“No radioactive substance was affected by the fire”, the watchdog said, adding that it de-activated its emergency centre in the evening as the fire had been brought under control.
More extensive checks will be carried out by a special research team on Thursday.
A Framatome spokesman earlier said no staffer was harmed.
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.