Why drought is unlikely to shut down Czech nuclear power plants
Hungary has shut down its Paks nuclear power plant after prolonged drought and extreme heat caused the level of the Danube to fall further. The situation has raised questions about whether climate change could create similar problems for Czech nuclear facilities. Petr Šuler of the ČEZ nuclear energy division says Temelín and Dukovany use a fundamentally different cooling system and are therefore much less dependent on river flow and water temperature.
The Paks nuclear power plantn normally provides around half of Hungary’s domestically generated electricity. Hungarian Prime Minister Péter Magyar said production would not resume until the river level rises again, something that is not expected in the immediate future.
The shutdown has forced Hungary to prepare emergency energy-saving measures and rely more heavily on electricity imports. Large industrial consumers may be required to reduce consumption, while Budapest has announced changes to metro and tram services intended to save power. Slovakia has also offered assistance.
The situation has raised questions about whether increasingly frequent droughts and heatwaves could create similar problems for nuclear power stations elsewhere in Central Europe, including the Czech plants at Temelín and Dukovany.
Different cooling systems, different risks
According to Petr Šuleř, head of communications for ČEZ’s nuclear energy division, the main difference lies in the cooling systems used by the plants. Paks relies on what is known as once-through cooling. In this system, large quantities of water are taken directly from a river, used to condense steam after it has passed through the turbines, and then returned to the river.
The returned water must meet strict environmental requirements, particularly limits on temperature. When the river level and flow fall, the plant may have less water available for cooling. At the same time, warmer river water is less effective at removing heat, while returning additional heat to a river with a low flow can place extra pressure on the local ecosystem.
Temelín and Dukovany use a different system: “With cooling towers, water circulates within the plant in a closed loop, and the excess heat that cannot be converted into electricity or used in heating systems is released into the atmosphere,” Petr Šuleř said.
Cooling towers are more expensive to build, but they make the plant far less dependent on river flow rates and water temperatures than facilities using once-through cooling. Petr Šuleř also stressed that this part of the process should not be confused with the systems that directly cool the reactor.
“This has nothing to do with cooling the reactor itself,” he said. “It is part of the conventional, non-nuclear section of the power plant and affects electricity generation efficiency rather than nuclear safety.”
All nuclear power plants must be able to shut down safely and continue removing residual heat from their reactors even in the event of a complete loss of the external water supply. From the point of view of electricity production, extremely severe hydrological conditions could still represent an operating concern. However, ČEZ does not expect either Temelín or Dukovany to face significant production restrictions because of water availability or river temperatures.
Preparing for longer droughts and hotter summers
Petr Šuleř says ČEZ has been taking the effects of climate change into account for many years. The company has invested in technological upgrades and measures designed to improve the efficiency of water use. Over time, it has gradually reduced the amount of water required to produce one megawatt-hour of electricity.
At Temelín, total water consumption last year was approximately 2.5 cubic metres per megawatt-hour generated, with part of that water later returned to the river. According to Petr Šuler, this was below the plant’s long-term average.
Further improvements are expected once the ongoing modernisation of the cooling-water treatment system is completed. “Our strategy is not only to ensure that the plants have sufficient water supplies in the future, but also to continually reduce the amount of water needed to produce the same amount of electricity,” Petr Šuler said.
Hot summer weather does have a measurable effect on output. Nuclear plants generally perform slightly better in winter because cooler air helps create better vacuum conditions in the condensers, improving overall efficiency. At Temelín, each unit can generate more than 1,100 megawatts during freezing winter weather. During recent record-high temperatures, output was around 1,070 megawatts per unit.
Petr Šuler said the difference between cold winter conditions and the hottest summer days is typically around one percent of nominal output. “The effect is measurable but relatively small,” he said. “It does not threaten either safety or the plant’s ability to supply electricity.”
He also pointed out that nuclear power plants operate in regions with much hotter climates than the Czech Republic, including desert areas. The Hungarian situation therefore highlights an important distinction. Drought can create serious problems for plants that depend heavily on the flow and temperature of a nearby river, but Czech nuclear facilities were designed with cooling towers that make them substantially less vulnerable to such conditions.
