Hungary’s Paks Nuclear Power Plant has begun the process of restarting its third turbine, marking another major step towards restoring the facility to full capacity after the Danube’s record-low water levels forced several units offline.
The restart of the 6th turbine in Unit 3 began on Friday evening and entered its final, most critical stage on Saturday night, Prime Minister Péter Magyar said during a live broadcast from the nuclear power plant.
Two turbines are currently operating at Paks. Once the third turbine is successfully connected to the electricity grid, the plant will gradually increase its output, with full capacity of around 2,000 megawatts expected to be reached by Wednesday.
A 49-hour process is nearing its final stage
According to Magyar, restarting a turbine takes around 49 hours, meaning preparations for the third turbine began almost two days before the live broadcast. By Saturday evening, the process had reached its final three hours. This is the most critical phase, as engineers begin bringing the turbine up to its operating speed.
Károly Vigh, the plant’s director of operations, explained that the turbine is initially kept turning at just 3–4 revolutions per minute. This prevents the turbine shaft from bending and ensures that heat is distributed evenly throughout the machinery.
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The restart is carried out in several stages. The turbine is first brought up to 600 revolutions per minute, followed by a technical inspection. It is then increased to 900 rpm and checked again before eventually reaching its operating speed of 3,000 rpm.
The final acceleration is particularly critical, with the turbine’s speed increasing by 600 revolutions per minute at a time. Once the turbine reaches 3,000 rpm, it can be connected to the electricity grid. However, it can take a further hour and a half to two hours before the turbine’s output appears on the grid operated by Hungary’s transmission system operator MAVIR.
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Another turbine is expected to follow
The restart of the third turbine is only part of the wider process to restore Paks to full operation. According to the latest schedule, the second turbine of Unit 1 could be ready for parallel connection to the grid from around 8 AM on Sunday.
Preparations have also begun for restarting Unit 4. The 7th and 8th turbines are expected to be the last ones to enter the restart process, with their restart scheduled to begin around midnight. Plant officials said that restarting turbines is not an unusual procedure for Paks: between six and ten planned turbine restarts are carried out each year as part of maintenance and repair work.
However, the current situation is highly unusual. Vigh said that three reactors have to be brought back into operation at the same time – something that has never happened before in Hungary. Around 20–25 people have been working continuously to restart an individual unit, while approximately 75 workers are involved in restarting three turbines simultaneously.
Emergency Danube works made the restart possible
The restart would not have been possible without the emergency measures introduced after the Danube fell to exceptionally low levels during the summer heatwave. The river’s water level dropped so dramatically that Paks was unable to draw enough cooling water for normal operation. Unit 3 was shut down on 29 July, while from 2 August only the two turbines of Unit 2 were operating at full capacity.
The government subsequently ordered the construction of a bottom sill in the Danube near the power plant, designed to raise and stabilise the water level at the cooling-water intake. Two barges were also temporarily sunk in the riverbed, while additional water was released through the Ráckeve lock system.
The emergency works have significantly improved conditions at Paks. The bottom sill currently has an estimated lifting capacity of around 20 centimetres, while more than 6,200 tonnes of rock have already been incorporated into the structure. Around 231 metres of the construction has been completed along the left bank.
Danube level has risen significantly
Magyar said the Danube at Paks was around -100 centimetres on Saturday, compared with approximately -140 centimetres earlier in the crisis. Forecasts suggest that the level could rise to around -74 centimetres by Thursday before beginning to fall again if no significant rainfall arrives. The forecast does not include the additional effect of the bottom sill.
The government therefore intends to continue construction despite the improving water level, in order to provide greater protection against another decline.
Earlier this month, the exceptionally low river level raised fears that Paks could face a complete shutdown, potentially creating a serious challenge for Hungary’s electricity supply. The emergency measures ultimately meant that a total shutdown could be avoided.
Full capacity now within sight
Magyar said the aim is for the Paks Nuclear Power Plant to return to its full 2,000 MW capacity by Wednesday. The gradual restart represents a dramatic turnaround from the situation earlier this month, when Hungary’s largest nuclear power plant was operating at only a fraction of its normal capacity because of the Danube’s record-low water level.
