Nuclear power is not a secondary source in Bulgaria. It is one of the foundations of the national electricity system and an important part of the country’s position as a regional power producer. The two operating reactors at the Kozloduy Nuclear Power Plant have a combined net capacity of just over 2 gigawatts and supplied nearly 15.8 terawatt-hours of electricity in 2024.
Their contribution commonly represents around one-third of Bulgarian electricity generation, although the exact share changes with demand, outages, renewable production, and electricity trade. This scale gives nuclear power a direct role in wholesale prices, energy security, industrial competitiveness, and exports to neighboring markets.
Bulgaria is now managing three nuclear tasks at the same time. It must keep Kozloduy Units 5 and 6 operating safely beyond their original design periods, complete the decommissioning of four older reactors, and decide whether to commit the country to two new AP1000 units. The result will determine whether Bulgaria remains a major nuclear electricity producer through the middle of the century or faces a large capacity gap as its existing fleet ages.
Two VVER-1000 Reactors Carry the Operating Fleet
Kozloduy is Bulgaria’s only operating nuclear power station. The site lies on the Danube River in the northwest of the country and originally contained six Soviet-designed pressurized water reactors. Units 1 through 4 were smaller VVER-440 reactors. They were permanently shut down between 2002 and 2006 as part of Bulgaria’s path toward European Union membership and are now being decommissioned.
Units 5 and 6 are larger VVER-1000 reactors. Each has gross capacity of about 1,040 megawatts and net capacity of approximately 1,003 megawatts. Unit 5 first connected to the grid in 1987, followed by Unit 6 in 1991. Modernization programs have upgraded safety systems, electrical equipment, instrumentation, control systems, and other plant components to support longer operating lives.
The current operating licenses run to 2027 for Unit 5 and 2029 for Unit 6. These dates do not necessarily represent final shutdown deadlines. Bulgarian authorities can grant further license periods if safety reviews, equipment condition, ageing-management programs, and regulatory requirements support continued operation.
Long-term operation is central to Bulgaria’s planning because new nuclear construction cannot replace the existing units immediately. Even an efficiently managed large-reactor project requires years of design, licensing, financing, procurement, civil construction, testing, and commissioning. Continued operation at Units 5 and 6 therefore provides the bridge between the current nuclear system and any future fleet.
Fuel Diversification Has Reduced a Major Strategic Exposure
For decades, Kozloduy’s VVER reactors were closely tied to Russian nuclear technology and fuel supply. Russia’s invasion of Ukraine changed the strategic meaning of that dependence. Bulgaria began accelerating plans to secure qualified alternatives that would allow the reactors to continue operating without relying on a single Russian supplier.
Unit 5 received its first Westinghouse VVER-1000 fuel reload in 2024 under a ten-year supply agreement. The fuel was introduced through a licensed transition process, with Westinghouse assemblies operating alongside existing fuel in a mixed core. By 2026, Westinghouse stated that its fuel made up half of the Unit 5 core.
Unit 6 follows a different route. Kozloduy signed a ten-year fuel supply arrangement with France’s Framatome beginning in 2025. Additional licensing work with Westinghouse is also creating another potential fuel design for the unit. This multi-supplier approach reduces concentration risk and gives Bulgaria more flexibility in future procurement.
Fuel diversification does not remove every Russian connection from the plant. The reactors remain VVER designs, and some services, components, technical knowledge, or legacy systems may still reflect their original supply chain. It does, however, address one of the most immediate operational dependencies: access to fresh reactor fuel. It also places Bulgaria within a wider European effort to create non-Russian fuel options for Soviet-designed reactors.
Units 7 and 8 Would Move Bulgaria to AP1000 Technology
Bulgaria’s planned nuclear expansion is centered on Kozloduy Units 7 and 8. The government selected Westinghouse AP1000 technology for the project, with Hyundai Engineering & Construction participating in the delivery team. Two units would add roughly 2.5 gigawatts of new nuclear capacity at the existing Kozloduy site.
The choice marks a major technological shift. Bulgaria would move from Soviet-designed VVER reactors to a Generation III+ American reactor design with passive safety systems. Building at Kozloduy offers several advantages, including an established nuclear workforce, transmission connections, security arrangements, cooling-water access, emergency planning, and a local economy familiar with the industry.
The project has advanced beyond a general political proposal, but it has not yet passed every commercial and financial threshold. Engineering work is developing the site-specific design, licensing documents, cost estimates, project schedule, and local supplier program. In May 2026, the project company said the engineering services contract would be extended for 14 months to complete additional technical and commercial work before a final investment decision.
The planned next stage is an engineering, procurement, and construction phase beginning in 2027. That schedule depends on parliamentary approval, financing, regulatory progress, contract terms, and confidence in the final cost. Large nuclear projects place substantial risks on governments and consumers if costs or construction periods increase. Bulgaria must therefore decide not only whether it wants the reactors, but also how those risks will be controlled.
New Reactors Are Tied to Coal Replacement and Regional Trade
The case for new nuclear capacity is closely connected to Bulgaria’s coal-dependent power sector. Lignite plants have historically provided domestic, dispatchable electricity and employment, especially in the Maritsa basin. European carbon costs and climate policy are weakening the long-term economics of that model.
Two AP1000 units could provide large volumes of low-carbon electricity as coal generation declines. They could support industrial demand, electrification, and exports across southeastern Europe. Nuclear output would also complement wind and solar by providing generation that is not affected by weather conditions.
The timing is difficult. Units 7 and 8 cannot solve near-term transition problems if construction stretches into the late 2030s. Bulgaria still needs grid investment, renewable development, storage, demand management, and transitional capacity. New reactors would form one part of the future system rather than replace the need for broader modernization.
The project company has also placed strong emphasis on domestic economic participation. Westinghouse and Hyundai have signed memoranda with Bulgarian suppliers, while universities and training programs are preparing engineers and technicians for AP1000 work. Local participation could keep more project spending inside Bulgaria and preserve nuclear expertise. It must, however, be supported by realistic qualification standards and a clear division between domestic work and specialized imported equipment.
Decommissioning Creates a Parallel Nuclear Responsibility
While Bulgaria plans new capacity, it is still managing the legacy of Kozloduy Units 1 through 4. Decommissioning involves removing radioactive systems, treating waste, maintaining security, monitoring the site, and eventually releasing facilities from regulatory control. It is a long industrial process rather than a simple closure.
Bulgaria also operates spent-fuel storage facilities and must maintain credible arrangements for radioactive waste management. These obligations continue regardless of whether Units 7 and 8 are built. A larger future fleet would increase the importance of long-term funding, storage capacity, regulatory independence, and workforce continuity across the full nuclear lifecycle.
The country’s nuclear future is therefore based on more than constructing new reactors. Bulgaria must safely extend the life of its current units, diversify fuel and services, complete decommissioning work, and establish a bankable AP1000 project. The existing Kozloduy fleet gives the country a strong technical base, but the next stage will depend on cost control and project governance.
If Units 7 and 8 reach construction under credible contracts, Bulgaria could preserve nuclear power as a central part of its electricity system for several more generations. If the project stalls, the country will eventually face a difficult replacement decision when Units 5 and 6 approach the end of their extended operating lives.
