Critical Analysis of Spent Fuel Structure in Radionuclide Release

由于60年来在民用和国防领域使用核能，英国产生了大量的核废料，其总量足以填满温布利体育场（45万立方米）。这些废物产生的辐射对公众构成的危害使其处置极具挑战性；任何解决方案都必须是长效的，因为废料的放射性将持续超过10万年。因此，包括联合王国在内的几个国家的政府建议，这种废物的长期处置应在地下几百米的深层地质设施中进行。工程地质处置场地的正式术语是地质处置设施（GDF）。这个人造设施将使用多层精心设计的安全壳，防止放射性元素（放射性核素）进入地下岩石环境并最终到达地面，从而将废物与未来的人口隔离开来。可以说，GDF最重要的部分是核废料本身；放射性核素向环境的释放是由地下水与废料的相互作用控制的——如果能证明这种材料在地下水存在下特别持久，则放射性核素的释放将非常小，并且GDF对未来人口的风险将很低。我的研究金的重点是了解一种特定类型的核废料（称为乏燃料）在与地下水接触时释放的放射性核素。许多国家都计划在GDF中处理乏燃料（例如瑞典，芬兰），但是英国的乏燃料是独一无二的，因为它来自仅存在于英国的核反应堆。这是一个问题，因为人们对这种材料与地下水接触时的潜在行为知之甚少；这就给这种材料在GDF中的长期安全性带来了不确定性。因此，该研究金的目标是发展对英国乏燃料的了解，了解其结构和化学如何影响与水接触后放射性核素的释放，并与其他乏燃料类型相比评估其性能。由于真正的乏燃料是极其危险的，奖学金研究小组将使用最先进的材料加工技术开发一种称为HIP-SIMFUEL的乏燃料类似物。HIP-SIMFUEL的开发将比现有的任何其他类似物更接近于乏燃料，这对从事乏燃料研究领域的科学家来说是一项重大进步。利用HIP-SIMFUEL和一套先进的高分辨率显微镜技术，我们将建立英国乏燃料结构和化学的第一个原子尺度的理解，我们将开发新的成像技术来评估这些特征在放射性核素释放到地下水的机制和速率中的作用。HIP-SIMFUEL的实验结果将与实际乏燃料颗粒的实验结果进行比较；我的团队将检查切尔诺贝利事故中排放到环境中的乏燃料颗粒，这些颗粒随后被天然地下水浸出多年。鉴于英国政府正在进行选择处置设施地点的任务，我的奖学金特别及时。这项研究代表了理解核废料在GDF中的长期性能的重要一步，将增强未来GDF行为的预测模型，并将有助于优化密封系统的设计。最终，这将提高英国和世界范围内核废料长期管理的安全性，并将增加公众对地质处置概念的信心。

As a result of 60 years of using nuclear energy in civil and defence operations, the UK has generated a large legacy of nuclear waste, with a total volume capable of filling Wembley Stadium (450,000m3). The hazards posed to the general public from the radiation arising from this waste make its disposal extremely challenging; any solution must be long-lived as the waste will be radioactive for more than 100,000 years. For this reason, the Governments of several countries, including the UK, propose that the long-term disposal of this waste should be in a deep geological facility, several hundreds of metres below the ground. The formal term for an engineered geological disposal site is a Geological Disposal Facility (GDF). This man-made facility will be used to isolate the waste from future populations by using multiple layers of containment carefully designed to prevent radioactive elements (radionuclides) from entering the underground rock environment and eventually reaching the surface. Arguably, the most important part of the GDF is the nuclear waste itself; the release of radionuclides to the environment is controlled by the interaction of groundwater with the waste - if this material can be shown to be particularly durable in the presence of ground water, the release of radionuclides will be very small and the risk to future populations from the GDF will be low. The focus of my Fellowship is on understanding the release of radionuclides from one particular type of nuclear waste, known as spent fuel, upon contact with groundwater. Many countries are planning to dispose of spent fuel in a GDF (e.g. Sweden, Finland), however the spent fuel in the UK is unique, because it originates from nuclear reactors that only exist in the UK. This is problematic because the potential behaviour of this material when it comes into contact with groundwater is poorly understood; this gives rise to uncertainty in the long-term safety of this material in a GDF. Therefore, the goal of this Fellowship is to develop an understanding of UK spent fuel, of how its structure and chemistry affect the release of radionuclides upon contact with water, and to evaluate its performance compared to other spent fuel types. Because real spent fuel is extremely hazardous, the Fellowship research team will develop an analogue for spent fuel, known as HIP-SIMFUEL, using state-of-the-art material processing technologies. The development of HIP-SIMFUEL, which will resemble spent fuel more closely than any other analogue currently available, represents a significant advancement for scientists working in the field of spent fuel research. Using HIP-SIMFUEL and a suite of advanced, high-resolution microscopy techniques, we will build the first ever atomic-scale understanding of the structure and chemistry of UK spent fuel, and we will develop novel imaging techniques to assess the role of these features in the mechanisms and rate of radionuclide release to groundwater. The results from experiments with HIP-SIMFUEL will be compared with those from real spent fuel particles; my team will examine particles of spent fuel that were discharged to the environment during the Chernobyl accident, which have subsequently been leached by natural groundwater for many years.My Fellowship is particularly timely, given the UK Government's ongoing task of selecting a site for the disposal facility. The research represents a significant step in the understanding of the long-term performance of nuclear waste in the GDF, will enhance predictive models of future GDF behaviour and will help optimise the design of the containment system. Ultimately, this will lead to enhanced safety of the long-term management of nuclear waste in the UK and worldwide, and will increase public confidence of geological disposal concepts.