Investigative magistrates suspect Lauvergeon may have spread false information and presented inaccurate accounts to hide asset depreciation at Uramin, whose uranium deposits in Namibia, Central African Republic and South Africa, turned out not be profitable.

In France, a formal investigation does not automatically lead to a trial but often does.

Lauvergeon's lawyer was not immediately available for comment, but Lauvergeon has repeatedly denied all wrongdoing in the Uramin affair and has said that the asset depreciations were partly due to the collapse of uranium prices after the Fukushima nuclear disaster in Japan in March 2011.

Areva has had to write down billions of euros on Uramin, which contributed to years of losses which eventually wiped out Areva's equity and led to a government rescue package early this year.

Lauvergeon led the state-owned nuclear company for ten years from 2001 to 2011, and was one of France's best-known CEOs, embodying the country's nuclear ambitions at home and abroad. Dubbed "atomic Anne" by French media, she was often cited as one of the world's most powerful women.

The judicial investigation was sparked by a critical report about the affair by France's top public auditor, the Cour des Comptes in 2014.

(Reporting by Simon Carraud, writing by Mathieu Rosemain, editing by Geert De Clercq)