© Gualtiero Boffi
The unique bacteria, discovered in a nuclear waste storage site in Siberia, shows promise as a tool for the creation of a natural barrier to the spread of radionuclides.
Researchers from the Moscow-based Frumkin Institute of Physical Chemistry and the Russian Academy of Sciences' Federal Research Center for Biotechnology have been able to isolate microorganisms which can be used to safeguard the surrounding environment from liquid radioactive waste.
Scientists made the discovery while conducting microbiological studies of the groundwater at the Seversky deep radiation burial site in Seversk, Tomsk region, Siberia, where liquid radioactive waste from the Siberian Chemical Combine, which supplies and reprocesses low enriched uranium for nuclear fuel, is stored.
Their research, recently published in
Radioactive Waste, a Russian scientific journal, suggests that the bacteria is capable of converting radionuclide ions, including those found in uranium and plutonium, into sedentary forms, thereby preventing the spread of dangerous radiation into the surrounding environment. Through lab experimentation, the scientists were able to fine tune the conditions necessary for the bacteria to carry out its useful work.
The researchers say their findings are a first step in creation a biogeochemical barrier for radionuclides for use in deep burial sites containing liquid radioactive waste.
Research into microbiological tools to limit the effects of nuclear waste have been conducted since the 1980s, with scientists from around the world saying microbial processes must be taken into account in projects to bury and store nuclear waste which can otherwise decay over a period of millions or even billions of years.
Comment: The discovery extends
research done in the UK.
Certain microbes can use radionuclides such as uranium and neptunium in place of oxygen, studies have found. In doing so, they convert them from soluble to insoluble forms, making them less mobile.
This should give us more confidence in waste disposal plans, says Jonathan Lloyd, a geomicrobiologist at the University of Manchester, UK, who presented the research at the annual meeting of the Microbiology Society in Edinburgh last week.
It had been thought that the presence of cement would result in conditions too alkaline for microbes to grow - it has a pH of around 11, similar to bleach. To see if this was so, Lloyd's team studied a lime kiln site in the UK's Peak District to see if microbes could be found growing in conditions similar to those that would be expected in a nuclear disposal site. "We went to see if there was biology there and there was," says Lloyd. "We found they could grow at pH values you would probably find developing around these cementitious waste forms."
The radiation levels typically found at nuclear waste dumps don't seem to pose a problem for bacteria either.
"It doesn't kill them," says Lloyd. "If anything, it actually stimulates the microbes."
The study found that the way bacteria process waste products means hazardous material is less likely to seep into the environment. Some nuclear waste contains cellulose, which can break down to form isosaccharinic acid (ISA) under alkaline conditions. ISA can form a soluble complex with uranium, helping it to leak out of the waste repository. But bacteria seem to use ISA as a carbon source and degrade it, keeping radionuclides in solid form - which means they stay in place.
Microbes may also help prevent radioactive gases escaping. Hydrogen produced by reactions in the repositories could build up pressure and cause them to crack open or explode. But microbes can use hydrogen and keep the levels down. They can also grow in fractures in the rock, form biofilms and clog up pores.
"At the moment, they have safety case models that are built on chemistry and physical containment. If you start including the biology, it means that those models are actually overly conservative, which is a good thing," says Lloyd.
Comment: The discovery extends research done in the UK.