Radiation induced formation gas bubbles in beryllium after neutron irradiation up to 6000 appm helium production

The current interest in mechanical properties and microstructure of neutron irradiated beryllium refers to its planned application in the Helium-Cooled Pebble Bed (HCPB) European concept of a breeding blanket of DEMO. Irradiation experiments in highneutron flux nuclear research reactors yield information about microstructural evolution of beryllium under conditions relevant to fusion (temperature, damage dose, helium and tritium productions) excluding 14 MeV neutrons impact which is not present in the neutron spectra of fission reactors. The HIDOBE-02 irradiation campaign accomplished at the HFR, Petten corresponds to 1246.5 Full Power Days at a reactor power level of 45 MW in the temperature range from 410°C to 680 °C. Transmission electron microscopy (TEM) has been to study the evolution of voids during neutron irradiation at different temperatures. The target preparation of specimens was
performed using focused ion beam (FIB). TEM study shows the formation of radiation induced hexagonal flat gas bubbles inside the grains, however at the lowest irradiation temperature of 410° the pebbles show the uniform shape. The diameters of the bubbles increase from a few nanometers for 410°C to more than hundred nanometers for 680 °C. ... mehrThe number density of bubbles decreases, correspondingly, by more than two orders of magnitude. The preferable formation of bubbles along the grain boundary and dislocation lines was observed. Analytical investigations using electron energy loss spectroscopy show the presence of He and H23 inside bubbles. Also the Si and Fe segregation on the voids was detected [2]. EDX mapping shows that the precipitates inside the grains and on the GBs have increased iron and aluminum content, indicating the formation of an Fe-Al-Be phase. In the material irradiated at 440°C, most of the precipitates also have Fe-Al-Be composition, while several other single- and multiphase precipitates were found. The Fe-Al-Be phase is observed as 10-15 nm precipitates within the grains and as 200 nm particles bound to a gas bubble at the GB. The present study shows detailed microstructural changes induced by neutron irradiation in beryllium.
[1] M. Klimenkov, et al. Journal of Nuclear Materials 455 (2014) 660–664
[2] M. Dürrschnabel, et al. Scientific Reports, 11, 7572 (2021)