When the River Runs Dry

Here is something to think about while sweating through another heatwave: the nuclear power plant 15 kilometers from Luxembourg's border is running on a single reactor because the river that cools it is almost empty.

On the night of July 31 to August 1, EDF shut down reactor 1 at Cattenom as a precautionary measure. The Moselle river's flow rate had dropped too low to guarantee safe cooling. Reactors 2 and 4 were already offline for scheduled maintenance. Only reactor 3 is still running [1]. The shutdown is expected to last a month, unless the river comes back to life sooner.

This is not a Cattenom problem. It is a continent-wide problem.

France: Chooz shut down too

The same night EDF took Cattenom's reactor 1 offline, they also shut down both reactors at the Chooz nuclear plant on the French-Belgian border. Same reason: the river is too low, the water too warm, the cooling capacity insufficient [2]. Three French reactors gone in a single weekend, not because of equipment failure or political protest, but because the rivers cannot do their job anymore.

July 2026 was France's hottest month on record [3]. Almost every department is on drought alert. Up to a quarter of France's streams have already run dry this summer. Groundwater tables dropped at 93% of observation points in June [4]. The rivers that nuclear plants depend on are not recovering between heatwaves anymore. They are just getting lower.

The Danube: Paks and Cernavoda

It gets worse further east. The Danube is at a record low, 28 centimeters below the previous record set in 2018. Hungary's Paks nuclear plant, which generates about half the country's electricity, was within 72 hours of a full shutdown as of July 30 [5]. The operator, MVM, said the water level had already reached "stage 3" of their four-stage emergency scale and they were preparing for stage 4, which means total shutdown.

The Danube is so low that the pumps cannot draw enough water even though, in theory, there is still enough flow to cool the reactors. The intake pipes were designed for a river that no longer exists [6].

Romania's Cernavoda plant, which produces about a fifth of the country's electricity, shut down unit 1 on July 28. Unit 2 was also expected to shut down but got a temporary reprieve after engineers confirmed its operating parameters were still safe. That reprieve could end at any time [7].

The design assumption that broke

Nuclear plants are not supposed to shut down because of warm rivers. They are designed around historical flow data, minimum water levels measured over decades. Paks was designed using a 100-year minimum water level for the Danube. That minimum has been exceeded twice now, in 2018 and again in 2026. The design assumption was: the river will never go below this point. The river disagreed.

This is the same pattern we see everywhere with climate change: infrastructure designed around historical norms fails when the norms shift. It is not that the engineers were careless. It is that the past is no longer a reliable guide to the present.

Why Luxembourg should care

Cattenom is not in Luxembourg, but it is close enough that we can see the cooling towers from certain hills on a clear day. It is one of the largest nuclear plants in France, with four 1'300 MW reactors. When three of four reactors are offline, that is roughly 3'900 MW of capacity gone from the European grid.

Luxembourg imports a significant share of its electricity. The country is part of the European grid, which means reduced French nuclear output affects prices and availability here. The Moselle flows through Luxembourg too. If it is low at Cattenom, it is low at our stretch of the river as well.

There is also the question of what happens if reactor 3, the last one running, has to shut down. EDF says the remaining reactor is operating safely. But the Moselle is not getting replenished. No rain is in the forecast for the next week. If reactor 3 goes, Cattenom produces zero electricity, and the Moselle becomes a river running past a silent plant.

The bigger picture

Across Europe, nuclear plants are colliding with a climate they were not designed for. France gets about 70% of its electricity from nuclear. Hungary gets about half. Romania gets about a fifth. When rivers drop, these plants cannot produce, and the countries that depend on them have to find replacement power on a grid that is already strained by heat and high demand from air conditioning.

The irony is sharp: nuclear power is supposed to be the low-carbon backbone of the energy transition, but the same climate change that makes us need clean energy is also making nuclear plants harder to run. You cannot cool a reactor with a dry river.

EDF says Cattenom's reactor 1 will be back by August 31 at the latest. That assumes the Moselle recovers. Last year, low river levels persisted into September. The year before, into October. The river will come back eventually. But "eventually" is not a grid management strategy.