By Forrest Crellin

PARIS (Reuters) – High water temperatures threaten to reduce France’s already unusually low nuclear output, piling more pressure on operator EDF at a time when half its reactors are offline due to maintenance and corrosion issues.

The valley between the Rhone and Garrone rivers has reached sweltering temperatures in recent days which are expected to hit around 40 degrees Celsius on Friday and remain above seasonal levels through early next week.

That is a problem because river water is often used to cool reactors before being returned at a higher temperature. Reactor production is limited during times of high heat to prevent the hot water re-entering rivers from damaging wildlife.

EDF has announced production restrictions at the Tricastin plant on the Rhone from July 16, the Blayais plant at the mouth of the Garrone from July 17, the Saint Alban plant on the Rhone from July 17, and the Bugey plant on the Rhone from July 19.

An extension of a recent output cut at the Golfech plant on the Garrone is also possible, Refinitiv analyst Nathalie Gerl said, adding data showed restrictions continued for several weeks during a similar powerful heatwave in 2018.

On Friday, French energy regulator ASN announced some modifications at the plants to guarantee a minimum power production level.

EDF has already been forced to cut planned output several times this year because of a host of problems at its reactors – and expects an 18.5 billion euros ($18.6 billion) hit to its 2022 core earnings because of production losses.

The French government is due to announce details of its plan to nationalise the indebted group, in which the state already owns 84%, by Tuesday.

The maximum river temperature before restrictions kick in at the Bugey plant is 26 degrees Celsius, while that at the Golfech, Tricastin and St. Alban plants is 28C, and Blayais is 30C.

Current nuclear availability is the lowest for at least four years because of corrosion problems and extended maintenance schedules at half of EDF’s 56 reactors.

That means France is importing power at a time it would normally be exporting it and EDF is buying electricity at high market prices, just as Europe is scrambling to find alternative energy supplies to Russia.

Things could get worse in the winter, unless EDF can restore full production – though Refinitiv forecasts at this stage point to a rebound to more normal output levels in coming months.

The current rising temperatures are also causing demand for air conditioning to increase, which could add to the stress on the grid.

“Supply will get particularly tight next week with demand about 6 GWh/h above normal on Monday and Tuesday,” Gerl said.

France is already importing quite heavily, from countries such as Spain, Switzerland, Germany and Britain. But exports to Italy could drop as a result, she added.

The power mix in France is diverse, with around 32% of production from wind, solar and hydro, grid operator RTE data show, so power production depends more on sun intensity and wind speeds than moderate temperatures.

However, rising river temperatures can have a knock-on effect as some coal-to-power stations also need cooling water from rivers and rely on rainfall or snowmelt to support river levels and allow unhindered coal barge transport.

If the amount of river water that can be used is limited to protect wildlife that can also curb vital water supply to coal stations and reduce production times and capacities.

The same goes for run-of-river hydroelectric power plants.

Low water levels after recent dry weather continue to prevent cargo vessels from sailing fully loaded on the Rhine in Germany, traders said.

EDF said on Friday high temperatures were unlikely to affect the performance of its British reactors.

(Reporting by Forrest Crellin Additional reporting by Vera Eckert Editing by Silvia Aloisi and Mark Potter)

FILE PHOTO: Steam rises from a cooling tower of the Electricite de France (EDF) nuclear power plant in Dampierre-en-Burly, France October 12, 2021. REUTERS/Benoit Tessier