Development of Advanced Ceramic Breeder Materials for Fusion Energy

用于聚变能的先进陶瓷增殖材料的开发

• 批准号: EP/R006288/1
• 负责人: Samuel Thomas Murphy
• 金额: $ 12.86万
• 依托单位: Lancaster University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FR006288%2F1
• 关键词: Development; Advanced; Ceramic; Breeder; Materials

Nuclear fusion offers the promise of abundant, clean, low cost energy. The fusion process involves fusing together two nuclei releasing large amounts of energy that can be harnessed for electricity generation. Future power stations will employ the reaction between two isotopes of hydrogen, tritium and deuterium, creating a helium atom and a neutron. Deuterium is available from seawater, however, tritium does not occur naturally due to its short half-life. Therefore, tritium will be created, or bred, in the reactor from lithium in a process called transmutation. Transmutation will occur immediately outside the main chamber of the reactor, in a region called the breeder blanket. One of the leading breeder blanket designs will use lithium containing pebbles, such as lithium metatitanate and lithium orthosilicate. Solid breeder materials are attractive as they have high lithium densities that will ensure excellent tritium production and their low reactivity with other reactor materials means they are safe. However the use of a solid breeder material means that following transmutation the tritium will be trapped in the pebbles and must be extracted from the crystal. For recovery the tritium must diffuse to the pebble surface where it can be carried away by the coolant. The rate at which the tritium can escape from the pebbles is a very important parameter to consider when designing a fusion reactor because if the rate drops too low and tritium is retained in the pebble the fusion reaction will be unsustainable. Therefore, the main goal of this research to understand the process of tritium diffusion in lithium ceramics to design materials that have high tritium release rates. The exact mechanism of tritium release will depend on the microstructure of the host material. All crystals contain defects, such as missing atoms (called vacancies), and these defects can either promote tritium release or act as traps and inhibit it. The types and concentrations of defects in a material depend on the exact conditions (i.e. temperature) and will evolve over time. Therefore, to understand the tritium release process we must first understand the microstructure of the ceramics and what defects are presentPrevious studies of tritium release have adopted a top down approach where experimentally observed tritium release rates under different conditions are used to infer the exact atomic level mechanism responsible. By contrast this proposal adopts a novel bottom up approach that uses advanced electronic structure calculations to build a tritium release model from first principles. A key advantage of this approach is that the calculations provide detailed understanding of the atomic rearrangement processes that constitute tritium diffusion and allow a rate to be determined for each process. Initially the intrinsic defect chemistry of the host materials will be examined. This will allow the identification of the defects present in the ceramic under different conditions. Once the intrinsic defect populations are established the interaction of tritium atoms with the defects will be studied. By examining the bonding between tritium and the defects it is possible to determine exactly where the tritium will sit in the crystal and to identify which defects will act as traps. The information gathered so far considers where tritium will sit in the crystal but it does not provide information about how quickly the tritium can move through the crystal. Therefore, the next step in the process is to understand how tritium hops between the defects available and to determine which types of hop are most likely under certain conditions. Finally, all of this information will be used to create a tritium release model from lithium ceramics. This model will be used to optimise the microstructure of the ceramics to deliver maximum tritium release to ensure the fusion process is sustainable.

核聚变提供了丰富、清洁、低成本能源的希望。聚变过程包括将两个原子核融合在一起，释放出大量的能量，这些能量可以用于发电。未来的核电站将利用氢的两种同位素氚和氘之间的反应，产生一个氦原子和一个中子。氘可以从海水中获得，然而，氚由于其半衰期短而不会自然产生。因此，氚将在反应堆中从锂中产生或繁殖，这一过程称为嬗变。嬗变将发生在反应堆主腔室的外面，一个被称为增殖层的区域。一种领先的增殖包层设计将使用含锂的卵石，例如偏钛酸锂和原硅酸锂。固体增殖材料是有吸引力的，因为它们具有高的锂密度，这将确保良好的氚生产，并且它们与其他反应堆材料的低反应性意味着它们是安全的。然而，使用固体增殖材料意味着在嬗变之后，氚将被捕获在鹅卵石中，并且必须从晶体中提取。为了回收，氚必须扩散到卵石表面，在那里它可以被冷却剂带走。在设计聚变反应堆时，氚从卵石中逃逸的速率是一个非常重要的参数，因为如果速率下降得太低，氚就会留在卵石中，聚变反应将是不可持续的。因此，本研究的主要目标是了解锂陶瓷中氚的扩散过程，以设计具有高氚释放率的材料。氚释放的确切机制将取决于主体材料的微观结构。所有的晶体都含有缺陷，例如缺失的原子（称为空位），这些缺陷可以促进氚的释放，也可以作为陷阱并抑制氚的释放。材料中缺陷的类型和浓度取决于确切的条件（即温度），并会随着时间的推移而演变。因此，要了解氚释放过程，我们必须首先了解陶瓷的微观结构和存在的缺陷。以前的氚释放研究采用了自上而下的方法，其中实验观察到的不同条件下的氚释放速率用于推断确切的原子水平机制。相比之下，该提案采用了一种新颖的自下而上的方法，该方法使用先进的电子结构计算从第一原理建立氚释放模型。这种方法的一个关键优点是，计算提供了详细的理解，构成氚扩散的原子重排过程，并允许确定每个过程的速率。首先，将检查主体材料的固有缺陷化学。这将允许在不同条件下识别陶瓷中存在的缺陷。一旦本征缺陷的人口建立的氚原子与缺陷的相互作用将被研究。通过检查氚和缺陷之间的键合，可以准确地确定氚在晶体中的位置，并确定哪些缺陷将作为陷阱。到目前为止收集的信息考虑了氚在晶体中的位置，但它没有提供关于氚在晶体中移动的速度的信息。因此，该过程的下一步是了解氚如何在可用的缺陷之间跳跃，并确定在某些条件下最有可能发生哪种类型的跳跃。最后，所有这些信息将用于创建锂陶瓷的氚释放模型。该模型将用于优化陶瓷的微观结构，以提供最大的氚释放，以确保聚变过程是可持续的。