Understanding Radioactive 'Hot' Particle Evolution in the Environment

虽然放射性一直存在于环境中，但在过去70年中，核材料在工业和军事上的使用导致了许多故意和意外的放射性材料泄漏。这些材料对人类和更广泛的生态系统的影响受环境中放射性核素的行为控制。放射性“热”粒子往往是释放到环境中的一个重要部分，因此，它们通常出现在核设施(如塞拉菲尔德)或受故意释放影响的地区(如英国的RavenGlass和Eskmeal)或事故(如切尔诺贝利和福岛)。释放后，粒子结合的放射性核素在环境中的表现与均匀分散的污染相比有很大的不同。然而，对于热粒子中放射性核素的组成和化学形态，或控制其长期稳定性、命运和影响的过程，特别是在分子水平上，人们显然缺乏了解。这在我们的放射性核素环境行为概念模型中留下了很大的空白，使我们很难促进对放射性核素的迁移和命运进行强有力的长期预测。归根结底，这些不确定性的影响是深远的：对我们预测环境中放射性核素行为的能力缺乏信心，影响了公众对优先问题的看法，例如核废料的地质处置和新核建设的实施。因此，更好地量化和了解热粒子在环境中的短期到长期行为和潜在影响是至关重要的。考虑到上述情况，我们将使用一系列实验室实验和现场样本，并结合最先进的表征工具，对环境中热粒子在几个月到几十年的时间尺度上的演变有一个清晰的了解。我们的大部分实验工作将集中于富铀热粒子，因为它们在环境中的普遍存在，我们将在流动柱中在一系列环境条件下改变这些粒子，为期一年。在整个过程中，我们将监测溶液化学的变化；此外，我们将使用一系列同步加速器、质谱学和电子显微镜技术来评估颗粒结构、化学和同位素组成随时间的变化，以及表征任何第二相的形成。作为我们的柱实验的补充，为了努力了解更长的时间尺度反应(几年到几十年)并评估更广泛的粒子类型的过程，我们将使用相同的技术来表征受污染的现场样本(例如来自Sellafield地区和Eskmeal射击场的粒子)。这项工作提供的信息将导致当环境中存在热粒子时放射性核素行为的概念模型得到大大改进。此外，通过与一系列关键利益攸关方(例如，环境影响评估、DSTL)合作，我们可以利用这些知识更好地预测受污染地点的辐射风险，并为土地管理/监测实践提供信息。

Whilst radioactivity has always been present in the environment, industrial and military use of nuclear materials over the past 70 years has led to numerous deliberate and accidental releases of radioactive materials. The impact of these materials on humans and wider ecosystems is controlled by the behaviour of the radionuclides in the environment. In turn, radionuclide behaviour and resultant bioavailability is dictated by their concentration and chemical form.Radioactive 'hot' particles are often an important part of releases to the environment and thus they are commonly found at nuclear sites (e.g. Sellafield) or in areas impacted by deliberate releases (e.g. Ravenglass and Eskmeals, UK) or accidents (e.g. Chernobyl and Fukushima). After release, particle-bound radionuclides have been shown to behave very differently in the environment when compared with homogeneously dispersed contamination. However, there is a distinct lack of knowledge about the composition of, and chemical form of radionuclides in hot particles, or of the processes that control their longer-term stability, fate and impact, particularly at the molecular scale. This leaves significant gaps in our conceptual models of radionuclide environmental behaviour, making it difficult to facilitate robust, long-term predictions of radionuclide transport and fate. Ultimately, the impact of these uncertainties is profound: a lack of confidence in our ability to predict radionuclide behaviour in the environment impacts on the public perception of priority issues, for example, the geological disposal of nuclear waste and the implementation of new nuclear build. As a result, better quantification and understanding of the short- to long-term behaviour and potential impacts of hot particles in the environment is crucial.Reflecting the above, we will use a range of laboratory experiments and field samples combined with state-of-the-art characterisation tools, to develop a clear understanding of hot particle evolution in the environment over timescales ranging from months to decades. The majority of our experimental work will focus on uranium-rich hot particles due to their prevalence in the environment, and we will alter these under a range of environmental conditions in flowing columns, for periods of > 1 year. Throughout, we will monitor changes in solution chemistry; further, we will use a range of synchrotron, mass spectrometry, and electron microscopy techniques to assess changes over time in particle structure, chemistry, and isotopic composition, as well as characterising the formation of any secondary phases. Complementary to our column experiments, and in an effort to understand longer timescale reactions (years to decades) and assess processes across a wider range of particle types, we will use the same techniques to characterise particles from contaminated field samples (e.g. from the Sellafield area and Eskmeals firing range).The information from this work will lead to a much-improved conceptual model of radionuclide behaviour when hot particles are present in the environment. Further, by working with a range of key stakeholders (e.g. EA, DSTL), we can use this knowledge to predict radiological risk at contaminated sites better and inform land management / monitoring practices.