Slovakia's Mochovce 4 reaches the grid, supplying its first electricity at 20% power
Serguey Asael Shinder2 min readSlovakia's newest nuclear unit, Mochovce 4, has been connected to the grid and supplied its first electricity, World Nuclear News reported. The VVER-440 unit was phased in at 20:41 on Thursday 15 October 2026 at 20% power output, operator Slovenské elektrárne said. The unit's total capacity is 471 MWe, and its generation equals about 13% of Slovakia's current total consumption.
A long construction history. Work on the first two VVER-440 units at the four-unit Mochovce plant began in 1982; units 3 and 4 were started in 1986 but stalled in 1992. The first two reactors came into operation in 1998 and 1999. A project to finish units 3 and 4 began about ten years later at an estimated EUR 6.7 billion (USD 7.6 billion), and Mochovce 3 entered commercial operation in October 2023. Unit 4 reached criticality on 6 August 2026, followed by tests and the physical start-up the previous month.
What happens next. The grid connection was two days later than planned after "a non-standard response was recorded in the electrical voltage measurement circuits of the non-nuclear part of the plant", which required parts of the technical tests to be repeated. The connection aligned and connected the unit's first turbogenerator; a similar process must follow for the second, with tests at each power level before output is raised in stages. The final test is a 144-hour run at 100% power — so full commercial output still lies ahead.
The wider picture. Slovakia already has five reactors generating more than 60% of its electricity — the other three Mochovce units and two at Bohunice (in operation since 1984 and 1985). At full capacity, unit 4 reinforces Slovakia's position as the country with the highest share of nuclear electricity. The government has plans for a new large unit at Bohunice and has been exploring small modular reactors. Slovenské elektrárne's majority shareholder is Slovak Power Holding BV, owned by the Czech group Energetický a průmyslový holding; the Slovak Republic holds 34%.
Source: World Nuclear News, "Mochovce 4 connected to the grid" — https://www.world-nuclear-news.org/articles/mochovce-4-connected-to-the-grid