Large thermal power plants can face operational limits tied to river conditions, a factor highlighted during Southeast Europe’s August heatwave. The constraints were reflected at Krško in Slovenia and Cernavoda Unit 2 in Romania, where cooling-water availability affected plant performance.
Krško reactor output cut during low Sava River flows
At Slovenia’s Krško nuclear power plant, reactor output was reduced to 80% during August 5–6. The operator said low Sava River flows and elevated temperatures made it more difficult to stay within environmental limits for cooling-water discharge.
The operator also stated that it was the first substantial reduction linked to such conditions since 2003. The event pointed to how temperature and river flow can affect nuclear operations even when the unit remains available.
Cernavoda Unit 2 shutdown as Danube levels decline
Romania saw a larger disruption after Nuclearelectrica began a controlled shutdown of Cernavoda Unit 2 on August 13. The company attributed the move to declining Danube water levels that continued to constrain operating conditions.
The developments were notable because nuclear generation is generally regarded as one of Southeast Europe’s most dependable sources of low-carbon electricity. At the same time, the events underscored that cooling requirements can be sensitive to weather-driven river conditions.
Cooling-water sensitivity and implications for future nuclear planning
Nuclear fuel supply differs from wind and solar generation because it is not directly dependent on weather conditions. However, prolonged combinations of high temperatures and low river flows can reduce nuclear output even when the reactor is technically available and operational.
The issue is expected to become more relevant as countries across Southeast Europe plan additional nuclear capacity. Hungary is developing Paks II, Romania is pursuing additional Cernavoda capacity alongside small modular reactor development, and Bulgaria continues to assess new nuclear projects.
Serbia has also reopened longer-term discussion around nuclear generation. For projects expected to operate for 60 years or more, investors and engineers may need to consider future hydrological and temperature conditions rather than relying only on historical river data.
Cooling-system choices and life-extension investment considerations
Cooling-system design could become a more material factor in engineering decisions and project economics. Alternative cooling technologies can reduce dependence on river water, though they may involve higher capital costs or efficiency penalties under certain operating conditions.
For existing nuclear stations, climate resilience may become a growing component of maintenance and life-extension investment as operators seek to preserve reliable output under increasingly challenging environmental conditions.
August did not undermine the investment case for nuclear power in Southeast Europe. It instead showed that nuclear availability should be treated as an engineering and environmental variable rather than an absolute constant.
As additional capacity is added across the region, maintaining output under heat and water stress could become increasingly important for system planners, investors, and lenders.
