Quantification of the extent of alkali-silica reaction occurring in cemented waste packages based on simplified model systems

International audienceNuclear power production generates radioactive waste, the management of which is an important industrial and environmental issue. Low - or intermediate - level radioactive aqueous waste can be concentrated by evaporation, stabilized and solidified with Portland cement before being sent to disposal. Interactions can however occur between the waste and the cement phases or aggregates, and decrease the stability of the final waste forms.The formation of a gel-like product, which results from an alkali-aggregate reaction, has been recently observed at the surface of cemented drums of evaporator concentrates. Its properties differ however from those usually reported for alkali-silica gels: (i) very low calcium concentration, (ii) significant presence of Zn2⁺, Cl⁻, B(OH)4⁻ and SO42⁻ ions, (iii) high formation rate, (iv) rather limited damage of the cementitious matrix considering the amount of gel produced. This work investigates the progress of alkali-silica reaction in the cemented drums at early age, by studying the deterioration rate of the aggregates in model systems.A synthetic alkaline solution, which mimics the pore solution including the waste, was used to degrade the siliceous aggregates under controlled conditions. Determination of the extent of degradation caused by alkali-silica reaction was achieved by weighing the residual flint aggregates and by quantifying their deterioration state by 29Si NMR, BET and gas pycnometry