"We have the Rossendorf beamline, as well as other beamlines at the ESRF and we have the know-how to study these elements in depth, to learn more about them. The benefits of our research, which is fundamental, can have direct impact both in the disposal of radioactive materials and in the development of new applications in chemical synthesis, electronics, nanotechnology, biology and medicine." KRISTINA KVASHNINA
From glowing stars to the Black Forest
Kvashnina's TOP group aims to study all the elements at the bottom of the table, but so far has been focused on uranium, thorium, plutonium, cerium, europium and praseodymium.
Europium is used to give fluorescence to materials, such as Euro notes, where invisible fluorescent ink is applied to fight against counterfeiting, or in glowing stars stickers for children. Cerium has been used as a sensor in catalytic converters in automotive applications, controlling the air-exhaust ratio to reduce NOx and carbon monoxide. Plutonium and uranium are used in nuclear power plants to generate energy, but the radioactive wastes of the plants is still a huge environmental problem. Uranium as a low radioactive natural element is widely present in rocks, for example in the Black Forest (Germany). Uranium is also the main component of highly radioactive spent nuclear fuel.
How do we deal with radioactive waste?
Nuclear plants use uranium and plutonium to produce electricity through nuclear fission reaction. After being used, the spent fuel needs to be reprocessed or disposed of in deep geological repositories in rocks. What happens to the radioactive elements in the environment?
"We need to know very well the physical and chemical properties of these elements to find the best way to get rid of them", explains Kvashnina. The best approach, according to Kvashnina, would be to recycle the fissile uranium and plutonium and re-use it in the reactor, but so far, this is technologically difficult. In many countries, like Sweden or Finland, radioactive wastes get stored in containers deep underground. How can we be sure that the wastes will be stable, won't react with the material of the container and won't dissolve ions in groundwater?
The challenge of the elements' behaviour
Knowing more about the elements and how the atoms interact would be a solution to repository for radioactive wastes. "We are trying to understand what happens with these elements at the nanoscale. For example, thanks to our research we have found why cerium is much more effective as a catalyst at the nanoscale than as large particle", says Kvashnina.
For plutonium and uranium, the main elements used in nuclear fuels, the story is more complicated. The TOP team has found that plutonium can form soluble and very low soluble compounds depending on what substances it is in contacted with. If plutonium is stored in a container but there is water nearby, it will react and create colloidal nanoparticles. "It is extremely dangerous as they may migrate far away", states Kvashnina. Uranium will also react differently depending on the conditions around it.
"All in all, we in our research we have found out that the bottom of the periodic table is like a zoo: you need to study the elements one by one, which we didn't think we'd had to when we started".
The role of the ESRF
The ESRF is one of the few places where experiments on actinides and lanthanides can take place. Neutron sources can do the job but they need sizeable samples, which are very difficult to get due to their dangerous nature. As for synchrotrons, the ESRF is still their best bet for research. "The knowledge and experience of the safety group, coupled with the very coherent beam and the smaller beamsize, make this an ideal place", explains Kvashnina. "The new machine EBS will give us a much better resolution than before, so we are very excited for the future".