Italy Heatwave Triggers Red Alert: Nuclear Plants Paused as River Water Overheats

Italy's Civil Protection Department has extended a red-alert heat warning across Rome, Sardinia, and Sicily, with peaks of 42-43 °C inland and 38-39 °C across much of central and southern Italy. The prolonged high temperatures have forced the temporary shutdown of nuclear units that rely on river water for cooling, exposing a vulnerability that will recur as the climate warms.

What Is Happening

Italy's four operating reactors at the Caorso and Trino Vercellese sites use river water for once-through cooling. As river temperatures climb, the plants hit regulatory thresholds for the temperature of discharged cooling water and are required to throttle or shut down. Both plants have been operating at reduced output for the past week, with full pauses on the hottest days.

"We have never seen river temperatures this high this early. The licensing limits are tight, and we hit them faster than the climate models predicted," said an engineer at one of the affected plants.

Where the Heat Is Worst

• Sardinia: 42-43 °C inland, brown-zone alerts across the island
• Sicily: 41-42 °C inland, hospitals reporting a 30% rise in heat-related admissions
• Rome and Lazio: 38-39 °C, with humidity making it feel closer to 45 °C
• Central and southern mainland: 38-39 °C, with several days still to run

Other Impacts

Retailers in Rome and Milan report that portable and split-system air conditioners are sold out for the second consecutive weekend. Power demand hit a record for July, with grid operator Terna warning of tight reserves during the late afternoon peak. Tourist sites including the Colosseum and Pompeii have introduced shaded rest stations and free water distribution.

Why Nuclear Cooling Is a Climate Story

Once-through cooling with river or lake water is common in older nuclear plants worldwide. As climate change pushes baseline river temperatures up, more plants will hit their discharge limits more often. France has already published guidance on retrofitting with cooling towers; the U.S. NRC is re-examining its heat-discharge rules. Italy's plants do not yet have cooling towers; retrofitting would take years and significant capital.

Adaptation in the Meantime

For now, Italy's options are limited: import more electricity from neighboring grids (which have less headroom than usual), run gas peakers harder (raising both cost and emissions), or accept reduced nuclear output. The country is also pushing demand-side measures - encouraging late-afternoon thermostat settings of 26 °C in public buildings - but the political pressure to keep power flowing is intense.

What to Watch

The current heat dome is forecast to break late this week, but meteorologists warn that a second pulse may arrive in mid-August. If it does, Italy will be testing its grid with virtually no buffer.