Brussels, 01 Aug 2006
Disposing of nuclear waste presents an enormous challenge for many countries around the world. Some waste, such as that from hospital nuclear medicine departments, contains only small amounts of radioactive materials, which decay in hours or days and so can be treated like ordinary waste.
However, waste with high levels of radioactivity is more problematic as it can take hundreds, if not thousands, of years for the radioactivity to diminish. In that time, sustainable techniques have to be found to isolate this hazardous waste from people and the environment.
German physicists now claim to have the answer to this complex problem. They have come up with a way of speeding up the decay of nuclear waste. The technique involves embedding the waste in metal and cooling it to ultra-low temperatures.
Claus Rolfs of Ruhr University in Bochum, Germany, developed the technique after replicating the fusion reactions that take place in the centre of stars. Fusion is the process by which multiple nuclei join together to form a heavier nucleus. It is accompanied by the release or absorption of energy depending on the masses of the nuclei involved.
Using a particle collider, Dr Rolfs fired protons and deuterons (nuclei containing a proton and a neutron) at various light nuclei. He noticed that nuclear fusion occurred at a greater speed when the atomic nuclei were encased in metal and then cooled. This can be explained by the fact that, due to the lower temperature of the metal, the free electrons get closer to the radioactive nuclei. These electrons accelerate positively charged particles towards the nuclei, thereby increasing the probability of fusion reactions.
Given that radioactive decay involves the exact opposite process to that of fusion, Dr Rolfs also fired radioactive nuclei, encased in metal and cooled, into the collider to see whether the free electrons could accelerate the ejection of positively charged particles from a radioactive nucleus. As expected, he observed that radioactive decay occurred and was accelerated considerably by the presence of the lower temperatures and metal casing. According to Dr Rolfs, the technique could potentially cut radioactive material's half-lives - the time it takes for a given radioactive isotope to lose half of its radioactivity - by a factor of 100 or more.
'We are currently investigating radium-226, a hazardous component of spent nuclear fuel with a half-life of 1,600 years. I calculate that using this technique could reduce the half-life to 100 years. At best, I have calculated that it could be reduced to as little as two years. This would avoid the need to bury nuclear waste in deep repositories - a hugely expensive and difficult process,' explains Dr Rolfs.
'The method we are proposing means that nuclear waste could probably be dealt with entirely within the lifetimes of the people that produce it. We would not have to put it underground and let our great-great-grandchildren pay the price for our high standard of living,' he added.
However, further research and testing is needed to fully authenticate the technique. 'We are working on testing the hypothesis with a number of radioactive nuclei at the moment and early results are promising,' he said. 'It is early days, and much engineering research will need to be done to put this idea into practice, but I don't think there will be any insurmountable technical barriers.'