The effect of hydrogen isotopes and helium on tritium diffusion and extraction from candidate fusion breeder blanket ceramics

在未来的聚变发电站中，放射性燃料氚将在聚变核心(增殖包层)周围的区域生产(繁殖)，固体和液体氚增殖设计正在世界各地开发。氚增殖材料将包含锂元素，它可以吸收聚变的中子，并转化为氚和氦(蜕变)。谢菲尔德大学正在开发固体增殖材料，并在聚变相关的环境中进行测试。大多数固体增殖体是多晶陶瓷，特别是含锂的陶瓷，如偏钛酸锂(Li2TiO3)，气体氚将通过这些陶瓷扩散并被提取出来。以前的工作已经发现，陶瓷颗粒尺寸与氚的有效扩散和提取以及陶瓷抵抗/恢复聚变中子辐照损伤的能力直接相关。在我们以前的工作中，我们发现Li2TiO3中含有小的空位型缺陷，这些缺陷在熔合相关的温度下生长。当氚在材料中扩散时，这些空位型缺陷和氦产生的变形有可能捕获氚，如果Li2TiO3要成为增殖包层材料的有力竞争者，必须确定这种捕获的程度。因此，该PHD项目的重点是确定候选含锂陶瓷的固有缺陷以及氦如何影响抗辐射损伤和氚扩散和提取。

In the fusion power stations of the future, the radioactive fuel tritium will be produced (bred) in a region surrounding the fusion core (the breeder blanket), with both solid and liquid tritium breeder designs being developed around the world. The tritium breeding material will comprise the element lithium, which can absorb fusion neutrons and transform into tritium and helium (transmutation). At the University of Sheffield, solid breeder materials are being developed and tested in fusion-relevant environments. Most solid breeders are poly-crystalline ceramics, specifically lithium-containing ceramics such as lithium metatitanate (Li2TiO3), through which the gaseous tritium will diffuse and be extracted. Previous work has found direct correlations between ceramic grain size and efficient tritium diffusion and extraction, as well as the ceramics ability to resist/recover from fusion neutron irradiation induced damage. In our previous work we found that Li2TiO3 contains small vacancy-type defects which grow at fusion relevant temperatures. These vacancy-type defects and the helium generated transmutation have the potential to trap tritium as it diffuses through the material, and the extent of this trapping must be determined if Li2TiO3 is to be a serious contender for a breeder blanket material. Therefore, the focus of this PhD project is to determine how defects, intrinsic to candidate Li-containing ceramics, as well as helium, impact radiation damage resistance and tritium diffusion and extraction.