Unit 5 and Unit 6 output levels
Bulgaria’s Kozloduy nuclear power plant has increased output at Unit 5 to around 950 MW following a recovery in Danube water levels. The rise reverses part of drought-driven curtailment that had cut the reactor to about 850 MW last week. Unit 6 is operating close to normal at around 971 MW.
The change returns 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.
Cooling-water constraints linked to Danube levels
Kozloduy reduced Unit 5 output after exceptionally low Danube levels lowered cooling-water availability. Before the restrictions, the reactor had been running at more than 1,000 MW. Bulgarian authorities have also announced hydrotechnical works, including a 250-300 metre river structure, intended to improve water access if conditions deteriorate again.
The partial recovery is described as significant because nuclear availability has become an unusually important short-term trading factor across the region. Hungary’s Paks plant cut output sharply during August due to low Danube levels before recovering. Romania’s Cernavodă plant has faced more severe disruption, leaving Romania without nuclear output during several recent trading sessions.
Regional price impact and market conditions
The combination of outages and curtailments 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 availability.
Hydrology exposure for nuclear, hydro and transport
The August events showed that nuclear generation can become vulnerable during extreme low-water periods. This affects system planning in Bulgaria, Romania and Hungary, where nuclear is relied on for stable, low-carbon electricity supply.
If cooling availability is increasingly affected 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, with low water able to reduce electricity supply while disrupting fuel logistics.
Bulgaria’s supply role and implications for operations
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 August experience is expected to influence future investment decisions.
Treatment of climate resilience is expected to become part of nuclear asset management rather than handled only as an exceptional engineering issue. Kozloduy’s latest recovery provides short-term relief while hydrological exposure remains a key factor for firm generation across Southeast Europe.
