Danube Low Slows Paks Reactors

Hungary's Paks nuclear plant supplies almost half the country's electricity (World Nuclear). By 29 July, one of its four reactors had been taken offline for the first time because the Danube had fallen too low (Intellinews). Prime Minister Péter Magyar warned that the whole plant could be shut by 4 or 5 August, possibly for weeks (Telex). Romania has already stopped one reactor at Cernavoda for the same reason (Agerpres).

For Malta, used to treating energy security as a question of interconnectors, LNG and small-island resilience, the lesson is familiar in a different form. Cheap, steady power often depends on infrastructure that looks boring until it fails. In Central Europe this week, that infrastructure is the Danube: too shallow and too warm at the height of summer demand.

How a river shuts a power plant

Nuclear plants do not use river water as fuel. They use it for cooling. Once steam has turned the turbines, the remaining heat has to go somewhere, and at Paks it is discharged into the Danube. Hungarian rules say the river may not exceed 30°C within 500 metres downstream of the discharge point (MVM Paks, UNECE). When the river is too low or too warm, operators reduce output because less electricity also means less waste heat.

The squeeze came quickly. On 27 July, MVM, Hungary's state energy group, began cutting generation after the Paks gauge hit a record -106 cm (MVM). Two days later, the first reactor was offline. Romania's Cernavoda ran into the same physics: Danube flow at Bazias fell to about 1,630 m³/s, putting pressure on cooling pumps (HotNews).

As we reported when the shutdowns began (To Brief), this is not a nuclear safety scare. Reactors are stopped well before damage thresholds are reached. The real problem is the loss of baseload: the steady, round-the-clock electricity that keeps the system balanced when demand peaks.

The evening trap

Solar has softened the daytime hit. Hungarian solar parks generated 1,504.8 GWh in June, more than Paks' 1,312.1 GWh (24.hu). But the grid does not only need power at noon. After 18:00, solar output falls while air-conditioning demand remains high.

Magyar said Hungary's evening load is around 6,000 MW. Losing the full 2,000 MW Paks plant would remove roughly a third of that capacity (Daily News Hungary). That is the point at which a technical cooling problem becomes a system-wide price problem.

Replacement power is dearer. Hungary was already importing more than 1,000 MW from neighbouring countries on recent evenings. Day-ahead electricity prices, the price paid for power delivered the following day, rose to 122.08 EUR/MWh in Hungary and 132.87 EUR/MWh in Romania after the shutdowns (Serbia Energy). Romanian Prime Minister Ilie Bolojan identified 20:00 to 23:00 as the danger period and urged citizens to reduce evening consumption (Agerpres).

Who pays when the river drops

Hungary is preparing to order large industrial users, including MOL and Samsung SDI, to reduce electricity use while protecting households and hospitals (Portfolio). That choice is politically understandable. It also means the cost does not disappear. It is moved onto factories, state utilities or taxpayers.

Bulgaria is the short-term winner. Romanian reporting found Bulgarian generators providing vital evening imports, with Profit.ro noting that "household power in Romania depends paradoxically on Sofia" (Profit.ro). But the advantage is thin. The Danube near Bulgaria's Ruse was already at -85 cm, below historical minimums (Club Z). If the drought worsens, Bulgaria's Kozloduy nuclear plant faces the same cooling limits.

Austria is adding to the pressure. Vienna's Freudenau hydropower plant on the Danube produced about 29% less than its 30-year average (MeinBezirk). When Hungary needs imported electricity to replace nuclear output, and Austria has less hydropower to sell, the pool of cheap evening power gets smaller.

The European Commission said on 31 July that it was monitoring the situation and was ready to convene the EU Electricity Coordination Group (Euronews). The drought has made the dependency visible: Central Europe's cheap evening electricity still rests, to a surprising degree, on rivers staying deep enough and cool enough to keep the plants running.