At a decommissioned nuclear site, thousands of tonnes of rubble will accumulate as reactors are dismantled. For decades, this concrete was treated as waste to be stored or buried at enormous cost. But a team of researchers from the University of Manchester, the UK National Nuclear Laboratory, and Clemson University has found that this same material may hold the key to cleaning up radioactive contamination — if used the right way.
In research published in ACS ES&T Water, the team discovered that crushed concrete can trap up to 98 percent of radioactive strontium-90 from groundwater within just 48 hours, simply by exposing it to air and treating it with phosphate. Strontium-90 is one of the most troublesome contaminants at historic nuclear sites like Sellafield in the UK and Hanford in the United States because it moves relatively easily through soil and groundwater, posing long-term environmental risks.
Professor Katherine Morris, BNFL Research Chair at the University of Manchester and senior author of the study, explained the significance: "Our work shows that crushed concrete doesn't just act as an inert waste material — it can actively remove strontium from solution and hold onto it in forms that are stable over long timescales."
The researchers sourced concrete from the UK's Nuclear Decommissioning Authority and conducted experiments lasting three months. They tested two scenarios: one mimicking sealed, low-oxygen underground conditions, and another representing shallow disposal environments where air is present. In air-exposed systems, the crushed concrete removed roughly 82 percent of strontium from solution within three months. Under sealed, air-limited conditions, that figure dropped to just 14 percent.
The mechanism behind this dramatic difference lies in a natural chemical process called carbonation. When concrete is crushed and exposed to air, it reacts with carbon dioxide to form calcite — a calcium carbonate mineral. Strontium atoms can substitute for calcium within the calcite crystal structure, effectively locking the radioactive element into a stable solid form. X-ray absorption spectroscopy confirmed this incorporation, providing concrete evidence (literally) of the long-term containment mechanism.
The team went further by testing phosphate treatments. When phosphate was added to air-exposed systems, strontium removal jumped to 98 percent within 48 hours. Microscopy revealed that poorly crystalline calcium phosphate coatings formed on the concrete surface, creating additional binding sites where strontium could be trapped for the decades needed for radioactive decay to run its course.
The implications are significant. Every year, decommissioning nuclear facilities generates enormous volumes of lightly contaminated concrete. Rather than expensively storing or disposing of this material elsewhere, site managers could potentially crush it, expose it to air, apply a phosphate treatment, and use it as an in-situ barrier against strontium migration. The waste becomes a tool.
"These results give us a clearer picture of what happens when concrete waste interacts with groundwater over time," Morris said. "By understanding the mechanisms that trap strontium, we can better support safe, evidence-based decisions about onsite disposal and long-term radioactively contaminated land management."
In the quiet work of cleaning up Cold War-era nuclear sites, this finding offers a rare double win: an existing waste product, transformed into an affordable cleanup technology.