Testing of innovative VVER fuel begins

During a scheduled refuelling at Balakovo 1, three innovative fuel assemblies were loaded into the VVER-1000 reactor core, Russian state nuclear corporation Rosatom said. Each assembly contains 312 fuel rods with a chromium cladding over a traditional zirconium alloy cladding; 18 of these rods use an oxide uranium-plutonium fuel matrix (MOX fuel).

"This combination of the fuel and structural materials is strategically important to integrate a closed fuel cycle not only for innovative fast neutron reactors, but also conventional thermal light water installations, which make up the backbone of modern nuclear power," Rosatom said. "The MOX technology enables the use of secondary nuclear materials, such as depleted uranium and plutonium extracted from spent fuel, for production of fresh nuclear fuel. The chromium-coated fuel rod claddings, originally developed for ATF [accident-tolerant fuel], not only enhance safety and resilience in severe accident scenarios but also allow for fully automated, 'unmanned' fuel fabrication, eliminating manual operations and minimising radiation exposure for shop-floor personnel."

In March, three fuel assemblies with uranium-plutonium REMIX fuel completed their third 18-month VVER-1000 fuel cycle at Balakovo unit 1. Six of the pilot fuel assemblies were loaded into the unit 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. 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.

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.

"Rosatom's strategic goal and our vision for the future is a dual-component nuclear energy system where fast and thermal reactors operate in a closed fuel cycle, with spent fuel from some installations becoming raw material for fresh fuel in others," said Alexander Ugryumov, Senior Vice President for Research and Development at TVEL, Rosatom's fuel division. "Today, we are already piloting fifth-generation fuel assemblies for VVER-1200, fuel rods with MOX fuel and chromium claddings, and even developing new technologies for fully automated pellets manufacturing. In the future, we plan to integrate all these innovations in a single product."