Recently an important article was published in the journal Chemistry about a means of more safely and efficiently reprocessing spent nuclear fuel. Nuclear energy currently produces about ten percent of the electricity in the world. However, the nuclear fuel that is used in nuclear power reactors becomes less efficient over time and needs to be replaced about every five years.
Spent nuclear fuel is still very radioactive and produces a lot of heat. Prior to being reprocessed or permanently disposed of, spend nuclear fuel is immersed in special cooling ponds under more than forty feet of water. The water provides shielding for the spent fuel and is continuously cooled and recirculated to remove the heat. It takes over a year in the cooling pool for the spent fuel rods to cool to the point where they can be reprocessed to remove uranium and plutonium which can then be used to create more fuel.
The elements americium, curium and neptunium, which are called the minor actinides, are produced by the nuclear reactions of the fissioning nuclear fuel. After the uranium and plutonium are removed, the minor actinides are still present and they account for most of the residual radioactivity and heat. These elements remain dangerously radioactive for about nine thousand years. This makes either storage or disposal very dangerous.
The removal of these actinide would make nuclear power a much safer and more sustainable power source. The remaining spent fuel following the removal of the actinides would only be dangerously radioactive for about three hundred years which is a more manageable time frame.
There are molecules called trazines that can be used to selectively remove or extract the actinides from spent nuclear fuel. These trazines have been known for quite some time. Researchers decided to determine how the modification of selected part of these molecules could alter their ability bind and extract the minor actinides at a molecular level. If useful modifications could be identified and exploited, it should be possible to design better versions of the molecules that would be more efficient for reprocessing spent nuclear fuel in the future.
The researched altered the size of the aliphatic rings in the current benchmark molecules. They were changed from six-part rings to five-part rings. It turned out that this minor alteration had surprising effects on the efficiency of these molecules to bind and extract minor actinides. The new configuration is much more efficient than the benchmark molecules. The researchers then used a variety of experimental techniques to discover exactly how the change in configuration improved efficiency.
Dr. Frank Lewis is a senior lecturer in organic chemistry in Northumbria University's Department of Applied Sciences. He said, “The findings are significant as they could allow better molecules to be designed in a more rational way, rather than simply by trial and error. The knowledge and insights we have gained by tuning the cyclic aliphatic part of these molecules could pave the way for the rational design of improved actinide selective ligands for reprocessing spent nuclear fuels. Modifying these molecules in different ways to improve their extraction properties could make future reprocessing more efficient and could be essential if they are to be used industrially in future. We believe that these results are of great importance to the field of nuclear energy, and this has been confirmed by the panel who reviewed the paper before publication.”