Record low Danube idles Hungarian nuclear reactors

Hungary's Paks nuclear plant generates nearly half the country's electricity (World Nuclear). By 29 July, one of its four reactors was offline for the first time ever because the Danube ran too low (Intellinews). Prime Minister Péter Magyar warned the entire plant could go dark by 4 or 5 August, potentially for weeks (Telex). Romania already shut one reactor at Cernavoda for the same reason (Agerpres). The drought gripping the Danube basin is removing cheap, steady generation at the worst possible moment: peak summer demand.

How a river shuts a power plant

Nuclear plants use river water for cooling, not fuel. After steam drives the turbines, leftover heat gets dumped into the river. Hungarian rules cap the Danube's temperature at 30°C within 500 metres downstream of the discharge point (MVM Paks, UNECE). When the river drops too low or runs too warm, operators cut output: less electricity means less waste heat to dump.

The constraint hit fast. On 27 July, MVM (Hungary's state energy group) began reducing generation after the Paks gauge hit a record -106 cm (MVM). Two days later, the first reactor went offline. Romania's Cernavoda faced the same problem: Danube flow at Bazias fell to roughly 1,630 m³/s, threatening cooling pumps (HotNews). As we reported when the shutdowns began (To Brief), this is not a safety crisis. Operators stop reactors well before any damage threshold. The problem is losing baseload — steady, round-the-clock generation — during peak demand.

The evening trap

Solar has cushioned the daytime blow. Hungarian solar parks produced 1,504.8 GWh in June, exceeding Paks' 1,312.1 GWh (24.hu). But after 18:00, solar drops while air-conditioning demand stays high. According to Magyar, Hungary's evening load runs around 6,000 MW; losing the full 2,000 MW Paks plant would cut roughly a third of that (Daily News Hungary).

Every replacement costs more. Hungary was already importing over 1,000 MW from neighbours on recent evenings, and day-ahead electricity prices — what buyers pay for power delivered the next day — jumped 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 20:00–23:00 as the critical window and urged citizens to cut evening use (Agerpres).

Who pays when the river drops

Hungary is preparing to order large industrial users — including MOL and Samsung SDI — to cut electricity use, while shielding households and hospitals (Portfolio). Shielding households does not make the cost vanish. It shifts it onto factories, state utilities or taxpayers.

Bulgaria has become the short-term winner. Romanian reporting found Bulgarian generators supplying crucial evening imports, with Profit.ro noting that "household power in Romania depends paradoxically on Sofia" (Profit.ro). The advantage is fragile. The Danube near Bulgaria's Ruse already stood at -85 cm, below historical minimums (Club Z). If the drought deepens, Bulgaria's Kozloduy nuclear plant faces the same cooling physics.

Austria tightens the squeeze. Vienna's Freudenau hydropower plant on the Danube produced roughly 29% less than its 30-year average (MeinBezirk). When Hungary needs imports to replace nuclear output and Austria has less hydropower to sell, the cheap power available for evening trade shrinks.

The European Commission said on 31 July it was monitoring the situation and stood ready to convene the EU Electricity Coordination Group (Euronews). The drought has made one thing measurable: how much cheap evening power in Central Europe still depends on rivers staying deep and cool.