Why Hungary's Largest Nuclear Plant is Shutting Down—and How the Industry is Adapting to Warming Rivers

For the first time in its 44-year history, Hungary's Paks nuclear power plant is going completely dark. The culprit is not a mechanical failure or a fuel shortage, but a severe drought that has reduced the mighty Danube River to a historic trickle.[1]

Paks is not just any power station; its four Soviet-built VVER-440 reactors normally generate 2,000 megawatts of electricity, accounting for nearly half of Hungary's domestic power supply. Prime Minister Péter Magyar confirmed that the final units are being powered down this weekend as the crisis deepens.[1][7]

The immediate cause of the shutdown is a matter of basic plumbing. The plant relies on the Danube for its cooling systems. However, a prolonged heatwave across Central Europe has pushed the river's water level at the Paks gauge to unprecedented lows. The water is projected to drop to negative 144 centimeters—shattering the previous record of negative 98 centimeters set in 2018.[1][3]

A negative reading does not mean the riverbed is bone dry; rather, it indicates the water has fallen below the gauge's established zero-reference level. But for the plant's engineering, the absolute depth is critical. When the water hits negative 134 centimeters, the intake pumps can no longer physically draw enough volume to safely cool the operating reactors.[1]

This shutdown is not an emergency scramble, but a highly choreographed safety protocol working exactly as designed. The International Atomic Energy Agency (IAEA) and the OECD Nuclear Energy Agency note that nuclear facilities are equipped with strict operational limits. When the "ultimate heat sink"—in this case, the Danube—cannot guarantee sufficient flow, the reactors are safely tripped and powered down.[4][5]

To understand why a river's depth dictates a nuclear plant's heartbeat, one must look at the mechanics of "once-through" cooling systems. These legacy systems withdraw massive volumes of water from a river, pass it through heat exchangers to condense the steam that drives the electricity-generating turbines, and then return the slightly warmer water back to the river.[6]

A fully operational plant like Paks requires roughly 100 cubic meters of water per second to maintain its thermal balance. When the reactors are shut down, that requirement plummets to just 5 cubic meters per minute to cool the residual decay heat—a fraction of the operational demand, which the current river levels can easily support.[3]

Often, river-cooled plants are forced offline not because the water is too low to pump, but because the water is too warm. Environmental regulations strictly cap the temperature of the water discharged back into the river to protect aquatic ecosystems from "thermal pollution."[6]

If a plant draws in water that is already baking under a summer heatwave, the added industrial heat could push the river's temperature past lethal thresholds for local flora and fauna. During recent summers, plants in France and Switzerland were forced to curtail output specifically to keep the Rhine and Rhone rivers from overheating.[4][6]

The Paks shutdown is sending ripples through the European energy market. Hungary is suddenly missing half of its domestic generation right as a brutal heatwave spikes air-conditioning demand. The government has requested that large industrial consumers, including the energy conglomerate MOL, voluntarily slash their electricity use by up to 40 percent during peak evening hours.[1][2]

Hungary is not alone in this struggle. In neighboring Romania, the Nuclearelectrica operator has already shut down one of the two reactors at the Cernavoda nuclear plant due to the same unprecedented low levels on the Danube. Romania has declared a state of alert, scrambling to import power from Ukraine, Greece, and Bulgaria.[2][3]

These dual shutdowns highlight a growing vulnerability at the intersection of climate change and energy infrastructure. Experts point out that while nuclear power is a vital low-carbon tool for mitigating climate change, its legacy river-based infrastructure is increasingly exposed to the very extreme weather it aims to prevent.[5]

Despite the dramatic headlines, the actual global impact of weather-related nuclear outages remains remarkably small. According to the IAEA, energy losses due to cooling water availability and other climate events accounted for just 0.3 percent of global nuclear generation in 2022. The technology itself is highly resilient; the vulnerability lies almost entirely in the plumbing of older, river-adjacent plants.[4]

Operators are not sitting idle. At Paks, the operating company, MVM, is already executing preparatory engineering work to lower the physical intake pipes deeper into the river channel. Within a few years, these modifications will allow the plant to continue pumping cooling water even if the Danube drops below the current historic lows.[3]

For the broader nuclear renaissance, the industry is fundamentally rethinking its geography and engineering. Modern plants are increasingly moving away from once-through river cooling. Instead, they utilize recirculating systems with massive cooling towers, which consume significantly less water by relying on evaporation rather than sheer flow volume.[6]

The ultimate solution to the cooling puzzle is the ocean. The IAEA reports that of the more than 100 gigawatts of nuclear capacity currently under construction or planned globally, more than 60 percent is slated for coastal locations. The sea provides an infinite, stable heat sink that is largely immune to the droughts plaguing inland waterways.[4]

The silencing of the Paks reactors this week is a stark visualization of the energy-water nexus. Yet, it is also a testament to the uncompromising safety culture of modern nuclear power. As engineers lower intake pipes and planners look to the coastlines, the industry is actively adapting to ensure that the low-carbon grids of the future remain resilient, even as the rivers that once powered them run dry.[1][4]