Ural federal university: Scientists Discover a Technology For Reprocessing Nuclear Fuel

Scientists have obtained fundamental information useful for creating an advanced technology for reprocessing (regeneration) of spent nuclear fuel (SNF). With this technology, SNF can be reused in nuclear power plants (NPPs). This is extremely important, since the deposits of uranium – the main component of spent nuclear fuel – are small in nature. The discovery was made by chemists while working on the problem of separating actinides and lanthanides in chloride melts.

An article about the research carried out and the results obtained was published in The Journal of Chemical Thermodynamics.

The goal of the scientists is to develop a pyrochemical method for reprocessing spent nuclear fuel in molten salt with subsequent extraction and reuse of uranium and plutonium in nuclear reactors, including fast neutron reactors. The latter belong to actinides. To restore the nuclear-physical properties of the fuel, it is necessary to clean it from fission products that “interfere” with the process. First of all, these are lanthanides. It is also necessary to remove the most dangerous elements – cesium and technetium.

In this regard, chemists are studying the electrochemical and thermodynamic properties of cerium compounds – one of the main fission products from the group of lanthanides – in a melt of lithium and potassium chlorides of eutectic composition. Used as a solvent, this melt is economical and has a low melting point. The optimum operating temperature of the melt is 450–500 degrees Celcium: an increase in temperature leads to the volatility of lithium chloride, in addition, the corrosion resistance of equipment deteriorates and energy costs increase.

The significance of the research is explained by Valery Smolenskiy, Chief Researcher of the Laboratory of Radiochemistry of the Institute of High Temperatures of the Ural Branch of the Russian Academy of Sciences, Senior Researcher of the Scientific Laboratory “Pyrochemical Technologies and Materials of a Closed Nuclear Fuel Cycle” of the Ural Federal University and the Institute of High Temperatures of the Ural Branch of the Russian Academy of Sciences.

“During the operation of a nuclear power plant, as a result of nuclear reactions, various fragmentation elements are formed, which have different degrees of activity and life expectancy. The most dangerous of them are isotopes of cesium and other lanthanides, as well as technetium, molybdenum, tungsten, and a number of noble metals. Among the dangerous elements and minor actinides are neptunium, americium, curium. During the operation of a nuclear reactor, lanthanides form only a few percent of the fuel volume, but at the same time they are highly active, dangerous and are the so-called “neutron poisons”, that is, they absorb the neutron flux. This leads to a decrease in the efficiency and safety of the reactor, ”the scientist states.

According to Valery Smolensky, the regenerated spent nuclear fuel intended for reuse at nuclear power plants and loading into reactors must be “clean” and not contain debris. Therefore, uranium and plutonium, which are part of the fuel, must be separated from fission products, in particular from lanthanides, including cerium. In addition, in countries that actively generate and use atomic energy, including Russia, there is a problem of accumulating nuclear waste: their storage is dangerous and costly, and the possibilities for storage are limited. This is also the reason for the development of technologies for processing spent nuclear fuel in molten salt. In our country, the task of reprocessing nuclear waste is supposed to be solved by creating a molten salt reactor-afterburner, in which the highly active and most dangerous fission products will be transmuted into inactive or short-lived elements.

The significance of the research is explained by Valery Smolenskiy, Chief Researcher of the Laboratory of Radiochemistry of the Institute of High Temperatures of the Ural Branch of the Russian Academy of Sciences, Senior Researcher of the Scientific Laboratory “Pyrochemical Technologies and Materials of a Closed Nuclear Fuel Cycle” of the Ural Federal University and the Institute of High Temperatures of the Ural Branch of the Russian Academy of Sciences.

“During the operation of a nuclear power plant, as a result of nuclear reactions, various fragmentation elements are formed, which have different degrees of activity and life expectancy. The most dangerous of them are isotopes of cesium and other lanthanides, as well as technetium, molybdenum, tungsten, and a number of noble metals. Among the dangerous elements and minor actinides are neptunium, americium, curium. During the operation of a nuclear reactor, lanthanides form only a few percent of the fuel volume, but at the same time they are highly active, dangerous and are the so-called “neutron poisons”, that is, they absorb the neutron flux. This leads to a decrease in the efficiency and safety of the reactor,” the scientist states.

According to Valery Smolensky, the regenerated spent nuclear fuel intended for reuse at nuclear power plants and loading into reactors must be “clean” and not contain debris. Therefore, uranium and plutonium, which are part of the fuel, must be separated from fission products, in particular from lanthanides, including cerium. In addition, in countries that actively generate and use atomic energy, including Russia, there is a problem of accumulating nuclear waste: their storage is dangerous and costly, and the possibilities for storage are limited. This is also the reason for the development of technologies for processing spent nuclear fuel in molten salt.

In Russia, the task of reprocessing nuclear waste is supposed to be solved by creating a molten salt reactor-afterburner, in which the highly active and most dangerous fission products will be transmuted into inactive or short-lived elements. For the processing of low-level fuel with a long holding time, the PUREX process is currently used, based on the use of hydrometallurgical methods. The regeneration of high-level fuel with a short holding time must be carried out in radiation-resistant media, such as salt and metal melts.

Currently, SNF reprocessing uses mainly MOX fuel for thermal reactors, consisting of uranium oxides or mixed oxides of uranium and plutonium. The resulting fission products are also present in MOX fuel mainly in the form of oxides. Therefore, in the process of regeneration, it is necessary to know both the electrochemical and thermodynamic properties of oxygen and anoxic compounds of fragmentation elements, including cerium.