INERT-GAS RELEASE FROM METALS AND UO2 DURING HIGH-TEMPERATURE ANNEALING - THE ROLE OF THERMAL VACANCIES

It has recently been suggested that if two well established phenomena - that of thermal vacancy production at grain boundaries or surfaces, together with bubble migration up vacancy gradients - were combined, t hen the large resulting enhancement of bubble diffusion toward the gra in boundaries could explain a long-standing difficulty in understandin g fission gas release in UO2 during high temperature annealing. Althou gh this paper partly reiterates this new approach, and includes its ap plication to a set of recent results, the main purpose is to extend th e approach to results on inert gas behaviour in metals where the coinc idence of gas release and swelling during annealing corroborate the id ea that thermal vacancies play an essential and important role in gas release. Of further importance are new results for silicon where the l ack of krypton release can be attributed to the low thermal vacancy co ncentrations in this material.