Predicting long-term performance of cement disposal systems for radionuclide-loaded zeolite and titanate ion exchangers

用于净化核废料流的最重要的方法之一是离子交换，例如福岛的清理工作、塞拉菲尔德的退役和其他核工业操作所产生的核废料流。在这个过程中，放射性污染通过与固体离子交换材料结合（或进入）而从水中去除。一旦这些离子交换材料（在本项目中以沸石或钛酸盐颗粒的形式使用）吸收放射性污染的能力被填满（成为“消耗”），这些颗粒必须以某种方式转化为固体形式，以确保它们能够稳定地储存和最终处理。已经提出并在许多地方试验了将离子交换剂胶结到固体废物形式中，并使用了各种类型的胶结剂。然而，对于离子交换剂和水泥如何长期相互作用，目前还没有一个很好的基本理解，而这正是拟议项目的核心焦点。这一信息对于在离子交换树脂的最终处理和处置中使用胶结的安全案例至关重要；我们必须能够预测这些材料在长期内的表现，包括了解在遥远的未来任何可能的放射性释放，以使其最小化或避免。该项目将产生与胶凝环境中离子交换材料稳定性相关的基本科学见解，使用传统和新开发的定制水泥类型。我们将利用吸附、溶解度和微观结构测量，以前所未有的精度描述水泥和废物形式。这一基本知识将用于建立一个预测模型，预测核废料最终处置所需的整个时间尺度（数万至数十万年）内废物形态的表现。这也将使我们能够为应该使用哪种类型的水泥提供建议，以及它们应该以何种方式应用，从而在超长时间内使放射性污染远离环境方面取得最佳效果。

One of the most important processes used to decontaminate nuclear waste streams, such as those resulting from cleanup operations at Fukushima, decommissioning at Sellafield, and other nuclear industry operations, is ion exchange. In this process, the radioactive contamination is removed from water by being bound onto (or into) a solid ion exchange material. Once the capacity of these ion exchange materials (which are used in the form of pellets of zeolites or titanates, in the cases of interest in this project) to take up radioactive contamination is filled ('becoming 'spent'), the pellets must somehow be converted into a solid form to ensure that they are stable for storage and final disposal. The cementation of ion exchangers into solid waste forms has been proposed and trialled in a number of locations, and using a variety of types of cements. However, there is not yet a good fundamental understanding of how the ion exchangers and the cements will interact in the long term - and this is the core focus of the proposed project. This information is essential to developing a safety case for the use of cementation for the final treatment and disposal of ion exchange resins; we must be able to predict how the materials will behave in the long term, including knowledge of any possible release of radioactivity in the distant future, to enable this to be minimised or avoided. This project will generate the essential fundamental scientific insight related to the stability of ion exchange materials in cementitious environments, using both traditional and newly-developed bespoke cement types. We will characterise the cements and waste forms to an unprecedented level of precision using sorption, solubility and microstructural measurements. This fundamental knowledge will be used to generate a predictive model for the performance of the waste forms over the full timescale required for final disposal of nuclear wastes, tens to hundreds of thousands of years. This will also enable us to provide recommendations for which types of cements should be used, and in which way they should be applied, to give the best outcomes in keeping radioactive contamination away from the environment in the ultra-long term.