Post-irradiation studies of beryllium reflector of fission reactor examination of gas release, swelling and structure of beryllium under annealing

Hot-pressed high-density (TShG-type) beryllium was irradiated at 100°C up to the fast neutron fluence of 1 × 10 26 n/m 2. Transmutation tritium and helium contents were 652 and 4400 appm, respectively. Post-irradiation studies of beryllium consist of optical and electron microscopy, density measurements before and after isochronal annealing at the temperature range of 300–1100°C and thermodesorption gas spectrometry. Investigation shows the following: (1) Slight swelling of beryllium after neutron irradiation. (2) Spatial non-uniformity in the distribution of the pores. (3) Complicated dependence of swelling on annealing temperature caused by formation of gas porosity. In the temperature range from 500 to 800°C, swelling of beryllium was probably caused by growth of bubbles because of tritium mobility. At the temperature above 900°C swelling of beryllium was probably caused by growth of bubbles because of helium mobility. (4) Full degassing of the irradiated beryllium took place below its melting temperature.