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

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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.