Inert gas release from metals and UO 2 during high temperature annealing: the role of thermal vacancies

Abstract

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, then the large resulting enhancement of bubble diffusion toward the grain boundaries could explain a long-standing difficulty in understanding fission gas release in UO 2 during high temperature annealing. Although this paper partly reiterates this new approach, and includes its application to a set of recent results, the main purpose is to extend the approach to results on inert gas behaviour in metals where the coincidence of gas release and swelling during annealing corroborate the idea that thermal vacancies play an essential and important role in gas release. Of further importance are new results for silicon where the lack of krypton release can be attributed to the low thermal vacancy concentrations in this material.