Scientists at the Urals Federal University (UrFU) in Russia have discovered that the use of gallium and indium can reduce the cost of the process of pyrochemical reprocessing of nuclear fuel, while maintaining its efficiency. The technology involves the use of molten salts and liquid gallium to separate components of used nuclear fuel. To reduce the cost of this process, physicists added indium – the technology remained just as effective, but the cost of the processing was reduced. The results of the study will make it possible to modernise modern methods of used nuclear fuel reprocessing and make them more efficient.
Details of the study are published in the international, peer-reviewed, open access journal, Alloys. “One of the options for reprocessing used nuclear fuel is a method using the molten salt – liquid metal alloy system,” explained Alexander Dedyukhin, leading engineer at the Department of Rare Metals & Nanomaterials at UrFU. “This method has many advantages, in particular, it is focused on the processing of high-level, low-ageing nuclear fuel with a high burnup, which cannot be achieved using other methods, for example, water technology. In addition, it is safer in environmental terms, since the amount of radioactive waste after processing is reduced.” He added: “When processing fuel using this method, gallium can be used, but we found that when adding indium, the processing efficiency remains just as high, but the cost of the process is reduced.”
Spent nuclear fuel consists primarily of uranium compounds as well as plutonium and fission products. After the used fuel is dissolved in the molten salt, it is brought into contact with a liquid alloy based on gallium and indium, resulting in a redistribution of components – the uranium is concentrated in the metal, and unnecessary fission products remain in the salt.
The use of metal alloys in nuclear fuel reprocessing is still being studied, but it is known that this technology can reduce the life radioactive waste and make the process faster and safer for the environment.
“The bottom line is that before fuel is processed, it is subjected to ageing so that short-lived radionuclides decay and the activity of the substance decreases,” Dedyukhin said. “If you process insufficiently aged fuel using, for example, water technology, then the water undergoes radiolysis, that is, decomposition, and the process is ineffective. And the use of molten salts with liquid metal alloys makes it possible to reduce the holding time of nuclear fuel. Again, one of the advantages is, as a rule, this results in a smaller volume of radioactive waste compared with water technology.”
Scientists conducted experiments and created three alloys based on gallium and indium, which contained 21.8%, 40% and 70% of indium. Scientists measured the solubility of nuclear fuel using a precipitation method, which involved taking samples of a saturated liquid metal solution for chemical analysis. The study showed that the efficiency of separating uranium and nuclear fuel components when using alloys based on gallium and indium is high, but decreases slightly with increasing proportion of indium in the alloy.
Image: The Urals Federal University (UrFU) in Russia
