On Thursday, 6 August 2026, at 22:10, the reactor of Mochovce Unit 4 reached criticality, followed by the achievement of minimum controlled power at 22:31. This represents one of the key milestones in the commissioning process of a nuclear generating unit, confirming the reactor's readiness for the subsequent stages of testing.

“The achievement of criticality and minimum controlled power is the result of the work of thousands of specialists who have contributed to the preparation, construction, inspection and start-up of Unit 4. It confirms that the plant is ready to proceed to the next phase of testing before the commencement of electricity generation,” said Martin Mráz, Mochovce Project Director.

This milestone will be followed by reactor physics tests and testing at various power levels. The objective is to verify the performance of all plant systems under operating conditions and to prepare the unit for synchronisation with the electricity grid.

Mochovce Unit 4 is the second of the two new nuclear units constructed at the power plant site. Once both units are in operation, Slovakia will rank among the countries with the highest share of electricity generated from nuclear energy in the world. The new unit will also strengthen domestic electricity production and contribute to the country's long-term energy security.

The achievement of criticality represents a major success for the project and confirms that Unit 4 continues to progress in accordance with the technological start-up schedule towards the generation of its first megawatt-hours of electricity.