An explosion at the French state-controlled utility Electricité de France (EDF)-operated Flamanville nuclear power plant forced the company to take the reactor offline.
According to the state-owned firm EDF, the explosion occurred in a "non-nuclear" part of the power plant due to a fire in the turbine hall.
The turbine is located a few dozen yards from the nuclear reactor, which is protected by a thick cement wall, reported The Wall Street Journal.
However, the cause of the fire was not immediately determined.
EDF said it will undertake an internal investigation to assess the cause of the fire and a subsequent explosion at the nuclear site.
A senior local official Olivier Marmion was reported by AFP news agency as saying: "It is a significant technical event but it is not a nuclear accident.”
Built in the 1980s, the Flamanville has two reactors have 1,300MW of combined power generation capacity.
EDF noted that there had been no injuries during the explosion, which neither caused environmental damage.
The second reactor at the power plant, however, is unaffected and is continuing its operations.
Areva and EDF are currently working on a project to build a new third-generation reactor, known as EPR, at Flamanville site.
Construction of the new plant commenced in 2007. Work was initially planned for completion in 2012 but has been delayed several times and is now scheduled for completion in late 2018, reported The Guardian.