Tests are currently underway in Scotland to determine whether the process of cleaning up toxic nuclear waste can be approached in a more environmentally sound manner. The method uses biosorption, a property of certain non-living biologic materials to naturally bind and concentrate metallic particles and to absorb common radioactive isotopes like Strontium-90. Once the radioactivity is absorbed into the materials, they can be gathered up and stored off-site.
Currently, removing radioactive isotopes from water requires artificially-made specialized ion exchange resins, but organizations are exploring the possibility of a more natural approach that works as well and is cost-effective. All of the considered materials are either naturally abundant in the area or waste products.
The project is a collaboration between the Environmental Research Institute (ERI) and Dounreay Site Restoration Ltd. (DSRL), the company responsible for cleanup and demolition of Scotland’s decommissioned Dounreay power plant.
Nuclear waste was disposed at Dounreay in a deep underground shaft – reaching over 65 metres below ground – from 1959 to 1977, at which point an explosion severely damaged the superstructure and waste operations were ended. A shallow concrete silo was then used until 1998.
The methods of waste disposal in the ‘60s caused significant ground contamination. Tens of thousands of radioactive fuel fragments – some of which are considered potentially lethal if ingested – escaped the plant between 1963 and 1984 into local beaches, the coastline and the seabed. Initially, the Scottish Environment Protection Agency aimed to return the seabed near the plant to “pristine condition,” but acknowledged in 2011 that for this to take place it would result in more harm than good. The cleanup process has been met with high levels of danger and difficulty, and it remains a work in progress to find the safest and most efficient approach.
Currently, the focus is on removing the radioactive particles present in liquid waste on the site.
DSRL approached the ERI, as they have had success using biosorption to remove toxic metals from liquids and copper from whiskey distillery effluents. The process has also been used elsewhere to extract tiny pieces of gold and silver from sewage and remove environmental contaminants like mercury and arsenic from wastewater.
While several biologic materials has been tested, crab shells come out on top. Superior mechanical-chemical stability and lower organic content means they don’t rot as much as the other materials. Along with coffee grinds and whiskey grains, they’re suitable for continuous flow column trials as they don’t restrict the water flow, allowing it to flow through the materials and the contaminants to be absorbed. Seaweed, on the other hand, absorbs too much liquid and expands, blocking the water flow.
Simulated Radioactive Liquid
The project remains at an early stage of the R&D process. At this point, they’ve conducted extensive research and completed bench scale laboratory trials using simulated radioactive liquid. The next phase involves small scale trials with actual shaft water to test the amount of time the materials will need to remain in the contaminated water.
In a statement from the two organizations, “on a per unit cost basis, we feel the cost of the bio-materials will be less than the specialised ion exchange resins.” However, they remain unsure as to how much of the material will be required and how this will affect the cost. An environmentally compliant waste disposal of the materials, for after they’ve treated the contaminated water, is also yet to be determined
However, the team is optimistic. Mike Gearhart, the leader of the Dounreay Shaft and Silo project team, said: “We are pleased to be working with ERI to identify a sustainable solution that can be sourced locally. We still have a number of issues to address but results to date have been very promising.”
It is a constructive second life for discarded sea shells or your morning cup of coffee.