Bulgaria has reduced output from Kozloduy nuclear unit 5 to around 850 MW as low Danube levels limit cooling-water availability. The curtailment extends drought-related pressure on firm generation across central and southeast Europe. The reactor had been running near 1,010 MW before hydrological restrictions started, implying a drop of roughly 15%. Unit 6 is reported as unaffected.
Kozloduy cooling-water works planned after deeper unit 5 reduction
Bulgarian authorities have announced plans to build a 250-300 metre levee near the plant to improve access to cooling water. Works are expected to take around 10-15 days. The deeper reduction at unit 5 indicates hydrological conditions remain difficult until the emergency works are completed.
The reduction is significant for supply because Kozloduy is described as one of Bulgaria’s main sources of low-marginal-cost baseload generation. The loss associated with unit 5 is around 160 MW. Similar water-related constraints have also affected other major Danube-based nuclear plants.
Danube constraints spread across regional nuclear and hydro availability
Romania’s Cernavodă station has experienced prolonged disruption, while Hungary’s Paks plant cut output sharply earlier in August before recovering. In parallel, weak hydrology has reduced hydro availability in several southeast European markets. Together, the nuclear and hydro constraints have supported elevated regional power prices.
Central SEE day-ahead markets have repeatedly traded in the €180-190/MWh range during August. Evening hours in some countries have exceeded €250/MWh. Paks output has largely recovered, but the regional premium has persisted. This indicates scarcity conditions have broadened beyond the Hungarian nuclear outage.
Cooling-water limits and market pricing during extreme heat
The current conditions also highlight a climate-risk issue for nuclear generation tied to cooling-water access. While nuclear plants are typically treated as firm supply, conventional reactors still depend on reliable cooling-water availability. Extreme heat can create a double effect by increasing electricity demand due to cooling loads while river conditions reduce generation capability.
The response described in the source involves both site-specific adaptation and wider system flexibility. For nuclear operators, it points to more investment in water-management and cooling infrastructure. For power systems, it increases the value of storage, interconnection, hydro flexibility, demand response and fast-start thermal generation.
The Kozloduy levee is described as a relatively modest infrastructure intervention, but it is framed as significant because it reflects climate adaptation entering nuclear operating expenditure. If low-water events become more frequent, utilities may need to incorporate such investment permanently into asset-management plans. The Danube is therefore becoming an increasingly important variable for regional power-market outcomes affecting hydro output, nuclear cooling and energy logistics simultaneously.
For traders, river conditions are increasingly part of short-term availability assessments for some of southeast Europe’s largest generation assets rather than a secondary hydrological indicator. This links Danube hydrology directly to near-term generation outlooks across multiple markets.
