France relies on nuclear energy more than any other country for its electricity needs.
French President Francois Hollande has vowed to close the Fessenheim plant by the end of his term in May 2017.
His decision stems from last year’s Fukushima nuclear disaster in Japan.
At least two people have been injured following a steam leak during maintenance at the Fessenheim nuclear power plant in Alsace, eastern France.
France's electricity utility, Electricite de France (EDF), said on Wednesday that the steam was at first mistaken for smoke and prompted reports that there was a fire at the plant.
The EDF noted that the steam wasn't radioactive and the plant's two reactors haven't been halted.
"During maintenance in the nuclear compound of the plant workers used hydrogen peroxyde, which triggered some steam release and this is why some people thought initially that a fire had broken out," a spokeswoman for EDF said on condition of anonymity.
"Out of the nine workers on the maintenance job, two had their hands slightly burnt and they are being treated at the plant's infirmary," she said, adding that the plant's two reactors "haven't been halted, they are running as normal."
Another spokeswoman for the EDF said that the steam was released as hydrogen peroxyde was injected into a water tank. She insisted that the steam was "not radioactive."
Commissioned in 1977, Fessenheim’s twin reactors are the oldest in France. Anti-nuclear campaigners have long pushed for the closure of the Fessenheim plant and warned of safety risks.