Danube drought strips Hungary of 2 GW

Hungary's sole nuclear power station went fully offline on 2 August after the Danube fell so low that cooling pumps could no longer reach the river surface. The Paks plant supplies close to 2 GW of baseload power, roughly half the country's electricity (MVM, World Nuclear Association). Downstream in Romania, the same drought had already forced one of two reactors offline at the Cernavodă nuclear plant, with the second running on an estimated four to five days of margin. Two countries discovered, within the same week, that power they had counted on as permanently available depends on rainfall.

One river, two shutdowns

The Paks shutdown took six days. When the Danube gauge dropped to -106 cm on 27 July, operator MVM began reducing output (MVM). By 30 July it warned that all four units would stop within 24 to 72 hours if water kept falling (VG). Nothing was wrong with the reactors. The problem was simpler: pump intakes sat above the dropping river surface, and without water flow a nuclear plant cannot shed the heat it produces. MVM set -134 cm as the final trigger and reached it on 2 August (Index, AP).

Romania's exposure ran in parallel. Apele Române, the national water authority, measured Danube flow at 1,650 m³/s at Romania's border on 28 July, roughly one-third of the seasonal average and close to the 1985 historic low (Apele Române). Nuclearelectrica shut Cernavodă's Unit 1 preventively, keeping Unit 2 online only after confirming its intake parameters still held (BVB/Nuclearelectrica, Energynomics). The government allocated 7 million lei for temporary barges to redirect river flow at a key bifurcation point upstream of the plant's intake (Agerpres). Even keeping a single reactor running now requires improvised civil engineering.

Who absorbs the shock

When supply shrinks this suddenly, grids protect households and hospitals first. That means large industrial users become the adjustable demand, the load that gets switched off so the lights stay on elsewhere.

Hungary's government formalised this with a decree giving MAVIR (the national grid operator) authority to order any consumer drawing more than 0.5 MW to cut load, with penalties at 200% of the spot price (444.hu, HVG). The price signal backed it up: Hungarian week-ahead power jumped to around €250–263/MWh, up from €217.90 a day earlier (Argus).

Romania saw an even sharper move. Peak-hour clearing prices on the day-ahead market swung from 63.3 lei/MWh at midday to 1,604 lei/MWh by evening, as demand hit shrunken supply (Agerpres). Nuclearelectrica warned clients of possible force majeure on contractual deliveries (ZF). The short-term winners are neighbouring exporters selling into that evening scarcity. Bulgaria was already supplying roughly 1,700 MW to Romania during peak hours, against Romanian evening consumption above 7,000 MW (Profit.ro). Scarcity rents crossed the border with the electrons.

A cooling-design problem, not a nuclear one

This was not a reactor failure. Other plants on the same continent, in the same heatwave, kept running. Slovenia's Krško switched to cooling towers, which shed heat into the air instead of the river (Delo). Czech plants at Dukovany and Temelín use similar designs and stayed less exposed (Seznam Zprávy). France's national audit court found that heat and water constraints already cut at least 1 TWh of French nuclear output in each of 2018, 2019 and 2020 (Cour des comptes). The European Commission said it was monitoring the situation and could call an emergency electricity coordination meeting (Euronews).

Europe cannot count capacity as firm if summer water levels can switch it off. Grid planners now need to price the upgrade: cooling towers, replacement capacity, or higher scarcity costs every drought year. Paks just showed the bill for not doing it sooner.