One person has been killed and four injured, one seriously, by an explosion at the southern French nuclear site of Marcoule, according to BBC.
There were no radioactive leaks after the blast, caused by a fire near a furnace in the Centraco radioactive waste storage site, officials said.
It produces MOX fuel, which recycles plutonium from nuclear weapons, but does not include reactors.
It is a major site involved with the decommissioning of nuclear facilities.
The Centraco treatment centre belongs to a subsidiary of national electricity provider EDF.
The explosion hit the area at 1145 local time (0945 GMT).
"For the time being nothing has made it outside," said a spokesman for France`s Atomic Energy Commission (CEA).
The International Atomic Energy Agency (IAEA) said it was in touch with the French authorities to learn more about the nature of the explosion.
Marcoule was opened in 1955 and is one of France`s oldest nuclear sites. It is located in the Gard department in Languedoc-Roussillon region, near France`s Mediterranean coast.
Nuclear energy provides more than 70% of France`s energy needs.
All the country`s 58 nuclear reactors have been put through stress tests in recent months, following the disaster at Japan`s Fukushima nuclear plant which was hit by an earthquake and tsunami.
EDF`s share prices fell by more than 6% as news of the blast emerged.