French power giant EDF (EDF.PA) said on Wednesday it had found faults on pipes in a safety system at its Civaux nuclear power station, and it would shut down another plant because it used the same kind of reactors.

The setback comes as France plans a major nuclear power station building program, diverging from neighbour Germany which retreated from nuclear power after the Fukushima nuclear disaster in Japan in 2011.

France's biggest electricity supplier said some faults were detected close to the welds on the pipes of the safety injection-system circuit in the two reactors of the Civaux power plant in western France.

A source close to the matter told Reuters the flaws were linked to corrosion.

As a result of the discovery, an outage at the Civaux plant will last longer than expected, the company said.

EDF said it would stop its plant in Chooz in eastern France because it uses the same kind of reactors.

The decisions will result in a loss of about 1 Terawatt-hour by the end of 2021, EDF said, adding that this would lead to a downward revision of its EBITDA estimate to a range of 17.5 to 18 billion euros, against the previous target of more than 17.7 billion euros, based on current market prices.

EDF had stopped one reactor at the Civaux plant for a routine 10-year checkup in August. In November it also halted its second reactor at the site protectively, previously planning to restart it on Dec. 24.

The extended outage could turn into a headache for President Emmanuel Macron as Frances pushes for nuclear energy to be included in an EU-wide list of favoured green and sustainable investments.

It will place more pressure on France's nuclear-reliant power network, after grid operator RTE warned that cold weather over the winter could strain tight winter supply margins.

Nuclear accounts for more than 70% of France's energy mix and the pandemic has delayed maintenance work on some nuclear reactors.