I have blogged many times about the problems involved with the disposal of nuclear waste. There are two main sources of nuclear waste. The first source is the contamination of sites in the U.S. and other countries where nuclear weapons were manufactured. The other source is the spent nuclear fuel rods that are piling up at nuclear power plants in the U.S. and abroad. Many scientists all over the world are working on issues surround nuclear waste and its disposal.
The U.K. has about one hundred and fifty-eight billion cubic feet of nuclear waste. Most of that waste is in ponds and silos at ground level at Sellafield in Cumbria. The government intends to bury the most radioactive of this waste underground encased in concrete. It is hoped that the physical barriers and the chemistry of the barrier materials will stop any of the radioactive materials from being released for thousands of years. A site for the U.K. geological repository has not yet been chosen.
It had been assumed that using concrete to embed the waste would result in an environment that was too alkaline for bacteria to flourish. However, Jonathan Lloyd, a geomicrobiologist at the University of Manchester, UK, presented research at the annual meeting of the Microbiology Society in Edinburgh last week that concluded that bacteria might do better than expected in the waste repository.
Concrete has a pH of about eleven. This is the same level that is found in bleach which is routinely used as a disinfectant to kill bacteria. Lloyd and his team went to a lime kiln which has a similar pH to see if they could find bacteria that could thrive in those conditions. “We went to see if there was biology there and there was. All the sorts of organisms we were interested in studying, we could find, and we found they could grow at pH values you would probably find developing around these cementitious waste forms.”
It turned out that the radiation level expected at the repository was also not a problem for the bacteria that Lloyd and his team found. Not only does the radioactivity not kill the bacteria, there is some evidence that it actually served to assist the bacteria in processing nutrients.
The activity of the bacteria can also alter the radioactive compounds in the waste in ways that make them less likely to be leached out and carried away by groundwater. There is cellulose in some radioactive materials found in the waste. The alkaline conditions found in the waste can convert the cellulose into isosaccharinic acid (ISA). ISA can form a soluble compound with uranium which could make it vulnerable to ground water. The bacteria found by Lloyd removes carbon from ISA which results in keeping the radioactive materials in a solid form that will not be threatened by ground water.
Finally, radioactive waste can generate hydrogen gas. The buildup of hydrogen gas in repositories could force open cracks to the surface above the repository which could allow radioactive gases to escape. Bacteria in the repository could reduce the level of hydrogen gas and reduce the threat.
There is also the possibility that the bacteria studied by Lloyd and his group could be used to removed radioactive contamination from water which would be a big advance in the handling of environmental contamination.
