Innovation in the Design of Improved Actinide Selective Extractants Suitable for use in Large Scale Spent Nuclear Fuel Reprocessing

在乏核燃料后处理中需要克服的一个关键挑战是将放射性毒性的次要锕系元素与非放射性毒性的镧系元素分离。在“钚和铀提取”（PUREX）过程之后，从镧系元素中提取和分离这些元素将减少剩余乏燃料的长期放射性毒性，并使这些元素能够通过嬗变（高能中子轰击）变得安全或用作先进的第四代反应堆的燃料。这种分离是至关重要的，因为镧系元素比锕系元素具有更高的中子捕获半径，因此可以防止中子链式反应，而中子链式反应会使锕系元素安全。三种含1，2，4-三嗪基团的N-给体配体可以很高的选择性从镧系元素中萃取分离次锕系元素。这些被称为bistriazinylpyridine（BTP）、bistriazinylbipyridine（BTBP）和bistriazinylphenanthrolines（BTPhens）。然而，尽管这些配体满足用于“选择性Actinide Extraction”（SANEX）分离方法的许多要求，但在工业规模使用之前仍有两个主要限制有待克服：它们在核工业可接受的溶剂中的溶解度范围有限（通常小于10 mM）。2.据我们所知，还没有研究探索其他含关键1，2，4-三嗪部分的N-供体配体家族。此外，以前还没有采用创新办法来改善上述限制。该研究提案旨在研究基于1，2，4-三嗪部分的新N-供体配体家族，用于选择性萃取锕系元素而非镧系元素。这将推动乏核燃料后处理和放射性废物管理领域的发展，并有可能在未来的大规模锕系元素-镧系元素分离过程中被核工业使用，这将支持目前核能的复苏。如果成功的话，这项拟议的研究将扩大目前可用的配体的范围，用于处理乏核燃料，并提供一种或多种铅结构，具有改进的溶剂萃取性能，适用于未来的工业用途。所提出的方法的新奇在于（i）合成新的配体家族，以前从未探索过用于从镧系元素中分离锕系元素。(ii)创新的配体设计方法的应用，解决了现有的1，2，4-三嗪基配体的两个最关键的缺点：低溶解度和提取速度慢。这种创新方法的灵感来自于药物发现的那些方面，特别是与溶解度和极性有关的方面（这可能影响有机/水界面的表面浓度，从而影响提取动力学）。这项研究是及时的，因为在英国和世界范围内经历了几十年的衰退之后，核能正在经历财富的复苏（“核复兴”），一些国家（包括英国）已经宣布了新反应堆建设的计划。这意味着未来乏核燃料的数量将继续增加。然而，目前没有任何工艺可以使这种材料安全地进行地质处置。因此，在不久的将来，开发一种可行的选择性提取锕系元素的工艺就显得更为重要。该项目包括两名学术合作者，他们在使用放射性核素对配体进行溶剂萃取测量和开发新的选择性锕系元素萃取过程方面具有广泛的专业知识。该项目还包括一名工业合作者，他在新技术和产品的商业化和开发方面具有专业知识，并且已经向全球核工业销售了一系列配体。

A key challenge that needs to be overcome in spent nuclear fuel reprocessing is to separate the radiotoxic minor actinides from the non-radiotoxic lanthanides. Extracting and separating these elements from the lanthanides after the 'Plutonium and URanium EXtraction' (PUREX) process will reduce the long lived radiotoxicity of the remaining spent fuel and enable these elements to be rendered safe by transmutation (high energy neutron bombardment) or used as fuel in advanced GenerationIV reactors. This separation is critical because the lanthanides have higher neutron capture radii than the actinides and would thus prevent the neutron chain reaction that would render the actinides safe. Three families of N-donor ligand containing the 1,2,4-triazine moiety have been developed that can extract and separate the minor actinides from the lanthanides with very high selectivity. These are known as bistriazinylpyridines (BTPs), bistriazinylbipyridines (BTBPs) and bistriazinylphenanthrolines (BTPhens). However, whilst these ligands fulfill many of the requirements for use in a 'Selective ActiNide EXtraction' (SANEX) separation process, two main limitations remain to be overcome prior to industrial scale use:1. Their limited solubility range in solvents acceptable to the nuclear industry (typically less than 10 mM). 2. Their relatively slow rates of extraction.To the best of our knowledge, there has been no research on the exploration of other N-donor ligand families containing the crucial 1,2,4-triazine moiety. Furthermore, the application of an innovative approach to improving the above limitations has not previously been carried out. This research proposal aims to investigate new families of N-donor ligand based on the 1,2,4-triazine moiety for the selective extraction of actinides over lanthanides. This will advance the fields of spent nuclear fuel reprocessing and radioactive waste management, with the potential for the ligands to be used by the nuclear industry in future large-scale actinide-lanthanide separation processes that will underpin the current resurgence in nuclear energy. If successful, this proposed research would expand the scope of currently available ligands for use in the processing of spent nuclear fuel and provide one or more lead structures with improved solvent extraction properties suitable for future industrial use. The novelty of the proposed approach lies in (i) Synthesis of new ligand families that have never been explored previously for the separation of actinides from lanthanides. (ii) The application of an innovative approach to ligand design that addresses the two most critical shortcomings of existing 1,2,4-triazine based ligands; low solubilities and slow rates of extraction. This innovative approach is inspired by those aspects of drug discovery that specifically relate to solubility and polarity (which can influence surface concentration at an organic/aqueous interface and hence extraction kinetics). The research is timely because, after several decades of decline in the UK and worldwide, nuclear energy is experiencing a resurgence in fortunes (the 'nuclear renaissance') and several countries (including the UK) have announced plans for new reactor build. This means the volume of spent nuclear fuel will continue to increase in future. However, no process is currently available to render this material safe for geological disposal. Thus it is even more important to develop a feasible selective actinide extraction process in the near future. The project includes two academic collaborators who have extensive expertise in performing solvent extraction measurements on ligands using radionuclides, and developing novel selective actinide extraction processes. The project also includes one industrial collaborator who has expertise in the commercialization and exploitation of new technology and products, and who already markets a range of ligands to the global nuclear industry.