Danube Drought Knocks Out Paks

Hungary's only nuclear power station went fully offline on 2 August after the Danube fell so low that the plant's cooling pumps could no longer reach the river surface. Paks supplies close to 2 GW of baseload electricity, about half the country's power (MVM, World Nuclear Association). Downstream, Romania had already been forced to shut one of the two reactors at Cernavodă, while the second was left with an estimated four to five days of margin.

For Malta, the lesson is familiar enough: infrastructure described as permanent often depends on a weak point nobody prices properly until it fails. In Hungary and Romania, that weak point was not the reactor. It was the river.

One river, two shutdowns

The Paks shutdown unfolded over six days. When the Danube gauge fell 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 the water kept dropping (VG).

There was no fault in the reactors themselves. The mechanics were more basic: the pump intakes were left above the falling river surface. Without enough water flow, a nuclear plant cannot remove the heat it produces. MVM set -134 cm as the final trigger, and the river reached it on 2 August (Index, AP).

Romania was exposed to the same river system. 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 historic low recorded in 1985 (Apele Române). Nuclearelectrica shut Cernavodă's Unit 1 preventively and kept Unit 2 online only after confirming that its intake parameters still held (BVB/Nuclearelectrica, Energynomics).

The Romanian government then allocated 7 million lei for temporary barges to redirect the river flow at a key bifurcation point upstream of the plant's intake (Agerpres). Keeping one reactor running had become a matter of improvised civil engineering.

Who absorbs the shock

When electricity supply drops this quickly, grid operators protect households, hospitals and essential services first. Large industrial users become the adjustable demand: the consumption that can be ordered down so the rest of the system keeps working.

Hungary made that explicit through a decree giving MAVIR, the national grid operator, authority to order any consumer drawing more than 0.5 MW to cut load. Penalties were set at 200% of the spot price (444.hu, HVG). The market moved accordingly: Hungarian week-ahead power rose to about €250–263/MWh, up from €217.90 a day earlier (Argus).

Romania's price shock was sharper. On the day-ahead market, peak-hour clearing prices moved from 63.3 lei/MWh at midday to 1,604 lei/MWh by evening, as demand collided with reduced supply (Agerpres). Nuclearelectrica warned clients of possible force majeure on contracted deliveries (ZF).

The immediate winners were neighbouring exporters able to sell into the shortage. Bulgaria was already supplying roughly 1,700 MW to Romania during peak hours, while Romanian evening consumption stood above 7,000 MW (Profit.ro). The scarcity premium crossed the border with the electricity.

A cooling-design problem, not a nuclear one

This was not a reactor accident. Other European nuclear plants, facing the same heatwave, kept operating because their cooling systems were designed differently. Slovenia's Krško switched to cooling towers, which release heat into the air rather than depending directly on river flow (Delo). Czech plants at Dukovany and Temelín use similar designs and were less exposed (Seznam Zprávy).

France has already seen the same constraint. The national audit court found that heat and water limits 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 convene an emergency electricity coordination meeting (Euronews).

The policy issue is now straightforward. Europe cannot treat power capacity as firm if a summer river level can remove it from the grid. Planners have three costs to compare: cooling towers, replacement capacity, or higher scarcity prices every drought year. Paks has just put a number on the cost of waiting.