Unit 4 of Slovakia’s Mochovce nuclear power plant has delivered its first megawatt-hours to the grid. Grid synchronisation took place on Thursday 15 October at 20:41, with the reactor at 20% power, operator Slovenské elektrárne announced.
The reactor is a VVER-440 pressurised water reactor with an installed capacity of 471 MWe. The first of the unit’s two turbogenerators has been connected to the grid. At full power the unit will produce roughly 3.5 million megawatt-hours a year, equal to about 13% of the country’s current electricity consumption. Criticality was reached on 6 August, followed by tests and checks on all equipment. The physical start-up phase began last month.
CEO Branislav Strýček described a moment awaited by generations of people who prepared, built and commissioned the project. For Slovakia, he said, it is a new source of low-emission electricity. The grid connection came two days later than planned: Prime Minister Robert Fico had announced it for Tuesday at the European Nuclear Energy Forum in Prague.
The construction site has a long history. Work on Units 1 and 2 began in 1982, and on Units 3 and 4 in 1986, before being suspended in 1992. The first two units entered operation in 1998 and 1999. The project to complete the other two restarted in 2008, with an estimated cost of €6.7 billion. Unit 3 entered commercial operation in October 2023. Unit 4 is the last to come online at the country’s second nuclear power plant.
Synchronisation is a technical milestone, not the start of commercial operation. Power is now being raised in steps, with tests at each level validated by the Slovak nuclear regulator, ÚJD SR. The process ends with a 144-hour full-power test. Slovenské elektrárne, controlled by Daniel Křetínský’s EPH group with a 34% state stake, aims for full operation by the end of the year.
With Mochovce 4 at full output, nuclear will cover around 77.5% of Slovak electricity demand, a higher share than France in percentage terms. For a mid-sized country, the decision to complete reactors started in the 1980s provides a stable generation base for decades to come.
