Output restrictions are expected at two nuclear plants along the Rhone river in eastern France due to high temperature forecasts, according to nuclear operator EDF.
The latest development follows a similar warning last year.
The hot weather is likely to halve the available power supply from the 3.6 gigawatt (GW) Bugey plant and the 2.6 GW Saint Alban plant from July 13 and July 16 respectively, the operator said.
However, production will be at least 1.8 GW at Bugey and 1.3 GW at Saint Alban to meet grid requirements, and may change according to grid needs, the operator said.
Kpler analyst Emeric de Vigan said the restrictions were likely to have little effect on output in practice, with cuts likely only at the weekend or midday when solar output was at its peak, so that the impact on power prices would be slim.
He added that the situation would need monitoring in coming weeks, however, noting it was unusually early in the summer for such restrictions to be imposed.
Water temperatures at the Bugey plant already eclipsed the initial threshold on July 9 where restrictions are possible, and are currently forecast to peak next week and then drop again, Refinitiv data showed.
The Garonne river in southern France has the highest potential for warming to critical levels, but the Golfech plant is currently offline for maintenance until mid-August, the data showed.
The nuclear operator has previously requested that thermal limits – which determine how much reactor-cooling water can be returned to the river during a heat wave – be lifted permanently, saying a study it conducted showed last year’s higher temperatures had no impact on biodiversity.