Controlled shutdown linked to Danube hydrology
Nuclearelectrica disconnected unit 1 of the Cernavoda nuclear power plant after exceptionally low Danube levels reduced the operating margin for cooling and nuclear safety. The operator said the unit entered a controlled shutdown on 28 July, following revised hydrological forecasts that placed the river near critical operational thresholds. The action removed one of Romania’s largest generating units from the system during a period of rising summer electricity demand.
Cernavoda has two operating CANDU reactors and is described as a foundation of Romania’s low-carbon baseload supply. With one unit offline, the domestic generation mix is affected and electricity available for export changes. Flows to Hungary, Serbia, Bulgaria, Moldova and Ukraine are therefore impacted by the reduced output.
Nuclear output drop and immediate market rebalancing
Romanian nuclear generation had already declined from an average 1,165 MW to 880 MW during the day when the shutdown began. Because the reactor was operating for part of that period, the expected full-day reduction after disconnection was described as substantially larger. The change in output coincided with a shift in system balance as consumption increased into summer.
The market response was immediate, with Romania moving from an average net export position of 350 MW to projected net imports of approximately 450 MW. Domestic generation fell to roughly 5,036 MW, while consumption was forecast at 5,486 MW. This gap required additional balancing support from neighbouring markets.
Bulgaria supplies balancing power as cross-border flows continue
Bulgaria became the principal balancing source, delivering approximately 1,266 MW to Romania. At the same time, Romania continued sending electricity toward Hungary and Serbia. The continued cross-border deliveries indicated that contractual arrangements and market flows do not always adjust immediately to a domestic production deficit.
The day-ahead price signal also moved higher on OPCOM, increasing by €22.1/MWh to €132.87/MWh. The level was marginally above the Hungarian price. Romania’s convergence with Hungary was linked to a shared constraint affecting nuclear output.
Nuclear constraints extend beyond Cernavoda amid low Danube levels
The shared constraint cited in market pricing involved derating at Hungary’s Paks unit 1, which was simultaneously reduced by approximately 254 MW due to low Danube levels. Nuclearelectrica described the Cernavoda unit 1 shutdown as preventive and consistent with established operating procedures. The company said the reactor remained in a safe condition, with no reported danger to personnel, the public or the environment.
Nuclearelectrica continued monitoring river conditions and warned that further measures could be required if hydrology deteriorated. Unit 2 could also face restrictions if Danube levels fall further, although no immediate shutdown was announced. A loss of both reactors would create a larger regional shock that could tighten power systems across Romania, Hungary, Serbia and Bulgaria simultaneously.
The operator’s statements framed Cernavoda availability as dependent on recovery in Danube flows, making river conditions a direct driver of Romanian electricity prices and cross-border trading positions.
