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.

The Fukushima plant, which used the same boiling water reactor as the Tokai plant, suffered core meltdowns and spewed out a massive amount of radioactive material after losing its external power supply and emergency power generators in the calamity.

Still, it is unclear when the Tokai plant will actually restart as construction work to enhance its safety will not be completed until March 2021. Also, it needs to obtain consent from all of its surrounding communities. It is the only nuclear power plant in the country to need consent from local governments beyond its host municipality.

In addition, the sole reactor in the complex turns 40 years old in November and faces two more screenings to extend its operation by up to 20 years beyond the normal 40-year limit. It is expected to pass the screenings.

It operator must also compile an evacuation plan covering the 960,000 residents within a 30-kilometer radius of the plant — the largest number of potential evacuees for a nuclear plant in the country due to its location in the metropolitan region.

In Tokyo, protesters gathered in front of the NRA office in the morning and shouted slogans against the restart.

Some civic group members submitted to the watchdog a letter calling for a decision against the plant’s resumption with the signatures of some 8,000 people. “A plant that passes a lax screening is not safe,” the document said.

Sengetsu Ogawa, 54, a local anti-nuclear activist in Ibaraki Prefecture, said, “I have doubts about the way the NRA conducts screenings as it is believed to rubber stamp operators’ applications (for restarts).”

“Japan has been rocked by major disasters such as floods and earthquakes for the past two months. Based on these circumstances, the NRA should conduct a screening again,” he said.

Tokai No. 2 is the eighth nuclear plant approved by the NRA to restart under stricter safety rules introduced after the Fukushima disaster.

Among plants with boiling water reactors, it is the second to be given the green light following the Kashiwazaki-Kariwa nuclear complex run by Tokyo Electric Power Company Holdings Inc., the operator of the crisis-hit Fukushima plant.

Japan Atomic Power applied for the restart in May 2014 with a plan to construct a 1.7-km-long coastal levee, predicting a potential tsunami as high as 17.1 meters.

With costs for safety measures at the plant estimated to reach some ¥180 billion ($1.6 billion), the operator, whose sole business is nuclear energy production, has struggled as none of its reactors has been online since the 2011 disaster.

Tepco and Tohoku Electric Power Co., which receive power supply from Tokai No. 2, have offered to financially support Japan Atomic Power.