PARIS (Reuters) - France's state-run utility EDF ramped up output at three nuclear reactors on Friday following repairs, while a power cut frayed nerves in Paris and a cold snap tested Europe's resolve to curb energy use to conserve war-restricted supplies.
Corrosion in EDF's 56-strong nuclear fleet has taken a record number of reactors out of action, reducing French nuclear output to a 30-year low and adding to the strain on Europe's energy network as it grapples the impact of the Ukraine war.
Following the invasion of Ukraine by major energy supplier Russia begun in February, Europe has filled up gas storage to around 90% of capacity and drawn up plans to reduce energy use, which will be put to the test as the first cold weather of the season drives up demand.
France's nuclear fleet will likely reach an available production capacity of 40 gigawatts next month, the head of the country's energy watchdog Emmanuelle Wargon told Europe 1 radio on Friday.
Grid operator RTE, however, says the country's power supplies will be stretched even if EDF manages to stick to its repair schedule, and partial load-shedding measures cannot be ruled out on cold days.
Analysts have said supply could fall short on Monday and Tuesday as temperatures in Europe plunge after what had been an unusually mild start to the peak demand winter season.
Energy prices, which have hit record levels this year, surged on Friday in response to nervousness demand would outstrip supply.
"We expect a supply gap of 2-8 GW (gigawatts) ... Not just in the morning evening peaks, but throughout the day from 7am to 9pm," Refinitiv analyst Nathalie Gerl said, referring to the start of next week.
She added that could mean power cuts, previously almost unknown in the world's seventh-largest economy.
The government, which has warned power cuts could happen this winter, said any outages would not exceed two hours and would be flagged ahead of time.
CITY OF DARKNESS
In what many saw as a foretaste of what lies ahead, several districts of southern Paris were plunged into darkness on Thursday night after a technical glitch at an electrical transformer of energy supplier Enedis, a subsidiary of EDF.
"Is it starting?", one Twitter user said, posting the image of a street in darkness as parts of central Paris were hit by the power cuts around 10:15 p.m. (2115 GMT) and power was restored around 11:00 p.m. Around 125,000 households were affected.
EDF said on its website on Friday its 1,300-megawatt (MW) Cattenom 4 nuclear reactor, which needed stress corrosion repair work, was ramping up in stages, but would not be fully operational until Sunday - later than previously flagged.
The unit was running at 480 megawatts as of 0651 GMT, around a third of its total capacity.
Company data on Friday indicated EDF's Bugey 3 reactor, which also underwent maintenance, was starting up and running at 900 megawatts out of 910 as of 0542 GMT. A third reactor, Cruas 2, was also coming back online.
Later on Friday, EDF Chief Executive Luc Remont and French Finance Minister Bruno Le Maire are due to hold a news conference at a nuclear site.
Le Maire earlier this week said EDF's maintenance and repair efforts were moving "in the right direction".
With a view to providing long-term solutions to Europe's energy worries, leaders, including from France and Spain, are meeting in Spain on Friday to discuss a construction timeline and financing for a hydrogen pipeline.
(Writing by Tassilo Hummel and Ingrid Melander; Editing by Barbara Lewis)