Low Danube puts 20% of Romania's power at risk

At Cernavoda, on Romania's lower Danube, the river carries roughly 1,600 cubic metres per second — less than 40% of its normal July flow (Digi24, Bloomberg). Nuclear reactors are heat machines. They produce electricity, but leftover heat must be absorbed by river water pumped through cooling systems. When the river drops too low, the pumps can't work safely. Reactors shut down. Reliable low-carbon power — electricity that runs regardless of wind or sun — disappears from the grid.

Romania declared a national energy alert for August on 31 July. This is a technical energy-system measure, not a constitutional emergency (Mediafax). Interim prime minister Ilie Bolojan said drought could put roughly 20% of national electricity output at risk (RRI, Agerpres). The weakest hours fall between 20:00 and 23:00, when solar fades and households are still drawing power.

The same river problem is spreading. Hungary's Paks plant has halved its output. Bulgaria's Kozloduy is under special monitoring. As we reported last week (To Brief), the heatwave had already shut Cernavoda's Unit 1. The crisis has since deepened.

Sinking barges to save a reactor

Cernavoda's Unit 1 was disconnected on 28 July. The Energy Ministry warned that forcing cooling pumps at such low flows risked damage requiring repairs lasting up to a year (Agerpres). Unit 2 survived an overnight review on 30 July and stayed connected under strict monitoring (Curs de Guvernare, Romania Insider).

To keep that last reactor running, Bolojan allocated 7 million lei from the government reserve for emergency works at a river junction upstream, redirecting flow toward Cernavoda's intake basin. Officials discussed sinking metal barges to steer the main current toward the plant (Adevarul, Digi24). Romania is physically re-engineering a stretch of river for one nuclear reactor.

Same river, same squeeze

Hungary is worse off. The Danube gauge at Paks hit -122 cm on 30 July, a record low (kormany.hu). By 31 July, one unit was shut and another at half power, leaving output at roughly half the plant's capacity. Plant operator MVM warned a full shutdown could become unavoidable within days (MVM Paks, HVG).

Bulgaria's Kozloduy, also Danube-cooled, was still running but had activated rules for operating when the river falls too low. Energy Minister Iva Petrova contacted Serbia about managing flows through the Iron Gate dam complex upstream (24 Chasa). Austria's largest hydro producer, Verbund, separately reported drought had cut its output to 68% of plan (Kleine Zeitung). Low water weakens nuclear and hydro at the same time.

Who pays when cheap power disappears

When nuclear drops off, costlier sources replace it. Romania expected peak demand around 7,300 MW against only 4,000–4,300 MW produced domestically, already importing about 1,700 MW by evening, mainly from Bulgaria (Profit.ro, EUAlive). Romania flipped from power exporter to importer.

Gas plants and battery operators gain, selling into scarcity hours. Nuclear operators lose revenue. Suppliers locked into fixed-price household contracts must buy expensive replacements on the wholesale market. Analysts at Hungary's Portfolio estimated that replacing Paks output through imports could widen Hungary's trade gap — what the country pays abroad for energy minus what it earns from exports — by up to 1% of GDP (Portfolio). Bolojan asked Romanian households to run washing machines and boilers after 23:00 (Mediafax).

The risk is not immediate blackouts. Several countries are losing cheap power at once, then looking to neighbours facing the same river problem. Forecasts show flows falling further toward 1,500 m³/s at Cernavoda and -130 cm at Paks by 3 August (RRI, kormany.hu). Emergency barges and load-shifting buy days, not weeks. Summer drought can now knock out reliable low-carbon power across several connected electricity markets at once. Europe's grid planning has not caught up with that reality.