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The river did not run dry. The cooling-water intakes sit at a fixed height — once the Danube drops below them, the pumps cannot lift water. On top of that, the law caps the temperature of the water returned: 500 m downstream of the outflow channel the Danube may not exceed 30 °C. Together these two limits forced the plant back.
The plant's design basis assumed the 100-year minimum was more than 1 m higher than the 2018 record. The current level has gone past that assumption.
The Danube's temperature is measured in several places. Paks, still upstream of the warm-water outfall, and at Dombori, 25 kilometres below the Paks gauge — the difference between them shows how much warmer the water flows on after the plant has used it for cooling. The relationship can be drawn at all because output this year covered the whole range: the record-low Danube pushed it from 2000 MW nominal down to 230 MW — three units stopped, the fourth ran at half steam — then it climbed back over three weeks. Per gigawatt the water warms by roughly — °C.
Why does so much heat end up in the river? Because heat cannot be turned into electricity without loss: a steam cycle needs a cold side for the unused heat to go — at Paks that is the Danube. The units are roughly 33%-efficient, so only a third of the heat made in the reactor becomes electricity; the other two thirds flow away with the cooling water. That is why the plant puts roughly twice as much energy into the river as heat: at 2000 MW of electricity, close to 4 GW.
The technical term "Paks thermal plume" does not mean this average excess but the sharply bounded warm band within the cross-section: it runs along the right bank, near the outfall it can be as much as 8–10 °C hotter than the untouched part of the section, and it stays distinguishable all the way to Mohács.
Drag the curve, or press play: the plume appears and fades with output.
The plant's cooling water is drawn from the Danube by the main cooling-water pump intakes — they sit at a fixed height, the river's level does not. That is exactly what caused the summer shutdown: the water dropped so low that the pumps had nothing left to draw.
Between Paks and Dunaszentbenedek, downstream of the plant — at river-kilometre 1526 of the Danube, below the mouth of the cold-water canal — a rock sill is being built on the riverbed. The first phase was completed by 29 August: 43 thousand cubic metres of rock, across the full width of the riverbed. The rest of the planned 145 thousand goes into reinforcing the bed below the sill, because the water, accelerated in the narrows, scoured out 8–13 metres. The sill does not block the river: the Danube keeps flowing, but the rock dams back the reach above it — the one the plant draws its water from.
This is how much higher the Danube stands at the Paks gauge than the Dombori gauge, below the sill, would warrant — daily mean. The solid line is the measured stage, the dashed one the computed stage without the sill.
still being built · phase 2The “schedule” is MAVIR’s own forecast, so the gap includes forecast error — on its own it does not prove deliberate saving, but it shows the direction well.
The layers add up to consumption: whatever is not generated at home is covered by imports.