Nuclear energy is the main source of electricity in Slovakia. Five operating reactors at Jaslovské Bohunice and Mochovce provide more than 2.3 GW of net capacity, while a sixth unit remains under construction at Mochovce. Nuclear plants supplied 18.4 TWh in 2024 and produced about 60.6% of national electricity, placing Slovakia among the world’s most nuclear-dependent power markets.
The country’s position was shaped by replacement and delay. Two older Bohunice reactors closed during Slovakia’s entry into the European Union, leaving the country more dependent on imports. Completion of Mochovce Unit 3 in 2023 restored a stronger domestic supply position. Unit 4 should deepen that shift, while plans for a much larger reactor at Bohunice show that Slovakia intends to remain nuclear-centered for decades.
Mochovce Unit 4 Is the Immediate Test
Slovakia’s five operating units are VVER-440 pressurized-water reactors. Bohunice Units 3 and 4 entered service during the 1980s. Mochovce Units 1 and 2 followed in 1998 and 1999, while Unit 3 first connected to the grid in January 2023.
Mochovce Unit 4 is now the most important near-term project. The reactor has a net design capacity of about 440 MW and shares the VVER-440 V-213 design used by Unit 3. Construction began during the Czechoslovak period, stopped in the 1990s and later resumed with extensive modernization and additional safety systems.
Hot hydro testing was completed in 2025, followed by further revision work. As of June 2026, the unit was still classified as under construction, with fuel loading dependent on licensing by Slovakia’s Nuclear Regulatory Authority. Technical completion does not automatically mean that a nuclear unit is ready to operate: fuel loading, first criticality, power testing and commercial commissioning each require further approval.
Each new Mochovce unit is designed to cover about 13% of Slovak electricity demand. Unit 3 has already shown the effect of adding one reactor to a small system. In 2025, the five operating units supplied a record 17.93 TWh to the grid. Once Unit 4 reaches full operation, Slovakia should hold a larger structural electricity surplus during periods of normal plant availability.
A High Nuclear Share Changes the Whole Power System
The fleet is operated by Slovenské elektrárne, which is 66% owned through Slovak Power Holding by the Czech energy group EPH; the Slovak state holds 34%. The company also operates major hydropower assets, allowing steady nuclear generation and flexible hydro output to work within the same portfolio.
This combination is increasingly important. European markets now experience more hours of very low or negative prices when solar and wind generation is high. Nuclear plants continue producing large volumes of electricity, so Slovakia needs assets that can respond when demand and prices move quickly.
Pumped-storage hydropower is central to that balance. Water can be pumped uphill when electricity is abundant and released through turbines when demand rises. Battery projects and shorter trading intervals provide further flexibility. Slovakia’s nuclear strategy therefore cannot be separated from storage, grid operation and cross-border electricity trade.
Slovenské elektrárne closed its last coal-fired plant in early 2024, leaving its generation portfolio free of direct carbon dioxide emissions. Nuclear power provides most of the volume, while hydropower provides more operational flexibility. Unit 4 will make that relationship even more important.
Fuel Diversification Has Become an Energy-Security Priority
Slovakia’s reactors were designed around Soviet and later Russian VVER technology, and Russian company TVEL has traditionally supplied their fuel. Technical compatibility supported reliable operation, but dependence on one supplier became a strategic concern after Russia’s invasion of Ukraine and the wider European effort to reduce Russian energy links.
Slovenské elektrárne is now building a diversified fuel chain. Agreements with Westinghouse and Framatome support alternative VVER-440 fuel development and supply. A long-term Cameco contract covers natural uranium and conversion services for a significant share of requirements through 2036, with deliveries intended to support Bohunice and Mochovce from 2028. An agreement with Urenco adds access to enrichment services.
This change cannot happen immediately. VVER-440 fuel assemblies must meet strict technical requirements, and new designs require testing and regulatory approval. Utilities must also coordinate uranium purchase, conversion, enrichment, fabrication, transport and storage. Slovakia is therefore creating overlapping supply options rather than making one rapid supplier change.
The result should be a fleet that still uses Russian-designed reactors but is less dependent on a Russian-controlled fuel chain. Because nuclear is Slovakia’s dominant electricity source, fuel diversification is directly linked to national supply security.
Bohunice Is Being Prepared for a Much Larger Reactor
Slovakia is planning beyond Mochovce Unit 4. In January 2026, Slovakia and the United States signed a civil nuclear cooperation agreement that includes development of a state-owned 1,200 MW unit of United States design at Jaslovské Bohunice. Westinghouse has been the expected technology partner, although detailed commercial, financial and regulatory arrangements remain necessary.
A reactor of this size would differ sharply from Slovakia’s 440 MW-class units. It would add capacity equal to more than half of the current operating nuclear fleet in one project. That could support growth in electricity demand, industrial electrification and exports, but it would also create a major financing requirement and increase the importance of grid planning.
The government has discussed operation around 2040. The project is therefore a long-term replacement and expansion decision rather than an answer to immediate supply needs. Slovakia has an experienced workforce and an established nuclear site, but a new reactor design would still require new licensing work, training and supply-chain arrangements.
Full state ownership is also significant. Existing plants operate within partly state-owned Slovenské elektrárne, while the new Bohunice unit is intended to remain under state control. The government would therefore carry much of the financing and delivery risk.
Small and Advanced Reactors Form a Second Track
Slovakia is also examining small modular reactors. The Project Phoenix feasibility study assessed Bohunice, Mochovce, Vojany and the U.S. Steel Košice industrial site. All four met baseline criteria covering water, grid access, geology and external risks.
SMRs could serve former fossil-fuel sites, industrial demand or phased additions smaller than a conventional reactor. Slovakia has not selected a technology or committed to construction, and detailed site, regulatory and commercial work remains necessary.
The country is also exploring lead-cooled fast-reactor technology through cooperation among state-owned JAVYS, Slovak engineering company VUJE and developer newcleo. The initiative links advanced reactor research with possible reuse of spent nuclear fuel. It remains early-stage, but it shows an effort to convert Slovakia’s operating experience into future engineering and research activity.
Decommissioning Completes the Nuclear Picture
The Bohunice site contains three permanently closed reactors: the A1 unit and the two V1 units. Their decommissioning requires dismantling, radioactive-waste processing, storage and site restoration. This creates a different nuclear capability from plant operation, but one that is becoming more valuable as older reactors close across Europe.
Slovakia must therefore manage the full nuclear cycle at once: operate aging units, commission a delayed reactor, diversify fuel, dismantle closed plants and prepare possible new technologies. Mochovce Unit 4 is the immediate priority. After that, the central question will be whether Slovakia can finance and deliver the large Bohunice project while keeping its existing fleet safe and productive. Success would preserve nuclear power as the foundation of Slovak electricity and strengthen the country’s role in regional power trade.