"Extremophile" bacteria have been found thriving in soil samples from a highly alkaline industrial site in Peak District of England. Although the site is not radioactive, the conditions are similar to the alkaline conditions expected to be found in cement-based radioactive waste sites. The researchers say the capability of the bacteria to thrive in such conditions and feed on isosaccharinic acid (ISA) make it a promising candidate for aiding in nuclear waste disposal.
In Europe, intermediate-level waste (ILW) generally refers to material that contains high amounts of radioactivity that requires shielding, but not cooling. It includes resins, chemical sludge, metal nuclear fuel cladding and contaminated materials from reactor decommissioning, and is often disposed of by being solidified in cement or bitumen before being buried in underground vaults.
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However, when ground waters eventually reach these waste materials, they react with the cement and become highly alkaline. This prompts a series of chemical reactions that trigger the breakdown of various cellulose-based materials present in the waste, resulting in the production of, amongst other things, ISA.
This is a concern because ISA has the ability to react with a wide range of unstable and toxic radioactive isotopes. If it binds to radioactive isotopes such as uranium, the toxic material become far more soluble, increasing the risk it will flow out of the underground vaults and make its way to the surface where it could contaminate drinking water or enter the food chain.
It is this process researchers at the University of Manchester believe the waste-eating bacteria could derail thanks to their ability to live in the highly alkaline conditions and use the ISA as a source of food and energy. They are also able to switch their metabolism to breathe using other chemicals in water, such as nitrate and iron, when there is no oxygen available – which is likely in underground nuclear waste disposal vaults.
The group is studying the biological processes the bacteria use to survive under such extreme conditions, as well as the stabilizing effects they have on radioactive waste.
"We are very interested in these Peak District microorganisms," says Professor Jonathan Lloyd, from the University of Manchester's School of Earth, Atmospheric and Environmental Sciences. "Given that they must have evolved to thrive at the highly alkaline lime-kiln site in only a few decades, it is highly likely that similar bacteria will behave in the same way and adapt to living off ISA in and around buried cement-based nuclear waste quite quickly.
"Nuclear waste will remain buried deep underground for many thousands of years so there is plenty of time for the bacteria to become adapted. Our next step will be to see what impact they have on radioactive materials. We expect them to help keep radioactive materials fixed underground through their unusual dietary habits, and their ability to naturally degrade ISA."
The team's findings appear in the Multidisciplinary Journal of Microbial Ecology.
Source: University of Manchester