Starts 11 May 2022 11:00
Ends 11 May 2022 12:00
Central European Time
Via Zoom
Duc Nguyen-Manh
United Kingdom Atomic Energy Authority



Abstract:

“We say that we will put the sun into a box. The idea is pretty. The problem is, we don’t know how to make the box” (Pierre Gilles de Gennes).
 
Nuclear fusion - the joining together of atomic nuclei of light elements such as the reaction between two hydrogen isotopes, deuterium (D) and Tritium (T) to form heavier helium atoms - is the process by which vast amounts of energy is produced in stars like our sun. If it can be harnessed on Earth it has the potential deliver a nearly unlimited and safe source of energy which does not produce the environmentally damaging CO2 emissions that are released by burning traditional fossil fuels. To achieve nuclear fusion in a machine on Earth, extraordinarily high temperatures of around 150 million degrees Celsius are needed, about 10 times higher than the temperature of the sun's core.  Most recently, the UK-based Joint European Torus (JET) laboratory in Culham, has made a breakthrough in the quest to develop practical energy fusion in producing 59 MJ of energy (more than double what was achieved in the 1997 test) but over only 5 seconds.  
 
The major technological challenges of fusion energy are intimately linked with the availability of suitable materials capable of reliably withstanding the extremely severe operational conditions of fusion reactors. The energetic spectrum associated with the D-T fusion neutrons (14.1MeV compared to<2MeV on average for fission neutrons) releases significant amounts of hydrogen and helium as transmutation products that might lead to a degradation of materials after a few years of operation.  Structural materials development, together with research on functional materials capable of sustaining unprecedented power densities during plasma operation in a fusion reactor, have been the subject of decades of worldwide research efforts underpinning the present fusion materials research programme. Overcoming the lack of a fusion-relevant neutron source for materials testing is an essential pending step in fusion roadmaps.
 
At the same time, fundamental understanding of the transient materials changes due to fusion neutron loading pose scientific and predictive computational challenges that require the development of an integrated framework to support the design effort for future fusion power plants. In this talk, we highlight the recent advances in developing an integrated multi-scale modelling based on first-principles calculations to investigate phase stability under and microstructure evolution of plasma-facing material components such as reduced-activation ferritic/martensitic (RAFM) steels for the first wall and W&W alloys for the divertor [1-5]. More attention will be focusing on our recent development of constrained thermodynamic approach in predicting free energies of the various phases in the presence of radiation-induced defects (saturated vacancies, interstitials, and precipitates) with the final microstructure of combinations of phases giving the lowest free energy. The model has been successfully employed not only to understand the origin of microstructures decorated by transmutation products in neutron irradiated W [6-7] but also to predict new W-based based high-entropy alloys with outstanding radiation resistance [8].
 
[1] D. Nguyen-Manh et al., Phys. Rev. B, 73, 010201 (2006); PRB, 80, 104440 (2009)
[2] D. Nguyen-Manh et al., Progress in Materials Science., 52, 255 (2007).
[3] D. Nguyen-Manh et al., J. Mater. Science, 47, 21 (2012)
[4] D. Nguyen-Manh et al., Annal of Nuclear Energy, 77, 246 (2015); NIMB, 352, 86 (2015)
[5] K. Arakawa et al., Nature Materials, 19, 508 (2020)
[6] D. Nguyen-Manh et al, Phys. Rev. Mater., 5, 065401 (2021)   
[7] M. J. Lloyd et al., Materialia, 22, 101370 (2022)
[8] O. Et-Atwani et al., Science Advances, 5, eaav2002 (2019).