The pressure eased upstream and intensified downstream
The Danube has produced two different nuclear-power outcomes in the same fortnight.
At Hungary's Paks nuclear plant, record-low water had cut output to just over 10% of its 2,000 MW capacity. Only one of eight turbines remained in operation. The plant came close to the first complete shutdown in its 44-year history, but it never completed that shutdown.
Rainfall in the upper catchment then raised the river at Paks by 19 centimetres from the previous week's low. Hungary began restarting a second turbine on 10 August. By 13 August, Reuters reported that the plant was operating at about 25% of capacity — meaningful relief for a facility that normally supplies around half of Hungary's electricity, but still far short of normal output.
Romania received no equivalent relief.
Farther downstream at Cernavodă, one of the plant's two 706 MW reactors had already been shut in late July. Authorities detonated a rock obstruction, dredged the riverbed and sank four rock-filled barges to redirect more water towards the cooling-water route. The works temporarily raised the water level around the operating reactor by about 4 centimetres and extended its operating time.
They did not reverse the river's decline. On 13 August, operator Nuclearelectrica began disconnecting Unit 2, leaving both reactors offline. When fully operating, the plant supplies roughly one-fifth of Romania's electricity.
This is not evidence that one fixed volume of water simply travelled from Hungary to Romania and transferred the problem with it. River response, local channel conditions and cooling-intake thresholds differ by site. It is evidence of something more important: two national power systems depended on the same drought-stressed river, and local relief at one plant did not amount to recovery across the basin.
The verified numbers
- 10 cm — the Danube stage reported at Budapest in early August, below the previous local record of 33 cm set in 2018.
- −134 cm — the record low reported on the local Paks gauge.
- +19 cm — the subsequent rise that allowed another Paks turbine to restart.
- Just over 10% → about 25% — Paks output at the crisis low and on 13 August respectively.
- 2 × 706 MW — Cernavodă's two reactors, both now offline.
- About 4 cm — the temporary lift around Cernavodă achieved by emergency water-diversion works.
- About 1,370 m³/s — the record-low flow reported at Romania's Danube entry point on 11 August, against a usual August average of about 3,900 m³/s.
- 330 MW — the capacity of Romania's Rovinari 4 lignite unit, brought out of reserve as part of the replacement plan.
Gauge readings such as 10 cm at Budapest and −134 cm at Paks are local stage references. They are not literal measurements of the river's total depth and should not be compared directly between sites.
Freight is the same constraint in a different form
Power stations need enough river water at their cooling intakes. Freight vessels need enough water beneath their hulls to carry an economic load. The shared input is the river; the operating thresholds are different.
Austria's transport ministry said on 4 August that freight shipping on its section of the Danube had largely come to a halt, even though no official navigation ban was in force. Available navigable depth had fallen to about 2.0 metres in the Wachau and 1.8 metres east of Vienna. Loads had to be cut so sharply that rail or road could become more economical.
On the Lower Danube, contemporary reporting supports the same mechanism without supplying a defensible universal tonnage figure: vessels were carrying lighter loads, while grain movements towards Constanța faced fewer barge rotations, longer waits and freight rates above seasonal norms.
One number from the earlier draft does not survive checking. The claim that barges designed for roughly 2,000 tonnes were carrying only 300–500 tonnes was drawn from Rhine reporting around Kaub and cannot be transferred to the Danube. It has been removed.
The Rhine nevertheless matters as a separate, simultaneous constraint. On 12 August, the navigation reading at Kaub fell to 12 cm, below the previous 25 cm record from 2018. The actual channel is roughly a metre deeper than that reference reading, but most vessels could no longer sail through the chokepoint. That restricted an important alternative corridor just as Danube freight capacity was also under pressure.
What the shutdown does — and does not — mean
Cernavodă's shutdown was controlled. The reactors were not damaged, and Nuclearelectrica said nuclear-safety margins remained the priority. Paks's partial restart likewise shows that the constraint can ease when local water conditions improve.
Neither country had reported a blackout caused by the nuclear reductions as of 13 August. Hungary used imports and temporary demand-saving measures during the worst of the Paks restriction. Romania said it would cover the loss through imports, wind generation, available hydropower and the 330 MW Rovinari 4 reserve lignite unit.
That is the system working — but at a cost. Replacement generation, emergency river engineering, additional imports and forced changes to freight patterns are the economic expression of the same physical constraint.
The Budapest comparison also needs care. Falling below the 2018 local record shows that this episode was more extreme at that gauge. Two record points alone do not establish a statistical trend. Longer hydrological series are required for that claim.
What we are watching
Cernavodă's restart conditions. Nuclearelectrica says the timing will depend on Danube forecasts and the restoration of adequate operating margins.
Whether Paks can move beyond 25% output. The 19-centimetre rise produced partial relief, not a return to normal operation. Hungary was still preparing longer-term river works on 13 August.
Danube freight capacity. Reduced loads and longer turnaround times matter most when several cargo streams compete for limited rail, road and river capacity.
The Rhine at Kaub. A second major European waterway at a record low reduces the system's room for substitution.
The lesson is not that the Danube "chose" one country over another. It is that a basin-wide drought can ease at one infrastructure node while worsening at another — and that energy and freight systems can become correlated because they depend on the same physical input.
EuroOilWatch — independent monitoring of European oil supply, reserves, infrastructure, prices and energy resilience. Confirmed facts are stated as confirmed; claims that could not be verified have been removed.
Sources
- Reuters, 13 August — Danube climate risk at Paks and Cernavodă
- Reuters, 13 August — Cernavodă Unit 2 shutdown
- Reuters, 10 August — Paks turbine restart
- Euronews, 10 August — Paks gauge and phased restart
- Associated Press, 3 August — Budapest record and regional energy pressure
- Reuters, 10 August — emergency water diversion at Cernavodă
- Austrian transport ministry, 4 August — Danube navigation conditions
- Bloomberg via gCaptain, 10 August — Lower Danube freight and Constanța
- Reuters, 12 August — record-low Rhine conditions at Kaub
Excluded from this version
The following claims from the earlier draft were not used: Djerdap 1 at 20% capacity; Verbund's alleged €370 million hydro-earnings loss; the Kpler quotation; EU gas storage around 55%; gas prices described as near post-2022 highs; Rotterdam–Rhine cargo allegedly 10% below normal; the 100–200 billion forint import estimate; a complete Paks shutdown; a measured 70–90 MWh daily rail saving; 300–500-tonne Danube barge loads; unusable Romanian river ports; and a complete halt to shipping on the Bavarian Danube.