An explosion at the southern French nuclear plant of Marcoule, located in the Gard department in Languedoc-Roussillon region, has killed one and injured four others.

The powerful explosion struck the area at 11:45 local time (09:45 GMT) on Monday, Associated Press reported.

French officials say the explosion was caused by a fire near a furnace in the Centraco radioactive waste storage site.

“According to initial information, the explosion happened in an oven used to melt radioactive metallic waste of little and very little radioactivity,” the French Nuclear Safety Authority said in a statement.

The agency further warned of the possibility of a radiation leak threat of an oven at the nuclear site.

The Marcoule plant is one of France’s oldest nuclear plants still operating and is located in the Gard department in Languedoc-Roussillon region.

The plant is a nuclear waste management facility that does not include any reactors. The site is partly used to produce MOX fuel that recycles plutonium from nuclear weapons.

Nuclear energy provides nearly 70 percent of France’s nuclear energy needs. France is the world’s most nuclear-reliant country with 58 nuclear reactors.