Short-term elemental release from Portland cement concrete in hypersaline leaching conditions

In the context of the long-term safety assessment of high-level nuclear waste (HLW) disposal, the initial release of metal ions from cementitious materials used as technical barriers is of great interest due to their possible interactions with HLW radionuclides (e.g. influencing the retention behaviour of radionuclides in engineered and natural barriers) due to water ingress. In the geochemical conditions in northern Germany, the porewater is of very high salinity, with salt contents of up to 2·5 M. In this work, the elemental composition of leaching water (with different types and amounts of salt) after 24 to 72 h contact with concrete was studied in order to simulate different water intrusion scenarios. It was found that in, addition to the main concrete elements (calcium, silicon, aluminium and iron), many trace elements were quantified in the concrete leachate. The influence of the concrete grain size in the leaching experiment showed that the use of particles <100 μm is necessary to obtain reproducible results. The influences of different solution salinities and the addition of calcium chloride and sodium sulfate on the leaching process were examined. For most elements, an increase in sodium chloride concentration enhanced the leaching process.