Impact of silica fume on cement performance
Organic ion exchanger resin beads are widely used in nuclear waste technology for pond water cleanup. They accumulate radioactive Cs and Sr in service. For disposal, the beads are encapsulated in cement but their stabilisation in cement has been difficult to achieve. The ion exchangers uptake calcium and inbibe water, as a result of which they swell, cracking the cement. Nuclear Electric had previously commissioned work on non-swelling formulations. These consist of mixtures of sulfate-resisting Portland cement, calcium hydroxide and silica fume. However, concerns have been expressed about cement durability in contact with brines. This thesis had as part of its objectives, (i) determination of the probable stability of the non-swelling matrix in MgSO4 brines and (ii) the corrosion potential of stainless steel in contact with the non-swelling cement. In addition, synthesis, characterisation work was performed on the reaction product of objective (i), M-S-H gel. Its alkali sorption capacity was determined as a function of both Mg/Si ratio and alkali concentration to assess its immobilisation potential.