The fire according to information transmitted to the watchdog was under control, the ASN said, but added this had not yet been confirmed.
A Framatome spokesman told Reuters the fire was under control and no staffer was harmed.
“We are still working on securing the site”, he said, adding that he could not yet comment on any pontential nuclear safety impacts.
Framatome is a unit of French nuclear energy giant EDF. According to the company’s website, the Romans-sur-Isere site where the fire erupted produces fuel for nuclear power reactors based on enriched uranium.