Fundamental Properties of Thoria Based Mixed Oxides

人们相当担心铀储量不足以促进大规模的国际核新建设。钍的丰度大约是铀的四倍，可以提供潜在的替代燃料循环。同样重要的是，超过500年后，钍基乏燃料和相关的后处理废物的放射性比传统铀燃料产生的放射性要低得多。此外，由于钍基燃料只产生非常少量的钚，因此不能用于生产依赖钚的常规核武器-在这方面，钍基燃料的防扩散能力要强得多。目前，除印度外，钍基燃料仅用于研究或原型发电反应堆。这是因为过去和现在都有充足的铀供应。相反，在印度，由于缺乏本土铀供应，推动了以二氧化钍为基础的民用核能方法的发展。印度即将完成这一发展的第二阶段。在今后十年中，它将继续迅速积累用于民用核能的钍基燃料的经验。这就需要有预测能力，以确定民用反应堆中受辐照的燃料的行为将符合其设计标准，特别是反应堆的安全系统。从一般意义上说，这反映了对以二氧化铀为基础的能源生产的需求。民用反应堆运行的安全案例演变的方式是复杂的，但利用了几十年来的发展。对于以二氧化铀为基础的燃料，这导致了安全可靠的运行，核燃料利用效率稳步提高。进一步提高效率是肯定的，但需要修改现有战略。特别是，必须进行更多的研究，以满足监管机构的裂变产物被安全和可靠地保留在燃料组件内，因为它在反应堆堆芯内花费更多的时间。这意味着燃料可以将裂变产物保留在其晶格中更长时间，并且燃料的导热性不会恶化。然而，与过去我们只能获得基于燃料性能预测的实验工作不同，我们现在拥有先进的建模技术，这些技术与实验一起可以更好地理解负责燃料行为的基本过程。在这个项目中，我们将使用先进的材料模拟技术来研究二氧化钍基材料的行为。这包括裂变产物通过晶格的运动和热导率。然后将这些预测与相关项目中对民用二氧化铀基材料的预测进行比较。还将与有关二氧化铀和二氧化钍的现有实验数据以及印度合作者正在生成的有关二氧化钍的数据进行比较。这样做的好处是可以在不同的系统上测试为二氧化铀开发的现有模型。我们已经为现有的燃料开发了模型，其中包括假设。与二氧化钍的比较为这些模型提供了更严格的测试。它还使我们能够了解在多大程度上有可能将基于二氧化铀的模型转化为预测二氧化钍燃料的演变。还将继续与印度正在进行的建模合作。

There is considerable concern that uranium reserves are not sufficient to facilitate large scale international nuclear new build. Thorium is around four times more abundant than uranium, and could offer a potential alternative fuel cycle. Just as importantly, beyond ~500 years, thorium based spent fuel and associated reprocessed wastes are much less radioactive than those arising from conventional uranium fuels. Furthermore, because they generate only very small amounts of plutonium, thorium based fuels are not useful for the production of conventional nuclear weapons, which rely on plutonium - in this regard they are much more proliferation resistant. At present, except in India, thorium based fuels have only used in research or prototype energy generating reactors. This is because there have been and remain sufficient supplies of uranium. Conversely, in India, the lack of an indigenous uranium supply has driven the development of a thorium dioxide based approach to civil nuclear energy. India is on the verge of completing the second stage in that development. It will continue to develop experience in thorium based fuels for civil nuclear energy applications rapidly over the next decade. This requires a predictive capability to establish that fuel being irradiated in a civil reactor will behave in a manner that is compatible with its design criteria, especially the safety systems of the reactor. In a general sense, this mirrors the requirement for uranium dioxide based energy generation. The manner in which a safety case for civil reactor operation evolves is complex but takes advantage of developments over decades. For uranium dioxide based fuels, this has resulted in safe and secure operation that has seen a steady improvement in the efficiency with which nuclear fuel is utilised. Further increases in efficiency are certain, but will require modifications to existing strategies. In particular, more research must be undertaken that satisfies regulators that fission products are retained safely and securely within the fuel assembly as it spends more time within the reactor core. This translates to fuel that can retain the fission products within its crystal lattice for longer and that the thermal conductivity of the fuel does not deteriorate. However, unlike in the past where we only had access to experimental work on which to base the fuel performance predictions, we now have advanced modelling techniques that together with experiment can provide better understanding of the fundamental processes responsible for fuel behaviour.In this project we will use advanced materials simulation techniques to investigate the behaviour of thorium dioxide based materials. This includes the movement of fission products through the lattice and thermal conductivity. These will then be compared to predictions that are being made on civil uranium dioxide based materials in related projects. Comparison will also be made to experimental data already available concerning uranium dioxide and thorium dioxide but also data being generated by collaborators in India on thorium dioxide. This has the advantage of testing existing models that have been developed for uranium dioxide on a different system. We have developed models for existing fuels that include assumptions. Comparison to thorium dioxide provides a more stringent test of those models. It also allows us to understand to what extent it might be possible to translate the uranium dioxide based models to predict the evolution of thorium dioxide fuels. Collaboration will also proceed with modelling being carried out in India.