Danube takes Cernavodă offline

Romania's last working nuclear reactor started shutting down on 13 August after the Danube fell below the level needed to cool the plant. Cernavodă Unit 2 is being taken offline two weeks after Unit 1 stopped for the same reason (Agerpres, Argus). Between them, the two units supplied about 1.4 GW of steady electricity, the kind that runs through the night and does not depend on wind, sun or rain.

Bucharest says the shortfall can be covered by imports, coal and wind. The weakness in that plan is familiar to any small EU state that depends on its neighbours in a tight market: interconnectors help only if someone across the border has spare electricity to sell. Romania is looking for help from countries under the same drought pressure.

Why a river shuts a reactor

Cernavodă needs a continuous flow of Danube water to cool its reactors. Romania's national water authority, ANAR, said the gauge at Cernavodă had fallen to -230 cm, a level officials described as unprecedented (Digi24, Mediafax).

Further upstream at Baziaș, the river was flowing at roughly 1,400 m³/s, about a third of the normal August average (Brussels Signal, Agerpres). Emergency works using rock barges bought days, not weeks.

The evening gap

Romania's replacement options look workable on paper. They are much less convincing during the hours when the system is under real pressure.

Imports are the main lever. Romania has 3.2–4.0 GW of cross-border cable capacity, which means that volume of electricity could physically enter the country. But cable capacity is not electricity. A neighbouring country still has to be producing the power and willing to sell it (Curs de Guvernare).

The other options are thinner. Bucharest can restart 330 MW of coal capacity at Rovinari, draw about 300 MW from drought-limited hydropower, and rely on wind that averages around 525 MW but can fall to 100 MW (Digi24). None of that replaces nuclear output that runs steadily all day and all night.

The difficult window is between 19:00 and 23:00. Solar power drops out, wind is uncertain, and households keep air conditioning and lights on. Even before Unit 2 stopped, Adevărul reported that Romania was already importing about 2,150 MW at evening peaks, with total consumption around 8,000 MW (Adevărul).

Energy analyst Dumitru Chisăliță warned that, on a bad evening, the issue may no longer be price but "who gets disconnected" (Mediafax). Officials say households are not at risk of curtailment. The emergency plan puts large industrial users first in line for forced reductions (EMI Bulgaria).

Price still matters. When low-cost nuclear disappears, Romania replaces it with coal and imports bought at market prices. Those costs hit wholesale markets first and household bills later. Nuclearelectrica has told customers it may invoke force majeure, the legal clause that releases a company from delivery obligations when extraordinary circumstances make performance impossible (ZF).

The neighbours Romania is counting on

The two neighbours that matter most are Hungary and Bulgaria.

Hungary is not a spare supplier. It is another buyer. Paks, Hungary's only nuclear plant, lost roughly 1,770 MW of its normal 2,000 MW output because of the same low Danube conditions (MVM Paks, kormany.hu). Budapest has authorised grid operator MAVIR to disconnect industrial users above 0.5 MW, with penalties set at 200% of the spot price (HVG).

Bulgaria is the region's main pressure valve. Its exports reached 2,180 MW on 7 August, with 1,355 MW going to Romania (economic.bg). But Bulgarian generation also changes by the hour. Solar power pushes exports up at midday. Evening supply depends more heavily on Kozloduy nuclear and Maritsa coal.

Bulgaria's energy minister said Kozloduy had roughly a week and a half of Danube margin left (DBR). If that margin narrows, the region's main cushion narrows with it.

Romania has notified the European Commission and asked for a regional adequacy assessment, which is the EU's check of whether enough generation and cross-border capacity exists to meet demand under stress (HotNews). The Commission said Europe's electricity system "remains stable despite extreme weather" (European Commission).

That may be true for Europe as a whole. It does not settle Romania's problem at 21:00. The risk is concentrated in the evening import window, when two drought-hit countries may both be trying to pull more than 2,000 MW from the same regional pool. Whether that leads to industrial curtailment depends on which Bulgarian plants are running at that hour, and how long Kozloduy's own Danube margin lasts. Bucharest controls neither.