Fracture behaviour of neutron irradiated beryllium

Beryllium might be used as a neutron multiplier in blankets for thermonuclear fusion machines. Beryllium is irradiated in the BR2 materials testing reactor at SCK·CEN at approximately 200, 400 and 600°C up to a neutron fluence of 2.1×1025 n m−2 (En>1 MeV). Four beryllium grades were irradiated and evaluated: S-200-F (vacuum hot pressed, 1.2 wt% BeO), S-200-FH (hot isostatic pressed, 0.9 wt% BeO), S-65 (vacuum hot pressed, 0.6 wt% BeO) and S-65-H (hot isostatic pressed, 0.5 wt% BeO). The main conclusions that can be drawn from a preliminary fracture toughness investigation can be summarised as follows: (1) All beryllium grades exhibit approximately the same behaviour from the fracture toughness point of view, although, small differences are observed in the initial tensile properties. (2) The ageing treatment does not significantly affect the tensile properties or the fracture toughness. (3) Irradiation results in strengthening of the material, loss of ductility and a decrease in the fracture toughness. However, the irradiation damage saturates after a specific neutron fluence. (4) Irradiation at higher temperature increases fracture toughness.