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Fusion Materials (FM TCP)

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Testing ceramic materials under extreme conditions

Materials able to withstand extreme temperatures and neutron bombardment in the fusion chamber are a priority for fusion. The FM TCP develops materials for the first wall and blanket of the fusion chamber capable of operating under extreme temperatures and with a high flux of neutrons. Silicon carbide and silicon carbide composites are the focus of recent testing as they are among the few than can withstand extreme temperatures for long periods of time. 

The predicted state of damage and cracking in a silicon carbide joint. Research on materials is crucial for advancements in fusion power.*

A significant challenge for fusion power science is to identify materials able to withstand extreme heat radiating from plasma as well as the effects of the neutron bombardment. Other important challenges include identifying materials that are able to provide safe, reliable and predictable performance as well as a long service life at elevated temperatures with minimum latent radioactivity to enable simplified, environmentally safe recycling. 

To date, materials R&D has focused on three candidate systems: steels, vanadium alloys, and silicon carbon composites. Steels containing alloys such as chromium, and tungsten have been the focus of much research and as such have the highest probability of being used in components for the demonstration phase of fusion (DEMO). Advanced steel alloys under development (oxide dispersion strengthened alloys) offer promise to withstand higher temperatures and improved resistance to radiation damage. Vanadium alloys (vanadium, chromium and titanium) also have attractive properties, especially for use with liquid lithium cooled fusion chamber wall (blanket) designs.

Compared to metals, silicon carbide (SiC) and SiC composites show promise due to their ability to withstand the highest temperatures. Further research is needed, particularly with regard to the effects of irradiation on the material and joints between SiC device components. The use of SiC for fusion will require development of advanced ceramic joining technologies for assembling components able to tolerate the extreme environment. Improved understanding of the effectiveness of joining the two fusion device components is crucial.

For these reasons, the FM TCP participants carried out irradiation experiments on SiC joints by inserting small test specimens into the fusion device High Flux Isotope Reactor (HFIR). The specimens were twisted (torsion) to test the strength and durability of various joining methods before and after irradiation. A computer-based model was developed to analyse the model results, which showed that high-strength joints were not likely to fail in a manner that enabled exact measurement of the true strength of the joint. Yet changes in joint strength associated with radiation damage could be revealed during tests after irradiation. The damage model provides a valuable tool for interpreting the experimental data by revealing the effects of various parameters on SiC joint strength and integrity.

Results from the experimental campaign showed that strength measurements combined with information on the location of the failure could be used to assess and improve joining methods for SiC components.**

* Graphic courtesy of Battelle Memorial Institute
 
** Henager, C.H. et al. (2014), “Low Activation Joining of SiC/SiC Composites for Fusion Applications: Modeling Miniature Torsion Tests”, Department of Energy Office of Energy Research, Fusion Reactor Materials Program, Vol. 56

Activities

  • Diagnostics and control insulating ceramics
  • Fundamental studies of irradiation effects
  • Irradiation facilities and post-irradiation tests
  • Modelling, computer simulation and validation
  • Reduced activation ferritic steels and advanced ferritic alloys
  • Silicon carbide composites
  • Tungsten and tungsten-based alloys
  • Vanadium base alloys

Participants

  IEA member 
countries
 Partner 
 countries 
Reg./Int. 
orgs.
Contracting Parties  5 3 1
Sponsors - -  -

For more information: www.frascati.enea.it/ifmif

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