Kozloduy unit 5 curtailment linked to low Danube cooling-water access
Bulgaria has reduced output from Kozloduy nuclear unit 5 to around 850 MW as low Danube levels limit cooling-water availability. The reduction follows hydrological restrictions that began while the reactor was operating near 1,010 MW. Output is now down by roughly 15%. Unit 6 remains unaffected.
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 cut at unit 5 indicates hydrological conditions are likely to remain difficult until the emergency works are completed.
Danube nuclear and hydro constraints lift central SEE day-ahead prices
The curtailment is material because Kozloduy is among Bulgaria’s main sources of low-marginal-cost baseload supply. The loss of around 160 MW coincides with water-related constraints affecting other major Danube-based nuclear plants. Romania’s Cernavodă station has faced prolonged disruption, while Hungary’s Paks plant cut output sharply earlier in August before recovering.
Weak hydrology has also reduced hydro availability across several southeast European markets. Together, these factors have helped keep regional power prices elevated. Central SEE day-ahead markets have traded repeatedly in the €180-190/MWh range during August, with evening hours in some countries exceeding €250/MWh.
Cooling-water limits reshape short-term availability outlook for traders and operators
Paks output has largely recovered, but the regional premium has persisted, indicating scarcity has extended beyond the Hungarian nuclear outage. Reduced Kozloduy availability adds to that pressure in the same period. The current conditions also point to a climate-risk issue for nuclear generation tied to cooling-water access.
Nuclear plants are typically treated as firm supply, but 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. For power systems, this raises the value of storage, interconnection, hydro flexibility, demand response and fast-start thermal generation.
Nuclear operators may respond through additional investment in water-management and cooling infrastructure. The Kozloduy levee is described as a relatively modest infrastructure intervention, but 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.
Danube conditions increasingly influence hydro output and nuclear cooling simultaneously
The Danube is becoming an increasingly important variable for regional power markets because it affects hydro output, nuclear cooling and energy logistics together. For traders, river conditions can no longer be treated as a secondary hydrological indicator. They are increasingly part of the short-term availability outlook for some of southeast Europe’s largest generation assets .
