Slovakia Just Plugged In a Reactor 40 Years in the Making, and It Will Lead Europe in Nuclear Share

On Tuesday evening, turbines at Slovakia's Mochovce nuclear power plant began feeding their first megawatt-hours into the national grid from a reactor that broke ground nearly four decades ago. Unit 4, a 471-megawatt VVER-440 reactor, was synchronised with the Slovak electricity system, the final step before full commercial operation. Prime Minister Robert Fico announced the milestone at a nuclear energy forum, marking the end of one of the longest-running construction projects in European energy.

"This very evening, we will witness the so-called synchronisation of this unit with the grid," Fico said at the forum. "Once operational, Slovakia will gain another stable energy source," he added, according to Reuters reporting on the announcement.

Once operational, Slovakia will gain another stable energy source. (Prime Minister Robert Fico, at a nuclear energy forum, October 13, 2026)

Synchronisation is not full operation. Operator Slovenske Elektrarne began powering up the unit in September, and with reactor power having reached 20 percent, the turbine generators can be brought into phase with the national system so electricity starts flowing. The company says the unit should be fully operational by year-end, after a series of power-ascension tests that include a 144-hour demonstration run at full capacity to verify the reactor, turbine, generator, and safety systems under operating conditions.

Forty years in the making

Few energy projects carry this much history. Construction on Mochovce's third and fourth units began in the mid-1980s under Czechoslovakia, then stalled in 1992 amid the country's breakup and years of political and financial uncertainty. The two half-finished reactors sat for decades while ownership, design standards, and financing were renegotiated. Completion proceeded only after long delays, design changes, and major financing commitments; Slovakia's Supreme Audit Office found serious weaknesses in project control and reported a cost close to 6 billion euros, according to a 2026 analysis in the journal Energies.

The revival began in earnest with Unit 3, which was synchronised with the grid on January 31, 2023, and materially increased the country's nuclear generation. Unit 4 followed the same commissioning playbook: fuel loading began on June 29, 2026, the unit reached criticality and minimum controlled power in August, and the Nuclear Regulatory Authority authorised the energy start-up on September 21. Unit 4 is the last of the four reactors at Mochovce, the country's second nuclear plant, and completes a fleet six decades in the making.

Why 77.5 percent matters

The numbers are what make this story bigger than one reactor. At full output, Unit 4 alone can cover around 13 percent of Slovakia's electricity consumption. With it running, nuclear power would cover the equivalent of 77.5 percent of national demand, ahead of France in percentage terms, according to the operator's figures cited by Reuters. France is usually cited as the world leader in nuclear reliance; Slovakia is about to take that title, at least as a share of domestic demand.

That is a deliberate energy strategy, not an accident. Slovakia's five currently operational reactors generate around half of its electricity. The entire fleet is built around the VVER-440 pressurised-water design, a Soviet-origin technology that gives the country standardised training, maintenance, and operating experience across every unit, but also concentrates dependencies on fuel design, components, and licensing support from a single origin. Slovakia signed an agreement with Westinghouse in 2023 to receive nuclear fuel as a step toward moving away from Russian-sourced fuel, and has been talking to France's Framatome about developing fuel for VVER-440 reactors.

Who owns the megawatts

Slovenske Elektrarne, the operator, is majority owned by Czech billionaire Daniel Kretinsky's EPH group, while the Slovak state holds a 34 percent stake that it has expressed interest in increasing. The government is separately planning to build a larger, 1,200-megawatt power plant at Bohunice under state leadership, alongside the two existing Bohunice reactors that entered service in the 1980s, and it is assessing the potential deployment of small modular reactors.

There is an important caveat to the headline figure. The 77.5 percent number describes nuclear's share of demand on paper once Unit 4 is in stable commercial operation; realised output will depend on commissioning performance, outages, and demand, as the Energies analysis notes. Units this standardised tend to run at high capacity factors, but until the 144-hour full-power run is complete, the number remains a projection.

What it means for Europe's energy math

Mochovce's completion lands in the middle of Europe's wider nuclear reconsideration. Countries that once planned phase-outs are now extending reactor lifetimes, and governments from Paris to Prague are discussing new builds as the twin pressures of decarbonisation and electricity demand collide. This is analysis, not fact: a 471-megawatt reactor finishing on budget would barely make headlines. But a reactor that started construction in 1986 actually reaching the grid demonstrates something the industry badly needs proof of, which is that long-delayed, Soviet-designed plants can still be completed and licensed in a modern regulatory regime.

The deeper question is who can replicate Slovakia's model. The VVER fleet benefits from deep standardisation, and the country has accepted the trade-offs: foreign ownership of the operator, Russian-origin technology, and a fleet share of electricity so high that any single outage ripples through the system. For Europe's nuclear renaissance, Mochovce Unit 4 is both an encouragement and a warning about what it takes to finish a reactor when you started one a generation ago. Related reading: Google's bet on nuclear power for AI data centers.