Danube Drought Cuts Hungary’s Power

The Danube is usually part of the background machinery of central Europe: a trade route, a border, a source of cooling water, a thing governments assume will be there. Last week it became the weak point in the power system.

Hungary lost most of the output from its only nuclear station. Romania came within centimetres of losing its last working reactor. Across the region, the immediate political choice was blunt enough: ask factories to stop first, so households can keep the lights on.

How a river switches off a reactor

A nuclear plant does not just need uranium and turbines. It also needs a reliable way to dump waste heat. River water provides the cold side of the system, carrying heat away after nuclear energy has been turned into electricity.

When the river falls too far, pumps struggle to draw enough water. When the water is warm or slow-moving, the plant can breach legal temperature limits when it sends heated water back downstream. In a drought, both constraints arrive together.

At Paks, Hungary's only nuclear station and normally a 2,000 MW source, the shutdown happened in steps. State energy company MVM began cutting output when the Danube fell below -106 cm at the plant gauge (MVM Paks). By 2 August, only one of eight turbogenerators was still running, producing about 240 MW (Portfolio, Telex). AP reported a full shutdown (AP). On either account, Hungary lost almost all of its nuclear baseload, the steady power that runs day and night, in a matter of days.

Romania's margin was even thinner. At Cernavoda, Unit 1 was already offline. Unit 2 stayed on the grid, but the supply basin was at 2.02 metres, only 12 centimetres above the point where pumps stop working (Ziua de Constanta). A side channel near the Bala canal was pulling about 85% of the Danube's flow away from the plant's cooling intake.

The response was not elegant, but it was practical. The military used controlled explosions to push water back towards the plant (Radio Constanta). That bought an estimated four to five more days (Agerpres).

Solar covers midday, not the evening

Romania's daytime power picture still looked grand on paper. On 3 August, it generated 6,009 MW against 5,212 MW of demand, with solar covering more than 45% (Agerpres). The difficulty comes when the sun goes down and air conditioning keeps running.

By the evening of 31 July, Romania was producing 5,239 MW, consuming 7,177 MW, and importing 1,938 MW to close the gap (Radio Timisoara). That is when lost nuclear power matters most: not at noon, when panels are working, but in the evening peak.

Europe's power markets are tied together by interconnectors, the high-voltage cables that move electricity from cheaper zones to more expensive ones. They are useful until too many countries need the same replacement power at the same hour. With Hungary and Romania both looking for evening supply, the cables became the bottleneck.

Slovenia's grid operator ELES limited cross-border capacity on the Austrian border for 3 August (ELES). Wholesale prices rose above €150/MWh, with evening peaks close to €270/MWh, well above normal summer levels (Serbia Energy).

Factories absorb the hit so households don't

Hungary and Romania made the same political calculation: industry would take the first hit. Hungary's emergency decree gave grid operator MAVIR the power to cut or disconnect large industrial and commercial users, with households protected until the end of the line (HVG).

Prime Minister Péter Magyar said large consumers had committed more than 630 MW of voluntary reductions by 3 August (Telex). That helps. It does not replace Paks. The station normally provides 2,000 MW, so voluntary restraint can only cover part of the hole.

In Romania, carmakers Dacia and Ford voluntarily halted production until 19 August, freeing about 200 MW (Agerpres). Nuclearelectrica, which runs Cernavoda, warned customers it may not be able to meet delivery contracts (ZF).

Household bills are protected for now by fixed contracts. That protection is real, but it is being paid for elsewhere in the system: by factories stopping lines, by imports moving through constrained cables, and by grid operators managing scarcity hour by hour.

Every megawatt of curtailed production means delayed cars, disrupted supply chains and losses that appear later. The system held through the weekend. If the rivers stay low, governments will have to decide whether voluntary savings become mandatory rationing, and how long they can keep buying replacement power at €270/MWh while shielding households at industry's expense.