Strontium Interactions with Crushed Concrete Waste: Implications for Management of Radioactively Contaminated Land

There is a global legacy of radioactively contaminated land at nuclear facilities, and 90 Sr is an important radioactive contaminant. Typically, at these sites, significant volumes of light contamination concrete waste occur. On-site disposal of concrete waste, potentially with pretreatment (e.g., crushing), is one disposal option for this lightly contaminated waste. Developing a mechanistic understanding of the long-term speciation and fate of 90 Sr in typical on-site disposal scenarios will underpin safety case development for this option. Here, uptake of stable Sr/radioactive 90 Sr with crushed concrete waste was explored in batch experiments with representative groundwater using a multitechnique approach combining direct speciation and low-level radioanalytical techniques. Experiments were conducted under air-limited and air-equilibrated conditions and with and without phosphate amendment. In the absence of air, the Sr uptake was low. With air, the Sr uptake was increased due to Sr-incorporated calcite formation. Phosphate-pretreated and phosphate-equilibrated crushed concrete again showed enhanced uptake from the solution due to increased sorption/incorporation on newly precipitated calcium phosphates. Overall, crushed concrete acts as a long-term sink for 90 Sr contamination when air recharge is sufficient to drive carbonate precipitation. Additionally, phosphate pretreatment of crushed concrete waste may enhance 90 Sr uptake to the solid phase.