Slovenské elektrárne started loading nuclear fuel into the reactor of unit 4 at the Mochovce NPP under the strict supervision of the Nuclear Regulatory Authority (ÚJD SR – Úrad jadrového dozoru Slovenskej republiky).
Fuel loading marks the transition from the construction phase to the active commissioning of the unit. It will be followed by pre-critical tests, the first controlled fission reaction and a gradual increase in output up to synchronisation with the electricity grid.
UJD SR issued the decision authorising the commissioning of Mochovce 4 after a thorough and detailed verification that all legislative conditions and technical requirements had been met. “Inspectors of the Authority assessed the unit’s readiness to begin active testing in all areas under review, both by examining the submitted documentation and reports on the results of inactive tests, and through daily inspection activities on site during construction, equipment installation, functional testing and the verification of personnel readiness. A high level of nuclear safety remains an absolute priority also in the next stage of physical and power start-up testing,” said UJD SR Chair, Marta Žiaková.
Construction of the first two 471 MWe VVER units at the four-unit Mochovce plant began in 1982. Construction of units 3&4, which started in 1986, was frozen in 1992. Units 1&2 began operation in 1998 and 1999 and work to complete units 3&4 resumed in 2009 but faced a series of delays. Units 3&4 with a design life of some 60 years, will supply some 26% of Slovakia’s total electricity consumption. Slovakia also has two VVER-440 units operating at the Jaslovské Bohunice NPP. The commissioning of Mochovce 4 will elevate nuclear energy to 77.5% of Slovakia’s domestic electricity mix, allowing the country to surpass France as the European leader in nuclear power reliance and cementing its status as a net electricity exporter.
“Mochovce unit 4 closes one of the key chapters in the development of Slovak energy,” said Branislav Strýček, Board Chairman and CEO of Slovenské elektrárne. “It is the moment when the long-standing efforts of thousands of people become tangible value for the country – stable, low-emission and price-predictable electricity. Mochovce 4 is a source of both professional and personal pride, and proof that even smaller countries and nations can achieve great things.”
However, the history of Mochovce 3&4 is a catalogue of project delays, political upheaval, and ballooning budgets. The 39-year timeline begins in 1987 when construction officially begins. In 1991 work stalled following the collapse of the USSR and funding shortages. Construction restarted in 2008 under majority shareholder Enel, with initial plans to finish by 2012-13. Multiple delays followed due to post-Fukushima safety retrofits, cramped spacing for modern thick cabling, and ownership restructuring.
Slovenské elektrárne is owned by a 66% majority stake through an intermediary vehicle called Slovak Power Holding (SPH). In 2016, Czech energy infrastructure group Energetický a průmyslový holding (EPH) bought a 50% stake in SPH from Enel in December 2024, EPH exercised its early call option to buy the remaining 50%. Following regulatory approval from the European Commission in March 2025, the deal officially closed two months later. Currently the state holds a 34% minority stake, with shareholder rights managed via the Ministry of Economy. EPH (via SPH) holds the 66% majority stake. The final price tag for completing units 3&4 was to €6.7bn ($7.66bn) up from an estimated €2.8bn in 2008.
