Nuclear Materials. New types of fuels and SNF reprocessing

Summary:

One of the important tasks of modern radiochemistry is the development of technologies contributing to the closure of the nuclear fuel cycle. Fast-neutron reactors are the basis of the closed nuclear fuel cycle. The operation of this type of reactors involves overcoming many engineering and scientific problems. One of them is the production and reprocessing of new fuel materials for this type of reactors. Uranium and plutonium containing materials based on oxides, nitrides, or carbides are suggested for use as fuel in fast-neutron reactors. Production of such fuels is a complex process requiring a massive data from actinide chemistry and materials science.

One of the problems is finding new ways to synthesize uranium dioxide, the basic material for fuel pellets. The most commonly used method to this end is the reduction of uranium(VI) compounds in hydrogen atmosphere under heating to 800-900 oC. There are also alternative schemes requiring heating to 90-100 oC and the use of such reducing agents as hydrazine. However, these processes require a more in-depth study, which are carried out in our laboratory.

Not less complex and ambitious task is the reprocessing of spent (i.e. already used in a nuclear reactor) fuel of the aforementioned types. Despite overall success in this field, there is still a great scope of work for a radiochemist. Studies of our Lab in this direction are related to the processes of tritium localization at the very beginning of spent fuel reprocessing. For this purpose, the process of volume oxidation of fuel in oxygen-containing atmosphere – voloxidation – was proposed earlier and is being actively developed now. Processes alternative to the classical method of fuel dissolution in nitric acid are also actively investigated. These processes are based on fuel material interaction with NOx-gases, or nitric acid vapor, and are referred to as nitrification.


Main scientific results:

  • We proved the possibility of using voloxidation in air and water vapor for uranium nitride-based fuels without the formation of difficult-to-localize nitrogen hemioxide.
  • We studied oxidation of UM3 inert intermetallides (M: Ru, Rh, Pd) in air, at temperatures 25-1500 oC. We showed the necessity of high-temperature voloxidation for uranium extraction from these compounds.
  • We managed to demonstrate the efficiency of nitratng atmospheres based on NOx-gases or nitric acid vapors to convert of spent fuel actinide components into water-soluble compounds.

Selected publications:

  1. Ю. М. Неволин, С. А. Кулюхин, А. В. Гордеев, А. А. Бессонов, С. Н. Калмыков. Газофазная конверсия оксидных фаз лантанидов и урана в водорастворимые соединения // Радиохимия, 2020.
  2. S. A. Kulyukhin, Y. M. Nevolin, V. G. Petrov, S. N. Kalmykov. Volume oxidation of uranium mononitride and uranium monocarbide in the dry NOx-gaseous atmosphere // Radiochimica Acta, 2020, DOI: 10.1515/ract-2019-3125
  3. С. А. Кулюхин, Ю. М. Неволин, А. В. Гордеев, А. А. Бессонов. Газофазное объемное окисление мононитрида урана // Радиохимия, 2019.
  4. С. А. Кулюхин, А. В. Гордеев, И. А. Румер, В. В. Кулемин, Ю. М. Неволин. Газофазная конверсия UN и UC в нитрирующей атмосфере // Атомная энергия, 2018.
  5. С. А. Кулюхин, Ю. М. Неволин, А. В. Гордеев. Газофазная конверсия соединений U, Sr и Mo в водорастворимые формы в нитрующей атмосфере // Радиохимия, 2017.
  6. S. A. Kulyukhin, Y. M. Nevolin, M. P. Gorbacheva, A. V. Gordeev. Gas-phase conversion of the U(VI), Sr, Mo, and Zr compounds in nitrating atmosphere // Journal of Radioanalytical and Nuclear Chemistry, 2016, DOI: 10.1007/s10967-016-4921-3