POSTIRRADIATION 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 d egrees C up to the fast neutron fluence of 1 x 10(26) n/m(2). Transmut ation tritium and helium contents were 652 and 4400 appm, respectively . Post-irradiation studies of beryllium consist of optical and electro n microscopy, density measurements before and after isochronal anneali ng at the temperature range of 300-1100 degrees C and thermodesorption gas spectrometry. Investigation shows the following: (1) Slight swell ing of beryllium after neutron irradiation. (2) Spatial non-uniformity in the distribution of the pores. (3) Complicated dependence of swell ing on annealing temperature caused by formation of gas porosity. In t he temperature range from 500 to 800 degrees C, swelling of beryllium was probably caused by growth of bubbles because of tritium mobility. At the temperature above 900 degrees C swelling of beryllium was proba bly caused by growth of bubbles because of helium mobility. (4) Full d egassing of the irradiated beryllium took place below its melting temp erature.