Investigation, development and assessment of innovative direct conditioning solutions for radioactive liquid organic waste within the Predis project

In the framework of the Horizon-2020 PRE-DISposal management of radioactive waste (PREDIS) project, research activities are on-going to address the key issue of Radioactive Liquid Organic Waste (RLOW), which consists in the lack of reliable disposal or treatment routes, by investigating, developing and assessing direct conditioning solutions based on geopolymers and alkali-activated materials as conditioning matrices. Such solutions have to lead to final waste forms exhibiting properties and performances compatible with safety and technical requirements related to disposal, as well as to prolonged storage and transport. During the first two and half years of the project, several formulations have been tested for the incorporation of specific types of RLOW. The study of the direct conditioning process targeted an incorporation rate (Waste Loading) up to 30%-40% by volume of the different RLOW types. Following an initial screening phase, three reference formulations, based on metakaolin, fly ash, blast furnace slags and mixes of raw materials, were identified as the most promising in terms of improving waste loadings and the properties of the waste forms. The reference formulations were tested and optimised in terms of choice and quantity of aluminosilicate precursors, alkaline activators, possible blended binder systems and additives facilitating the organic waste emulsification (surfactants), to achieve waste forms with good rheological and mechanical properties. The robustness of the formulations was assessed with reference to waste, raw materials, and process variability. After a qualitative screening, based on a predefined set of criteria, a limited number of formulations were selected to further consolidate the reference formulations by testing them with real RLOW and to investigate the feasibility of scale-up by exploratory pilot scale tests planned for the last year of the project.