The effects of neutron irradiation on γ-uranium and some fissile alloys of cubic crystal structure

Abstract

Dimensional and density changes and optical and electron microscope observations are reported on neutron irradiated γ-uranium and on a series of fissile alloys of single phase cubic crystal structure which are not subjected to severe internal stresses of the type occurring in α-uranium on thermal cycling or irradiation growth. The materials of cubic crystal structure showed little change of shape on irradiation though volume increases up to 100 % were observed. No irradiationinduced cracks were found and volume increases were entirely due to bubbles of fission product gasses which were nearly spherical except when they were large enough to link together. Average bubble sizes ranged from small fractions of a micron in specimens with small volume increases, up to a few hundred microns in specimens with nearly 100 % volume increase. Detailed measurements indicated that in each case surface tension forces provided the chief restraint to bubble growth. For a given burn-up and irradiation temperature, volume increases were largely determined by the number of bubbles present.