Hungary was forced to shut down most of the Paks nuclear power plant — its only nuclear facility — after record-low Danube water levels made safe cooling impossible. It is the first such shutdown in the plant's 44-year operating history.

The closure comes as a severe heatwave grips Central and Southern Europe. Budapest and Vienna are forecast to reach 37°C on August 3, 2026, and temperatures in Zagreb, Rome, Tirana, Bucharest, and Paris are all exceeding 33°C. The heat is expected to persist for up to five days.

Paks generates a large share of Hungary's electricity. The plant runs four pressurized water reactors — a common design in which water under high pressure carries heat from the reactor core to a separate cooling circuit, and that cooling circuit draws water from the Danube. With the river's level projected to fall further, the plant was expected to be fully powered down later in the week of August 3, 2026. Reuters reported on August 1 that the second-to-last generating unit would be shut due to the continuing decline, following an earlier warning from Prime Minister Péter Magyar that a complete shutdown was possible that weekend.

The shutdown carries substantial capacity implications. According to plant operator documentation, a full closure of Paks would remove roughly 2,000 MW of generating capacity from Hungary's energy system, with an additional loss of approximately 4,000 MW anticipated across the broader grid. Those figures point to the plant's centrality to Hungarian energy security.

The regional dimension is stark. Romania and Serbia reported their lowest-ever water levels in early August 2026, disrupting hydropower generation across the Lower Danube basin. The same drought conditions affecting Paks are simultaneously degrading output from hydroelectric dams downstream, compounding the regional energy shortfall at a moment of peak cooling demand.

Hungarian authorities moved quickly to curb consumption. On August 3, many digital advertising screens across the country were switched off as part of a broader energy-saving push. Prime Minister Magyar warned that "the hardest five days are ahead."

Paks is designed to shut down automatically via its protection systems if any of its systems are damaged, while reinforced safety systems remain available. The plant's Danube-water supply infrastructure consists of steel pipes laid in tunnels, shafts, and partially buried sections, as documented in a Hungarian Atomic Energy Authority (OAH) thematic expert review. The current crisis tests the resilience of that arrangement under conditions that, while severe, are not wholly without precedent in the regulatory record. A 2020 OAH memorandum noted that under similar Danube water level and temperature conditions, the planned Paks-2 units would need to be de-rated — their output reduced — to continue operating safely.

The broader context here extends beyond the immediate crisis. The Paks shutdown exposes a structural vulnerability in inland nuclear generation: pressurized water reactors dependent on river cooling face shrinking thermal margins as drought frequency and intensity increase across Central Europe. Hungary's 10th National Report on Nuclear Safety references the KNPA fund, established to provide realistic coverage for decommissioning costs after the plant's eventual shutdown. The current event is not a decommissioning scenario — the plant's protection systems are functioning as designed — but it is a live stress test of the assumptions underpinning both the existing plant's operating limits and the regulatory case for Paks-2 expansion. If the Danube's low-water regime becomes more frequent, the de-rating provision contemplated in the 2020 OAH document may shift from an edge-case contingency to a recurring operational constraint, with corresponding implications for capacity factors and baseload reliability.

This is not a uniquely Hungarian problem. The simultaneous hydropower disruptions in Romania and Serbia illustrate that the Danube's hydrological stress is basin-wide, affecting multiple generation technologies across several national grids at once. For regional energy planners, the event crystallizes a question that has circulated in European energy policy circles without a forcing event: whether the interdependencies between river hydrology, nuclear cooling, and hydropower output in the Danube basin are adequately captured in current stress tests and grid reliability models. The fact that Paks has operated for 44 years without a drought-induced shutdown makes this episode a meaningful data point, even if its policy consequences will have to be worked through in the months ahead.