It was recalled that current explanations for irradiation swelling in this metal were based upon the assumption that swelling arose from bubble growth rather than void growth. However, the factors which governed cavity formation in Be were more complex than in cubic metals; where theories were based upon elastic interaction differences between vacancies and self-interstitial atoms. However, Be was an hexagonal close-packed metal in which diffusion was anisotropic. The diffusional anisotropy difference between point defects then changed the cavity bias for their absorption and led to a dependence of the dislocation bias upon the distribution of dislocations over crystallographic directions. This resulted in new critical quantities, for the bubble-void transition, that controlled the transition from low-dose to high-dose irradiation effects. It was shown here how the critical parameters which controlled irradiation swelling in Be depended upon the dislocation distribution and anomalously high self-diffusion anisotropy. The results were in agreement with the experimentally observed resistance of Be to void swelling in the early stages of irradiation; where a-type dislocations predominated over c-type dislocations. A mechanism for the radiation-induced generation of c-type dislocation loops was proposed which could lead to the subsequent transformation of bubbles into voids.

V.I.Dubinko, V.R.Barabash: Journal of Nuclear Materials, 1996, 233-237B, 832-6