Three Dimensional Optical Imaging of Neptunium Redox Speciation-A Feasibility Study

当今社会面临的最紧迫问题之一是管理核能生产所产生的现有和未来的废物形式。在这里，锕系元素的氧化还原化学在核裂变的许多方面起着至关重要的作用，包括安全处置策略和新的回收和再循环路线。了解工程环境中锕系元素的化学性质对于管理核电生产中现有和未来的裂变产物（核废料），特别是地下地质处置至关重要。特别是，在高放射性废物中发现的大量关键放射性核素镎的氧化还原化学是复杂的、可变的，目前还没有很好地了解。在拟议的地质处置设施的整个使用期内，主要危险之一是镎的化学性质发生变化，可能导致处置库的沥滤，破坏一级安全壳，进入工程环境。由于镎特殊复杂的氧化还原和化学形态，影响其与工程和天然封装材料（包括主岩和回填材料）相互作用的氧化还原化学和形态的关键机制信息缺乏，仍然是该领域面临的主要化学挑战之一。在这项可行性研究中，我们将解决的前景，使用单光子和双光子荧光和磷光光谱和显微镜作为一种非破坏性的技术来解决这个问题。我们的目标是可视化，定位和空间映射的不同氧化态的镎，可以共存于溶液中的模型条件下使用定义良好的配合物和水离子与无处不在的地质相关的矿物二氧化硅，氧化铝和方解石在以前看不见的细节水平（亚微米分辨率）。我们最近已经证明，镎（V）和（VI）的发射发生在电磁光谱的绿色和蓝色区域，并同样强烈的铀酰（VI）离子，其光学性质是众所周知的，并已被我们用于荧光和磷光显微镜成像。这意味着这两种氧化态可以同时检测，因此可以使用高度灵敏、信息丰富的三维成像来了解微米尺度以下的镎基地球化学。这将为在一系列异质系统中处理核废料的安全情况增加急需的重要信息。

One of the most pressing problems facing society today is the management of existing and future waste forms arising from nuclear energy production. Here, the redox chemistry of the actinide elements plays a crucial role in many aspects of nuclear fission including safe disposal strategies and new recovery and recycling routes. Understanding the chemistry of actinides in engineered environments is imperative for the management of existing and future fission products (nuclear waste) arising from nuclear power production, particularly for underground geological disposal. In particular, the redox chemistry of neptunium, a key radionuclide found in appreciable quantities in high level waste is complex, changeable and currently not well understood. Over the lifespan of the proposed geological disposal facility, one of the principal hazards is a change in chemistry of neptunium that may result in leaching from the repository, breaching primary containment and entering the engineered environment. Due to the particular complex redox and chemical speciation of neptunium, crucial mechanistic information on redox chemistry and speciation that affects its interactions with engineered and natural encapsulating materials including the host rock and backfill material is lacking and remains one of the principal chemical challenges facing this field. In this feasibility study, we will address the prospect of using one and two photon fluorescence and phosphorescence spectroscopy and microscopy as a non-destructive technique to address this problem. We aim to visualise, locate and spatially map the different oxidation states of neptunyl that can co-exist in solution in model conditions using well defined complexes and aqua ions in with the ubiquitous geologically relevant minerals silica, alumina and calcite at previously unseen levels of detail (sub micrometer resolution). We have recently demonstrated that neptunyl(V) and (VI) emission occurs in the green and blue regions of the electromagnetic spectrum and are equally as intense as the uranyl(VI) ion, whose optical properties are well known and have been used by us for fluorescence and phosphorescence microscopy imaging. This means that both oxidation states can be detected simultaneously so that highly sensitive, informative three-dimensional imaging can be used to understand neptunyl geochemistry below the micron scale. This will add much needed important information to the safety case for nuclear waste disposal in a range of heterogeneous systems.