Bulgaria’s Kozloduy nuclear power plant has raised output from Unit 5 to around 950 MW as Danube water levels recovered, reversing part of a drought-driven curtailment that had reduced the reactor to about 850 MW last week.
Unit 6 remains close to normal operation at around 971 MW.
The restoration returns approximately 100 MW of firm generation to the Bulgarian system and eases one source of pressure that helped tighten Central and Southeast European electricity markets during August.
Kozloduy cut Unit 5 output after exceptionally low Danube levels reduced cooling-water availability.
The reactor had been operating at more than 1,000 MW before the restrictions.
Bulgarian authorities also announced plans for hydrotechnical works, including a 250-300 metre river structure, aimed at improving water access if conditions deteriorate again.
The partial recovery is significant because nuclear availability has become an unusually important short-term trading factor across the region.
Hungary’s Paks plant also cut output sharply during August because of low Danube levels before recovering.
Romania’s Cernavodă plant has faced more severe disruption, leaving Romania without nuclear output during several recent trading sessions.
The combination 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 should reduce some Bulgarian import requirements and add low-marginal-cost generation to the regional system.
But it does not eliminate the underlying hydrological risk.
The August events demonstrated that nuclear generation, traditionally considered one of the most weather-resistant sources of firm power, can become vulnerable during extreme low-water periods.
That matters for system planning.
Bulgaria, Romania and Hungary rely heavily on nuclear generation as a source of stable, low-carbon electricity.
If climate conditions increasingly affect cooling availability, operators may need to invest more heavily in water-management and cooling infrastructure.
The same Danube conditions also affect hydro generation and river transport.
Low water can therefore reduce electricity supply while simultaneously disrupting fuel logistics.
That has turned the river into an increasingly important regional energy-market variable.
For Bulgaria, Kozloduy remains central to both domestic supply and exports.
Restoring Unit 5 toward full output should improve the country’s position as autumn demand begins to increase.
The plant’s experience in August is nevertheless likely to influence future investment decisions.
Climate resilience will increasingly need to be treated as part of nuclear asset management rather than as an exceptional engineering issue.
Kozloduy’s latest recovery provides short-term relief.
But the deeper lesson for Southeast Europe is that firm generation is becoming more exposed to hydrology than planners previously assumed.
