Research News
Dr. Joachim Knebel, spokesman of the Helmholtz Nuclear Safety Research Programme at the KIT. Photo: KIT
Research for safe waste disposal
Nuclear power plants not only generate electricity, but also produce radioactive waste, which must be safely stored for millennia. As part of an international cooperative effort, scientists at the Karlsruhe Institute of technology (KIT) are working to convert highly radioactive nuclear wastes into less dangerous materials in a process called partitioning and transmutation — i.e. separation and conversion. The upcoming decades will show whether it is technically feasible.
The transmutation of especially dangerous, long-lived waste into less problematic materials can mitigate the problem of nuclear waste disposal in the future, believes Dr. Joachim Knebel of the KIT, who is the spokesman for the Helmholtz Nuclear Safety Research Programme. The highly radioactive waste materials make up only about 1 percent of spent fuel elements and mostly consist of plutonium and other so-called minor actinides. It is precisely these materials that are to be transmuted into other, less dangerous isotopes that decay much more quickly. Permanent storage will still be necessary, explains Knebel, but it will bring fewer problems: "We could reduce the storage of radioactive waste from geologic time spans lasting hundreds of thousands of years to historical periods of fewer than 500 years."
The first step is to partition the dangerous isotopes from the spent nuclear fuel rods. This process alone requires substantial research. The next step is transmutation. To achieve this, the long-lived radioactive waste must be bombarded with fast neutrons, which split the nuclei of the plutonium and other highly radioactive materials and convert them into less dangerous materials. But these fast neutrons must be created specifically for this purpose by bombarding a mixture of liquid metal – called the “spallation target” – with protons.
KIT researchers are working on this process. They are examining the behaviour of the liquid metal mixture that is supposed to create the fast neutrons in the transmutation facility. “When the protons strike the spallation material, a great deal of heat is produced and must be dissipated. We are examining cooling methods and optimising these processes,” says Knebel. The transmutation of radioactive nuclear waste is still a long way off and many research issues have not yet been resolved, but there are already ideas on how and where a transmutation facility could be built for demonstration purposes. The nuclear research centre in Mol, Belgium, is one possible location. Nevertheless, Joachim Knebel believes it will take 15 to 20 years to build such a facility.
