Danube Forces Cernavodă Offline

Romania’s nuclear shutdown did not begin in a control room. It began on the river.

On 13 August, Cernavodă Unit 2, the country’s last operating nuclear reactor, began a controlled shutdown after the Danube fell below the plant’s minimum cooling threshold. Unit 1 had stopped two weeks earlier for the same reason (Agerpres, Argus). Between them, the two reactors supplied about 1.4 GW of steady power, running through the night, through wind lulls, and through the hours when solar disappears.

Bucharest says imports, coal and wind can fill the hole. The difficulty is that Romania’s main back-up is electricity bought from neighbours dealing with the same drought.

Why a river shuts a reactor

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

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

The evening gap

On paper, Romania has options. In the hours that matter, they look much thinner.

Imports are the biggest lever. Romania has 3.2–4.0 GW of cross-border wire capacity, meaning that volume of electricity could physically flow into the country. But interconnectors are only pipes. Someone at the other end has to be generating power and willing to sell it (Curs de Guvernare).

The domestic substitutes are smaller. A coal unit at Rovinari can restart with 330 MW. Drought-limited hydropower can provide about 300 MW. Wind averages around 525 MW, but can fall to 100 MW (Digi24). None of that replaces nuclear power that runs steadily around the clock.

The real pressure arrives between 19:00 and 23:00. Solar generation is gone, wind cannot be ordered up, and households are still running air conditioning and lights. Even before Unit 2 stopped, Adevărul reported that Romania was already importing about 2,150 MW at evening peaks, while total consumption was running at around 8,000 MW (Adevărul).

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

Price has not disappeared from the story. Once cheap nuclear power drops out, Romania has to replace it with coal and imports priced by a tight regional market. Those costs land first in wholesale prices and later in consumer bills. Nuclearelectrica has told customers it may invoke force majeure, the legal clause that releases a company from delivery obligations in extraordinary circumstances (ZF).

The neighbours Romania is counting on

The two countries that matter most are Hungary and Bulgaria.

Hungary is not Romania’s rescue route. It is a rival buyer. Paks, Hungary’s only nuclear plant, lost about 1,770 MW of its normal 2,000 MW output because of the same low Danube (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 relief valve. Its exports reached 2,180 MW on 7 August, with 1,355 MW going to Romania (economic.bg). But Bulgarian output has its own rhythm. Solar power pushes exports up around midday. Evening supply depends 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 biggest cushion narrows with it.

Romania has notified the European Commission and asked for a regional adequacy assessment, the EU check on 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 is less useful to Romania at 21:00, when two drought-hit countries may each be trying to pull more than 2,000 MW from the same neighbourhood. Whether that ends in industrial curtailment depends on which Bulgarian plants are running in that hour, and how long Kozloduy’s own Danube margin lasts. Bucharest controls neither.