One of the big problems with nuclear power is the fact that dangerous radioactive waste is left when nuclear fuel is consumed in a power reactor. Spent nuclear fuel rods are rapidly filling cooling pools all over the U.S. and the U.S. will have no permanent geological repository until 2050 at the soonest. Countries all over the world that have nuclear power reactors are faced with the same problems with regard to spent nuclear fuel. It can take over two hundred thousand years for the radioactivity in spent fuel rods to return to the level of natural uranium in the ground.
Switzerland is currently creating an underground repository to hold spent nuclear fuel. When siting a geological repository, attention is usually given to such things as geological faults, composition of rock strata, movement of ground water and man-made barriers to the release of radiation and radioactive materials. Researchers at École polytechnique fédérale de Lausanne have recently discovered something new that should be considered in siting and construction a permanent geological repository for spent nuclear fuel.
When steel casks containing spent nuclear fuel rods corrode, hydrogen gas can be released. The hydrogen gas is generated by the decomposition of the cladding on the fuel rods. This gas can build up pressure that might alter the rock strata, making it more porous and prone to penetration by ground water.
The EPFL research team has discovered that there is a community of seven kinds of bacterial that live hundreds of feet underground in the rock strata in which the Swiss are constructing their repository. Far from being a cause of concern, it turns out that this bacterial community may be beneficial to the repository. This is a closed community of bacteria that have never been identified before. At the bottom of the food chain there is a bacteria that feeds on hydrogen and sulfur in the rock. In a nuclear repository, the bacteria would be able to feed on the hydrogen and reduce the risks associated with hydrogen release.
In tests, the EPFL team monitored the growth and composition of the bacterial community in the presence of increased hydrogen gas such as would be generated by spent fuel rods. They found that the community adapted to the increased hydrogen and flourished. This is good news for the designers of geological repositories.
In the future, it would make sense to deliberately seed the rock in and around the geological repository with these bacterial colonies so they can consume hydrogen gas and reduce risk. The steel casks containing the spent fuel rods are embedded in bentonite. Bentonite is an absorbent aluminium phyllosilicate clay consisting mostly of montmorillonite. The bentonite used in repositories contains sodium and it swells when exposed to water. Its function in the repository is to prevent the penetration of ground water. The EPFL team suggests that a porous layer of material could be placed between the bentonite surrounding the casks and the rock containing the repository. This layer would be an ideal habitat for the bacterial community. They could feed on sulfur in the rock and hydrogen gas leaking from corroding casks.
