Rheology Mapping of Complex Fluids: Challenges in the processing of nuclear waste

The UK’s nuclear sector is actively undertaking substantial decommissioning projects of its legacy facilities. One key challenge is the safe recovery and processing of waste for long term storage. A particular waste is corroded magnesium alloy clad uranium metal fuel that has formed sludge and is currently contained in open and closed facilities on the Sellafield site. Encapsulating the sludge for long term storage is a high priority for the industry. To mobilize and process the material it is important to understand its rheology and how the use of secondary additives can modify the rheology favourably. Flow modifiers (colloidal silica) have been shown to significantly lower yield stress of concentrated sludges making them easier to process. However, there is limited understanding on modifying the rheology using geo-polymers, an additive that is used to eventually solidify the waste when activated. This project will map the rheological space of these complex fluids containing flow enhancers and geo-polymers. By fundamentally understanding the nature of the interactions between the different chemical species, and determining how those interactions modify sludge rheology, it will be possible to design processes that can handle variable waste streams and produce encapsulated wastes safe for long term storage.