Bulgaria is continuing its gradual effort to reduce dependence on Russian nuclear fuel, although the transition of the second operating unit of the Kozloduy Nuclear Power Plant to alternative fuel is still facing regulatory procedures. The next key milestone will be the completion of the transition of Unit 5 to Westinghouse fuel, while the licensing process for Unit 6 is still underway.

 

Bulgaria continues to implement its nuclear fuel diversification program at the Kozloduy Nuclear Power Plant, which is a key source of electricity for the country. On September 24, Elisaveta Tsvetanova, Deputy Chair of the Bulgarian Nuclear Regulatory Agency, said that Unit 6 would not yet be able to switch to fuel supplied by the US company Westinghouse during the upcoming fuel cycle. The reason is that the licensing process has not yet been completed, meaning that Russian nuclear fuel will be used during the scheduled outage of the unit in October.

In April, the regulator received an application for the licensing of six fuel assemblies manufactured in Sweden using Westinghouse technology. The initial documentation has already been reviewed, but the agency requested additional information concerning the program for monitoring the performance of the fuel assemblies during operation. According to Tsvetanova, the documents are currently being examined, and the regulator may involve an external consultant in part of the technical assessment. The delay is therefore primarily related to nuclear safety and licensing requirements rather than a decision to abandon Bulgaria's fuel diversification program.

The situation with Unit 5 is considerably more advanced. The phased transition to Westinghouse fuel began in spring 2024. During scheduled maintenance and refueling in May–June 2026, Westinghouse RWFA fuel assemblies were loaded into the reactor for the third time. According to the Bulgarian nuclear regulator, the new fuel has so far been operating without identified problems, while the complete replacement of Russian fuel in Unit 5 is expected to be completed by spring 2027.

For decades, the operating reactors at Kozloduy depended on Russian nuclear fuel and technology, making diversification of supplies an element of Bulgaria's energy security strategy. At the same time, this is not an immediate withdrawal from Russian fuel, but a gradual transition in which new fuel assemblies undergo testing and extended monitoring. This is particularly important for VVER-1000 reactors, where changes to fuel design require confirmation of compatibility with the existing reactor system and compliance with nuclear safety requirements.

Bulgaria's experience is already relevant to the wider European nuclear energy sector. According to Kozloduy NPP, Bulgaria became the first EU member state to practically implement fuel diversification for a VVER-1000 reactor. In 2026, Unit 5 continued operating with Westinghouse fuel, while a similar arrangement is expected to be implemented for Unit 6 in the future.

At the same time, it is important to distinguish between the two tracks. Westinghouse is responsible for fuel diversification for Unit 5 and is preparing alternative fuel for Unit 6, while Sofia has also signed a contract with French company Framatome to supply fuel for Unit 6. As part of the broader strategy, this creates the possibility of establishing several alternative supply channels rather than relying on a single supplier. According to BTA, the Framatome contract provides for up to 12 refueling cycles for Unit 6 between 2025 and 2034, although Framatome fuel must also undergo the necessary licensing procedures.

Energy diversification extends beyond the existing reactors. Bulgaria is also developing plans for new Units 7 and 8 at Kozloduy based on US AP1000 technology. In 2024, Sofia and Washington signed an intergovernmental agreement on cooperation in developing Bulgaria's civilian nuclear program, while Westinghouse and Hyundai Engineering & Construction were given key roles in preparing the new reactor project.

 

Thus, the transition of Kozloduy to alternative nuclear fuel is becoming part of a broader restructuring of Bulgaria's energy infrastructure. In the short term, Russian fuel will continue to play a role, particularly for Unit 6. However, as Westinghouse licensing progresses and cooperation with Framatome develops, Sofia will have greater scope to reduce its technological and fuel dependence on Russian suppliers. At the same time, the success of this strategy will depend not only on political decisions, but also on the operational performance of the new fuel, compliance with nuclear safety requirements, and the ability to ensure stable alternative supplies throughout the reactors' operating lifetimes.

#NEWS

#BULGARIA

25.09.2026 08:56