Southeast Europe’s August heatwave highlighted a less familiar vulnerability for nuclear generation: the dependence of large thermal power plants on river conditions.
At Slovenia’s Krško nuclear power plant, reactor output was reduced to 80% during August 5–6 as low Sava River flows and elevated temperatures made it more difficult to remain within environmental limits governing cooling-water discharge.
According to the operator, it was the first substantial reduction caused by such conditions since 2003.
Romania experienced a more significant disruption.
Nuclearelectrica began a controlled shutdown of Cernavoda Unit 2 on August 13 as declining Danube water levels continued to constrain operating conditions.
The events are significant because nuclear generation is generally regarded as one of Southeast Europe’s most dependable sources of low-carbon electricity.
Unlike wind and solar generation, nuclear fuel supply is not directly dependent on weather conditions.
Cooling requirements, however, can become increasingly weather-sensitive.
A prolonged combination of high temperatures and low river flows can therefore reduce nuclear output even when the reactor itself remains technically available and operational.
That issue is likely 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 the longer-term discussion around nuclear generation.
For projects expected to operate for 60 years or more, investors and engineers will increasingly need to consider future hydrological and temperature conditions rather than relying solely on historical river data.
Cooling-system design could therefore become a more material factor in both engineering decisions and project economics.
Alternative cooling technologies can reduce dependence on river water, but they may also involve higher capital costs or efficiency penalties under certain operating conditions.
For existing nuclear stations, meanwhile, climate resilience could become a growing component of maintenance and life-extension investment as operators seek to preserve reliable output under increasingly challenging environmental conditions.
August does not undermine the investment case for nuclear power in Southeast Europe.
It does, however, demonstrate that nuclear availability should be treated as an engineering and environmental variable rather than an absolute constant.
As the region adds more nuclear capacity, the ability of plants to maintain output under heat and water stress could become an increasingly important consideration for system planners, investors and lenders.
