How much of a threat do heat waves pose to nuclear plants?

This summer's heat waves in Europe knocked out or reduced power at several nuclear plants, raising questions about how well nuclear energy holds up as the climate warms. In France and Switzerland, plants shut down because river water got too warm to safely release back into waterways. Along the Danube, plants in Hungary, Romania, and Bulgaria cut output or paused because drought dropped river levels below the intake pumps that pull in cooling water. Hungary temporarily sank barges near its Paks plant to raise the water level enough to keep cooling water flowing.

Experts say the problem is largely about how individual plants were built decades ago, not a fundamental flaw in nuclear power. Plants with cooling towers — the tall structures common in the U.S. and Asia — recycle water in a closed loop and are far less vulnerable to hot, low rivers. Nearby plants in the Czech Republic and Slovakia, which use cooling towers, kept running through the same heat wave. Adding a cooling tower to an existing plant is possible but expensive, with a past California study estimating roughly $135 million in today's dollars, and such upgrades take years.

For homeowners, the immediate takeaway is limited: this is a story about how power grids and utilities keep the lights on during extreme heat, not a program or rebate that affects your house directly. Arizona's Palo Verde plant, which runs on recycled wastewater instead of river water, is cited as a model for building nuclear plants that hold up better in hot, dry conditions.