The blast happened Monday in a furnace in the Centraco site, in the southern Languedoc-Roussillon region, about 20 miles from the city of Avignon.
The furnace is used to melt radioactive metallic waste, but the Nuclear Safety Authority said no radioactive leaks have been detected. The agency quickly pronounced the accident as "terminated," saying the situation had been brought under control in less than an hour.
In a statement, the agency said the building that houses the furnace wasn't damaged, no leaks were reported and residents who live near the site were not evacuated.
Officials said those who were injured were not contaminated with radiation. One of the injured suffered severe burns.
The cause of the blast was under investigation.
France is the world's most nuclear-dependent nation. It relies on the 58 nuclear power plants that dot the country for about three-quarters of its total electricity, and it's also a major exporter of nuclear technology throughout the world.
The Associated Press contributed to this report.