Romania sank four barges in the Danube in August 2026 as part of an effort to maintain sufficient water levels to its Cernavoda nuclear power plant, which uses river water for cooling purposes. The plan to sink these four barges follows falling water levels on the Danube, affected by severe droughts across Europe this summer. The river’s flow had fallen to a record low of 49,440 cubic feet per second for this time of year.
The four barges were filled with stones before being sunk into the river as part of efforts to divert water flow to the country’s only nuclear power plant. A large rock was also destroyed to aid redirection efforts. The sinking of these four ships constituted an unprecedented event which ultimately failed to prevent the closure of the factory. Romanian nuclear energy company Nuclearelectrica announced on August 13 that it would begin a controlled shutdown of the plant’s second and final reactor due to a lack of available cooling water.
The first had already been closed in July. The Cernavoda nuclear power plant uses water as its primary cooling mechanism, and this shutdown illustrates how an adequate water supply is essential to the operation of a nuclear power plant. Without a regular supply of river water, this plant cannot operate safely.
How water cools nuclear power plants
Nuclear power plants work by generating heat from nuclear fission and converting surrounding water into steam, which drives turbines connected to electrical generators. Water is essential for this steam conversion. The mechanical power transmission process is more efficient the greater the temperature difference between the internal heat source and the external environment where the heat is released. This is why water-cooled nuclear power plants are built near cold water sources.
The water is recycled after the steam is used to drive the turbines, which is achieved by cooling and condensing the steam at low pressure. Cernavoda’s nuclear cores are cooled and moderated by heavy water (deuterium oxide). Although the river is not used as the primary cooling mechanism, it is used as an external heat sink. Water-cooled nuclear power plants require water to cool not only when the reactor is operating, but also after it is shut down.
Heat will continue to be generated by nuclear decay even after a plant shuts down, which is why all water-cooled nuclear power plants have a backup water supply. This is a reserve in case the main water source is compromised, although the Cernavoda nuclear power plant was shut down before needing to tap this supply source. Water cooling systems are essential to stopping nuclear meltdowns, which previously occurred due to cooling system failures.
Other ways to cool nuclear power plants
The closure of the Cernavoda nuclear power plant is an example of why it may sometimes be better to consider alternative cooling methods, especially if the plant’s water supply is vulnerable to climate change. Ironically, nuclear power plants could be used to produce desalinated seawater, which is one of three unexpected uses of nuclear power. Dry cooling techniques are viable options in cases where water sources are scarce and rely on air as a heat transfer mechanism.
One type of air cooling works similarly to a car radiator, where airflow driven by a fan passes through a system of finned tubes into the vapor condenser. In this case, the heat is transferred to the ambient air. Solutions like these require less than 10% of the amount of water used by water-cooled installations, but lose up to 1.5% of the power output to drive the fans.
Another type of air cooling works similarly to the fan-driven example, but in this case the water is enclosed and cooled by the flow of air through finned tubes in a cooling tower. Heat is still transferred to the air, but this method is not as efficient. Lead-cooled nuclear reactors are also beginning to emerge and may be the future of nuclear power. In this case, molten lead is used to passively cool nuclear cores by convection.
