Engineering Against the Elements: How Hungary Saved the Paks Nuclear Power Plant from Historical Low Water Levels

In an extraordinary feat of hydraulic engineering, Hungary has successfully prevented the total shutdown of its largest power facility, the Paks Nuclear Power Plant, amidst a period of catastrophic drought. As the Danube—a critical lifeline for the facility’s cooling systems—dropped to historical lows, the nation’s energy grid faced an existential threat. Through a combination of daring, short-term improvisations and massive, long-term civil engineering projects, Hungarian authorities have managed to stabilize the plant’s cooling infrastructure, allowing production to return to full capacity.

The Crisis: When 2,000 MW Hangs by a Centimeter

The Paks Nuclear Power Plant is the backbone of Hungary’s energy sector, providing roughly half of the country’s electricity. However, the plant relies on a continuous intake of approximately 100 cubic meters of water per second from the Danube to cool its four operational reactors.

By early August 2024, the situation had reached a critical inflection point. As the riverbed neared exposed levels, the water intake infrastructure—designed decades ago—began to fail. Because the intake suction pipes are fixed at a specific elevation, they could no longer draw sufficient volume once the river surface dropped below a certain threshold. At the peak of the crisis, three of the four reactor blocks were forced into idling or reduced output, dropping the plant’s contribution to the grid to just 10% of its 2,000 MW capacity.

Chronology of the Struggle

The descent into the crisis was rapid. Throughout July, the Danube’s water level plummeted, setting daily records for low volume. By July 30, the river gauge at Paks hit −121 cm (relative to the zero-point).

• Late July: The plant began a systematic, step-by-step reduction in output to match the diminishing cooling water supply.
• August 1–15: The plant operated at only a fraction of its capacity. The threat of a full, unprecedented shutdown of the 40-year-old facility loomed large.
• August 17: A critical threshold of −129 cm was reached. Engineers warned that if the level dropped just three more centimeters to −132 cm, another turbine would have to be disconnected, further crippling the nation’s power supply.
• August 18–20: Emergency hydraulic measures, including the partial sinking of industrial barges, began to show measurable results.
• August 22: With the water level stabilized, Block 3 was successfully brought back online.
• August 26: Prime Minister Péter Magyar announced that the plant was on track to reach 100% capacity once again.

Tactical Engineering: Barges and River Diversions

To bridge the gap while permanent solutions were implemented, the Hungarian government authorized a radical short-term strategy. Two massive, 80-meter-long, 10-meter-wide barges were positioned directly in front of the plant’s intake channels.

These vessels were not merely moored; they were partially submerged in a controlled manner by filling their ballast tanks with water. By sinking them, the engineers created an artificial flow obstacle, effectively "damming" the local area to raise the water level at the intake points. To ensure these 80-meter structures could withstand the immense force of the river’s current, crews drilled 70-centimeter-wide ground screws eight meters deep into the riverbed, anchoring the barges with heavy-duty 26mm steel cables.

Simultaneously, authorities manipulated the flow of the Ráckeve-Soroksár branch of the Danube. By adjusting sluices and weirs upstream, engineers diverted an additional 20 cubic meters per second into the main channel. The combined effect of the barges and the diverted water raised the local river level by 10 to 15 centimeters—just enough to keep the cooling pumps functioning and prevent the critical -132 cm threshold from being breached.

The Long-Term Solution: A Massive Sohlschwelle

While the barges served as a stopgap, the Hungarian government is investing 6.1 billion Forint (approximately €16.8 million) into a permanent solution: a Sohlschwelle (a submerged riverbed sill).

This massive civil engineering project involves the installation of 145,000 cubic meters of stone across a 300-meter-wide section of the Danube. The structure, set at a 45-degree angle to the bank, is designed to generate a backwater effect during periods of low flow, effectively raising the water level by up to 50 centimeters in the critical area.

The construction is a two-pronged effort: workers are building outward from the Dunaszentbenedek bank while simultaneously utilizing pontoons and barges to place material from the Paks side. The first phase, requiring 35,000 cubic meters of stone, is scheduled for completion by September 11, with the entire project expected to be finalized by late November.

Regulatory and Safety Context

Throughout the ordeal, the Hungarian Atomic Energy Authority (OAH) maintained that at no point was the nuclear safety of the plant compromised. They emphasized that while electrical output had to be sacrificed to protect the pumps, the cooling systems for the shutdown reactors remained well within safety margins.

The data provided by MVM, the plant operator, highlights the disparity between operational and safety-level water needs: while running at full capacity, the plant requires 100 m³/s of water; however, a fully shut-down plant, safely dissipating decay heat, requires only 2.5 m³/s. This vast difference explains why the plant was able to remain safe even when it could no longer generate power.

A Regional Challenge

Paks is not an isolated case. The summer of 2024 has served as a wake-up call for nuclear operators along the Danube. In Romania, the Cernavodă nuclear plant was forced to shut down two 706 MW reactors, and in Bulgaria, the Kozloduy plant had to reduce the output of Block 5 by 12%—a historic first for both facilities.

These events underscore a growing vulnerability in Europe’s energy infrastructure. As climate change leads to more frequent and prolonged periods of drought, the traditional reliance on "once-through" cooling systems is being tested.

Future Implications: Resilience and Redesign

The crisis at Paks has triggered a fundamental review of the plant’s future. The operator, MVM, has already initiated a technical redesign of the water intake system. The goal is to lower the suction intakes permanently, ensuring that future low-water events do not necessitate such dramatic, last-minute interventions.

Furthermore, the experience has cast a long shadow over the expansion plans for "Paks II," which will see two additional reactor units built on the site. Reports indicate that the government is currently re-evaluating the cooling concepts for these new reactors to ensure they are climate-resilient from day one.

The struggle at Paks proves that even the most robust industrial powerhouses are subject to the shifting whims of the climate. As Europe faces a future of increasingly volatile hydrological cycles, the Paks project serves as a masterclass in crisis management, showing that when the river fails, the only option left for an engineer is to reshape the river itself.