Slovak utility Slovenské elektrárne begins power start-up of Mochovce 4 nuclear unit

Slovakia’s new Mochovce 4 nuclear unit, with an installed capacity of 440 MW, has moved closer to commercial operation. Technicians have begun the unit’s power start-up, during which it will be connected to the grid and start generating electricity. Before its official commissioning, the unit will still undergo tests at various power levels. Construction of the VVER-440 unit began in 1987, but was officially halted after six years until 2009.

Slovenské elektrárne announced that its new Mochovce 4 nuclear unit moved from the physical start-up phase to the power start-up phase on Monday afternoon. For the VVER-440 nuclear unit, with a net installed capacity of 440 MW, this represents a key milestone on the path to commercial operation.

"During power start-up, reactor output will gradually increase to its nominal level. Prescribed operational tests and measurements will be carried out at each power level. These will verify the proper functioning of technological systems, safety features and reactor behaviour under different operating conditions," said Branislav Strýček, chairman of the board and CEO of Slovenské elektrárne.

The new reactor will now undergo a gradual increase in output. First, technicians will verify basic operating parameters at 5% power. At 20% power, the amount of steam generated will allow the unit’s turbogenerators to be connected to the electricity grid and begin supplying electricity. Before the final 144-hour test at full power, operators will also verify the unit’s behaviour at 35%, 55%, 75% and 90% power.

"We have successfully completed the fuel loading and physical start-up stages. We now face a series of operational tests during which we will gradually increase the unit’s output and confirm the readiness of individual equipment for long-term operation. This milestone confirms the high level of expertise of the Slovenské elektrárne project team," added Martin Mráz, project director for the completion of the Mochovce plant.

Completion after a long pause

Czechoslovakia began constructing the third and fourth nuclear units at the Mochovce plant in 1987. However, construction work was halted in 1993 and could only resume in 2009. Mochovce 3 began commercial operation in 2023, while Mochovce 4 is scheduled to do so later this year.

Once the final unit is completed, the capacity of Slovak nuclear power plants will rise to 2.75 GW. Slovakia’s third Mochovce nuclear unit has already helped the country become a net exporter of electricity. Following completion of the fourth unit, the country will achieve a very high share of nearly 80% of zero-emission nuclear energy in domestic consumption.