Immobilisation matrices for intermediate level nuclear wastes using sulphate activated BFS/OPC and PFA/OPC composite cements

Abstract The highly alkaline pore solution of ordinary Portland cement composites currently used by the nuclear waste immobilisation industry causes corrosion of encapsulated reactive metals which generates hydrogen, causes loss of wasteform integrity and may release radioactive material to the environment. This work has investigated using near neutral salts as additives to composite cement powders in order to develop less alkaline cement pastes and reduce the corrosion of reactive metals. The effect of adding anhydrite and gypsum to ordinary Portland cement partially replaced by blast furnace slag or pulverised fuel ash was investigated. Adding the sulphate salts significantly changed the composition and microstructure of the bulk cement and the aluminium corrosion layer with ettringite the main phase detected. The amount of aluminium hydroxide formed during corrosion was significantly reduced by adding the sulphate salts as was the rate of hydrogen generation.