Neutrons and charged particles produced by nuclear reactions in the deuterium-tritium plasma of a fusion tokamak device affect physical and mechanical properties of structural materials in the components surrounding the plasma. These changes, for example irradiation-induced embrittlement or the loss of thermal conductivity, result primarily from the processes occurring at the atomic scale. Fast neutrons or ions initiate collision cascades, in which radiation defects are formed. Collision cascades do not change the chemical composition of materials but produce fairly stable, relatively well localized, and mobile distortions of atomic structure; these are radiation defects. The defects migrate either as Brownian thermal particles or are driven by elastic stresses, they interact, react, coalesce, and grow. On the micro-meter mesoscopic scale, the generation of radiation defects drives a particular type of microstructural evolution, which occurs only in irradiated materials. For example, observations show that the otherwise thermodynamically stable iron and tungsten alloys decompose under irradiation. Magnetic properties of iron and iron alloys also change under irradiation, affecting the conditions of magnetic plasma confinement.
The presentation will describe two areas of modelling where significant advances have been made recently: atomistic and elastic continuum models for mesoscopic defects, and models describing the dynamics of magnetism in iron-based alloys, and its relation to the structure and stability of such alloys under high temperature and irradiation conditions.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053 and from the RCUK Energy Programme (grant number EP/P012450/1).