsten is brittle. Thus design with tungsten is challenging. The industrial supply chain for high quality and reproducable tungsten production is not yet established.
  • Copper-Chromium-Zirconium – or more accurately Cu-1.0%Cr-0.1%Zr – is considered the primary material for the water-cooling pipes for the divertor within a fusion reactor.
  • Vanadium-Chromium-Titanium – otherwise known as V44, V-4%Cr-4%Ti – is recognized as an attractive structural material for the liquid lithium blanket of a demonstration fusion reactor (DEMO), because of its good levels of high temperature strength, creep resistance, irradiation tolerance and a relatively low ductility loss due to radiation-induced defects. Vanadium itself is also a very low activating element within the blanket environment, providing a significant advantage in decommissioning and remote handling of components. Presently there is no industrial supply chain or infrastructure that can produce the tonnage of V44 that would be required by fusion reactor designs.