Power start-up is the final major phase before the unit is put into operation. Over the coming months, specialists from Slovenské elektrárne will gradually increase reactor power and verify the performance of the plant’s technological and safety systems under conditions approaching normal operation.
The start of power start-up was preceded by approval from the Nuclear Regulatory Authority of the Slovak Republic, which confirmed the unit’s readiness for the next phase of commissioning after evaluating the results of physical start-up, carrying out inspections and reviewing the relevant documentation.
The start of power start-up is one of the final major milestones before Unit 4 is put into operation. We are entering a phase in which the readiness of the plant’s technology will be verified directly as reactor power increases. Following the successful completion of this phase, Slovakia will gain a new, stable source of electricity that will contribute to the country’s energy security and the achievement of its climate targets for decades to come.
Branislav Strýček, Chairman of the Board and Chief Executive Officer of Slovenské elektrárne
During power start-up, reactor power will be gradually increased to its nominal level. At each power level, the prescribed operational tests and measurements will be carried out to verify the correct operation of the technological systems and safety features, as well as the behaviour of the reactor under various operating conditions.
“We have successfully completed the fuel loading and physical start-up phases. Ahead of us is a series of operational tests during which we will gradually increase the unit’s power and confirm the readiness of individual components for long-term operation. The achievement of this milestone demonstrates the high level of expertise of the Slovenské elektrárne project team and the quality of the work carried out by everyone involved in the completion of the plant,” said Martin Mráz, Project Director for the Completion of Mochovce Nuclear Power Plant.
Once commissioned, Mochovce Unit 4 will increase the generating capacity of Slovakia’s largest electricity producer and contribute to a further increase in the share of low-carbon nuclear energy in the Slovak energy mix. The unit is equipped with a VVER-440/V213 reactor and has an installed electrical capacity of 471 MW.
Power start-up is the final major phase before the commercial operation of a nuclear unit. Following the successful completion of physical start-up, reactor power is gradually increased and the power plant begins generating electricity for the Slovak electricity system for the first time. At each power level, dozens of tests, measurements and inspections are carried out to examine the behaviour of the reactor, turbine, generator and safety systems under actual operating conditions. After evaluating the results, the Nuclear Regulatory Authority of the Slovak Republic may authorise progression to the next power level.
During power start-up, reactor power will be gradually increased. At each power level, tests and measurements will be carried out to verify the operation of the technological and safety systems.
5% – Verification of the unit’s basic operating parameters.
20% – When reactor power is increased to 20%, sufficient steam will be produced in the steam generators to synchronise the turbine generators with the Slovak electricity system, allowing the first megawatt-hours of electricity to flow into the grid.
35%, 55%, 75%, 90% – Verification of the unit’s operating characteristics as power is gradually increased, including dynamic tests to verify the functionality of individual technological systems and their interaction under various operating conditions.
100% – The unit’s nominal power level and final tests before commercial operation. The successful completion of a 144-hour test run at 100% nominal power will confirm the full functionality of the new unit and the achievement of its design parameters.
About the company
With a 66% share of Slovakia’s total electricity generation, Slovenské elektrárne, a.s., is the country’s largest electricity producer. Following the closure of its last coal-fired power plant at the end of the first quarter of 2024, the company now generates all its electricity without direct CO₂ emissions. It operates five nuclear units, 31 hydroelectric power plants and two photovoltaic power plants.
The company’s commitment to generating electricity from low-carbon sources makes it a leader in sustainable energy generation in Central and Eastern Europe. The company has been included five times in the prestigious Europe’s Climate Leaders ranking, compiled by the Financial Times and Statista since 2021.
Who are the shareholders?
Slovenské elektrárne, a.s., has two shareholders. The majority shareholder, with a 66% stake, is Slovak Power Holding B.V. (SPH), which is owned by the Czech energy group Energetický a průmyslový holding (EPH). The second shareholder is the Slovak Republic, which holds a 34% stake in Slovenské elektrárne.
