A powerful thunderstorm forced the shutdown of one of the reactors at the Balakovskaya nuclear power plant (NPP) in central Russia, the plant's press service said on Friday.

"A thunderstorm on the border of the Saratov and the Samara regions in the late evening of July 7 damaged two power supply lines serving the fourth reactor at the Balakovskaya nuclear power plant, causing an automatic safety shutdown," the plant's press service said in a statement.

Radiation levels around the nuclear power plant remain unchanged and the work of the fourth reactor will resume after the repairs on two damaged power lines have been done.

The Balakovskaya plant has four modernized VVER-1000 nuclear reactors with power output of 1,000 MWt each.

Only two of them are currently operational as the first reactor was shut down for scheduled maintenance on June 8 for 60 days.

The recent disaster in Japan has confirmed the vulnerability of plants with even most sophisticated safety features.