Danube low water prompts shutdown risk at Paks and Cernavoda amid Europe-wide cooling constraints

Hungary: Paks enters advanced Danube low-water stage

Magyar Villamos Művek (MVM), the Hungarian operator, said the Danube level is 28 centimetres below the previous record set in 2018. That earlier record had been one metre below the 100-year minimum water level used in the design of Paks nuclear power plant.

MVM said the plant has already been reducing total output without a safety issue, but noted that while the current extremely low water level and water flow rate would allow sufficient water to cool the units, the suction level required for pumps is higher than the water level and is expected to continue decreasing.

MVM said Danube low-water conditions are divided into four stages based on intake measurements and that the plant is currently in stage 3. It added that forecasts show a realistic chance of a stage 4 event, under which all units would have to be shut down and then cooled. It stated that implementing a complete shutdown must be carried out within 24–72 hours, based on forecasts that change several times a day.

For cooling during a full shutdown, MVM said 5 cubic metres of water per minute would be needed, compared with 100 cubic metres per second for operating units. It said standby and reserve pumps are in place and that Paks is prepared to keep units in a safe condition during extremely low water conditions lasting for weeks. Restarting would occur in stages once the appropriate water level is reached, depending on the level.

MVM attributed the record-low Danube levels to climate-change-related hydrology, saying low water has persisted all year, and to deepening of the river bed. It also pointed to preparatory work to lower intake pipes, saying that within a few years the plant should be able to continue production even with a lower water level than the current one.

Romania: Cernavoda unit 1 shut; unit 2 may be next

In Romania, Nuclearelectrica announced that Cernavoda unit 1 was being shut down and disconnected from the National Energy System due to the unprecedentedly low level of the Danube caused by severe drought.

The company said the shutdown followed forecasts from the National Institute of Hydrology and Water Management and described the action as preventive to protect nuclear safety and the reliability of facilities, with “no impact on nuclear safety, personnel or the environment.”

It later indicated that unit 2 was likely to be shut down, but then updated its position: unit 2 would remain online after analysis of operating parameters and equipment carried out during the night of 29 to 30 July 2026 found that operating parameters allow continued operation in safe conditions.

Nuclearelectrica added that shutdown of unit 2 may still be necessary at any time considering the current situation and hydrological forecasts. It said Cernavoda is Romania’s only nuclear power plant, with two 650 MWe Candu reactors that generate about a fifth of national electricity.

Broader context: heatwave cooling-water controls across Europe

The heatwave’s impact is extending beyond the Danube basin. In France, EDF temporarily took Bugey unit 3, Chooz unit 2 and Golfech 2 offline to comply with regulations on cooling water discharges, while eight other reactors operated at reduced power.

The measure was described as an environmental protection requirement to avoid discharging too much hot water into rivers already warming due to the heatwave.

In Switzerland, the two units at Beznau were temporarily shut down, or operated at lower power over recent weeks due to high temperatures in the River Aare.