Nuclearelectrica disconnected Unit 1 at the Cernavoda nuclear power plant after exceptionally low Danube levels reduced the operating margin for cooling and nuclear safety. The unit entered a controlled shutdown on 28 July. The action followed revised hydrological forecasts showing the river approaching critical operational thresholds.
The shutdown removed one of Romania’s largest generating units from the system during a period of rising summer electricity demand. Cernavoda operates two CANDU reactors and provides Romania with low-carbon baseload generation. With one unit offline, the domestic supply balance is affected and electricity available for export changes for markets including Hungary, Serbia, Bulgaria, Moldova and Ukraine.
Nuclear output decline and shift from net exports to imports
Romanian nuclear generation had already dropped from an average of 1,165 MW to 880 MW during the day when the shutdown began. Because the reactor was operating for part of that period, the full-day reduction after disconnection was expected to be substantially larger. The market response followed quickly after Unit 1 was taken out of service.
Romania moved 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. The change in balance coincided with cross-border flows continuing in parallel with the domestic deficit.
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. This indicated that contractual and cross-border market flows do not always adjust immediately to changes in domestic production.
The OPCOM day-ahead price rose by €22.1/MWh to €132.87/MWh, marginally above the Hungarian price. Romania’s price convergence with Hungary reflected a shared nuclear constraint linked to river conditions. Paks Unit 1 was simultaneously derated by approximately 254 MW due to low Danube levels.
Preventive shutdown status and potential restrictions for Unit 2
Nuclearelectrica said the shutdown was preventive and aligned with established operating procedures. The company reported that the reactor remained in a safe condition, with no danger to personnel, the public or the environment. It continued monitoring river conditions and warned that additional measures could be needed if hydrology deteriorates.
No immediate shutdown was announced for Unit 2, although it could face restrictions if Danube levels fall further. A scenario involving loss of both Cernavoda reactors would create a significantly larger regional shock across Romania, Hungary, Serbia and Bulgaria simultaneously.
The situation highlights that nuclear availability can be influenced by hydrological risk when river conditions affect cooling margins. Cernavoda’s operational status therefore depends on recovery in Danube flows, which in turn affects Romanian electricity prices and cross-border trading positions.
