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Electricite de France SA said it found manufacturing deviations on equipment at six of its 58 nuclear reactors in the country, though it believes the issue doesn’t require immediate attention.

The French nuclear safety authority, which said Sept. 12 that at least five reactors were affected after EDF disclosed that it was investigating the issue two days earlier, will have to decide whether the units need to be halted for repairs. EDF, which is France’s largest power generator, produced 72% of the country’s electricity last year from its nuclear plants.

EDF has identified 16 steam generators installed on six operating reactor units -- two at Blayais and one each at Bugey, Fessenheim, Dampierre-en-Burly and Paluel -- the utility said Wednesday in a statement.

The uncertainty over the reliability of some EDF reactors has already sent power prices surging both in France and neighboring countries, and the utility’s shares have tanked amid concern that a prolonged halt would curb the company’s earnings.

EDF’s repeated problems with the quality of reactor components, which include faulty welds at its flagship Flamanville project and anomalies in manufacturing records at the Creusot forge, add to growing global concerns about the suitability of nuclear energy as a cleaner alternative to burning fossil fuels.

EDF is also facing issues with some of its aging U.K. nuclear stations, while rival French utility Engie SA had to halt some reactors in Belgium last year, raising fears of a blackout. As well as questions about the safety of reactors following the Chernobyl and Fukushima disasters, there are doubts about their economic viability as the cost of renewable energy plunges.

Framatome SA, a French supplier of atomic equipment taken over by EDF and partners almost two years ago, has informed the utility that the heat treatment of some steam generator welds didn’t adhere to temperature rules, EDF said Sept. 10. The issue concerns components that have been installed in some reactors as spare parts.

To contact the reporter on this story: Francois de Beaupuy in Paris at fdebeaupuy@bloomberg.net

To contact the editors responsible for this story: James Herron at jherron9@bloomberg.net, Helen Robertson, Rakteem Katakey

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