Optimising Blends of Blast Furnace Slag for the Immobilisation of Nuclear Waste - 16245

The legacy of nuclear waste at the Sellafield site in the UK is an ongoing issue, and the current preferred route for the disposal of low and intermediate level waste is encapsulation in a cementitious matrix, formulated by blending Portland cement with blast furnace slag (BFS). Due to demands and economic challenges faced by the cement and steel industries, the supply of BFS to the UK nuclear industry has been inconsistent. These changes have caused the industry to move from a unique BFS powder supply with a certain specification to a combination of standard commercially available cementitious powders. The material currently used at the Sellafield site is a blend of ground granulated blast furnace slag (GGBS) and a coarser fraction of the same composition called Calumite, combined with Portland cement. This work involves future-proofing the supply of BFS for the UK nuclear industry by optimising the blend of the two fractions of BFS in order to replicate the unique specification required by Sellafield Ltd. The main emphasis is on the particle size distribution (PSD) and how this impacts the properties of the final wasteform. The study investigates the performance properties of the blended grouts such as workability, particle packing and heat evolution. Results show that the PSD of the cement powders affect both the physical and chemical properties of the cementitious matrix produced. (authors)