Transition away from Russia-supplied fuel expected to take four years
Unit 5 of Bulgaria’s Kozloduy nuclear power station has completed its first fuel cycle using 43 Westinghouse-made RWFA (Robust Westinghouse Fuel Assembly) fuel assemblies, the country’s national nuclear regulator said.
The Bulgarian Nuclear Regulatory Agency (NRA) also said the fuel assemblies have operated safely in the Russia-designed VVER-1000 reactor core.
In May 2025, another 42 RWFA assemblies were loaded into the reactor for a second fuel cycle run.
A standard VVER-1000 pressurised water reactor core uses 163 fuel assemblies arranged in a hexagonal lattice.
Bulgaria was previously getting its nuclear fuel from Russia’s state company Tvel. In December 2022, following Russia’s invasion of Ukraine earlier that year, Sofia signed new 10-year fuel contracts with US-based Westinghouse and France’s Framatome for Kozloduy-5 and Kozloduy-6.
The first Westinghouse assemblies were loaded into Unit 5 in June 2024.
According to the NRA, the phased transition process to the new fuel at Kolzoduy-5 will take four years and is expected to be completed in 2027.
Kozloduy on the Danuber River in northern Bulgaria is the country’s only commercial nuclear power station. Its two reactor units provide about a third of Bulgaria’s electricity.
