Mochovce 4 connected to the grid

The phasing-in of the new VVER-440 unit to the country's electricity system took place with the reactor at 20% power output, at 20:41 on Thursday 15 October, Slovenske elektrárne said.

The total capacity of the new unit is 471 MWe and its generation is equal to about 13% of Slovakia's total current consumption.

Branislav Strýček, Chairman and CEO of Slovenske elektrárne, said: "For the first time in history, Mochovce unit 4 is supplying electricity to the Slovak electricity system. This is a moment that generations of people who prepared, built and commissioned this project have been waiting for. Today we see the result of their work in the form of a new low-emission source of electricity for Slovakia."

Construction of the first two VVER-440 units at the four-unit Mochovce plant started in 1982. Work began on units 3 and 4 in 1986, but stalled in 1992. The first two reactors were completed and came into operation in 1998 and 1999, respectively, with a project to complete units 3 and 4 beginning ten years later at an estimated cost of EUR6.7 billion (USD7.6 billion). Mochovce 3 entered commercial operation in October 2023.

Mochovce 4 reached criticality on 6 August, which was followed by a series of tests and checks that all equipment was working as designed, before the physical start-up last month.

Thursday's phasing-in to the grid took place two days later than originally planned after "a non-standard response was recorded in the electrical voltage measurement circuits of the non-nuclear part of the plant", necessitating a repeat of parts of the technical tests.

The grid connection involved the first turbogenerator of Mochovce 4 being aligned and connected - a similar process must take place for the second turbogenerator, followed by tests and checks at each power level before the output is increased in a series of stages. The final test will be a 144-hour run at 100% power.

Slovenské elektrárne's majority shareholder is Slovak Power Holding BV, which is owned by the Czech energy group Energetický a průmyslový. The second shareholder is the Slovak Republic, which has a 34% stake.

Slovakia already has five nuclear reactors generating more than 60% of its electricity. As well as the other three Mochovce units, there are two at Bohunice, which went into commercial operation in 1984 and 1985, respectively. When the new unit is running at full capacity it will reinforce the Slovak Republic's position as the country with the highest proportion of its electricity generated by nuclear power. The Slovak government has plans for a new large unit at Bohunice, and has also been exploring the potential for small modular reactors in the country.