Abstract
Present knowledge on the formation mechanism of helium bubbles, which will enhance void swelling and lead to production of surface roughening and blistering as well as the high temperature intergranular embrittlement of metals during irradiation, is reviewed. Helium is strongly bound to a vacancy or a vacancy cluster (void), and it can stabilize the cluster, thereby increasing cluster lifetime by dramatically reducing thermal vacancy emission and by promoting thermal self-interstitial atom emission from the cluster. The thermal stability of a helium bubble greatly depends on the helium-to-vacancy ratio, i.e., the helium density, of the bubble. The characteristic precipitation (agglomeration) behavior of helium into voids in metals during irradiation was compared with that of other solute atoms, such as hydrogen and copper.
