They have now been placed in a used fuel pool before being sent for post-irradiation study at the Research Institute of Atomic Reactors (JSC SSC RIAR).
Instead of using standard enriched uranium, the REMIX (from Regenerated Mixture) fuel features a mixture of reprocessed uranium and plutonium from used nuclear fuel from VVER reactors. The fuel would allow light-water reactors, as well as fast neutron reactors, to reuse irradiated fuel and help Russia’s efforts to close its nuclear fuel cycle.
Six of the pilot fuel assemblies were loaded into Balakovo unit 1 at the end of 2021. Three of the assemblies were removed after the second 18-month fuel campaign, with three completing the standard three 18-month operating cycles.
The REMIX fuel cycle would see used fuel assemblies reprocessed so that uranium and plutonium can be recycled as an unseparated mixture. They are topped up with some freshly enriched uranium and made into new fuel, which goes back to be used again. This cycle can be repeated as many as five times, with waste fission products removed each time and vitrified in glass ready for permanent geological disposal. In theory, with three fuel loads in circulation, a reactor could run for 60 years using the same fuel, with LEU recharge and waste removal on each cycle.
Compared with uranium-plutonium fuel for fast reactors – such as MOX fuel – REMIX has a lower plutonium content and the fuel performs within the same parameters as fuel made only from fresh low-enriched uranium, Rosatom says. This means a reactor would not need any modification to start using REMIX.
Alexander Ugryumov, Senior Vice President for Scientific and Technical Activities at TVEL – Rosatom’s fuel division – said: “Based on the operation of experimental fuel rods and then full-scale fuel assemblies, we have accumulated 10 years of experience irradiating REMIX fuel in a high-power commercial reactor. After completing post-irradiation studies of the irradiated fuel rods, we will be able to qualify and offer uranium-plutonium fuel for VVER reactors for the first time. The next step will be loading VVER reactors with assemblies of uranium-plutonium fuel containing depleted uranium and up to 5% plutonium. Thus, we are creating a full line of products and solutions within the balanced nuclear fuel cycle concept, from reprocessed uranium to various uranium-plutonium compositions.”
Yuri Ryzhkov, Deputy Chief Engineer for Safety and Reliability at the Balakovo plant, said: “The pilot operation of REMIX fuel was conducted in strict coordination with Rostekhnadzor (Russia’s nuclear regulator) and under the supervision of specialists from Rosatom’s Fuel Division. After each fuel cycle, the fuel elements and structural components were inspected using the fuel handling machine’s standard television camera. No deviations were detected during the operation period, and the neutronic and service life characteristics remained within the design limits.”
