Romanian nuclear producer Nuclearelectrica disconnected unit 1 of the Cernavoda nuclear power plant after exceptionally low Danube levels reduced the operating margin available for cooling and nuclear safety.
The unit entered a controlled shutdown on 28 July, following revised hydrological forecasts indicating that the Danube was approaching critical operational thresholds. The decision removed one of Romania’s largest generating units from the system during a period of rising summer consumption.
Cernavoda has two operating CANDU reactors and is the foundation of Romania’s low-carbon baseload supply. The loss of one unit therefore has a material effect on the domestic balance and the electricity available for export to Hungary, Serbia, Bulgaria, Moldova and Ukraine.
Romanian nuclear generation had already fallen from an average 1,165 MW to 880 MW during the day on which the shutdown began. Because the reactor operated for part of that period, the full-day reduction following disconnection was expected to be substantially larger.
The market response was immediate. Romania moved from an average net export position of 350 MW to projected net imports of approximately 450 MW. Domestic generation declined to roughly 5,036 MW, while consumption was forecast at 5,486 MW.
Bulgaria became the principal balancing source, delivering approximately 1,266 MW to Romania. At the same time, Romania continued to send electricity toward Hungary and Serbia, demonstrating that contractual and cross-border market flows do not always adjust immediately to the domestic production deficit.
The OPCOM day-ahead price increased by €22.1/MWh to €132.87/MWh, marginally above the Hungarian price. Romania’s convergence with Hungary reflected the shared nuclear constraint: Paks unit 1 was simultaneously derated by approximately 254 MW because of low Danube levels.
Nuclearelectrica described the shutdown as preventive and consistent with established operating procedures. The reactor remained in a safe condition, with no reported danger to personnel, the public or the environment. The company continued to monitor river conditions and warned that further measures could be required if hydrology deteriorated.
Unit 2 could also face restrictions if the Danube falls further, although no immediate shutdown was announced. The loss of both reactors would create a significantly larger regional shock, potentially tightening Romania, Hungary, Serbia and Bulgaria simultaneously.
The shutdown demonstrates that nuclear generation, while low-carbon and generally stable, is not insulated from hydrological risk. Cernavoda’s availability now depends on the recovery of Danube flows, making river conditions a direct driver of Romanian electricity prices and cross-border trading positions.
