Mechanical compression tests of beryllium pebbles after neutron irradiation up to 3000 appm helium production

• Compression tests of highly neutron irradiated beryllium pebbles have been performed.
• Irradiation hardening of beryllium pebbles decreases the steady-state strain-rates.
• The steady-state strain-rates of irradiated beryllium pebbles exceed their swelling rates.

Resultsof mechanical compression tests of irradiated and non-irradiated beryllium pebbles with diameters of 1 and 2 mm are presented. The neutron irradiation was performed in the HFR in Petten, The Netherlands at 686–968 K up to 1890–2950 appm helium production. The irradiation at 686 and 753 K cause irradiation hardening due to the gas bubble formation in beryllium. The irradiation-induced hardening leads to decrease of steady-state strain-rates of irradiated beryllium pebbles compared to non-irradiated ones. In contrary, after irradiation at higher temperatures of 861 and 968 K, the steady-state strain-rates of the pebbles increase because annealing of irradiation defects and softening of the material take place. It was shown that the steady-state strain-rates of irradiated beryllium pebbles always exceed their swelling rates.