Bulgaria’s Kozloduy nuclear power plant has increased output at Unit 5 to around 950 MW following a recovery in Danube water levels. The change reverses part of a drought-driven curtailment that had lowered the reactor to about 850 MW last week. Unit 6 remains close to normal operation at around 971 MW.
The restoration is expected to add approximately 100 MW of firm generation to the Bulgarian system. It also eases one source of pressure that tightened Central and Southeast European electricity markets during August.
Danube low-water curtailment and cooling-water constraints
Kozloduy reduced Unit 5 output after exceptionally low Danube levels cut cooling-water availability. Before the restrictions, the reactor had been operating at more than 1,000 MW. Bulgarian authorities also announced hydrotechnical works, including a 250-300 metre river structure, intended to improve water access if conditions deteriorate again.
The partial rebound in output comes as nuclear availability has become an important short-term trading factor across the region. Hungary’s Paks plant also cut output sharply during August due to low Danube levels before recovering.
Nuclear disruptions, regional prices and market conditions
Romania’s Cernavodă plant faced more severe disruption, leaving Romania without nuclear output during several recent trading sessions. The combination of outages and reductions contributed to high regional prices. Central SEE day-ahead markets repeatedly traded above €170-180/MWh, while evening hours climbed above €250/MWh as solar output declined.
Kozloduy’s recovery is expected to reduce some Bulgarian import requirements and add low-marginal-cost generation to the regional system. However, it does not remove the underlying hydrological risk associated with Danube water levels.
Cooling-water exposure and implications for system planning
The August events showed that nuclear generation can be affected by extreme low-water periods despite its typical weather resilience for firm power. This matters for system planning across Bulgaria, Romania and Hungary, where nuclear generation is relied on for stable, low-carbon electricity. If cooling availability becomes increasingly constrained by climate conditions, operators may need greater investment in water-management and cooling infrastructure.
The same Danube conditions also influence hydro generation and river transport. Low water can reduce electricity supply while disrupting fuel logistics, turning the river into a more significant variable for regional energy markets. For Bulgaria, Kozloduy remains central to domestic supply and exports.
Restoring Unit 5 toward full output should improve Bulgaria’s position as autumn demand begins to increase. The plant’s experience during August is expected to affect future investment decisions related to nuclear asset management under changing hydrological conditions.
