After enduring wars, crises, and decades of shifting governments, Bulgaria's Kozloduy nuclear plant has encountered a problem it never anticipated: a river it sits on is too shallow.
Kozloduy will reduce power production for the first time in its history because the Danube has dropped to levels not seen in decades. Starting Friday, one of its two reactors will generate 120 megawatts less than usual.
The plant itself is fine. The issue is cooling water.
Kozloduy runs two reactors, each with a capacity of 1,040 megawatts. Those reactors need the Danube to keep things from overheating. A shore-based pumping station is supposed to handle low river levels, but the water has dropped so far that even that system needs help.
"Extreme meteorological and hydrological condition" is to blame, the Energy Ministry said. In plain terms: the river is running low, and the plant has to slow down to stay safe.
What makes this unusual is the timing. Kozloduy managed to run at full strength through most of the summer, whereas its counterparts in Hungary and Romania, which also rely on the Danube, had already been forced to scale back their generation. Bulgaria held out longer, but now the water has caught up with it.
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The plant supplies about one-third of Bulgaria's electricity and anchors the national grid. It has operated for 52 years, yet it has never before had to cut output because of water levels.
The Danube has long been a critical artery for European energy. Several countries, including Austria, Serbia, and Romania, operate power plants along its banks, and the river is also a key route for shipping coal, oil, and other fuels. When drought shrinks the river, those plants and supply chains feel the pinch.
This is not just a local problem with a local fix.
The Danube is Europe's largest river, and its low levels have already disrupted shipping across the region. Barges carrying grain, fuel, and other goods are moving less or not at all. That slowdown helps push energy prices higher, since moving fuel by river is cheaper than moving it by truck or rail.
The Energy Ministry says the water situation is not improving. "Forecasts for river levels upstream of the Bulgarian section continue to show a downward trend," the ministry said, meaning the cut could last a while and maybe get deeper.
The catch: a river that powers one of the region's biggest plants is also a river that everyone else depends on. When it shrinks, the effects ripple through power grids and supply chains at the same time.
Here is the part that matters for anyone watching energy markets.
Bulgaria has managed to stay a net power exporter, meaning it still sends more electricity out than it brings in. The country's ability to remain a net exporter stems from a combination of two factors: a large battery fleet (over 5 GW) that stores power when prices are low and releases it when they climb, plus solar generation from the region that helps meet daytime peaks.
A nuclear plant cutting output used to be a bigger deal for the region's power supply. Storage and solar are softening the blow, which is a sign that the energy grid is getting more flexible than it used to be.
But the bigger lesson is about water. Low river levels are not just a shipping story or a farming story anymore. They are an energy story, and they are becoming a regular one. If the Danube stays low, power prices in the region could stay higher, and the plants that depend on river water will keep having to make choices they never had to make before.
For investors, the takeaway is not about one Bulgarian reactor. It is about how weather is becoming a bigger factor in energy prices everywhere.
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