First principles simulation of resistivity recovery in irradiated beryllium

Future fusion devices like ITER or DEMO require closed fuel cycles. These vitally depend on neutron multiplying materials as part of a breeding blanket module like beryllium pebbles in the European Helium-Cooled Pebble-Bed. During operation the beryllium pebbles will accumulate point defects, tritium, and helium due to inevitable exposure to highly energetic neutron irradiation as emitted by the fusion plasma. A detailed knowledge of the characteristics of point defects is decisive for reliable simulations of microstructure evolution in irradiated beryllium. Such models are a prerequisite for predicting tritium inventory during operation as well as after the blanket ́s end of life since tritium retention and release is the paramount safety concern. A well-established experimental approach to assess the dynamics of relevant atomic defects consists in measuring electrical resistivity recovery (ERR) after irradiation during annealing. Within this approach, temperatures corresponding to electrical recovery steps are correlated with activation energies which are associated with different type of reactions between defects.
In this work, results of our ongoing efforts to model and understand the ERR of beryllium are presented. ... mehrTo that end, we introduce a rate equation-based approach to model ERR spectra (see picture below) utilizing density functional theory results as input. Within this approach, electrical resistivity
recovery models comprising the volume of spontaneous recombination of monovacancies and self-interstitial atoms in beryllium as well as various
additional defects are considered. As a result, an intricate interplay between
different defect dynamics is uncovered, suggesting a clear route for further research to obtain systematically improved electrical resistivity recovery models.