The nuclear watchdog on Wednesday formally approved the restart of an almost 40-year-old nuclear power plant northeast of Tokyo that has sat idle since it was damaged during the 2011 earthquake and tsunami disaster, which also caused meltdowns at the Fukushima No. 1 plant.

The Tokai No. 2 plant in Tokai, Ibaraki Prefecture, operated by Japan Atomic Power Co., is the first nuclear plant affected by the disaster to clear screening by the Nuclear Regulation Authority.

The earthquake on March 11, 2011, left the plant without an external power source, and a 5.4-meter tsunami incapacitated one of its three emergency power generators. The plant managed to cool down its reactor over three and a half days after the disaster as the two other power generators remained operational.