The third 18-month cycle of pilot operation of fuel assemblies based on uranium-plutonium REMIX fuel has been completed at unit 1 of Russia’s Balakovo NPP. REMIX fuel, developed for VVER light water reactors comprises a mixture of regenerated uranium and plutonium from used fuel reprocessing, with the addition of enriched uranium.
Compared with mixed oxide uranium-plutonium (mox) fuel for fast reactors, REMIX has a lower plutonium content (up to 1.5%). Its neutron spectrum is the same as standard enriched uranium fuel, so the behaviour of the fuel in the reactor core and the amount of plutonium produced from irradiated uranium are generally identical. REMIX fuel can be used without changes to reactor design or significant additional safety measures.
Six fuel cassettes, fully loaded with REMIX fuel elements were loaded into the VVER-1000 reactor at Balakovo 1 at the end of 2021. The last three of these six assemblies were removed from the core during ongoing routine maintenance at the power unit. They had gone through the standard operating cycle for VVER-1000 nuclear fuel (three fuel cycles of 18 months each).
After being unloaded from the reactor core, the irradiated fuel assemblies were placed in a pool, which already held three cassettes recovered in 2024, after completion of the second fuel campaign. The irradiated REMIX assemblies will later be sent for post irradiation examination to the Scientific Research Institute of Atomic Reactors (NIIAR – Nauchno Issledovatelskii Institut Atomnikh Reaktorov) in Dimitrovgrad.
In the future, the use of REMIX fuel will make it possible close the nuclear fuel cycle including both fast reactors and classical light-water thermal reactors. This will expand the raw material base of nuclear energy and enable the reuse of used fuel instead of storing it.
“Taking into account the operation of experimental fuel elements, and complete fuel cassettes, we have already accumulated 10 years of experience in irradiating REMIX fuel in a high-power commercial reactor,” said Alexander Ugryumov, Senior Vice President for Scientific & Technical Activities at Rosatom’s Fuel Division, TVEL. By carrying out post-reactor studies of irradiated fuel elements, we will be able to qualify and offer to the market for the first time uranium-plutonium fuel for VVER reactors. The next step will be to load the VVER reactor with assemblies with uranium-plutonium fuel containing depleted uranium and up to 5% plutonium. In this way we will create a complete line of products and solutions as part of a Balanced Nuclear Fuel Cycle, from regenerated uranium and various uranium-plutonium compositions.”
Yuri Ryzhkov, Deputy Chief Engineer for Safety & Reliability at Balakovo NPP said the REMIX pilot operation was carried out in strict coordination with regulator Rostechnadzor and under the control of specialists from TVEL. “After each fuel cycle, the fuel elements and structural elements were inspected using the standard television camera of the reloading machine. During the period of operation, no deviations were identified, the neutron-physical and resource characteristics did not exceed design limits.”
